冷凝条件对基于混合工质的内燃机余热有机朗肯循环热力性能的影响

利用建立的内燃机余热有机朗肯循环模型，选取R245fa分别与环己烷、环戊烷组成非共沸混合工质，对3种冷凝条件下的有机朗肯循环进行热力学分析，研究了冷凝条件对非共沸混合工质有机朗肯循环性能的影响规律，提出了确定混合工质冷凝温度的方法。结果表明：冷凝条件是影响系统性能的重要因素，在定泡点冷凝温度工况下，纯工质的热力性能优于混合工质的热力性能；在定露点冷凝温度工况下，配比合适的混合工质的热力性能优于纯工质的热力性能。混合工质的冷凝温度应根据冷却介质进出口温度、混合工质的温度滑移和传热窄点温差进行优化；当冷却介质的温升小于混合工质的最大温度滑移时，随着R245质量分数的增加，系统输出净功出现两个极大值，但输出净功最大值出现在热力性能较优工质所占比例大的质量分数点；当冷却介质温升大于混合工质的最大温度滑移时，输出净功最大值出现在温度滑移最大的混合工质质量分数点。

Effects of condensation condition on cycle performance of the organic Rankine cycle (ORC) for recovering waste heat of engine using zeotropic mixtures

The effects of condensation conditions on the cycle performance of ORC (organic Rankine cycle) using zeotropic mixtures as working fluids for recovering exhaust heat of engine were analyzed in this paper. R245/cyclohexane and R245 fa/cyclopentane were selected as working fluids. Fixed condenser bubble temperature, fixed condenser dew temperature and optimized condensation temperature were considered as condensation conditions. The impacts of condensation conditions on the cycle performance were performed by establishing energy and exergy model of the ORC. Method determining condensation temperature was presented when using zeotropic mixtures as working fluids. Results showed that condensation condition is an important factor affecting the cycle performance. The cycle performance of pure component is better than that of mixture under the fixed condenser bubble temperature, however, the conclusion is opposite under the fixed condenser dew temperature. The condensation temperature of mixture should be optimized according to the inlet and outlet temperature of cooling air, temperature glide of mixture and pinch point temperature. Two optimal working fluids mass fractions maximize the net power output for cooling air increases less than the maximum condensation temperature glide, while the highest net power output appears at the higher mass fraction of the better cycle performance component. For the cooling air increases more than the maximum condensation temperature glide, the maximum net power output appears at the mass fraction of the maximum temperature glide.