Exergy-based ecological performance analyses and multi-objective optimizations for an endoreversible three-reservoir chemical potential transformer

In this paper, exergy-based ecological-function (ECF) optimal performances for endoreversible three-reservoir chemical potential (CHP) transformer with linear and diffusive mass transfer (MT) laws are studied. Exergy output is the output chemical energy of heating space. The optimal relationship between dimensionless ECF and coefficient-of-performance is derived firstly. Influences of CHP ratio of mass reservoirs and MT coefficient ratios on the cycle dimensionless ECF optimal performance are analyzed. Moreover, in order to maximize coefficient-of-performance, rate-of-energy-pumping, minimize entropy-generation-rate and maximize ECF, multi-objective optimizations for endoreversible three-reservoir CHP transformer with linear and diffusive MT laws are performed using NSGA-Ⅱ. MT law only changes the values of ECF and coefficient-of-performance, but the shape of the characteristic relationship curve remains unchanged. The linear MT law is a special case of diffusion MT law. Compared with single-objective optimization result for maximizing ECF, multi-objective optimization greatly decreases entropy-generation-rate and increases coefficient-of-performance at the expense of small sacrifices of rate-of-energy-pumping and ECF. Taking quadru-objective optimization as an example, the rate-of-energy-pumping of 17.5% and ECF of 7.14% are sacrificed, which greatly decreases the entropy-generation-rate by 42.86% and increases coefficient-of-performance by 9.69%. Multi-objective optimization can better coordinate the contradiction among objectives and improve comprehensive performance of three-reservoir CHP transformers.