Experimental evaluation and energy impact of a recuperative low-temperature heat exchanger in an autocascade system for ultra-low temperatures

• Autocascade (AC) system with a recuperative heat exchanger (RLHX) is evaluated. • The mixture R600a/R1150 (70/30 %) is used for achieving −80 °C. • RLHX increases cooling capacity by 57.1 % and COP by 63.6 % at −80 °C. • RLHX reduces high pressure and increases compressor’s suction temperature. • AC system with RLHX approaches two-stage cascade efficiency for −80 °C. Autocascade refrigeration systems are one of the most used technologies for ultra-low temperature applications with low capacities. This study presents an experimental evaluation of an autocascade refrigeration system incorporating a recuperative low-temperature heat exchanger (RLHX) to enhance its performance in achieving ultra-low temperatures. The system operates with an optimized refrigerant mixture of R600a/R1150 (70/30 % by mass) and is designed to maintain a target temperature of −80 °C. A comparative analysis is conducted between autocascade cycles with and without RLHX, assessing thermodynamic parameters, cooling capacity, and coefficient of performance (COP). The introduction of the RLHX leads to a significant improvement in energy efficiency, with a measured 57.1 % increase in cooling capacity and a 63.6 % enhancement in COP at environment temperature of 25 °C and target temperature of −80 °C. Additionally, the system benefits from reduced compressor discharge temperatures and lower high-side pressures, improving overall operational stability. The results suggest that integrating an RLHX into autocascade systems can reduce the efficiency gap between autocascade cycles and traditional two-stage cascade systems, increasing their feasibility especially in applications with low capacities or spatial constraints.