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首页> 外文会议>International topical meeting on nuclear thermal hydraulics, operations and safety;NUTHOS-5 >Post-dryout heat transfer and entrained droplet sizes at low pressure and low flow conditions
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Post-dryout heat transfer and entrained droplet sizes at low pressure and low flow conditions

机译：低压和低流量条件下的干燥后传热和夹带的液滴尺寸

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The entrainment mechanisms and the entrained droplet sizes with relation to the flow regimes are investigated. Through the analysis of many experimental post-dryout data, it is shown that the most probable flow regime near dryout or quench front is not annular flow but churn-turbulent flow when the mass flux is low. A correlation describing the initial droplet size just after the CHF position at low mass flux is suggested through regression analysis. The history-dependent post-dryout model of Varone and Rohsenow replaced by the Webb-Chen model for wall-vapor heat transfer is used as a reference model in the analysis. In the post-dryout region at low pressure and low flow, it is found that the suggested one-dimensional mechanistic model is not applicable when the vapor superficial velocity is very low. This is explained by the change of main entrainment mechanism with the change of flow regime. In bubbly or slug flow a number of tiny droplets generated from bubble burst become important in the heat transfer after dryout. Therefore, the suggested correlation is valid only in the churn-turbulent flow regime (j_g~*=0.5 approx 4.5). It is also suggested that the droplet size generated from the churn-turbulent surface is dependent not only on the pressure but also on the vapor velocity. It turns out that the present model can predict the measured cladding and vapor temperatures within 20 percent and 25 percent, respectively.
机译：研究了与流态相关的夹带机理和夹带液滴尺寸。通过对许多实验后干燥数据的分析表明，当质量通量较低时，在干燥或淬火前沿附近最可能的流动方式不是环形流动而是搅动湍流。通过回归分析表明，在低质量通量的CHF位置之后，描述了初始液滴尺寸的相关性得到了建议。在分析中，将以历史为基础的Varone和Rohsenow的变干后模型替换为Webb-Chen模型进行壁蒸气传热的韦伯-罗森诺模型作为参考模型。在低压低流量的后吹干区域，发现当蒸汽表观速度非常低时，建议的一维力学模型不适用。这主要是由于主要夹带机制随流动状态的变化而变化的。在气泡状或团状流中，气泡破裂产生的许多细小液滴在变干后的传热中变得很重要。因此，建议的相关性仅在搅动湍流状态下有效（j_g〜* = 0.5约为4.5）。还建议从搅动湍流表面产生的液滴尺寸不仅取决于压力，还取决于蒸气速度。事实证明，本模型可以预测测得的包层和蒸汽温度分别在20％和25％之内。

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