A critical review of recent advances in CFD modelling of spiral wound membranes

1. CFD Modelling of Spiral
Membrane Modules
A Seminar in Chemical Engineering
Kaushal Sanjayrao Kaloo
16CHE135
Department of Chemical Engineering
Institute of Chemical Technology,
Mumbai

2. 1. Introduction
and Scope of
the study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
2
Figure: Feed spacer configurations: (a) non-woven (b)
partially woven (c) middle layer (d) fully woven
Two essential functions of feed spacer:
1. Structural support to the adjacent membranes
2. Enhanced mass transfer through the membrane
surface.
Objectives of ongoing research:
1. minimizing the trans-membrane pressure drop
2. decreasing concentration polarization
3. minimizing membrane fouling

3. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on
flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
3
lf = 2mm
lf = 2mm
Figure: Variation in the velocity profiles with Reynold's number
and axial distance between two filaments (Sousa, et al. 2014).
Gradient: Blue=0.0 m/s to Red: 0.58 m/s
lf = 8mm
lf = 8mm
Re=250
Re=10
Figure: Eddy generation at high velocities (Liang, et al.
2016) . Gradient: Blue=0 m/s to Red=3.4 m/s
Re=64

4. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on
flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
4
0
4000
8000
12000
16000
0 100 200 300
P/L(Pa/m)
Re
L=4 mm L=2 mm
Figure: Variation of pressure drop with Reynold's number and
filament spacing (Sousa, et al. 2014)
Factors that influence pressure drop (Shakaib et al. 2009):
Feed
attack
angle
(α)
Filament
thickness
Filament
spacing

5. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on
flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
5
Figure : Pressure gradient along the membrane surface
with spacer (Vrouwenvelder, et al. 2010). Gradient:
Blue=0.0 kPa to Red=0.06 kPa
Pressure drop in spacer-filled membrane channel
• Discretized drop in pressure along the direction of
flow
• Within spacer diamonds, almost no pressure
gradient is observed
• Resistance offered by the spacer filaments to the
flow is much higher than that offered by the
membrane wall

6. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
6
Figure: Concentration polarization in membrane (a) without spacer (b)
with spacer (Li, Bui and Chao 2016). Gradient: Blue: 13 mol/m3 to Red:
15.5 mol/m3
(a)
(b)
Concentrated island
• Li, Bui and Chao (2016) found that near the
spacer filaments, the convective flux is low. This
isolates the stagnant zone with smaller flux.
• Salt concentration increases immediately before
and after the flow impinges on a spacer
filament.
• Higher likelihood of fouling

7. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
7
Figure 10: Concentration polarization in different spacer geometries: (a) non-woven (b) partially woven (c) middle
layer and (d) fully woven (Gu, Adjiman and Xu 2017) Gradient: Blue: 605 mol/m3 to Red: 650 mol/m3
(a) (b)
(c) (d)

8. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
8
0
5
10
15
20
25
30
0 50 100 150 200 250
SCEx10^4
Re
Empty channel Non-woven
Middle layer Fully woven
0
0.5
1
1.5
2
100 125 150 175 200
SCEx10^4
Re
Spacer Configuration Efficacy
• Kavianipour, Ingram and Vuthaluru (2017) took
trade-off between mass transfer enhancement
and pumping energy requirements in devising SCE
• 𝑆𝐶𝐸 =
𝑆ℎ
𝑃𝑛
; High SCE values are desirable for
spacer configurations.
• Non-woven geometry has the highest SCE for low
Reynolds numbers (Re<120) while for higher Re
(Re>120) the fully-woven configuration has a
slightly better SCE.

9. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane
fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
9
Membrane fouling
• Biomass attachment: expressed as mole of
biomass attached to spacer mesh per unit area of
membrane per day
• Biomass growth: Monod growth kinetics
(expressed as mole of biomass per unit time)
• Biomass detachment: Based on stress created by
liquid past biofilm
(a)
(b)
(c)
Figure: Biofouling in (a) non-woven (b) fully
woven (c) middle-layer spacer configurations
(Radu et al. 2010)

10. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane
fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
10
Figure: Vortex shedding due to forced slip velocity (Lim, et al.
2018) Gradient: Blue=0 m/s to Red= 0.28 m/s
No vortex shedding
Vortex shedding
Permeate flux enhancement
• 5-7% higher pumping energy requirements
• more than 2X increase in maximum shear stress
• Flow perturbation at resonant frequency
• Potential reduction in biofouling

11. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
11
Authors Pressure drop Mass transfer Spacer characteristics
Guillen and Hoek
(2009)
𝑓 = 0.25 +
189.29
𝑅𝑒
; 𝑅𝑒
= 200 𝑡𝑜 500
𝑆ℎ = 0.46 𝑅𝑒0.36
𝑆𝑐0.36
; 𝑆𝑐
= 620
L/D = 9
 not specified
Circular, middle
layer
Koutsou et al. (2009) Not available 𝑆ℎ = 0.13𝑅𝑒0.66 𝑆𝑐0.4; 𝑆𝑐
= 1 − 100
L/D =6 to 8
 =90◦ to 120
Configuration not
mentioned
Koutsou and
Karabelas (2015)
∆𝑃
𝐿
= 5.82𝑅𝑒−0.64; 𝑅𝑒
= 100 − 200
𝑆ℎ ∝ 𝑅𝑒 𝑎; 𝑎
= 0.66 − 0.73;
Sc = 1 − 100
L/D= 10
 = 120◦
Novel spacer
Li et al. (2016) 𝑓 = 𝑅𝑒−0.33 ; 𝑅𝑒 = 100 −
300
𝑆ℎ 𝑅𝑒0.4 ; 𝑆𝑐 = 560 L/D = 6
 not specified
Circular, fully
woven
Kavianipour et al.
(2017)
𝑃
𝐿 𝑅𝑒 𝑎;
𝑅𝑒 = 100 − 400;
𝑎 = 1.06 𝑡𝑜 1.55
𝑆ℎ 𝑅𝑒 𝑎 ; 𝑆𝑐 = 660;
a = 0.257 − 0.549
L/D = 8
 =90◦
Circular, different
configurations

12. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
12
Figure 13: Comparison of pressure drop in ideal vs real
spacer geometry (Picioreanu, Vrouwenvelder and van
Loosdrecht 2009)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 2 4 6 8 10 12 14 16 18 20
Pressure(kPa)
Module Length (mm)
Real geometry Ideal geometry
Idealized spacer geometry
Figure: (Left) Microscopic image of the spacer diamond; (Right)
Realistic spacer geometry; (Right after transition) Idealized spacer
geometry

13. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
13
2D vs 3D modelling
• Vrouwenvelder, et al. (2010) observed that the velocity field at 75% of the
channel height showed a profile that differs strongly from the channel
centre.
• With the presence of a spacer, the velocity flow nearer to the membrane
is mostly parallel to the spacer filaments. This behaviour is not observed
at the channel centre.
• Local phenomena such as mass transfer, velocity profiles vary
significantly in the transverse direction.

14. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
14
Boundary conditions
1. Permeable wall
• Local permeate flux calculation
• Membrane permeability is not constant
• Higher computational time and cost
2. Impermeable wall
• Constant concentration at the wall
1. 100% w/w of solute (worst-case fouling)
2. Saturated concentration of solute
• Easier computation

15. 1. Introduction
and Scope of the
study
2. Fluid Dynamics
2.1 Velocity profiles, flow transition
2.2 Pressure drop
2.3 Effect of spacer geometry on flow
3. Mass Transfer
3.1 Concentration polarization
3.2 Effect of spacer geometry
on mass transfer
4.1 Membrane fouling
4.2 Permeate flux
enhancement
5. Critical
Review
CFD Study of Spiral Membrane Modules
15
Study Sherwood
number, Sh
Power number, Pn
x 10-3
Spacer configuration
efficacy, SCE x 104
Saeed et al. (2015) 29 473.1 0.66
Kavianipour et al. (2017)
with same boundary
conditions as Saeed et al.
(2015)
27.6 296.8 0.93
Kavianipour et al. (2017) 54.2 294.6 1.84

16. CFD Study of Spiral Membrane Modules
16
Effect of spacer geometry on
fluid dynamics and mass
transfer (Koutsou, et al./
Shakaib et al./Guillen and
Hoek)
2009
2010
Effect of spacer
geometry on
membrane
biofouling
(Radu, et al.)
2014
Hydrodynamics
and mass
transfer
characteristics of
RO membrane
(Sousa, et al.)
Novel spacer
design to enhance
mass transfer
(Koutsou and
Karabelas)
2015
Spacer
Configuration
Efficacy
(Kavianipour, et al.)
2017
2018
Permeate flux
enhancement
using forced
velocity slip
(Lim, et al.)
Flow transition
dynamics
(Qamar, et al.)
2019