Energy performance assessment of an auto-cascade cycle for ultra-low temperatures with the pair R1150 - R600a

Most of the research about auto-cascade refrigeration systems for ultra-low temperature applications is performed from a theoretical perspective due to the complexity of designing, testing, and measuring systems that work in two-phase conditions in most components of the cycle. A recent developed method has provided the opportunity to understand its thermodynamic peculiarities, which generally differ from the assumptions considered in simulation. This work presents for the first time, a consistent experimental evaluation of an auto-cascade refrigeration system for space temperatures between −80 to −60 °C. The work energetically optimizes a plant with the pair R1150/R600a using three different charging compositions (25/75 %, 30/70 % and 35/65 %) at a heat rejection temperature of 25 °C. Then, for the best option (340 g at 30/70 %), presents the thermodynamic evaluation at three heat rejection levels (25, 30, 35 °C) under steady-state conditions. Experimental measured COP ranged from 0.155 at a heat rejection temperature of 25 °C to 0.087 at 35 °C, with a rated cooling capacity decreasing from 139 W at 25 °C to 87 W at 35 °C.