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首页> 外文期刊>International Journal of Heat and Mass Transfer >Modeling of transition boiling under an impinging water jet
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Modeling of transition boiling under an impinging water jet

机译：撞击水射流下过渡沸腾的建模

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摘要

Liquid jet impingement is known for its high capability of extracting heat from the surface it impinges on. Steady state subcooled boiling experiments were carried out in the stagnation region of a water planar jet of 0.6 and 0.75 m/s jet velocity and 15 ℃ of subcooling. The transition boiling regime is found to have a region of constant heat flux. After the critical heat flux (CHF) is reached, the heat flux decreases till a local minimum value is reached; called the first minimum. The heat flux then increases till it reaches a relatively constant value, even with the increase of the surface degree of superheat. The constant heat flux region is called the shoulder heat flux. With the aid of high speed imaging, Rayleigh-Taylor instability has been observed at the liquid-vapor interface which is accelerated by gravity and jet dynamic pressure. A modified expression for the interface acceleration is proposed. The vapor layer formed in the transition boiling is not stable; it follows periodic cycles of break up and formation. Two surface wetting mechanisms are proposed based on observations: (ⅰ) direct liquid touching the surface at moderate degrees of superheat and (ⅱ) liquid columns intruding the vapor layer and touching the surface at discrete locations at high degrees of superheat. A new wall heat flux partitioning model is proposed. The proposed model divides the wall heat flux, based on the two observed wetting mechanisms, into two components: (ⅰ) quenching heat flux and (ⅱ) intrusion heat flux. The current model estimates the wall heat flux during transition boiling covering the surface superheat range from the CHF till the Leidenfrost point with a normalized root mean square error (NRMSE) of 33%.
机译：液体射流撞击以其从撞击表面吸热的高能力而著称。在射流速度为0.6和0.75 m / s的水平面射流和15℃的过冷度的停滞区域进行了稳态过冷沸腾实验。发现过渡沸腾区具有恒定的热通量区域。达到临界热通量（CHF）后，热通量将减小，直到达到局部最小值为止。称为第一个最小值。然后，即使表面过热度增加，热通量也增加直至达到相对恒定的值。恒定热通量区域称为肩部热通量。借助于高速成像，已经观察到在液体-蒸汽界面处的瑞利-泰勒不稳定性，其在重力和射流动压力的作用下会加速。提出了接口加速度的修正表达式。在过渡沸腾中形成的蒸气层不稳定。它遵循分解和形成的周期性循环。根据观察结果，提出了两种表面润湿机制：（ⅰ）在中等过热度下直接使液体接触表面，以及（ⅱ）侵入蒸气层的液柱在高温下不连续的位置接触表面。提出了一种新的壁面热通量分配模型。所提出的模型基于观察到的两种润湿机制将壁热通量分为两个部分：（ⅰ）淬火热通量和（ⅱ）侵入热通量。当前模型估计过渡沸腾过程中的壁热通量覆盖了从CHF到Leidenfrost点的表面过热范围，归一化均方根误差（NRMSE）为33％。

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