Electrohydrodynamic-Enhanced Natural Convection in an Enclosure by a Nonsymmetric Electric Field

摘要

The present study investigates heat transfer enhancement of natural convection in an air-filled enclosure by a nonsymmetric electric field. The geometry considered is a two-dimensional cavity with an aspect ratio of five. The electrical field is generated from a wire electrode charged with a high voltage of direct current with a positive polarity. Ionized air produced by corona discharge is issued from the wire, which impinges on the differentially heated walls and leads to substantial heat transfer enhancement. Numerical calculations have covered a wide range of parameters (that is, Vo = 12, 15, and 18 kV; and 104 Ra 106). In the presence of an electric field, the flow and temperature fields may become steady, steady periodic, or nonperiodic. At low Rayleigh numbers, it is observed that the flow and temperature fields are basically oscillatory in nature. When the Rayleigh number is sufficiently increased, a steady state may be reached. Owing to the presence of oscillatory flows, there is a significant increase in heat transfer. It is found that heat transfer enhancement increases with the applied voltage but decreases with the Rayleigh number. In addition, it is found that heat transfer enhancement can be maximized by placing the electrode closer to and leaning toward the leading edge of the heat transfer surface: that is, to perturb the thermal boundary layer as early as it begins to develop.