Title of Invention

A REFRIGERATOR SYSTEM AND A FALLING FILM EVAPORATOR THEREFOR.

Abstract TITLE: A REFRIGERATOR SYSTEM AND A FALLING FILM EVAPORATOR THEREFOR. A refrigeration sytem comprises: a condenser receiving comrpessed gas from a compressor and condensing it to liquid state; an expansion device downstream of the condenser for forming a two-phase mixture of refrigerant gas and liquid refrigerant; and a fallilng film evaporator having a shell, a tube bundle, a vapor outlet connected to the compressor and tubes of the bundle and a refrigerant distributor, the tubes running horizontally in the shell, the distributor being disposed above the tube bundle within the shell and receiving liquid refrigerant from the expansion device, for depositing liquid refrigerant vertically downward onto the top of the tube bundle, said tube bundle defining at least one vapor lane allowing unobstructured flow path for the refrigerant gas out of the interior of the tube bundle to an exterior side thereof at a velocity and in a manner such that the flow of liquid refrigerant downward through said tube bundle and across said vapor lane is generally unaffected by the cross-flow of refrigerant vapor out of the interior of said tube bundle through said vapor lane.
Full Text A REFRIGERATOR SYSTEM AND A FALLING FILM EVAPORATOR
THEREFOR
Background of the Invention
The present invention relates to a refrigerator system and a falling film
evaporator therefor. More particularly, the present invention relates to a falling
film evaporator for a vapor compression refrigeration chiller.
At its simplest, a vapor compression refrigeration, refrigerator or chiller
includes a compressor, a condenser, an expansion device and an evaporator.
Refrigerant gas is compressed in and is delivered from the compressor
to the condenser, at a relatively high pressure, where it is cooled
and condensed to the liquid state. The condensed refrigerant passes
from the condenser to and through the expansion device. Passage
of the refrigerant through the expansion device causes a pressure drop

therein and the further cooling thereof. As a result, the
refrigerant delivered from the expansion device to the
evaporator is generally a relatively cool, saturated two-phase
mixture.
The two-phase refrigerant mixture delivered to the
evaporator is brought into contact with a tube bundle disposed
therein and through which a relatively warmer heat transfer
medium, such as water, flows. That medium will have been
warmed by heat exchange contact with the heat load which it is
the purpose of the refrigeration chiller to cool..
Heat exchange contact between the relatively cool
refrigerant and the relatively warm heat transfer medium
flowing through the tube bundle causes the refrigerant to
vaporize and the heat transfer medium to be cooled. The now
cooled medium is returned to the heat load to further cool it
while the heated and now vaporized refrigerant is directed out
of the evaporator and is drawn into the chiller"s compressor
for recompression and delivery to the condenser in a continuous
process.
More recently, environmental, efficiency and other
similar issues and concerns have resulted in a need to re-think
evaporator design in vapor compression refrigeration chillers
in view of making such evaporators more efficient, from a heat
exchange efficiency standpoint, and in view of reducing the
size of the refrigerant charge needed in such chillers. In
that regard, environmental circumstances relating to ozone
depletion and global warming have taken on significant
importance in the past several years. Those issues and the
ramifications thereof have driven both a need to reduce the
amount and change the nature of refrigerants used in
refrigeration chillers.

So-called falling film evaporators have, for some
time, been identified as promising candidates for use in
refrigeration chillers to address efficiency, environmental and
other issues and concerns in the nature of those referred to
above. While the use and application of evaporators of a
falling film design in vapor compression refrigeration chillers
is theoretically beneficial, their design, manufacture and
incorporation into such chiller systems has proven challenging.
In traditional shell-and-tube flooded evaporators,
the shell of the evaporator is largely filled with liquid
refrigerant and a majority of the tubes in the tube bundle are
immersed therein. Two-phase refrigerant is directed upward to
the evaporator"s tube bundle from a distributor located at the
bottom of the shell. Refrigerant vapor generated in such
evaporators entrains liquid refrigerant droplets and carries
them upward to the uppermost, unimmersed rows of tubes within
the tube bundle for heat exchange therewith. Good axial
distribution of the two-phase refrigerant mixture within the
shell is important to ensure that the tube bundle is and
remains fully wetted. As will be appreciated, flooded
evaporators, by their nature, require that the chiller system
employ a relatively large refrigerant charge.
One recent attempt to address issues relating to
the amount of refrigerant used in a refrigeration system is
identified in U.S. Patent 5,839,294 which suggests the
employment of what it refers to as a "hybrid" falling film
evaporator. Despite the reference to this evaporator as a form
of falling film evaporator, the 294 patent states that in its
preferred embodiment, about one-half of the tubes in its tube
bundle are immersed in liquid refrigerant and that in some
cases, up to three quarters of the tube bundle would be.
Further, that patent teaches and relies upon the use of

Pressure and spray heads or nozzles to distribute refrigerant
onto the portion of the tubes in the tube bundle that are not
immersed in liquid refrigerant. The use of pressure to spray
liquid refrigerant onto a tube bundle penalizes the efficiency
of the heat exchange process due to the fact that a portion of
the liquid refrigerant in the spray will be carried out of the
evaporator in the stream of refrigerant gas that flows to the
compressor therefrom without having come into heat exchange
contact with a heat exchanger tube internal of the evaporator.
Further, when pressurized or spray systems are used, a larger
amount of liquid refrigerant will fall into the evaporator"s
liquid pool without contacting a heat exchanger tube than will
be the case in true or non-hybrid falling film evaporators.
Non-hybrid falling film evaporators go
significantly further to reduce the amount of refrigerant
needed for efficient evaporator and chiller system operation by
virtue of the fact that relatively very little liquid
refrigerant is carried out of the evaporator entrained in the
refrigerant gas that flows out of the evaporator to the
compressor and significantly less refrigerant makes its way to
the bottom of the evaporator shell without having come into
heat exchange contact with a tube in the tube bundle. Still
further, only a relatively small portion of the tubes in the
tube bundle are immersed in the relatively shallow pool of
liquid refrigerant that does collect at the bottom of the
evaporator shell.
In true falling film evaporators, liquid
refrigerant is deposited, preferably in a low-energy, gentle
fashion, onto the evaporator"s tube bundle from above and
gravity is relied upon to cause liquid refrigerant to fall
generally vertically downward through the bundle in droplet and
film form. Because of these characteristics, falling film

evaporators require a reduced amount of refrigerant to function
and will typically provide superior thermal performance to that
of flooded and/or hybrid evaporators due to the improved heat
transfer coefficient that results from the creation of the thin
film of liquid refrigerant that flows over and around the
majority of the individual tubes in the tube bundle. Further,
evaporator efficiency and performance is improved as a result
of the elimination of the adverse hydrostatic head effects
caused by the relatively more large and deep pool of liquid
refrigerant which is found in evaporators of the flooded type.
With respect to falling film evaporators, in
operation, the vaporization of refrigerant liquid within the
tube bundle of such evaporators generates vapor which tends to
travel generally upward but along the path of least resistance
in order to exit the tube bundle. Because the refrigerant
delivered onto a tube bundle in a falling film evaporator is
from above and because such delivery requires the use of
distributor apparatus to provide for the uniform distribution
and deposit of refrigerant onto the tube bundle, generally
along its entire length and width, refrigerant vapor generated
in the tube bundle, which will naturally tend to rise, must be
conducted both vertically and horizontally out of the tube
bundle and around the refrigerant distributor so as to conduct
it to a location from where it can be drawn from the evaporator
into the system"s compressor.
The specific vapor flow path in a tube bundle is
affected by bundle geometry, tube patterns and by flow
conditions therein, including vapor buoyancy effects. Managing
vapor flow within the tube bundle of a falling film evaporator
is therefore of significant importance to the efficiency of the

heat exchange process that occurs therein as is ensuring that
the flow of refrigerant, when it is initially received from the
distributor at the top of the tube bundle, is "evened out" for
downward flow therethrough.
If the downward flow of liquid refrigerant as it
initially occurs in the upper portion of the tube bundle is not
"evened out" thereacross, the efficiency of the heat transfer
process within the evaporator and of the vapor compression
refrigeration chiller as a whole will be degraded by oversupply
of liquid refrigerant to one portion of the bundle and
undersupply to another. Further, if local_vapor_velocity
within the tube bundle becomes too high, particularly in a
direction which is laterally across the tube bundle, breakdown
of the film of liquid refrigerant, that develops around
individual tubes and the existence of which is critical to the
heat transfer process can occur. Such breakdown can lead to
the existence of localized dry regions in the tube bundle. The
existence of such localized dry regions, or "dry out" as it is
referred to, like maldistribution of the liquid refrigerant as
it is initially received at the top of the tube bundle,
degrades the overall heat transfer performance of a falling
film evaporator.
Exemplary of the use of a true, non-hybrid falling
film evaporators in vapor compression refrigeration chillers is
the relatively new, so-called RTHC chiller manufactured by the
assignee of the present invention. Reference may be had to
U.s. Patents 5,645,124; 5,638,691 and 5,588,596, likewise
assigned to the assignee of the present invention and all of
which derive from a single U.S. patent application, for their
description of early efforts as they relate to the design of
falling film evaporators for use in vapor compression
refrigeration chillers and of refrigerant distribution systems

therefor. Reference may also be had to U.S. Patents 5,561,987
and 5,761,914, likewise assigned to the assignee of the present
invention which similarly relate to chiller systems that makes
use of a falling film evaporator.
In the RTHC chiller, which is currently state of
the art in the industry, the tube bundle can be categorized as
being generally homogenous in terms of its tube patterns and
tube bundle geometry. Proactive control of the flow of
refrigerant vapor generated within the tube bundle of the RTHC
chiller is not critical for the reason that a dedicated liquid-
vappr separator component is employed in that chiller, upstream
of the evaporator"s refrigerant distributor. As a result of
the use of such a dedicated liquid-vapor separator component,
the refrigerant delivered into the distributor within the
evaporator of the RTHC chiller is in the liquid phase only. As
a result of the need to distribute only liquid phase
refrigerant onto the tube bundle within the RTHC evaporator,
the distributor therein is of a design which does not generally
inhibit the upward flow of refrigerant vapor upward and out of
the evaporator. The requirement for and use of a dedicated
liquid-vapor separator component does come, however, at
significant expense in terms, of chiller material and
fabrication costs.
More recently, a refrigerant distributor of a new
and highly efficient design has been developed by which the
generally controlled and predictable distribution of a two-
phase, vapor-liquid refrigerant mixture within a falling film
evaporator in a vapor compression refrigeration system is
successfully accomplished. That two-phase refrigerant
distributor is the subject of co-assigned and co-pending U.S.
Patent Application 09/267, 413 filed on March 12, 1999. The
efficiency and effectiveness of this two-phase distributor has

