Operating a Train of Cryogenic Centrifugal Compressors at Lower Flow Rates and Constant Compression Ratio

Abstract

Cryogenic centrifugal compressors are presently the only «industrial» machines used to reach temperatures lower than 4.4 K (Tore Supra, Fermilab, TJNAL)^1,2,3. When the full cryogenic power is not needed, the processed flow is reduced. But the flexibility of a centrifugal compressor train is limited: reducing the processed flow rate leads to troubles (stall) and subsequently, surge. One of the easiest way to avoid such a situation is to inject electrical power into the liquid helium bath in order to provide the compressor train with a constant flow rate. This is not a very satisfactory procedure on a thermodynamical point of view... Other solutions have been proposed which generally lead to the operation of some parts of the room temperature helium circuits at sub atmospheric pressure, which is not consistant with a very long term reliable operation. Operating two parallel trains, each one processing half the nominal flow is another solution not very much flexible but which investment is roughly doubled.