Date of Award

Spring 2005

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Kody Varahramyan

Abstract

Microreactors have been widely studied over the past two decades for different chemical reactions, to develop new analytical capabilities, and to obtain high mixing performance in the reactors. The main objectives of this work are to investigate the effect of different microchannel structures on the fluid properties and mixing behavior in microreactors, and to design, fabricate, and test a novel microreactor for higher conversion in a chemical reaction. The development of this novel microreactor is intended to provide a valuable guideline in achieving enhanced chemical mixing and to make available a solid research base for optimization of the yield of chemical reactions in microchannels.

Most of the current microreactors are designed with straight or zigzag microchannels [3]. In this research work, we have developed a novel omega-shaped microreactor, which yields higher conversion through mixing enhancement. It offers the advantages of reducing the mixing distance of the reactant species, stretching and folding the flow, generating vorticities which overcome any uneven distribution of the reactant, and consequently improve conversion efficiency in a typical reaction.

Fluid properties of the omega channel reactor have been investigated by means of computational fluid dynamic (CFD) simulation to validate the criteria of the omega channel design. A stochastic Markov chain process has been used to study fluid flow, and to describe the residence time distribution functions for the microreactors considered in this work.

Based on theoretical predictions, three kinds of microreactors with straight, zigzag, and omega-shaped microchannels, have been designed and fabricated using optical lithography and dry etching methods. To compare the efficacy of the microreactors, Fischer-Tropsch reactions have been carried out using sol-gel encapsulated ion and cobalt catalysts in the microchannels. The experimental results show that the conversion efficiency for an omega-shaped reactor is 17% greater than that for a conventional straight channel microreactor, and is 12% greater than that for the zigzag-shaped channel microreactor. The data is consistent with the CFD simulation and stochastic modeling results.

The novel omega-shaped microreactor offers a better alternative to straight and zigzag channel microreactors and provides a better micro-fluidic system for microscale total analysis applications.

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