eliminated the need for a separate loquid-vapor separator
component in chillers that employ falling film evaporators.
While elimination of the dedicated and expensive liquid-vapor
separator component is very clearly beneficial, it does come at
the cost of adding some complexity and design difficulties to
the overall evaporator design.
In that regard, in order for a distributor to
accomplish efficient and even distribution of two-phase
refrigerant to the tube bundle in a falling film evaporator, it
will typically be of a generally solid and impervious design
that will overlie the majority of the length and width of the
evaporator"s tube bundle. Distributors of such a design do
not, therefore, generally facilitate the unobstructed vertical
flow of refrigerant vapor to and out of the upper region of the
evaporator.
Because the two-phase refrigerant distributor is a
generally impervious component that overlies the majority of
the length and width of the tube bundle, refrigerant vapor
generated within the tube bundle must be caused to flow
horizontally, in a cross-flow direction with respect to the
downward flow of liquid refrigerant through the tube bundle, in
order to conduct such vapor to the sides of the tube bundle
from where it can be drawn upward and out of the evaporator
shell unobstructed by the distributor. Such flow must be
managed to minimize both the disruption of the distribution of
refrigerant out of the distributor onto the top of the tube
bundle and the downward flow of liquid refrigerant through the
tube bundle.
The need therefore exists for a falling film
evaporator for use in a vapor compression refrigeration system
in which the need for a dedicated liquid-vapor separator
component is obviated by the use of a two-phase refrigerant

distributor _yet._which provides for the pro-active control _o_f
the flow of refrigerant vapor within and out of its tube bundle
and shell in a manner which minimizes the disruption of the
distribution of refrigerant onto the tube bundle from above and
the downward flow of liquid refrigerant therethrough.
Summary of the Invention
It is a primary object of the present invention to
provide for the control of vapor folw withing a tube bundle in
an evaporator of the falling film type in which a refrigerant
distributor is employed.
It is another object of the present invention to
provide a tube bundle for use with a two-phase refrigerant
distributor in a falling film evaporator in a vapor compression
refrigeration systems which obviates the need for a vapor
liquid separator in such system.
It is an additional object of the present invention
to provide a falling film evaporator in which the distribution
of liquid refrigerant onto, the top of the tube bundle is in
controlled and predictable, quantities.
It is another object of the present invention to
provide a falling film evaporator which, by its employment of
appropriately sized and positioned vapor lanes, is capable of
conducting refrigerant gas out of the tube bundle therein
without substantially disrupting the downward flow of liquid
refrigerant therethrough.
It is a further object of the present invention to
prevent the local "dryout" of tube surfaces in the tube bundle
of a falling film evaporator by conducting refrigerant gas
created within the bundle laterally thereoutof in a controlled
manner which minimizes the stripping of liquid refrigerant from
the surfaces of individual tubes within the bundle.

It is a still further object of the present
invention to provide a tube bundle for a falling film
evaporator in which the geometry thereof is optimized so as to
"even out", quickly and in the upper portion thereof, the flow
of liquid refrigerant received from a two-phase refrigerant
distributor disposed vertically above the tube bundle and to
Optimize the tube pattern/geometry lower in the hundle to take
advantage of the homogeneous downward flow of liquid
refrigerant that will have been established as a result of the
evening out of liquid flow in the upper portion of the bundle.
It is an additional object of the present invention
to provide an evaporator in which the efficiency of the heat
exchange process is enhanced by it avoidance of the use of
pressure to spray refrigerant onto the evaporator tube bundle.
It is another object of the present invention to
provide for the efficient vaporization of liquid refrigerant in
a falling film evaporator and to obviate the need to
recirculate or redeposit any such refrigerant that makes its
way to the bottom of the evaporator shell.
It is a still further object of the present
invention to reduce the exit velocity of refrigerant vapor
generated in the tube bundle, of a falling film evaporator and
to prevent the stripping of liquid refrigerant film from the
tubes thereof by such gas through the use of vapor lanes sized
and located within the tube bundle to accomplish that purpose
It is also an object of the present invention to
provide a falling film evaporator in which the tube bundle
thereof defines vapor lanes for the conduct of refrigerant gas
thereoutof and in which the waterbox pass partitions of the
evaporator are configured to coincide with such vapor lanes so
as to simplify and reduce the expense of evaporator and
waterbox construction.

It is a still further object of the present
invention to provide a tube bundle for a falling film
evaporator which, by its nature, by its tube pattern and by its
use of vapor lanes, is amenable to accbmmodating tubes of
several diameters and pitch spacings and of being replicated
within a common evaporator shell in a modular fashion so as to
provide for evaporators of different capacities and
efficiencies but which use a common shell.
These and other objects of the present invention,
which will become apparent when the following Description of
the Preferred Embodiment and appended drawing figures are
considered, are achieved by the use vapor lanes and optimized
tube bundle geometry in a falling film evaporator that employs
a two-phase refrigerant distributor. The vapor lanes and tube
geometry control the cross-flow velocity of the refrigerant gas
created interior of the bundle. That gas must pass laterally
out of the tube bundle and around the distributor in order to
exit the evaporator shell and to enter the compressor in the
refrigeration system in which the evaporator is employed.
Control of the cross-flow velocity of refrigerant gas flowing
out of the interior of the evaporator"s tube bundle is
accomplished, in the preferred embodiment, by efficiently
distributing two-phase refrigerant into the evaporator shell
generally across the length and width of the tube bundle and by
the definition of vapor lanes within the tube bundle that
facilitate the passage of refrigerant gas out of the bundle in
a manner which minimizes the disruption of the downward flow of
liquid refrigerant through the bundle and the heat exchange
process ongoing therein. By appropriately managing the
distribution and flow of liquid refrigerant downward through
the bundle as well as the lateral or cross-flow of refrigerant
vapor out of the bundle and by locating the vapor lanes used in

vapor flow management to coincide with the waterbox pass partitions of the
evaporator, not only is the heat transfer process within the evaporator enhanced
but the fabrication and material cost thereof is significantly reduced.
Accordingly, the present invention provides a refrigeration system
comprising : a refrigerant gas compressor; a condenser, said condenser receiving
compressed gas from said compressor and condensing said gas to the liquid
state ; a first expansion device, said expansion device being downstream of said
condenser and creating a two-phase mixture of refrigerant gas and liquid
refrigerant ; and a falling film evaporator, said evaporator having a shell, a tube
bundle, a vapor outlet and a refrigerant distributor, said vapor outlet being
connected for flow to said compressor and the tubes of said tube bundle running
horizontally in said shell, said refrigerant distributor being disposed above said tube
bundle within said shell and receiving liquid refrigerant from said expansion device,
said distributor depositing liquid refrigerant vertically downward, generally
unassisted by pressure, onto the top of said tube bundle, said tube bundle having
at least two tube sections and defining at least one vapor lane, said vapor lane
being an essentially unobstructed flow path between said tube sections that is
sized to facilitate the conduct of refrigerant gas out of the interior of said tube
bundle to an exterior side thereof at a velocity and in a manner such that the flow
of liquid refrigerant downward through said tube bundle and across said vapor lane
is generally unaffected by the cross-flow of refrigerant vapor out of the interior of
said tube bundle through said vapor lane.

Accordingly, the invention further provides a falling film evaporator for a
vapor compression refrigeration system comprising : a shell, said shell having a
vapor outlet ; a tube bundle, the tubes of said bundle running horizontally in said
shell, said tube bundle having at least one vapor lane and at least two tube
sections, said vapor lane being an essentially unobstructed flow path that is
defined between said at least two tube sections through which refrigerant gas flows
from the interior to an exterior side of said tube bundle and thence to said vapor
outlet, said vapor lane being sized so that the flow of refrigerant gas therethrough
to said exterior side of said tube bundle is at a velocity which generally does not
disrupt the downward flow of liquid refrigerant through said tube bundle and across
said vapor lane ; and a refrigerant distributor, said refrigerant distributor being-
mounted vertically above said tube bundle within said shell and depositing liquid
refrigerant, in generally predictable and controlled quantities, onto the top of said
tube bundle by force of gravity and generally unassisted by pressure so that
said liquid refrigerant falls out of said distributor generally vertically downward onto
the top of said tube bundle.
Accordingly the present invention further provides a method for controlling
vapor flow internally of a falling film evaporator which employs a two-phase
refrigerant distributor and which is used in a vapor compression refrigeration
system comprising the steps of : positioning said refrigerant distributor vertically
above a tube bundle within the shell of said evaporator; delivering a two-phase

mixture of liquid refrigerant and refrigerant gas into said distributor ; flowing said
two-phase refrigerant mixture internal of said distributor so that at least the liquid
portion of said two-phase mixture is made available for distribution generally
throughout the length and width thereof ; depositing, in a generally vertically
downward direction and in relatively low-energy droplet form, the liquid refrigerant
portion of said two-phase mixture across the portion of the top of said tube bundle
that is overlain by said distributor; flowing liquid refrigerant deposited onto the top
of said tube bundle generally vertically downward therethrough ; defining at least
one generally unobstructed vapor lane within said tube bundle that runs from the
interior to an exterior side thereof, said vapor lane dividing said tube bundle
generally into tube sections and being sized to conduct refrigerant gas from the
interior to an exterior side of said tube bundle at a velocity which generally does
not disrupt the downward flow of liquid refrigerant through said tube bundle and
across said vapor lane ; and flowing the refrigerant gas conducted via said vapor
lane out of the interior of said tube bundle to the vapor outlet of said evaporator by
a path that is generally unobstructed by said distributor.
DESCRIPTION OF THE ACCOMPANYING DRAWING FIGURES
Figure 1 is a schematic illustration of the water chiller of the present
invention in which the falling film evaporator is employed.

Figures 2 and 3 are schematic end and lengthwise cross-sectional views of
the falling film evaporator of the present invention.
Figure 4A is an exploded view of the preferred two-phase refrigerant
distributor employed in the evaporator of the present invention.
Figure 4B is a partial cutaway top view of the refrigerant distributor of Figure
4A.
Figure 4C is a view taken along line 4C-4C of Figure 4B.
Figure 5 is a cross-sectional view of the falling view of the falling film
evaporator of the present invention illustrating the tube bundle configuration of the
preferred embodiment thereof.
Figure 6 graphically illustrates the terms triangular pitch and rotated
triangular pitch as applied to tubes in a heat exchanger tube bundle.
Figure 7 illustrates the effect of vapor cross-flow on liquid refrigerant
droplets in a falling film evaporator.
Figure 8 is a view taken along line 7-7 of Figure 1.

