Thermal-exergy efficiency trade-off optimization of pressure retarded membrane distillation based on TOPSIS model

Abstract

There has been an increasing interest in recovering low-grade heat and desalination simultaneously using pressure retarded membrane distillation (PRMD). As an energy-based process driven by temperature difference, the analysis of energy efficiency is significant. This work aims to analyze the effect of various operating parameters on thermal and exergy efficiencies of a counter-flow PRMD system. As the optimal value corresponding to the maximum thermal efficiency does not coincide with that leading to the maximum value of the exergy efficiency, a multi-objective optimization based on TOPSIS model and entropy weight method was conducted. A mathematical model including mass and heat transfer, and exergy balance for membrane module was firstly established to definite the effect of various parameters on PRMD performance. Then the highest scored condition was obtained, and thermal efficiency and exergy efficiency reached 78.75% and 43.4% respectively. Compared with the performance under the single-objective optimization for exergy efficiency, the exergy efficiency under the multi-objective optimization was reduced by only 5.73%, but the thermal efficiency is increased by 21.84%. Besides, the working conditions under multi-objective optimization with different feed solution concentrations are also presented. The PRMD system is trade-off optimized, which provides a reference for cost reduction and large-scale deployment.