Heat Transfer Enhancement in Rectangular Channels Using a Corona Jet Caused by Longitudinal Flat Electrodes

Abstract

Heat transfer in rectangular channels can be significantly enhanced by formation of secondary flows. Secondary flow fields appear within the channels and influence the boundary layer growth and improve the convective heat transfer. When a high potential is applied to two electrodes, the consequent high electric field in the gap between the electrodes may exceed the partial break-down limit of the gas molecules. The neutral gas molecules are ionized close to the emitting electrode and accelerate in the direction of the electric field. The accelerating ions impose an electric body-force to the gas and induce a bulk flow. Depending on the location and geometry of the electrodes, the electrically-induced flow field might have different specifications. If the electrodes are laid on the opposite walls of channel and extended in the longitudinal direction, the electric body-force would cause a secondary flow on the cross section of the channel. The electrically-induced flow field disturbs the boundary layer and enhances the convective heat transfer coefficient. However, the enhancement level is more remarkable in natural convection. In this study, the influence of a corona jet on heat transfer in rectangular channels with flat and longitudinal electrodes will be studied. The emitting and collecting electrodes are metallic strips attached to opposite walls of the channel and are extended along the axis of the channel. The electric field governing equations are solved numerically using finite-volume method and the third-order QUICK scheme is utilized for discretization of the charge fluxes. The distribution of electric field and charge density on the cross section of the channel is obtained to find the electric body-force at each point. In the presence of electric and buoyancy forces, the momentum and energy equations are solved to determine the level of enhancement of convective heat transfer using corona discharge.