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Entropy 2017, 19(1), 25; doi:10.3390/e19010025

Similarity Theory Based Radial Turbine Performance and Loss Mechanism Comparison between R245fa and Air for Heavy-Duty Diesel Engine Organic Rankine Cycles

1
State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China
2
Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing 100081, China
*
Author to whom correspondence should be addressed.
Academic Editor: Brian Agnew
Received: 13 November 2016 / Revised: 27 December 2016 / Accepted: 5 January 2017 / Published: 14 January 2017
(This article belongs to the Special Issue Advances in Applied Thermodynamics II)
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Abstract

Organic Rankine Cycles using radial turbines as expanders are considered as one of the most efficient technologies to convert heavy-duty diesel engine waste heat into useful work. Turbine similarity design based on the existing air turbine profiles is time saving. Due to totally different thermodynamic properties between organic fluids and air, its influence on turbine performance and loss mechanisms need to be analyzed. This paper numerically simulated a radial turbine under similar conditions between R245fa and air, and compared the differences of the turbine performance and loss mechanisms. Larger specific heat ratio of air leads to air turbine operating at higher pressure ratios. As R245fa gas constant is only about one-fifth of air gas constant, reduced rotating speeds of R245fa turbine are only 0.4-fold of those of air turbine, and reduced mass flow rates are about twice of those of air turbine. When using R245fa as working fluid, the nozzle shock wave losses decrease but rotor suction surface separation vortex losses increase, and eventually leads that isentropic efficiencies of R245fa turbine in the commonly used velocity ratio range from 0.5 to 0.9 are 3%–4% lower than those of air turbine. View Full-Text
Keywords: organic Rankine cycle; radial turbine; similarity theory; entropy generation organic Rankine cycle; radial turbine; similarity theory; entropy generation
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Zhang, L.; Zhuge, W.; Zhang, Y.; Chen, T. Similarity Theory Based Radial Turbine Performance and Loss Mechanism Comparison between R245fa and Air for Heavy-Duty Diesel Engine Organic Rankine Cycles. Entropy 2017, 19, 25.

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