Title of Invention	A DEVICE USEFUL FOR MEASURING THE FLOW RATE OF CRYOGENIC LIQUIDS FLOWING THROUGH A TUBE.
Abstract	The present invention relates to a device useful for measuring the flow rate of cryogenic liquids flowing through a tube. Particularly, the present invention provides a device useful as a flow meter for measurement of flow rate of liquid nitrogen or any other cryogenic liquid through tubes without offering any additional resistance to the flow.

Full Text

This invention relates to a device useful for measuring the flow rate of cryogenic liquids flowing through a tube. The present invention particularly relates to a device useful as a flow meter for measurement of flow rate of liquid nitrogen (LN2) or any other cryogenic liquid through tubes • without offering any additional resistance to the flow. Large amount of liquid nitrogen is nowadays routinely infused in coal mines through boreholes for control of fire. For this purpose the cryogenic liquid from tankers is flushed to underground mines direct through boreholes or through super insulated tubes laid along boreholes. For best results it is imperative that flow of LN2 be measured accurately. To the best of our knowledge the existence of flow meter for measuring flow rate of cryogenic liquids through such tubes is not known. However , presently the following practices are being adopted for measuring flow rate of liquid nitrogen to control fire in underground mines. The level difference of LN2 in a tanker is measured with the help of a meter which is suitably calibrated. This level difference serves as an indicator for measuring flow rate of inert cryogenic liquid flushed. If there is any leakage in the tanker, flow of cryogenic liquid can not be measured accurately by this process. Further if LN2 or any other cryogenic liquid is flushed through two or more boreholes simultaneously flow through individual borehole can not be measured. The known flow meters using orifice principle, Venturimeter, Rotameter, the flow meter using vortex principle are not well suited for measurement of flow rate of cryogenic liquid because of typical cryogenic properties of the liquid. Further they always offer some amount of resistance to the flow being measured. The main object of the present invention is to a provide a device useful for measuring the flow rate of cryogenic liquids flowing through a tube. Another object of the present invention is to provide a device for measuring flow rate of inert cryogenic liquid precisely, as the rate of injection as well as the total amount of LN> injected in an underground fire area arc two very important parameters for quick control of lire and optimisation of use of LN.>. Yet another object is to measure the flow rate without hindering/offering additional resistance to the flow of cryogenic liquid. Figs 1, 2 & 3 of the drawings accompanying this specification shows the sectional elevation, sectional side view (at AA) and sectional plan (at I IB) respectively of the device of the present invention. Accordingly, the present invention provides a device useful for measuring the flow rate of cryogenic liquids flowing through a tube, which comprises two coaxial tubes (5) & (6) integrated at both ends by means such as plugs (3) & (4), the space between the coaxial tubes being air-free and filled with insulating material known in the art; the said coaxial tubes(5) & (6) being provided at the bottom walls with a segmental opening with sealed ends in such a manner so as to accommodate a closed ended hollow cylinder (7) having a matching inner surface profile as that of inner surface of the said tube (5), the outer surface of the said hollow cylinder (7) having insulatingly (9) fixed onto it one end of a conducting strip (8), the strip (8) being rotatably fixed at its middle portion by means (10,12,14) such as a hinge (10), support (12), and fixed frame (14) in such a manner that the inner surface of the cylinder (7) flushes with the inner wall of the tube (5) and allows lateral movement of the said cylinder (7) due to drag force of cryogenic liquid flow, the said frame (14) having two insulators (17) fixed onto it to support a stretched potentiometer wire (13) in such a manner that the said wire (13) and the free end of the said conducting strip (8) are in contact to form the junction of two arms of a wheatstone bridge (13) & (21), the conducting strip (8) being provided between the hinged point (10) & potentiometer wire contact end with a coaxial coil (II), one end of the coil (11) being connected through a slackening wire (18) to one end of another coaxial coil (19) insulatingly (22) fixed onto the said frame (14), the frame (14), strip (8), wire (13), coils (11) & (19) being enclosed in a dual walled (15, 16) jacketed and insulated casing in such a manner as to allow electrical connections to be taken out from the two ends of potentiometer wire (13), hinged portion of the conducting strip (8) and the free ends of the coaxial coils (II) & (19) and connected to a wheatstone bridge (21) and a microprocessor unit (20) respectively. In an embodiment of the device of the present invention the overall density of the set-up consisting of the hollow cylinder, conducting strip and attached coaxial coil may be same as that of the cryogenic liquid, the flow rate of which is to be measured. In another embodiment the