|Title of Invention||
REFRIGERATION CUM HEATING SYSTEM
|Abstract||REFRIGERATION CUM HEATING SYSTEM|
|Full Text||FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
(See Section 10)
TITLE OF INVENTION
(a) INDIAN INSTITUTE OF TECHNOLOGY Bombay (b) having administrative office
at Powai, Mumbai 400076, State of Maharashtra, India and (c) an autonomous
educational Institute, and established in India under the Institutes of Technology Act
The following specification particularly describes the nature of the invention and the manner in which it is to be performed.
FIELD OF INVENTION
The present invention relates to refrigeration cumAheating system. based on
adsorption cycle that can be heated by various sources such as solar energy,
direct fuel firing and waste heat.
BACKGROUND OF INVENTION
Heat driven .sorption refrigeration cycles have existed in literature since 1909, and refrigeratorsare commercially available since 1920"s. Environment friendly solid sorption systems with non-polluting refrigerants can efficiently use natural gas or solar energy as primary energy. Further this provides a system with no moving parts making it silent and maintenance free. Adsorption heating and cooling is therefore a good alternative to classical vapor compression systems. Adsorption cooling units are attractive as they can be operated at temperatures in which liquid absorption systems cannot work. The desirable features are higji oeffjcient of performance (COP), high specific cooling power (SCP) and theffiermodynamic efficiency, which is the ratio between the COP and the Carnbt COP.
The thermodynamic efficiency of the adsorption heat pumps is much lower than that of the conventionally employed compression heat pumps. Adsorption heat pumps are generally suitable for waste heat and solar energy based operation.
US Patent483227_disclose an adsorption based heat pump providing semi-continuous or substantially continuous refrigeration and/or heating. The -limitations of such systems are intermittency in supply of useful cooling or heating effects and varying heat delivery temperatures.
.Continuous delivery of output with small" temperature variation is achieved "through "regenerative cycles" in which at least two reactors operate out of phase with internal heat recovery. US Patent 537,815, US Patent 5,046, 319 of Jones, and US Patent 4,694.659, US Patent 4,6,10,148 of Shelton disclose^arioas ways of implementing separate heat transfer fuiled loop passing through the bed for regeneration. Heat transfer fluid loop in the regenerative cycle helps increase COP. However, in such systems pumps are required to circulate the heat transfer fluids through the beds, valves and their control systems are needed to regulate and divert the flow in various loops. This results in operational complexity and increased capital cost due to requirements of pumps valves and their controls.
systems are not suitable for very small capacities (e.g. 50 to 500 W).
US Patent 5fjy!ZJi.0^discloses an efficient adsorption based thermal compressor
"which used heat recycling. The system uses a thermal storage device for storing the heat released during adsorption which is used in next cycle during generation. Technology for heat transfer fluid loops is disclosed in US Patent "0,647,507." Its cost is high and requires thermal storage, pumps and associated con^olirThese systems are also not suitable for very small capacities (e.g. 50 to 500 W).
US Patent ^4,76.5^335 and US Patents,079,92.8 disclose a scheme of cascading reactors, each using a solid adsorbent and refrigerant. Heat released during
adsorption in one module is used for generation in the subsequent module. COP is increased by exchanging heat between the reactors. But, this-arrangement is not appropriate for small refrigeration systems.
US Patent 5,477,705 discloses an adsorption system in which the reactor has separate compartments. It has means for circulation of heat transfer fluid through hot and cold reactors in such a fashion that a solid someni tempefature front successively passes through the first compartment to the last arfd vice versa. This allows the efficient recycling of heat. However this requirement of several valves and controls complicates the system and increases the capital cost. Literature review by Wang and Dieng ("Literature review on solar adsorption technologies for ice-making and air-conditioning purposes and recent developments in solar technology", Renewable & Sustainable Energy Reviews, Vol. 5, pp. 313-342, 2001) on solar adsorption systems indicates that to produce simple and cost effective devices more attention is needed to reduce the number of valves.
US Patent 4.594.856 describes a single stage pressure equalization technique, which increases the COP, but the complexity of the system makes this system inappropriate for small capacities.
