Refrigeration – Processes – Evaporation induced by sorption
Patent
1997-05-09
1998-12-08
Doerrler, William
Refrigeration
Processes
Evaporation induced by sorption
62480, 62434, F25B 1708
Patent
active
058455078
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
The present invention relates to a thermal compressive device particularly, but not exclusively, for use in the compression of a fluid in a heat pump or cooling system.
Heat pumps and cooling systems are used to remove heat from or to introduce heat to a region which causes the temperature of the region to be lowered or raised. This is done by circulating a fluid which is in turn compressed, condensed and evaporated.
In adsorptive heat pumps and cooling systems the circulating fluid is adsorbed and desorbed from a material, an adsorbent, to achieve the desired compression of the fluid. This has the benefit that the energy needed to drive the adsorptive system can be in the form of heat which means that the heat pump or cooling system may be gas or oil fired or even solar powered rather than powered by electricity. Of course electricity may still be required to operate control mechanisms and circuitry but the energy demand of such control circuitry is sufficiently low for it to be powered by a conventional battery. This means that adsorptive heat pumps and cooling systems may be operated in areas which are not connected to an electricity supply grid and can be inherently more efficient in their use of primary energy since they use heat directly rather than in a converted form such as electricity.
To enable a better understanding of the basic adsorptive process an ideal solar refrigerator, shown schematically in FIG. 1, will now be described. An adsorptive refrigerator such as the solar powered refrigerator shown relies on the principle that certain materials for example active carbons, zeolites or silica gels are able to adsorb large quantities (for example 30% by weight) of most gases within their micropores and that the quantity of a gas, or adsorbate as it is commonly referred to, adsorbed by such a material, or adsorbent as it is commonly referred to, at a particular pressure is inversely dependent on the temperature of the adsorbent. Hence, at low temperatures larger quantities of gases or adsorbates may be present within the material or adsorbent than at higher temperatures. In a physical adsorption process no overall chemical reaction occurs between the adsorbent and adsorbate. Instead the adsorbate becomes trapped or held within the micropores or structural matrix of the adsorbent without any overall change in state of the matrix. In a chemical adsorption process a reversible chemical reaction occurs which may result in changes in the matrix structure.
As shown in FIG. 1, the adsorptive solar refrigerator consists of an insulated box 1, the interior of which is to be cooler than the surrounding environment, a liquid receiver 2, an evaporator 3, a condenser 4 and a solar collector 5. The receiver 2, evaporator 3, condenser 4 and collector 5 are all in communication with one another by means of conduits 6 within which the adsorbate circulates. The solar collector 5 contains an adsorbent and is positioned so as to be exposed to the sun. The collector 5 is connected to the condenser 4 which is positioned so as to be able to reject heat to the environment. The condenser 4 is in turn connected to the receiver 2 and the evaporator 3, both of which are located within the insulated box 1 and are also connected to each other.
The cycle of the refrigerator begins in the morning when the collector 5 is at ambient temperature and the evaporator 3, but not the receiver 2, is full of cold liquid refrigerant which also functions as the adsorbate. The adsorbent in the collector 5 contains the maximum quantity of refrigerant since the collector 5 is at its lowest cycle temperature. As the sun heats up the collector S, the temperature of the adsorbent rises and some refrigerant is desorbed in a gaseous form from the collector 5. Since the refrigerator system has a fixed volume, as refrigerant is desorbed, the pressure in the system rises. The gaseous refrigerant is not condensed because the saturation temperature corresponding to the system pressure is below ambient temperature. During the day, as more hea
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Critoph Robert Edward
Thorpe Roger
Doerrler William
University of Warwick
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