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International Symposium on Heat and Mass Transfer in Refrigeration and Cryogenics
September, 1-5, 1986, Dubrovnik, Yugoslavia

DOI: 10.1615/ICHMT.1986.IntSympHMTinRefCryo


ISBN Print: 978-3-54017-957-3

The Effect of an Electric Field on Boiling Heat Transfer of Fluorocarbon R-11

pages 140-151
DOI: 10.1615/ICHMT.1986.IntSympHMTinRefCryo.100
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RÉSUMÉ

For many years, smoothed or small-finned tubes have been mainly used in the heat exchangers of refrigerating machines. As these are made by simple manufacturing processes their costs are very low, but their heat transfer performance is not very high, causing their size and volume to be very large.
In recent years, enhanced tubes have been developed in order that a variety of energy source, such as waste heat, be utilized to save natural energy sources. This has taken place especially with the many new evaporating tubes. These have been developed so that there can be heat exchange with lower temperature energy sources. These tubes have many different kinds of prepared surfaces which promote boiling heat transfer with a smaller temperature difference. Examples of these are "Hi-Flux Tube", "Thermoexcel Tube", "ECR-40 Tube", etc. These tubes are made by coating the tube surface with sintered metal or preparing the tube surface mechanically. The enhancement of the heat transfer coefficient in these tubes is more than ten-fold of that in smoothed tubes. The enhanced tubes have been used in refrigerating machines, but, they are made by a complicated process, and therefore are very costly. Furthermore, the enhancement of refrigerant-oil mixtures is reduced. Therefore, their applications are limited and they have not yet replaced the former tubes.
Heat exchangers utilizing all the previous types of tubes cannot control the performance of a system as this is controlled by the compressor or heat sources. Active control of the heat exchangers can be achieved though, by using an electric field. Recently the effects of electrohydrodynamics (EHD) on heat transfer have been investigated, especially in natural convection, condensation and boiling in the high temperature difference region. Most of the effect of EHD on natural convection has been investigated and agreement between experiments and theoretical analyses has been confirmed. But in condensation and especially boiling, theoretical analyses have not been carried out as extensively because of their complicated phenomena.

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