Date of Award

December 2019

Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

Committee Member

Xiangchun Xuan

Committee Member

Rodrigo Martinez-Duarte

Committee Member

Phanindra Tallapragada

Committee Member

Chenning Tong


There are numerous fluids present in our surrounding, with each fluid possessing different properties than the other, for example blood and water. Study of these fluids and their properties is a part of science called fluid rheology. Study of fluid rheology has been conducted for many decades now for better understanding of the fluids, especially non-Newtonian, and the use of microfluidics in this study has increased day by day due to the simplicity of process. Another reason for use of microfluidics in fluid rheology is that the rheological properties of non-Newtonian fluids are more noticeable on a micron scale as compared to macron scale which makes it easy to find its applications and relation to naturally occurring micro flow. Understanding of these fluids is important to us because of the wide range of applications it can find in the fields of lab-on-a-chip devices, biomedical and chemical devices.

In this work, we focus on investigating effects of different non-Newtonian fluid flow in two different microchannel geometries- contraction and cavity channel. These geometries can be found in different lab-on-a-chip devices very commonly. The fluid flow in these micro-channels is sensitive to different parameters like geometry of channel, flow rate and fluid properties. This work focuses on unifying the theories related to such flows at different parameters by setting a basic parametric component as the channel geometry.

For the first contraction channel, we use a planar contraction-expansion microchannel. The contraction ratio is 10:1:10 and six different fluids were studied. The flow was compared at a wide range of Reynolds number, from 0.08 to 127, and Weissenburg number, from 27 to 28000. Most commonly analyzed PAA and PEO solutions were studied along with less explored Xanthan gum solution and PVP solution with water and water/glycerol mixture as a Newtonian base case. Different vortex growth patterns were observed and compared. A critical value of Reynolds number is found which denotes the onset of flow circulations. The effect of elasticity is found to stabilize the flow, the shear thinning de-stabilizes the flow and inertia induces lip vortex formation. The combined effect of all properties also agrees with primary understanding each property. This analysis simplifies the fluid flow phenomenon and the effects of rheological properties.

Similar study is conducted for the second channel, which is a cavity channel with planar geometry. Effect of shear thinning, elasticity and inertia of fluids was studied and compared in this case also. The expansion ratio was 1:10:1 approximately, with Reynolds number ranging from 0.04 to 239 and Weissenburg number from 25 to 104. Study of such fluids in the expansion channel was conducted for the first time which is capable of explaining the flow behavior in a suddenly expanded part of microchannel. Different vortex growth patterns are observed in this case as well. A new solution is used in this experiment which is Sodium Hyaluronate, whose results also conform to our understanding of the effects of the rheological properties. Vortex size and type are characterized for each experiment to give an overview of the complete phenomenon.



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