Effect of counter current airflow on film dispersion and heat transfer of evaporative falling film over a horizontal elliptical tube
Effect of counter current airflow on film dispersion and heat transfer of evaporative falling film over a horizontal elliptical tube
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DOI：
10.1016/j.ijheatmasstransfer.2019.07.029
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发表时间：
2019-10
影响因子：
5.2
通讯作者：
Yee-Ting Lee;Sihui Hong;C. Dang;L. Chien;A. Yang
中科院分区：
文献类型：
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作者：
Yee-Ting Lee;Sihui Hong;C. Dang;L. Chien;A. Yang
研究了逆流对水平椭圆管降膜蒸发换热性能的影响。数值分析基于流体体积模拟来捕捉下降膜的扩散演化，并结合用户定义的函数来模拟水面对环境的蒸发效应。传热系数的计算结果与文献中的实测数据吻合较好，验证了计算模型的正确性。通过数值计算，详细阐述了逆流气流与管内蒸发液膜的形成过程和传热过程的相互作用机理。从本质上讲，向上的气流可以在水-气界面处引起剪切应力，从而形成较厚的波浪膜。逆流气流对管下部的强化传热效果比管上部明显。通过系统地改变入口液体质量流量（0.093-0.186 kg/m-s）和逆流气流速度（0-3 m/s），对水膜蒸发器的热性能进行了数值模拟。模拟结果表明，壁面温度梯度较大，强化了传热效果，当r = 0.149 kg/m-s，Vair = 3 m/s时，平均传热系数为4.15 kW/m2 K。
This study explores the influence of counter current airflow on evaporative heat transfer performance of falling films on a horizontal elliptical tube. The numerical analysis was based on the volume-of-fluid simulations to catch the dispersal evolution of descending films in conjunction with user defined function to model the evaporation effect at the water surface to the ambiance. The calculated results of heat transfer coefficients were in reasonably good agreement with the measured data from the literature for validation of the computational model. Calculations were performed to elaborate the interaction mechanism of counter current airflows with the formation process and heat transfer of evaporative liquid films on the tubes. In essence, upward air streams can induce the shear stresses at the water-air interface to form thicker wavy films. The counter current airflow has a more pronounced effect on heat transfer enhancement in the lower part of the tube than the upper part. Numerical experiments were also extended to assess the thermal performance of water film evaporators by systematically varying the inlet liquid mass flow rate of 0.093–0.186 kg/m-s and counter current airflow velocity of 0–3 m/s, respectively. The simulations results reveal steeper temperature gradients at the wall to enhance heat transfer outcomes, achieving an averaged heat transfer coefficient of 4.15 kW/m2K forΓ= 0.149 kg/m-s andVair= 3 m/s.