Refrigerators, Brayton

Gas-Cycle Systems. In principle, any permanent gas can be used for the closed gas-cycle refrigeration system however, the prevailing gas that is used is air. In the gas-cycle system operating on the Brayton cycle, all of the heat-transfer operations involve only sensible heat of the gas. Efficiencies are low because of the large volume of gas that must be handled for a relatively small refrigera tion effect. The advantage of air is that it is safe and inexpensive. 

Absorption Air-Conditioning Brayton Gas Refrigeration Cycle Stirling Refrigeration Cycle Ericsson Cycle Liquefaction of Gases Nonazeotropic Mixture Refrigeration Cycle Design Examples Summary... 

The basic gas Brayton refrigeration cycle is the reversed Brayton gas power cycle. The components of the basic gas refrigeration cycle include a compressor, a cooler, a turbine, and a heater, as shown in Fig. 6.26. 

The T-s diagram of the basic gas Brayton refrigeration cycle, which consists of the following four processes, is shown in Fig. 6.27 ... 

Figure 6.27 T-s diagram of the basic Brayton refrigeration cycle. 

The basic gas Brayton refrigeration cycle analysis is given by Example 6.12. 

A 5-ton air Brayton refrigeration system is to be designed according to the following specifications ... 

An ideal Brayton refrigeration system uses air as a refrigerant. The pressure and temperature of air at compressor inlet are 14.7 psia and 100°F. The pressure and temperature of air at the turbine inlet are 60 psia and 260°F. The mass rate of air flow is 0.031bm/sec. Determine (a) the cooling load, (b) the compressor power required, (c) the turbine power produced, and (d) the cycle COP. 

The Brayton gas refrigeration cycle is a reversed Brayton gas power cycle. 

Hall, J.L., J.A. Barclay, Analyzing Magnetic Refrigeration Efficiency A Rotary AMR-Reverse Brayton Case Study , Advances in Cryogenic Engineering, V. 43B, pp. 1719-1728, 1998... 

If, in the heat pumps, the energy of compression is not recovered but is wasted in letdown valves (as the pressure of the working fluid is reduced to the low pressure of the evaporator (Joule-Thomson cycle), the liquefaction efficiency will be low (35-60%). This range of efficiencies is a function of the liquefier size and refrigerant used. If the letdown valves are replaced by turbo expanders (Brayton cycle), which recover some of the compression energy during pressure letdown, and if helium or neon refrigerants are used, the efficiency can theoretically reach 80-90%. 

Refrigeration down to 80°K is therefore provided by LN2. The next step of refrigeration from 80 to 30°K is carried out using the Brayton cycle, in which high-pressure H2 is expanded in a number of turbo expanders in series. From 30°K to liquefaction, the Joule-Thomson cycle is used, where high-pressure gas is throttled to low pressure to provide further cooling. 

The Claude cycle is shown in Figure 6. This is a compound cycle which is actually a combination of the simple Joule-Thompson cycle and Brayton cycle. Most modern air separation plants utilize a variation of the Claude cycle to provide the refrigeration needed to liquefy air for distillation. 

The principle of the heat pump, which is the same as that involved in the refrigeration operation, has been known for over 100 years. In the last four decades, heat pump applications have been limited only by economics. Among many types of heat pumps (e.g., vapor compression, absorption, ejector, Brayton cycle, and thermoelectric), only the first found wide application because of its high effideucy and relatively simple construction. 

The quest for reduced size, weight, and vibration in small space cryocoolers has also created interest in the development of a reverse Brayton cycle cooler. The use of miniature turbomachinery is now making it possible to extend the operating range of the Brayton cryocoolers down to applications requiring from 1 to 5 W of refrigeration at temperatures from 4.2 to... 

In the development of their miniature reversed Brayton cycle refrigerator, Sixsmith and co-workers have also encountered a need for a compact coun-... 

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