LOSS IN SCREEN

1. Journal of Mechanics Engineering and Automation 3 (2013) 29-34
Flow Loss in Screens: A Fresh Look at Old Correlation
Ramakumar Venkata Naga Bommisetty, Dhanvantri Shankarananda Joshi and Vighneswara Rao Kollati
Engineering Aerospace, MCOE, Honeywell Technology Solutions Pvt. Ltd., Bangalore 560037, India
Received: December 7, 2012 / Accepted: January 5, 2013 / Published: January 25, 2013.
Abstract: Pressure losses in flow components are generally characterized either by pressure loss coefficients or by discharge
coefficients. The pressure drop for incompressible flow across a screen of fractional free area α is often calculated from widely used
correlation provided in Perry’s Handbook. This correlation was developed based on experimental work which have covered a wide
range of fractional free area (α = 0.14 to 0.79). The present work aims at validation for a flow in plain square mesh screen with a
particular fractional free area (porosity, α) of 0.25 using CFD (Computational Fluid Dynamics) approach. The simulations are carried
out for wide range of screen Reynolds number (Re = 0.1 to 105
) covering both laminar and turbulent flow regimes. Initial simulations
are carried out for incompressible fluid (water) and further extended to compressible fluid (air). Discharge coefficients obtained from
the simulations are compared with experimental values. Effect of compressibility on discharge coefficients is described.
Key words: Pressure loss coefficient, discharge coefficient, screen, fractional free area, CFD (computational fluid dynamics),
compressibility.
1. Introduction
Fluid flow through screens takes place in a number
of technical areas including filtering, mining and
mineral processing, porous beds and a variety of flow
straightening and turbulence reduction applications.
Information on flow characteristics of these screens is
very important factor while selecting the screens for
different applications. Several experimental studies
were carried out earlier to generate these flow
characteristics for general purpose screens. Kays and
London [1] did investigation on friction factor for four
woven metal screens. Armour and cannon [2]
investigated hydraulic resistance of five types of
woven metal screens through experiments made in a
circular channel with single layer of metal screen. They
provided an equation for the calculation of pressure
drop based on the flow velocity, the porosity and the
geometry of the screen. Brundrett [3] did investigation
on the prediction of pressure drop for incompressible
Corresponding author: Ramakumar Venkata Naga
Bommisetty, Ph.D., technology specialist, research fields:
turbine cooling, heat transfer and CFD. E-mail:
ramakumar.bommisetty@honeywell.com.
flow through screens. They developed a pressure loss
correlation which predicts flow through screens for the
wire Reynolds number range of 10−4
to 104
using the
conventional orthogonal porosity and a function of
wire Reynolds number. The correlation was extended
by the conventional cosine law to include flow which is
not perpendicular to the screen.
Sodré and Parise [4] designed an experimental
procedure to investigate the friction factor of
plain-square woven metal screen adopted in Stirling
engine regenerator. They developed an equation to
evaluate the pressure drop in annular bed of screens.
Wu et al. [5] conducted experiments to measure
pressure drop of the flow through woven metal screens.
Four woven metals screens with different porosities of
the plain-square type were tested and based on the
tested study, an empirical equation was developed for
friction factor characteristic of plain square type woven
metal screens. They also developed five empirical
equations respectively for five types of metal screens
(Plain square, fourdrinier, full twill, plain dutch and
twilled dutch types). Along with these resources,
pressure drop across the screens is widely obtained
DAVID PUBLISHING
D

2. Flow Loss in Screens: A Fresh Look at Old Correlation30
from Perry’s Chemical Engineer’s Handbook [6] in
which pressure drop (Δp) across the screens for
incompressible fluids (for constant densities) is
expressed as
2
2
V
Kp
ρ
=Δ (1)
where ρ = fluid density, V = superficial velocity based
upon the gross area of the screen, K = pressure loss
coefficient.