Cycle time plays an important role in determining the compactness of the system. Cycle time can be decreased in adsorption refrigerators and heat pumps by improving heat and mass transfer rates. But, increasing heat transfer area to increase heat transfer rates leads to increase in thermal mass which increases thermal cycling losses and leads to reduction in COP. The present invention addresses drawbacks of the prior art.
The desirable features of the adsorption refrigeration system are:
a. improved COP
b. high specific cooling power leading to compact unit
c. regeneration without separate fluid loops
d. reduced cycle time
e. simple operational controls
f. flexibility of using waste heat
SUMMARY OF THE INVENTION
The main object_of this invention is to provide low cost and compact refrigeration cultivating system,"based on adsorption refrigeration cycle that can be heated oy various sources like solar energy, direct fuel firing and waste heat.
Another object of the invention is to provide a system cu. _. _ plurality of
adsorption modules operating put of phase, to give continuous refrigeration and/or heating.
Yet another object of the invention is to increase the COP of the system without a separate loop circulating the heat transfer fluid.
Another object of the invention is to provide regeneration using multi stage
pressure equalization process.
Yet another object of the invention is to reduce cycle time withoufraffecting COP.
Yet another object of the invention is to reduce life cycle cost of the adsorption system.
Another object of the invention is to use waste heat as heat source
Yet another object of the invention is to provide a means for simpJe control of the system
Another object of the invention is to achieve high, specific cooling power
This invention provides a compact refrigeration cum heating system comprising a. judicious combination of
• a heat source
• set of adsorption modules that operate out of phase, to give continuous refrigeration and/or heating,
• switchable heat pipes in thermal contact with the wall and/or partition of the adsorption modules,
• heat pipes and
• heat recovery unit
functioning to provide regeneration resulting in high COP, reduced cycle time, high specific cooling power and thermodynamic efficiency.
Features and advantages of this invention will become apparent in the following detailed description of the preferred embodiments of this invention with reference to the accompanying drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is the schematic of the refrigeration cum heating system using solar
FIG. 2 is the schematic of the module piping.
FIG. 3 is the adsorption cycle represented on Activated Carbon/Ammonia PTX
FIG. 4 is the schematic of switchable heat pipes used in solar refrigeration cum heating
FIG.1 shows the schematic of one of the embodiments of SR
supplied to and removedpism the adsorption modules using the switchable heat pipes. The valves 505 506 507, 607 of the switchable heat pipes and other control valves 71 fmay bVarranged in such a way, so that they"can be, controlled using cams driven by a single motor 701 thereby making the operation simple. Heating heat pipe consists of switchable heat pipes with hot end^501 integrated with solar collector 700 and switchable heat pipes with cold ends 504 an.C6Q4 in thermal contact with adsorption modules 550 and 650 respectively, riot end 501 and cold ends 504 and 604 are connected using a pinchable connection 502.
FIG.2 shows details of the module piping for a set of two modules 500, 600. Each module 500/600 is made up of a containment vessel 550 containing suitable adsorbant and the containment vessel 550 which is in thermal contact with hot end and cold ends of switchable heat pipes. Size and number of such sets may be varied depending on the desired capacity. Module 500 is in thermal contact with hot -end 504 and cold end 531 of switchable heat pipe. Similarly module 600 isln thermal contact with hot_ead_.6Q4 and cold end 631 of switchable heat pipe. Either hot or cold end is operational ai any instant. The modules 500, 600 are filled with the adsorbent and have outlets 552/652, which has a mesh of suitable density to prevent adsorbent particles from escaping along with the refrigerant. This exit has a three-way connector 553, 653. One side is used for connecting the two modules through a valve 711 and the other side 702 leads to the condenser and evaporator. Incorporation of plurality of modules enables continuous cooling and heating effect.
