Effects of electric field on flow boiling heat transfer characteristics in a microchannel heat sink with various orientations

Abstract

This study investigates the effects of the electric field in an inclined microchannel heat sink with a hydraulic diameter of 2 mm. The saturated flow boiling performance of a dielectric liquid R141b is experimentally characterized. An electrode fabricated with enameled copper wires is placed above the medium and energized to generate an electric field between it and the heated surface with the applied voltage from 0 V to 200 V. The thermal performance, with/without electric field, under various orientations from 0° to 90°, is evaluated at an inlet mass flux of 51.58 kg/(m2·s) and initial temperature of 299.15 K. Results show that the onset of nucleation boiling is delayed by the electric field. Electric field brings more production and rotary/lateral motion of bubbles which contributes to advance the flow pattern transition. Under the electric field, elongated bubbles burst and some vortexes appear in the liquid film, which has been recorded by the high-speed video camera. Overall, the electric field can remarkably promote the flow boiling heat transfer coefficient (HTC) in lower vapor quality regions, and the maximum enhancement ratio is obtained as 1.48 under present conditions. However, the microchannel prematurely dries out due to the electric field. In this research, flow boiling HTCs are sensitive to orientation. With a constant applied voltage, the performance declines between 0°∼90° while a special transition happens between 45°∼60° Based on the Gungor-Winterton correlation, and revised with the exponential function as well as a non-dimensional number representing the electric field force, a new HTC asymptotic model is developed by first considering the effects of the electric field with an error of ±15% to the experimental data.