The relation between pressure loss coefficient and
discharge coefficients for such screens is obtained by
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
⎟
⎠
⎞
⎜
⎝
⎛
= 2
2
2
11
α
α
C
K (2)
where C = discharge coefficient and α = the fractional
free area or porosity which is defined as surface area of
opening to the total area.
The discharge coefficient (C) for the screen with
aperture Ds is given as a function of screen Reynolds
number, Re = Ds(V/α)ρ/μ in a graphical form. This
information is useful for plain square-mesh screens
with wide range of porosity, α = 0.14 to 0.79. This
graphical curve fits most of the data within ±20 percent.
But this information is limited to incompressible flows.
An attempt has been made in this paper to model a
screen and generate flow characteristics for a typical
screen to cover a wide range of screen Reynolds
number (Re = 0.1 to 105
) using CFD. Commercial
software ANSYS ICEMCFD (version 12.1) [7] is used
for model and mesh generation. ANSYS CFX (version
12.1) [8] is used for solving and post processing. The
reason for this tool’s selection is its flexibility and
robustness for creating unstructured mesh using
tetrahedral elements with embedded prism layers at the
walls [7] and the solving capability of the tool with
great accuracy [8]. All the simulations are performed
under steady state conditions with quality and trust
regarding grid refinement and iterative errors. Initial
simulations are carried out with incompressible fluid
(with water) and then extended to compressible fluids
(with air). Discharge coefficients are calculated from
pressure drop across the screen and are compared with
the correlation available [6] for both the
incompressible and compressible flows. Effect of
compressibility on discharge coefficient is also
explored.
2. Numerical Set-Up
In order to simplify the simulations, a screen with
an array of 5 × 5 holes is considered, shown in Fig. 1.
As shown, holes are square in section with side of
0.015 mm and the gap between each hole is 0.015 mm.
This screen leads to fractional free area (porosity) of
0.25. Screen length of 0.015 mm is considered for
present study. This represents a typical screen used for
flow straightening application. In order to have some
duct length for flow to develop, an entry and exit duct
of lengths 1mm each are considered. The full domain
considered for the present study is shown in Fig. 2.
ANSYS ICEMCFD (version 12.1) is used for model
generation and mesh generation. Tetrahedral elements
with prism layers are considered for grid
generation. For the grid refinement study the grid is
refined uniformly (by changing the maximum element
size) while the number of nodes have changed by 2-3
times.
Regarding the boundary conditions for the
simulations, the top, bottom and side faces
(surrounding faces) are considered as walls. Velocity
inlet condition is used for domain inlet. Pressure
outlet with gage pressure of zero is applied for domain
outlet. Simulations are also performed with symmetry
boundary condition for surrounding faces and no
considerable change is found in pressure drop with
change of boundary condition. High resolution
scheme is used to solve the continuity, momentum,
energy and turbulence equations. The simulations are
considered well converged when the monitored
properties got stabilized and the RMS residuals has
dropped to 1e-4. For the simulations with screen
Reynolds number less than 10, flow is considered as
laminar [6]. At higher Reynolds number, flow is
considered as turbulent and standard k-ε model is used
for turbulence closure.

3. Flow Loss in Screens: A Fresh Look at Old Correlation 31
(a) Front view of the screen with an array of 5 × 5
(b) Isometric view of the screen
Fig. 1 Geometric details of the screen.
(a) (b)
(c) (d)
Fig. 2 (a) Mesh for the full domain; (b) Mesh distribution
near the screen; (c) Mesh in the fluid domain; (d) Mesh and
prism layer distribution in the screen.
3. Results
This part is divided into 3 sections dealing with grid
refinement, screen characteristics for incompressible
fluids and screen characteristics for compressible
fluids.
3.1 Grid Refinement Study
This grid refinement study is performed with
Reynolds number of 100 for three meshes. The
parameter of interest is static pressure drop across the
screen. Simulations are performed with nodes of
0.09M, 0.17M and 0.5M. The difference of static
pressure drop across the screen is about 1.2% and the
value obtained with 0.17M is closer to the experimental
value compared to the other meshes. This accuracy is
by all means good enough and since the computational
time is reasonable with mesh of 0.17M nodes, this
mesh is used for further analysis.
