Performance and Exergy Analysis of Transcritical Organic Rankine Cycle Associated with Mixture Working Fluids

orc2019 Tracking Number 52

The low-enthalpy heat in geothermal fluids is extracted by using a binary cycle and is converted into electricity. Conventional ORCs are used widely in low-enthalpy geothermal power plants as an effective solution to convert low-grade heat into power. However, conventional ORCs are characterized by high exergy destruction during heat transfer in the evaporator and condenser. The isothermal evaporation destruction and exergy loss of the heat source can be reduced by employing transcritical organic Rankine cycles (TRCs) to generate more electricity. In the present study, a thermodynamic analysis of the mixtures R245fa/R134a, R245fa/R1234yf and R245fa/R290 associated with TRC was conducted to investigate effects of the inlet pressures of expander on irreversibility, first law efficiency, and specific power. The mixtures were examined at the heat source temperature ranging from 160 to 210 ℃. Meanwhile, the inlet pressures of expander for R245fa/R134a, R245fa/R1234yf were ranged from 4 to 8 MPa, and R245fa/R290 was ranged from 5 to 9 MPa, respectively. In the present study, the first thermodynamic efficiency of the mixtures was significantly affected by the inlet temperatures and the inlet pressures of expander, especially at higher inlet temperature and pressure. However, the specific power was slightly increased with the inlet pressures of the expander. Finally, a maximum themal efficiency and specific power corresponding to a optimal pressure were observed at each inlet temperature due to the evaporate and condense irreversibility and, pmp and expander irreversibility decreased and increased with the inlet pressure, respectively.