Experimental investigation on the performance of a micro-ORC system for different operating conditions

Abstract

The micro-ORC systems are widely considered a reliable solution for domestic power production from renewable sources. The investigation of the optimal operating conditions to maximize system efficiency is an interesting challenge. In this study, a preliminary experimental campaign has been carried out on a biomass-fired micro-ORC system. The system is designed for stationary applications for domestic users, with a gear pump, a scroll expander and R245fa as the working fluid. The performance characterization of the micro-ORC under steady-state conditions has been obtained varying the water flow rate in the condenser at constant pump and expander speeds. The temperature of the hot source (thermal oil) is the maximum achievable in each operating condition. The temperature at the expander inlet and the condenser and evaporator pressure strongly influence the system performance. The increase in water flow leads to a decrease in the condenser pressure and a reduction of the superheating degree of the organic fluid. The system reaches the maximum electric power output of approximately 2565 W with a water flow rate of about 20 l/min. The highest electrical efficiency increases as the refrigerant flow rate decreases and reaches the highest value of 8.1% for the minimum investigated water flow rate.