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