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Three-dimensional study of microchannel with elliptical rib

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Physics of Fluids
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Flow past objects in the microchannel are used to disturb the flow and thereby achieve adequate mixing. A three-dimensional numerical investigation has been carried out to analyze the flow characteristics around an elliptical rib with various aspect ratios (AR) ranging from 0.4 to 0.6, where the major axis was aligned parallel to the free stream. The study encompassed Reynolds numbers (Re) ranging from 18 to 202, calculated based on a hydraulic diameter of 184.61 μm. The fluid flow equation has been solved using the control volume method in ANSYS FLUENT software, under the assumptions of steady, incompressible, and laminar flow around the elliptical rib. The elliptical ribs are placed symmetrically about the vertical mid-plane in a rectangular microchannel. Main characteristics, such as bubble length, separation angle, maximum vorticity, and skin friction coefficient on the ellipse surface, were obtained with and without heat flux using water as the working fluid. The impact of blockage on the steady flow properties was investigated by varying the AR of the elliptical rib. Change in AR causes the variation of 4.42% observed in the Nusselt number (Nu). It has been found that a pair of steady vortices starts to form at lower Re for higher AR. The bubble length and separation angle form early with heat flux compared to the without heat flux. The skin friction coefficient significantly drops the channel with heat flux compared to without heat flux. Considering the third direction along the height of the elliptical rib in the microchannel, the deviation in the bubble length and separation angle is 12.23% and 45.35%, respectively, at AR of 0.6, when heat flux is applied to the bottom wall.
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Three-dimensional study of microchannel
with elliptical rib
Cite as: Phys. Fluids 36, 073630 (2024); doi: 10.1063/5.0217857
Submitted: 7 May 2024 .Accepted: 9 July 2024 .
Published Online: 29 July 2024
Deepak Kumar Raj ( ) and Aparesh Datta ( )
a)
AFFILIATIONS
Department of Mechanical Engineering, National Institute of Technology Durgapur, Durgapur, West Bengal 713209, India
Note: This paper is part of the special topic, Microscopic Channel Flows.
a)
Author to whom correspondence should be addressed: adatta96@gmail.com
ABSTRACT
Flow past objects in the microchannel are used to disturb the flow and thereby achieve adequate mixing. A three-dimensional numerical
investigation has been carried out to analyze the flow characteristics around an elliptical rib with various aspect ratios (AR) ranging from 0.4
to 0.6, where the major axis was aligned parallel to the free stream. The study encompassed Reynolds numbers (Re) ranging from 18 to 202,
calculated based on a hydraulic diameter of 184.61 lm. The fluid flow equation has been solved using the control volume method in ANSYS
FLUENT software, under the assumptions of steady, incompressible, and laminar flow around the elliptical rib. The elliptical ribs are placed
symmetrically about the vertical mid-plane in a rectangular microchannel. Main characteristics, such as bubble length, separation angle, max-
imum vorticity, and skin friction coefficient on the ellipse surface, were obtained with and without heat flux using water as the working fluid.
The impact of blockage on the steady flow properties was investigated by varying the AR of the elliptical rib. Change in AR causes the varia-
tion of 4.42% observed in the Nusselt number (Nu). It has been found that a pair of steady vortices starts to form at lower Re for higher AR.
The bubble length and separation angle form early with heat flux compared to the without heat flux. The skin friction coefficient significantly
drops the channel with heat flux compared to without heat flux. Considering the third direction along the height of the elliptical rib in the
microchannel, the deviation in the bubble length and separation angle is 12.23% and 45.35%, respectively, at AR of 0.6, when heat flux is
applied to the bottom wall.
Published under an exclusive license by AIP Publishing. https://doi.org/10.1063/5.0217857
I. INTRODUCTION
Electronic devices are progressively decreasing in size with each
passing day. The heat flux generated by the tiny sophisticated elec-
tronic devices is tremendously high. Hence, temperature rise is the
main reason for reducing the durability of costly electronic equipment.
The applications of microchannel heat sinks are in the field of laser
processing,
1
fusion,
2
and defense equipment.
3
The use of macro chan-
nel and free cooling methods are ineffective in maintaining the mini-
mum temperature of the equipment. Tuckerman and Pease
4
were the
first to use rectangular microchannels with water as the working fluid,
successfully removing heat flux up to 790 W/m
2
while maintaining a
temperatureriseof71C. The higher surface to volume ratio of micro-
channel augments the heat transfer capability of microchannel. Over
the years, water is widely used as a working fluid in microchannels due
to its nontoxic behavior and easy availability.
Initially, there are many experimental studies based on rectangu-
lar shapes with motivation of improving the heat transfer. Later on,
though different shapes, such as rhombic,
5
trapezoidal,
6
and
hexagonal
6,7
shapes of cross section, have been considered, but the
deviation in heat transfer from rectangular cross sections was not sig-
nificant. It has been found that the numerical tool is the powerful tool
for solving NavierStokes equation for solving the microchannel con-
jugate heat transfer problem. Additionally, the results obtained from
experimental studies agree quiet well with numerical results.
8
The vari-
ation in thermo-physical properties of the working fluid in numerical
simulations provides more realistic results. Consequently, different
researchers have used nanofluids to enhance heat transfer by increas-
ing thermal conductivity.
9,10
However, the precipitation effect of nano-
fluids can block the small channels of microchannels, posing a
challenge.
The continuous growth of thermal boundary layer in the smooth
channel decreases heat transfer. To address this, various disruptive
structures, such as cavities,
1113
vortex generators,
1416
and ribs,
1719
have been employed by researchers to enhance heat transfer. Although
these structures improve heat transfer in microchannels, they also
cause a significant pressure drop due to increased drag force. This
Phys. Fluids 36, 073630 (2024); doi: 10.1063/5.0217857 36, 073630-1
Published under an exclusive license by AIP Publishing
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