Abstract

This paper presents the analysis and design of a compressor for application to a Fatty Acid Methyl Ester (FAME) Methyl Linoleate (MLL) bio-refrigerant cascade working cycle. This working fluid is being used in the topping cycle of an active electronics payload cooling system design to operate at elevated temperatures and pressures such as those witnessed by a Venus lander. The twin-screw, three-stage compressor operates at escalated temperatures of approximately 520 °C (960 °F). The total compressor power of 143.4 W is shared as 43.5 W, 47.7 W, and 53.3 W over stages 1, 2, and 3, respectively. The screw compressor is baselined with a D = 1 inch diameter rotor and an L/D (stroke/bore) ratio of L/D = 2 per stage. The compression ratio corresponds to a volume ratio of 6.5. The swept volume for a 4+6 rotor configuration is estimated to be 1.13 CFM at 2000 RPM with an asymmetric profile and no leakage. The volumetric efficiency of the compressor is estimated to be on the order of 80% due to the higher molecular weight of the FAME/MLL working fluid. The SCORG turbomachinery software is used to verify the thermodynamics analysis and affords a volumetric displacement of 0.025 L/rev at 2000 RPM and 80% adiabatic efficiency.

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