Working fluid ranking using cosmo and Refprop softwares for a mobile waste heat recovery system

A simulation methodology is developed for the working fluid assessment using COSMO and REFPROP softwares for a WHR system that employs Rankine cycle to generate useful work by utilizing waste exhaust heat of a heavy-duty internal combustion engine. The methodology has two distinct approaches for working fluid assessment compared to the methodologies in literature. First, it compares the working fluids in transient cycles rather than at a limited number of steady state operating points. Secondly, a fixed condensation pressure is used as a constraint rather than fixed condensation temperature. These two approaches enable a more realistic working fluid assessment. Two fluid properties are developed with COSMO and REFPROP softwares. These fluid properties models are interchangeable without any need to modify the main integrated model. A Rankine cycle model is developed in Simulink to carry out thermodynamic calculations. A cooling model is also developed in GT-SUITE in order to factor in the effect of pump and fan power consumption. These three models are integrated in Simulink model. A Matlab script is written for each fluid properties model to run the integrated model iteratively for different working fluids. Simulations are carried out for 146 working fluids that are commonly analyzed in literature. Simulation results show that ethenol provides the highest fuel economy benefit when working fluid properties are calculated with COSMO software whereas cyclopentane provides the highest fuel economy benefit when working fluid properties are calculated with REFPROP. Moreover, COSMO fuel economy results are compared to REFPROP fuel economy results and it is shown that COSMO results are in good agreement with REFPROP results. However, the use of predictive softwares such as COSMO affects the working fluid ranking. Hence, an empirical software or data should be used for fluid properties for a precise working fluid ranking. As a result, it is concluded that cyclopentane is the most suitable working fluid to be used in a WHR system for a heavy-duty engine for the best fuel economy and environmental safety.