Experimental Investigation of Pressure Drop with Particle Loading in Nuclepore Filters

This paper presents an experimental investigation of the increase in pressure drop with particle loading in Nuclepore filters. The average increase in pressure drop per unit time and particle mass concentration was measured as a function of particle size, density, and hygroscopicity. Two different Nuclepore filter pore diameters were tested (2 and 5 mu m, respectively) at filter face velocities ranging from 4 to 52 cm/s. Our results showed that the increase in the pressure drop with particle loading inversely proportional to the square root of particle specific gravity and depends weakly on particle diameter (to the power of- 0.2). Furthermore, the increase in the pressure drop with particle loading is proportional to the filter face velocity and inversely proportional to the cube of the pore diameter. Particle interception and impaction on the pore edges are the main deposition mechanisms that are responsible for raising the pressure drop over time across the filter, especially for particles having Stokes numbers below 5. Particle deposition due to diffusion inside the pores is important for particles smaller than 0.2 mu m. These observations agree well with previously published studies on particle deposition on the pore edges in Nuclepore filters. Our tests also showed a dramatic decrease in the pressure drop with loading for hygroscopic particles as the relative humidity increases from 10% to 50%. The pressure drop with loading decreases almost inversely proportional to the relative humidity for ammonium sulfate particles.