Realistic Air Filter Media Performance Simulation. Part I: Navier-Stokes / Finite-Volume CFD Procedures

A review of published studies of numerical techniques for air filter performance simulation shows that there are two general approaches to such simulations. One describes gases flowing through filter media as continuous fluids, influenced by themacro properties viscosity, density, and pressure. The alternate approach treats gases as molecules in random motion, impacting their own kind and solid surfaces on a micro-scale. The appropriate form for a given filter medium and operating condition depends on the gas properties and the Knudsen number (Kn) of the smallest fibers in the filter medium simulated. When no fiber Kn exceeds 0.01, the Navier-Stokes equation and finite-volume solutions should simulate filter media pressure drop and particle capture reliably, if correct particle and fiber boundary conditions, including "slip" at boundaries, are employed. In addition, fibrous media geometry must be modeled in enough detail to make simulation results match experimental data. Part I of this study reviews literature related to filter media flow and particle-capture simulation in the continuum regime using the finite-volume method for flow calculations; appropriate boundary conditions and parameter values are suggested. Part II discusses media simulation in flow regimes where other equations and computation techniques must be use