A Flow Rate Control Approach on Off-Design Analysis of an Organic Rankine Cycle System

This study explored effects of off-design heat source temperature (TW, in) or flow rate (mW) on heat transfer characteristics and performance of an organic Rankine cycle system by controlling the flow rate of working fluid R245fa (i.e., the operation flow rate of R245fa was controlled to ensure that R245fa reached saturation liquid and vapor states at the outlets of the preheater and evaporator, respectively). The results showed that the operation flow rate of R245fa increased with TW, in or mW; higher TW, in or mW yielded better heat transfer performance of the designed preheater and required higher heat capacity of the evaporator; heat transfer characteristics of preheater and evaporator differed for off-design TW, in and mW; and net power output increased with TW, in or mW. The results further indicated that the control strategy should be different for various off-design conditions. Regarding maximum net power output, the flow rate control approach is optimal when TW, in or mW exceeds the design point, but the pressure control approach is better when TW, in or mW is lower than the design point.