A pair of miniature helium expansion turbines

Two miniature cryogenic turboexpanders are discussed. These were developed to provide first and second stage expansion in small helium liquifiers or refrigerators. The design of each is virtually identical although the design operating conditions varied more than 30% in specific speed. The expanders run at high speeds in pressurized helium bearings with an integral brake heat exchanger. The vital components are contained in a cartridge, held in place by a single nut, which can be removed and replaced in less than one minute. Specifications and descriptions are discussed are parameters itemized. The assembly is diagramed with an photo of the brazed bearing assembly and titanium shaft. Expander operation is discussed. A subsequent discussion is recorded concerning the efficiency of the turbine, which is similar to that of an NBS turbine.