Faculty Publications
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Item Compressive cyclic response of PEM fuel cell gas diffusion media(Elsevier Ltd, 2021) Koorata, P.K.; Bhat, S.D.The fuel cell gas diffusion media (GDM) is a highly porous carbon-fiber-reinforced thin composite layer. The experimental response of these materials is observed to be highly nonlinear at low-stress levels. The cyclic mechanical response of GDM is investigated in terms of stiffness and damage parameters. The prediction of the state of deformation in GDM is vital in relating GDM's properties to ohmic and transport losses. To this end, a compressible form of the phenomenological model is proposed to capture the experimental cyclic response accurately. The model is constituent dependent; that is, the cumulative cyclic stress-strain response of GDM is a function of individual constituent phases present in the material. These individual constituents are porous matrix and reinforced fibers. The model hence derived for a typical GDM material, can predict residual strain, hysteresis, and damage quotient associated with the stress softening. This advanced model is implemented in the numerical domain to evaluate the response of the polymer electrolyte fuel cell (PEFC) unit cell. The stress-strain distribution fields are analyzed and compared with those of conventional GDM models. The results point to a remarkable deviation from the conventional notion of structural analysis. © 2020 Hydrogen Energy Publications LLCItem Numerical investigation on the sensitivity of endplate design and gas diffusion material models in quantifying localized interface and bulk electrical resistance(Elsevier Ltd, 2021) Shinde, U.; Koorata, P.K.A localized non-intuitive relationship between electrical interface contact resistance and bulk properties such as bulk electrical resistance and permeability in the fuel cell gas diffusion layer (GDL) is reported. A numerical method is adopted to investigate contact pressure and hence the interface contact resistance at the interfaces of bipolar plate (BPP)|GDL and GDL|Polymer electrolyte membrane (PEM). The results are observed to be sensitive to GDL material models as well as endplate designs. This means, endplates designed to improve the electrical contact resistance or contact pressure at the BPP|GDL interface may not necessarily assure an improvement in bulk properties, in fact, it is observed in this study that these properties are inversely related. Further, a differential deformation in GDL along with consolidation effect is predicted with compressible version of hyperelastic material model. More importantly, it is revealed that the selection of material models plays a significant role in the deformation behaviour of the GDLs irrespective of the clamping design adopted. © 2021 Hydrogen Energy Publications LLCItem Numerical investigation on the improved reactant mass transport with depth-dependent flow fields in polymer electrolyte fuel cell under inhomogeneous gas diffusion layer compression(Elsevier Ltd, 2021) Padavu, P.; Koorata, P.K.; Bhat, S.D.In this work, a numerical model is developed to analyse the effects of depth-dependent reactant flow field geometry under inhomogeneous gas diffusion layer (GDL) compression on the mass transport process and performance of polymer electrolyte fuel cell (PEFC). The types of depth-dependent flow channels considered in this study are: converging channel (depth continuously decreasing) and diverging channel (depth continuously increasing), and the conventional flow field designs. The model is investigated for local and global inhomogeneity due to GDL compression. The localized inhomogeneity is introduced in the flow-field rib as well as channel regions. The results are compared for reactant concentration, water concentration, local current density, and the polarization curve for different flow channel combinations. It is observed that the availability of reactants is higher in case of converging channel design, which leads to an increase in cell performance at higher currents. However, this is subjected to GDL inhomogeneity in compression. We observe in this study that such inhomogeneity, instead of having a significant impact on cell performance, lead to minimal influence in terms of reduction in cell performance. This we observe is due to improved H2 availability at anode and reduced O2 distribution at cathode that ultimately impacts respective hydrogen oxidation reaction (HOR) and reduction in oxygen reduction reaction (ORR). This study aims to investigate the cases for altered variation in cell performance due to change in depth-dependent flow fields. © 2021Item Electrical/flow heterogeneity of gas diffusion layer and inlet humidity induced performance variation in polymer electrolyte fuel cells(Elsevier Ltd, 2023) Shinde, U.; Koorata, P.K.; Padavu, P.A three-dimensional single-flow channel computational model is used to investigate the performance characteristics of polymer electrolyte fuel cells (PEFC). The combined influence of non-uniform interfacial contact resistance (ICR) and inlet relative humidity (RH), along with the heterogeneous flow properties of the gas diffusion layer (GDL) on the PEFC performance is evaluated. The study considers combinations of full and partial humidification of anode and cathode reactants. Results reveal heterogeneous GDL with non-uniform ICR distribution results in a slight ∼4.4% reduction in current density at 0.3V compared to the homogeneous case. However, under same electrical/flow heterogeneities, the current density is observed to increase by ∼19% to ∼1.3A/cm2 under fully humidified anode and partially humidified cathode (i.e., RHa|RHc = 100%|60%) as compared to ∼1.1A/cm2 under symmetric RHa|RHc = 100%|100%. Interesting observations are made on the temperature distribution and cathodic water fractions. The variation in anodic inlet humidity