Download Md A. Ansari , S. Kumar 1. Indian Institute of Science, Bangalore

Alternative Designs to Harness Natural Convection in
Flow Batteries
1
Ansari ,
1
Kumar
Md A.
S.
1. Indian Institute of Science, Bangalore, Karnataka, India
Abstract: The earlier work in our group has established that natural convection plays a
Results
dominant role in SLRFB. We used it to run a battery in which interestingly, the contents
are agitated for brief spells when no current flows through it. The present work focuses on
electrode configurations that harness the role of natural convection. In one such
configuration, electrodes are positioned away from cell wall instead of keeping them flush
with it, a practice followed in the previous configurations. The results are promising.
Introduction
Energy Storage
Velocity (mm/s): Free Convection Charging
Lift-15mm
Std-15mm
Smart Grid/5MWh VRFB Battery
Energy Demand
(http://www.eia.gov/totalenergy)
20 s
Cell Chemistry
•Cathode Reaction
charge 

Pb2  2e 
 Pb
discharge
2.0
( E 0  0.13V / SHE )
Std-15mm-tb-2cm
20s
40s
60s
80s
100s
1.5
Charging
1.0
0.5
0.0
-0.5
-1.0
-1.5
• Anode Reaction
20s
40s
60s
80s
100s
2.5
Y-Velocity(mm/s)
(Hazza et al. (2004))
2.5
Y-Velocity(mm/s)
SLRFB Battery
•Challenges: High cost
of vanadium & periodic
replacement of
expensive membrane
(http://www.renewableenergyworld.com/)
60 s
Velocity between electrode spacing at mid-line
(http://energystorage.org/energy)
(http://zebu.uoregon.edu/disted/ph162/l8)
40 s
2.0
Lift-15mm-tb-2cm
Charging
1.5
1.0
0.5
0.0
0
2
4
6
8
10
12
14
14
16
Electrode Spacing(mm)
18
20
22
24
26
Electrode Spacing(mm)
( E 0  1.56V / SHE )
charge 
2




Pb  2 H O 
 PbO  4 H  2e
2
2
discharge
charge 
  2e
•Side Rxn PbO  H O 

PbO

2
H

•Challenge: Cycle Life
2
Results
2
discharge
Effect of cell designs on performance
Previous Work
2.2
Design Experiments to Probe
Role of Convection/Mixing
(Mahendra , PhD Thesis, IISc, 2015)
std-8mm-tb-3cm
std-8mm-tb-2cm
lift-8mm-tb-2cm
3.2
Simulation
Cell Potential(V)
(Verde et. al., Energy Envi. Sci., 2013)
2.0
Cell Potential(V)
Beaker cell… Intense Agitation
3.4
Lift-15mm-tb-2cm
Std-15mm-tb-2cm
1.8
1.6
1.4
3.0
Simulation:Charge
2.8
2.6
2.4
2.2
2.0
1.2
0
2000
4000
1.8
6000
0
1000
Time(s)
(a)Performance at 300 rpm
Std-15mm-tb-2cm
Simulation:Charging
Objective of Present Work
10
15
20
25
lift-15mm-tb-2cm
Simulation:Charging
450
30
std-8mm-tb-2cm
lift-8mm-tb-2cm
1000s
2000s
3000s
2.3
400
350
300
250
200
150
20
2.2
2.1
2.0
1.9
25
Anode Length(mm)
30
35
40
45
50
Experiment
0
1000
2000
3000
Time(s)
Anode Length(mm)
Velocity Vector at 100s
Computational Method:
Conclusions
Model Equations
[Newman & Alyea. Electrochemical system(2004 )]
Nernst Planck Eqn
c
i   N
t
i
N   D c  Fz c um   c u
i
i i
ii i
i
Poisson Eqn
2   F  z c
 i ii
Mass Balance Eqn
Lift cell
5
500
1000s
2000s
3000s
Cell Potential(V)
450
400
350
300
250
200
150
100
50
0
(c)Intermittent mixing
@ 300rpm
Standard cell
2.4
[Pb(II)](mol/m3)
Effect of Free Convection
Cell Potential
Experimental Verification
(b)No mixing
[Pb(II)](mol/m3)
(a)Continuous mixing @ 700rpm
3000
Time(s)
Concentration of Ions at Electrode
(b)Performance
@ 700 rpm
2000
Initial & Boundary Conditions Charge Neutrality
Charge Conservation
 zici  0
i
 j  0
j  Fz N
i i i
Navier Stokes Eqn
 u   (u )u  p  2u  F
t
Buoyancy Force
Coeff. of Expansion
Cell Potential
.u  0
F   g   (c0  c )
i i i i




1

    
i
 c 
 i T ,P,c
ji
V
 E  E     iR

cell
Alternative designs implemented are able to increase the battery
performance. Model and experiment are in good agreement. The efforts
are underway to explore new designs, such as slotted or grid type
electrodes, as length scale in vertical direction impacts natural convection
significantly.
References
[1]Hazza et al. A novel flow battery: A lead acid battery based on an electrolyte with
soluble lead(II) Part I. Preliminary studies. Physical Chemistry Chemical Physics,
6(8), 1773-1778 (2004).
[2]Nandanwar, M. N. & Kumar, S. Modelling of Effect of Non-Uniform Current Density
on the Performance of Soluble Lead Redox Flow Batteries. Journal of the
Electrochemical Society, 161(10), A1602-A1610 (2014).
[3]Shah et al. A mathematical model for the soluble lead-acid flow battery. Journal of
the Electrochemical Society, 157(5), A589-A599 (2010).
[4]Verde, et al. Achieving high efficiency and cyclability in inexpensive soluble lead
flow batteries. Energy & Environmental Science, 6(5), 1573-1581, (2013).
Acknowledgment: We thank DST-IRHPA & IISc for all their support .
Excerpt from the Proceedings of the 2016 COMSOL Conference in Bangalore