Prediction of bubble departure in forced convection boiling: A mechanistic model
Prediction of bubble departure in forced convection boiling: A mechanistic model
复制标题
DOI：
10.1016/j.ijheatmasstransfer.2015.01.103
复制
发表时间：
2015-06
影响因子：
5.2
通讯作者：
M. Colombo;M. Fairweather
中科院分区：
文献类型：
--
作者：
M. Colombo;M. Fairweather
在使用时间平均欧拉多相方法的沸腾流动的计算流体动力学模拟的上下文中，描述这种复杂现象所需的许多子模型是特别重要的。这里感兴趣的是，壁沸腾需要计算蒸发对全局热传递的贡献，这又依赖于活性成核位点密度、气泡离开直径和气泡离开频率的确定。本文提出了一种改进的流动沸腾汽泡脱离直径的机理模型。该模型是基于在一个单一的成核位置上的力的平衡作用在气泡，与一个新的方程控制气泡的增长建议。该配方考虑了气泡下微层的蒸发、气泡表面周围过热液体的热传递以及由于过冷液体的存在而在泡帽上的冷凝。验证的增长方程提供了通过比较池沸腾和流动沸腾条件下的实验。在泡罩上引入冷凝允许对于周围液体的不同过冷温度再现气泡的生长。此外，灵敏度研究保证了气泡离开直径对相关物理量（例如质量流量、热通量、液体过冷度和压力）的依赖性，并正确考虑了通道壁的任何倾斜度。对三个不同的数据库过冷流动沸腾与水和一个额外的数据库饱和沸腾与制冷剂R113的预测气泡离开直径和气泡升空进行了验证。整个数据集确保在尽可能广泛的参数和操作条件范围内进行验证。在所有条件下都获得了令人满意的预测精度。本配方提供了一个适当的起点，预测的行为的蒸汽气泡在更一般的条件下，其中包括剥离后滑动，气泡离开的频率，气泡合并和气泡收缩和崩溃，由于冷凝。
In the context of computational fluid dynamic simulations of boiling flows using time-averaged Eulerian multi-phase approaches, the many sub-models required to describe such a complex phenomena are of particular importance. Of interest here, wall boiling requires calculation of the contribution of evaporation to global heat transfer, which in turn relies on determination of the active nucleation site density, bubble departure diameter and frequency of bubble departure. In this paper, an improved mechanistic model for the bubble departure diameter during flow boiling is developed. The model is based on the balance of forces acting on a bubble at a single nucleation site, with a new equation governing bubble growth proposed. The formulation accounts for evaporation of the micro-layer under the bubble, heat transfer from superheated liquid around the bubble surface, and condensation on the bubble cap due to the presence of sub-cooled liquid. Validation of the growth equation is provided through comparison against experiments in both pool boiling and flow boiling conditions. Introduction of condensation on the bubble cap allows reproduction of the growth of the bubble for different sub-cooling temperatures of the surrounding liquid. In addition, a sensitivity study guarantees dependency of the bubble departure diameter on relevant physical quantities such as mass flow rate, heat flux, liquid sub-cooling and pressure, with any inclination of the channel walls correctly accounted for. Predictions of bubble departure diameter and bubble lift-off are validated against three different databases on sub-cooled flow boiling with water and an additional database on saturated boiling with refrigerant R113. The whole data set guarantees validation is performed over a range of parameters and operating conditions as broad as possible. Satisfactory predictive accuracy is obtained in all conditions. The present formulation provides an appropriate starting point for prediction of the behaviour of vapour bubbles under more general conditions which include lift-off after sliding, the frequency of bubble departure, bubble merging and bubble shrinking and collapse due to condensation.