Analysis, development and experimental evaluation of ultra-low temperature cascade refrigeration systems with natural refrigerants

Abstract

Refrigeration is essential for preserving sensitive products by maintaining temperatures below ambient. Vapor compression cycles are the standard method, but their efficiency drops as the temperature lift increases. Ultra-low temperature (ULT) applications, such as vaccine or biomedical storage, require significant temperature differences, making conventional systems inefficient and environmentally harmful. This thesis proposes a more sustainable solution using a cascade vapor compression cycle with natural refrigerants R290 (propane) and R170 (ethane). A detailed theoretical analysis identifies critical points, particularly at the expansion valve inlet, addressed by incorporating an interstage heat exchanger. An experimental prototype confirms the theoretical results, achieving COP improvements of up to 40 % at −70 °C and 20 % at −80 °C compared to the R404A/R23 baseline. The natural refrigerant pair also delivers greater cooling capacity with a lower mass flow rate and reduces CO₂-equivalent emissions by 37 %. These findings highlight the technical and environmental potential of natural refrigerants in ULT systems.