A combined computational and experimental investigation on evaporation of a sessile water droplet on a heated hydrophilic substrate
A combined computational and experimental investigation on evaporation of a sessile water droplet on a heated hydrophilic substrate
复制标题
DOI：
10.1016/j.ijheatmasstransfer.2018.02.065
复制
发表时间：
2018-07-01
影响因子：
5.2
通讯作者：
Bhardwaj, Rajneesh
中科院分区：
文献类型：
--
作者：
Kumar, Manish;Bhardwaj, Rajneesh
我们通过数值和实验研究了加热基底上固着液滴的蒸发。我们开发了二维轴对称坐标的有限元（FE）模型，以解决液滴和基底中的热量以及周围环境中的液体蒸气质量的耦合传输，同时假设液滴的扩散限制和准稳态蒸发。使用迭代方案实现双向耦合，并使用欠松弛来确保数值稳定性。有限元模型根据已发布的蒸发质量通量和液-气界面温度的空间分布进行验证。我们讨论双向耦合比单向耦合精确得多的情况。在实验中，我们使用高速摄像机在不同的基底温度下可视化蒸发的微升水滴的侧视图，并使用红外摄像机从顶部记录液气界面的温度。我们研究了液-气界面温度分布反演对基底厚度与润湿半径之比、基底热导率与液滴热导率之比以及接触角的依赖性。绘制状态图来划分这些变量的温度剖面的反演。不同基底温度下测量的蒸发质量率与计算值的比较表明，蒸发质量率相对于基底温度呈非线性增加，有限元模型预测的这些值与实验数据接近。将先前和当前模型获得的时间平均蒸发质量率与测量结果进行比较表明，模型中应考虑界面处的蒸发冷却和扩散系数随温度的变化，以便准确捕获测量结果。我们将时变液滴尺寸和液气界面温度分布的测量结果与数值结果进行了比较，发现了良好的一致性。我们量化了衬底加热引起的蒸发质量通量和蒸发质量速率的增加，并提出了衬底加热、衬底厚度与润湿半径之比、衬底-液滴导热率比和接触角对蒸发质量速率的综合影响。 (C) 2018 Elsevier Ltd. 保留所有权利。
We numerically and experimentally investigate evaporation of a sessile droplet on a heated substrate. We develop a finite element (FE) model in two-dimensional axisymmetric coordinates to solve coupled transport of heat in the droplet and substrate, and of the mass of liquid vapor in surrounding ambient while assuming diffusion-limited and quasi-steady evaporation of the droplet. A two-way coupling is implemented using an iterative scheme and under-relaxation is used to ensure numerical stability. The FE model is validated against the published spatial profile of the evaporation mass flux and temperature of the liquid-gas interface. We discuss cases in which the two-way coupling is significantly accurate than the one-way coupling. In experiments, we visualized side view of an evaporating microliter water droplet using a high-speed camera at different substrate temperatures and recorded temperature of the liquid gas interface from the top using an infrared camera. We examine the dependency of inversion of the temperature profile across the liquid-gas interface on the ratio of the substrate thickness to the wetted radius, the ratio of the thermal conductivity of the substrate to that of the droplet and contact angle. A regime map is plotted to demarcate the inversion of the temperature profile for a wide range of these variables. A comparison of measured evaporation mass rate with the computed values at different substrate temperature show that the evaporation mass rate increases non-linearly with respect to the substrate temperature, and FE model predicts these values close to the experimental data. Comparisons of time-averaged evaporation mass rate obtained by the previous and present models against the measurements suggest that the evaporative cooling at the interface and variation of diffusion coefficient with the temperature should be taken into account in the model in order to accurately capture the measurements. We compare the measurements of time-varying droplet dimensions and of temperature profile across the liquid-gas interface with the numerical results and found good agreements. We quantify increase in the evaporation mass flux and evaporation mas rate by the substrate heating and present the combined effect of substrate heating, the ratio of the substrate thickness to the wetted radius, substrate-droplet thermal conductivity ratio and the contact angle on the evaporation mass rate. (C) 2018 Elsevier Ltd. All rights reserved.