| dc.description.abstract | This study selects a working fluid operating in an organic Rankine cycle at various climatic conditions for a number of major cities in the United States. Energy and exergy analyses are conducted for the cycle operating using a low-grade waste heat-source. Hydrocarbons are considered as working fluids based on their environmental and cycle performance characteristics. First law efficiency, dimensionless exergy-destruction in the evaporator, second law efficiency, and the volume power coefficient of the cycle are analyzed for different cycle operating pressures, heat-sink temperatures, and heat-source inlet temperatures for a constant turbine-work output. The average annual temperature of cities in the United States is considered as the heat-sink temperature. The system parameters for the working fluids are calculated at different pressure and source inlet temperatures from 400 K to 500 K. A rank-matrix with appropriate weights for each parameter is employed to select the optimal working fluid and the cycle operating pressure. After consideration of the environmental impact and the rank-matrix method of working fluid selection, dimethyl ether was found to be the most promising working fluid for heat-source inlet temperatures of 400 K and 450 K. In comparison, diethyl ether is a better working-fluid prospect for a heat-source temperature of 500 K. The optimal mode of cycle operation was also selected for various heat-source inlet temperatures; subcritical operation is preferred at 400 K, while a supercritical operation is preferred for 450 K and 500 K. The evaporator pressure corresponding to the best performance for each heat-source temperature is achieved at 4298±52 kPa and 6803±93 kPa for dimethyl ether at 400 K and 450 K, respectively, and 5226±85 kPa for diethyl ether at 500 K. | |
