Fine/ultrafine particle air filtration and aerosol loading of hollow-fiber membranes: A comparison of mathematical models for the most penetrating particle size and dimensionless permeability with experimental data

Abstract

Hollow-fiber membranes (HFMs) have widely been applied to many liquid treatment applications such as wastewater treatment, membrane distillation and membrane contactor/bioreactor applications. However, they have rarely been used for aerosol filtration thus far. In this work, we tested air filtration performance of air filter modules composed of polypropylene HFMs. The experimental results of most penetrating particle size (MPPS) and permeability were then compared with theoretically predicted values. Filtration efficiency and MPPS were measured using a monodisperse (20, 35, 50, 70, 100, 140, 280 and 400 nm) and a polydisperse aerosol (15–594 nm). Dimensionless permeability was predicted using models assuming isotropic 3D pore structure and compared with permeability measured using capillary flow porometry. Finally, an experiment to observe pressure drop with long-term particle loading was carried out. In the experiments with the monodisperse aerosol, no penetration was observed regardless of particle size. Therefore, face velocity was increased and high concentrations of the polydisperse aerosol were used to increase the penetration. The MPPS was then found to be 333 and 250 nm at a flowrate of 10 and 40 L/min, respectively. The MPPS model for diffusion and interception dominant regime proposed by Lee and Liu (1986) was closest to these results. Dimensionless permeability varied depending on the conditions for which the individual models were derived. For example, the RUC (representative unit cell) model underestimates the results while the results predicted using the empirical formula of Davies (1953) differ significantly from the measured values. The loading experiments have shown significantly prolonged fouling by high concentrations of submicron particles compared to conventional fibrous filters.