Experimental testing of a small-scale two stage Organic Rankine Cycle engine operating at low temperature

Abstract

Abstract This paper presents the testing results, both at partial and full load operation of a prototype two-stage, heat-to-power conversion engine based on the Organic Rankine Cycle with net capacity of 10 kWe at 130 °C. This engine has been developed to operate in a wide range of thermal load input, coming from thermal sources of variable heat supply. The intense fluctuation of the temperature and heat input dictates the use of a two-stage engine, so that the operation becomes flexible and efficient even at low thermal load. For the two-stage expansion, two scroll expanders have been connected in series with the first expander by-passed at low heat input. The engine has been tested in the lab supplied with heat from an electrical heater for several heat transfer fluid temperatures between 80 and 130 °C. The current work mainly focuses on the results of the operation at 130 °C, however a brief comparison of the results with other operating temperatures is also included. The measurements have shown that thermal efficiency is kept high enough even at low temperature, while the second expander operates with isentropic efficiency up to 66%. The maximum thermal efficiency reached is 8.87% and the maximum power production 7.53kWe for two-stage operation.