Natural cooling capability in a vertical channel modeling compact electronic equipment was investigated by experiment and numerical simulation. Temperature rise of the heating walls of the channel model and velocity profiles of natural air flow in the channel were obtained. The effects of the clearance between the heating walls on the natural cooling capability were discussed. The clearance was varied from 4 mm to 20 mm in this study. It is clarified that the optimum size of the clearance existed between 8 mm to 10 mm.

View full abstract

This paper describes nonlinear photoemission properties of carbon nanotubes both in terms of experiment and theory. In experiments, we performed photoluminescence excitation spectroscopy where carbon nanotubes were excited with high-intensity optical pulses. We found that, as the intensity of excitation pulses increases, all the photoemission peaks from different structure carbon nanotubes showed clear saturation in intensity. Each peak exhibited a saturation value that was independent of excitation wavelength, indicating that there is an upper limit on the density of excitons. We propose that this behavior is a result of efficient exciton-exciton annihilation through which excitons decay nonradiatively. In order to explain the experimental results, we have developed a model taking into account diffusion-limited limited exciton-exciton annihilation and spontaneous decays of excitons in one dimension. The solution of the model reproduced the experimental results well, from which the exciton densities in carbon nanotubes were estimated. The validity of the model was confirmed by its comparison with Monte Carlo simulations. We also show that the conventional rate equation for exciton-exciton annihilation fails to fit the experimentally observed saturation behaviors, especially at high excitonic densities. Finally, we discuss possible influences of the existence of the upper density limit on some photoelectric applications of carbon nanotubes.

View full abstract

The electrolytic capacitor is one of the most important components for the thermal analysis of electronic equipment. To predict component and system temperatures, the thermal flow simulation technique has been applied to thermal design of electronic equipment. In this study, we examined a compact modeling method for electrolytic capacitors in order to simulate thermal flow based on the computational fluid dynamics (CFD) code. To obtain fundamental data for the thermal modeling method, first, we conducted experiments to identify the major thermal path of electrolytic capacitors in actual electronic equipment by using a switch mode power supply unit. Next, to verify the validity of the thermal model, a benchmark experiment was conducted to obtain actual measurement data of the temperature rise of electrolytic capacitors under various operating conditions. The thermal model of the electrolytic capacitor was presented based on the CFD code. In this paper, we describe in particular the snap-in type electrolytic capacitor.

View full abstract

The present study illustrates the effects of number of tube rows with vortex generators as well as the arrangement of different vortex generator geometries on local Nusselt number distributions and on friction factors. Trends of local Nusselt numbers and friction factors are provided as they vary with the number of tube row, Reynolds number from 500 to 2000, and the application of vortex generators on the fin surface. It is found that the type and configuration of the vortex generators are the most influential factors on decay of local fin-surface heat transfer enhancement as the number of tube rows increased. Moreover, it is also found that the combination of different vortex generators on the different tube rows could result to better heat transfer performance of the heat exchanger.

View full abstract

To clarify the mechanism of drying behavior of droplet remained on a silicon wafer in Marangoni drying used for rinsing and drying process in semiconductor manufacturing industries, the drying time of the droplet during organic gas dissolution have been investigated by using a CCD camera. And the concentration of organic component in the droplet has been measured with a micro-optical concentration sensor. In addition, numerical method that evaluating the drying time and the concentration is derived from phase equilibrium has been analyzed. There are qualitatively in good agreement. Finally, to get a guide line for decreasing watermark, organic and water concentration of atmosphere gas required have been proposed by using the numerical analysis.

View full abstract