Analysis Of Transcritical And Subcritical Organic Rankine Cycle And Experimental Study

Nowadays, energy crisis appears to be more and more serious, thus the utilization of low temperature heat source has attracted more attention, of which organic Rankine cycle(ORC) can make a great contribution to. In this paper, both transcritical and subcritical ORC simulation models are built for the optimization of the systems with a heat source of geothermal water at a temperature of 110℃. Refrigerants R115, R125, R143 a, R218, R404 a and R507 a are used for transcritical cycles and R123, R245 fa, R600, R600 a and R601 are used for subcritical cycles. The net power output, thermal and exergic efficiencies and the UA value are calculated for parametric optimization. A calculation method for ensuring the location of the pinch point is proposed. The simulation results are compared with the data from other papers and the models are proved to be correct. In addition, a 500 W ORC power generation experiments are conducted with R245 fa as working fluid and the thermodynamics and heat transfer properties are studied. The conclusions can be summarized as follows:To begin with, the net power outputs of the transcritical cycles are higher than those of the subcritical ones. The system with R218 achieved the highest optimum net power output.With the increment of the evaporating pressure and the turbine inlet temperature, the thermal and exergy efficiencies of the transcritical cycles increase at first and then decrease, but the efficiencies of the subcritical cycles increase. The overall UA values of subcritical cycles are lower than those of transcritical cycles. The UA values of subcritical cycles increase with the increasing turbine inlet temperature and decrease with the increasing evaporating pressure, and the UA values of subcritical cycles decrease with the increasing turbine inlet temperatureMoreover, there exists pressure drop in the evaporator during the experiments. The outlet pressure of the evaporator is regarded as the evaporating pressure. Within the range of the working conditions, the variation trend of the net power output, thermal and exergic efficiencies and the UA value increase with the increment of the evaporating pressure, consistent with the simulation results. With the increase of the mass flow rate of the working fluids, the pressure drop in the evaporator increases, the average heat transfer coefficient increases and the superheated degree decreases. With the superheated degree increases, the LMTD(logarithmic mean temperature difference) increases, and the heat flux increases.