| dc.description.abstract | The study examines the performance of zeotropic mixtures consisting of different hydrocarbons with carbon dioxide as working fluids for a supercritical organic Rankine cycle. Four hydrocarbons, i.e., dimethyl ether, R1234yf, diethyl ether, and isobutane, are considered in this study based on their flammability and environmental characteristics such as global warming potential, ozone depletion potential, and toxicity. The zeotropic mixtures are developed using the National Institute of Standards and Technology database, REFPROP 9.1, on a molar concentration basis that varies from 0.2 to 0.8 (20% to 80% hydrocarbon). The performance indicators such as cycle efficiency, volumetric power coefficient, exergy destruction, etc., are assessed for different cycle operating pressures and heat source inlet temperatures varying from 400 K to 500 K. After detailed analysis, the dimethyl ether was the best possible working fluid from all the pure hydrocarbons considered in this study, whereas the zeotropic mixture of dimethyl ether and carbon dioxide was the optimal working fluid from all the zeotropic blends considered. Finally, the performance of the optimal zeotropic mixture was assessed for a system located in Houston, TX using the lowest and highest annual temperature of Houston (i.e., 278 K and 308 K). The results showed that the zeotropic mixture of dimethyl ether and carbon dioxide performs better at lower heat sink temperature (i.e., during winter conditions) with a maximum cycle efficiency of 17.7% and exergy efficiency of 41.0% at a reduced pressure of 2.12 (13,827 kPa) and a fractional molar concentration of 0.8 (80% hydrocarbon). | |