is observed to have no impact on temperature distribution in the membrane, whereas variation in cathodic inlet humidity is effective in reducing the temperature in the channel regime with a 4K (kelvin) difference among all the cases. It is noted here that the overpotential map is not an indicator for performance loss, at least at full inlet humidity. This parameter is observed to depend on water concentration in the cathode. The study provides a detailed analysis of the distribution of reactant mass fraction, water concentration, current density, temperature, cathodic overpotential, and cell performance for all the simulated cases. © 2022 Hydrogen Energy Publications LLCItem Model based evaluation of water management and membrane hydration in polymer electrolyte fuel cell with reactant flow-field gradients(Elsevier Ltd, 2023) Padavu, P.; Koorata, P.K.; Kattimani, S.Efficient water management and intrinsic membrane hydration are critical requirements of polymer electrolyte fuel cells (PEFC) under high load current. PEFC undergoes performance loss during high current demand due to reactant depletion, water flooding, and membrane hydration. Hence, water management and membrane hydration become vital for endured life of PEFC itself. Further, flow field optimization assists in overcoming the critical transport factors affecting the PEFC performance. A model-based approach is envisioned to understand effective water management wherein reactant flow channel gradients are designed to investigate its advantages and limitations. Here, we show efficient water management of these cells at high current demand where reactant distribution governs the cell characteristics. On comparing the current density distribution of the flow field designs under both Maximum Humid and Partial Humid inlet conditions, we observe a 16.46% increase in current density distribution in converging design (partial humid condition) compared to the lowest current density obtained in diverging design (max humid condition) at 0.4 V. Further, we observed that the current density distribution in the converging design improved by 3.68% and 6.19% compared to the straight (conventional) and diverging design, respectively, under max humid condition at 0.4 V. Similarly, under the partial humid condition, the current density improved in the converging design by 3.46% and 4.98% compared to conventional and diverging designs respectively at 0.4 V. Using a comprehensive numerical analysis of reactant flow channel gradient designs, we show that the membrane hydration of operating cells is controlled through variation in transport characteristics. © 2023 Elsevier LtdItem Numerical investigation on the effects of inhomogeneous gas diffusion layer and impact of interfacial contact resistance on the performance of polymer electrolyte fuel cells(Elsevier Ltd, 2024) Shinde, U.; Koorata, P.K.; Padavu, P.In this study, a three-dimensional single channel is numerically modeled to simulate the polymer electrolyte fuel cell (PEFC) with a homogeneous and inhomogeneous gas diffusion layer (GDL). The influence of interfacial contact resistance (ICR) between GDL and current collector ribs (GDL|CC) is also studied. In the present study, GDL is considered as a single component (homogeneous) in one case and inhomogeneous with varying electrical and flow properties to illustrate the inhomogeneity in another case. The inhomogeneity in GDL is primarily caused by localized deformation due to non-uniform contact pressure during fuel cell assemblies. The consideration of ICR is observed to have a significant effect on both the ohmic and mass transport regions of the polarization curve. Inhomogeneous GDL with ICR, considered close to a practical scenario, shows a ∼7% drop in performance evaluation at 0.3V. The study reveals increased consumption of reactants at higher current loads when ICR is assumed negligible. This study examines the effects of homogeneous GDL, inhomogeneous GDL, and the impact of ICR on the distributions of reactant concentration, water concentration, temperature, current density, and polarization curve in PEFC. This study presents the practical aspects of PEFC considering inhomogeneous GDL electrical and flow properties. © 2023 Hydrogen Energy Publications LLCItem Low stress creep response of PTFE sealants applied to PEM fuel cells(John Wiley and Sons Inc, 2024) Kumar, V.; Koorata, P.K.Viscoelastic properties of polytetrafluoroethylene (PTFE) play a crucial role in forecasting its long-term behavior in engineering applications. An attempt is made to explore the viscoelastic properties of PTFE sealants that are utilized in polymer electrolyte membrane fuel cell (PEMFC). It is to be noted that PTFE sealants are vulnerable to creep under constant loading at elevated temperatures. Moreover, the creep of sealants will lead to leakage of reactants from the cell, which affects the performance of PEMFC. PTFE is an excellent choice as a sealant material in low-temperature polymer electrolyte membrane fuel cell (LT-PEMFC), which operates in the temperature range of 60–80°C. PTFE can be prominently used as sealants in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC), as it possesses no significant change in its physical properties within the temperature range of −150 to 300°C along with the working conditions of HT-PEMFC. In LT-PEMFC, the sealants will typically be subjected to low stresses in the range of 1–5 MPa. In this article, the creep response of PTFE sealant material is extensively studied at various temperatures of 25 (room temperature), 35, 45, 55, and 65°C and at three stress levels of 2, 3, and 4 MPa. The time–temperature superposition principle is utilized to develop master curve at a reference temperature of 25°C, to forecast long-term creep characteristics of PTFE sealants. Moreover, the master curve for creep compliance is developed for 4.5 h. © 2024 Wiley Periodicals LLC.