A comparison of heat transfer correlations applied to an Organic Rankine Cycle

Abstract Organic Rankine Cycles (ORC) are often based on the utilization of special dry or isentropic fluids, namely substances with a vertical or positive slope of the saturated steam curve. Several heat transfer correlations for boiling process are available in literature. However, only a few of them are specifically developed and validated for the case of the organic fluids. Such correlations are tested and extrapolated by means of suitable experimental devices and with a specific organic fluid, presenting non-negligible percentage error variations when compared with experimental results concerning different organic fluids. This paper investigates the impact of the overall heat transfer coefficient evaluated by means of different correlations available in literature on the main output parameters of an Organic Rankine Cycles, using a zero-dimensional numerical model. Two case studies are investigated, both of them powered by medium-enthalpy geothermal source which provides a constant thermal load. The first case study concerns a 1.20 MW el ORC, powered by geofluid at 160 °C and 7.00 bar and using n-pentane. The second ORC case study is supposed to provide 8.00 kW el and to be powered by geofluid available at 95.0 °C and 3.00 bar and using R245fa, in agreement with the results available in literature. Both of the models are developed and simulated in Engineering Equation Solver (EES) environment.