Figure 9 illustrates generally how tubes and tube
bundles of different diameter and spacing can be accommodated
in the falling film evaporator of the present invention, such
different tube bundle configurations capable of making use of
vapor lanes of the same size and location and therefore common
water boxes and water box baffles.
Figure 10 illustrates an alternative embodiment of
the present invention in which multiple refrigerant
distributors are employed.
Figure 11 schematically illustrates the addition of
an oil concentrator in the evaporator of the present invention.
Description of the Preferred Embodiment
Referring first to Figure 1, the primary components
of chiller system 10 of the preferred embodiment are a
compressor 12, which is driven by a motor 14, a condenser 16,
an economizer 1,8 and an evaporator 20. The compressor,
condenser, economizer and evaporator are serially connected for
refrigerant flow in a basic refrigerant circuit as will more
thoroughly be described.
Compressor 12 is, in the preferred embodiment, a
multi-stage compressor of the centrifugal type. It is to be
understood, however, that the use of falling film evaporators
of the type described herein in chillers where the compressor
is of other than the centrifugal type is contemplated and falls
within the scope of this invention.
Generally speaking, the relatively high pressure
refrigerant gas delivered into condenser 16 from compressor 12
is condensed to liquid form by heat exchange with a relatively
cooler fluid, most typically water, which is delivered into the
condenser through piping 22. As will be the case in most

chiller systems, a portion of the lubricant/oil used within the
compressor will be carried out of the compressor entrained in
the high pressure gas that is delivered thereoutof to the
condenser. Any lubricant entrained in the compressor discharge
gas will fall or drain to the bottom of the condenser and make
its way into the liquid refrigerant pooled there.
The liquid pooled at the bottom of the condenser,
including the oil therein, is driven by pressure out of the
condenser and to and through, in the case of the preferred
embodiment, a first expansion device 24 where a first pressure
reduction in the refrigerant occurs. This pressure reduction
results in the creation of a two-phase refrigerant mixture
downstream of the first expansion device which generally
carries any lubricant that has made its way into the condenser
along with it. This two-phase refrigerant mixture and any
lubricant flowing therewith is next delivered into economizer
18. From there, the majority of the gaseous portion of the
refrigerant, which is still at a relatively elevated pressure,
is delivered through conduit 26 back to compressor 12 which, in
the case of the preferred embodiment, is a two-stage
compressor.
The delivery of such gas back to compressor 12 is
to a location where the refrigerant undergoing compression is
at a relatively lower pressure than the gas delivered thereinto
from the economizer. The delivery of the relatively higher
pressure gas from the economizer into the lower pressure gas
stream within the compressor elevates the pressure of the lower
pressure refrigerant by mixing with it, without the need to
expend energy in mechanical compression to do so. The
economizer function is well known and it is to be understood
that while the preferred embodiment describes a chiller in
which a multiple-stage centrifugal compressor and an economizer

are employed, the present invention is equally applicable, not
only to chillers driven by other kinds of compressors, but to
chillers which employ only a single compression stage and/or to
chillers which may or may not employ an economizer component.
The refrigerant not delivered back to the
compressor through conduit 26 exits economizer 18 and passes
through piping 28 to a second expansion device 30. Second
expansion device 30 is preferably and advantageously disposed
in or at the top of shell 32 of evaporator 20, proximate the
inlet to refrigerant distributor 50 which is disposed therein
although it need not be. The preferred embodiment of
distributor 50 itself and its application in a falling film
evaporator in the general sense are the subject of U.S. Patent
Application 09/267,413, filed March 12, 1999 and assigned to
the assignee of the present invention.
A second pressure reduction in this refrigerant
occurs as a result of its passage through expansion device 30
and a relatively cool, relatively low pressure two-phase
refrigerant mixture is delivered from second expansion device
30, together with any lubricant being carried therein, into
distributor 50. By positioning expansion device 30 adjacent
the entrance to distributor 50, reduced stratification in the
flow of the two-phase refrigerant mixture into and through the
distributor, which can be created if the flow path for
refrigerant from the expansion device into distributor 50 is
lengthy, is achieved and the ability of the distributor to
deliver two-phase refrigerant in a more controlled, predictable
and, in the preferred embodiment, uniform manner across the
length and width of tube bundle 52 is enhanced.
Tube bundle 52 has a generally horizontal top 52a
and two generally vertical exterior sides 52b and 52c. Once
deposited onto the top of tube bundle 52 liquid refrigerant and
oil trickle downward through the tube bundle, in a manner that

will be further described. A portion of this liquid
refrigerant and oil will make its way to the bottom of the
evaporator shell and will form a pool 54 thereat. From there,
the oil will be returned to the compressor, such as by pump 34
and oil return line 36, as will further be described.
Referring additionally now to Figures 2, 3 and 4,
the preferred embodiment of the falling film evaporator 20 of
the present invention is schematically illustrated in end and
lengthwise cross-sectional views thereof. As will be
appreciated, refrigerant distributor 50, around which
refrigerant gas must flow in order to exit evaporator 20,
extends along at least the majority of the length L and width W
of at least the upper portion of tube bundle 52 within
evaporator 20. The greater the extent to which the length and
width of the tube bundle is overlain by distributor 50, the
more efficient will be the heat exchange process within
evaporator 20 due to the more complete wetting and productive
use of the tube surface available in the evaporator for heat
transfer purposes.
Referring now primarily to Figures 4A-C,
refrigerant distributor 50, which in the preferred embodiment
is the two-phase distributor taught and claimed in above-
referenced U.S. Patent Application 0-/267, 413, includes a first
stage distributor section 50a which overlies a cover plate 50b.
Ensconced within cover plate 50b are a second stage distributor
plate 50c and an injection plate 50d. Bottom plate 50e covers
the underside of distributor 50. Generally speaking, two-phase
refrigerant enters distributor 50 through inlet 50f and flows
bi-directionally to the ends of first stage distributor
portion. Along the way, two-phase refrigerant passes through
apertures 50g in cover plate 50b and enters the diamond shaped
slots 50h in distributor plate 50c. As a result of such flow,

two-phase-refrigerant will have been distributed in a
controlled and predictable manner generally along the length
and width of distributor 50 and, therefore, along the length
and width of tube bundle 52 in the process.
The refrigerant next flows through injection holes
50i that are defined in plate 50d, such holes being relatively
small and located in rows which underlie one of the diamond-
shaped slots 5Oh in plate 50c. Because it is at a pressure
greater than the pressure in the evaporator shell, the
refrigerant sprays through holes 50i and impinges upon solid
portions of bottom plate 50e. However, because there is a
volume or space between plate 50d and bottom plate 50e of the
distributor, the relatively higher pressure two-phase
refrigerant that passes through injection holes 50i and which
impinges on solid portions of bottom plate 50e loses the
majority of its kinetic energy in the process.
As a result, liquid trickles out of relatively
large apertures 50j in bottom plate 50e generally unassisted by
pressure and due to the force of gravity and distributor 50
distributes liquid refrigerant in predictable and controlled
quantities over the portion of the top of the tube bundle it
overlies. In the preferred embodiment, though not necessarily
in other embodiments, such quantities will generally be uniform
across the overlain portion of the top of the tube bundle. Any
refrigerant gas entering distributor 50 or generated therein
passes out of apertures 50j, which, once again, are relatively
large, and is conducted away from distributor 50 in a manner
which is described below but which does not generally affect
the vertically downward deposit of liquid refrigerant from the
distributor onto the top of the tube bundle.

It is to be understood, with respect to the
evaporator of the present invention, that distributor 50 will
preferably be any kind of distributor which is capable of
successfully distributing two-phase refrigerant across a tube
bundle in the absence of dedicated liquid-vapor separation
apparatus or methodology the purpose of which is to separate
refrigerant gas from refrigerant liquid in or upstream of the
refrigerant distributor internal of the evaporator shell. The
particular two-phase distributor illustrated in Figures 4A-C,
while preferred, is presented only with respect to its ability
to successfully distribute a two-phase refrigerant mixture
across a tube bundle in a controlled and predictable manner and
is not, in its detail and workings, presented in any way to
restrict or affect the scope of the present invention.
Therefore, two-phase refrigerant distributors of other designs
are contemplated and fall within the scope of the present
invention. Still further, however, the present invention, in
its broadest sense, has application in systems where a
distributor is employed which is designed to distribute single-
phase liquid refrigerant. Once again, however, in its
preferred empoaiment, the present invention has been designed
in view of vapor compression refrigeration systems employing a
falling film evaporator in which a two-phase refrigerant
distributor that uniformly distributes liquid refrigerant onto
the top of the evaporator tube bundle is employed.
By the use of a two-phase refrigerant distributor,
the need for a separate and/or dedicated liquid-vapor separator
component or structure within chiller system 10, upstream of
the evaporator"s refrigerant distributor, is eliminated.
However, because distributor 50, in the preferred embodiment,
receives and distributes a two-phase refrigerant mixture, it is
a structure which generally overlies and does not readily

facilitate the -unobstructed upward flow of refrigerant gas
within the evaporator shell to a location from where it can be
drawn into compressor 12. Therefore, provision must be made to
efficiently conduct refrigerant gas that is generated in or
received into the interior of the evaporator upward from tube
bundle 52 and around distributor 50. The conduct and movement
of such gas must be in a manner which minimizes the disruption
and/or adverse effects thereof on the downward flow of liquid
refrigerant through the tube bundle and on the heat exchange
process occurring therein.
Tube bundle 52 is comprised of a plurality of
horizontally running individual tubes 58 which are positioned,
as will more thoroughly be described, in a pattern under
distributor 50 to maximize contact with the liquid refrigerant
that issues out of the lower face 60 of distributor 50 onto the
upper portion of the tube bundle. Such liquid refrigerant is
in the form of relatively large, low energy droplets.
In addition to the relatively large droplets of
liquid refrigerant that dribble out of the distributor onto the
tube bundle, at least some refrigerant gas, formed by flashing
internal of the distributor or upstream thereof, will issue out
of distributor 50 and will preferably be immediately directed
laterally outward and around the distributor into the upper
portion of the evaporator without significantly disrupting the
deposition of liquid refrigerant droplets onto the tubes in the
upper portion of the tube bundle. For that reason, a vapor
space 62 is defined between the top of the tube bundle and the
lower face 60 of the refrigerant distributor. The vapor space,
by its sizing, facilitates the lateral movement of gas that
issues directly out of distributor 50 while minimizing the
effect thereof on the deposit of the liquid refrigerant
droplets onto the tube bundle. In a refrigeration system

wherein a single-phase liquid refrigerant distributor is
employed within the evaporator of the present invention, the
need for vapor space 62 would be eliminated since little gas is
generated in or issues from such a distributor.
The gas issuing out of the distributor and which is
conducted out of vapor space 62, in the preferred embodiment,
combines at the upper periphery of tube bundle 52 with the
refrigerant gas that is generated by the heat exchange process
that occurs within the tube bundle. This gas then passes
upward and around distributor 50, as indicated by arrows 64,
and flows through suction baffles 66 which also serve as
mounting flanges for the distributor within the evaporator
shell. Baffles 66 define perforations 66a along their length
and, in the preferred embodiment, run generally the full length
of the distributor.
Flanges 66 position/support distributor 50 within
the evaporator shell and distribute/regulate the flow of
refrigerant vapor into the upper portion 68 thereof which is
generally above distributor 50 and flanges 66. As such,
flanges 66 function as a suction baffle by which the flow of
refrigerant vapor into the upper portion 68 of evaporator 20 is
distributed/regulated, generally along the length of the
evaporator shell, prior to being drawn from upper portion 68 of
the evaporator into the compressor 12 of system 10 through
vapor outlet 70. Such distribution/regulation makes the flow
of gas out of the evaporator and to the suction side of the
compressor more uniform. By configuring and using the flanges
66 for this purpose, the need for a discrete and separate
suction baffle mounted within upper portion 68 of evaporator
shell 32 is eliminated. Further, the perforated flanges act as
a barrier to the movement of liquid refrigerant out of the
lower portion of the evaporator shell into upper portion 68.

