Simulation of low pressure impactor collection efficiency curves

The collection efficiency of the low pressure impactors has been studied using numerical simulations. Flow field was modeled by solving the equations describing the time-average flow field (RANS) with a commercial CFD solver. Particle tracks were calculated separately using Lagrangian methods. Simulation results were verified against published experimental results. Effect of turbulent velocity fluctuations on the impactor resolution was investigated by comparing the ratio of the simulated to experimental impactor resolutions as a function of the turbulence level of the jet. It was found that the turbulence is the dominant mechanism reducing the resolution when the local Reynolds number is over 1800. Effect of jet-to-plate distance on the resolution of the low pressure impactor was studied in the case of low turbulence level. Highest resolution was achieved when the ratio of jet diameter to jet to plate distance (S/W) is 2. When the ratio is lower or higher, resolution is reduced because there is an increase in nonuniformity of the impaction conditions across the jet.

Research highlights
► The collection efficiencies of low pressure impactors were studied using RANS based numerical simulation methods.
► Turbulence is the dominant mechanism reducing the steepness of the collection efficiency curve when the local Reynolds number (Re  ) in the jet exceeds 1800.
► For Re<1800Re<1800, the uniformity of the impaction conditions defines the steepness of the collection efficiency curve.
► Round orifice, high jet velocity impactor operates with the best resolution when the ratio of jet-to-plate distance to jet diameter is 2.