Falling film hydrodynamics and heat transfer under vapor shearing from various orientations

Chuang-Yao Zhao, Qiong Li, Fang-Fang Zhang, Di Qi, Hasan Yildizhan, Jun-Min Jiang
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Abstract

Vapor shearing is a common issue encountered in the operations of falling film heat exchangers. The vapor stream effect depends on its orientation. This study investigates liquid film hydrodynamics and heat transfer performance under the influence of vapor streams from different orientations. The results indicate that both orientation and velocity of vapor determine the encountering time and position of the films on the tube's two sides. The liquid film thickness uniformity and the liquid column deflection vary significantly depending on the orientation and velocity of the vapor. Zones of accelerated liquid film, climbing liquid film, liquid stagnation, and transition of liquid film flow pattern are observed. The gradient of film thickness along the tube axis and the deflection in time-averaged peripheral film thickness increase as the vapor orientation varies from 0° to 90° and subsequently decrease as the vapor orientation varies from 90° to 180°. Vapor streams have more pronounced effects on time-averaged peripheral film thickness in regions close to the liquid inlet and outlet. Vapor streams result in changes in peripheral heat transfer coefficients toward the downstream side depending on the orientation and velocity of the vapor. The impact of vapor streams on the overall heat transfer coefficient does not directly correlate with the velocity of the vapor when maintaining the same orientation.
不同方向蒸汽剪切作用下的落膜流体力学和热传导
蒸汽剪切是降膜式热交换器运行过程中经常遇到的问题。蒸汽流的影响取决于其取向。本研究探讨了不同方向蒸汽流影响下的液膜流体力学和传热性能。结果表明,蒸汽的取向和速度决定了薄膜在管子两侧的相遇时间和位置。液膜厚度的均匀性和液柱的挠度随蒸汽的方向和速度的变化而显著不同。观察到了液膜加速区、液膜爬升区、液膜停滞区和液膜流动模式过渡区。当蒸汽取向从 0° 变化到 90° 时,沿管子轴线的液膜厚度梯度和时间平均外围液膜厚度偏转增加;当蒸汽取向从 90° 变化到 180° 时,液膜厚度梯度和时间平均外围液膜厚度偏转减小。在靠近液体入口和出口的区域,蒸汽流对时间平均外围膜厚的影响更为明显。蒸汽流导致下游侧的外围传热系数发生变化,这取决于蒸汽的取向和速度。在保持方向不变的情况下,蒸汽流对整体传热系数的影响与蒸汽速度没有直接关系。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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