Mixing at the microscale is a challenging process. While various mixing methods have been developed, the use of bubbles driven by thermocapillary force remains unexplored. Surface tension is highly dependent on temperature and bubble movement can be controlled by applying specific temperature fields, which can be utilized to enhance mixing. In this study, we use the phase-field lattice Boltzmann method to simulate the migration of a bubble driven by thermocapillary force and investigate its impact on mixing. Before addressing the main problem, we validate the model through three tests—two for thermocapillary force and one for mixing—all of which confirm the model's accuracy. In the main study, the movement of a bubble in a microchannel is simulated under specific temperature fields, which force the bubble to move against the flow direction. An undulatory movement pattern of the bubble is achieved, induced by the temperature fields, which resulted in enhanced mixing. The simulation results indicate that this method is effective at high Peclet numbers, where mixing is more difficult. The highest mixing enhancements are observed at the higher Peclet numbers. At Pe=200—the highest Peclet number in our simulation—the mixing index increased by factors of 2.68, 3.38, and 3.55 for Reynolds numbers of 0.5, 1, and 2, respectively, demonstrating the method's effectiveness under challenging mixing conditions. These mixing enhancements were achieved by releasing only a single bubble. Furthermore, bubble release frequency emerges as another critical parameter, affecting the temperature field and consequently, the bubble's trajectory.
Banaee et al. (Tue,) studied this question.