Mechanism of temperature-difference-induced spiral flow in microchannel and investigation of mixing performance of a non-invasive micromixer

Abstract

Liquid mixing is important in Micro-TAS, but the mixing is difficult in microscale because the flow is difficult to disturb in low Reynolds number region. There are few methods to mix the microscale fluid in a non-contact manner and high mixing efficiency. In the case of the contact mixing method, the system tends to be complicated and large. This paper proposes a novel non-contact micromixer that uses two Peltier modules and generates a temperature difference inside a microchannel to generate a spiral flow. Our previous study has experimentally found that the temperature difference creates the spiral flow. In this study, the mechanism of the spiral flow was clarified by numerical calculation and the mixing efficiency was verified. As the result, the spiral flow was found to be generated by natural convection. The effect of natural convection on the channel volume was relatively large in the submillimeter scale, and it was found that the temperature difference could be used most effectively for mixing. When a temperature difference of 1.18 °C/mm was applied to a rectangular channel with a width and depth of 4 mm, and inflow velocity was 50 μm/s, the distance to complete the mixing was 3.56 mm. In low Reynolds number and high Peclet number environment of Re = 0.2, Pe = 4120, natural convection was utilized in the sub-milli scale channel and mixing was achieved at the short distance. By using a metal channel, the temperature difference generated inside the channel could be increased. We have developed an efficient micro mixer that can simplify the channel shape and reduce its size by controlling only the temperature from the outside of the chip.