Effects caused by the internal heat exchanger at the low temperature cycle in a cascade refrigeration plant

摘要

This work analyses and quantifies the effects caused by the use of an internal heat exchanger (IHX) at theCO2 subcritical cycle in an HFC134a/CO2 cascade refrigeration plant that incorporates a gas-cooler at theexit of the low temperature compressor. Previous theoretical and experimental studies showed that theIHX reduces the refrigeration capacity and COP of the subcritical cycle, however, it has been seen that italso lowers the heat to be rejected at the condenser. This reduction, when the cycle is a part of a cascadesystem, allows reducing the heat load of the high temperature cycle, modifying the working conditions ofthe cascade plant. The modifications result in an increment of the overall coefficient of performance of thecascade system. The analysis here presented is based on the evaluation of an experimentalHFC134a/CO2 refrigeration plant, which has been analysed with and without internal heat exchanger in anevaporating temperature range from -40 to -30 ºC and in a condensing one from 30 to 50 ºC. The plantincorporates a gas-cooler at the exit of the CO2 compressor. The experimental results confirm that the IHXslightly reduces the cooling capacity but it can increment the overall COP up to 3.7 %.