| SM ISO690:2012|
MARDARSKII, Orest; CHERNICA, Ion; BOLOGA, Mircea. Evolution of the boiling and heat exchange process under the action of electric field. In: Materials Science and Condensed Matter Physics. Editia a 8-a, 12-16 septembrie 2016, Chişinău. Chişinău: Institutul de Fizică Aplicată, 2016, p. 336. ISBN 978-9975-9787-1-2.
|Materials Science and Condensed Matter Physics
Editia a 8-a, 2016
Conferința "International Conference on Materials Science and Condensed Matter Physics" |
8-th Edition, Chişinău, Moldova, 12-16 septembrie 2016
A tendency is now observed of reduction of overall dimensions of electronic, optoelectronic, and radio technical apparatuses with increasing of the unit output of the heat power. This makes the problems of heat dissipation more complicated, generates a need for substantiation and development of advanced heat exchange methods. Usually such conventional methods are used to intensify the heat dissipation as increasing of the cooling surface, formation of capillary and porous structure at the heating surface, increasing of the circulation rate of the heat carrier. Intensification of heat exchange under the action of electric field is defined by the thermal and electrophysical properties of the heat carrier, the shape and dimensions of electrodes, field intensity and the degree of its inhomogenuity, dimensions of the heating surface and its orientation in the gravitation field. In this communication the results are presented of the investigation of boiling process in a high volume under the action of electric field. A stainless steel tube with its diameter of 4 mm supplied with a caprolon capillary structure deposited on its surface was used as a heat dissipation element. Hexane (boiling temperature of 68.7 оС) was used as a heat carrier. A high-voltage flat electrode is located over the heating surface at various distances (0.75, 2.00, and 3.50 mm) from it. Electrodes that allow vapor bubbles to pass through and solid ones were used in the experiments. The experimental dependences of the heat dissipation intensity versus the heat flux density, electric field strength, interelectrode gap value, and orientation of the heat dissipation surface in gravitation field were obtained. The found local characteristics of the heat transfer coefficient give evidence that the influence of the electric field strength on the boiling process reduces up to decay. The results are in a qualitative agreement with the published data. Application of the capillary structure on the heating surface allows one to intensify the boiling process in comparison with a smooth surface. The influence of orientation of the heat dissipating surface in gravitation field on the heat exchange intensity is noted. The slope angle of the heating surface was varied from 0 to 15о. The heat transfer coefficient was up to 25% greater in comparison with horizontal orientation of the heat exchange surface. The considerable heat exchange intensity was observed in the experiments when a vapor proof electrode was used as a high voltage one. The analysis of visual observations of the process of bubble boiling in a large volume was performed. It was shown that when a vapor proof electrode was used the generated bubbles coalesced in the interelectrode gap with formation of greater bubbles. They move along the electrode surface and form a relatively thin liquid layer on the heating surface, and the layer’s thickness determines the heat exchange intensity. The speed of motion of the vapor bubbles increases when the slope angle of the heating surface increases. This results in the reduction of the thickness of the liquid layer near the heating surface and consequently the boiling shifts to the range of higher values of the heat transfer coefficient. The influence of interelectrode gap on the heat exchange intensity was studied. It was shown that the heat transfer coefficient attains its maximum at the optimal value of the interelectrode gap. Using the Π-method of dimensional analysis we have obtained the expression for heat flux density that describes the main characteristics of boiling and is in a good agreement with the experimental data.