Koichi Murakami

Effects of changes in frequency of ultrasonic vibrations on heat transfer

The heat transfer coefficients during natural convection of water on a downward-facing horizontal surface and that on a vertical surface were measured under the influence of ultrasonic vibrations. The multi-type oscillation used in this experiment was able to operate at three frequencies-28, 45, and 100 kHz-not only continuously, but also intermittently, When ultrasonic vibrations of 28 and 45 kHz were applied to water, cavitation bubbles were generated and the heat transfer coefficient increased remarkably. When an ultrasonic vibration of 100 kHz was applied, the increase in the heat transfer coefficient was small compared to those at 28 and 45 kHz. At 100 kHz, cavitation was not observed at this low ultrasonic power. The uniformity of heat transfer, which depends on the profile of the standing wave due to the ultrasonic vibration, was improved by the method of repeatedly applying multiple vibrations

The behavior of pressurized gas injected into liquid between horizontal disks : Residual liquid film on disks after passage of gas front

The behavior of a bubble of gas suddenly injected from a nozzle into a liquid between horizontal circular disks is studied experimentally and analytically. A thin liquid film remains as a residue on the upper disk after the passage of the interface. The Morton number affects the residual liquid film thickness. At high gas flow rates, the residual liquid film thickness is almost constant. At low gas flow rates, it is dominated by the surface tension and the viscosity of the liquid.

Channel flow by applying ultrasonic vibration

The flow pattern in a channel by ultrasonic vibration has been investigated as a basic research into non-contact fluid control. An ultrasonic transducer is fixed to the center of the bottom of a square test channel, and a standing wave field is formed in this channel. By applying ultrasonic vibration into the flow, cavitation bubbles are generated at the sound pressure antinode in the channel when Re=2000. Consequently, cavitation bubbles act on the fluid as a barrier causing a separation in the flow and the velocity is reduced locally.

An Experimental Study on Properties of Local Burning Velocity for Hydrogen Added Hydrocarbon Premixed Turbulent Flames

This study is performed to investigate directly the local flame properties of turbulent propagating flames at the same weak turbulence condition (u′ /SL0 = 1.4), in order to clarify basically the influence of the addition of hydrogen to methane or propane mixtures on its local burning velocity. The mixtures having nearly the same laminar burning velocity with different rates of addition of hydrogen δH are prepared. A two-dimensional sequential laser tomography technique is used to obtain the relationship between the flame shape and the flame displacement. The local flame displacement velocity SF is quantitatively obtained as the key parameters of the turbulent combustion. Additionally, the Markstein number Ma was obtained from outwardly propagating spherical laminar flames, in order to examine the effects of positive stretch and curvature on burning velocity. It was found that the trends of the mean values of measured SF with respect to δH , the total equivalence ratio Φ and fuel types corresponded well its turbulent burning velocity. The trend of the obtained Ma could explain the local burning velocity of turbulent flames only qualitatively. Based on the Ma, the local burning velocity at the part of turbulent flames with positive stretch and curvature, SLt , is estimated quantitatively. As a result, a quantitative relationship between the estimated SLt and the SF at positive stretch and curvature of turbulent flames could be observed for mixtures with increasing the Lewis number.© 2011 ASME

A study on boiling in a horizontal channel with a rectangular section (in the case of a heated bottom wall)

The characteristics of boiling in a horizontal channel with changing conditions of the length of the heated wall and the channel height have been studied experimentally. Behavior of bubbles on the heated wall and growth of bubbles in the channel were observed by a high-speed camera. As a result, the behavior of the growth of bubbles which was classified into three types according to channel height had an influence on the time variation of the degree of superheat, heat transfer, and burnout heat flux in the channel. When the liquid on the bottom wall became thin, nucleate boiling with a vapor dome was observed on the heated wall