Helium gas refrigerator

The refrigeration to operate a pair of such coils is about 50 kw. It is assumed that a helium gas refrigeration cycle would be an attractive possibility with the refrigerator gas passing directly through the coils. The cycle involved might resemble that of a helium liquefier, except liquid temperature would never be reached. 

Warm-up tests of the cryopump cold plate demonstrated a low refrigerative requirement. As a result it becomes possible to supply the refrigeration with dense helium gas from sources other than closed-cycle refrigerators. A simple source of the gas is accelerated boil-off gas from a liquid-helium storage dewar. 

The experiment assembly was loaded into the Low-Temperature Irradiation Facility (LTIF), a combination of a continuously operating liquid-helium refrigerator and a cryostat next to the core of the swimming-pool-type Oak Ridge Bulk Shielding Reactor. The sample chamber was then purged with dry helium gas and evacuated to about 13 Pa (0.1 torr) several times before initial cooldown. 

Helium gas purification systems. Where the concentration of moisture and atmospheric contaminants in the helium stream are very low, e.g., about 500 parts per million or less and where the system is operating at low pressure, the helium stream may be cooled to low temperatures inside the Norelco circulating cold gas head, and thence purified in a conventional adsorption system as illustrated by the process diagram, Figure 10. Calculations show that a refrigerator of this type has the capacity to purify about 4000 SCFH of helium of the aforenoted specifications. 

Example 4.12. Many of the large hydrogen liquefaction plants use a precooled Claude cycle with one expander similar to that shown in Fig. 4.13. This system could also be used as a refrigerator to cool helium gas. For the operating conditions shown below, determine the following ... 

Example 4.13. Helium gas is compressed from 0.303 MPa and 275 K to 4.04 MPa and 300 K in a Claude refrigerator utilizing a wet expander with a saturated-vapor compressor. Twenty percent of the compressed gas is diverted through the main expander entering at 190 K and leaving at 0.303 MPa. The helium enters the low-temperature compressor at 0.101 MPa as saturated vapor and leaves at 0.303 MPa. If... 

Example 4.16. An A. D. Little refrigerator operates between the pressure limits of 0.101 and 2.02 MPa using helium gas as the working fluid. The maximum temperature in the space to be cooled is 90 K and the temperature of the gas leaving the compressor is 300 K. Assume that the regenerator is 100 % effective and the compressor has an efficiency of 100%. The expansion process in the expansion space is assumed to be isentropic. Determine the refrigeration effect, the COP, and FOM for the system. 

Assuming that the helium gas behaves as an ideal gas in the temperature and pressure range under consideration, the ideal COP for an isobaric-source refrigerator can be found with the aid of Eq. (4.4) as... 

A cold-gas refrigeration system with helium as the working fluid operates between 0.101 and 1.52 MPa at 300 K. The 1.52-MPa gas is cooled to 20 K whereupon it is expanded to 0.101 MPa to provide the refrigeration effect. The refrigeration system utilizes an isothermal and reversible compressor, ideal heat exchanger, a reversible adiabatic expander, and an... 

A Philips refrigerator is used to maintain a temperature of 77.8 K while rejecting heat to an ambient sink of 300 K. The working fluid used in the system is helium gas. The pressure limits for the system are 0.101 MPa minimum and 1.01 MPa maximum. Determine the refrigeration effect, the coefficient of performance, and the figure of merit for the system, assuming that all processes in the system are ideal and the helium may be considered to behave as an ideal gas. 

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