Project #4: Simulation of Fluid Flow in the Screen-Bounded Channel in a Fiber Separator

Lana Sneath and Sandra Hernandez

4th year - Biomedical Engineering

Faculty Mentor: Dr. Urmila Ghia

Department of Mechanical

and Materials Engineering

NSF Type 1 STEP Grant, Grant ID No.: DUE-0756921

Outline

• Motivation• Introduction to Bauer

McNett Classifier (separator)

• Problem Description• Goals & Objectives

• Methodology• Verification Case• Porous Boundary

Model• Future Work

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Problem Background• Toxicity of asbestos exposure varies with length of

asbestos fibers inhaled• Further study of this effect requires large batches of

fibers classified by length • The Bauer McNett Classifier (BMC) provides a

technology to length-separate fibers in large batches

Figure 1: Bauer McNett Classifier (BMC) Figure 2: Schematic of BMC

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Background – Bauer McNett Classifier (BMC)

• Fiber separation occurs in the deep narrow channel with a wire screen on one side wall

• Fibers align with local shear stress vectors [1]

• For successful length-based separation, the fibers must be parallel to the screen

Open to atmosphere

= deep open channel

Figure 3: Top View of One BMC Tank

A

B

CAL

1. Civelekogle-Scholey, G., Wayne Orr, A., Novak, I., Meister, J.-J., Schwartz, M. A., Mogilner, A. (2005), “Model of coupled transient changes of Rac, Rho, adhesions and stress fibers alignment in endothelial cells responding to shear stress”, Journal of Theoretical Biology, vol 232, p569-585 3

Wire Screen

Background – Bauer McNett Classifier (BMC)

Fibers length smaller than mesh opening

Fibers length larger than mesh opening

Figure 4: Fibers parallel to screen

Figure 5: Fibers perpendicular to screen

Off-plane angle 90°Off-plane angle 0°

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Deep Open Channel Dimensions

General Dimensions:• Length (x) = 0.217 m• Height (y) = 0.2 m• Width (z) = 0.02 m• Aspect ratio = 10; Deep open

channel

Screen dimensions:• Length (x) = 0.1662 m• Height (y) = 0.1746 m• Thickness (z) = 0.0009144 m

screen

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Figure 6: General Dimensions

Figure 7: Porous Model Dimensions

Goals and ObjectivesGoal: Numerically study the fluid flow in a deep open

channelObjectives:a) Verify boundary conditions and variables of the porous model

• Simplified porous plate problemas verification case

b) Simulate and study the flow in the open channel of the BMC apparatus, modeling the screen as a porous boundaryc) Determine the orientation of shear stress vector on the porous boundary

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MethodologyComputational Grid

Figure 8: Porous Model Channel Geometry in FLUENT

Table 1: Distribution of grid points and smallest spacing near boundaries

• Create channel geometry in CFD software

• Generate grid of discrete points

• Determine the proper boundary conditions to model the porous boundary

– Verification case: Laminar flow over a porous plate

• Enter boundary conditions into the CFD software

• Run simulation

• Determine shear stress from flow solutions

• Interpret results

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Boundary Conditions• u, v, w are the x, y, and

z components of velocity, respectively

• Average Inlet Velocity= 0.25m/s

• Turbulent Flow (Reynolds Number >5000)

• Reynolds Stress Model• Transient Simulation

8Figure 9: Boundary Conditions

Free-Slip Wall, v=0, du/dy=0, dw/dy=0

No-Slip Wall, u = v = w = 0

Inlet, u = u(y,z), v = w =0

Outlet, pstat = 0

Porous-Jump, Permeability(K) = 9.6e-10, Pressure-Jump Coefficient(C2)=7610.7 1/m, screen thickness = 9e-4 m; Values correspond to a 16 mesh [5]

Solid Wall Model Porous Boundary Model

Verification Case - Porous Plate Objective

• Determine proper boundary conditions to

use in the Porous Boundary Model case• Verify fluid flow behavior• Observe how axial flow is inhibited by the plate

Methodology:• Create 2D geometry in Gambit

• Calculate Reynolds number for Laminar flow

• Generate grid points• Run simulations in FLUENT

• Run 4 different cases: changing the mesh boundary condition to determine it’s effect

• Interpret results

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Figure 10: Laminar Flow Across Porous Flat Plate

Case #1: All Solid Walls

Case #2:Two Walls, One Pressure Outlet

Verification Case - Boundary Conditions (1 of 2)

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Verification Case - Boundary Conditions (2 of 2)Case #3:

One Wall and Two Pressure OutletsCase #4:All Pressure Outlets

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Verification Case - Velocity Magnitude Contours

Case #1: Velocity Magnitude Contours for All Walls

Case #2:Velocity Magnitude Contours for Two Walls

and One Pressure Outlet

Case #3:Velocity Magnitude Contours for One Wall

and Two Pressure Outlets

Case #4:Velocity Magnitude Contours for All Pressure Outlets

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Conclusion:• All cases show a boundary layer and flow crossing the porous plate

Verification Case - Streamlines for Case #1: All Walls

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Verification Case – Darcy’s LawModel Pressure Drop

Calculated Using Darcy’s Law

Pressure Drop Fluent

Percent Error

All Walls 3.48E-03 3.51781-03 1.19%

Two Walls and One Pressure Outlet

-3.73E-03 -3.679068E-03 1.25%

One Wall and Two Pressure Outlets

2.54E-03 2.53E-03 0.32%

All Pressure Outlet -8.593229E-03 -8.68129E-03 1.01%

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Table 2: Pressure Drop Verification via Darcy’s Law

Conclusion:• Hand calculations were equivalent to FLUENT’s values. • Better understanding how FLUENT uses the porous-jump condition.

Porous Boundary Open Channel - Velocity Magnitude Contours

Figure 11: Isometric View of Axial Variation of Velocity on Central Plane

Figure 12: Front View of Axial Variation of Velocityon Central Plane

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Porous Boundary Open Channel - Shear Stress

Figure 13:Axial Variation of Shear Stress on the Back Wall

at y=0.1 z= 0

Figure 14: Axial Variation of Shear

Stress on Screen at y=0.1 z= 0.02

Figure 15:Axial Variation of Velocity at Line y=0.1, z=0.01

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Future Work• Continue running the porous boundary open

channel model until the fluid flow solution has been calculated for at least 3 minutes to achieve a steady state solution

• Investigate reasoning behind the zero shear stress at the porous boundary

• Compare verification case results for pressure drop calculations to literature

• Interpret results further

 

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Acknowledgements

• Dr. Ghia for being an excellent faculty mentor and taking the time to make sure we fully understood the concepts behind our research.

• Graduate Students Prahit, Chandrima, Deepak, Nikhil, and Santosh for taking time out of their schedule to teach us the software and help us with any problems we encountered.

• Funding for this research was provided by the NSF CEAS AY REU Program, Part of NSF Type 1 STEP Grant, Grant ID No.: DUE-0756921

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Appendix: Porous Plate Calculation• Darcy’s Law pressure drop calculations:

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