Modeling and prediction of loading characteristics of electret filter media for PM2.5

Abstract

Electret filter media are widely used to improve indoor air quality. However, their filtration performance may degrade severely as particles deposit, resulting in the increasing risk of human/instrument exposure to PM2.5 pollution. Therefore, it is of great significance to predict the performance evolution of electret filter media during particle loading to better meet practical applications. Herein, a novel model was developed to estimate and predict the loading characteristics of electret media, considering the charge screening effect due to particle deposition, the surface charge decay caused by conductance, and the particle deposition morphology affected by RH and particle hygroscopicity. The deposited particles were innovatively divided into homogeneous- and dendritic-deposition particles (HPs/DPs), and the two can be transformed into each other through the collapse of DPs and the growth of HPs. The humidity factor related to relative humidity (RH) and particle hygroscopicity was proposed to quantitatively describe the mutual conversion between DPs and HPs based on experimental results. In addition, a new calculation method of electrostatic efficiency considering deposition distance was proposed to describe screen effect. Furthermore, the dynamic charge decay of electret media caused by the deposition of conductive particles was modelled according to Kirchhoff's current law. The developed simple and efficient model had no adjustable parameter. It showed satisfactory predictive ability under various particle loading conditions in comparison with the results of experiments and references.