Augmentation Mechanism of Forced-Convection Heat Transfer by Applying Electric Fields in the Restricted Region near the Wall

By applying electric fields using the array of wire electrodes installed near the heat transfer wall along the main stream, in the range of low Reynolds number, the heat transfer coefficients of liquid were augmented to the same order as that in turbulent flow, and the pressure drop was increased but still remained on the same order as that in laminar flow. It was clarified that the ratio of Colburn's J factor to the friction factor for evaluating the performance became 4.4 times for Re = 1470 and 1.9 times for Re = 20000 with the electric field of 10 kV/cm. Furthermore, by analyzing the power spectrum of the flow velocity and electric current, the peak regions around 1 Hz were found to be increased by applying electric fields, which means the fluctuation of negative ion flow emitted from the cathode, as clarified by the voltage-current characteristics of the electrostatic probe in the higher-potential region.