Two adsorption modules 500, 600 are connected through valve 711 to allow pressure equalization between the two adsorption modules 500, 600, at end of generation and/or adsorption phases. The refrigeration sub-system operates on an adsorption refrigeration cycle with pressure equalization for heat recovery. The two-module operate out of phase, i.e. one module is being heated while the other is being cooled. During pressure equalization between two modules or two sets of modules, refrigerant from a module or a set of module at high pressure is allowed to flow to a module or a set of modules at relatively lower pressure. This method of regeneration between two modules or sets of modules reduces the requirement of heat input from the external heat source in the generation phase and thus increases COP.
Pressure equalization between two sets of modules is single stage pressure equalization. Multi-stage pressure equalization is achieved if pressure equalization is effected sequentially between three or more modules or sets of modules. Vapour and heat regeneration efficacy increases with increase in number of stages of regeneration. Multi-stage regeneration eliminates the need for heat transfer fluid loops and the associated complex valve arrangements and controls otherwise needed for regeneration. Vapour equalisation technique enhances COP of the system and also reduces cycle time. Cycle time is reduced because the time required to equalize pressure is a fraction of the time required to regenerate the heat using heat transfer fluid loops. Also the auxiliary power required to pump the heat transfer fluids is eliminated.
Adsorption modules 500, 600 used in refrigeration cum heating system, are shown in FIG.1. The thermal bonding between adsorption module and hot/cold
ends can be achieved by co-extruding the three tubes or by welding the two smaller diameter pipes to the main module tube or by any other suitable means.
The module design may be further modified based on the application requirements. Shape of module and the heat pipes may be varied on, the basis of the ease of fabrication or other application constraints. Diametersjof thernqdule and heat pipe are governed by the desired capacities. Number of heat-pipes, of each type can be varied to increase or decrease the heat transfer rate. In some cases, the heat pipes either for heating or cooling are not required. Due to some constraints, it might not be possible to make the heat pipe run along the complete length of the module. Heat pipes may be thermally affixed on the inner side of the module wall, or they may be co-extruded along with the main pipe or affixed by any other means. But the basic idea of using the heat pipes for supplying and removing the heat from the adsorption modules, and integrating the same with the walls of the module to avoid the need of separate fins to facilitate heat transfer within the adsorbent bed still holds. In this design the wall of the module acts as a fin to facilitate heat transfer thereby reducing the overall thermal mass of the system, leading to lower cycle times and higher COP.
Hot/cold ends 501, 534, 504, 531, 604, 631 of switchable heat pipes, used in refrigeration cum heating system, use a system to isolate hot end from cold end or vice versa. FIG.4 shows switchable heat pipes, which consists of hot end, evaporator 501 and cold end, condenser 504, flexible tube 502 and pincher 505. The heat receiving section is integrated into the heat source and the heat giving section is integrated into the heat sink. When the heat pipe is in operation, the flexible tube is in the un-pinched position. Fluid in the hot end 501 evaporates absorbing heat from the heat source and passes to the cold end 504 and/or 604 passing through the flexible tube 502 and/or 602. In the cold end these vapours condense, delivering the heat. The condensate is transferred back to the hot end 501 due to capillary action of the wick or it drains back due to the gravitational action. To switch off the heat pipe, the flexible tube 502, 602 is pinched using the pinchers 505, 605, 507, 607. This isolates the hot end 501 and the cold end 504 and the heat pipe ceases to operate.