two coaxial coils used may be such that the current flow through the coils is in opposite direction to one another. In yet another embodiment the microprocessor unit used may be such as having Analogue to Digital Converter (ADC) port. Digital to Analogue Converter (DAC) port, plurality of memory locations and display unit interface. The following basic principles have been used in the device of the present invention to measure rate of flow of LN2 flushed through tubes laid along a borehole intersecting an opening below ground to control fire. When cryogenic liquids such as liquid nitrogen is passed through a pipe it exerts a Drag Force at the wall of the pipe along the direction of flow. This Drag Force is proportional to the square of the velocity of the fluid, roughness of the pipe wall, density and viscosity of the fluid. For a particular fluid and pipe system all the parameters are constant, only the velocity changes with the quantity of flow. Therefore, force on a small segment of the pipe wall is proportional to square of the velocity and hence square of flow rate of the liquid. In fact a detailed experimentation has lead to the following well established empirical relation. Τ = 0.034 p Um2( v / Ur)0.25 (1) Where t is the drag stress on pipe wall, N m"2 p is the density of the fluid, Kg/m3 v is the viscosity, m2/sec Um is the velocity of the fluid in the pipe, m/sec r is the radius of the pipe, m. The flow criterion in the pipe may be regarded as a boundary layer on a flat plate which has been wrapped round an axis at a distance 8 from the plate equal to radius r of the pipe. The axial velocity Um is equivalent to the undisturbed stream velocity U of the flat surface boundary layer. The drag force is the product of t and the surface area of the walls over the length 8x, that is tP8x where P is the perimeter of the pipe. Therefore, drag force is proportional to the square of velocity of fluid flow and hence proportional to square of the volume flow rate. However, for the volume flow rate of our interest and pipe diameter normally used in infusion of LN2 in mines the drag force would be small, so for accurate measurement of the volume flow rate the system must have a device to measure small force accurately. This is embodied as the device of the present invention in the following manner: A small segment of the pipe wall is cut, removed and replaced by a hollow cylinder having its inner surface the same profile as that of the inner wall of the pipe. A thin metal strip is fixed at the centre of the outer surface of the hollow cylinder. The metal strip is hinged at around its middle portion such that inner surface of the cylinder flushes with inner wall of the pipe and the cylinder can easily move laterally due to drag force on it. The gap between the cylinder and the pipe is however kept small. The material of the hollow cylinder, the metal strip and the volume of the cylinder are so fixed that overall density of entire set-up is same as that of LNi. Therefore when the system is immersed in LNi no downward or upward force is experienced by the set-up due to gravity or buoyancy. The free end of the metal strip smoothly slides on a potentiometer wire and its contact point forms the junction of two arms of a wheatstone bridge. The other two arms of the bridge are so adjusted that when there is no flow of liquid through the pipe the contact point is at the middle of the potentiometer wire and a small amount of unbalanced voltage is available between the junctions of the bridge. This unbalanced voltage is fed to 'Analogue to Digital Converter' (ADC) port of a microprocessor based unit and the converted digital data is stored in the memory location Mi of the microprocessor unit. As the fluid flows through the pipe the hollow cylinder is dragged towards the direction of flow (say to the right) and the free end of the metal strip is pushed towards the opposite direction (say to the left), consequently the junction of the wheatstone bridge changes, thereby changing the unbalanced voltage. The arrangement of the bridge is such that as the free end of the metal strip moves towards left the unbalanced voltage increases. The new unbalanced voltage becomes input to the ADC port and the corresponding digital value is stored in some other memory location. As the flow increases after certain interval of time the corresponding digital values of the unbalanced voltage are stored in successive memory locations. When the flow becomes steady the digital value is stored in memory location M2. The processor then compares the values stored in memory locations MI and M2. Depending upon the value difference stored in Mi & M2 the processor correspondingly gives an output analogue signal through the 'Digital to Analogue Converter' (DAC) port. This analogue voltage is fed as the input to two coaxial coils connected in series and arranged parallel to each other. One coil is fixed while the other is mounted on the metal strip attached to the hollow cylinder. Winding in the coils are such that current flow through the coils is in opposite direction to each other. It can be proved that under the aforesaid circumstances the force of repulsion, F between these two coils is approximately given by: F-1.5^171. i,ib.a2b2x/(a2 + x2)3/2 where, x is the distance between the coils along their axis a, b are the radius of the coils