Numerical study of a bubble driven micromixer based on thermal inkjet technology

摘要

An efficient microfluidic mixing approach utilizing the periodic explosive boiling mechanism from the thermal inkjet technology is proposed in this work. The main purpose of the work is to examine the effect of the configuration of thin-film microheaters on the mixing performance of the simple Y-microchannel via numerical simulations. The proposed micromixer can drive the mixing flow without an external pump because the repeated growth-collapse cycles of the vapor bubble result in a pumping effect in the microchannel. The adaptive Cartesian grid based finite-volume method is employed to solve the Navier-Stokes equations with the volume-of-fluid method for tracking the vapor-liquid interface. The complex dynamics of the vapor bubble induced by pulse heating is simplified as a gas polytropic expansion/compression process. Four microheater configurations are examined with the proposed numerical method. Our results have shown that mixing is limited for the microheater placed symmetrically along the center plane of the downstream branch of the Y-micromixer. However, for the asymmetrically placed microheater, mixing is greatly improved due to the secondary crossflow and asymmetric vortex created by the bubble collapse. When two off-centered microheaters are used and fired alternately, the mixing performance is further enhanced by disturbing the flow in a wiggling manner. Finally, when the microheaters are placed in the inlet channels instead of the downstream channel, periodic alternate switching of inlet flows due to the bubble actuation can effectively segment the mixing species, which results in the highest mixing index of 0.956 among all four configurations. The proposed micromixer shows great promise in the microfluidic mixing applications due to its simplicity and high efficiency.