Electrohydrodynamic Enhancement of Heat Transfer for Developing Air Flow in Square Ducts

Abstract

Corona discharge in air was used to generate a secondary flow that significantly improved the convective heat transfer coefficient in the developing region of a square duct. A wire electrode, charged with a high voltage, was placed at the center of the duct. The electrode ionized the air and created a corona current, which was measured experimentally and used in the computations. The conservation differential equations for flow, energy, and electric field were considered for the 3D flow in the developing region of the duct, and they were solved numerically. The computational results indicated that the secondary flow gradually evolves into a fully-developed eight-cell vortical structure that creates flow mixing and turbulence and enhances the heat transfer coefficient. In this study, the ranges of Reynolds number and applied voltage were 500–10,000 and 0–11.7 kV, respectively. The normalized Nusselt number, Nu/Nuo, ranged from 1.06 (Re = 10,000 and 8.1 kV) to 13.58 (Re = 2000 and 11.7 kV), but the pressure drop penalty was relatively low. The normalized friction factor, f/fo, ranged from 1.01 (Re = 10,000 and 8.1 kV) to 7.28 (Re = 2000 and 11.7 kV). The computations were verified by comparison with the published literature.