Electrolyte flow distribution is an important factor that contributes to the performance of the overall efficiency of a redox flow battery system. In the present paper, a comparative study of the hydrodynamics of the serpentine and interdigitated flow fields has been performed. Ex situ experiments were conducted using the two flow fields in conditions typical of flow battery applications. Limited in situ testing has also been conducted. These bring out the surprising result that the pressure drop in the interdigitated flow field is less than that in the serpentine for the same flow rate. Computational fluid dynamics studies show strong under-the-rib convection in the reaction zone exists in both flow fields but with a shorter residence time in case of the interdigitated. It is posited that this may explain the superior electrochemical performance of cells with interdigitated flow fields. © 2014 Springer Science+Business Media Dordrecht.

Sreenivas Jayanti

Department Of Chemical Engineering

T. Jyothi Latha

Computational fluid dynamics

efficiency

Electrolytes

Flow fields

Hydrodynamics

Pressure drop

Residence time distribution

Serpentine

Comparative studies

Electrochemical performance

ELECTROLYTE FLOWS

HYDRODYNAMIC ANALYSIS

IN-SITU TESTING

INTERDIGITATED FLOW FIELD

Overall efficiency

REDOX FLOW BATTERIES

Secondary batteries

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Applied Electrochemistry

In this paper, we present a study of the effect of electrode intrusion into the flow channel in an all-vanadium redox flow battery. Permeability, pressure drop and electrochemical performance have been measured in a cell with active area 100 cm2and 414 cm2 fitted with a carbon felt electrode of thickness of 3, 6 or 9 mm compressed to 1.5, 2.5 or 4 mm, respectively, during assembly. Results show that the pressure drop is significantly higher than what can be expected in the thick electrode case while its electrochemical performance is lower. Detailed flow analysis using computational fluid dynamics simulations in two different flow fields shows that both these results can be attributed to electrode intrusion into the flow channel leading to increased resistance to electrolyte flow through the electrode. A correlation is proposed to evaluate electrode intrusion depth as a function of compression. © 2017 Elsevier B.V.

Journal of Power Sources

Effect of electrode intrusion on pressure drop and electrochemical performance of an all-vanadium redox flow battery

In this paper, we present experimental studies of electrochemical performance of an allvanadium redox flow battery cell employing an active area of 103 cm2, activated carbon felt, and a novel flow field, which ensures good electrolyte circulation at low pressure drops. Extended testing over 151 consecutive charge/discharge cycles has shown steady performance with an energy efficiency of 84% and capacity fade of only 0.26% per cycle. Peak power density of 193 mW cm2 has been obtained at an electrolyte circulation rate of 114 ml min1, which corresponds to stoichiometric factor of 4.6. The present configuration of the cell shows 20% improved in peak power and 30% reduction in pressure drop when compared to a similar cell with a different electrode and a serpentine flow field. © Author(s) 2017.

Journal of Electrochemical Energy Conversion and Storage

High energy efficiency with low-pressure drop configuration for an all-vanadium redox flow battery

A comparative study of the electrochemical energy conversion performance of a single-cell all-vanadium redox flow battery (VRFB) fitted with three flow fields has been carried out experimentally. The charge-discharge, polarization curve, Coulombic, voltage and round-trip efficiencies of a 100 cm2 active area VRFB fitted with serpentine, interdigitated and conventional flow fields have been obtained under nearly identical experimental conditions. The effect of electrolyte circulation rate has also been investigated for each flow field. Stable performance has been obtained for each flow field for at least 40 charge/discharge cycles. Ex-situ measurements of pressure drop have been carried out using water over a range of Reynolds numbers. Together, the results show that the cell fitted with the serpentine flow field gives the highest energy efficiency, primarily due to high voltaic efficiency and also the lowest pressure drop. The electrolyte flow rate is seen to have considerable effect on the performance; a high round-trip energy efficiency of about 80% has been obtained at the highest flow rate with the serpentine flow field. The data offer interesting insights into the effect of electrolyte circulation on the performance of VRFB. © 2016 Elsevier B.V. All rights reserved.

