Numerical simulations can aid in the development of more efficient air filters, not only by increasing separation efficiency and reducing air-flow pressure drop but also by enhancing filter loading capacity thereby increasing resource efficiency. However, in order to correctly determine time-varying performance parameters, an accurate representation of the filter media structure and a sufficiently accurate physical numerical model are required.

In the present work, particle deposition on a single filter fiber (representing the smallest unit of a fibrous filter media) is investigated. A two-step simulation process is used based on the coupled CFD-DEM approach; the latter employing OpenFOAM-8 as flow solver and well-established DEM contact models, which include adhesive/cohesive force interactions and a suitable set of DEM model parameters for the investigated particle/fiber system. In the first step, the flow field around the fiber and deposited particles is solved in a resolved fashion using the immersed-boundary (IB) method.

From this, the force and moment vector acting on each deposited particle due to aerodynamic interaction is computed by integrating viscous stresses and pressure over the particle surface. This information is used in the second step in which the deposition of particles (newly admitted to the flow field) on the existing fiber/particle structure is computed. The particles are propagated within the already computed flow field (via one-way coupling) while taking into account contact forces between all particles (free or deposited) and between particles and fiber. Aerodynamic forces acting on the free particles are computed using a simple drag-model whereas aerodynamic forces (and moments) acting on deposited particles are retained from the previous step. Particle-particle and particle-fiber interactions are solved directly by the employed DEM algorithm. Subsequently, the first step is repeated including now the newly deposited particles.

Using the prescribed two-step procedure, the deposition of polystyrene particles on a single filter fiber is investigated at various Stokes numbers in the inertia and interception regimes. Considered is a straight fiber under cross-flow conditions with particles being admitted to the gas stream at low volumetric concentration.

The present investigation shows that, depending on the Stokes number different morphologies of particle deposits result. Predictions are found to be in good agreement with experimental observations. More importantly, the present numerical results provide important insights into the dynamics of deposition formation not captured by other simplified approaches such as the frequently employed “stick on first contact” model for particle/particle and particle/fiber interaction. For example, simulation results for the case in which particle dendrites are formed reveal the ...