Experimental Evidence for Nonuniform Flow in a Horizontal Evaporation/Condensation Aerosol Generator

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Abstract
The formation of deposition patterns in the cooling zone during operation of a horizontal evaporation/condensation nanoparticle generator was studied to obtain information about flow conditions during particle formation. Quartz reactor tubes were used together with a simple light attenuation measurement to characterize deposition as a function of axial location. Results for the onset and pattern of deposition for four different metals—indium, gallium, silver, and lead—were obtained, and size distributions for indium and gallium particle nanoparticles at different temperatures were measured. Distinct deposition bands could be observed resulting from vapor deposition, nanoparticle deposition, or a combination of both. The location of the bands varied with metal and evaporation temperature. Experimentally observed fluctuations in temperature, bimodal size distributions obtained at the highest furnace temperatures, as well as asymmetric deposition patterns suggested the flow in the cooling portion of the generator is nonuniform, possibly as a result of buoyancy. These results are important for the design of nanoparticle generation systems, in that horizontal evaporation/condensation generators are often chosen on the basis of assumed simplicity with respect to flow, and this may not always be the case.

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