• Energy Research

Abstract In this work, the methanol steam reforming catalyst was considered into the anodic compartment of a high temperature polymer electrolyte fuel cell (HT-PEMFC), where reforming and electrochemical, reactions occur simultaneously. To avoid the anode electro-catalyst poisoning by methanol, a Pd-Ag membrane, with a thickness of a few micrometres, was considered between the reforming catalyst and the membrane electrode assembly. A 3-dimensional non-isothermal simulator was developed in Fluent (Ansys™) considering a packed bed membrane reactor cell (PBMR-C) combined with a HT-PEMFC in a single unit. The performance of the combined unit depends on the permeability, selectivity and stability of Pd-Ag membrane at 473 K. Therefore, a self-supported Pd-Ag membrane with a thickness of 4 μm, was produced with no defects by magnetron sputtering. The membrane showed a H2/N2 molar selectivity of ca. 5800 and permeability of 2.94 × 10–6 mol·m·s–1·m–2·bar−0.8 at 473 K. The novel PBMR-C/HT-PEMFC after proper validation was analysed by simulation, showing high performance, similar to the one obtained with a HT-PEMFC fed with hydrogen and allowed efficient heat integration between electrochemical and MSR reaction. The PBMR-C/HT-PEMFC also demonstrated to be very compact. The advantageous and limitations of the combined PBMR-C/HT-PEMFC unit are discussed based on the simulated results.

Abstract In this work, the methanol steam reforming catalyst was considered into the anodic compartment of a high temperature polymer electrolyte fuel cell (HT-PEMFC), where reforming and electrochemical, reactions occur simultaneously. To avoid the anode electro-catalyst poisoning by methanol, a Pd-Ag membrane, with a thickness of a few micrometres, was considered between the reforming catalyst and the membrane electrode assembly. A 3-dimensional non-isothermal simulator was developed in Fluent (Ansys™) considering a packed bed membrane reactor cell (PBMR-C) combined with a HT-PEMFC in a single unit. The performance of the combined unit depends on the permeability, selectivity and stability of Pd-Ag membrane at 473 K. Therefore, a self-supported Pd-Ag membrane with a thickness of 4 μm, was produced with no defects by magnetron sputtering. The membrane showed a H2/N2 molar selectivity of ca. 5800 and permeability of 2.94 × 10–6 mol·m·s–1·m–2·bar−0.8 at 473 K. The novel PBMR-C/HT-PEMFC after proper validation was analysed by simulation, showing high performance, similar to the one obtained with a HT-PEMFC fed with hydrogen and allowed efficient heat integration between electrochemical and MSR reaction. The PBMR-C/HT-PEMFC also demonstrated to be very compact. The advantageous and limitations of the combined PBMR-C/HT-PEMFC unit are discussed based on the simulated results.

AbstractFlow field design is crucial for achieving higher performance in polymer electrolyte membrane fuel cells (PEMFCs). This study uses a two‐phase, multi‐component, and three‐dimensional model to simulate the performance of PEMFCs that use interdigitated flow field design with intermediate blocks on the cathode side. A detailed parametric study is presented to investigate the effects of various geometric and operational parameters. Of the parameters studied, inlet mass flow rate, relative humidity, and rib width had the greatest impact on cell performance. The results show that increasing the cathode stoichiometric ratio resulted in higher fuel cell performance for blocked interdigitated designs compared to parallel designs. In addition, using cathode channels with higher height values resulted in lower PEMFC performance for all flow fields. Higher values of rib/channel width ratio resulted in lower cell performance due to liquid water accumulation in the rib regions. However, at higher rib/channel width ratios, the positive effect of using interdigitated flow designs was more pronounced. Moreover, at a low relative humidity of RH = 25%, a 10.4% higher performance was obtained for the interdigitated type II compared to cases with RH = 100%, due to more effective over‐rib convection and higher water removal.

AbstractFlow field design is crucial for achieving higher performance in polymer electrolyte membrane fuel cells (PEMFCs). This study uses a two‐phase, multi‐component, and three‐dimensional model to simulate the performance of PEMFCs that use interdigitated flow field design with intermediate blocks on the cathode side. A detailed parametric study is presented to investigate the effects of various geometric and operational parameters. Of the parameters studied, inlet mass flow rate, relative humidity, and rib width had the greatest impact on cell performance. The results show that increasing the cathode stoichiometric ratio resulted in higher fuel cell performance for blocked interdigitated designs compared to parallel designs. In addition, using cathode channels with higher height values resulted in lower PEMFC performance for all flow fields. Higher values of rib/channel width ratio resulted in lower cell performance due to liquid water accumulation in the rib regions. However, at higher rib/channel width ratios, the positive effect of using interdigitated flow designs was more pronounced. Moreover, at a low relative humidity of RH = 25%, a 10.4% higher performance was obtained for the interdigitated type II compared to cases with RH = 100%, due to more effective over‐rib convection and higher water removal.

