The development of a polymer electrolyte fuel cell (PEFC) without external humidification is one of the most important issues to increase total efficiency and reduce cost. We have so far developed hybrid pattern gas flow channels consisting of interdigitated and serpentine gas flow channels for PEFCs without external humidification. The PEFC performance was improved when using the serpentine hybrid flow channels compared with the conventional flow channels. For further study, we have analyzed resistances of the cells with electrochemical impedance spectroscopy in the present study. The proton transfer resistance through the ionomer at the catalyst layer is dominant and its value for the hybrid flow channel is less than half that for the serpentine flow channel. The smaller resistance is possibly ascribed to the interdigitated design that can uniformly distributed reactant gas to each flow channel. The oxygen partial pressure is thereby relatively uniform at the active area. Thus, the interdigitated design can provide uniform current and water distribution. In addition, the hybrid flow channel has a low-pressure serpentine flow channel that helps the catalyst layer to hydrate. Un-reacted gas that contains modest water vapor flows through the channel and supplies water to the catalyst layer.
Instantaneous velocity and reactive concentrations are simultaneously measured in a planar liquid jet with a secondorder chemical reaction (A+B→R) by combining an I-type hot film probe with an optical fiber probe based on the light absorption spectrometry. Conditional statistics conditioned on the mixture fraction ξ are investigated experimentally. The results show that the reactive concentrations strongly depend on ξ . It is also shown that the conditional mean concentration is close to the concentration at the frozen limit in the upstream region of the jet, and in the downstream direction, the conditional mean concentration becomes close to the concentration at the equilibrium limit because of the reaction progress. The rms value of reactive concentration fluctuation is small compared with the conditional mean concentration. In the conditional moment closure methods, the conditional mean reaction rate is often approximated by using the conditional mean concentration of reactant species. The results show that the conditional mean reaction rate is well approximated by using the product of conditional mean concentrations of reactant species A and B. It is found that the conditional statistics measured in the downstream region is little dependent on the lateral position of the jet flow.
The authors develop a small and simple steam-reforming reactor in a home-use size for n-dodecane as a heavy-hydrocarbons fuel. Under such a well-controlled condition by a thermal diffuser as the reactor satisfies two target-temperature criteria, the authors measure the inside-temperature profile and the hydrogen molar fraction (concentration) CH2, together with the molar fractions CCH4, CCO and CCO2 of other main gass components such as CH4, CO and CO2, respectively, using a gas chromatograph. In addition, the authors conduct theoretical calculations based on the thermal-equilibrium theory, and reveal CH2, CCH4, CCO and CCO2, as well as experiments. As a result, the authors successfully achieve suitable inside-temperature profiles. The steam-reforming reaction becomes more active at the position where temperature T > 800 K. The effects of the steam-to-carbon molar ratio S/C upon CH2, CCH4, CCO and CCO2 are shown, experimentally and theoretically. The experimental results agree well with the theoretical ones. Besides, carbon balance and conversion ratio show high accuracy in experiments.
The direct numerical simulation of a spectral method is performed to study the flow structure of a turbulent channel flow at low Reynolds number, where the turbulent and quasi-laminar regions alternatively appear in the streamwise direction. The turbulent region is punctuated by the high-speed and low-speed fluids at the upstream and downstream sides, respectively. As a result, both the bulk and friction Reynolds numbers decrease from upstream to downstream regions, which makes the low Reynolds number effects pronounced at the downstream turbulent region; attenuation of turbulent diffusion into the wall vicinity and decrease in dissipation rate there. Differences between streamwise vortical structures in upstream and downstream turbulent regions are also investigated, which elucidates the effects of local mean flow on the vortices even in the wall vicinity as well as low Reynolds number effects.
When a train enters a tunnel at high speed, an impulsive pressure wave, called a micro-pressure wave, is radiated from a tunnel exit portal. Because it is one of the important wayside environmental problems in high-speed railways, many studies about its countermeasures have been conducted. The principal countermeasure applied to the Shinkansen on the ground side is a tunnel entrance hood. In this paper, a new countermeasure to install a tunnel exit hood to reduce the micro-pressure wave has been proposed. The tunnel exit hood has an inside partition which divides the inside of the hood into two parts in the vicinity of its mouth with the end of one part closed. It has been shown that the tunnel exit hood can be effective in reducing the magnitude of the micro-pressure wave.
