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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

AUGMENTATION MECHANISM OF FORCED-CONVECTION HEAT TRANSFER BY APPLYING ELECTRIC FIELDS IN THE RESTRICTED REGION NEAR THE WALL

Get access (open in a dialog) DOI: 10.1615/IHTC10.2440
pages 135-140

摘要

By applying electric fields in the restricted region near the wall by using the array of wire electrodes installed near the heat transfer wall along the main stream in the range of low Reynolds number, the heal transfer coefficients have been augmented to the same order as the one in the turbulent flow and the pressure drop has been increased but still remained in the same order as the one in the laminar flow. These effects would be useful for the enhancement of the liquid-phase forced-convection heat transfer to improve the performance of heat exchangers with the heat transferring medium of CFC alternatives maintained in the range of low Reynolds number, such as in the case of an oil cooler utilizing HCFC-123. In this paper, the ratio of the enhancement of the heat transfer coefficients to the increase of the pressure drop has been experimentally clarified that the ratio has been arranged by use of the ratio of Colburn j factor to the friction factor to be 4.4 times for the Reynolds number of 1470 and 1.9 times for the Reynolds number of 20000. Furthermore, by analyzing the power spectrum of the flow velocity in the liquid, the spectrum has been cleared to have some larger values only in the region near 1 Hz for the Reynolds number of 20000 compared with the one under no electric field. Since this difference of the turbulent power spectrum around 1 Hz appeared both in the power spectrum of the velocity and the electric current, the mechanism of making the turbulence would be the fluctuation of the current, which would mean the fluctuation of the injection rate of negative ions from the cathode as cleared by the voltage-current characteristics of the electrostatic probe in the higher potential region under the electric fields larger than 6 kV/cm. The peak of the spectrum around 1 Hz would correspond to the fluctuation of current over the time period which would be necessary for the negative ions to reach the positive electrode from the cathode.