Parametric analysis of organic Rankine cycle based on a radial turbine for low-grade waste heat recovery

Organic Rankine cycle (ORC) is one of the promising technologies to convert low-grade waste heat into electricity. This study comprehensively investigates the thermodynamic performance of ORC system and the aerodynamic characteristics of radial turbine. An optimized coupling model for the ORC with a radial turbine is developed, and the particle swarm optimization algorithm is applied to maximize the turbine efficiency dynamically. The model is used to evaluate the effect of heat source temperature on the cycle performance and parameter selection for turbine design optimization. The results show that optimal turbine efficiency can be achieved within the considered heat source outlet temperature range, as high pressure ratio and high mass flow rate can both degrade the turbine efficiency. Among the four studied organic fluids, the ORCs using R123 and R245fa can achieve desirable cycle performances. For the turbine design, lower degree of reaction is beneficial for turbine efficiency gains. The optimized rotational speed and ratio of wheel diameter are dependent on heat source temperature, while which has almost no effects on velocity ratio, loading coefficient, and flow coefficient. The reasonable ranges of partial turbine design parameters are also proposed in this work.