Numerical study of a novel passive micromixer design

Miniaturization is the trend in analytical chemistry and life sciences. In the past two decades, miniaturization of fluid handling and fluid analysis has been emerging in the interdisciplinary research field of microfluidics. Some of the microfluidic applications are drug delivery, lab-on-a-chip, pharmaceutical development, synthesis of amino acids etc. Most of these applications are used for biochemistry analysis and require rapid mixing in minute quantities. Microchannel flows, due to very low flow rate, are characterized by very low Reynolds number (Re≪100). Owing to laminar flow conditions it is difficult to achieve effective mixing of two fluids as is the case for turbulent flow. If the mixing is obtained primarily by a diffusion mechanism then fast mixing becomes impossible because biological reagents usually have very low diffusivity on the order of 10^-10 m²/s. Hence microfluidic mixing is a very challenging problem because it requires fast and efficient mixing of low diffusivity fluids under laminar flow conditions [1-3]. In this paper, problem of microfluidic mixing is studied numerically using the CFD code FLUENT™[4-11]. To present the study, mixing of two low diffusivity fluids (D = 10^-10 m²/s) is numerically investigated in ⊢ microchannel. Due to laminar flow conditions very poor mixing is observed in ⊢ microchannel. Previously established geometric modification called “two-way split flow technique” is applied to the baseline case. This technique involves splitting of both the inlets of the ⊢ microchannel in half such that the net flow rate at the outlet remains the same. Application of this technique is shown to improve mixing by ~250% when it is compared to ⊢ microchannel. Based on two-way split flow design technique, novel split-and-merge (SAM) mixer designs are proposed. All the SAM mixer designs proposed show an improvement in mixing between 3- - 00 - 500% when compared with ⊢ microchannel, for same flow conditions and residence times. Pressure drops of proposed SAM mixer designs are less than 50% higher than ⊢ microchannel. Hence all the micromixer designs based on two-way split flow techniques are shown to be efficient and low pressure drop mixers.