Experimental optimization and evaluation of an R600a/R1150 auto-cascade refrigeration systems for ultra-low temperature applications

Auto-cascade refrigeration systems are the most employed systems for ultra-low temperature applications, especially for small capacity systems. Recent investigations have allowed to analyze them energetically and thermodynamically, starting a research line focused on enhancing their energy performance from experimental approaches. This work focuses on the energy optimization of a real auto-cascade system working with the mixture R600a/R1150 [70/30 %], which has been evaluated using two compressor models for R404A and R290 as well as the optimization of the two capillary tubes used in the system. Results indicate that overall efficiency of the R290 compressor is up to 21 % higher than with R404A, leading to COP increments between 35 and 81 %. Optimum capillary lengths have been determined in terms of COP and energy consumption, reaching similar values, however, the inner parameters of the system change as function of these lengths, which needs to be considered in prototypes design.