Flow Induced by a Two Stage Electrohydrodynamic Gas Pump in a Square Channel

Previous studies have shown that electric field in the form of corona wind can be used for gas pumping and heat transfer enhancement. In this study, fluid flow induced by a two stage electrohydrodynamic (EHD) gas pump in a square channel has been evaluated by experimental measurement and numerical simulations for its potential in the enhancement of gas pumping and heat transfer. Using the finite difference and finite volume method respectively, the three-dimensional governing equations for the electric and flow fields are solved. The EHD induced flow in a square channel is calculated first, and its results are compared with the collected experimental data to validate the computational code. This study is implemented for a two stage EHD gas pump with three emitting electrode configurations:  8, 24, and 56 respectively to seek the relation between the number of stages and emitting electrodes. The EHD pump is evaluated for a wide range of operating voltages starting from 20 kV up to 28 kV for further improvement in its performance over a single stage. To achieve the maximum enhancement, the emitting electrodes of the EHD gas pump are flush mounted on the channel walls so that the corona wind produced directly disturbs the boundary layer thickness and improves the heat transfer. This is leading to a higher velocity near the channel walls and resulting in an inverted parabolic velocity profile at the center of the channel, which is opposite to the fully developed velocity profile of a forced flow.

Both corona current and corona wind velocity inside the channel are obtained for operations using positive corona discharges. Velocities are measured at three cross-sections along the tube length and then integrated to obtain the volume flow rate. According to the findings, the EHD gas pump can produce and sustain gas flows with a maximum velocity and its maximum performance is better than conventional cooling fan. The numerical results, which complements the experimental work, enable vivid flow visualizations inside the channel, providing a great understanding of the development of the induced flow. The performance of the EHD gas pump is then evaluated against that of conventional fans used in personal computers. The pumping power required for the heat transfer enhancement is also critically evaluated. The enhancement produced by the EHD gas pump is found to be higher than other techniques and with a smaller power penalty. The results show that EHD technique has a great potential for many engineering applications.