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Modelling thermocapillary migration of a microfluidic droplet on a solid surface

Liu, Haihu and Zhang, Yonghao (2015) Modelling thermocapillary migration of a microfluidic droplet on a solid surface. Journal of Computational Physics, 280. pp. 37-53. ISSN 0021-9991

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Abstract

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.

Item type: Article
ID code: 52126
Keywords: thermocapillary migration, lattice Boltzmann method, multiphase flow, wetting boundary condition, microfluidics, droplet dynamics, Mechanical engineering and machinery, Mechanical Engineering, Computational Mechanics, Condensed Matter Physics
Subjects: Technology > Mechanical engineering and machinery
Department: Faculty of Engineering > Mechanical and Aerospace Engineering
Technology and Innovation Centre > Advanced Engineering and Manufacturing
Depositing user: Pure Administrator
Date deposited: 06 Mar 2015 15:18
Last modified: 05 Apr 2019 22:53
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URI: https://strathprints.strath.ac.uk/id/eprint/52126
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