Alternative Designs to Harness Natural Convection in Flow BatteriesMd A. Ansari1, S. Kumar1
1. Indian Institute of Science, Bangalore, Karnataka, India
Abstract: The earlier work in our group has established that natural convection plays a
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.
Results
Conclusions 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).
SLRFB Battery •Cathode Reaction
arg2 2arg
ch ePb e Pb
disch e
0( 0.13 / )E V SHE
arg2 2 4 22 2arg
ch ePb H O PbO H e
disch e
• Anode Reaction0( 1.56 / )E V SHE
arg2 2
2 2arg
ch ePbO H O PbO H e
disch e
•Side Rxn
Energy Storage
Energy Demand
•Challenges: High cost
of vanadium & periodic
replacement of
expensive membrane
VRFB Battery
(http://energystorage.org/energy)
•Challenge: Cycle Life
(b)Performance
@ 700 rpm
Beaker cell… Intense Agitation
(a)Continuous mixing @ 700rpm (b)No mixing
(c)Intermittent mixing
@ 300rpm
Design Experiments to Probe
Role of Convection/Mixing (Verde et. al., Energy Envi. Sci., 2013)
(Mahendra , PhD Thesis, IISc, 2015)
Effect of Free Convection
Velocity Vector at 100s Cell Potential
Objective of Present Work
Standard cell Lift cell
Model Equations
ci Nt i
N D c Fz c u c umi i i i i ii
2 F z ci ii
0z ci ii
0j j F z Ni ii
2( )u u u p u Ft
. 0u
0( )F g c ci i ii
1
, ,i c
i T P cj i
Initial & Boundary Conditions
Mass Balance Eqn
Nernst Planck Eqn
Poisson Eqn
Charge Neutrality
Charge Conservation
Navier Stokes Eqn
Buoyancy Force
Coeff. of Expansion
Computational Method:
Velocity (mm/s): Free Convection Charging
Lift-15mm
Std-15mm
20 s 40 s 60 s
0 2 4 6 8 10 12 14-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
Y-V
elo
cit
y(m
m/s
)
Electrode Spacing(mm)
20s
40s
60s
80s
100s
Std-15mm-tb-2cm
Charging
14 16 18 20 22 24 26
0.0
0.5
1.0
1.5
2.0
2.5
Y-V
elo
cit
y(m
m/s
)
Electrode Spacing(mm)
20s
40s
60s
80s
100s
Lift-15mm-tb-2cm
Charging
Velocity between electrode spacing at mid-line
0 5 10 15 20 25 30
50
100
150
200
250
300
350
400
450
[Pb
(II)
](m
ol/m
3)
Anode Length(mm)
1000s
2000s
3000s
Std-15mm-tb-2cm
Simulation:Charging
20 25 30 35 40 45 50150
200
250
300
350
400
450
500
[Pb
(II)
](m
ol/m
3)
Anode Length(mm)
1000s
2000s
3000s
lift-15mm-tb-2cm
Simulation:Charging
Concentration of Ions at Electrode
Cell Chemistry
[Newman & Alyea. Electrochemical system(2004 )]
Cell Potential
Effect of cell designs on performance
V E E iRcell
Acknowledgment: We thank DST-IRHPA & IISc for all their support .
Introduction
Previous Work
(http://www.eia.gov/totalenergy)
Smart Grid/5MWh
(http://zebu.uoregon.edu/disted/ph162/l8) (http://www.renewableenergyworld.com/)
(a)Performance at 300 rpm
(Hazza et al. (2004))
Experimental Verification
0 2000 4000 6000
1.2
1.4
1.6
1.8
2.0
2.2
Cell P
ote
nti
al(
V)
Time(s)
Lift-15mm-tb-2cm
Std-15mm-tb-2cm
Simulation
0 1000 2000 30001.9
2.0
2.1
2.2
2.3
2.4 std-8mm-tb-2cm
lift-8mm-tb-2cm
Cell P
ote
nti
al(
V)
Time(s)
Experiment
0 1000 2000 30001.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
Cell P
ote
nti
al(
V)
Time(s)
std-8mm-tb-3cm
std-8mm-tb-2cm
lift-8mm-tb-2cm
Simulation:Charge
Results
Excerpt from the Proceedings of the 2016 COMSOL Conference in Bangalore