Thermodynamic Analysis and Comparison of CO2/Propane and C02/Isobutane Cascade Refrigeration System

This study thermodynamically analyzes a cascade refrigeration system that uses carbon
dioxide and propane (R744-R290) or carbon dioxide and isobutane (R744-R600a) as an
alternative to ammonia-carbon dioxide system (R717-R744). Parametric study will be
used to determine the optimal condensing temperature of the cascade-condens~ to
maximize the COP given specific parameters for food processing application under
fixed cooling capacity and condensing temperature. The parameters that have been
varied are the evaporating temperature for low temperature circuit, the cascade
condenser temperature <lifference, the low temperature circuit condensing temperatllre
and degree of subcooling and superheating. The results show that COP increases with
evaporating temperature (The), b11t <lecreases as temp~atllre difference in cascade
condenser ( L1 Teas) increases. Moreover, an increase of superheat reduced the COP of
the system while increase of subcooling increased the COP of the system.