The objective of this paper is to identify the requirements for accurate predictions of impaction efficiency on tubes using Reynolds Averaged Navier-Stokes (RANSs) approach. Flows which pass a cylinder have been computed using steady-state and time-dependent simulations with emphasis on numerical related errors, boundary layer and turbulence modelling. Inertial impaction on the front face of the cylinder and eddy impaction on the rear face have been considered. Accurate predictions of the impaction efficiency are obtainable only when the flow-field in the neighbourhood of the deposition surface is accurately resolved. The paper formulates the measures needed for accurate predictions of the particle arrival rate. (C) 2012 Elsevier Ltd. All rights reserved.