Modelling thermocapillary migration of a microfluidic droplet on a solid surface

JOURNAL OF COMPUTATIONAL PHYSICS

卷:280

Article

Liu, Haihu^1,2  Zhang, Yonghao² 

[1] Xi An Jiao Tong Univ, Sch Energy & Power Engn, Xian 710049, Peoples R China

[2] Univ Strathclyde, Dept Mech & Aerosp Engn, James Weir Fluids Lab, Glasgow G1 1XJ, Lanark, Scotland

关键词: Thermocapillary migration;    Lattice Boltzmann method;    Multiphase flow;    Wetting boundary condition;    Microfluidics;    Droplet dynamics;   

DOI  :  10.1016/j.jcp.2014.09.015

来源: Elsevier

【 摘 要 】

A multiphase lattice Boltzmann model is developed to simulate immiscible thermocapillary flows with the presence of fluid-surface interactions. In this model, interfacial tension force and Marangoni stress are included by introducing a body force term based on the concept of continuum surface force, and phase segregation is achieved using the recolouring algorithm proposed by Latva-Kokko and Rothman. At a solid surface, fluid-surface interactions are modelled by a partial wetting boundary condition that uses a geometric formulation to specify the contact angle, and a colour-conserving boundary closure scheme to improve the numerical accuracy and suppress spurious velocities at the contact line. An additional convection-diffusion equation is solved by the passive scalar approach to obtain the temperature field, which is coupled to the hydrodynamic equations through an equation of state. This model is first validated by simulations of static contact angle and dynamic capillary intrusion process when a constant interfacial tension is considered. It is then used to simulate the thermocapillary migration of a microfluidic droplet on a horizontal solid surface subject to a uniform temperature gradient. We for the first time demonstrate numerically that the droplet motion undergoes two different states depending on the surface wettability: the droplet migrates towards the cooler regions on hydrophilic surfaces but reverses on hydrophobic surfaces. Decreasing the viscosity ratio can enhance the intensity of thermocapillary vortices, leading to an increase in migration velocity. The contact angle hysteresis, i.e., the difference between the advancing and receding contact angles, is always positive regardless of the contact angle and viscosity ratio. The contact angle hysteresis and the migration velocity both first decrease and then increase with the contact angle, and their minimum values occur at the contact angle of 90 degrees. (C) 2014 Elsevier Inc. All rights reserved.

【 授权许可】

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