Water management plays an important role in obtaining high performance from a polymer electrolyte membrane fuel cell (PEMFC).
To reduce the volume and energy consumption of widely-used bubble humidifiers, membrane humidifiers were fabricated by using
an ultrafiltration (UF) membrane and Nafion membranes. The performance of the membrane humidifiers was examined as a function
of gas flow rate and operating temperature. A single cell was operated using the UF membrane humidifiers exhibiting almost
the same performance with that employing bubble humidifiers. 相似文献
Composite membranes were prepared by grafting plasma-polymerized films onto the surface of nonporous poly (dimethylsiloxane)
films. Gas permeabilities of the composite membranes were measured at 35°C, 1 atm for N2, 02, CO2 and CH4. The permeation properties of the composite membrane was analyzed using the series resistance model. There was a great interfacial
resistance to CH4 permeation through the composite membrane. The interfacial resistance was negligible for the other gases. The interfacial
resistance seems to be a result of an interfacial layer caused by the interaction between the bulk two layers. For CH4 gas, the permeation rate through the composite membrane was affected by the direction of flow. The directional dependence
was negligible for the other gases. 相似文献
Dynamic mechanical properties of three different styrene-based ionomer blends containing ca. 5 mol% of ionic repeat units were investigated; the three ionic units were itaconate (ITANa), methacrylate (MANa), and styrenesulfonate (SNa). For SNa-MANa ionomers, it was observed that this ionomer system showed only two loss tangent peaks, implying that this ionomer system resembles a typical miscible system. When the ion content increased, however, the ionomer blend showed two cluster loss tangent peaks, indicating the presence of phase-separated cluster regions. This suggests that, with increasing ion content, the role of ionic units becomes more important than that of host non-ionic units to determine ionomer properties. In the case of ITANa-MANa and ITANa-SNa ionomers, however, it was suggested that the multiplets of the MANa and SNa ionomers might be disrupted upon the addition of the ITANa ionomers. In addition, the SEM images showed that the fracture surfaces of ionomers changed upon blending. 相似文献
Nano-sized silicon carbide (SiC) powder was prepared by thermal plasma process using silicon tetrachloride (SiCl4) and methane (CH4). The synthesized powder was characterized by X-ray diffraction pattern, scanning electron microscopy, transmission electron
microscopy, FT-IR spectroscopy and particle size analyzer. The powder was dominated by β-SiC including some of α-SiC and free
carbon species. The quality of the powder was varied with process conditions such as the molar ratio of H/Si and C/Si, and
collecting positions. It was known that the conversion to SiC was mainly affected by the addition of hydrogen gas because
it promoted the decomposition and reduction of SiCL. CH4 was easily decomposed to carbon species for the formation of SiC as well as removal of impure oxygen, but excessive carbon
suppressed the formation of crystalline SiC and resulted in the solid carbon contamination. The optimum ratio of H/Si was
approx. 26 and that of C/Si was 1.1. For collecting positions, the powder collected at the vessel and filter was preferable
to that at the reaction tube. The average size of the powder synthesized was estimated to be below 100 nm and uniform in distribution. 相似文献
In this paper, we consider a problem of global stabilization for a class of approximately feedback linearized nonlinear systems. In order to handle more nonlinearity over the existing results, we provide a new feedback controller with two gain-scaling factors and we show that more nonlinearity can be treated by our control scheme. Moreover, we analytically show that the considered nonlinear systems can be stabilized by the proposed controller. Through comparison practical examples, we illustrate the improved features of our proposed control method.
In this paper, we consider a problem of global asymptotic stabilization for nonlinear systems with the perturbed nonlinearity. We provide a stabilizing controller with two gain-scaling factors and a new controller design method with matrix inequality approach. In particular, we provide a new procedure for selecting gain-scaling factors which are associated with stabilizing the closed-loop system. As a result, our proposed control method widens the class of considered nonlinear systems and yields better control performance over the existing methods. Via several comparison examples, we illustrate the improved features of the proposed control method over the existing ones.
It has been observed that the forming limit curve at fracture (FLCF) of steel sheets, with a relatively higher ductility limit
have linear shapes, similar to those of a bulk forming process. In contrast, the FLCF of sheets with a relatively lower ductility
limit have rather complex shapes approaching the forming limit curve at neck (FLCN) towards the equi-biaxial strain paths.
In this study, the FLCFs of steel sheets were measured and compared with the fracture strains predicted from specific ductile
fracture criteria, including a criterion suggested by the authors, which can accurately describe FLCFs with both linear and
complex shapes. To predict the forming limit for hydro-mechanical deep drawing of steel sheets, the ductile fracture criteria
were integrated into a finite element simulation. The simulation, results based on the criterion suggested by authors accurately
predicted the experimetal, fracture limits of steel sheets for the hydro-mechanical deep drawing process. 相似文献