Hiromitsu Masuda

Investigation of Flooding Phenomena in PEMFC by Two-Phase Flow Numerical Simulation

Water Problem, which is represented by the flooding and the drying in PEMFC, is one of the critical issues relating to the recent trend of high current density operation of it. For spreading the practical use of PEMFC, we must grasp this problem exactly and resolve it. Two-phase flow numerical simulation is useful for this purpose. In this study, we numerically analyzed a unit-PEMFC two-dimensionally considering the two-phase flow based on the multiphase mixture model developed by Cheng and Wang, adding the authors’ equivalent electric circuit. We simulated not only steady state but also unsteady state. A slightly abrupt change in current density distribution appeared on the point where the interface between the one- and the two-phase zone in GDL was appeared. The distribution of water saturation after cell operation start changed with time passed: the liquid water tend to focus on the GDL after once it spread in both GDL and flow channel.Copyright

Numerical Simulation of Two-Phase Flow and Transient Response in Polymer Electrolyte Fuel Cell

It is important to elucidate the transient characteristics of polymer electrolyte fuel cells (PEFC), especially when PEFC is applied to relatively small-scale power applications where it will be subjected to a wide range of loads, and may have frequent starts and stops. In addition, the water management problem, which is represented by flooding in cell and drying in proton exchange membrane (PEM), is another issue to address. The flooding is caused by liquid water accumulated in GDL and/or flow channel; the liquid water hinders mass transfer of gases to and from active layers; it can lead to rapid deterioration of cell performance. And the water management relates to the transient response of PEFC frequently. Based on these issues we wrote a numerical simulation program for unit-PEFC, which can simulate the successive events of vapor condensation, liquid saturation growth, corresponding to the dynamic change of cell voltage. We formulated mass, momentum and energy conservation equation with equivalent electric circuit; we discretized and numerically solved them. As for the gas/liquid two-phase flow formulation in GDL, we utilized multi-phase mixture (M2 ) model. As for the multi-component diffusion formulation, we utilized Stefan-Maxwell equation. Using the program, we simulated the transient response to rapid increase of load current. When the current density changed from 0.5 A/cm2 to 1.0 A/cm2 instantaneously, cell voltage (Vcell ) changed in the following manner. Just after the change of current, Vcell decreased instantaneously corresponding to IR resistance and decreased again in 10−1 s time-scale with the re-distribution of oxygen and with the charge of electric double layer capacitor. Then Vcell increased slightly in 101 s time-scale with PEM wetting. Finally, Vcell decreased in 102 ∼ 103 s time-scale with the development of liquid saturation in GDL.Copyright

Estimation of Flooding in PEMFC Gas Diffusion Layer by Differential Pressure Measurement

The flooding, especially in gas diffusion layer (GDL), is one of the critical issues to put PEMFC to practical use. However, the experimental data of the flooding in GDL is so insufficient that the optimization design to solve the flooding problem in GDL has not established until now. In this study we show a method to estimate the water saturation, namely the water droplet occupation for unit volume in GDL. We fabricated a simple interdigitated cell where the supply gas is enforced to flow under rib. This structure made it possible to capture the water droplet in GDL with the measurement of differential pressure through the cell. We operated the cell and measured the differential pressure, and estimated the water saturation with assuming that the flow in GDL is Darcy flow and that the GDL can be treated as sphere packed bed. In addition to deferential pressure measurement, we measured the ionic resistance in polymer electrolyte membrane by AC impedance method. We evaluated the effect of the water saturation on the decrease of cell voltage.Copyright

Transient Response Analysis of Polymer Electrolyte Fuel Cell Considering Equivalent Circuit, Mass and Heat Conservation

Elucidating the transient characteristics of a polymer electrolyte fuel cell in consideration of its applications, such as electric vehicles, is an important step in its development. In this study, we created a mathematical model to predict the transient behavior of a unit-PEFC, analyzed the model numerically, and compared the results with experimental results. Consequently, we elucidated that the transient behavior of a PEFC is summarized by two physical phenomena: (1) water redistribution in the polymer electrolyte membrane, (2) the discharge/charge of electric double layer capacitance.Copyright

A Study on Passive-Adaptive Vibration Control Elements Using Dilatant Materials.

Adaptive vibration control is a method that changes vibration system characteristics according to the vibration level. To construct adaptive vibration control elements that do not require any external energy, called passive adaptive vibration control elements, we have proposed a method that uses nonlinear viscoelastic materials. This paper describes how we constructed these elements using dilatant materials and reports on the experiments we conducted with them. The results show that the vibration of mass supported by these elements is reduced when the vibration level is high. They also show that vibration is isolated by these elements when the vibration level is low.