This paper presents a combined volume-of-fluid and discrete Lagrangian particle tracking method which can be used to simulate oil-mist or coalescing filters, and gauge their effectiveness. The solver is built on the open-source OpenFOAM CFD libraries, which are extended to include a physically accurate model for motion of small particles, coupled with a volume-offluid treatment as particles coalesce, or are collected on the fibres. A key part of the method is accounting for particles as they change between a discrete Lagrangian treatment to a volume-offluid treatment. Results from an investigation into an idealised filter geometry are used to demonstrate that the method is feasible, robust and that realistic behaviour of an oil-mist filter can be captured. Successful implementation of the method should lead to a better understanding of the behaviour of oil mist filters, and will allow design options to be explored through simulation, in addition to experimentation.