S. Jayanti

Hydrodynamic analysis of flow fields for redox flow battery applications

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.

Shape optimization of flow split ducting elements using an improved Box complex method

ABSTRACT Iterative search methods, such as the Box complex method, can be used for inverse shape design problems. In the present article, an improved version of the Box complex method is proposed specifically for computational fluid dynamics-based optimization of fluid flow ducting elements. The original Box complex method is improved by (1) assigning non-uniform weights for the estimation of the centroid, (2) using a reduced reflection factor for accelerated convergence, and (3) introducing measures to prevent premature breakdown of the iterative process. The success of the improved Box complex method over the original Box complex method is demonstrated on two benchmark functions and by applying it to two fluid flow problems of engineering. The improved method is shown to substantially accelerate the convergence with approximately 50% reduction in computational effort for the T-junction and manifold problems.

An Improved Model to Predict Flooding/Dehydration in PEM Fuel Cells

Maintaining proper water balance between the production of water due to reaction and its removal by evaporation is very important for the successful operation of a Polymer Electrolyte Membrane (PEM) fuel cell. Imbalance between the two processes can result in either flooding of the electrodes/ gas channels or the dehydration of the membrane. The water management issue is especially critical for ambient temperature operation of the fuel cell. Several experimental and theoretical studies relevant to water management have been carried out to investigate means of reducing the flooding of electrodes/channels or the dehydration of membrane. Bernardi [9] and Wang et al. [11] have developed theoretical models for the prediction of when flooding/dehydration may take place. In the present study, an improved model is developed which combines the advantages of these two models. The Bernardi [9] model is extended to include mass transfer resistances. Following Wang et al. [11], the Stefan-Maxwell description of multicomponent diffusion is replaced by Fickian diffusion. In addition, water vapour diffusion to both anode and cathode sides is included in the model. The overall model is in the form of a closed-form expression for the critical or threshold or balance current density at which the water production rate and the water vapour evacuation rate are exactly balanced. The model shows that the balance current density is a function of operating conditions, properties of electrode, flow and geometric parameters in the gas channels. It has been validated by comparing the predictions with the experimental data of Tuber et al. [5] and Eckl et al. [8].Copyright