Eru Kurihara

Nonlinear analysis of periodic modulation in resonances of cylindrical and spherical acoustic standing waves

The nonlinear resonance of cylindrical acoustic standing waves of an ideal gas contained between two coaxial cylinders is theoretically investigated by the method of multiple scales. The wave motion concerned is excited by a small-amplitude harmonic oscillation of the radius of the outer cylinder, and the formulation of the problem includes the wave phenomenon in a hollow cylinder without the inner one as a limiting case. The spherical standing wave in two concentric spheres is also studied in parallel. The resonance occurs if the driving frequency falls in a narrow band around the linear resonance frequency, and in the weakly nonlinear regime, no shock wave is formed in contrast to the plane wave resonance. A cubic nonlinear equation for complex wave amplitude can then be derived by the method of multiple scales. Using a first integral of the cubic nonlinear equation, we shall demonstrate that the resonant oscillation is accompanied by a periodic modulation of amplitude and phase when the dissipation eff...

Transport Phenomena Within the Cathode for a Polymer Electrolyte Fuel Cell

A one-dimensional two-phase steady model is developed to analyze the coupled phenomena of cathode flooding and mass-transport limitation for a polymer electrolyte fuel cell. In the model, the liquid water transport in the porous electrode is driven by the capillary force based on Darcys law, while the gas transport is driven by the concentration gradient based on Ficks law. Furthermore, the catalyst layer is treated as a separate computational domain. The capillary pressure continuity is imposed on the interface between the catalyst layer and the gas diffusion layer. Additionally, through Tafel kinetics, the mass transport and the electrochemical reaction are coupled together. The saturation jump at the interface between the gas diffusion layer and the catalyst layer is captured in the results. Meanwhile, the results further indicate that the flooding situation in the catalyst layer is much more serious than that in the gas diffusion layer. Moreover, the saturation level inside the cathode is largely related to the physical, material, and operating parameters. In order to effectively prevent flooding, one should first remove the liquid water residing inside the catalyst layer and keep the boundary value of the liquid water saturation as low as possible.

Decision of the Best Blend Proportional Factor Value of Two Staggered Grids Used in LBM for PEFC Simulation

The appropriate blend proportional factor value which combines two kinds of staggered grids used in Lattice Boltzmann Method (LBM) for simulating the multiphase flow phenomena with large density ratio in the Polymer electrolyte fuel cell (PEFC) is fixed on. The shape deformation of the water droplet is found when using the two kinds of staggered grids to prevent the pressure oscillation when solving the Poisson equation of this LBM model and the shape of the water droplet varies with the changes of the blend proportional factor values. Two methods are adopted to find out the two staggered grids’ appropriate blend proportional factor value that can diminish or minimize the deformation of the droplet. The first one is to compare the simulation results of different blend proportional factors with the theoretical value and find the one mostly approaches the theoretical value; the second one is to compare the current velocity divergences of the two staggered grids using the results calculated by different blend proportional factor values. A water droplet resting in a tunnel is simulated with different blend proportional factor values and the appropriate value is decided.Copyright

Numerical Study of Pressure Drop in the Separator Channel and Gas Diffusion Layer of Polymer Electrolyte Fuel Cell and Deformation Effect of Porous Media

The flow behavior in the separator channel and gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC) has been investigated by using a transient, isothermal and three-dimensional numerical model. Gas channel and gas diffusion layers are considered as the important parts of PEFC as they transport reactant gases to the catalyst layer and also byproduct from the catalyst layer. The deformation of GDL plays an important role on the performance of polymer electrolyte fuel cell since the physical properties such as porosity and permeability of the GDL and the cross sectional area of the gas channel are affected by the structural deformation of GDL. In this present investigation, non-uniform deformations shape of GDL are taken into consideration and chosen as in the experimental data. Numerical simulations are performed for a wide range of porosity and permeability values. Further, the effects of these parameters on the pressure distribution are measured. It is revealed that the increase of porosity and permeability parameter caused the decrease of pressure drop (difference of pressure from inlet and outlet) but the decreasing rate is not uniform. It is also found that there is an effective range of porosity and permeability values for which these parameters have a very strong effect on the pressure drop. The results obtained by numerical simulation are also compared with the experimental as well as theoretical solution.Copyright