The efficient operation of falling film evaporator-
20 is predicated on the controlled, predictable and, in the
preferred embodiment, uniform deposition of liquid refrigerant
onto the upper surface of tube bundle 52 at relatively low
velocity and in relatively low-energy droplet form, the
creation by such droplets of a film of liquid refrigerant
around the individual tubes in the tube bundle and the falling
of any refrigerant which remains in the liquid state after
contact with a tube, still in low-energy droplet form, through
vapor lanes 72 and 74, as will further be described, and onto
other tubes lower in the tube bundle where a film of liquid
refrigerant is similarly formed therearound.
Referring additionally now to Drawing Figure 5, the
pattern and nature of the individual tubes 58 in tube bundle 52
of the preferred embodiment is illustrated and will more
thoroughly be described. As will be appreciated, the tubes and
tube pattern in the tube bundles illustrated in Drawing Figures
2 and 3 are meant only to illustrate the evaporator of the
present invention in a more general sense whereas the more
detailed tube bundle pattern/configuration is preferred.
Generally speaking, tube bundle 58 is comprised, in
the preferred embodiment, of an upper triangular-pitch tube
section 80, one or more rotated triangular-pitch tube sections
82 therebelow and a lower, preferably triangular-pitch tube
section 84, generally at the bottom of the evaporator shell.
The individual tube sections are separated/defined by vapor
lanes, such lanes being avenues which are generally
unobstructed by individual tubes and which facilitate the flow
of refrigerant gas generated internal of the tube bundle
laterally and/or diagonally thereoutof while minimizing the
disruption of the downward flow of liquid refrigerant droplets
therethrough.

In the preferred embodiment of Figure 5, a
horizontal vapor lane 86a is defined between upper triangular-
pitch tube section 80 and rotated triangular-pitch tube section
82a which is immediately therebelow. Rotated triangular-pitch
tube section 82b is separated from rotated triangular-pitch
tube section 82a by diagonal vapor lane 88a while rotated
triangular-pitch tube section 82c is separated from rotated
triangular-pitch tube section 82b and from lower triangular-
pitch tube section 84 by diagonal vapor lane 88b and horizontal
vapor lane 86b respectively. Tube bundle 58 can, in some
cases, include individual tubes 58a in a lower portion thereof
which are outside of the area of tube bundle 52 overlain by
distributor 50. Such tubes are shown in phantom in Figure 5
and their use is made possible by arranging the tubes within
tube bundle 52 to facilitate the horizontal flow of liquid
refrigerant to such tubes as will more thoroughly be described.
Referring additionally now to Figure 6, an
explanation of the terms "triangular-pitch" and "rotated
triangular-pitch" as they apply to tube bundle sections 80,
82a, 82b, 82c and 84 will be provided. Bundle sections 80 and
84 have been referred to as "triangular-pitch" tube sections
while sections 82a, 82b and 82c have been referred to as
"rotated triangular-pitch" bundle sections. Tubes 90a, 90b,
90c, 90d, 90e and 90f are illustrated in Figure 6 in
triangular-pitch configuration. The vertical distance between
such tubes and the tube which is vertically beneath them in the
tube bundle is illustrated at 92. Tubes 94a, 94b, 94c, 94d,
94e and 94f are illustrated in rotated triangular-pitch
configuration. The vertical distance between tubes in this
pitch configuration is illustrated at 96. Since the triangles

formed by the centers of tubes in both configurations are
typically isosceles in nature, the rotated triangular-pitch
configuration is arrived at simply by rotating the triangular
pitch configuration 30° around the common center 100 of tubes
90a and 94a, which, for purposes of illustration and
explanation, coincide in Figure G.
As will be appreciated, the distance 96 between
vertically adjacent tubes in a rotated triangular-pitch
configuration is less than the vertical distance 92 between
vertically adjacent tubes in a triangular-pitch configuration.
As will further be appreciated, tubes in vertically adjacent
horizontal rows which are oriented in rotated triangular-pitch
configuration are immediately above and below each other so
that liquid refrigerant drips or falls from a first horizontal
tube row directly downward onto tubes in the horizontal tube
row immediately below. Where tubes are oriented in triangular
pitch, the tubes in vertically adjacent horizontal rows do not
align vertically so that liquid refrigerant falling off of a
first tube does not fall onto a tube in the horizontal row of
tubes immediately below.
If perfectly uniform initial liquid refrigerant
distribution were obtainable across the top of a tube bundle
and liquid refrigerant was not susceptible to being
horizontally displaced in its downward flow therethrough, the
pattern of the tube bundle would preferably and consistently be
of the rotated triangular-pitch type throughout the bundle
because the vertical distance between tubes in that
configuration is shorter, making for a more compact heat
exchanger. However, because initial refrigerant distribution
across the top of a tube bundle is generally but not perfectly
uniform and in order to promote refrigerant mixing so as to

further even out the distribution and availability of liquid
refrigerant as near to the top of a tube bundle as is possible,
it has been found that the use of tubes in the triangular-pitch
pattern in the upper portion of the tube bundle is beneficial.
It must be realized, however, that the vertical and horizontal
spacing between individual tubes in any section of the tube
bundle will vary from one evaporator/application/size/
configuration to the next and even within individual tube
sections of a tube bundle and that nothing herein is meant to
suggest or limit the scope of the present invention to tubes
within a tube bundle that are horizontally and/or vertically
equally spaced or spaced or configured in one particular
fashion or another.
Referring back now to Figures 1, 2, 3, 4A, 4B, 4C
and 5, two-phase refrigerant mixture is introduced into vapor
space 62 from distributor 50. The vapor portion thereof will,
for the most part, flow laterally through and out of the vapor
space although a portion of such vapor, as well as vapor which
is created by the contact of liquid refrigerant with tubes in
tube bundle sections 80 and 82a, will make its way into
horizontal vapor lane 86a from where it will be conducted,
following the path of least resistance offered by the vapor
lane, to the outer upper periphery of the tube bundle.
The liquid portion of the mixture deposited onto
the top 52a of the tube bundle flows downward, first through
tube section 80, wherein the flow of such liquid refrigerant is
generally evened out and distributed across the width of the
bundle as a result of the triangular-pitch tube pattern
employed, and makes its way across vapor lane 86a into tube
section 82a. The flow of liquid refrigerant continues downward
within the tube bundle through tube sections 82b and 82c and
across vapor lanes 88b and 86b respectively until any remaining

liquid refrigerant and any oil entrained therein makes its way
to and pools in the bottom of evaporator 20, nominally at a
level indicated at 102, where tube section 84 is found- Such
refrigerant undergoes flooded heat exchange contact with the
portion of the tubes of tube section 84 that are immersed in
such liquid while the oil-rich fluid located there is returned
to the system compressor by pump 34 through line 36. The
efficiency of the vaporization process eliminates the need for
means, such as a pump, for recirculating liqrid refrigerant
within the evaporator to bring it into contact with tubes in
the tube bundle a second or additional times to achieve
vaporization.
It is to be understood that the downward flow of
liquid refrigerant in a falling film evaporator is preferably
in low energy, low velocity droplet form with any liquid
refrigerant that remains in the liquid state after flowing as a
film around a tube surface coalescing to form droplets or, in
some instances, a curtain or sheet of liquid at the bottom of
such tube which falls gentiy onto a tube vertically below it in
the tube bundle. Such refrigerant, after being deposited onto
a lower tube, re-form as a film thereon and flow downward
across the surface thereof with any unvaporized portion of such
liquid, in the same manner, again coalescing at the bottom of
such lower tube. By the creation of a film of liquid
refrigerant around the individual tubes in a tube bundle, the
efficiency of the process by which heat is transferred from the
fluid flowing internal of a tube to refrigerant film coating
the exterior of the tube is enhanced as is the overall
efficiency of the evaporator as a whole. To the extent that
conditions exist within the tube bundle of a falling film

evaporator that cause -liquid refrigerant to be blown off of
individual tubes or to become entrained in refrigerant vapor in
mist form, however, the efficiency of the heat transfer process
suffers.
With the above in mind, vapor lanes 86a, 86b, 88a
and 88b facilitate the flow of refrigerant vapor out of the
interior of tube bundle 52 to the exterior sides 52b and 52c
thereof in a controlled manner which minimizes the effect of
vapor crossflow on the downward flow of liquid refrigerant
droplets thereacross. As will be appreciated, vapor lanes 86a
and 86b are generally horizontal while vapor lanes 88a and 88b
are generally horizontal but have a vertically upward bias at
their exterior ends.
In determining the proper size for a vapor lane,
the thermophysical properties of the refrigerant, the expected
liquid refrigerant droplet diameter and the expected local
vapor velocities are taken into account. Vapor velocity and
mean liquid refrigerant droplet diameter do vary locally

throughout a tube bundle and must be accounted for in
calculating the preferred size of the vapor lanes. Critical to
such analysis are two factors, the first being Weber number
determination and the second being local droplet deflection.
The Weber number is a quantity associated with
inertial and surface tension forces that exist in a gas-liquid
droplet system. As is known to those skilled in the art, if
the Weber number exceeds a certain critical value, vapor cross-
flow will disrupt falling liquid droplet flow between tube rows
in a heat exchanger and will result in the creation of still
fine droplets thereof. Such relatively still smaller droplets
have the tendency to become entrained in the refrigerant vapor
flowing within the tube bundle. The entrainment of such
droplets forms a mist, and a more or less homogenous two-phase
flow pattern within the bundle.

