Kunio Hijikata

EHD study of the corona wind between wire and plate electrodes

The corona wind, with a velocity of several meters per second, is caused by applying high electric tension to bring about corona discharge in gases. In this paper the corona wind is experimentally and theoretically analyzed from an electrohydrod ynamical (EHD) standpoint. Experiments have been performed mainly in nitrogen by a two-dimensional electrode arrangement of a fine wire anode and a plate cathode. The voltage-current characteristics of an electrostatic probe indicate that positive ions predominate in the whole space except in an extremely narrow region close to the wire. A theoretical analysis has been conducted based on the model that positive ions produced by ionization near the wire electrode move toward the plate, introducing the bulk convective motion of neutral molecules as the result of collisions of ions and neutral molecules. The electric potential distribution in the space and pressure distribution on the plate calculated numerically agree well with the experimental data. Consequently, it is made clear that the corona wind is caused by the Coulomb force exerted on ions and collisions of ions and neutral molecules of gas.

Effect of gate voltage on hot‐electron and hot phonon interaction and transport in a submicrometer transistor

This paper studies the effects of gate voltage on heat generation and transport in a metal–semiconductor field effect transistor made of gallium arsenide (GaAs) with a gate length of 0.2 μm. Based on the interactions between electrons, optical phonons, and acoustic phonons in GaAs, a self‐consistent model consisting of hydrodynamic equations for electrons and phonons is developed. Concurrent study of the electrical and thermal behavior of the device shows that under a source‐to‐drain bias at 3 V and zero gate bias, the maximum electron temperature rise in this device is higher than 1000 K whereas the lattice temperature rise is of the order of 10 K, thereby exhibiting nonequilibrium characteristics. As the gate voltage is decreased from 0 to −2 V the maximum electron temperature increases due to generation of higher electric fields whereas the maximum lattice temperature reduces due to lower power dissipation. The nonequilibrium hot‐electron effect can reduce the drain current by 15% and must be included ...

Transport phenomena of liquid CO2 in pressurized water flow with clathrate-hydrate at the interface

Dissolution rate of a liquid CO2 droplet in the pressurized water flow has been experimentally measured for both cases with and without clathrate on the surface, and various effects of flow velocity, temperature and pressure on the dissolution rate have been clarified. Based on the results, shrinking or dissolution mechanism of CO2 droplet covered with clathrate film has been discussed in detail. Further, the dissolution behavior of liquid CO2 droplets dispersed into the sea water has been numerically simulated using measured dissolution rates.

Optimized Performance of Condensers with Outside Condensing Surfaces

The purpose of this paper is to find an optimum surface geometry of vertical condenser tubes where condensation takes place on the outer surfaces. The guiding principle on optimum condensation performance is to make the thickness of condensate liquid on the surfaces as thin as possible. A vertical tube with longitudinally parallel tiny fins is preferable because condensate is made thinner over the widest possible region. According to an analysis, there are four controlling factors for the optimum fin; sharp leading edge, gradually changing curvature of fin surface from tip to the root, wide groove between fins to collect condensate and horizontal discs attached to the tube to remove condensate. The analytical result is checked by experiments using R-113. The optimum fin shape, fin pitch and spacing of discs are found by numerical calculations for R-113 and water.

Dissolution rate of liquid CO2 in pressurized water flows and the effect of clathrate films

The dissolution rate of liquid in CO2 in seawater, when a CO2 clathrate-hydrate film exists at the interface, is a key factor for estimation of CO2 sequestration in ocean and marine environmental impact assessment. Liquid CO2 dissolution phenomena in CO2 sequestration in the ocean include (i) dissolution and diffusion of liquid CO2 droplets at intermediate sea depths and (ii) CO2 dissolution in undercurrent flows from a liquid CO2 pool at seabeds deeper than 3000 m. For the first case, the present paper presents a data base of clathrate-hydrate covered CO2 droplet surface concentration, which is essential for an analysis of CO2 droplet dissolution behavior. Effects of pressure and temperature are included. A numerical simulation for dissolving liquid CO2 droplets released at an intermediate ocean depth is presented. The effects of released droplet size and ambient CO2 concentration on dissolution behavior are clarified. For the second case, an experiment simulating dissolution of liquid CO2 stored at a seabed into an undercurrent flow was conducted. The pool surface was covered with clathrate and the surface concentration of the clathrate-covered CO2 pool was estimated. Applying the measured surface concentration and mass transfer coefficient obtained from the actual conditions of deep ocean data, the time scale of CO2 dissolution into an undercurrent flow was estimated, which is important for estimation of CO2 disposal in the deep ocean.

