Thermocapillary actuation of a small droplet in a microchannel

J.-C. Chen
National Central University, TW

Keywords: thermocapillary actuation, microchannel flow, Droplet

Summary:

The aim of this work is to investigate numerically the thermocapillary actuation behavior of a small silicon droplet in a microchannel. The finite element method with the two-phase level set method is employed to solve the Navier-Stokes equations coupled with the energy equation. The lower wall of the microchannel is subjected to a uniform temperature gradient, while the upper one is either adiabatic or isothermal. The thermocapillary flow motion inside the droplet is significantly affected by the thermal condition of upper wall. When the upper wall is maintained at the ambient temperature, a pair of asymmetric thermocapillary convection vortices always appears inside the droplet. For the adiabatic case, a pair of asymmetric thermocapillary convection vortices occurs inside the droplet initially and they turn into a thermocapillary vortex as time lasts long enough. The droplet accelerates initially for both isothermal and adiabatic cases. It then decelerates slowly to approach a quasisteady state for the isothermal case. On the other hand, it decelerates slowly and continuously for the adiabatic one as time increases constantly. The actuation velocity is enhanced by the reduction of the microchannel height for both isothermal and adiabatic cases. For the adiabatic case, the actuation velocity of the droplet for different microchannel heights approaches the same value as time keeps increasing.