Micro-fluid mixing is an important aspect of many of the various micro-fluidic
systems used in biochemical production, biomedical industries, micro-energy
systems and some electronic devices. Typically, because of size
constraints and laminar flow conditions, different fluids may only have the
opportunity to mix by diffusion, which is extremely rate limited. Therefore, active
or highly effective passive mixing techniques are often required. In this study, two
pulsed injectors are used to actively enhance mixing in a high aspect ratio
microchannel (125 ��m deep and 1 mm wide). The main channel has two adjacent
flowing streams with 100% dye and 0% dye concentrations, respectively. Two
injectors (125 ��m deep and 250 ��m wide) are located on separate sides of the
channel, with one downstream 2 mm (equivalent to two main channel widths or
eight injector widths) from the other. This results in an asymmetric mixing as the
flow proceeds downstream. A dye solution is used to map local mixing
throughout the channel by measuring concentration variations as a function of both
space and time. The primary flow rates are varied from 0.01 to 0.20 ml/min
(Reynolds numbers of 0.3 to 26.6), the injector flow rate ratios are varied from
0.125 to 2, and the pulsing frequencies are varied from 5 to 15 Hz.
Images of the concentration variations within the channel are used to
quantify mixing by calibrating the intensity of the image with the concentration of
the dye solution. The degree of mixing (DoM) is used as a measure of quality and
is defined based on the integration across the channel of the difference between the
local concentration and the 50% concentration values. DoM is normalized by the
50% concentration value and subtracted from one to yield a parameter that varies
from 0 (no mixing) to 1 (perfect mixing). It is shown that there is a high degree of
repeatability of concentration distribution as a function of phase of the pulsing
cycle. A mixing map is constructed over the range of variables tested which
indicates an optimum set of flow and pulsing conditions needed to achieve
maximum mixing in the main channel flow. The flow rate ratio between the
injectors and main channel is found to be the most influential parameter on overall
mixing. The highest DoM in the main channel was found to be 0.89. It is also
noticed that improved mixing can occur at very low flow ratios under a unique set
of primary flow and low frequency pulsing conditions. In general, there is an
inverse relationship between primary flow rate and pulsing frequency to achieve
better overall mixing. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31550 |
| Date | 12 February 2003 |
| Creators | Siripoorikan, Bunchong |
| Contributors | Liburdy, James A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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