| Summary: | In this paper, the performance of 13 working fluids in two Organic Rankine Cycles, which operate as the bottoming cycles for recovering waste heat from gas turbine modular helium reactor (GT-MHR), is investigated. Working fluids are classified in three dry, isentropic and wet fluids. The effect of varying pump
temperature and evaporator pressure on the thermal efficiency, total exergy loss of the combined cycle is studied for each category, and the results are compared. The results are calculated for an optimum pressure ratio in which thermal efficiency is maximum. According to the results, dry fluids show a higher thermal efficiency while wet fluids have the lowest values. However, the highest value for thermal efficiency is for R141b, which is an isentropic fluid. Furthermore, the results indicate that pump temperature increase, reduces the total thermal efficiency and increases the total exergy loss of the combined cycle. Increasing evaporator pressure leads to an optimum pressure that
maximizes total thermal efficiency. According to the optimized pressure ratio and evaporator pressure, R141b in isentropic fluids, R123 in dry fluids and R717 in wet fluids have the highest thermal efficiency values.
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