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.
Highlights
In recent years, automobile industry has made great progress in improving internal combustion engine thermal efficiencies
The results indicated that the relative deviation to of adapt main performance at the design working condition was no more than 5%, and under all working were as working fluidpoint for organic Rankine cycle (ORC)
The results indicated that the relative deviation of main performance parameters at the design point working condition was no more than 5%, and under all working conditions were no more than 10%
Summary
Automobile industry has made great progress in improving internal combustion engine thermal efficiencies. (1)ofthe working fluid can beforanlow additional degree of freedom a better design of power size applications, it is possible to design an efficient, reliable and cost-effective organic vapor the thermodynamic cycle for a specific heat source temperature, especially some of which are very expander. A radial turbine, for the heavy-duty diesel engine ORC application, is numerically simulated using R245fa and air as the working fluid to compare the differences of their performance and loss mechanism. R245fa, a typical organic fluid, is chosen as the working fluid because of its environmental friendly properties [27], good thermodynamic performance in the heavy-duty diesel engine applications [28] and high turbine nominal efficiency for small power size applications [20]. The similarities and differences of turbine entropy generation and loss mechanisms are discussed to explain the total-to-static isentropic efficiency difference
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