A study of virtual impactor

A virtual impactor is an instrument used for separation, sampling, and classification of particulate matters (aerosols). It consists of a flow acceleration nozzle, and a receiving tube placed at a distance directly under the nozzle. A particle-laden flow is directed through the nozzle and split into the minor flow and the major flow. The minor flow is passed through the receiving tube while the major flow travels radially outward. The particles that are contained in the flow are classified according to their inertia since large particles pass into the receiving tube while the small ones follow the flow streamlines into the space between the nozzle and the receiving tube.; The virtual impactor is usually operated at a low flow rate ({dollar}<{dollar}20 lpm) and a minor flow rate of 5-10% of the total flow. The objectives of this work are to study: (i) the feasibility of a virtual impactor operated at a 1% minor flow ratio or even lower; (ii) the feasibility of a virtual impactor operated at a high total flow rate; and (iii) the mechanisms of internal particle losses on various parts of the virtual impactor.; Monodisperse oleic acid particles with uranine tracer are generated from the Vibrating Orifice Monodisperse Aerosol Generator. The subsequent depositions of these particles on the filters and the surfaces of the virtual impactor are indications of particle penetration rate into the receiving tube and internal particle losses.; The experimental results show that a virtual impactor can be operated at low minor flow ratios and high flow rates with fairly sharp separation characteristics. Design of a virtual impactor can be optimized such that the particle wall losses inside the virtual impactor are minimized. The mechanisms for internal particle losses are explored. The particle losses on the backside and upstream surfaces are the result of inertial impaction. The turbulent flow analysis suggests that the particle wall losses associated with large-cut size virtual impactor are the result of turbulent deposition.