Shengjun Zhang

Fluid Selection for a Low-Temperature Geothermal Organic Rankine Cycle by Energy and Exergy

A detailed energy and exergy analysis of a low-temperature geothermal organic Rankine cycle is presented, screening the appropriate working fluids for specific heat source conditions. The results have been calculated with pinch point analysis approach for fixed temperature and mass flow rate of the heat source, fixed pinch points in evaporator and condenser and fixed condensing and sink temperatures by varying the high pressure of the cycle via computer program. And calculations are compared based on the optimum condition of each working fluid resulting from trading-offing the net power output, outlet volume flow rate and expansion ratio of the turbine and total UA of the system. Of 26 fluids investigated, R245fa appears as the most suitable for low-temperature geothermal power conversion applications. R134a, R142b, R600a and R236fa also offer attractive performances.

Performance Simulation and Experimental Testing of Moderately High Temperature Heat Pump Using Non-azeotropic Mixture for Geothermal District Heating

A water-to-water geothermal heat pump is a suitable technology to exploit heat from low-temperature geothermal sources for high-temperature district heating. A distributed parameter model simulation analysis was conducted for the system using non-azeotropic mixture of R245fa and R152a (0.63/0.37) under the condition that the input temperature and the flow rate of the heat transfer fluids were provided. The model was built by interconnecting different sub-models: the heat exchanger models, a compressor model and a thermostatic expansion valve model. Measured performance of the heat pump was presented and used to validate the cycle model. This model was proved to be accurate enough to serve as an optimization tool for further study. Keywords-Geothermal energy; Heat pump; Non-azeotropic mixture; Simulation