Experimental investigation on multi-vane expander operating conditions in domestic CHP ORC system

Abstract

Small- and micro-power ORC systems designed for domestic use by prosumers should be cheap and reliable. The main part of the ORC system cost is the price of heat exchangers and the expander. Multi-vane expanders are positive displacement volumetric machines which are nowadays considered for application in micro-power domestic ORC systems. The multi-vane expander design is very simple, which translates into low production costs. Compared to the other types of volumetric machines and micro turbines, which are adopted in micro-power domestic ORC systems, multi-vane machines feature a lower gas flow capacity, lower expansion ratios, and an advantageous ratio of the power output to the external dimensions. These machines are insensitive to the negative influence of the gas-liquid mixture expansion. Moreover, the multi-vane expander can be easily hermetically sealed, which is one of the key issues in the ORC system design. Multi-vane expanders feature power outputs of several hundred W to approximately 5 kW. Maximum gas pressure on the inlet to multi-vane expander reaches approximately 10 bar. The issues concerning the application of multi-vane expanders in such systems are innovative and not fully scientifically described. The solution of these problems requires comprehensive study and experimental analysis.This paper reports the results of experimental investigations carried out on domestic CHP ORC system adopting multi-vane expander under varied operating conditions. The experimental results showed that the expander indicated work varies in the range of 0.96—4.18 kJ/kg while its internal efficiency varies in the range of 17.2—58.3 % depending on the experimental conditions. Moreover, the results of numerical investigations on multi-vane expander operating conditions are presented. The numerical model of the expander was validated using the data obtained from the experiment and analyses were performed in ANSYS CFX software. The results proved that multi-vane expanders are suitable for domestic ORC systems and are a promising alternative to the other types of volumetric expanders used in such systems.