Performance investigation of ultra-high pressure ratio cryogenic turboexpanders for helium liquefaction system

Availability of ultra-high pressure ratio turboexpanders present numerous options to the helium liquefier/refrigerator designer as it allows to conceptualize a compact plant by making use of high-pressure process compressors and eliminates placement of turboexpanders in series for large pressure heads in the process cycle. Setting out with this objective, a new series of cryogenic turboexpanders comprising of two high pressure ratio variants has been developed at Bhabha Atomic Research Centre (BARC). These turboexpanders are designed using the Enhanced midstream design method (EMDM) which has been reported by the authors earlier. Enhancement of pressure ratio of these variants from the earlier reported value of 4 to the new value of 6 is achieved through redesigning the inlet nozzle. For each variant of the turboexpanders, two types of inlet nozzle are designed using the EMDM. Type 'A' is based on an aerofoil section with ideal blade loading and type 'B' is based on a non-aerofoil section and non-ideal blade loading distribution. These remodelled, ultra-high pressure ratio variants of the turboexpanders are experimentally investigated using the BARC developed helium refrigerator CP1000.