Effects of Buoyancy on Electrohydrodynamic-Enhanced Forced Convection in a Vertical Channel

Abstract

Buoyancy effects on heat transfer enhancement using an electrohydrodynamic (EHD) technique is numerically examined for laminar forced convection in a horizontal channel. Attention is also focused on the effect of added buoyancy on the flow stability. The flow Reynolds numbers and thermal buoyancy strength considered are in the range of 6 x 10 2 ≤ Re ≤ 1.8 x 10 3 and 10 4 ≤ Gr ≤ 10 6 , respectively. The electrical field is generated by positive corona from a wire electrode charged with dc high-voltage (10 ≤ V 0 ≤ 17.5 kV). In terms of an EHD number, this corresponds to 0.36 < N ehd ≤ 23.56. The results show that heat transfer enhancement increases with the applied voltage. For a given electric field, oscillation in the flow and temperature fields is observed for flows at small Reynolds numbers. In addition, the flow and temperature fields become more unstable with an increase in the thermal buoyancy strength. Because of the existence of secondary flows, there is an improvement in heat transfer. However, it is observed that thermal buoyancy has a negligible effect on the heat transfer enhancement for Gr < 10 6