Abstract
Passive micromixers are of great importance in biomedical engineering (lab-on-chips) and chemical processing (microreactors) fields. Various hydrodynamic principles such as lamination, flow separation, and chaotic advection were employed previously to improve mixing in passive mixers. However, mixing enhancement due to velocity gradients in the flow, which is known as the Taylor dispersion effect, has been seldom studied. In the present study, thin rectangular slabs oriented in the flow direction are placed in the mixing channel of a T-micromixer. The thin rectangular slabs are referred to as Taylor Dispersion Obstructions (TDOs) as they are designed to create velocity gradients in the flow. The mixing performance of T-micromixer with and without TDOs is estimated in the Re range of 0 to 350. It is observed that there is no effect on mixing in the presence of TDOs in the low Re (0 < Re < 100), as the velocity gradients created in the flow are considerably small. The vortex formed in the flow for Re of 100 to 220 damped the gradients of velocity created in the flow (due to the presence of TDOs) which resulted in negligible improvement in the quality of mixing. However, considerable enhancement in mixing performance is obtained at high Re (250 to 350) with the presence of TDOs in the mixer. The increase in inertial effects at higher Recreated larger gradients of velocity near the walls of TDOs and mixing channel walls and thereby a significant enhancement in mixing performance is obtained due to Taylor dispersion.
Highlights
The majority of micromixers utilized in various applications belong to passive type mixers as they are robust, easy to integrate into complex microsystems and cheap compared to active type mixers
It is found that at lower Re (0 to 100), the velocity gradients created in the flow due to the presence of Taylor Dispersion Obstructions (TDOs) (Taylor Dispersion Obstruction) are smaller in amplitude and not significant enough to create axial dispersion and enhance the mixing
The effect of Taylor dispersion type obstructions for the creation of velocity gradients in the flow of T-micromixer to improve its efficiency was investigated in the current study
Summary
Micromixing is an essential function for many important applications in the field of bio-medical and bio-chemical engineering. Micromixers are used in the applications of protein folding studies (Chan et al, 1997), DNA micro-arrays (Zhang et al, 2007), and cell separation and detection (Lu et al, 2006). In chemical processing, they are utilized for organic synthesis (Suga et al, 2003), extraction (Freitas et al, 2005) and chemical production (Bayer et al, 2004). The active type mixers utilize an external energy source like magneto hydrodynamic (Bau et al, 2001), ultrasonic (Yaralioglu et al, 2004) or electro-kinetic (Chen and Cho, 2008) instabilities to induce mixing in the microchannel. The majority of micromixers utilized in various applications belong to passive type mixers as they are robust, easy to integrate into complex microsystems and cheap compared to active type mixers
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