Master of Science (MS)


Mechanical Engineering

Document Type



Passive (diffusional) mixing has been used in designing high-aspect-ratio micro-mixers for the purpose of performing the Liagase Detection Reaction (LDR). A simple model was used to design such mixers optimized for pressure drop or time required to deliver a prescribed volume of mixture. The types of mixers considered are simple, cheap, and durable and can perform over a broad range of volumetric flow rates at reasonably modest pressure drops. The fluids typically have a very low diffusion coefficient of=1.2x10^10m^2/s, and thus diffusional mixing can only be effective in high-aspect-ratio micro-channels. A realizable aspect ratio of 6 has been considered initially because it is easily releasable using the LIGA technique. Numerical simulations were performed on various diffusional-based micromixer configurations. Two variants of a Y-type mixer with contraction and several variants of a mixer employing jets in cross-flow have been simulated. The various mixers have been evaluated in terms of volumetric mixing efficiencies and maximum pressure drops. One of the mixers with jets-in-cross-flow was found to perform best. In addition, the effect of jet width and expansion after the mixing were assessed. Experimental validations for the jets-in-cross-flow mixer were performed. The mixer was manufactured using a micromilled brass mold insert hot embossed into a Polymethyl-methacrylate (PMMA) substrate, which was then covered with 0.125mm PMMA coverslip. A chemiluminescence technique was applied for the first time to make Qqualitative observations of the mixing zones. Quantitative mixing efficiency experiments were performed by using Rhodamine B fluorescent dye solution and de-ionized water. The experimental results show good agreement with numerical simulations.



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Committee Chair

Dimitris E. Nikitopoulos