Nonlinear Resonant Oscillations Generated between Two Coaxial or Eccentric Cylinders

A resonant gas oscillation generated between two coaxial or eccentric cylinders is studied. In the resonance of plane waves, it is known that shock waves can be generated in an acoustic resonator even if the acoustic Mach number M is sufficiently small. In contrast to the plane wave, however, the resonance of the cylindrical wave does not always show such a discontinuity. In this case, a periodical amplitude modulation of the resonant oscillation of the gas is observed. In the resonant oscillation generated between two eccentric cylinders, depending on the frequency of the sound source (the outer cylinder), the oscillation or pulsation mode can be generated even if the sound source pulsates symmetrically about the axis.

Dynamics of an aspherical bubble oscillating near a rigid sphere

Behavior of a non-spherical bubble oscillating near a rigid sphere was investigated in the framework of the Lagrangian formalism and multipole expansion of the bubble boundary. In this study, shape oscillations of the bubble are taken into account up to the third oscillation mode (octupole mode) to illustrate the liquid jet formation on the bubble surface. To account for interaction between the bubble and the rigid sphere, corrections of the velocity potential in a liquid containing the bubble and the sphere will be considered up to terms of fifth order in the inverse separation distance. Derived equations describes typical bubble behavior such as volume oscillations, translation, and shape oscillations. This paper presents the motion of the bubble in the vicinity of the rigid sphere by using numerical computations of the equations. In particular, it is discussed that the dependencies of bubble behavior on the density and radius of the sphere.

Transport Phenomena Within the Porous Cathode for PEM Fuel Cell

In the paper, a two-phase, one-dimensional steady model of a proton exchange membrane fuel cell is developed for the porous cathode electrode. The interacted phenomena of cathode flooding and mass-transport limiting are investigated. In the model, the catalyst layer is treated as a separate computational domain with finite thickness and structure. Furthermore, through the Tafel kinetics, the mass transport processes of oxygen and liquid water are coupled. The transport of liquid water across the porous electrode is driven by the capillary force based on the Darcy’s law. However, the transport of gas is driven by the concentration gradient based on the Fick’s law. From the simulated results, it is found that the thin catalyst layer is very detriment for better understanding of the concurrent phenomena inside the electrode of a fuel cell, particularly, the flooding phenomena. More importantly, the saturation-level jump at the gas diffusion layer and catalyst layer interface is attained in order to satisfy the continuity of the capillary pressure on both sides of the GDL and CL interface. Meanwhile, the results show that the flooding phenomenon within the CL is more serious than that in the GDL, which has a significant influence on the mass transport of oxygen. Finally, the effect of some important parameters, such as the boundary value of saturation, absolute permeability, the cathode surface overpotential, on the saturation distribution inside the electrode is also obtained.Copyright

Numerical Simulation of Nonlinear Resonant Oscillations in an Elliptical Cylinder

A resonant gas oscillation generated in a cylinder with elliptical cross section is numerically studied. Resonant gas oscillations in circular cylinder have distinctive features such as shock free oscillation and periodic amplitude modulation. These phenomena are from the nature of the geometry of the sound field (dispersive effect). In contrast to the cylindrical wave, the resonance of the plane wave always emanates a shock wave if the dissipation effect of the gas is sufficiently small. Resonance of cylindrical and plane wave are one dimensional phenomena. On the other hand, the wave propagation in elliptical cylinder is essentially two dimensional problem and the geometry of the ellipse is defined by the eccentricity. Thus the resonant gas oscillation in elliptical cylinder shows interesting natures due to the two dimensionality of the system, such as the presence of even and odd oscillation mode. This study shows the dependence of the behavior of resonant oscillation on the eccentricity, and nonlinear...