The invention relates to refrigeration systems and, more particularly, to a refrigeration apparatus that is effective to significantly improve the operating efficiency of a system that includes an ejector operatively connected to move refrigerant between a heat exchanger and a precooler vessel. The invention is particularly useful in raising refrigeration efficiency and capacity in refrigeration systems that are operated to produce cooling below 4.2.degree. K. (Kelvin).
One relatively recent application of such an ultra-cold producing refrigeration system was in conjunction with the cooling of super-conducting magnets, which were to be employed in a combination storage ring/accelerator that was to be constructed and operated at Brookhaven National Laboratory. That proposed system was designed to be operated to produce magnet cooling at 3.8.degree. K., using a forced-flow supercritical helium coolant system. Historically, in the design and construction of such ultra cold systems, the main or so-called warm compressor, or vacuum pump has been used to pump a cold helium bath in the system to a desired pressure. Those familiar with the art know that such an approach has several major disadvantages. An alternative approach is to use a helium ejector which is able to convert refrigeration from 4.5.degree. K. to lowered temperatures without requiring connections to ambient temperature. Because of that feature, even though helium ejectors are not very efficient, they are recognized as a desirable, simple mechanical element and are widely used in ultra-low temperature refrigeration circuits.
Experience with such ultra-cold refrigeration systems has indicated that only about one-third of the refrigeration that is produced at 4.5.degree. K. can be effectively transferred and made available for cooling the magnets, or other desired load, at about 3.8.degree. K. Although the remainder of the cooling effect can be used for liquification or other purposes within the refrigeration system, it cannot be regarded as directly useful in cooling the load at the desired lower temperature.
In recent attempts to improve the efficiency of delivering refrigeration availability to the load, the benefit of using cold compressors in association with a cold expander was studied, as reported for example by the present applicant and his co-workers in a paper entitled, "Cycle Design for the ISABELLE Helium Refrigerator", which was published by Plenum Press, New York (1982) in Advances in Cryogenic Engineering, Vol. 27 (pg. 501, et seq). Even with the benefits of such cold expander/cold compressor systems now established, it remains desirable to still further improve the operating efficiency of ultra-cold refrigeration systems.