i., ih are the current through the coils a & b respectively u is the magnetic permeability of the medium In our case ia = ih = i, a & b are fixed and x is also constant for central position of the metal strip. Therefore, F = ki2 (2) where k = 1.5 µ . a2b2 x / (a2 + x2 )3/2 For the equilibrium of the hollow cylinder A. τ. li = k. i2. \2 (3) where li and 12 are the distances of the cylinder and the coil from the hinge of the metal strip, A is the area of the cylinder surface exposed to the liquid flow. Substituting the value of T in equation (3) the above expression may be written as: A[Q.034 p Um2( v / Ur)025] 1, - k. i2.12 or, Um2 - K. I2 where K = k.12 / A[0.034 p Um2( v / Ur)025] 1, or, Um is proportional to I Since the volume flow of liquid through the pipe is proportional to velocity of the liquid, volume flow rate through the pipe is directly proportional to current flow through the coil. Thus if the output analogue voltage is adjusted so that flow of current through the set of coaxial coils increases till the repulsive force produced between them pushes the metal strip back to its initial central position. This is confirmed by the processor as it gets an input value same as stored in memory location MI. At this point current through the coil ceases to increase and remains constant. Under the circumstances the value of the current flowing through the coils becomes a measure of the applied force on the metal strip and hence the flow rate of the liquid. This value is calibrated and displayed in terms of flow rate (litre/min). When the flow starts decreasing and gradually stops the processor still supplies current to the coils. As a result the metal strip slides to the right direction and the input voltage to the microprocessor reduces and may become negative. When the input digital value becomes less than the value stored at MI or negative the processor reduces the output analogue voltage and less current flows through the coils indicating reduced flow through the tube. As the flow reduces further current through the coils also reduces. Finally when flow reduces to zero and the microprocessor stops generating output analogue voltage, current through the coil is also zero. The description of an embodiment of the present invention with reference to Figs. 1, 2 & 3 of the drawing accompanying this specification is as follows: The device essentially consists of two coaxial tubes (5) & (6) integrated with plugs (3) & (4) at both the ends. A small segment at the bottom of the coaxial tubes (5) & (6) is cut, removed to accommodate a hollow cylinder (7). A metal strip (8) rounded off at the bottom is welded with the cylinder (7). The metal strip (8) hinged at (10) supported on a metal flat (12) is fitted with a coil (11) mounted at its lower portion. The lower portion of the metal strip (8) is electrically insulated from the upper portion by an insulator (9). The metal flat (12) is fitted in such a way that the metal strip being hinged at (10) can slide on a potentiometer wire (13) and its contact point forms the junction of two arms of a whetstone bridge (13) & (21). The metal flat (12) is supported on a frame (14), two ends of the frame (14) are welded with the tube (6). The horizontal segment of the frame (14) accommodates part of the whetstone bridge circuit (13). Potentiometer wire is mounted on two insulators (17) which is based on the frame (14).The bigger coil (19) is fixed at one side of the frame (14) but electrically insulated from it by an insulator (22) while the coil (11) moves with the metal strip (8) and a slackening wire (18) connects the coil (11) & (19). The whole system is enclosed in two parallel metal casing (15) & (16) maintaining an air free space between them which is filled up with insulating material. Two ends of the potentiometer wire (13) are connected with whetstone bridge (21) at the outside of the casing (15) & (16). Further, the two ends of the coils (19) & (11) and a connection from the hinge (10) of the metal strip (8) are brought out of the casing (15) & (16) and connected to the microprocessor unit (20). The working of the device of the present invention for accurate measurement of flow of liquid nitrogen or other cryogenic liquid is given below: Cryogenic liquid is passed through the pipe (2) connected with the liquid container (1) into the device. The liquid passes through the tube (5) produces a drag force which makes the hollow cylinder (7) slide horizontally in the direction of flow. The hollow cylinder (7) is fixed with a metal strip (8) hinged at (10) with a metal flat (12). The metal flat (12) is fixed at the bottom of the metal frame (14), to make the system rigid, the metal frame (14) is welded with the tube (6). During the movement of rectangular cylinder (7) due to drag force of the liquid in the right hand direction, the opposite end of the metal strip (8) will move towards the left hand direction on the hinge (10). The lower portion of the metal strip (8) is provided with a coil (11) while the bottom end of the metal strip (8) is in contact with a potentiometer wire forming two arms of a whetstone bridge. The potentiometer wire (13) is mounted on two insulators (17) which is based on the frame (14). At no flow condition the metal strip (8) would make contact with the middle of the wire (13) which would send a very small positive voltage to