The creation of mist flow within a bundle results
in increased pressure drop in the vapor flowing out of the
bundle as well as the removal of liquid refrigerant from the
bundle without its having had a chance for heat exchange
contact with a tube in the tube bundle. Therefore, such mist
flow not only results in detrimental and efficiency-robbing
pressure drop within the evaporator but can starve a portion of
the tube bundle, most often its lower central portion, of
liquid refrigerant and cause the dryout thereof. That too is
detrimental to the efficiency of the evaporator. Vapor lanes
are therefore sized to minimize the creation of mist flow in
the tube bundle and the pressure drop associated within it.
The maximum acceptable Weber number for combined
droplet/vapor flow in a tube bundle is determined for a
particular bundle configuration and location via experimental
test. Vapor lanes are then sized and positioned within the
tube pattern so as to maintain local Weber numbers below such
maximum values for each section of the tube bundle. By doing
so, refrigerant vapor flows preferentially out of the tube
bundle at predetermined locations and velocities which minimize
the affect of vapor flow out of the tube bundle on the downward
flow of liquid refrigerant within the tube bundle.
Referring now to Figure 7, the effect of vapor
lanes on the flow of liquid and vapor within the tube bundle is
further explained. In that regard, if angle a exceeds angle 9,
liquid droplet 110 will be horizontally displaced to the extent
that in falling downward it will bypass the row of tubes
vertically aligned directly below the tube of its origin.
Vapor lanes are therefore sized and located in the tube bundle
so as to control angle ?.

In a rectangular tube bundle, diagonal liquid flow
is generally not desirable, possibly other than in the very
upper region of the tube bundle where a triangular-pitched
geometry is used to even out of the flow of liquid refrigerant
across the width of the tube bundle and where the effect of
vapor flow is not, relatively speaking, as significant. Vapor
lanes are employed in such bundles to maintain, to the extent
possible, angle a less than angle 6 so that liquid droplets
fall vertically downward onto the tube below in the same
vertical row.
In heat exchangers where the tube bundle is not
necessarily rectangular in nature and may contain individual
tubes which are horizontally outside of the portion of the tube
bundle overlain by the distributor or which are, for instance,
trapezoidal, with the lower portion of the tube bundle being
wider than the upper portion, the use of vapor lanes to
selectively permit angle a to exceed angle 8 may be desirable
in some regions of the tube bundle to promote controlled
horizontal liquid refrigerant migration within the bundle.
Regardless the design strategy used, the use of vapor lanes of
appropriate size and which are appropriately positioned
provides for optimum falling-film performance by maximizing the
wetted tube surface area therein as a percentage of the total
tube surface area available for heat transfer.
The use of vapor lanes has the additional advantage
of permitting water box baffles (also referred to as ribs) to
be located within or aligned with vapor lanes when positioned
against the tube sheet on the side thereof which is opposite
the side of the tube sheet where the tube bundle is disposed.
Such baffles/ribs apportion and direct the flow of fluid
through the tubes in defined sections of the tube bundle. By

the use of appropriately placed and spaced vapor lanes, not
only is the lateral exit of vapor from the tube bundle
facilitated but the need to machine clearances or a complicated
water box baffle configuration to account for non-uniform the
tube patterns and/or the lack of a defined "lane", such as the
vapor lanes in the preferred embodiment, is eliminated.
Appropriately spaced and placed vapor lanes will, therefore,
facilitate multiple water box options and pass strategies while
eliminating time consuming, expensive and complicated machining
steps in the fabrication of evaporator waterboxes.
For example, in the two-pass water box baffle
configuration of evaporator 20 in Figures 2, 3 and 8 the fluid
to be cooled by refrigerant in evaporator 20 is delivered first
into waterbox 200 through inlet piping 202 and then into lower
volume 204 of the waterbox which is upstream of tube sheet 206
and below water box baffle 208. Such fluid then enters the
ends 210 of that portion 212 of the individual tubes 58 of the
tube bundle that open into lower volume 204 and flows down the
length of evaporator 20 in a first pass therethrough.
At the other end of evaporator 20 the fluid is re-
directed by waterbox 214 into the tubes in the upper section of
the tube bundle. The fluid flows back down the length of
evaporator 20 through such tubes in a second pass. The fluid
then enters upper volume 216 of waterbox 200 which is defined
downstream of tube sheet 206 and above baffle 208. The fluid
then flows out of evaporator 20 through outlet piping 218.
As will be appreciated, the fluid to be cooled in
evaporator 20 in the embodiment of Figures 2, 3 and 8 makes two
passes through the evaporator and is thus afforded two chances
to be cooled by the refrigerant therein. Volumes 204 and 216
in waterbox 200 are separated by water box baffle 208 which is

configured to follow and coincide with(albeit on the other
side of the tube sheet) a vapor lane, such as vapor lane 74,
defined in the tube bundle pattern. By their existence, such
vapor lanes result in generally linear and relatively large and
well defined solid and flat surface on the tube sheet against
which the waterbox baffle can abut.
It is to be noted that the flow of the fluid to be
cooled through the tube bundle in evaporator 20 can either be
bottom to top or top to bottom. In the case of a falling film
evaporator, bottom to top flow, as illustrated in Figure 3, is
preferred in order to take advantage of the high heat flux that
will be found in the relatively shallow pool 54 of oil-rich
liquid refrigerant that will exist at the bottom of a falling
film evaporator. In the case of a flooded evaporator, where
the liquid level is high within the evaporator shell and
wherein the majority of the tubes in the tube bundle are
immersed, the vertical direction of the flow of the fluid
through the tube bundle is not as critical.
In prior evaporators, waterbox baffles were often
complicated and had to be configured/machined to weave their
way around open tube ends in an evaporator"s tube sheets for
lack of a well defined, solid and contiguous surface on a tube
sheet against which to abut. The fabrication and assembly of
evaporator 20, by virtue of the fact that the abutment of the
edge of waterbox baffle 208 against the tube sheet can coincide
with the location of a vapor lane in the tube bundle, such as
vapor lane 74, is therefore facilitated and the expense thereof
is reduced.
In applications where it is preferable for the
load-cooling fluid to make three passes through the evaporator,
the water box baffles are configured to follow two vapor lanes
such as vapor lanes 72 and 74 in Figure 2. In that

circumstance the water box baffles are positioned to first
cause the load-cooling fluid to pass in a first direction down
the length of the evaporator through the tubes located
vertically below vapor lane 74. The fluid is then directed by
the water box baffle arrangement to make a second lengthwise
pass of the evaporator through those tubes in the tube bundle
that are below vapor lane 72 but above vapor lane 74. A third
pass back through the evaporator is accomplished through the
portion of the tube bundle above vapor lane 74. In Figure 2,
the inlet and outlet to the waterbox are on the same side of
evaporator 20. As will be apparent, in a three-pass
configuration the inlet and outlet piping through which the
load cooling fluid flows would connect to opposite ends of the
evaporator.
Referring now to Figure 9, it will be appreciated
that the vapor lanes in evaporator 20 can also be configured
within tube bundle 52 in a manner which allows for the use of
individual tubes 58 of different diameters within individual
tube sections. In that regard, tube bundle 52 is comprised of
sections 300, 302, 304, 306 and 308 which are defined by vapor
lanes 310, 312, 314 and 315. Within each of tube sections 300,
302, 304, 306 and 308 multiple tube diameters and/or tube
pitches (spacing) may be employed with the size and location of
the vapor lanes therebetween being maintained constant.
For instance, larger diameter tubes 320, which are,
perhaps, one inch in diameter, may be used throughout the tube
bundle in applications or instances where use of a lower
efficiency evaporator is sufficient or is appropriate for cost
or other reasons. This size tube and the spacing thereof in a
tube section is illustrated to the left of line 324 in Figure
9. Smaller diameter tubes 322 which may, for instance, be

three-quarter inch diameter, tubes, can be used where a higher
efficiency evaporator is appropriate or justified. This size
tube and the spacing thereof in a tube section is illustrated
to the right of line 324 in Figure 9.
The use of smaller diameter tubes will allow for
the placement of more tubes in a tube section than will the use
of larger diameter tubes, making comparatively more tube
surface available for heat transfer in the same space/volume,
all while maintaining vapor lane sizing/location constant to
facilitate the cost effective fabrication of such different
evaporators. As will be appreciated, tubes of more than one
diameter can be used in an evaporator although evaporator and
tube sheet fabrication would be complicated thereby.
By the use of more or fewer tubes within individual
tube sections, while maintaining vapor lane sizing and location
generally constant, the capacity of the evaporator for heat
transfer may be increased or decreased, as required for a
particular application. Further, by the use of commonly
positioned and sized vapor lanes but tubes of different
diameters, as taught hereby, it has been found that evaporators
of multiple capacities and efficiencies can be fabricated using
a shell the length and inside diameter of which are the same.
Such an evaporator design is therefore appropriate for use in
chillers across a significant portion of the tonnage range of a
chiller product line. As will be appreciated, the fabrication
expense associated with producing the family of chillers is
thereby reduced while the ease and efficiency of fabrication is
enhanced since the remainder of the chiller components, their
size and location relative to the evaporator need not change.
Referring now to Figure 10, an alternative
embodiment of the evaporator of the present invention
illustrates the still further versatility thereof. In that
regard, not only does the evaporator of the present invention

permit the use of multiple different tube patterns and multiple
tube diameters and tube pitches within a tube bundle while
maintaining vapor lane position and sizing constant, it
facilitates the use of more than one distributor by which to
accomplish refrigerant distribution across the top of the tube
bundle.
In that regard, in the evaporator of the embodiment
of Figure 10, two, two-phase refrigerant distributors 400 and
402 run generally the length of evaporator 20 and are supported
in structure 4 04 which incorporates not only combination
suction baffles/mounting flanges 66, as was the case in the
earlier described embodiment, but perforations 406 which run
generally the length of the tube bundle 52 between the
individual distributors 400 and 402. Perforations 406
communicate between upper portion 68 of the interior of the
evaporator shell and the space 408 between individual right and
left tube banks 410 and 412. Each tube bank will include
discrete tube sections defined by vapor lanes.
The perforations 406 of structure 404 between
individual distributors in an evaporator employing multiple
two-phase distributors are sized so that local vapor velocities
within the underlying tube bundle are controlled and are kept
below a critical value which, if exceeded, would disrupt liquid
flow downward through the tube bundle, particularly in
locations where such disruption might cause liquid to be
carried out of the tube bundle and, potentially, into upper
portion 68 of the evaporator shell. Keeping lateral vapor
velocities in the tube bundle as low as possible, particularly
in locations immediate the underside of two-phase distributors,
is advantageous and the definition of an internal vapor space
such as space 4 08 and a vertical exit for gas from that space,
such as through perforations 406, accomplishes that purpose.

