Experimental evaluation of CO2/R-152a mixtures in a refrigeration plant with and without IHX

In recent years, CO2-based mixtures have been considered as a way to improve the performance of refrigerating plants using pure CO2 as refrigerant. Combining CO2 with a fluid with higher critical temperature generates a blend which allows to run a refrigeration plant in subcritical conditions at higher heat rejection temperature when compared to pure carbon dioxide, and consequently reach higher COP. This work evaluates from an experimental point of view two CO2/R-152a mixtures, ([90/10 %] and [95/5 %]), used as refrigerants in a single-stage refrigeration plant with and without internal heat exchanger, and compares the results to those obtained using pure CO2. The work analyses the main energy parameters of the plant for secondary fluid inlet temperature of 2.5 °C at the evaporator, and in the range from 20 °C to 40 °C with 5 °C step at the condenser/gas-cooler. The use of such mixtures, compared to the use of pure CO2, allowed to obtain a higher COP in the base cycle for heat rejection temperature above 25 °C, reaching the largest increment at the highest temperature while, when working with IHX cycle, no improvements in the COP were measured.