Finite Volume Method Used for Numerical Investigations of Electrochemical Devices

Abstract

The chapter provides a general overview on the Finite Volume MethodFinite Volume Method (FVM) and on Computational Fluid DynamicComputational Fluid Dynamic (CFD). It introduces the FVM by using a general scalar transport equation and it describes the main steps of a CFD investigation. All these are applied to the mass, momentum, species, energy and potential conservation equations, equations that govern the operation of Proton Exchange Membrane (PEM) fuel cells. The importance of spatial discretizationSpatial discretization and of interpolation schemesInterpolation schemes used in CFD investigations is point out by analysing few parameters with impact on the fuel cellFuel cell operation. Two cases have been considered. First case based on a fuel cell with a simplified configuration, namely a single serpentine channel, revealed the influence of spatial discretization on the accuracy of the simulation results with regards to current density, pressure and temperature. The second case based on a lab-scale fuel cell with two configurations for channels (7 serpentine and 7 parallel) have been used to analyse the effect of three interpolation schemes (first order, second order, QUICK) on the PEM fuel cell operation; therefore, pressure, hydrogen and water mass fraction profiles were considered for comparison. It was found out that besides the differences in the results accuracy due to spatial discretization and interpolation schemes, the design/geometry used in the CFD investigation may or may not emphasize these differences. If for the 7-serpentine channels fuel cell the interpolation scheme did not show much changes in the accuracy of the results not the same conclusion was drawn for the 7-parallel channels fuel cell where the accuracy of the results improved with increasing the order of the interpolation scheme. A mesh-independent solution on a well-posed problem will provide valuable and accurate results only if the numerical methods are appropriate and the interpolation schemes are of high order. The modeling of fuel cells using CFD techniques, as of any other device, can be an important alternative to the experiment, providing information that is critical to design, operation and optimization, the requirement being to use appropriate model, assumptions and boundary conditions and, of course, an adequate numerical method.