Finite-time thermodynamic modeling, analysis and four-objective optimizations for Rallis cycle with NSGA-II and multiple decision-making methods

An endoreversible air-standard Rallis-cycle model with heat-transfer loss is established using finite-time thermodynamics herein. Firstly, power (P), efficiency (η), efficient power (Ep) and power density (Pd) expressions are derived. Secondly, impacts of compression ratio, heat transfer loss, pressure ratio and cut-off ratio on performances are analyzed. Thirdly, applying NSGA-II, multi-objective optimizations (MOOs) based on dimensionless P (P‾), η, dimensionless Ep (E‾p), dimensionless Pd (P‾d) and their different combinations, totally fifteen combinations including 1 four-objective, 4 three-objectives, 6 two-objectives, and 4 single-objectives, are carried out with expansion ratio (σ) of isothermal process as optimization variable. For the same combination, deviation-indexes (Ds) obtained by LINMAP, TOPSIS and Shannon Entropy decision-making methods are compared, and scheme with the smallest value is the best. Results show that, cycle η can be improved with sacrifice of less P when Ep is chosen as objective; compared with the maximum P‾ objective, although part of η is sacrificed, the size is reduced when the maximum P‾d is taken as objective; when optimizing objective combination of P‾−P‾d−E‾p−η, the optimal σ is mainly distributed between 7 and 13, and D obtained by TOPSIS method is the smallest. The most significant contributions are establishment of endoreversible Rallis-cycle model, comparative analyses under different performance indicators, and MOOs with four objectives.