Aerosols flowing in a tube under vacuum conditions, e.g., in semiconductor processing equipment, are often found to have a nonuniform profile due to low Reynolds number flow (Bae et al. 1998). A novel method to produce spatially uniform aerosols in a flow tube at low pressure has been developed. The method employs a counter-flow injection configuration. Two identical critical orifices of 200 #mu#m in diameter are installed opposite each other in an aerosol mixing chamber. The opposing aerosol jets from the two orifices resutl in turbulent and uniform mixing of the two aerool streams. Aerosols 0.3 #mu#m or less in diameter, at a pressure as low as 1 Torr, are shown to be distributed uniformly over a cross section of a tube with an inner diameter of 3.48 cm. This method has been further improved to provide spatially unfiorm aerosols at lower pressures by using a pressure reducer downstream of the aerosol mixing chamber. The arrangement provides spatially uniform aerosols at a pressure as low as 0.2 Torr.
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