Determination of an analytical relationship between entropy generation and mixing efficiency for micromixer applications.

Abstract

This thesis presents a detailed computational analysis for a simple tee micro-mixing geometry. Micromixers have broad applications in heat exchangers and lab-on-chip (LOC) devices. Simply, a micromixer seeks to efficiently and quickly exchange one or more physical quantities, such as temperature or molecular concentration. The measure of how completely these quantities are exchanged is known as the mixing efficiency. For LOC devices an effective design will be simple and cost effective to manufacture, and provide the greatest mixing efficiency for the smallest device as rapidly as possible. The work here has two main objectives. First, an analytical relationship is sought that functionally relates the entropy generation to the mixing index for a simple tee shaped micromixer. Second, the work will serve as a guide to improve an existing micromixer through its developed methods. A thorough computational fluid dynamics (CFD) analysis is performed for a wide range of Reynolds numbers typical to micromixers with varying flow parameters. The result are several analytical relationships that relate the relevant quantities of entropy generation rate and mixing efficiency to the known flow and fluid parameters. Additionally, a simple relationship is derived that relates the mixing efficiency directly to the entropy generation rate effectively proving a direct relationship between the two quantities. Finally, the relevant results are used to propose a design for a micromixer that provides high mixing efficiencies for a wide range of operating conditions.