Application of response surface methodology and desirability approach to optimize the performance of an ultra-low temperature cascade refrigeration system

In this paper, multi-objective optimization of an ultra-low temperature cascade refrigeration system is presented using response surface methodology and desirability approach. Evaporation temperature, high-temperature circuit and low-temperature circuit condensation temperature, cascade temperature difference, and superheat degrees of the compressor suction are chosen as the variables, whereas COP, total exergy destruction and exergy efficiency are adopted as the responses that simultaneously maximizing COP and exergy efficiency while minimizing the exergy destruction. The quadratic models for three responses are obtained after the analysis of variance. The interactive influences of the variables on the responses are indicated. The results present that the maximum deviations between the predicted and actual values for the COP and exergy efficiency are 0.84% and 0.96%, whereas the deviations for the exergy destruction are within +/- 2% accounting for 96% of the samples. Evaporator temperature, condenser temperature, cascade temperature difference, ect. are found to be important parameters which cause great conflicts among the objective functions. A group of optimum values for the input variables are selected and validated. The derivations between predicted modeling and simulation values for the COP, total exergy destruction, and exergy efficiency are -0.604%, 2.886%, and 0.0452%, respectively, indicating that the method is efficient to optimize the performance.