Refrigeration – Processes – Reducing pressure on compressed gas
Patent
1997-05-16
1998-03-31
Wayner, William E.
Refrigeration
Processes
Reducing pressure on compressed gas
62172, 62402, 417408, F25B 900, F04B 1700
Patent
active
057325600
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a system for performing cooling as specified in the preamble of claim 1 and to a method for the operation of such a system as specified in the preamble of claim 8.
Refrigeration systems usually employ a two-phase cycle with a refrigerant that alternates between gaseous and liquid states. Such systems have a large cooling capacity due to the amount of heat that can be taken up when the refrigerant evaporates and are therefore superior to any alternative in most applications, normally also for air-conditioning. However, the equipment in such a system is circumstantial and expensive and requires a closed piping circuit to isolate the usually pollutional refrigerant from the environment. And since refrigeration systems at the end transfer the cold through air or another gas, these conventional systems incorporates both a primary cooling medium, i.e. the refrigerant in the closed circuit and a secondary cooling medium, i.e. the air that transfers the cold to the object to be cooled.
Since long it has been known that refrigeration also can be attained by an air cycle cooling system, also called open reversed Brayton cycle. In such a system the air (or another gas) itself is the working medium in the refrigeration cycle. There is thus no need for a special refrigerant that is cyclically condensed and evaporated and there is no need to transfer the cold from a refrigerant to the air, since they are one and the same. Such systems therefore also eliminate the risk for pollution. In a cooling system according to this principle the gas, normally air is first compressed, whereby the pressure and the temperature rise. The warm compressed gas is then cooled in a heat exchanger and thereafter expanded with substantially the same pressure ratio as that of the compressor. The air leaving the expander will be cooler than the air entering the compressor and can perform its cooling purpose, e.g. air-conditioning, which normally takes place at atmospheric pressure, i.e. the same pressure as the compressor inlet pressure if located at ground level.
However, the air cycle cooling system has a very small cooling capacity in comparison with a conventional refrigeration system. Therefore the parts making up the system has to be comparatively large and, in relation to the cooling capacity expensive, in particular since reciprocating piston machines and/or dynamic machines normally are used for the compression and expansion. Such systems therefore in most situations are not a practical alternative to conventional refrigeration systems and have consequently very rarely come into use.
Should such a cooling cycle be-employed in a system where the nature of the means requiring cooling is such that a substantial over-pressure will prevail in the delivery line, the demands of the components of the cycle will be still more critical. Due to the over-pressure, the temperature at the outlet of the expander will be higher than if the expander outlet pressure had been closed to the inlet pressure of the system. This requires to be compensated by a correspondingly higher compressor pressure ratio for reaching a sufficiently low expander outlet temperature. One situation when this problem will occur is when the cold air is used to cool electronic equipment, e.g. in air-craft. Since the air in such an application has to pass through a large number of very narrow channels, the air leaving the expander receives a substantial over-pressure due to the flow resistance in this pattern of narrow channels.
In the specification and the claims the following expressions are to be understood as indicated: compressor. compressor. expander. expander.
It is earlier known to use machines of the vane-type for the compression and expansion in air cycle cooling systems as disclosed in U.S. Pat. No. 3,686,893. And in U.S. Pat. No. 3,965,697 another type of rotary displacement machines is used in such a cycle. The machines used in these disclosures, however, have not large enough volume capacity to be a practical alternative in this kind
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Ohman Henrik
Thuresson Erik
Svenska Rotor Maskiner AB
Wayner William E.
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