Browsing by Author "Koorata, Poornesh Kumar"

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Effects of Gas Diffusion Layer Compression on Electromechanical Properties and Polymer Electrolyte Fuel Cell Performance
(National Institute Of Technology Karnataka Surathkal, 2023) Shinde, Umesh; Koorata, Poornesh Kumar
The Gas diffusion layer (GDL) is an essential functional component of the Polymer electrolyte fuel cells (PEFC) as it enables the efficient transport of reactants and offers mechanical stability. The influence of compressive loads on the performance of GDL has been the subject of extensive research. In this thesis, a numerical method is explored to investigate interface properties in the bipolar plate (BPP)|GDL and GDL|Polymer electrolyte membrane (PEM) under material and geometrical heterogeneities. Observations indicate that the results are sensitive to GDL material models and endplate designs. This implies that endplates designed to improve the electrical contact resistance and contact pressure at the BPP|GDL interface may not necessarily guarantee an improvement in bulk properties due to a localised, nonintuitive relationship between the electrical interface contact resistance (ICR) and bulk properties. The combined influence of non-uniform ICR and inlet relative humidity (RH), on a single flow channel, along with the heterogeneous flow properties of the GDL, is considered for the PEFC performance evaluation. The results indicate that heterogeneous GDL with non-uniform ICR distribution leads to a ~4.4% decrease in current density at 0.3V compared to homogeneous GDL under full humidification. However, the current density increases by ~19% under fully humidified anode and a partially humidified cathode. Furthermore, the GDL heterogeneity caused by the two clamping designs is simulated to predict the transport characteristics and performance of a 25cm2 active area PEFC. Compared to the conventional endplate design, the proposed endplate configuration offers increased cell performance, which may result from the uniform GDL properties. In addition, the experimental cyclic response of commercially available GDLs with/without MPL (microporous layer) is envisioned for mechanical response at various temperatures and hotpress conditions. The GDL with MPL has a substantial strain response with low force resistance, but GDL w/o MPL has a higher stress-to-strain ratio. The significance of pre- and post-hotpress conditions demonstrated that mechanical response increased by more than 120% in post-hotpress conditions. The thesis concludes with a newly developed phenomenological material model to predict cyclic electrical conductivity in GDLs.
Kinetics/Kinematics of Intact and Arthritic Knee Cartilages and A Novel Approach to Enhance Wear Characteristics of Uhmwpe Tibial Inserts for Prosthetic Knee
(National Institute Of Technology Karnataka Surathkal, 2023) R, Vaishakh; Koorata, Poornesh Kumar
Osteoarthritis is a severe and progressive disorder that affects the knee joint due to cartilage degradation from daily rigours activities. Articular cartilage is more susceptible to knee arthritis compared with other soft tissues. Hence, understanding degradation phenomena are more critical and require understanding the tissue's stress fields. Experimental methods have limitations, such as inaccessible cadaveric knees and obtaining in-vivo data from intact and arthritic knees is difficult and imprecise. Hence the numerical method is the most effective technique for understanding the cartilage’s mechanical behaviours under different conditions. The cartilage constituents make the cartilage geometrically and mechanically heterogeneous. A 3D finite element knee joint model is used to compute the articular cartilage response during multiple activities. Various material models are available to model the heterogeneity of articular cartilage. Multiple constitutive models are compared for the prediction of mechanical response. In addition, the influence of the inhomogeneous distribution of collagen fiber in cartilage is investigated for intact and arthritic knee kinematics cases. In reality, the cartilage structure is heterogeneous, and the computational study shows the importance of heterogeneity in the mechanical response of the knee joint. Conventionally the knee implant-bearing material (UHMWPE) is homogeneous. Incorporating the heterogeneous characteristics in the bearing material may help enhance the implant's mechanical characteristics. The proposed model generates property-modulated characteristics in the bearing material using gamma irradiation, and the heterogeneous characteristics are incorporated into the knee implant. UHMWPE's tribological and chemical characteristics are analysed experimentally, and the wear rate and volume are calculated. The wear rate decreases as the radiation dose increase to a particular level and then increases as the dose increases further. Compared with the conventional technique, a reduction in wear rate for the material is observed for the proposed technique. Also, the hardness of the UHMWPE is measured, and its value increases as the irradiation dose increases.
