Effect of Electrode Placement on Flow pattern Enhancing Hot-Air Drying Rate with Electrohydrodynamic Force
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Abstract
This research aims to elucidate the effect of electrode placement both in the flow direction (Ex) and normal to the flow direction (Ey) on airflow subjected to electrodynamic force (EHD) enhancing hot-air drying rate. Additionally, numerical simulations of two-dimensional fluid flow with EHD force are conducted to explore the effect of electrically-driven flow patterns on enhancing the drying rate (DR). In the experimental setup, four electrode wires are suspended perpendicularly from the upper wall of the wind tunnel, while two ground wires, having the same length as the packed bed, are positioned above the packed bed surface and aligned parallel to the flow. At the inlet of the test section, the average velocity and temperature of inlet air are controlled at 0.33 m/s and 60OC, respectively. In addition, a high electrical voltage of 20 kV is applied. The initial saturation (Sint) of the packed bed is 0.5, and the drying period lasts for 12 hours.
The experimental results indicate that, even in the absence of applied heat, the EHD force can enhance the evaporation of moisture from the packed bed. Moreover, the DR of the hot-air flow with EHD is approximately 1.4 – 2.2 times higher than that without EHD. Higher DRs are observed when Ex is positioned near the front end of packed bed surface, but tend to decrease when Ex is located further downstream. Simulation results illustrate that the effect of EHD force induces vortices in front of the electrodes and also increases the air velocity behind these vortices. However, the occurrence of vortices results in low airflow velocities in their front regions. Consequently, when Ex is increased, vortices and high air velocity manifest further downstream. Moreover, the EHD force weakens as the gap between electrode and ground increases. Therefore, when Ey > 4 cm, the DR tends to decrease. However, when Ey = 2 cm, the EHD force only influences the low-temperature layer of airstream near the surface, compelling it towards the packed bed surface. As a result, surface temperature is not significantly increased.
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References
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