High Speed Cryogenic Turboexpander Rotor for stable operation up to 4.5 kHz Rotational Speed

BARC has been working towards the development of gas bearing supported high speed turboexpander rotors for use in indigenous helium liquefiers and refrigerators. Extensive experiments have been carried out to obtain the dynamic characteristics of the rotor both during coast-up as well as coast-down operations. The objective of these experiments is to identify the critical speeds of the rotor and relate it with the bearing clearance. This would enable design of radial bearings with proper clearance so as to avoid the occurrence of critical speed near the range of rated rotor operational speeds. The present paper documents the experience of stable rotation of several 16 mm diameter cryogenic turboexpander rotors during recent laboratory test runs. Snap shots from FFT analyzer during the experiments as well as synchronous response to unbalance for coast-up and coast-down operations have been included.