Kinetics/Kinematics of Intact and Arthritic Knee Cartilages and A Novel Approach to Enhance Wear Characteristics of Uhmwpe Tibial Inserts for Prosthetic Knee
(National Institute Of Technology Karnataka Surathkal, 2023) R, Vaishakh; Koorata, Poornesh Kumar
Osteoarthritis is a severe and progressive disorder that affects the knee joint due to cartilage degradation from daily rigours activities. Articular cartilage is more susceptible to knee arthritis compared with other soft tissues. Hence, understanding degradation phenomena are more critical and require understanding the tissue's stress fields. Experimental methods have limitations, such as inaccessible cadaveric knees and obtaining in-vivo data from intact and arthritic knees is difficult and imprecise. Hence the numerical method is the most effective technique for understanding the cartilage’s mechanical behaviours under different conditions. The cartilage constituents make the cartilage geometrically and mechanically heterogeneous. A 3D finite element knee joint model is used to compute the articular cartilage response during multiple activities. Various material models are available to model the heterogeneity of articular cartilage. Multiple constitutive models are compared for the prediction of mechanical response. In addition, the influence of the inhomogeneous distribution of collagen fiber in cartilage is investigated for intact and arthritic knee kinematics cases. In reality, the cartilage structure is heterogeneous, and the computational study shows the importance of heterogeneity in the mechanical response of the knee joint. Conventionally the knee implant-bearing material (UHMWPE) is homogeneous. Incorporating the heterogeneous characteristics in the bearing material may help enhance the implant's mechanical characteristics. The proposed model generates property-modulated characteristics in the bearing material using gamma irradiation, and the heterogeneous characteristics are incorporated into the knee implant. UHMWPE's tribological and chemical characteristics are analysed experimentally, and the wear rate and volume are calculated. The wear rate decreases as the radiation dose increase to a particular level and then increases as the dose increases further. Compared with the conventional technique, a reduction in wear rate for the material is observed for the proposed technique. Also, the hardness of the UHMWPE is measured, and its value increases as the irradiation dose increases.
Thermomechanical Stability of Low and High-Temperature Pem Fuel Cell Sealants
(National Institute Of Technology Karnataka, Surathkal., 2024) Kumar, Vikas; Koorata, Poornesh Kumar
Sealants are vital components in Polymer electrolyte membrane fuel cell or PEM fuel cell that prevent the leakage of reactant gases from the perimeter of the cell. The sealants also help to avoid the direct mixing of reactant gases in the cell and provide insulation between the anode and cathode electrode of the cell. The present thesis emphasizes the physical and chemical characteristics of commercial sealant materials silicone rubber, ethylene propylene diene monomer (EPDM) rubber, fluoroelastomer (FKM) rubber, and polytetrafluoroethylene (PTFE). In addition, the time-dependent viscoelastic property, particularly the creep characteristics of PTFE sealant is investigated. In PEM fuel cell, the components are subjected to an assembly pressure of 1–5 MPa, leading to compressive stress in the components. Therefore, the creep response of PTFE sealant is explored at various temperatures in the range of 25–65ºC, at three stress levels of 2 MPa, 3 MPa, and 4 MPa. The time-temperature superposition (TTS) method is employed to construct the creep compliance master curve at a reference temperature of 25°C, and thereby, to predict the long-term creep behavior of PTFE sealant. The creep compliance master curve obtained offers the prediction for 4.5 hours. The present thesis further investigates in detail the influence of PTFE sealants’ accelerated creep on the performance of a 1cm2 active area PEM fuel cell. It is reported that at the cell voltage of 0.4V, the current density for case 1 (without creep) and case 2 (sealants’ accelerated creep) are 1.309655 and 1.041806 Acm-2, respectively. Furthermore, an experimental investigation is carried out to examine the collective impact of relative humidity (RH) and temperature on the dynamic viscoelastic characteristics of EPDM, FKM, and PTFE sealants in PEMFCs. These three sealants are subjected to four different RH conditions of 0, 50, 70, and 90% during the temperature sweep test from room temperature (RT) up to 90°C. Similarly, these sealants are exposed to four different temperatures of 30, 45, 60, and 80°C, during the RH sweep test conducted from 5 to 90% RH. The findings from the dynamic properties, which include the storage modulus (E’), and loss modulus (E”) of the sealants indicate that the degradation of PTFE sealant is the least, while that of FKM sealant is highest, under the combined temperature and RH environmental conditions of PEMFC.