Hydrodynamic modelling of direct methanol liquid feed fuel cell stacks (original) (raw)
Related papers
Modeling Flow Distribution for Internally Manifolded Direct Methanol Fuel Cell Stacks
Chemical Engineering & Technology, 2000
A model is presented for the liquid feed direct methanol fuel cell, which describes the hydraulic behavior of an internally manifolded cell stack. The model is based on the homogeneous two-phase flow theory and mass conservation equation. The model predicts the pressure drop behavior of an individual fuel cell, and is used to calculate flow distribution through fuel cell stack internal manifolds. The flow distribution of the two-phase fluids in the anode and the cathode chambers is predicted as a function of cell operating parameters. An iterative numerical scheme is used to solve the differential equations for longitudinal momentum and continuity.
Modelling Transport Phenomena and Performance of Direct Methanol Fuel Cell Stacks
Chemical Engineering Research and Design, 2000
A prototype direct methanol fuel cell (DMFC) stack has been designed and built at Newcastle University, based on a¯ow bed design developed with the aid of ā ow visualization study and¯uid¯ow modelling. In addition, a series of engineering models have been developed that predict the stack voltage,¯uid distribution from the stack manifolds, the overall system pressure, the chemical equilibrium in both anode and cathode¯ow beds and the thermal management of the stack. The results of this work are presented in terms of an overall engineering model that incorporates all the aforementioned models. The initial steady state performance data of the prototype stack presented was obtained as a result of our experience of scaling up the system to achieve the designed power outputs.
Pressure drop modelling for liquid feed direct methanol fuel cells
Chemical Engineering Journal, 1999
A pressure drop model is presented for the direct methanol fuel cell, based on the homogeneous two-phase¯ow theory and mass conservation equation, which describes the hydraulic behaviour of an experimental large cell (active area 272 cm 2). The model allows an assessment of the effect of operating parameters, e.g. temperature gradient, current density,¯ow rate and pressure on pressure losses in the anode and the cathode side of the cell. It is designed to assist the fuel cell system designer to estimate¯ow and pumping requirements, tube sizing and auxiliary equipment and to be used to calculate¯ow distribution through fuel cell stack manifolds.
Pressure and flow distribution in internal gas manifolds of a fuel-cell stack
Journal of Power Sources, 2003
Gas-flow dynamics in internal gas manifolds of a fuel-cell stack are analyzed to investigate overall pressure variation and flow distribution. Different gas-flow patterns are considered in this analysis. Gas-flow through gas channels of each cell is modeled by means of Darcy's law where permeability should be determined on an experimental basis. Gas-flow in manifolds is modeled from the macroscopic mechanical energy balance with pressure-loss by wall friction and geometrical effects. A systematic algorithm to solve the proposed flow model is suggested to calculate pressure and flow distribution in fuel-cell stacks. Calculation is done for a 100-cell molten carbonate fuel-cell stack with internal manifolds. The results show that the pressure-loss by wall friction is negligible compared with the pressure recovery in inlet manifolds or loss in outlet manifolds due to mass dividing or combining flow at manifold-cell junctions. A more significant effect on manifold pressure possibly arises from the geometrical manifold structure which depends on the manifold size and shape. The geometrical effect is approximated from pressure-loss coefficients of several types of fittings and valves. The overall pressure and flow distribution is significantly affected by the value of the geometrical pressure-loss coefficient. It is also found that the flow in manifolds is mostly turbulent in the 100-cell stack and this way result in an uneven flow distribution when the stack manifold is incorrectly, designed.
Fluid dynamic study of fuel cell devices: simulation and experimental validation
Journal of Power Sources, 1994
The paper is concerned with the mass flow distribution in fuel cell stacks. In particular, the flow through the manifold system connected to the parallel arrangement of the cell channels is modelled and numerically treated. The numerical results are recognized to be more realistic than those obtained by means of an approximate analytical solution since more detailed effects could be accounted for. This evidence is confirmed by experiments carried out at a stack model device consisting of 100 cells. Pressure and velocity distributions were measured for various Reynolds numbers and geometrical shapes of the manifolds. The agreement between the experimental and numerical results is good. Keywordsr Fuel cell stacks; Fluid dynamic study 0378-7753/94/$07.00 0 1994 Elsevier Science S.A. All rights resewed SSDI 0378-7753(94)02014-T
Flow distribution in the manifold of PEM fuel cell stack
Journal of Power Sources, 2007
In this study, the pressure variation and the flow distribution in the manifold of a fuel-cell stack are simulated by a computational fluid dynamics (CFD) approach. Two dimensional stack model composed of 72 cells filled with porous media is constructed to evaluate pressure drop caused by channel flow resistance. In order to simplify this model, electrochemical reactions, heat and mass transport phenomena are ignored and air is treated as working fluid to investigate flow distribution in stacks. Design parameters such as the permeability of the porous media, the manifold width and the air feeding rate were changed to estimate uniformity of the flow distribution in the manifold. A momentum-balance theory and a pressure-drop model are presented to explain the physical mechanism of flow distribution. Modeling results indicate that both the channel resistance and the manifold width can enhance the uniformity of the flow distribution. In addition, a lower air feeding rate can also enhance the uniformity of flow distribution. However, excessive pressure drop is not beneficial for realistic applications of a fuel-cell stack and hence enhanced manifold width is a better solution for flow distribution.
