Takuya Honda

Deformation and solidification of a droplet on a cold substrate

The numerical simulation of a droplet deformation and solidification on a cold substrate was performed with SMAC algorithm. The substrate temperature histories and the degree of deformation were measured by use of a droplet of n-eicosane and n-cetane. The numerical results showed good agreement with the measured ones. The solidification of a droplet on a substrate occurs immediately after the deformation. A simple model to estimate the deformation and the solidification time was also proposed. Both the normalized deformation and solidification time are proportional to the 0.2 power of the Reynolds number. The solidification time is two orders of magnitude higher than the deformation time.

Thermal plasma decomposition of chlorofluorocarbons

Dichlorodifluoromethane was decomposed by a thermal argon plasma generated by a DC are discharge. The experiments and the kinetic calculations showed that the complete decomposition of the chlorofluorocarbon proceeded with the simultaneous additions of hydrogen and oxygen. Both the expertimental and calculated results confirmed that it is favorable, for the decomposition, not to quench the products but to add an excess of hydrogen over the stoichiometric amount, which leads to a reduction in chlorine formation.

Enhancement of the deposition rate of TiO2 film in radio frequency reactive sputtering

Titanium oxide thin films were prepared using rf reactive sputtering in which a titanium target was sputtered in a mixture of Ar and reactive O2 gas. The flow modulation of reactive gas was proposed to enhance the deposition rate of the film which is generally low in continuous flow reactive sputtering. The experimental results indicated that the deposition rate could be enhanced maintaining the film stoichiometric ratio of TiO2. The enhancement occurred because the modulated flow appeared to reduce the formation of compounds on the target surface which inhibit sputtering under continuous flow conditions. The effects of the flow modulation were understood by adapting a reactive sputtering theoretical model.

Heat transfer from rarefied ionized argon gas to a biased tungsten fine wire

Abstract Experimental and theoretical studies have been made of heat transfer from a rarefied, partially ionized argon plasma jet (500 Pa, 9000 K) to a biased tungsten fine wire. The heat flow rates to the wire were obtained from its electrical resistance variations. When the wire is biased, the resistance cannot be measured accurately because the current through the bias circuit obstructs the measurements. Therefore, the current was broken by a switching circuit for a short time (0.1 ms) every 3 ms to measure the resistance. The variation of heat flow rates with a biased potential could be obtained, and the accommodation coefficients of argon atoms and ions were determined, resulting in 0.62 for argon atoms and 0.48 for argon ions.

THE ROLE OF NATURAL CONVECTION DURING MELTING AND SOLIDIFICATION OF PCM IN A VERTICAL CYLINDER

Abstract Measurements of heat transfer during melting and solidfkation of n-eicosane and rt-hexadecane were performed in vertical cylinders with two different lengths and diameters. Radial temperature distibutions were measured with lime at different heights in all the tests. To evaluate the rate of heat charged and discharged from the cylinder at different heights, the data were recorded and processed directly usinj; on-line computer. A theoretical model was developed based on solving the one-dimensional unsteady heat conduction equation in both phases. Convection in the liquid was included using an effective thermal conductivity; a lumped parameter that includes also the effect of the two-dimensional heat transfer during melting. The model, which may be used for the prediction of both melting and solidfkation experiments, takes into account the effect of initial subcooling or superheating and includes the heat capacity of the cylinder containing the PCM. The agreement of the model was good not only with...

Computational modeling of reactive gas modulation in radio frequency reactive sputtering

Computer simulation of reactive sputtering was carried out to explain the enhancement of the deposition rate of complete oxide film using reactive gas flow modulation. The model dealt with the preparation of TiO2 film with a titanium target and oxygen in rf reactive sputtering. The computed results showed good agreements with the experimental data obtained in our previous work. The effects of the flow modulation were elucidated with the calculated timewise variations for partial oxygen pressure and target coverage. The effects of modulation patterns were also evaluated using the simulation.

Thermal quenching effects on plasma synthesis of NO and plasma decomposition of CO2

Effects of the thermal quenching process in the synthesis of NO and the decomposition of CO2 were studied using a thermal argon plasma and different-i.d. cooling tubes. Four tubes of different i.d.s were used to change the cooling rate. The conversions obtained in both reactions increased with decreasing quenching tube diameter. Furthermore, the concept of quenching temperature was introduced. This temperature was obtained from two time constants of reaction and cooling rate. The conversions into CO can be estimated in a similar manner to the NO synthesis with a proper modification for radicals which remain at high concentrations at the quenching temperature.

Kinetic measurement on the isobutene/water/tert‐butanol chemical heat pump; dehydration of tert‐butanol

For this heat pump kinetic study, the dehydration rate of tert-butanol (an endothermic reaction) was measured under conditions suitable for operating a chemical heat pump. The proposed Langmuir-Hinshelwood rate equation agreed well with the experimental rate data. The heat pump kinetic study was examined in a batchwise operation by using both the endothermic reaction rate equation and a previously proposed rate equation for the exothermic reaction. Although the endothermic reaction rate was suitable for a heat pump, an improvement of the endothermic reaction rate was desired since it was found to be too slow. The endothermic reaction was about 5 to 20 times slower than the exothermic reaction. The absorbed and released heat rates per batch cycle were almost the same as for conventional heat pumps.

Two-Temperature Scaling for Molecular Dynamics Simulation at Constant Temperature

Molecular dynamics simulations for a binary system are carried out using a temperature scaling procedure under isothermal conditions to keep the temperature constant. However, the temperatures of each atomic species are diverse in the cases of component atoms with significantly different masses. The causes of the deviation of atomic temperatures in the ordinary scaling method with one thermostat are examined. The deviations appear when the mass ratio of light atoms to heavy is below 0.4. We apply the two-temperature control method using different heat baths for individual species to render the temperatures of the two different species the same, although this generally breaks the momentum conservation law as reported by Nose [Mol. Phys. 57 (1986) 187 and Prog. Theor. Phys. Suppl. (1991) No. 103, 1]. It is found that the deviation from the conservation law of the system is not very large and the method is useful except under extraordinary conditions.

The effect of gas injection on a thermal argon plasma flow in a water-cooled tube

The effect of gas injection on an atmospheric thermal argon plasma flow in a water-cooled tube was investigated experimentally and numerically. The injection gas is argon, helium, or nitrogen. The static pressure with helium injection increases greatly because of its high thermal conductivity, while little increase occurs for nitrogen injection because of the dissociation. The increasing rate of the static pressure depends on the ratio of the momentum term to the viscosity term. The heat flux to the tube wall with gas injection changes less than that without injection. The numerical results showed variations similar to the experimental ones.