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51.
Tae Jung Ha Jong-Ho Kim Han-Ik Joh Soo-Kil Kim Go-Young Moon Tae-Hoon Lim Chonghun Han Heung Yong Ha 《International Journal of Hydrogen Energy》2008
Adequate control over the concentration of methanol is critically needed in operating direct methanol fuel cell (DMFC) systems, because performance and energy efficiency of the systems are primarily dependent on the concentration of methanol feed. For this purpose, we have built a sensor-less control logic that can operate based on the estimation of the rates of methanol consumption in a DMFC. The rates of methanol consumption are measured in a cell and the resulting data are fed as an input to the control program to calculate the amount of methanol required to maintain the concentration of methanol at a set value under the given operating conditions of a cell. The sensor-less control has been applied to a DMFC system employed with a large-size single cell and the concentration of methanol is found to be controlled stably to target concentrations even though there are some deviations from the target values. 相似文献
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Fibers from a crystalline polymethacrylonitrile were prepared by dry spinning using trifluoroacetic acid as solvent. Stretchability increased when the solvent retained in the fiber was extracted with methanol. Tensile properties are well acceptable for practical use. It is notable that the stress–strain curve for the polymethacrylonitrile (PMAN) fiber shows clear yield point even under hot-wet condition (90°C in water). Thus, the PMAN fiber is expected to have improved “hot-wet properties” compared with conventional acrylic fibers. From the data in the compliance and resiliency maps, the PMAN fiber is expected to be one of the most promising fibers having wool-like properties. 相似文献
55.
Semiconductor memory elements have been fabricated on silicon utilizing electron-beam evaporated TiO2 as the charge storage insulator medium. The dielectric and charge storage properties of TiO2 films have been characterized as a function of TiO2 deposition conditions and post-deposition annealing. Our results show that both dielectric constant and charge storage properties are enhanced by evaporation of the TiO2 in an oxygen ambient and substrate heating during evaporation. Post-deposition annealing in an oxygen ambient is also shown to increase the dielectric constant. M-TiO2-SiO2-Si structures with a 1000 Å layer of TiO2 typically exhibit 5 V memory windows for a ±15 V write/erase pulse. 相似文献
56.
Han-Ik Joh Sang Youp Hwang Jae Hyung Cho Tae Jung Ha Soo-Kil Kim Sang Heup Moon Heung Yong Ha 《International Journal of Hydrogen Energy》2008
In this study, a 400 W-class direct methanol fuel cell (DMFC) stack is developed for large size portable applications and its operating behaviors under the various conditions are monitored. The DMFC stack comprising of 42-cells is assembled with graphite bipolar plates and membrane–electrode assemblies (MEAs) having an active area of 138 cm2 per each. The stack is operated by varying the concentrations of methanol, stoichiometry (λ), and the electric load. In addition, other associated factors, such as voltage and temperature distributions along the individual unit cells, pressure drops inside the stack, voltage behaviors in response to the dynamic change of the electric load and the pHs of the effluent solutions from the outlets of both electrodes, are also studied in a detailed manner. The stack produces a power of 400 W under an operating condition of feeding 0.8 M methanol and 34 l/min air at 1 atm, and uniform distributions of temperature and voltage prevail in all the 42 unit cells. A long-term operation coupled with performance restoration processes shows that a typical single cell used in this stack is able to run with a good stability for more than 500 h without any substantial degradation in the performance. 相似文献
57.
Branched carbon nanotubes (b-CNTs) were synthesized by carbonization of polyvinylidene fluoride (PVDF) fibers containing a Pt catalyst. The solid fibrous polymer converted into carbon nanotubes with simultaneous growth of branches on the surface of the tubes during carbonization. The Pt particles were expected to decompose PVDF polymer inside the tubes into volatile carbonaceous species leaving a hollow center, and also to act as catalytic sites for the growth of carbon branches. The resulting b-CNTs had a high degree of graphitization and a large electrochemical surface area, and also showed a possibility as a supporting material for electrocatalysts. 相似文献
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Sadao Sato Yukio Sakata Joh Aoki Kazuhisa Kubota 《Polymer Engineering and Science》2006,46(10):1387-1393
A probe consisting of a cartridge heater was inserted into melted polypropylene composites (PP/mica = 5, 10, and 20 wt%) flowing in a die having a diameter of 10 mm, and the effects of mica on the heat transfer coefficient and the heat transfer behavior from the surface of the probe to the flow compound material were examined experimentally. As a result, the heat transfer coefficient of the PP/mica composites increases 15–20% depending on the flow velocity and filler content. In general, the Prandtl number (Pr) for high‐viscosity (η) melted polymer is greater than one (Pr > 1), and the Prandtl number for polypropylene composites increases as the viscosity increases and decreases depending on the flow velocity and the temperature. The relationship between Pr and η is directly proportional, and the β value, which is given by the slope of the Pr ? η diagram, is a constant that shows the viscosity dependency of the Prandtl number. The β value can be determined by the ratio of the specific heat to the thermal conductivity. The Nusselt number depends on the mica content of the filler and increases gradually. POLYM. ENG. SCI. 46:1387–1393, 2006. © 2006 Society of Plastics Engineers 相似文献
60.
The majority of storm runoff pollution is trapped in particles smaller than 100 microm in diameter. Solid particles smaller than 100 microm in diameter are not easily separated by conventional types of hydrodynamic separator, and remain in suspension in overflow. To overcome this problem, a HDFS (hydrodynamic filter separator) has been developed for treatment of the microparticles in urban storm runoff. We conducted a laboratory scale study on treatable potential of microparticles using HDFS that combined HDS with perlite filter. To determine the efficiency for various operation conditions, a series of experiments was performed with different solids concentrations and surface loading rate. The operation ranges of surface loading rates were 100 to 2,800 m3/m2/day, and influent solids concentrations were varied from 800 to 1,900 mg/L. Also, the particle size distribution was monitored to investigate the effects of surface loading rates on the particle size. Results indicated that the HDFS-inside type showed greater efficiency at solids separation than the other type. 相似文献