Thermodynamic analysis of a cascade refrigeration cycle for venus lander electronics cooling

This paper presents the results of a thermodynamic analysis of a two-stage cascaded vapor compression refrigeration cycle developed for high-temperature high-pressure applications, such as the one encountered in Venus surface lander missions. The bottoming cycle uses ammonia, whereas the topping cycle uses fatty acid methyl ester methyl linoleate (FAME-MLL) as theworking fluid. Theworking fluid FAME-MLLis selected for its critical point temperature of 526°C, which is greater than the localVenus atmospheric temperature of 465°C, thus providing a temperature potential to reject heat to the Venus environment. The FAME-MLL cycle employs an ejector in order to alleviate overloading the compressor. Thepaper presents the thermodynamic model of the system followed by predictionsof systemperformancein terms of ejector flowrate, condenser temperature, evaporator temperature, and compressor efficiency.The results herein show that, over the ranges of ejector entrainment ratios of 2 < ω < 3 and compressor efficiencies of 70% < η_c < 80%, the system coefficient of performance (COP) falls within the range of 0.7 < COP < 0.8. The main objective of this research is to provide an active thermal control system architecture thatwillmaintain a payload on Venus rejecting 100W at 100°C for an extendedperiod of days or weeks. Thus, the overall longevity of the mission is deemedmoreimportant than a system with a large COP value. Thus, the conceptual design provided herein is seen to meet the primary objectives.