An attempt has been made in this present work to design, fabricate and performance evaluate an integrated single stage centrifugal compressor and permanent magnet synchronous motor which is a key component of the reverse brayton cycle cryocooler. An off the shelf compressor – the driven and electric motor – the driver was not available commercially to suffice the requirements of the reverse brayton cryocooler. The integrated compressor-motor system was designed and tested with air as the working fluid at mass flow rate of 7.3 grams per sec, with a compression ratio of 1.58 and driven by a 2 KW permanent magnet synchronous motor at a design speed of 108,000 rpm. A permanent magnet synchronous motor rotor was designed to operate to operate over 200,000 rpm at 77 Kelvin temperature. It involved iterative processes involving structural, thermal and rotordynamic analysis of the rotor. Selection of high speed ceramic ball bearings, their mounting, fit and pre-load played prominent role. Attempts were made to resolve misalignment issues for the compressor – motor system, which had severe impact on the rotordynamic performance of the system and therefore losses at high speeds [15], [16]. A custom designed flexible coupler was designed and fabricated to run the compressor – motor system. An integrated compressor – motor system was an innovative design to resolve considerably several factors which hinder a high operational speed. Elimination of the coupler, reduction of number of bearings in the system and usage of fewer components on the rotor to increase the stiffness were distinct features of the integrated system. Several custom designed test-rigs were built which involved precision translation stages and angle brackets. Motor control software, an emulator, a DSP and a custom designed motor controller was assembled to run the motor. A cooling system was specially designed to cool the stator – rotor system. A pre-loading structure was fabricated to adequately pre-load the bearings. Flow measurement instruments such as mass flow meter, pressure transducers and thermocouples were used at several locations on the test rig to monitor the flow. An adjustable inlet guide vane was designed to control the tip clearance of the impeller.

Graduation Date





Kapat, Jayanta


Master of Science (M.S.)


College of Engineering and Computer Science


Mechanical, Materials, and Aerospace Engineering









Release Date

October 2018

Length of Campus-only Access


Access Status

Masters Thesis (Open Access)