USING A SINGLE NATURAL REFRIGERANT AS A BETTER GWP ALTERNATIVE TO R23 FAMILY: DESIGN OF ULTRALOWTEMPERATURE MULTI-STAGE FLASH INTERCOOLING TRANSCRITICAL REFRIGERATION CYCLE

Ultralow-temperature (ULT) refrigeration is essential for various applications, including food, pharmaceutical, and cryogenic processes, where stringent temperature control is required. However, the energy intensity and the use of high-GWP refrigerants in these systems contribute to global warming and climate change. R23 and later R23 mixtures, like R508b, have been considered as zero ozone-depleting potential refrigerants, but their excessive global warming potential has always been a topic of concern. The theoretical replacements are multi-refrigerant multi-cascade cycles which are not efficient or economical enough to be accepted by manufacturers. R1150, R744a and R170 are considered as an environmentally friendly refrigerants to replace R23 family. However, their infra-room critical temperature makes them suitable only in bottoming cycles of cascade systems. This project presents an innovative approach to the single-refrigerant ULT refrigeration cycle. An optimized four-stage flash intercooling turboexpander cycle was designed and thermodynamically analyzed. COP around 0.5 is achievable, even though the cycle has a temperature lift of 140°C and an approximate compression ratio (CR) of 100. Pressure optimization caused the compressors to achieve isentropic efficiency ranging from 0.6 to 0.7, with compression ratios between 2.5 and 4. Different refrigerants and operating conditions were simulated under realistic assumptions and the positive impact of using turboexpanders on performance was confirmed.