In an organic Rankine cycle (ORC), the study of the cycle efficiencies and the turbine is essential to know the performance in the generation of electrical energy. The proper selection of a working fluid is relevant, because it must be environmentally friendly and compatible with the ORC plant. This article presents an experimental study for the analysis of the cycle and thermal efficiencies on a 1-kW ORC system and the isentropic efficiency of its scroll expander. The test was performed on a 1-kW ORC with scroll expander system with R245fa as the working fluid. Furtheremore, it was considered a working temperature below 100 ◦C, which is used in waste heat recovery systems, to determine the performance of the ORC. The enthalpy is estimated with the Coolprop software. For estimating the cycle and thermal efficiency, the net power and the thermal power, which are supplied to evaporate the working fluid, were considered. The isentropic efficiency of the expander was calculated by the scroll mechanical work and the hydraulic work at the scroll expander. The results show that the mean isentropic efficiency of the fluid in the prototype test for ORC in the generation of 1000 W was about 60%, a promising value for the generation of electrical energy using the residual heat from industry.

Introduction

In recent years, the demanding level of industrial energy in the world has been increasing due to the advance and development of its processes. For this reason, the energy transition has made the researchers to perform works for fossil fuel reduction using alternative energies [1]. Furthermore, the thermal energy processes are mainly supplied by fixed sources such as incinerators, fire boilers, drying furnaces, exo-thermal processes, purge or exhaust of vapor systems by chimneys, generating the possibility to reuse the residual heat to reintegrate it in the processes, obtaining fossil fuel savings and generating electric energy [2], [3]. However, waste generation energy is increasing and if it is not treated well, it may occur harmful effects on health, environment and social economy [4]. One of the most efficient techniques that has demonstrated advances in the residual heat reuse, is the one which integrates the organic Rankine cycle (ORC) [5]–[۸], because it is possible to use in a stable manner, heat sources lower than 100 ◦C in order to heat a working fluid, taking advantage of its mechanical energy and transforming it into electric energy [9]. The general ORC process has three main stages: the heat source (heating), the conversion system of electric thermal energy (generating) and the heat sinking (condensation) [10], [11].