This novel construction and arrangement gives this heat the flexibility to use it in diverse ways. Heat pipe cross-section used may be of any shape (such as circular, elliptical, rectangular, etc.). Cross-sectional area of the heat pipe is decided on the basis of the desired capacity of heat transfer. The flexible tube used to connect the heat receiving section and the heat giving section can be made of any material as long as it can be pinched/squeezed to isolate the two sections as long as the material of the flexible tubing is compatible with the fluid used in the heat pipe. A wick may be provided on the inner wall of the heat receiving section, heat giving section and flexible tubing to facilitate the draining back of the fluid. There is no restriction on the type of wick that should be used, except that in the flexible tube section the wick should be also flexible. A sealant has to be applied to seal the flexible tube and metal tube joints. Sealant should be able to withstand pressures at which heat pipe is supposed to operate. Any material may be used for making the heat receiving or condenser sections 501, 504 of the heat pipe as long as it is compatible with the working fluid. Any
the application, location, etc. Purpose of the heat recovery tank is to recover the heat released from the adsorption modules 500, 600 during the adsorption phase and use it for heating purposes. Heat is being transferred from the adsorption modules to the heat recovery tank 709 using the heat pipes 504, 531, 604, 631. Each heat recovery tank 709 will have heat pipes coming from at least two adsorption modules 500, 600 and each heat pipe 504, 531, 604, 631 would be operational during the adsorption phase of the respective module. Condenser 703 shown in FIG.1 is an evaporative condenser. Design of the same will depend on space and location constraints. Each condenser should condense refrigerant coming through at least two adsorption modules during the generation phase but only one of them is operational at any given time. These will then lead to the evaporator 707, which has to be customized for a particular application like for chilling water, for producing ice or for cold storages, etc.
The system described in this invention may also function without pressure equalisation. In such cases the COPs obtained will be low, as compared to the system operating with heat regeneration as described above.
In the embodiment shown in FIG.1 the adsorption system consists of two adsorption modules 500, 600 working completely out of phase, say Module 1 and Module 2. The pressure equalisation cycle shown on the PTX graph in FIG. 3, may be divided into 4 phases.
Phase I. During this phase Module 1 is first preheated from ph.i to g.i followed by the generation phase g.i to g.o. Module 2 is first pre-cooled from pc.i to a.i, followed by the adsorption phase a.i to a.o. During this phase Module 1 has the switchable heat pipe, for heating, activated and Module 2 has the switchable heat pipe, for cooling, activated. Heat is supplied to the module to be heated through the heat source by means of the heat pipe. Module 1 is heated till it reaches the generation temperature and desorbs all the ammonia. Till that time Module 2, which is under going adsorption phase is being cooled and the heat is being transferred to the heat recovery tank.
Phase II. During this phase pressure is equalised between modules 1 and 2. Module 1 is depressurised from g.o to pc.i. During this the temperature of the module reduces and the concentration of ammonia in the adsorbent reduces. Module 2 is pressurised from a.o to ph.i. During this the temperature of the module increases slightly and the concentration of ammonia in the adsorbent increases.
Phase III This phase is just the reverse of Phase I, i.e. Module 2 is now undergoing pre-heating and generation and Module 1 is now under going pre-cooling and adsorption.
Phase IV In this phase pressure equalisation is again done between the two modules followed by Phase I.
The results.of an adsorption refrigeration cum heating system, using adsorption cycle with pressure" equalisation for heat regeneration, with activated carbon/ ammonia as working adsorbent - adsorbate pair are given to serve as a non-limiting example of the present invention.
Table 1 presents the simulation results for a system using solar collector as the heat source. Some of the important parameters th"at are considered fixed for the system in this example for simulation are as follows:
1. Evaporator temperature -5°C
2. Generator outlet temperature 199°C
3. Adsorber outlet temperature 40°C
4. Maximum pressure in module 23 bar
5. Pressure factor of safety 1.5
6. Intensity of solar radiations 750 W/m2
7. Duration for which radiation is available 6 h
8. Efficiency of solar collector 45%
9. Dry bulb temperature 30°C
10. Wet bulb temperature 22°C
11. Minimum wall thickness . 1 mm
12. Diameter of Heat pipes 6.35 mm
13. Shape of Module Circular
14. Shape of Heat pipes Circular
Table 1: Simulation results for an optimised system using solar collector as heat source.
