In this work, we present a semi-numerical 2-D model for predicting the instantaneous pressure drop and collection efficiency of filters made up of rectangular and triangular pleats in both depth and surface filtration regimes. Inspired from previous CFD simulations, our semi-numerical model adopts appropriate average velocity profiles in the axial and lateral directions to approximate the flow field inside rectangular and triangular pleat channels. The model therefore circumvents the need to obtain a CPU-intensive solution for the partial differential equations governing the flow through a filter, i.e., Navier-Stokes equations. The above-mentioned analytical flow field can then be used to predict the trajectory of the particles flowing through the pleat channels by numerically solving the equation of motion for each particle a simple set of second order ordinary differential equations. With the particles trajectories obtained, the deposition location and so the dust-cake profile can be approximated. This allows one to predict the instantaneous pressure drop and collection efficiency of a filter (filter's service life) with a CPU-time of practically zero min. The model developed in this work is aimed at providing the aerosol filtration industry with a fast, but yet fairly accurate method of designing pleated filters. A brief parametric study is presented for model demonstration. In addition, a comparison between the predictions of our model and some experimental data from literature is presented for completeness of the study. (C) 2014 Elsevier B.V. All rights reserved.