Effect of off-design heat source temperature on heat transfer characteristics and system performance of a 250-kW organic Rankine cycle system

This work investigated the effect of off-design heat source temperature on the heat transfer characteristics and system performance of a 250-kW organic Rankine cycle system. R245fa was used as a working fluid. The net power output was 243 kW and the system thermal efficiency was 9.5% under design conditions. For an off-design heat source temperature (TW,in), the operating pressure was controlled to meet that R245fa reached the saturation liquid and vapor states at the outlet of the preheater and evaporator, respectively. The results demonstrated that the increase rate in evaporation temperature was almost the same as that in TW,in; higher TW,in yields better heat transfer performance of the preheater and required a smaller evaporator heat capacity; and the net power output and system thermal efficiency increased linearly with increasing TW,in. The net power output increased by 41.9%, whereas the total heat transfer rate increased by only 7.0% for the studied range of TW,in. In conclusion, an off-design operation was studied by the pressure control approach within a heat source temperature variation of −10.3 °C to +19.8 °C from design, resulting in variations of −13.6% to +22.6% and −11.5% to +17.4% in the net power output and system thermal efficiency, respectively.