While distributors 400 and 402 are functionally
similar to distributor 50 of the preferred embodiment, the use
of two such distributors as opposed to one results in the
creation of an additional flow area, in the form of the space
4 08 between the tube banks, by which to conduct vapor out of
and away from the tube bundle and into the upper portion 68 of
the evaporator. Additionally, by the use of multiple
distributors which are narrower in width but which still
overlie the tubes at the top of the tube bundle, the
performance of the distributors themselves is enhanced for the
reason that while the lengthwise distribution of two-phase
refrigerant is relatively simple and efficient, the widthwise
distribution thereof within the distributor is not.
Further, additional cost reductions and economy of
scale in the production of evaporators of the design of the
present invention can be accomplished by employment of an
appropriate number of identical distributors in accordance with
the capacity of the evaporator in which such distributors are
used. For instance, two or more modular tube banks, such as
tube banks 410 and 412, can be employed in such an evaporator
with each tube bank being overlain by one two-phase refrigerant
distributor. Each tube bank can, for example, be designed to
provide a specific number of tons of cooling and can be
separately fabricated.
As mentioned above, the narrower the distributor,
the better is the ability of the distributor to apportion two-
phase refrigerant across the width of the tube bundle it
overlies. By the use of two 250 ton tube banks and a
refrigerant two-phase distributor associated with each, as is
the case with the evaporator of Figure 10, a 500 ton evaporator
can economically be fabricated, distributor width can be
advantageously reduced, vapor exit from the tube bundle

enhanced (as the result of the creation of a space between
individual tube banks) and vapor lane width can be reduced, as
can the footprint of the chiller and diameter of the evaporator
shell. All of these factors cooperate to significantly reduce
the cost of the evaporator"s water boxes and tube sheets, the
cost of the evaporator overall and, therefore, the overall cost
of the chiller.
Referring additionally now to Figure 11, it will be
appreciated that a relatively shallow pool 500 of liquid
refrigerant will exist in the lower portion of the evaporator
shell. That pool, as noted earlier, will contain oil that must
be returned to the chiller"s compressor for use therein.
Generally speaking, the liquid pool at the bottom of evaporator
20 submerges no more than 25% of the total heat transfer
surface area present within tube bundle 52 (25% of the total
tube count in circumstances where a single tube diameter is
used throughout the tube bundle).
While about one-third of the tubes in the tube
bundle will typically be disposed in the lower tube section
502, one-half or less of the tubes in the lower tube section
will typically be immersed in the liquid pool. It is also to
be noted, with respect to the tubes in lower section 502 of
tube bundle 52, that they are of triangular pitch configuration
for the reason that more tubes can be packed thereinto taking
into account the curvature of the shell at the bottom thereof
which is the shell location that most affects tube bundle
geometry.
The nominal level of the liquid pool is indicated
at 504. While the tubes immersed in pool 500 will be in direct
heat exchange contact with the surrounding liquid, the
remainder of the tubes in the lower section of the tube bundle
will not only receive liquid refrigerant dripped from above

that has made its way downward through the tube bundle, but
liquid refrigerant that is sprayed upward from the surface of
pool 500 as a result of the boiling of liquid refrigerant that
occurs within the pool. Preferably, the spray resulting from
such boiling is not sufficiently energetic to cause significant
splashing/spraying of liquid refrigerant upward into vapor lane
506 -or to result in a significant portion of the liquid portion
of the spray being carried out of the vicinity of the tube
bundle entrained refrigerant vapor.
Schematically illustrated in Figure 11 is the
addition of an oil concentrator 508 to evaporator 20. As has
been mentioned, a certain amount of oil will flow out of
refrigerant distributor £0 together with the two-phase
refrigerant issuing thereoutof. As the liquid refrigerant
portion of the two-phase mixture evaporates in its downward
flow through the tube bundle, the concentration of oil in the
remainder of the downward-flowing liquid refrigerant increases.
In the embodiment of Figure 11, a portion of the tubes in lower
tube section 502, such as tubes 510, are disposed internal of
oil concentrator 508 which runs generally the length of the
i
evaporator shell
Concentrator 508 defines an inlet 512 generally at
one end of the evaporator shell. Liquid from pool 500 is drawn
into the concentrator through inlet 512, is drawn therethrough
and is then drawn out of the concentrator via outlet 514 by
apparatus such as pump 34 or an eductor (not shown). Outlet
514 is located at the opposite end of the evaporator shell from
inlet 512. Therefore, liquid flows out of concentrator 508
after flowing down the length thereof through the volume 516
which the concentrator defines.

During the flow of such liquid down the length of
the evaporator shell within concentrator volume 516, it is in
heat exchange contact with the tubes 510 that are disposed
therein and through which relatively warm fluid flows. During
such flow, refrigerant boils out of the liquid, still further
concentrating the oil in the liquid that flows through the
concentrator. The refrigerant vaporized in this process is
conducted out of concentrator 508 through one or more vapor
outlets 520 that communicate between concentrator volume 516
and a location from which it can flow to/into upper portion 68
of the evaporator shell without affecting the downward flow of
liquid refrigerant through the tube bundle.
With this arrangement, oil return from the
evaporator to the system compressor is enhanced and oil
concentration in the majority of the liquid pool within the
evaporator is kept low. Because the amount and concentration
of oil in the evaporator is less, the level of pool 500 and the
control thereof is more forgiving than is the case when oil
concentration in the evaporator pool is higher. As an
alternative to the use of a single inlet to oil concentrator
508 and the exit of liquid which drawn down the entire length
thereof, two or more concentrator inlets can be employed with
outlet 514 being located generally about one-half the distance
down the length of the evaporator shell.
It is to be noted that in the ideal case the design
criteria for evaporator 20, with respect to the distribution of
refrigerant across its tube bundle, is to make such
distribution as uniform as possible. That is the criteria to
which the evaporator of the preferred embodiment is designed.
However, the present invention does contemplate evaporators in
which non-uniform distribution of refrigerant across the tube

bundle is purposefully and strategically accomplished so that
refrigerant is distributed internal of the shell in greater
quantities in some locations than in others. In each case,
however, by the use of appropriately located and spaced vapor
lanes, the overall heat transfer efficiency of the evaporator
will be enhanced.
While the present invention has been described in
terms of preferred and alternative embodiments, it will be
appreciated that other modifications and alterations thereto
are contemplated that fall within the teachings herein and
that, as such, the scope of the present invention is not
limited to the described embodiments.

WE CLAIM:
1. A refrigeration system (10) comprising :
a refrigerant gas compressor (12);
a condenser (16), said condenser receiving compressed gas from said compressor
and condensing said gas to the liquid state ;
a first expansion device (24), said expansion device being downstream of said
condenser and creating a two-phase mixture of refrigerant gas and liquid refrigerant; and
a falling film evaporator, said evaporator having a shell (32), a tube bundle, a vapor
outlet (70) and a refrigerant distributor (50), said vapor outlet being connected for flow to
said compressor and the tubes (58) of said tube bundle running horizontally in said shell,
said refrigerant distributor being disposed above said tube bundle within said shell and
receiving liquid refrigerant from said expansion device, said distributor depositing liquid
refrigerant vertically downward, generally unassisted by pressure, onto the top of said tube
bundle, said tube bundle having at least two tube sections and defining at least one vapor
lane (72, 74), said vapor lane being an essentially unobstructed flow path between said
tube sections that is sized to facilitate the conduct of refrigerant gas out of the interior of
said tube bundle to an exterior side thereof at a velocity and in a manner such that the flow
of liquid refrigerant downward through said tube bundle and across said vapor lane is
generally unaffected by the cross-flow of refrigerant vapor out of the interior of said tube
bundle through said vapor lane.

2. The refrigeration system as claimed in claim 1, wherein a portion of the
liquid refrigerant deposited by said distributor onto the top of said tube bundle
makes its way to the bottom of and pools in said evaporator, the majority of the
tubes of said tube bundle being disposed above said pool.
3. The refrigeration system as claimed in claim 2, wherein said at least one
vapor lane is sized so that the downward flow of liquid refrigerant across said
vapor lane within said tube bundle is substantially unaffected by the conduct of
refrigerant gas through said vapor lane to an exterior side of said tube bundle.
4. The refrigeration system as claimed in claim 3, wherein said distributor is
positioned in said shell so that refrigerant conducted out of the interior of said
tube bundle to an exterior side thereof by said vapor lane flows to said vapor
outlet generally unobstructed by said refrigerant distributor.
5. The refrigeration system as claimed in claim 4, wherein said refrigerant
distributor is a two-phase refrigerant distributor which receives both liquid
refrigerant and refrigerant gas from said first expansion device, said distributor
depositing liquid refrigerant in generally controlled and predictable quantities
across the length and width of the portion of the top of the tube bundle that is
overlain by said distributor.

6. The refrigeration system as claimed in claim 5, wherein one quarter or
fewer of the tubes in said tube bundle are unimmersed in said pool at the bottom
of said evaporator.
7. The refrigeration system as claimed in claim 5, wherein said at least one
vapor lane is defined within said tube bundle so as to provide a generally
unobstructed flow path from the interior of said tube bundle to two exterior sides
thereof, and wherein liquid refrigerant is deposited in generally uniform quantities
across the length and width of the portion of the top of the tube bundle that is
overlain by said distributor.
8. The refrigeration system as claimed in claim 5, wherein the flow of liquid
refrigerant out of said distributor is generally in droplet form, and wherein said
refrigerant distributor and said tube bundle define a vapor space therebetween,
the vertical dimension of said vapor space being the distance between the
underside of said distributor and the top of said tube bundle, said distance being
predetermined to facilitate the lateral flow of refrigerant gas out of said vapor
space at a velocity which does not substantially disrupt the generally vertically
downward deposit of liquid refrigerant droplets from said distributor onto the top
of said tube bundle.

9. The refrigeration system as claimed in claim 8, wherein said at least one
vapor lane provides a generally continuous flow path from the interior of said tube
bundle to two exterior sides thereof from where said refrigerant gas flows from
said two exterior sides of said tube bundle to said vapor outlet via flow paths that
are essentially unobstructed by said distributor.
10. The refrigeration system as claimed in claim 5, wherein refrigerant flowing
from said compressor, to and through said condenser, to and through said first
expansion device and to and through said distributor carries with it oil that
becomes entrained in said refrigerant within said compressor, said oil making its
way into said pool of liquid refrigerant at the bottom of said evaporator shell, said
refrigeration system also comprising apparatus for returning oil that makes its
way into said pool of liquid refrigerant at the bottom of said evaporator to said
compressor.
11. The refrigeration system as claimed in claim 10, wherein said distributor
overlies the majority of the length and width of the top of said tube bundle, and
wherein said at least one vapor lane facilitates the conduct of refrigerant gas from
the interior of said tube bundle to first and second exterior sides thereof, said
distributor depositing liquid refrigerant in generally uniform quantity across the
length and width of the top of the tube bundle which is overlain by said distributor.