Effect of flow field on the performance of an all-vanadium redox flow battery

Electrolyte distribution using parallel flow field for redox flow battery (RFB) applications shows severe non-uniformity, while the conventional design of using the carbon felt itself as the flow distributor gives too high pressure drop. An optimized flow field design for uniform flow distribution at a minimal parasitic power loss is therefore needed for RFB systems. Since the materials and geometrical dimensions in RFBs are very different from those used in fuel cells, the hydrodynamics of the flow fields in RFBs is likely to be very different. In the present paper, we report on a fundamental study of the hydrodynamics of a serpentine flow field relevant to RFB applications. The permeability of the porous medium has been measured under different compression ratios and this is found to be in the range of 5-8 × 10-11 m2. The pressure drop in two serpentine flow fields of different geometric characteristics has been measured over a range of Reynolds numbers. Further analysis using computational fluid dynamics simulations brings out the importance of the compression of the porous medium as an additional parameter in determining the flow distribution and pressure drop in these flow fields. © 2013 Elsevier B.V. All rights reserved.

Ex-situ experimental studies on serpentine flow field design for redox flow battery systems

The paper describes a flow field design which is based on the improvement of the local cross-flow conditions in a split serpentine flow field. The layout of the flow field is such that the cross-flow is higher in the oxygen-depleted portion of the adjacent serpentine channel in a split serpentine flow field with more than one serpentine channels. The present arrangement offers the quadruple advantage of uniform reactant distribution over the entire cell active area; low overall pressure drop, thereby reducing the parasitic power losses; effective liquid water evacuation in the U-bends; and more oxygen replenishment in the oxygen-deficient portions of the serpentine channel. Computational fluid dynamics (CFD) and experimental analysis carried out on the proposed design with three serpentine channels confirm the benefits. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.

International Journal of Hydrogen Energy

An improved serpentine flow field with enhanced cross-flow for fuel cell applications

The flow field is one of the main components of a fuel cell, which distributes the reactants to the active area of the cell and evacuates the products formed. Interdigitated flow field (IFF) is one among the different types of flow field designs that forces the reactants or products to flow through the electrode, thereby increasing the cell performance by decreasing concentration polarization loss, however, at the cost of higher-pressure drop. Prior understanding of the reactant and water vapour distribution in a flow field helps in obtaining the best flow field design. In the present paper, a model for the flow distribution and the pressure drop in an IFF has been developed using the analogy between fluid flow and electrical network in which the pressure is made analogous to the voltage and the flow rate to the current. The model, which ultimately reduces to the solution of a set of simultaneous algebraic equations, is capable of predicting the flow split among a set of inlet and outlet channels of an interdigitated flow field as well as the overall pressure drop for laminar, turbulent and two-phase flow conditions for arbitrary number of parallel channels. The results from the hydrodynamic network model have been validated against CFD simulations. This model can therefore be used for the optimization of interdigitated flow field design. © 2009.

A hydrodynamic network model for interdigitated flow fields

Serpentine flow-fields have long been used in polymer electrolyte membrane (PEM) fuel cells for effective transportation of reactants from the flow-field to the reaction sites. It has been observed in the literature that localized flooding near the U-bend region of serpentine flow-fields occurs at high current densities. This has been attributed to the boundary layer separation and recirculation of flow in the U-bend. In the present study, it is established, using computational fluid dynamics (CFD) simulations, that this is due to lower channel-to-channel cross-flow in the electrodes between consecutive serpentine channels rather than to the flow-field in the gas distribution channels. © 2008 Elsevier B.V. All rights reserved.

Effect of channel-to-channel cross-flow on local flooding in serpentine flow-fields

Parallel-channel configurations for gas-distributor plates of planar fuel cells reduce the pressure drop, but give rise to the problem of severe flow maldistribution wherein some of the channels may be starved of the reactants. This study presents an analysis of the flow distribution through parallel-channel configurations. One-dimensional models based on mass and momentum balance equations in the inlet and exhaust gas headers are developed for Z- and U-type parallel-channel configurations. The resulting coupled ordinary differential equations are solved analytically to obtain closed-form solutions for the flow distribution in the individual channels and for the pressure drop over the entire distributor plate. The models have been validated by comparing the results with those obtained from three-dimensional computational fluid dynamics (CFD) simulations. Application of the models to typical fuel-cell distributor plates shows that severe maldistribution of flow may arise in certain cases and that this can be avoided by careful choice of the dimensions of the headers and the channels. © 2004 Elsevier B.V. All rights reserved.

Journal	Journal of Applied Electrochemistry
Publisher	Kluwer Academic Publishers
ISSN	0021891X
Open Access	No