the microprocessor unit (20) which however would respond only when unbalance voltage exceeds this value. The other parts of the whetstone bridge circuit (21) is placed outside the casing (15) & (16). The movement of contact with whetstone bridge circuit (13) will unbalance the bridge, output of which is fed to a microprocessor unit (20). The microprocessor unit (20) will now produce a DSc current proportional to the bridge (13) output and fed to the coil (19) and coil (11). Both the coils (19,11) are connected with a thin slack wire (18) so that the same current flows through both the coils but in opposite directions. The slack wire (18) does not produce hindrance to the movement of the coil (11) with the respect to coil (19). The coil (19) is fixed with the metal frame (14) but insulated from it by an insulator (22), while coil (II) can move with the metal strip (8).The current in the coils (19,11) will produce repulsive force which will move the metal strip (8) back till a balance position is attained reducing, the bridge (13) output below a prefixed small value, under which condition the microprocessor unit (20) will stop further increase in value of current supplied to the coil. The value of this current is calibrated against the flow rate of cryogenic liquid through the device and displayed in a liquid crystal display panel. Any change in the flow rate of liquid will produce corresponding change in drag force on the hollow cylinder (7) and the microprocessor unit (20) will effect change in the current flowing through the coils (19,11) to keep the metal strip (8) in the central position. The, main advantages of the device of the present invention are: 1. Precise measurement of flow of inert cryogenic liquid at any time is assured by this invention. 2. Avoids rough estimation of flow of LNG from a tanker at a particular time, thus enabling the user to make proper plan for flushing LNG through borehole to control fire in underground mine. 3. Helps in optimising LN2 flushing through boreholes, thus combating of fire is possible in minimum time. 4. Can be made economically. 5. Since the sensing element is such that its average density is same as that of liquid whose flow is to be measured, the device need not be kept in horizontal position. 6. Can also be used for measurement of flow rate of any other non-conducting liquid. 7. The system does not introduce any resistance to the flow of liquid being measured. We Claim: 1. A device useful for measuring the flow rate of cryogenic liquids flowing through a tube, which comprises two coaxial tubes (5) & (6) integrated at both ends by means such as plugs (3) & (4), the space between the coaxial tubes being air-free and filled with insulating material known in the art; the said coaxial tubes(5) & (6) being provided at the bottom walls with a segmental opening with sealed ends in such a manner so as to accommodate a closed ended hollow cylinder (7) having a matching inner surface profile as that of inner surface of the said tube (5), the outer surface of the said hollow cylinder (7) having insulatingly (9) fixed onto it one end of a conducting strip (8), the strip (8) being rotatably fixed at its middle portion by means (10,12,14) such as a hinge (10), support (12), and fixed frame (14) in such a manner that the inner surface of the cylinder (7) flushes with the inner wall of the tube (5) and allows lateral movement of the said cylinder (7) due to drag force of cryogenic liquid flow, the said frame (14) having two insulators (17) fixed onto it to support a stretched potentiometer wire (13) in such a manner that the said wire (13) and the free end of the said conducting strip (8) are in contact to form the junction of two arms of a wheatstone bridge (13) & (21), the conducting strip (8) being provided between the hinged point (10) & potentiometer wire contact end with a coaxial coil (11), one end of the coil (11) being connected through a slackening wire (18) to one end of another coaxial coil (19) insulatingly (22) fixed onto the said frame (14), the frame (14), strip (8), wire (13), coils (11) & (19) being enclosed in a dual walled (15, 16) jacketed and insulated casing in such a manner as to allow electrical connections to be taken out from the two ends of potentionmeter wire (13), hinged portion of the conducting strip (8) and the free ends of the coaxial coils (11) & (19) and connected to a wheatstone bridge (21) and a microprocessor unit (20) respectively. 2. A device as claimed in claim 1, wherein the two coaxial coils used are such that the current flow through the coils is in opposite direction to one another. 3. A device as claimed in claim 1, wherein the microprocessor unit comprises of Analogue to Digital Converter (ADC) port. Digital to Analogue Converter (DAC) port, plurality of memory locations and display unit interface. 4. A device useful for measuring the flow rate of cryogenic liquids flowing through a tube substantially as herein described with reference to the examples and drawing accompanying the specification.

Documents:

2525-del-1998-abstract.pdf

2525-del-1998-claims.pdf

2525-del-1998-correspondence-others.pdf

2525-del-1998-correspondence-po.pdf

2525-del-1998-description (complete).pdf

2525-del-1998-drawings.pdf

2525-del-1998-form-1.pdf

2525-del-1998-form-19.pdf

2525-del-1998-form-2.pdf

2525-del-1998-form-3.pdf