This paper presents an experimental analysis conducted on a low-temperature micro-ORC energy system, to assess its performance operating with partial evaporation (PE-ORC). Temperatures of the heat source in the range between 40 °C and 75 °C have been tested, and for each value, the vapour quality at the expander inlet has been varied by regulating the feed-pump rotating speed. The thermodynamic state of the working fluid in two-phase conditions has been estimated by means of a thermal balance at the heat exchangers, using the measured values of temperature, pressure and flow rate.

Detailed experimental results are provided, with special focus on the performance of evaporator, expander and feed-pump, highlighting the difference in their behaviour compared with the regular operation with dry expansion of the same micro-ORC system. Relevant improvements have been observed in the evaporator effectiveness, mainly due to the reduction of the pinch point temperature difference. Also, the volumetric and total efficiencies of the feed-pump are improved substantially. On the other hand, the net power output and the expander efficiency resulted penalized by the operation with partial evaporation. The maximum power output obtained was close to 1.2 kW, with heat source temperature equal to 75 °C and fluid quality close to 1. The power output is reduced, at constant temperature, by decreasing the vapour quality at the expander inlet.

The results suggest that operating a small-scale ORC system with partial evaporation may lead to some improvements to the performance of the cycle, especially regarding the evaporator performance. Moreover, with values of fluid quality at the expander inlet between 0.8 and 1, the penalization on the expander performance, compared to the dry expansion mode, is limited. However, a proper redesign of the power plant for the specific purpose is required in order to make partial evaporation an effective solution. Specifically, the expander and pump geometry and control require to be optimized for the particular working conditions, the recuperator must be removed, and the evaporator should be designed for the optimal exploitation of the heat source.

本文介绍了对低温微 ORC 能源系统进行的实验分析，以评估其在部分蒸发 (PE-ORC) 下运行的性能。已对 40 °C 至 75 °C 范围内的热源温度进行了测试，并且对于每个值，通过调节进料泵转速来改变膨胀机入口处的蒸汽质量。工作流体在两相条件下的热力学状态已通过热交换器处的热平衡，使用温度、压力和流量的测量值来估计。

提供了详细的实验结果，特别关注了蒸发器、膨胀机和进料泵的性能，突出了它们与同一微型 ORC 系统干膨胀的常规操作相比的行为差异。在蒸发器效率方面已观察到相关改进，主要是由于夹点温度差的减小。此外，进料泵的容积效率和总效率也大大提高。另一方面，部分蒸发操作会降低净功率输出和膨胀机效率。获得的最大功率输出接近 1.2 kW，热源温度等于 75 °C，流体质量接近 1。在恒定温度下，通过降低膨胀机入口处的蒸汽质量来降低功率输出。

结果表明，运行带有部分蒸发的小型 ORC 系统可能会改善循环性能，特别是在蒸发器性能方面。此外，膨胀机入口处的流体质量值介于 0.8 和 1 之间，与干式膨胀模式相比，对膨胀机性能的不利影响是有限的。然而，为了使部分蒸发成为有效的解决方案，需要针对特定​​目的对发电厂进行适当的重新设计。具体来说，膨胀机和泵的几何形状和控制需要针对特定​​的工作条件进行优化，必须拆除同流换热器，并且蒸发器的设计应针对热源的最佳利用进行设计。