Abstract Organic Rankine Cycle is an efficient and reliable technology for the thermal-to-electricity conversion of low-grade heat sources but the variability in boundary conditions often forces these systems to operate at off-design conditions. The development of reliable models for the performance prediction of organic Rankine cycle power systems under off-design conditions is therefore crucial for system-level integration and control implementation. In this paper, a mathematical model for the evaluation of the expected performance of organic Rankine cycle power units in a large range of operating conditions based on experimental data collected in a medium-size solar organic Rankine cycle power plant is presented. Two different empirical approaches for the performance prediction of heat exchangers and machines, namely, constant-efficiency and correlated-based approaches, are proposed and compared. In addition, empirical correlations based on experimental data are proposed for the preliminary assessment of the energy demanded during the start-up phase and the corresponding duration. Results demonstrate that a good achievement in terms of accuracy of the model and reliability of the simulation performance can be obtained by using a constant-efficiency approach, with average errors lower than 5% and 2.5 K for the expected net power and outlet oil temperature respectively. The use of polynomial correlations leads to a more accurate estimation of the performance parameters used for evaporator and the turbine (in particular the evaporator heat effectiveness and the isentropic and electromechanical efficiency for the turbine), which strongly affect the main output variables of the model and, at the same time, are remarkably influenced by the operating conditions. A reduction in the average error in the prediction of the net power and outlet temperature of the heat transfer fluid to about 4% and 1.5 K respectively is therefore achieved by this approach. Average errors of 18.5% and 12.5% are achieved for the start-up time and the corresponding energy absorbed, respectively. Although the results obtained in terms of accuracy could be improved, these correlations can give an initial indication about the duration and energy required during this phase.

中文翻译：

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中型太阳能有机朗肯循环装置非设计模拟的实验验证模型

摘要 有机朗肯循环是一种高效可靠的低品位热源热电转换技术，但边界条件的可变性往往迫使这些系统在非设计条件下运行。因此，开发用于非设计条件下有机朗肯循环电力系统性能预测的可靠模型对于系统级集成和控制实施至关重要。在本文中，基于在中型太阳能有机朗肯循环发电厂中收集的实验数据，提出了一个数学模型，用于评估有机朗肯循环发电机组在大范围运行条件下的预期性能。换热器和机器性能预测的两种不同经验方法，即，提出并比较了恒定效率和基于相关的方法。此外，还提出了基于实验数据的经验相关性，用于初步评估启动阶段和相应持续时间所需的能量。结果表明，采用恒效率方法在模型精度和仿真性能可靠性方面取得了较好的效果，预期净功率和出口油温的平均误差分别小于5%和2.5 K . 多项式相关性的使用可以更准确地估计用于蒸发器和涡轮机的性能参数（特别是蒸发器的热效率以及涡轮机的等熵和机电效率），这对模型的主要输出变量有很大影响，同时受运行条件的影响显着。因此，通过这种方法可以将传热流体的净功率和出口温度的预测平均误差分别降低到约 4% 和 1.5 K。启动时间和吸收的相应能量的平均误差分别为 18.5% 和 12.5%。尽管可以改进在精度方面获得的结果，但这些相关性可以初步表明该阶段所需的持续时间和能量。因此，通过这种方法可以将传热流体的净功率和出口温度的预测平均误差分别降低到约 4% 和 1.5 K。启动时间和吸收的相应能量的平均误差分别为 18.5% 和 12.5%。尽管可以改进在精度方面获得的结果，但这些相关性可以初步表明该阶段所需的持续时间和能量。因此，通过这种方法可以将传热流体的净功率和出口温度的预测平均误差分别降低到约 4% 和 1.5 K。启动时间和吸收的相应能量的平均误差分别为 18.5% 和 12.5%。尽管可以改进在精度方面获得的结果，但这些相关性可以初步表明该阶段所需的持续时间和能量。