Material Module No. of Weight of
Diameter heat pipes Cycle Time SCP ice
(mm) COP (min) (W/kg) (kg/m2.day)
Aluminium 38.1 1 0.40 57.7 162 6.574
SS304 38.1 1 0.38 34.9 143 6.143
Aluminium 38.1 2 0.39 16.0 312 6.303
Though this system can operate with various heat sources, one of the very common applications of the adsorption systems is solar refrigeration. Solar refrigeration is an important use of solar energy because the supply of solar energy and the demand for cooling are greatest during the same season. It has the potential to improve the quality of life of people who live in areas where the supply of electricity is far from sufficient. The success of solar cooling is dependent on the availability of low cost and high performance of solar collectors. In the disclosed refrigeration cum heating system if solar energy is used as the input, solar collector contribute to more then 80% of the system cost. Still the costs have been brought down significantly by reducing the solar collector area required per kg of ice produced per day and the cost of adsorption modules. This
has been made possible in the present invention due to high COP of the system with low cycle time. After optimizing the system to minimize the system cost the overall system is expected to cost one-third of the currently commercially available solar refrigeration system. In addition to that system is very compact and gives hot water as an additional utility.
With this invention as described, modifications and variations can be made without departing from the spirit of invention.
1. A refrigeration cum heating system working on an adsorption refrigeration cycle comprising one or more adsorption modules; said each module consisting of plurality of "passages" in thermal contact with the walls of the containment vessels; one of the passages is connected to the heat source means through a means for actuating or isolating heat pipes and another to the heat sink means; output of the said adsorption module is connected to the evaporator through a condenser
wherein the arrangement of the said passages around the containment vessel is such that it overcomes problems of low thermal conductivity of adsorbents without increase in the thermal mass of the system.
2. A refrigeration cum heating system as claimed in claim ■ 1 - _ !, wherein said
adsorption module having
• cross-sectional shape of the module is varied based on peak pressures in module and space constraint;
• size of the module is varied based on desired capacity and optimisation
• number of "passages" for transferring heat to and from the module is varied on the basis of desired capacity of heat pipe, SCP;
• the "passages" either for heating or cooling is/are optionally eliminated;
• the material of construction for the module and passages is preferably; metallic with high thermal conductivity above 10 W/m.K;
• the "passages" are in thermal contact with the wall of the main cylinder; constructed by co-extrusion, welding, thermal paste or any suitable means.
3. A refrigeration cum heating system as claimed in claims 1-2 wherein "Passages" used as heat pipes in the refrigeration system are of variable cross-sectional shape and size based on the desired capacity of heat transfer and space constraints.
4. A refrigeration cum heating system as claimed in claims 1-3 wherein "Passages" in the refrigeration system are optionally switchable heat pipe(s).
5. A refrigeration cum heating system as claimed in claim 5 wherein Switchable heat pipe(s) optionally uses a pinchable flexible tubing with pinching device for isolating the heat receiving and the heat giving sections.
6. A refrigeration cum heating system as claimed in claims 4-5 wherein flexible tube i s used i n t he heat pipes to c onnect t he h eat r eceiving and t he h eat giving sections, is made of any pinchable/squeezable material that are compatible with the working fluid.
7. A refrigeration system as claimed in claim 1 wherein the number of adsorption modules is varied as per the desired cooling capacity of the system.
8. A refrigeration cum heating system as claimed in claims 1-2 and 7 is optionally operable with adsorption refrigeration cycle with single and multistage pressure equalization for heat regeneration in the adsorption module increasing COP and reducing cycle time.
9. A refrigeration cum heating system as claimed in claims 1-2 and 7 wherein a valve may optionally be used to connect two or more modules for single/multi¬stage pressure equalization.
10. A refrigeration cum heating system as claimed in claims 1-9 wherein a single shaft with cams pinching the squeezable tubes facilitates control of the flow of heat to and from the adsorption module and flow of the refrigerant.
|Indian Patent Application Number||151/MUM/2002|
|PG Journal Number||20/2007|
|Date of Filing||19-Feb-2002|
|Name of Patentee||INDIAN INSTITUTE OF TECHNOLOGY, BOMBAY|
|Applicant Address||HAVING ITS ADMINISTRATIVE OFFICE AT POWAI, MUMBAI - 400 076, STATE OF MAHARASHTRA, INDIA AND AN AUTONOMOUS EDUCATIONAL INSITUTE ESTABLISHED IN INDIA UNDER THE INSTITUTES OF TECHNOLOGY ACT 1961.|
|PCT International Classification Number||N/A|
|PCT International Application Number||N/A|
|PCT International Filing date|