Separation performance of a rectangular jet virtual impactor has been studied with attention to flow rate ratio, nozzle Reynolds number and nozzle width ratio. The constructed impactor is a two dimensional and symmetric type. The flows of particle -air mixture divides into two major flows (deflected flow) and one minor flow (undeflected flow). The separation efficiency is measured by the photographs of optical microscope. The experimental results indicate that the separation efficiency curve and 50% cut - off Stokes number are not sensitive to the nozzle Reynolds number. However, if the Stokes number is replaced by the aerodynaic particle diameter, 50% particle cut - off size decreases as Reynolds number increases. 50% cut - off stokes number decreases as the flow rate ratio and nozzle width ratio increase. The contamination of minor flow increases as the flow rate ratio increases.
