Wanchai Asvapoositkul

Effect of the Electrode Arrangements in a Tube Bank on the Characteristic of Electrohydrodynamic Heat Transfer Enhancement: Low Reynolds Number

Enhancement in heat transfer using the electrohydrodynamic (EHD) technique is numerically examined in laminar forced convection across a tube bank with six different wire electrode arrangements. The electric field is generated by the wire electrodes charged with high DC voltages ranging from 7.5 to 17.5 kV. The Reynolds number corresponding to the flow considered is between 100 and 1,500. The numerical modeling of the laminar forced convection includes the interactions among the electric field, the flow field, and the temperature field. It is found that the heat transfer is significantly enhanced by the EHD at a low Reynolds number, and the short distance between the wire electrodes and the tube surface from which different electrode arrangements are reported for aligned and staggered tube configurations. The value Nu/Nu 0 of an aligned configuration increases from row to row and appears to be similar with that of a staggered configuration.

The Effectiveness–NTU Approach for Evaluation of an Air-Cooled Heat Exchanger

A newly developed empirical model based on the effectiveness–NTU approach was developed for a dry-cooling simulation to evaluate the thermal performance of air-cooled heat exchangers. The value of this model is that air-cooled heat exchanger performance can be studied in a variety of working conditions. This information is useful in dry-cooling system evaluation. The purpose of this study was to present a calculation that would be accurate and simple to implement, and could be applied to evaluate and optimize the thermal performance for hybrid (wet/dry) cooling towers, in which dry- and wet-cooling towers are designed to work in combination. This study was only limited to a dry-cooling section. The tests showed that the predictions of the model were accurate and efficient.