12. The refrigeration system as claimed in claim 11, wherein a majority of the
tubes in said tube bundle are oriented in a rotated triangular-pitch configuration.
13. The refrigeration system as claimed in claim 12, wherein a minority
portion of the tubes in said tube bundle are oriented in a triangular-pitch
configuration, the tubes in the uppermost portion of said tube bundle being
oriented in said triangular-pitch configuration.
14. The refrigeration system as claimed in claim 10, wherein said first
expansion device is disposed adjacent the entrance to said distributor so as to
reduce stratification in the two-phase refrigerant mixture received by said
distributor from said first expansion device, and wherein said refrigerant
distributor and said tube bundle define a vapor space therebetween, the vertical
dimension of said vapor space being the distance between the underside of said
distributor and the top of said tube bundle, said distance being predetermined to
facilitate the lateral flow of refrigerant gas out of said vapor space at a velocity
which does not substantially disrupt the vertically downward deposit of liquid
refrigerant by said distributor onto the top of said tube bundle.
15. The refrigeration system as claimed in claim 10 comprising an oil
concentrator, said oil concentrator being disposed in the bottom of said
evaporator, at least one tube of said tube bundle being disposed in said oil
concentrator, a portion of the mixture of liquid refrigerant and oil that pools at the

bottom of said evaporator entering said oil concentrator, a portion of the liquid
refrigerant that enters said concentrator being vaporized by heat exchange
contact with said at least one tube, refrigerant vaporized in said concentrator
exiting said concentrator and being returned into the interior of said evaporator
shell and the remaining portion of the liquid refrigerant and oil in said
concentrator being delivered from said oil concentrator to said compressor by
said oil return apparatus.
16. The refrigeration system as claimed in claim 5 comprising a baffle, said
baffle being interposed between the vapor outlet of said evaporator and the
location at the exterior side of said tube bundle to which said vapor lane conducts
refrigerant gas from interior of said tube bundle, said baffle regulating the flow of
refrigerant gas to said vapor outlet.
17. The refrigeration system as claimed in claim 16, wherein said baffle
supports said distributor within said shell.
18. The refrigeration system as claimed in claim 17, wherein said baffle
defines a plurality of apertures through which refrigerant gas flows enroute from
said tube bundle to said vapor outlet.

19. The refrigeration system as claimed in claim 17, wherein said tube bundle
defines at least two vapor lanes, each of said at least two vapor lanes providing
a generally unobstructed flow path from the interior of said tube bundle to two
exterior sides thereof and at least one of said vapor lanes having a vertically
upward bias.
20. The refrigeration system as claimed in claim 5, wherein said evaporator
has a tube sheet and a waterbox, said waterbox and said tube bundle being
disposed on opposite sides of said tube sheet, the ends of the tubes of said tube
bundle penetrating said tube sheet, said waterbox having a baffle, said waterbox
baffle, by its abutment with said tube sheet, being determinative of which of the
tubes in said tube bundle initially receive the heat transfer medium that flows into
said evaporator, said waterbox baffle abutting said tube sheet in a location that
corresponds to a vapor lane defined by said tube bundle on the other side of said
tube sheet.
21. The refrigeration system as claimed in claim 5, wherein said tube bundle
defines at least two vapor lanes, each of said at least two vapor lanes being
generally unobstructed flow paths running from the interior to first and second
exterior sides of said tube bundle.

22. The refrigeration system as claimed in claim 21, wherein each of said at
least two vapor lanes are sized so that the downward flow of liquid refrigerant
thereacross within said tube bundles is substantially unaffected by the conduct of
refrigerant gas out of the interior of said tube bundle through said vapor lanes,
and wherein a portion of at least one of said at least two vapor lanes has a
vertically upward bias.
23. The refrigeration system as claimed in claim 21, comprising a baffle for
regulating the flow to said vapor outlet of refrigerant gas which is conducted to
the exterior sides of said tube bundle through said vapor lanes, said baffle
supporting said distributor within said shell.
24. The refrigeration system as claimed in claim 1, wherein said evaporator
has at least two refrigerant distributors, each of said distributors receiving a two-
phase refrigerant mixture from said expansion device.
25. The refrigeration system as claimed in claim 24, wherein said tube bundle
has at least two horizontally adjacent tube banks, each of said tube banks being
overlain by at least one two-phase refrigerant distributor and cooperating to
define a generally vertically running space therebetween, each of said tube banks
defining at least one vapor lane to facilitate the flow of refrigerant gas from
interior thereof into said vertically running space, the flow path for refrigerant gas

from said vertically running space to said vapor outlet being generally
unobstructed by a refrigerant distributor.
26. The refrigeration system as claimed in claim 25, wherein said distributors
are supported in said shell by a baffle, said baffle regulating the flow of
refrigerant gas to the vapor outlet of said evaporator.
27. The refrigeration system as claimed in claim 1, wherein said evaporator
has a waterbox and a tube sheet, said tube bundle and said waterbox being
disposed on opposite sides of said tube sheet, said tube sheet being penetrated
by the ends of the tubes of said tube bundle, the portion of said tube sheet that is
unpenetrated by said tube ends and which corresponds to the location of a vapor
lane defined by said tube bundle being generally solid and continuous, said
waterbox having a baffle, said baffle abutting said generally solid and continuous
portion of said tube sheet that corresponds to the location of a vapor lane defined
by said tube bundle and directing the flow of said heat transfer medium, as it
enters said evaporator, into said first portion of the tubes.
28. The refrigeration system as claimed in claim 27, wherein said first portion
of the tubes of said tube bundle is generally vertically below said second portion
of the tubes of said tube bundle so that the flow of said heat transfer medium
into, through and out of said evaporator is from the bottom to the top of said tube
bundle.

29. The refrigeration system as claimed in claim 1 comprising an economizer and a
second expansion device, and wherein said refrigerant distributor is a two-phase
refrigerant distributor that overlies the majority of the length and width of the top of said
tube bundle and deposits liquid refrigerant in generally uniform quantity thereover, said
second expansion device receiving liquid refrigerant from said condenser and creating a
two-phase mixture of liquid refrigerant and refrigerant gas that is communicated to said
economizer, the gaseous portion of said two-phase mixture being communicated from said
economizer to said compressor and the liquid portion thereof being communicated to said
first expansion device.
30. A falling film evaporator for a vapor compression refrigeration system comprising:
a shell, said shell having a vapor outlet;
a tube bundle, the tubes of said bundle running horizontally in said shell, said tube
bundle having at least one vapor lane and at least two tube sections, said vapor
lane being an essentially unobstructed flow path that is defined between said at
least two tube sections through which refrigerant gas flows from the interior to an exterior
side of said tube bundle and thence to said vapor outlet, said vapor lane being sized so
that the flow of refrigerant gas therethrough to said exterior side of said tube bundle is at a
velocity which generally does not disrupt the downward flow of liquid refrigerant through
said tube bundle and across said vapor lane ; and
a refrigerant distributor, said refrigerant distributor being-mounted vertically
above said tube bundle within said shell and depositing liquid refrigerant, in generally
predictable and controlled quantities, onto the top of said tube bundle by force of
gravity and generally unassisted by pressure so that said liquid

refrigerant falls out of said distributor generally vertically downward onto the top of
said tube bundle.
31. The falling film evaporator as claimed in claim 30, wherein a portion of the
liquid refrigerant issuing from said distributor makes its way to the bottom of and
pools in said evaporator, the majority of the tubes of said tube bundle of said
evaporator being disposed vertically above said pool.
32. The falling film evaporator as claimed in claim 31, wherein said refrigerant
distributor is a two-phase distributor and is positioned so that the flow of refrigerant
gas out of said vapor lane to said vapor outlet is generally unobstructed by said
refrigerant distributor.
33. The falling film evaporator as claimed in claim 32, wherein said at least one
vapor lane is sized so that the velocity of refrigerant gas flowing therethrough from
the interior of said tube bundle to said exterior side thereof does not substantially
affect the vertically downward flow of liquid refrigerant across said vapor lane
within said tube bundle.
34. The falling film evaporator as claimed in claim 33, wherein the liquid
refrigerant deposited onto the top of said tube bundle by said distributor is
generally in droplet form and is in generally uniform quantity across the length

and width of the portion of the top of the tube bundle which is overlain by said
distributor.
35. The falling film evaporator as claimed in claim 34, wherein said at least
one vapor lane provides a generally continuous and unobstructed flow path for
refrigerant gas from the interior of said tube bundle to two exterior sides thereof
from where said refrigerant gas flows to said vapor outlet essentially unobstructed
by said distributor.
36. The falling film evaporator as claimed in claim 35, wherein said refrigerant
distributor, in addition to receiving and distributing liquid refrigerant and
refrigerant vapor internal of said shell, receives oil that makes its way thereto
from the compressor of said vapor compression refrigeration system, said oil
making its way into said pool of liquid refrigerant at the bottom of said evaporator
shell.
37. The falling film evaporator as claimed in claim 35, wherein said refrigerant
distributor and said tube bundle define a vapor space therebetween, the vertical
dimension of said vapor space being the distance between the underside of said
distributor and the top of said tube bundle, said distance being predetermined so
as to facilitate the lateral flow of refrigerant gas out of said vapor space at a
velocity which essentially does not disrupt the generally vertically downward fall of
liquid refrigerant droplets from said distributor onto the top of said tube bundle,

said at least one vapor lane likewise being sized so that the velocity of refrigerant
gas flowing therethrough from the interior to the exterior of said tube bundle does
not substantially affect the vertically downward flow of liquid refrigerant through
said tube bundle and across said vapor lane.
38. The falling film evaporator as claimed in claim 35, comprising a baffle, said
baffle being interposed between said vapor outlet and the locations at the exterior
sides of said tube bundle to which said at least one vapor lane delivers refrigerant
gas from the interior thereof and regulating the flow of refrigerant gas from the
exterior sides of said tube bundle to said vapor outlet.
39. The falling film evaporator as claimed in claim 38, wherein said baffle
supports said distributor within said shell.
40. The falling film evaporator as claimed in claim 35, comprising an oil
concentrator, said oil concentrator being disposed in the bottom of said
evaporator, at least one tube of said tube bundle being disposed in said oil
concentrator, a mixture of liquid refrigerant and oil entering said oil concentrator
from the pool of liquid refrigerant and oil that is found at the bottom of said
evaporator, a portion of the liquid refrigerant in said mixture that enters said
concentrator being vaporized within said concentrator, the vaporized refrigerant
exiting said concentrator and being returned into the interior of said evaporator
shell, the remaining portion of said mixture in said concentrator containing an

increased concentration of oil as a result of the vaporization of liquid refrigerant
within said oil concentrator.
41. The falling film evaporator as claimed in claim 35, wherein a majority of the
tubes in said tube bundle are oriented in a rotated triangular-pitch configuration
so that liquid refrigerant flowing downward through the majority of the tubes in
said tube bundle falls generally from a first horizontal row of tubes in said tube
bundle onto tubes in the horizontal row of tubes immediately below.
42. The falling film evaporator as claimed in claim 41, wherein a minor portion
of the tubes in said tube bundle are oriented in a triangular-pitch configuration.
43. The falling film evaporator as claimed in claim 35, wherein said evaporator
has a tube sheet and a waterbox, said tube bundle and said waterbox being on
opposite sides of said tube sheet, the ends of the tubes of said tube bundle
penetrating said tube sheet, said waterbox having a baffle which, by its abutment
with said tube sheet, determines which of the tubes in said tube bundle initially
receive the heat transfer medium that flows into said evaporator, said waterbox
baffle abutting said tube sheet in a location that corresponds to a vapor lane
defined by said tube bundle on the other side of said tube sheet.