3.2 Screen Characteristics for Incompressible Fluids
As mentioned earlier, simulations are performed
with incompressible fluid of water. Seven number of
simulations with screen Reynolds number of 0.1, 1, 10,
100, 1000, 10000 and 100000 are performed. Flow
with screen Reynolds number up to 10 is considered as
Laminar and the simulations with other Reynolds
number are treated as turbulent. K-ε turbulence model
is used for turbulence closure. For the selected
Reynolds numbers, inlet velocity is calculated from
screen opening dimension and fractional free area. This
value is supplied as the boundary condition at inlet.
Two rating stations, one at upstream of screen and
the second one at downstream of screen, are considered
for pressure drop calculation. Upstream station is
considered at a distance of two hydraulic diameter of
screen opening. Downstream rating station is
considered at a distance of five hydraulic diameters of
channel. Static pressures at these two rating stations are
obtained from the converged solutions and discharge
coefficients are calculated using Eqs. (1)-(2).
Discharge coefficients for various screen Reynolds

4. Flow Loss in Screens: A Fresh Look at Old Correlation32
number are compared with the available experimental
values [6], shown in Fig. 3. As is shown in Fig. 3,
predicted discharge coefficient matches very well with
experimental data up to Reynolds number of 10 (i.e., in
the laminar region).
For turbulent region, simulations under predicted the
discharge coefficients compared to the corresponding
experimental data. Discharge coefficient has increased
with increase in screen Reynolds number up to the
screen Reynolds number of 1000 and there is no
change in discharge coefficient with further increase in
Reynolds number. Simulations are also able to predict
the similar trend but the discharge coefficient got
stabilized at 0.92 against the experimental value of 1.4.
Discharge coefficients have crossed the value of unity
in the experiments which is not observed with the
simulations.
Velocity and pressure contours at selected planes
along the stream wise direction are shown in Figs.
4a-4b), for screen Reynolds number of 1000. Location
of selected planes and stream lines are shown in inset
of Fig. 4. Complete mixing and uniform flow is
observed on the upstream locations of the screen. As
expected, higher velocities are found near the screen
regions. Presence of screen is highlighted on the
downstream locations. A fully developed profile in
velocity is observed at outlet. From the contours of the
pressure, it can be noticed that huge pressure drop is
required to cross the screen. Pressure drop across the
channel as a function of screen Reynolds number is
shown in Fig. 5.
Fig. 3 Effect of screen Reynolds number on discharge
coefficients.
(a) Velocity contours at selected planes
along the streamwise direction
(b) Pressure contours at selected planes along
the stream wise streamwise direction
Fig. 4 Contours of CFD results.
Fig. 5 Pressure drop across the channel for various screen
Reynolds numbers.

5. Flow Loss in Screens: A Fresh Look at Old Correlation 33
The pressure drop across the screen is found to be
proportional to the Reynolds number (velocity) for
Reynolds number less than 10, and then increased as
square of the Reynolds number for Reynolds number
greater than 100. These observations are in line with
the assumption of laminar flow lower Reynolds
number (< 100) and turbulent for higher Reynolds
number.
3.3 Screen Characteristics for Compressible Fluids
Simulations with compressible fluid, air, have been
carried out to cover the similar range of Reynolds
number. Simulations are run with the geometry shown
in Fig. 1 up to screen Reynolds number of ~ 100. It is
found difficult to get converged solutions for further
increase in Reynolds number because of high mach
numbers obtained in the screens. Dimensions of the
screen are scaled and simulations are performed for
further increase in Reynolds number. Using scaling, it
has been possible to increase the Reynolds number
even with lower mach numbers in the screen. Fig. 6
shows the comparison of predicted discharge
coefficients with experimental and incompressible
simulations. The maximum Mach number obtained at
the entrance of screen in these calculations is 0.4. The
maximum density variation across the screen is about
20% (for Reynolds number of 100). With this low
Mach number and lower density variation, no
considerable differences are observed in the
dependence of discharge coefficient on Reynolds
number. But slightly lower discharge coefficients are
found with compressible fluid compared to
incompressible fluids in turbulent region (Reynolds
number > 100). Discharge coefficient for compressible
fluid became constant at 0.85 against the value of 0.92
for incompressible fluid.
