Second-law analysis and optimization of Reverse Brayton cycles of different configurations for cryogenic applications

Abstract

Second-law of thermodynamics (2 nd law) and exergy analyses and optimization of four Reverse Brayton Refrigeration (RBR) cryogenic cycle configurations: Conventional 1-stage compression cycle; Conventional 2-stage compression cycle; 1-stage compression Modified cycle with intermediate cooling of the recuperator using an auxiliary cooler; and an Integrated 2-stage expansion RBR cycle are performed. The conventional RBR cycles are analyzed for low and high pressure ratio applications using multistage compressors with intercooling. Analytical solutions for the conventional cycles are developed including thermal and fluid flow irreversibilities of the recuperators and all heat exchangers in addition to the compression and expansion processes. Analytical solutions are used to find the thermodynamic bounds for the performance of the cycles. Exergy irreversibility diagrams of the cycles are developed and the effects of important system parameters on RBR cycle performance are investigated. 2 nd law/exergy analyses, and optimization of the cycles with intermediate cooling of the recuperator, considering the cooling temperature and the recuperator effectiveness and pressure drop, are included. The effect of the 2 nd law/exergy efficiency of the auxiliary cooler on the total system efficiencies is presented. © 2012 American Institute of Physics.