This study describes the effect of an electric field on nucleate boiling and critical heat flux (CHF) in pool boiling. A dielectric liquid of AE-3000 was used as the working fluid. A heating surface was polished to a surface roughness of 0.05 pm. A microsized elec trode, in which slits were provided, was designed to generate a nonuniform electric field and produce electrohydrodynamic (EHD) effects with the application of high dc voltages. The obtained results confirmed CHF enhancement as the EHD effects increased CHF to 86.2 W/cm2 with a voltage o f -3000 V, which was four times greater than pool boiling in the absence of the electrode. The usual traveling wave on the bubble interface, induced by the Kelvin-Helmholtz instability, was modified by adding the EHD effects. The travel ing wave model exhibits the essential features of the phenomenon and shows good agree ment with the experimental data.

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This paper describes results from an experimental study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling at atmospheric pressure. A dielectric liquid ofHFE-7100 (3 M Co.) was used as working fluid. A heating surface was polished with the surface roughness (Ra) of 0.05 ßm. A microsized electrode, in which the slits were provided, was designed in order to generate non uniform high electric fields and to produce electrohydrodynamic (EHD) effects with the application of high voltages. The obtained results confirmed the enhancement of CHF since the EHD effects increased the CHF to 4TWIcn? at the voltage of -1500V, which was three times as much as CHF for the free convection boiling. From the observations of the behavior of bubbles over the electrode and of the boiling surface condition, the instability between the liquid and the vapor increased the heat flux, the heat transfer coefficient (HTC), and the CHF. The usual traveling wave on the bubble interface induced by the KelvinHelmholtz instability was modified by adding the EHD effects. The ratio of critical heat flux increase with and without the electric field was sufficiently predicted by the frequency ratio of liquid-vapor surface at the gap between the boiling surface and the electrode.

A micro-electrohydrodynamic (EHD) pump is experimentally tested. In order to improve the static pressure performance, the EHD pump examined in this paper was fabricated with a series of thin stainless steel wires (the outer diameter is 0.3 mm). The overall dimensions of the EHD pump were 30 × 30 × 4.9 mm and of the pumping channel were 24×24×0.9 mm. An electrode pair consisted of one emitter electrode and two collector ones. The five sets of pumps were prepared for experiment. Those pumps were consisting of the number of electrode pairs from 1 to 5. The static pressure is measured with dibutyl-sebacate as a working fluid which has a dielectric constant, ε/ε 0 = 4.8 and a low electric conductivity, σ = 4.7 × 10 −10 S/m. The experimental results are compared with the theoretical results. In the theoretical model, the pressure is generated by Coulomb force which forces to move the unipolar ions in the high electric field. The experimental results indicate that the pressure increase as the number of electrode pairs increases and is generated up to 350 Pa at an applied voltage of 1 kV with 5 electrode pairs. Also, the experimental results show a good agreement with the theoretical ones. It is found that the theoretical model is useful for design of the high performance EHD pumps.

In this paper, we report an ultrasonic motor capable of high-velocity revolution applicable for long continuous high operation as a microfan. This study is a response to the new challenge of developing a new field of applications for an ultrasonic motor. Ultrasonic motors using a longitudinal-flexural coupling-vibration mode of a thin plate with a vibrating piece or step-horn are considered. A stator vibrator consists of a metal plate sandwiched by two thin unipoled piezoelectric ceramic plates, the electrodes of which are not divided, and this ultrasonic motor can be driven by a single ac source. Not only the coupling between a longitudinal vibration and flexural one but also the transformation of a longitudinal vibration velocity by a vibrating piece λ/4 long and step-horn λ/2 long are used. They will be effective at making the rotary speed fast. As a result, an ultrasonic motor 0.55 mm thick rotated a shaft 1.5 mm in diameter over 8,000 rpm under conditions of an applied voltage of 30 Vp-p and an input power of only 0.16 W.