44. The falling film evaporator as claimed in claim 35, wherein said evaporator
has at least two refrigerant distributors, each of said distributors being two-phase
refrigerant distributors.
45. The falling film evaporator as claimed in claim 35, wherein said tube
bundle has at least two tube banks, each of said tube banks being overlain by at
least one refrigerant distributor, said tube tanks cooperating to define a generally
vertically running space therebetween and each of said tube banks defining at
least one vapor lane to facilitate the flow of refrigerant gas from the interiors
thereof into said vertically running space, the flow path for refrigerant gas to said
vapor outlet from said vertically running space being generally unobstructed by a
refrigerant distributor.
46. The falling film evaporator as claimed in claim 35, wherein said tube
bundle defines at least two vapor lanes, both of said vapor lanes defining a
generally continuous and unobstructed flow path from the interior of said tube
bundle to two exterior sides thereof.
47. The falling film evaporator as claimed in claim 35, comprising an
expansion device, said expansion device being disposed adjacent the inlet to
said refrigerant distributor and delivering two-phase refrigerant thereinto.

48. A method for controlling vapor flow internally of a falling film evaporatorwhich
employs a two-phase refrigerant distributor and which is used in a vapor compression
refrigeration system as clained in claim I comprising the steps of:
positioning said refrigerant distributor vertically above a tube bundle within the shell
of said evaporator;
delivering a two-phase mixture of liquid refrigerant and refrigerant gas into said
distributor;
flowing said two-phase refrigerant mixture internal of said distributor so that at least
the liquid portion of said two-phase mixture is made available for distribution generally
throughout the length and width thereof;
depositing, in a generally vertically downward direction and in relatively low-energy
droplet form, the liquid refrigerant portion of said two-phase mixture across the portion of
the top of said tube bundle that is overlain by said distributor;
flowing liquid refrigerant deposited onto the top of said tube bundle generally
vertically downward therethrough ;
defining at least one generally unobstructed vapor lane within said tube bundle that
runs from the interior to an exterior side thereof, said vapor lane dividing said tube bundle
generally into tube sections and being sized to conduct refrigerant gas from the interior to
an exterior side of said tube bundle at a velocity which generally does not disrupt the
downward flow of liquid refrigerant through said tube bundle and across said vapor lane ;
and flowing the refrigerant gas conducted via said vapor lane out of the interior of
said tube bundle to the vapor outlet of said evaporator by a path that is generally
unobstructed by said distributor.

49. The method as claimed in claim 48 comprising the step of collecting at
least a portion of the liquid refrigerant that is deposited onto the top of the tube
bundle and flows downward through said tube bundle in a pool at the bottom of
said evaporator shell.
50. The method as claimed in claim 49 comprising disposing a minor portion
of the tubes of said tube bundle in said pool of liquid refrigerant that is collected
in the bottom of said evaporator shell.
51. The method as claimed in claim 50 comprising the step of sizing said
vapor lane so that the downward flow of liquid refrigerant across said vapor lane
is substantially unaffected by the conduct of refrigerant gas from the interior of
said tube bundle through said vapor lane to an exterior side thereof.
52. The method as claimed in claim 51, wherein said step of defining said
vapor lane comprises the step of providing a generally unobstructed and
continuous flow path for the conduct of refrigerant gas out of the interior of said
tube bundle to two exterior sides thereof.
53. The method as claimed in claim 52, wherein said step of depositing liquid
refrigerant onto the top of said tube bundle comprises the step of depositing
generally uniform quantities of liquid refrigerant across the length and width of
said tube bundle that is overlain by said distributor.

54. The method as claimed in claim 53 comprising the step of defining a vapor
space between said distributor and the top of said tube bundle, the vertical
dimension of said vapor space being the distance between the underside of said
distributor and the top of said tube bundle, said distance being predetermined to
facilitate the lateral flow of refrigerant gas out of said vapor space at a velocity
which does not substantially disrupt the generally vertically downward deposit of
liquid refrigerant from said distributor to the top of said tube bundle.
55. The method as claimed in claim 53 comprising the step of orienting a
majority of the tubes of said tube bundle that are located vertically above said
pool in said evaporator in a rotated triangular-pitch configuration so that the
downward flow of liquid refrigerant through said majority of tubes located above
said pool is from the tubes in one horizontal row of tubes in said tube bundle
downward onto corresponding vertically aligned tubes in the horizontal row of
tubes immediately below said one horizontal row.
56. The method as claimed in claim 53 comprising the step of regulating the
flow of refrigerant gas from said tube bundle to said vapor outlet by the use of a
baffle.
57. The method as claimed in claim 56 comprising the step of supporting said
distributor in said evaporator shell with said baffle.

58. The method as claimed in claim 53 comprising the step of reducing the
stratification in the two-phase mixture of refrigerant received into said distributor
by disposing an expansion device adjacent the entry to said refrigerant
distributor.
59. The method as claimed in claim 53 comprising the step of defining a
plurality of vapor lanes in said tube bundle.
60. The method as claimed in claim 53, wherein said evaporator comprises a
tube sheet and a waterbox, the ends of the tubes of said tube bundle penetrating
said tube sheet and said tube bundle and waterbox being disposed on opposite
sides of said tube sheet, and comprising the step of directing the heat transfer
medium that flows through said evaporator into a first portion of the tubes of said
tube bundle by the use of a waterbox baffle that abuts said tube sheet in a
location that corresponds to a vapor lane defined by said tube bundle.
61. The method as claimed in claim 53, wherein said tube bundle has at least
two tube banks, each of said tube banks being overlain by a refrigerant
distributor, and comprising the steps of defining a generally vertically running
space between said tube banks ; defining at least one vapor lane in each of said
tube banks that opens into said generally vertically running space ; conducting
refrigerant gas out of the interior-of each of said tube banks into said

vertically running space ; and, conducting refrigerant gas from said vertically
running space to the vapor outlet of said evaporator through a flow path that is
generally unobstructed by a refrigerant distributor.
62. The method as claimed in claim 53 comprising the steps of receiving oil as
well as two-phase refrigerant into said distributor; flowing said oil out of said
distributor and downward through said tube bundle into said pool of liquid
refrigerant at the bottom of said evaporator shell; and returning a mixture of liquid
refrigerant and oil from said pool at the bottom of said evaporator to the
compressor of said vapor compression refrigeration system.
63. The method as claimed in claim 62 comprising the step of increasing the
concentration of oil in the mixture of liquid refrigerant and oil that is returned from .
said evaporator pool to said compressor in said returning step by vaporizing a
portion of the liquid refrigerant in said mixture within said shell.
64. The method as claimed in claim 53 comprising the steps of reducing the
pressure of liquid refrigerant received from the condenser a first time so as to
create a lower pressure mixture of liquid and gaseous refrigerant; delivering said
gaseous refrigerant portion of said lower pressure refrigerant mixture to the
compressor of said refrigeration system ; lowering the pressure of the liquid
portion of said lower pressure refrigerant mixture a second time so as to create a
second and still lower pressure mixture of liquid refrigerant and

refrigerant gas ; and wherein the twophase mixture of refrigerant delivered in said
delivering step is said second and still lower pressure mixture of liquid refrigerant
and refrigerant gas.
A refrigeration system (10) comprises :
a condenser (16) receiving compressed gas from a compressor (12) and
condensing it to liquid state ;
an expansion device (24) downstream of the condenser (16) for forming a
two-phase mixture of refrigerant gas and liquid refrigerant; and
a falling film evaporator (20) having a shell (32), a tube bundle, a vapor
outlet (70) connected to the compressor and tubes of the bundle and a refrigerant
distributor (50), the tubes running horizontally in the shell, the distributor (50) being
disposed above the tube bundle within the shell and receiving liquid refrigerant
from the expansion device (24), for depositing liquid refrigerant vertically downward
onto the top of the tube bundle (52), said tube bundle defining at least one vapor
lane (72, 74) allowing unobstructed flow path for the refrigerant gas out of the
interior of the tube bundle (52) to an exterior side thereof at a velocity and in a
manner such that the flow of liquid refrigerant downward through said tube bundle
and across said vapor lane is generally unaffected by the cross-flow of refrigerant
vapor out of the interior of said tube bundle through said vapor lane.

Documents:

IN-PCT-2002-549-KOL-CORRESPONDENCE.pdf

IN-PCT-2002-549-KOL-FORM 27.pdf

IN-PCT-2002-549-KOL-FORM-27-1.pdf

IN-PCT-2002-549-KOL-FORM-27.pdf

in-pct-2002-549-kol-granted-abstract.pdf

in-pct-2002-549-kol-granted-assignment.pdf

in-pct-2002-549-kol-granted-claims.pdf

in-pct-2002-549-kol-granted-correspondence.pdf

in-pct-2002-549-kol-granted-description (complete).pdf

in-pct-2002-549-kol-granted-drawings.pdf

in-pct-2002-549-kol-granted-examination report.pdf

in-pct-2002-549-kol-granted-form 1.pdf

in-pct-2002-549-kol-granted-form 13.pdf

in-pct-2002-549-kol-granted-form 18.pdf

in-pct-2002-549-kol-granted-form 3.pdf

in-pct-2002-549-kol-granted-form 5.pdf

in-pct-2002-549-kol-granted-form 6.pdf

in-pct-2002-549-kol-granted-gpa.pdf

in-pct-2002-549-kol-granted-letter patent.pdf

in-pct-2002-549-kol-granted-reply to examination report.pdf

in-pct-2002-549-kol-granted-specification.pdf


Patent Number 216036
Indian Patent Application Number IN/PCT/2002/549/KOL
PG Journal Number 10/2008
Publication Date 07-Mar-2008
Grant Date 06-Mar-2008
Date of Filing 29-Apr-2002
Name of Patentee AMERICAN STANDARD INTERNATIONAL INC.,
Applicant Address 1370 Avenue of the Americas,33 RD Floor, New York 10019, USA
Inventors:
# Inventor's Name Inventor's Address
1 MOEYKENS SHANE N1946 SUMMIT DRIVE LA CROSSE, WI 54601, UNITED STATES OF AMERICA.
2 LARSON JAMES W 2620 GREENWOOD DRIVE, LA CROSSE, WI 54601, UNITED STATES OF AMERICA.
3 HARTFIELD JON P 486 SOUTH 20TH STREET LA CROSSE, WI 54601, USA.
4 RING HARRY K ROUTE 2,BOX 13, HOUSTON, MN 55943, USA.
PCT International Classification Number F25B 39/02
PCT International Application Number PCT/US00/30735
PCT International Filing date 2000-11-08
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 09/466,397 1999-12-17 U.S.A.