Abstract
In this paper, a high-speed on-chip mixer using two effects is proposed, i.e., push/pull inequality and wettability. Push/pull inequality and wettability are effective for generating a rotational fluid motion in the chamber and for enhancing the rotational speed by reducing the viscous loss between the liquid and channel wall, respectively. An on-chip mixer is composed of three components, a microfluidic channel for making the main fluid flow, a circular chamber connected to the channel for generating a rotational flow, and an actuator connected at the end of the channel allowing a push/pull motion to be applied to the liquid in the main channel. The flow patterns in the chamber under push/pull motions are nonreversible for each motion and, as a result, produce one-directional torque to the fluid in the circular chamber. This nonreversible motion is called push/pull inequality and eventually creates a swirling flow in the chamber. Using hydrophilic treatments, we executed the experiment with a straight channel and a circular chamber to clarify the mixing characteristics at different flow speeds. According to the results, it is confirmed that the swirling velocity under appropriately tuned wettability is 100 times faster than that without tuning.
Highlights
Mixing is an important operation for both macro- and micro-scale reactions in various fields, in particular chemistry and biomedical research
Under the assumption that the periodic push/pull action is given at the input side of the main channel, We showed that the swirling flow pattern in a chamber connected to the main channel can be changed depending on the geometrical parameter
We confirmed that the push/pull inequality is effective for producing such a large-scale swirling flow
Summary
Mixing is an important operation for both macro- and micro-scale reactions in various fields, in particular chemistry and biomedical research. The degree of difficulty is determined based on the Reynolds number (Re) and is written as Re = UL/μ, where U, L, and μ are the velocity of the liquid, the representative dimension of the vessel, and the kinematic viscosity coefficient, respectively. The difference between passive and active approaches is whether the vortex is generated naturally without any actuator or actively with an additional actuator. There are various studies [6,7,8,9,10,11,12,13,14,15,16] in which the common strategy for generating the vortices is to mix two liquids in a microfluidic channel using a special configuration
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