Dynamic modeling and control strategy of an organic Rankine cycle with concentration regulation of the zeotropic mixture working fluid

Zheng Miao, Yuchen Zhang, Peiwei Yan and Jinliang Xu

Energy, 2025, vol. 335, issue C

Abstract: Fluctuations in heat source/sink conditions degrade the performance of the organic Rankine cycle system and hinder its widespread application. The concentration regulation of the mixture working fluid is proposed in this work as a control approach to enhance the adaptability of the system to heat source/sink fluctuation. Two control strategies, constant-evaporation-pressure operation and constant-output-power operation, are investigated through the developed dynamic model of a 4-kW organic Rankine cycle prototype. The results indicate that, compared to the temperature glide of the mixture during phase change, a more significant mechanism of concentration regulation is the variation of the average evaporation and condensation temperatures. The trade-off between the exergy destructions of the evaporator and condenser results in the optimal system performance at a specific mixture concentration. The mixture concentration alongside the mixture mass flow rate enables dual-objective control of the system. The concentration-adjustable organic Rankine cycle exhibits superior performance in both constant-evaporation-pressure and constant-output-power operations compared to the fixed-concentration organic Rankine cycle and the basic organic Rankine cycle with pure working fluid in two aspects: the enlargement of the effective control range and the improvement of system performance. Under the fluctuation of heat source/sink conditions, the control range of the concentration-adjustable system is about 3–3.3 times wider than the fixed-concentration system, while the performance of the concentration-adjustable system is about 9.01 %–14.81 % higher in terms of the thermal efficiency and about 9.72 %–13.64 % higher in terms of the exergy efficiency than the basic organic Rankine cycle.

Keywords: Organic Rankine cycle; Dynamic modeling; Concentration regulation; Mixture working fluid; Control strategy (search for similar items in EconPapers)
Date: 2025
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:335:y:2025:i:c:s0360544225037351

DOI: 10.1016/j.energy.2025.138093

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