Micropump using boiling propagation as the actuation mechanism is proposed. A film heater on a silicon (Si) substrate placed facing a microchannel is powered pulsewise. Boiling propagation is triggered at a high wall superheat by generating a vapor bubble at the end of the heater. The repetition of unidirectional propagation over the heater length produces continuous pumping action in the microchannel. The propagation configuration, propagation velocity, propagating bubble size, maximum allowable repetition frequency and the wall superheat range for the occurrence of propagation are investigated under pool boiling conditions using ink for a thermal inkjet printer. The results obtained for Si substrate are compared with those on a quartz glass (SiO₂). No significant difference in the propagation behaviors and the pumping head is observed between the Si and SiO₂ substrates for a given pulse period, wall superheat and repetition frequency. However, a larger pulse power is required for the Si substrate because of its higher heat diffusion property. The resulting larger heat storage in the substrate before the boiling onset causes the delay of bubble collapse after the pulse heating. The gradual increase in the temperature of the thin Si substrate during the repetition of the pulse heating results in a lower allowable repetition frequency and therefore in lower pumping performance compared with those for the SiO₂ substrate.

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Plasma enhanced chemical vapor deposition (PECVD) is recognized as one of the viable fabrication techniques of carbon nanotubes. The outstanding advantage of PECVD is that free-standing, vertically-aligned carbon nanotubes (VA-CNTs) are synthesized due to the electric field normal to the substrate. This feature draws intense attention for the fabrication of nanoelectronic devices such as high-resolution scanning nanoprobes, interconnects, and field emission devices. However, carbon nanotubes synthesized in PECVD are overwhelmingly carbon nanofibers (CNFs) or multi-walled carbon nanotubes (MWNTs) with measurable structural defects. Tremendous interest in the preparation and characterization of vertically-aligned single-walled carbon nanotubes (VA-SWNTs) and related applications had not been realized in the scope of PECVD until recently. Here we present a fabrication technique of high-purity vertically-aligned single-walled carbon nanotubes using atmospheric pressure plasma enhanced chemical vapor deposition. By now, we have developed the atmospheric pressure radio-frequency discharge (APRFD) for this purpose. Although densely mono-dispersed Fe-Co catalysts of a few nanometers is primarily responsible for VA-SWNT growth, carbon precipitation was virtually absent in the thermal CVD regime at 700°C. On the other hand, high-yield VA-SWNTs were grown at 4 μm min^-1 by applying the atmospheric pressure radio-frequency discharge. The results proved that cathodic ion sheath adjacent to the substrates, where a large potential drop exists, also plays an essential role for the controlled growth of SWNTs, while ion damage to the VA-SWNTs is inherently avoided due to high collision frequency among molecules in atmospheric pressure. In this paper, operation regime of APRFD and tentative reaction mechanisms for VA-SWNT growth are discussed along with optical imaging of near substrate region of APRFD.

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This paper deals with the liquid-vapor structure under vapor mass in the high heat flux region of water and R141b. The liquid-vapor structure was measured in two dimensional space by an optical fiber probe (tip diameter < 10 μm). Experimental data were analyzed with emphasis upon the void fraction, the vapor contact frequency to which the boundary of liquid-vapor contacted at the tip of the optical fiber probe, and the time series of optical probe signal with surface temperature. Time-space averaged results confirm the existence of a liquid layer and very rapid liquid-vapor phase-changes in the liquid layer in water. On the other hand, the time-space averaged results of R141b do not indicate the existence of the liquid layer. This suggests that the liquid-vapor structure of R141b differs from that of the water and the so-called macrolayer model owing to its small surface tension.

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In this study, effects of thermal conduction in the wall on mixed convective heat transfer in a horizontal square duct are examined numerically. The working fluid is water. Two side walls and bottom wall in the heated section of the horizontal square duct are heated at a constant temperature (T_W = 60°C), and fluid temperature at the entrance is 15°C. The upper wall of the heated section and all walls of the entrance section are constructed by acrylic plate. Numerical conditions are Re = 100 and Ri = 39.88, respectively. The SIMPLE procedure and QUICK scheme are employed to solve the governing equations through a control volume method. Obtained results have been compared with heat transfer and flow without the thermal conduction in the duct wall. The comparison indicates that the reverse flow appears near the upper wall. The reverse flow length on the heated section increases and approaches to an experimental result. Two recirculation flows on the side walls across the section move to the bottom wall, and the recirculation size on the bottom wall grows up. The spiral flow is generated in the duct and its spiral pitch increases. The position at which the local Nusselt number collapses moves downwards is compared with the case without the thermal conduction in the duct wall.

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Compressed Natural Gas (CNG) direct injection engine has many advantages for the reduction of CO₂ emission. For further improvement of those engines, a numerical simulation technique has been developed for the analysis of combustion process. Prior to an in-cylinder calculation, the wall function was modified to improve the accuracy of the wall heat loss. Then the nozzle-to-cylinder entire calculation was performed. Good agreements were obtained in comparison with the experiment for the behavior of impinging jets. This method was applied to the analysis of the difference of combustion processes between CNG and conventional gasoline direct-injection engines. It is accordingly found that the velocity and the turbulence of in-cylinder gas are increased by the fuel injection into CNG engine and thus the combustion speed is enhanced significantly.

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Heat treatment by superheated steam has been utilized in several industrial fields including sterilization, desiccation, and cooking. In particular, cooking by superheated steam is receiving increased attention because it has advantages of reducing the salt and fat contents in foods as well as suppressing the oxidation of vitamin C and fat. In this application, quick startup and cut-off responses are required. Most electrically energized steam generators require a relatively long time to generate superheated steam due to the large heat capacities of the water in container and of the heater. Zhao and Liao (2002) introduced a novel process for rapid vaporization of subcooled liquid, in which a low-thermal-conductivity porous wick containing water is heated by a downward-facing grooved heating block in contact with the upper surface of the wick structure. They showed that saturated steam is generated within approximately 30 seconds from room-temperature water at a heat flux 41.2 kW⁄m². In order to quickly generate superheated steam of approximately 300°C, which is required for cooking, the heat capacity of the heater should be as small as possible and the imposed heat flux should be so high enough that the porous wick is able to dry out in the vicinity of the contact with the heater and that the resulting heater temperature becomes much higher than the saturation temperature.
The present paper proposes a simple structured generator to quickly produce superheated steam. Only a fine wire heater is contacted spirally on the inside wall in a hollow porous material. The start-up, cut-off responses and the rate of energy conversion for input power are investigated experimentally. Superheated steam of 300°C is produced in approximately 19 seconds from room-temperature water for an input power of 300 W. The maximum rate of energy conversion in the steady state is approximately 0.9.

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The flooding phenomenon in polymer electrolyte fuel cells (PEFCs) is studied experimentally by using MEMS-based thin film gas diffusion layer (GDL). The flooding criteria of PEFC are calculated by considering the saturation vapor pressure and mass transfer flux. In the experiment, a drop in cell voltage is observed as time passes due to flooding. Through theoretical study, we predicted the current density when voltage started to drop. Comparison between experimental and calculation results showed that the prediction was in good agreement with the experiment. It was revealed that in low gas flow rate the flooding limit is determined by the maximum amount of containable water vapor in outlet gas flow while in high gas flow rate it is dependent on the maximum flux of mass transfer from the catalyst layer to the gas channels.

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