0
Research Papers: Fundamental Issues and Canonical Flows

Numerical Study of Capillary Flow in Microchannels With Alternate Hydrophilic-Hydrophobic Bottom Wall

[+] Author and Article Information
Auro Ashish Saha

Department of Mechanical Engineering, Indian Institute of Technology, Bombay, Mumbai 400076, Indiaasaha@iitb.ac.in

Sushanta K. Mitra1

Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G2G8, Canadasushanta.mitra@ualberta.ca

1

Corresponding author.

J. Fluids Eng 131(6), 061202 (May 13, 2009) (12 pages) doi:10.1115/1.3129130 History: Received June 10, 2008; Revised April 01, 2009; Published May 13, 2009

A two-dimensional numerical simulation of flow in patterned microchannel with alternate layers of different sizes of hydrophilic and hydrophobic surfaces at the bottom wall is conducted here. The effect of specified contact angle and working fluid (de-ionized (DI) water and ethanol) on capillary phenomena is observed here. The volume of fluid method is used for simulating the free surface flow in the microchannel. Meniscus profiles with varying amplitude and shapes are obtained under the different specified surface conditions. Nonsymmetric meniscus profiles are obtained by changing the contact angles of the hydrophilic and hydrophobic surfaces. A meniscus stretching parameter is defined here and its relation to the capillary phenomena in the microchannel is discussed. Flow variation increases as the fluid traverses alternately between the hydrophilic and hydrophobic regions. The pattern size and the surface tension of the fluid are found to have significant influence on the capillary phenomena in the patterned microchannel. Smaller pattern size produces enhanced capillary effect with DI water, whereas no appreciable gain is observed for ethanol. The magnitude of maximum velocity along the channel height varies considerably with the pattern size and the contact angle. Also, the rms velocity is found to be higher for smaller alternate patterned microchannel. The meniscus average velocity difference at the top and bottom walls increases for a dimensionless pattern size of 0.6 and thereafter it decreases with the increase in pattern size in the case of DI water with hydrophilic-hydrophobic pattern. Using such patterned microchannel, it is possible to manipulate and optimize fluid flow in microfluidic devices, which require enhanced mixing for performing biological reactions.

Copyright © 2009 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

Geometry of microchannel

Grahic Jump Location
Figure 2

Meniscus in channel in front view

Grahic Jump Location
Figure 3

Validation of numerical model with analytical solution (20) and experimental data (27): (a) Verification with analytical solution and (b) verification with experimental data

Grahic Jump Location
Figure 4

The snapshot image of the evolution of meniscus front for Case 1 (θ1=30 deg, θ2=120 deg) when the microchannel is 25%, 50%, 75%, and 90% filled (isocontour of F=0.5 is applied to identify the meniscus): (a) DI water with40μm alternate pattern; (b) ethanol with 40μm alternate pattern; (c) DI water with 20μm alternate pattern; and (d) ethanol with 20μm alternate pattern

Grahic Jump Location
Figure 5

The snapshot image of the evolution of meniscus front for Case 2 (θ1=0 deg, θ2=90 deg) when the microchannel is 25%, 50%, 75%, and 90% filled (isocontour of F=0.5 is applied to identify the meniscus): (a) DI water with 40μm alternate pattern; (b) ethanol with 40μm alternate pattern; (c) DI water with 20μm alternate pattern; and (d) ethanol with 20μm alternate pattern

Grahic Jump Location
Figure 6

The variation of meniscus stretch with liquid volume fraction for Cases 1 and 2 for two different working fluids: (a) DI water and (b) ethanol

Grahic Jump Location
Figure 7

The variation of meniscus stretch with liquid volume fraction for a nonpatterned microchannel for two different working fluids: (a) DI water and (b) ethanol

Grahic Jump Location
Figure 8

The position of capillary meniscus with time for Cases 1 and 2 for two different working fluids: (a) DI water and (b) ethanol

Grahic Jump Location
Figure 9

The position of capillary meniscus with time for a nonpatterned microchannel for two different working fluids: (a) DI water and (b) ethanol

Grahic Jump Location
Figure 10

Meniscus displacement of the capillary with time on the bottom wall with DI water (contact angles θ1=30 deg and θ2=120 deg) for 20 μm and 40 μm patterned microchannels

Grahic Jump Location
Figure 11

Meniscus velocity distribution along the channel height for Cases 1 and 2 for two different working fluids: (a) DI water and (b) ethanol

Grahic Jump Location
Figure 12

Meniscus displacement of the capillary with time on the top and bottom wall with DI water (contact angles θ1=30 deg and θ2=120 deg) for 20 μm patterned microchannel

Grahic Jump Location
Figure 13

Meniscus average velocity difference of top and bottom walls with dimensionless pattern size for DI water and ethanol

Grahic Jump Location
Figure 14

Comparison of the position of the capillary meniscus with time for nonpatterned microchannel with DI water (contact angle θ=30 deg) for different velocity inlet boundary conditions with different grid sizes: (a) velocity inlet=constant and (b) velocity inlet=time varying

Grahic Jump Location
Figure 15

Comparison of the position of the capillary meniscus with time for nonpatterned microchannel with DI water (contact angle θ=30 deg) for different pressure inlet boundary conditions with different grid sizes: (a) pressure=0N/m2 and (b) pressure=1000N/m2

Grahic Jump Location
Figure 16

Comparison of flow field variables with liquid volume fraction for nonpatterned microchannel with DI water (contact angle θ=30 deg) with different grid sizes

Grahic Jump Location
Figure 17

Comparison of the position of the capillary meniscus with time for nonpatterned microchannel with DI water (contact angle θ=30 deg) with different time-step sizes

Grahic Jump Location
Figure 18

Comparison of the profile of the capillary meniscus for nonpatterned microchannel with DI water (contact angle θ=30 deg) at different grid resolutions when the microchannel is half filled

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In