Experimental investigations on high pressure ratio cryogenic turboexpanders for helium liquefier

•Experimental performance evaluation of cryogenic turboexpander.•Two variants of high pressure ratio turboexpander for helium liquefier.•Low temperature experiments using helium liquefier and 20 K refrigerator.•Experimental evaluation of heat-in-leak through turboexpander mounting.•Improvements in performance using Enhanced Midstream Design Method.•Mass flow measurement using process turboexpander.•Performance improvement of helium liquefier with turboexpanders. Experimental investigations of two variants of a high pressure ratio cryogenic turboexpander, from a new series of turboexpanders for Bhabha Atomic Research Centre (BARC), are presented in the article. Both the variants are designed based on an earlier reported enhanced midstream method. The new turboexpanders are designed with larger turbine impeller-diffuser radial clearances and smaller turbine impeller L/D ratio as compared to previous series of BARC turboexpanders. The experimental investigations are carried out in BARC developed helium refrigerator CP1000 and helium liquefier LHP50. Different aspects of turboexpander performance, as defined by isentropic efficiency, pressure ratio and power developed in response to variation in parameters such as turboexpander flow and operational specific speeds, are presented in detail. The idea of using process turboexpanders for the mass flow measurements is also briefly studied using the results of the experiments. Experiment is also devised to compute heat-in-leak from turboexpander mountings and the results are used to critically analyse and provide corrections to the thermodynamic performance of the turboexpanders achieved during other experiments. From the two new variants of the turboexpanders investigated here, the better performing one is selected and mounted on LHP50 as TEX-2 for determining the maximum helium liquefaction capacity. LHP50 plant performance is then compared to the earlier reported liquefaction capacities with previous versions of BARC turboexpanders.