Thermodynamic analysis of optimal intermediate temperatures in R134a–R410A cascade refrigeration systems and its experimental verification

In this study, the optimal intermediate temperature of a cascade refrigeration system with R134a and R410A, which is designed for a water heating purpose, is investigated by thermodynamic analysis. Theoretical analysis is targeted for establishing a mathematical model to enable the prediction of optimal intermediate temperatures that make the system operate with its maximum efficiency. The proposed model is only based on the thermodynamic laws and the thermodynamic properties of refrigerants. As major design parameters of the analysis, the R134a condensing temperature, the R410A evaporating temperature and the temperature difference in a cascade heat exchanger are applied. To validate the result of the thermodynamic analysis, the experiment is also conducted in the prototype of a cascade water heating system. The experiment is carried out under the steady-state condition and the same parameters as those of theoretical analysis are employed in experiments. The comparison between the result of thermodynamic analysis and that of experiments provides a good agreement.