Aerosol Deposition in Transport Lines

Abstract

Particle deposition in contraction fittings with half-angles of 12 degrees, 45 degrees, and 90 degrees; expansion fittings with half-angles of 3 degrees, 6 degrees, 12 degrees, 45 degrees, and 90 degrees; and large-diameter transport lines (up to 102 mm diameter) was measured experimentally. Aerosol losses in the transition fittings were found to be a function of three parameters; namely, Stokes number, area ratio, and half-angle. Based on experimental data, correlations were developed that allow prediction of particle losses in contraction and expansion fittings as a function of Stokes number, area ratio, and half-angle. A correlation was also developed for large transport tubes that allows prediction of non-dimensional dep0sition velocity as a function of non-dimensional relaxation time and flow Reynolds number.

For a given half-angle, losses in a contraction fitting correlate well with the parameter Stkc(1-Ao, Ae) Aerosol particle deposition in the contraction fittings was also modelled numerically and the numerical results show good agreement with experimental data. In general, losses in a contraction fitting decrease with decreasing half-angle and area ratio.

Losses in expansion fittings increase with decreasing half-angle down to an angle of approximately 12 degrees thereafter, losses decrease with decreasing half-angle. Losses decrease with decreasing area ratio. A 90 degree expansion half-angle fitting produced the lowest aerosol losses. The correlation for large-diameter transport tubes shows good agreement with previous correlations for deposition in small diameter tubes as well for the full range of tube sizes (13 mm to 102 mm diameter) and Reynolds numbers (up to 55,000) tested. For large tubes, the correlation shows improved prediction characteristics as compared to earlier models. For example, penetration of 20 um aerodynamic diameter aerosol particles through a I 02 mm diameter tube at a flow rate of 2260 L/min was measured to be 59%. The present model predicts a penetration of 62%, while two previously reported models that do not include Reynolds number effects, predict 80% and 82%. The correlations presented in this study should be useful sub-models for predicting aerosol losses in transition fittings and large-diameter transport system; in general, models that are used to evaluate overall losses in aerosol transport systems.