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ISSN Online: 2377-424X

ISBN Print: 0-85295-345-3

International Heat Transfer Conference 10
August, 14-18, 1994, Brighton, UK

ELECTROHYDRODYNAMICAL (EHD) RESEARCH OF SATURATED POOL BOILING HEAT TRANSFER - CRITICAL HEAT FLUX ON SMALL SCALE SURFACE AND MEASUREMENT BY CAPACITANCE PROBE

Get access (open in a dialog) DOI: 10.1615/IHTC10.4730
pages 153-158

Sinopsis

The enhancement of the saturated pool boiling heat transfer by utilizing electric fields has been experimentally researched. For the heat transferring medium HCFC-123 was selected as one typical example of the important CFC alternatives, which included HFC and HCFC having relatively low electrical conductivity that were still thousands times larger than those of CFC. By selecting small scale boiling heat transfer surface of 5 mm in diameter, the nucleate boiling heat transfer without the enhancement effect of the movement of boiling bubbles along the heat transfer surface has been realized to quantitatively examine the bubble deformation effect of the electric fields on the mechanism of the boiling heat transfer enhancement. The boiling curves on the small scale boiling surface have been experimentally obtained, which showed the enhancement ratio to be about twice compared with the curve in case of no electric fields. Therefore, by comparing these data with our previously obtained nucleate boiling curves on the larger heat transfer surface of 50 mm in diameter, which showed the enhancement ratio of about 50 times for the same heat flux conducted in the liquids having the nearly same electrical conductivity, it has been clarified that the effect of the deformation of bubbles in the electric fields making the larger bottom area would cause the enhancement ratio of about twice and that the additional effects of making the violent motion of the boiling bubbles along the surface and of making the smaller critical wave length of Taylor instability would cause the additional enhancement ratio.
To measure the thickness of the thin liquid film on the heat transfer surface at the bottom of the boiling bubble even in the electric fields, a high speed capacitance probe has been devised and manufactured by use of a heterodyne detector. By use of this high speed capacitance probe, the average time required for the supply of the liquid to the thin film region has been decreased by applying electric fields and this increase of frequency for the supply of the liquid to the thin film region would also enhance the critical heat flux.