Heat generation and transport in submicron semiconductor devices

The reduction of semiconductor device size to the submicrometer range leads to unique electrical and thermal phenomena. The presence of high electric fields (order of 10 7 V/m) energizes the electrons and throws them far fom equilibrium with the lattice. This makes heat generation a nonequilibrium process. For gallium arsenide (GaAs), energy is first transferred from the energized electrons to optical phonons due to strong polar coupling. Since optical phonons do not conduct heat, they must transfer their energy to acoustic phonons for lattice heat conduction. Based on the two-step mechanism with corresponding time scales, a new model is developed to study the process of nonequilibrium heat generation and transport in a GaAs metal semiconductor field effect transistor (MESFET) with a gate length of 0.2 μm. When 3 V is applied to the device, the electron temperature rise is predicted to be more than 1000 K. The effect of lattice heating on electrical characteristics of the device shows that the current is reduced due to decrease in electron mobility. The package thermal conductance is observed to have strong effects on the transient response of the device

Effect of dissolved gas on bubble nucleation

Abstract The aim of this research is to make an experimental study of an effect of a dissolved gas on the liquid-gas homogeneous phase transition, and to compare the result with a bubble nucleation prediction. The experiment was performed under the condition of no existence of gas bubble in a liquid. The superheat limit of the liquid was experimentally studied using a technique in which a droplet containing a dissolved gas was suspended in an immiscible fluid medium. The result shows that with an increase of the content of a dissolved gas homogeneous nucleation occurs at lower temperatures and in the presence of a sufficient dissolved gas at pressures above the saturation pressure of the pure solvent.

Unsteady heat and mass transfer from spheres

Abstract This paper reports theoretical and experimental results on unsteady heat and mass transfer from small spherical bodies for small Strouhal numbers. Experiments are done in a stream consisting of steady and unsteady components. Unsteady flows are generated by an acoustic resonance in a tube and fluctuate purely sinusoidally. In heat-transfer experiments in an air stream several spherical thermistors are used and the time-averaged Nusselt number is shown to be well correlated, both experimentally and theoretically, by means of Reynolds number with time-averaged velocity as its characteristic velocity and the ratio of velocity amplitude of unsteady component to steady component. Unsteady mass-transfer experiments are done by evaporation of small droplets of water and prophyl-alcohol in an air stream. The results are found to be represented by a similar correlating relation to that for heat transfer. A resonant oscillation of deformation of a droplet is observed due to surface tension and during this resonance the Sherwood number is found to increase proportionally to the unsteady component of the stream.

Methodology and evaluation of priorities for energy and environmental research projects

To evaluate and prioritize energy-related projects, not only technological issues but also resource and social aspects must be included. We use an analytic hierarchy process (AHP) for incorporating these two features. Technological issues are divided into three categories; resource and social aspects are divided into five categories. Each category is further subdivided, forming a tree-like hierarchy. Nineteen energy-related characteristics and seven environmental characteristics are used to describe a proposed research project. By utilizing the estimated relative importance of each selected characteristic, seven different planning perspectives have been identified: short-, intermediate-, and long-range strategies for Japan, short- and intermediate-range strategies for less developed countries (LDCs), and intermediate- and long-range global strategies.

Measurement of CO2 diffusion coefficient and application of LIF in pressurized water

This paper deals with estimation of the diffusion coefficient in an H2O CO2 system under high pressure and the use of laser-induced fluorescence (LIF) for measuring CO2 dissolution. A liquid CO2 droplet without CO2 clathrate was placed in the flow where the velocity profile is uniform. The diffusion coefficient is estimated by measuring the liquid CO2 droplet-dissolution rate and using the empirical mass transfer coefficient. The measured diffusion coefficient agrees well with the Wilke-Chang equation at pressures of 29.4 and 39.2 MPa. We have used LIF for measurement of the large non-uniform, two-dimensional pH distribution induced by CO2 dissolution. A sheet laser beam was provided by a YAG laser and the two-dimensional LIF intensity was detected by an image-intensified CCD diode-array camera.