Abstract:

For a thermal power system, cold source temperature fluctuates throughout a year in many areas due to the change of ambient temperature. Therefore, off-design operation of an organic Rankine cycle (ORC) system is often unavoidable. The effect of cooling water temperature on ORC performance was studied by using R123 working fluid to generate power from low-grade waste heat. When the inlet temperature of cooling water in the condenser was increased but the hot source temperature was kept constantly, the condensation pressure was increased and the evaporation pressure was increased slightly, whereas the heat load of evaporator and condenser as well as the pressure difference and ratio between the inlet and outlet of scroll expander was decreased. Hence, the electric power output and thermal efficiency of the system were decreased. In the range of study that the cooling water temperature increased from 21.82℃ to 42.10℃, the electric power output declined from 2.357 kW to 1.535 kW, thermal efficiency declined from 7.25% to 5.76%, and the electric power output and thermal efficiency linearly decreased by 34.87% and 23.86%, respectively. Under these operating conditions, the electric power output decreased by 0.0411 kW and 1.74% at every 1℃ increase of cooling water temperature. Therefore, cold source temperature significantly affected the performance of an ORC system with low-grade waste heat, which could serve as important reference for designing cold source system and optimizing ORC system performance with consideration of local weather conditions.

Key words: organic Rankine cycle, thermodynamics, entropy, recovery, cooling water temperature

摘要：

利用搭建的ORC余热发电测试系统，实验研究了冷却水温度对ORC系统性能的影响。结果表明：当热源温度不变时，随着冷却水温度的升高，冷凝压力增加，蒸发压力稍有增加，冷凝器和蒸发器的负荷减小，膨胀机的压差和压比减小，系统的输出电功和热效率降低。在实验测试范围内，当冷却水温度从21.82℃升至42.10℃时，输出电功从2.357 kW降至1.535 kW，热效率从7.25%降至5.76%，输出电功与热效率分别降低34.87%和23.86%。也意味着在此工况范围内，冷却水温度每升高1℃，系统输出电功降低0.0411 kW和1.74%。通过研究冷源温度对ORC系统性能的影响，为今后结合当地气候因素设计冷源系统和优化系统性能提供重要的实验依据。

关键词: 有机朗肯循环, 热力学, 熵, 回收, 冷源温度