Thermocapillary convection in superimposed layers of self-rewetting fluids: Analytical and lattice Boltzmann computational study
Thermocapillary convection in superimposed layers of self-rewetting fluids: Analytical and lattice Boltzmann computational study
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DOI：
10.1016/j.ijheatmasstransfer.2023.124049
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发表时间：
2022-10
影响因子：
5.2
通讯作者：
Bashir Elbousefi;W. Schupbach;K. Premnath;S. Welch
中科院分区：
文献类型：
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作者：
Bashir Elbousefi;W. Schupbach;K. Premnath;S. Welch
自重湿流体（SRFs），如长链醇的水溶液，表面张力与温度呈反常的二次依赖关系，具有最小值和正梯度。与表面张力随温度呈负梯度的普通流体（NFs）相比，SRFs可以显著改变界面动力学，最近已被用于增强各种应用中的流动和热输运。在这项工作中，首先，我们开发了一个新的热毛细对流的解析解，在一个微通道内的两个SRF层的叠加中，一边是正弦加热，另一边保持在均匀的温度。然后，构建了一种鲁棒中心矩晶格玻尔兹曼方法，该方法采用涉及Allen-Cahn方程的相场模型，用于界面跟踪、双流体运动和能量输运的数值模拟。分析技术和计算技术通常在定量上是相互一致的。此外，还研究了各种特征参数对热毛细管驱动运动的大小和分布的影响。与NFs相比，srf中的热毛细流动模式明显不同：在其他条件相同的情况下，srf会产生8个周期性的逆旋转热毛细对流涡旋，而NFs仅表现出4个这样的涡旋。此外，在这种涡旋结构中，循环流体运动的方向在SRFs中趋向于界面上的热区，而在NFs中则相反。在模拟中发现，这些特征即使在界面变形时也能保持。通过调整表面张力对温度的敏感系数，不仅可以明显地控制热毛细速度的大小，而且可以控制整体的流动模式。研究还表明，与其他流体层相比，如果将非均匀加热壁面附近的SRF层做得相对较薄或具有较高的导热系数或较小的粘度，则可以增强热毛细对流。当流体厚度比从1/3变为3时，峰值Marangoni速度增加了约1个数量级，当无量纲二次表面张力敏感系数加倍时，峰值Marangoni速度增加了2倍。
Self-rewetting fluids (SRFs), such as aqueous solutions of long-chain alcohols, exhibit anomalous quadratic dependence of surface tension on temperature having a minimum and with a positive gradient. When compared to the normal fluids (NFs) that have negative gradient of surface tension on temperature, the SRFs can be associated with significantly modified interfacial dynamics, which have recently been exploited to enhance flow and thermal transport in various applications. In this work, first, we develop a new analytical solution of thermocapillary convection in superimposed two SRF layers confined within a microchannel that is sinusoidally heated on one side and maintained at a uniform temperature on the other side. Then, a robust central moment lattice Boltzmann method using a phase-field model involving the Allen-Cahn equation for interface tracking, two-fluid motion, and the energy transport for numerical simulations of SRFs is constructed. The analytical and computational techniques are generally shown to be in good quantitative agreement with one another. Moreover, the effect of the various characteristic parameters on the magnitude and the distribution thermocapillary-driven motion is studied. The thermocapillary flow patterns in SRFs are shown to be strikingly different when compared to the NFs: For otherwise the same conditions, the SRFs result in eight periodic counterrotating thermocapillary convection rolls, while the NFs exhibit only four such vortices. Moreover, the direction of the circulating fluid motion in such vortical structures for the SRFs is found to be towards the hotter zones on the interfaces, which is opposite to that in NFs. These features are found to be sustained even as the interfaces deforms in simulations. By tuning the sensitivity coefficients of the surface tension on temperature, it is shown that not only the magnitude of the thermocapillary velocity can be significantly manipulated, but also the overall flow patterns as well. It is also demonstrated that the thermocapillary convection can be enhanced if the SRF layer adjacent to the nonuniformly heated wall is made relatively thinner or has higher thermal conductivity ratio or has smaller viscosity when compared to that of the other fluid layer. The peak Marangoni velocity is found to be increased by a factor of 2 by doubling the dimensionless quadratic surface tension sensitivity coefficient and by about an order of magnitude as the fluid thickness ratio is changed from 1/3 to 3.