The performance of PEMFC (Polymer Electrolyte Membrane Fuel Cells) with different configuration of gas feeding channels is investigated. Multi-component mixture model is used in order to simulate the two phase flow and transport in cathode gas diffusion layer of PEM fuel cell. This model reduces the numerical simulation complexity by reducing the number of nonlinear governing equations. A wide detailed parametric study is done to investigate different operational parameter such as; pressure difference, operating temperature, different geometrical parameters such as; gas diffusion layer thickness, and various material parameters such as porosity and wettability. Computational simulations have been conducted and the simulation results were compared with the available results in literature and showed very little difference. Results have been presented with different polarization curves, power density and local current density curves and also the plots of saturation level at catalyst layer surface. Furthermore the changes in the place of the interface between single and two phase zones is presented for further understating of the effects of different parameters. This parametric study confirms qualitatively to the validity of the considered model for systematic simulation of the PEM fuel cells.

The performance of PEMFC (Polymer Electrolyte Membrane Fuel Cells) with different configuration of gas feeding channels is investigated. Multi-component mixture model is used in order to simulate the two phase flow and transport in cathode gas diffusion layer of PEM fuel cell. This model reduces the numerical simulation complexity by reducing the number of nonlinear governing equations. A wide detailed parametric study is done to investigate different operational parameter such as; pressure difference, operating temperature, different geometrical parameters such as; gas diffusion layer thickness, and various material parameters such as porosity and wettability. Computational simulations have been conducted and the simulation results were compared with the available results in literature and showed very little difference. Results have been presented with different polarization curves, power density and local current density curves and also the plots of saturation level at catalyst layer surface. Furthermore the changes in the place of the interface between single and two phase zones is presented for further understating of the effects of different parameters. This parametric study confirms qualitatively to the validity of the considered model for systematic simulation of the PEM fuel cells.

Abstract A numerical study is performed on the effects of surface waviness and nanoparticle dispersion on solidification of Cu–water nanofluid inside a vertical enclosure for different Grashof numbers. A geometry with sinusoidally curved wavy surface can be used to enhance heat transfer performance if it is carried out in an appropriate way. Therefore, the enclosure has wavy surfaces on right side with higher temperature and left side with lower temperature, while the top and bottom walls are both flats with insulated condition. Computations are conducted for the surface waviness ranging from 0 to 0.4, Grashof number from 104 to 106 and nanoparticle dispersion from 0 to 0.1. An enthalpy porosity technique is used to trace the solid and liquid interface inside the enclosure. To validate the results, the numerical solutions for special cases in a rectangular cavity were compared with previously published works which are in good overall agreement with those results. The numerical results show that for surface waviness of 0.25 and 0.4, a maximum of 60% decrease in solidification time for Gr = 106 is observed in comparison with Gr = 105 which indicates the increasing effects of natural convection on solidification due to distortion on surface. Therefore, surface waviness can be used to control the solidification time based on enhancing different mechanism of solidification.

Abstract A numerical study is performed on the effects of surface waviness and nanoparticle dispersion on solidification of Cu–water nanofluid inside a vertical enclosure for different Grashof numbers. A geometry with sinusoidally curved wavy surface can be used to enhance heat transfer performance if it is carried out in an appropriate way. Therefore, the enclosure has wavy surfaces on right side with higher temperature and left side with lower temperature, while the top and bottom walls are both flats with insulated condition. Computations are conducted for the surface waviness ranging from 0 to 0.4, Grashof number from 104 to 106 and nanoparticle dispersion from 0 to 0.1. An enthalpy porosity technique is used to trace the solid and liquid interface inside the enclosure. To validate the results, the numerical solutions for special cases in a rectangular cavity were compared with previously published works which are in good overall agreement with those results. The numerical results show that for surface waviness of 0.25 and 0.4, a maximum of 60% decrease in solidification time for Gr = 106 is observed in comparison with Gr = 105 which indicates the increasing effects of natural convection on solidification due to distortion on surface. Therefore, surface waviness can be used to control the solidification time based on enhancing different mechanism of solidification.

Effects of Grashof number and volume fraction of Cu–water nanofluid on natural convection heat transfer and fluid flow inside a two-dimensional wavy enclosure has been investigated numerically. Also, in the presence of nanofluid, the second law of thermodynamics is applied to predict the nature of irreversibility in terms of entropy generation. Finite-Volume numerical procedure with non orthogonal body fitted collocated grid arrangement is used to solve the governing differential equations. Calculation were performed for the Grashof numbers from 104 to 106, nanoparticles volume fraction from 0% to 10% and surface waviness ranging from 0.0 to 0.4 for different patterns of wavy enclosure. Streamlines, isothermal lines, counters of local entropy generation and the variation of local and average Nusselt number are presented and compared with considering the effects of different parameters. The results show that the average heat transfer rate decreases as nanoparticles volume fraction and Grashof number increase. Also, besides decreasing heat transfer rate, the nanoparticles can be used for decreasing the entropy generation.