Experimental investigation of organic Rankine cycle performance using alkanes or hexamethyldisiloxane as a working fluid

An experimental investigation of the organic Rankine cycle (ORC) is carried out using butane, pentane, cyclopentane or hexamethyldisiloxane as a working fluid. Thermal and exergy efficiencies are used to assess system performance over a wide range of heat source temperature, turbine inlet pressure and superheating degree. The results indicate that both of these efficiencies increase with rising heat source temperature and turbine inlet pressure. Under the present experimental conditions, without using an optimized turbine, the highest thermal efficiency and exergy efficiency are 8.0% and 25.2%, respectively. The results show that hexamethyldisiloxane is a better working fluid than the alkanes under all studied experimental conditions. Moreover, it is found that a small superheating degree may be beneficial. Exergy loss analysis indicates that most of the loss occurs in the evaporator and that a working fluid with a high critical temperature is advantageous for ORC systems driven by a heating cycle with a heat transfer fluid.