International Journal of Hydrogen Energy, 2017
In this study, a three dimensional model is constructed to investigate the flow distributions and the pressure variations for a 40-cell solid oxide fuel cell (SOFC) stack. Computational fluid dynamics (CFD) is used to optimize the design parameters of external manifold in the stack. The model consists of equations for the network with chamber structure of manifold. Simulation results indicate that the flow uniformity strongly depends on geometric shapes of manifold, including the joined position between tube and manifold, the dimension of manifold and the number of tubes. The ratio of flow velocity which describes the uniformity of flow distribution can be decreased by optimizing the geometrical structure of manifolds. In addition, it is
A Multi-Fluid Model for Water and Methanol Transport in a Direct Methanol Fuel Cell
Energies
Direct-methanol fuel cell (DMFC) systems are comparatively simple, sometimes just requiring a fuel cartridge and a fuel cell stack with appropriate control devices. The key challenge in these systems is the accurate determination and control of the flow rates and the appropriate mixture of methanol and water, and fundamental understanding can be gained by computational fluid dynamics. In this work, a three-dimensional, steady-state, two-phase, multi-component and non-isothermal DMFC model is presented. The model is based on the Eulerian approach, and it can account for gas and liquid transport in porous media subject to mixed wettability, i.e., the simultaneous presence of hydrophilic and hydrophobic pores. Other phenomena considered are variations in surface tension due to water–methanol mixing and the capillary pressure at the gas diffusion layer–channel interface. Another important aspect of DMFC modeling is the transport of methanol and water across the membrane. In this model, ...
Modelling of polymer electrolyte membrane fuel cell stacks based on a hydraulic network approach
International Journal of Energy Research, 2004
Polymer electrolyte membrane (PEM) fuel cells convert the chemical energy of hydrogen and oxygen directly into electrical energy. Waste heat and water are the reaction by-products, making PEM fuel cells a promising zero-emission power source for transportation and stationary co-generation applications. In this study, a mathematical model of a PEM fuel cell stack is formulated. The distributions of the pressure and mass flow rate for the fuel and oxidant streams in the stack are determined with a hydraulic network analysis. Using these distributions as operating conditions, the performance of each cell in the stack is determined with a mathematical, single cell model that has been developed previously. The stack model has been applied to PEM fuel cell stacks with two common stack configurations: the U and Z stack design. The former is designed such that the reactant streams enter and exit the stack on the same end, while the latter has reactant streams entering and exiting on opposite ends. The stack analysed consists of 50 individual active cells with fully humidified H 2 or reformate as fuel and humidified O 2 or air as the oxidant. It is found that the average voltage of the cells in the stack is lower than the voltage of the cell operating individually, and this difference in the cell performance is significantly larger for reformate/air reactants when compared to the H 2 =O 2 reactants. It is observed that the performance degradation for cells operating within a stack results from the unequal distribution of reactant mass flow among the cells in the stack. It is shown that strategies for performance improvement rely on obtaining a uniform reactant distribution within the stack, and include increasing stack manifold size, decreasing the number of gas flow channels per bipolar plate, and judicially varying the resistance to mass flow in the gas flow channels from cell to cell.
One-dimensional thermal model for direct methanol fuel cell stacks
Journal of Power Sources, 1999
Ž .Ž. Using the one-dimensional thermal model for the direct methanol fuel cell DMFC presented in Part 1 , based on the differential Ž 2. thermal energy conservation equation, which describes the thermal behaviour of a DMFC stack comprised of up to 25 large 272 cm cells, temperature profiles are predicted along the stack length. The model is used to assess the effect of operating parameters Ž. temperature gradient, current density, flow rate and pressure on the temperature profile along the stack. In addition, it enables investigation of the stack thermal management and the effect of altering a number of systematic parameters such as the number of cells in the stack, the active and exposed area and the interactions between the physical properties of the various components. The model aids the fuel cell system designer to gain an insight in the stack structure and select materials and geometric configurations that are optimal from a thermal management point of view.