Abstract Compared with direct steam generation (DSG), direct vapor generation (DVG) system based on organic working fluid has better application potential in low and medium temperature distributed system. However, there is a lack of understanding of the two-phase flow instability that commonly occurs in DVG systems and can cause fatal damage to the system. In this paper, Ledinegg instability is considered as a common flow instability, and its occurrence characteristics and avoidance strategies are presented. First, a theoretical model was established to study Ledinegg instability of organic working fluid. Then, the effects of heat flux q, inlet subcooling Tc, length-to-diameter ratio L/D and fluid properties are analyzed. Particularly, a characteristic parameter RL representing the possibility of Ledinegg instability is proposed for the first time in performance evaluation of Ledinegg instability. The results show that as L/D decreases from 200 to 100, RL reduces from 0.88 to 0.25. As q increases from 10 kW/m2 to 30 kW/m2, RL increases from 0.54 to 1.03. When Tc is less than 3 °C, RL approaches 0 and Ledinegg instability disappears. With the increase of surface tension σ and the latent heat of vaporization r, the decreases of vapor-liquid density ratio ρsv/ρsl and the decreases of vapor-liquid viscosity ratio μsv/μsl, RL increases. The physical equation describing RL of Ledinegg instability is helpful to guide DVG system to reduce or avoid Ledinegg instability in design and operation.

中文翻译：

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太阳能集热器内直接产生蒸汽的 Ledineg 不稳定性分析

摘要 与直接蒸汽发生（DSG）相比，基于有机工质的直接蒸汽发生（DVG）系统在中低温分布式系统中具有更好的应用潜力。然而，人们对DVG系统中常见的两相流动不稳定性缺乏了解，并可能对系统造成致命损坏。在本文中，Ledinegg 不稳定性被认为是一种常见的流动不稳定性，并提出了它的发生特征和避免策略。首先，建立了研究有机工质Ledinegg不稳定性的理论模型。然后，分析了热通量q、入口过冷度Tc、长径比L/D和流体性质的影响。特别，在雷丁内格不稳定性的性能评估中，首次提出了代表雷丁内格不稳定性可能性的特征参数RL。结果表明，随着 L/D 从 200 减小到 100，RL 从 0.88 减小到 0.25。随着 q 从 10 kW/m2 增加到 30 kW/m2，RL 从 0.54 增加到 1.03。当 Tc 小于 3 °C 时，RL 接近 0，Ledineg 不稳定性消失。随着表面张力σ和汽化潜热r的增加，汽液密度比ρsv/ρsl减小，汽液粘度比μsv/μsl减小，RL增大。描述Ledinegg不稳定性RL的物理方程有助于指导DVG系统在设计和运行中减少或避免Ledinegg不稳定性。结果表明，随着 L/D 从 200 减小到 100，RL 从 0.88 减小到 0.25。随着 q 从 10 kW/m2 增加到 30 kW/m2，RL 从 0.54 增加到 1.03。当 Tc 小于 3 °C 时，RL 接近 0，Ledineg 不稳定性消失。随着表面张力σ和汽化潜热r的增加，汽液密度比ρsv/ρsl减小，汽液粘度比μsv/μsl减小，RL增大。描述Ledinegg不稳定性RL的物理方程有助于指导DVG系统在设计和运行中减少或避免Ledinegg不稳定性。结果表明，随着 L/D 从 200 减小到 100，RL 从 0.88 减小到 0.25。随着 q 从 10 kW/m2 增加到 30 kW/m2，RL 从 0.54 增加到 1.03。当 Tc 小于 3 °C 时，RL 接近 0，Ledineg 不稳定性消失。随着表面张力σ和汽化潜热r的增加，汽液密度比ρsv/ρsl减小，汽液粘度比μsv/μsl减小，RL增大。描述Ledinegg不稳定性RL的物理方程有助于指导DVG系统在设计和运行中减少或避免Ledinegg不稳定性。随着表面张力σ和汽化潜热r的增加，汽液密度比ρsv/ρsl减小，汽液粘度比μsv/μsl减小，RL增大。描述Ledinegg不稳定性RL的物理方程有助于指导DVG系统在设计和运行中减少或避免Ledinegg不稳定性。随着表面张力σ和汽化潜热r的增加，汽液密度比ρsv/ρsl减小，汽液粘度比μsv/μsl减小，RL增大。描述Ledinegg不稳定性RL的物理方程有助于指导DVG系统在设计和运行中减少或避免Ledinegg不稳定性。