Degree Type

Dissertation

Date of Award

2011

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Michael G. Olsen

Abstract

Two of the areas that have become relevant recently are the areas of mixing in micro-scale devices, and manufacturing of functional nanoparticles. MicroPIV experiments were performed on two different mixers, one a wide microchannel with the surface grooves, in the laminar regime, and the other, a confined impinging jets reactor, in the laminar and turbulent regimes.

In the wide microchannel with surface grooves, microPIV data were collected at the interface and the midplane at the Reynolds numbers of 0.08, 0.8, and 8. The experiments were performed on three internal angles of the chevrons, namely 135°, 90°, and 45°. The normalized transverse velocity generated in the midplane due to the presence of the grooves, is the strongest for the internal angle of 135°, and in that, the normalized transverse velocity is maximum at the Reynolds numbers of 0.08 and 0.8.

MicroPIV experiments were performed in a confined impinging jets reactors at Reynolds numbers of 200, 1000, and 1500. The data was collected in the midplane, and turbulent statistics were further computed. The high velocity jets impinge along the centerline of the reactor. Upon impinging, part of the fluid turns towards the top wall and the majority of it turn towards the outlet. This high velocity impingement causes and unstable zone called the impingement zone, which moves about the centerline line, causing the jets to flap back and forth. Spatial correlations were computed to get an estimate of the size of the coherent structures. Large eddy simulation was performed on the CIJR for the Reynolds numbers of 1000 and 1500, using OpenFOAM. The Reynolds number is based on the inlet jet hydraulic diameter. Excellent agreement was found with the experimental and simulation data.

Turbulent reactive mixing in a rectangular microscale confined impinging-jets reactor (CIJR)

was investigated using the pH indicator phenolphthalein in this study for three di_erent jet

Reynolds numbers of 25, 1000 and 1500. Laminar flow regime was observed at Reynolds number of 25 whereas the flow was turbulent at Reynolds numbers of 1000 and 1500. An image processing technique was applied to instantaneous images to extract quantitative mixing data by identifying regions with pH ≥ 9.3 and regions with pH < 9.3. The ensemble-averages were computed using these thresholded images to compare mixing performance between different Reynolds numbers. Finally, the spatial auto-correlation fields of the thresholded images fluctuations were evaluated, based on which large-scale turbulent structure were analyzed.

DOI

https://doi.org/10.31274/etd-180810-2727

Copyright Owner

Vishwanath Somashekar

Language

en

Date Available

2012-04-30

File Format

application/pdf

File Size

120 pages

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