Numerical Study On The Filtration Characteristics Of Electret Filters

Electret filters are mainly used to remove micron and submicron particles. Its salient character is of high filtration efficiency and low pressure drop. Nowadays, with the increasing of air pollution, electret filter is not only can effectively improve the quality of indoor air, but also decrease the pressure drop to achieve the purpose of saving energy to some extent.The internal gas flow field and its law of the static electret filter were obtained by computational fluid dynamics (CFD) technology in this study, and the pressure drop and dimensionless drag coefficient of the static electret filter with different face velocities were also calculated. In addition, two second-order prediction models of the electret filter filtration performance were studied based on response surface methodology (RSM) by means of the statistical software Minitab. Finally, the filtration characteristic of the dynamic electret filter was simulated by CFD, and the filtration characteristics of the dynamic electret filter with different operating conditions for the charged particles (particle size is ranging from 0.05μm to 0.5μm) were compared. The following conclusions can be obtained:(1) When the air flows through the static electret filter, the periodic flows occur between the first and last array fibers of the static electret filter along the direction of the flow, and the pressure drop increases linearly with the face velocity. In addition, filtration efficiency of the static electret filter is decreased with increasing the horizontal distance between the fibers of the static electret fibers, and increased with the fiber diameter of the static electret filter and face velocity. However, when the face velocity reaches a certain value, the filtration efficiency is decreased with the face velocity.(2) The optimal predicted results show, when the dimensionless horizontal distance, the vertical distance, the fiber diameter and Reynolds number are 0.155, 0.120, 0.070, 4.787 respectively, the electret filter can be achieved 99.4% of high filtration efficiency, while maintained 42.228 Pa of low pressure drop. Furthermore, a satisfactory composite desirability of 0.967 can be obtained at this filtration performance.(3) The electrostatic force is dominant for the smaller particle (﹤0.1μm) among all the capture mechanisms (such as electrostatic, inertial, interception and diffusion), and the electrostatic force becomes weak with increasing the particle size. Additionally, the penetration ratio of the dynamic electret filter is increased with the face velocity when the particle size is ranging from 0.05μm to 0.5μm.(4) The pressure drop of the dynamic electret filter with the same structure is independent of the charges of the particle basically, and is increased linearly with the face velocity. (5) As can be seen from the particle trajectory, the particles are deposited on the back of dynamic electret filter fiber because of the electrostatic force.