Static Mixers for Enhanced Reactant Distribution in Redox Flow Cells

Static Mixers for Enhanced Reactant Distribution in Redox Flow Cells Nicholas Gurieff, Declan Finn Keogh, Chris Menictas, Victoria Timchenko School of Mechanical and Manufacturing Engineering, UNSW Sydney, NSW, Australia ICESI 2020, 1-4 March, Sydney, Australia

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Polarisation Problem

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 Current limited by reactant availability

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 Concentration overpotential a function

 Mass transfer requirements balanced against parasitic pump work  Mechanical cell architecture

Potential

of flow rate and concentration

Concentration Overpotential

innovations can help Time

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Multiphysics Modelling  Modelling of electrochemistry and fluid dynamics  Validated models with high performance computing  Single cell geometries with flowthrough porous felt electrodes

Static Mixers MIXER

MEMBRANE

FELT

POSITIVE HALF-CELL NEGATIVE HALF-CELL CURRENT COLLECTOR

ENDPLATE

Address internal concentration gradients to improve electrolyte and electrode utilisation

1-ELEMENT

2-ELEMENTS

V3+ Concentration Minimum (mol/m^3)

Number of Elements 50 40 30 20 10 0

3-ELEMENTS

0

1

2

Mixer Elements

Gurieff, N. et al. (2019). Enhanced Reactant Distribution in Redox Flow Cells. Molecules, 24(21), 3877.

3

Half-cell modelling for sensitivity studies

POSITION

V3+ Concentration Minimum (mol/m^3)

Mixer Position 50 40 30 20 10 0 Ref

1/3 Position

1/2

2/3

Helical Mixers Shift from blade to helical style mixers to reduce parasitic pressure drop at higher flow rate

Blade vs Helical Mixers Pressure (Pa) 150

160

170

180

190

200

Uniform

Minimum V3+ Concentration

Blade

Differential Pressure

Helical

0

10

20

30

Concentration (mol m^-3)

40

50

Distribution at ¼ Depth Concentration profiles for unmixed and mixed cells mol m-3 UNIFORM

BLADE

HELICAL

Distribution at Outlet Concentration profiles for unmixed and mixed cells mol m-3

Mixer Assemblies Blade and helical mixer elements assembled for manufacturing and use in laboratory cells

Additive Manufacturing Blade and helical mixer assemblies 3D printed in rigid and flexible materials

Experiment Preparation Mixer assembly prepared for experimental testing in digitally manufactured lab cell

Efficiency and Capacity  Mixers >1% voltage improvement  Wedge cell 1% voltage improvement resulted in 15% energy efficiency improvement at 120 mA cm-2 and usable capacity increase

Voltage (V)

2.0 1.5 1.0 0.5 0

1 Time (hours)

2

3

4 Flat

5 Wedge

Gurieff et al. (2019). Performance enhancing stack geometry concepts. In The International Flow Battery Forum. Lyon, France.

Summary  Decrease pressure differential  Reduce concentration polarisation  Improve energy efficiency  Increase usable capacity  Enhance value

Nicholas Gurieff UNSW Sydney, Australia n.gurieff@unsw.edu.au

Acknowledgements This research is supported by an Australian Government Research Training Program Scholarship