In addition to the aforementioned simulations, few
more simulations are also performed in the screen
Reynolds number range of 100-1000 with the initial
screen dimensions to study the compressibility effects.
Mach number in the screen is observed to be transonic
Fig. 6 Effect of compressibility on discharge coefficient.
in these simulations. Huge pressure drop is observed
across the screen because of high mach exist in the
screen. Variation of discharge coefficient with screen
Reynolds number is shown in Fig. 6. As there is a
considerable variation of fluid density on upstream and
downstream locations, Screen Reynolds number is
calculated based on upstream location. Drastic
reduction in discharge coefficients is observed in these
simulations with increased screen Reynolds number.
Compressible effects have shown large impact on
discharge coefficients. For the same Reynolds number
for 1000, discharge coefficient has reduced from 0.8 to
0.41. It is noted that density variation across the screen
plays an important role in discharge coefficients. So,
the available correlation is found suitable for density
variation below 20%.
4. Conclusions
A numerical study is carried out to find the flow loss
in screens. Commercially available CFD code ANSYS
CFX 12.1 is used for numerical study. Simulations are
performed for both incompressible and compressible
fluids. Laminar model is used for screen Re ≤ 10 and
Standard k-ε turbulence model for higher screen
Reynolds Numbers. Based on the present study, the
following conclusions can be derived:
Predicted discharge coefficient values of
incompressible fluid matched with the available
experimental results up to screen Reynolds number of
10. But for the turbulent region, predicted discharge
coefficients are lesser compared to the experimental

6. Flow Loss in Screens: A Fresh Look at Old Correlation34
values;
Discharge coefficient has increased with increase
in Reynolds number up to screen Reynolds number of
1000 and then constant discharge coefficient is obtained
with further increase in Reynolds number. The constant
discharge coefficient obtained from the simulation is
0.91 against the value of 1.4 in experiments;
For compressible fluids, predicted discharge
coefficients are in line with incompressible fluids till
the density variation across the screen is about 20%;
Considerable reduction (maximum of 50%
reduction) is noticed in discharge coefficient with
higher density change for compressible fluids;
Density change of fluid in the screen is found to
be stronger influencing parameter for flow loss in
screens compared to the screen Reynolds number.
Acknowledgments
The authors are thankful to the management of
Honeywell and HTS for permitting them to share the
findings.
References
[1] W.M. Kays, A.L. London, Compact Heat Exchangers,
McGraw-Hill, 1964.
[2] J.C. Armour, J.N. Cannon, Fluid flow through woven
screens, AIChE Journal 14 (3) (1968) 415-420.
[3] E. Brundrett, Prediction of pressure drop for
incompressible flow through screens, Journal of Fluids
Eng. 115 (2) (1993) 239-241.
[4] J.R. Sodré, J.A.R. Parise, Friction factor determination for
flow through finite wire-mesh woven-screen matrices,
Journal of Fluids Eng. 119 (1997) 847-851.
[5] W.T. Wu, J.F. Liu, W.J. Li, W.H. Hsieh, Measurement and
correlation of hydraulic resistance of flow through woven
metal screens, International Journal of Heat and Mass
Transfer 48 (2005) 3008-3017.
[6] D.W. Green, R.H. Perry, Perry’s Chemical Engineers
Handbook, 8th ed., McGraw-Hill, 2008.
[7] ANSYS, User Manual ANSYS ICEM CFD/AI*
Environment Release 12.1, ANSYS, Inc., Southpointe 275
Technology Drive, Canonsburg, PA 15317, November
2009.
[8] ANSYS, User Manual ANSYS CFX Release 12.1,
ANSYS, Inc., Southpointe 275 Technology Drive,
Canonsburg, PA 15317, November 2009.