Abstract
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.
Highlights
An organic Rankine cycle (ORC) is identical to a steam Rankine cycle, except it employs organic fluids with low boiling point as working fluids to generate power from low-temperature heat sources [1]
Commercial ORC units were typically designed for nominal operating points or heat source temperature; the system performances of these ORC units suffered under off-design conditions [1,2]
These results indicate that the control strategy indicate thatTothe control strategy net should be output, significantly different for various off-design conditions
Summary
An organic Rankine cycle (ORC) is identical to a steam Rankine cycle, except it employs organic fluids with low boiling point as working fluids to generate power from low-temperature heat sources [1]. The heat transfer coefficients of the heat exchangers were not examined Their analytical results showed that, for the lower flow rate of the heat source fluid, the constant pressure operation with variable inlet guide vanes yielded higher net power output than the sliding pressure operation. On the TW,in or mW considerably improved the system output and thermal basis of previous studies [6,7], this work uses a different control approach under off‐design conditions efficiency. On the basis of previous studies [6,7], this work uses a different control approach under to analytically examinetothe effect of off‐design sourceoftemperature or flow ratetemperature on the heat transfer off-design conditions analytically examine heat the effect off-design heat source or flow characteristics ( in the preheater and evaporator) and system performance of a 250‐kW. Performance of a 250-kW ORC system by using the flow rate control approach
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