MULTIOBJECTIVE OPTIMIZATION OF CASCADE REFRIGERATION SYSTEM USING NH3-CO2 AND NH3-N2O REFRIGERANT PAIRS

Abstract

In this paper a comparative analysis based on multiobjective optimization of a cascade refrigeration system using NH<sub>3</sub>-CO<sub>2</sub> and NH<sub>3</sub>-N<sub>2</sub>O refrigerant pairs has been done. Exergetic effciciency and overall cost rate have been taken as the two conflicting objective functions, and evaporator temperature, condenser temperature, LTC condenser temperature, and cascade heat exchanger temperature difference are the four design variables. The optimization work has been carried out using genetic algorithm, which results in a nondominated optimal solution represented in the form of pareto-optimal curve, and the technique for order performance by similarity to ideal solution (TOPSIS) method is used to select a unique solution. The results show that NH<sub>3</sub>-N<sub>2</sub>O is a better alternative as compared to NH<sub>3</sub>-CO<sub>2</sub> refrigerant pair from a multiobjective optimization point of view. The corresponding optimal operating conditions have also been suggested for both the refrigerant pairs.