The Effect of Roughness on Aerosol Deposition in Tubes

Abstract

Experimental measurements of simulated roughness within tubes and the subsequent aerosol penetration performance through these tubes were conducted for a aerosol particle size range of 5 nm to 20 nm and a flow rate range of 28 L/min to 169.9 L/min. The relative roughness for each of the tubes tested are as follows: clean aluminum pipe and clean copper tube, F,/D = 10-4; fine sandpaper pipe, F,/D = 0.017-12 helical ridges per linear centimeter copper tube, F,/D = 0.046; coarse sandpaper pipe, F,/D = 0.065. Non-dimensional quantities were used to produce an empirical model relating roughness to aerosol penetration. The dependent variable, aerosol penetration, was encompassed in the non-dimensional deposition velocity (v,) and modeled as a function of the dependent variables, non-dimensional particle relaxation time (,c,) and relative roughness (&/D). In addition, a method was developed for estimating when to remove the sampling transport lines for cleaning due to the roughness within the transport line. The empirical correlation fits the data over the range of 0. I < 'C, < I 00 and 0.000 I < F,/D < 0. 1. For the aerosol aerodynamic particle size of 5 nm and flow rates between 28 and 84 L/min, the correlation remains within 10% of the experimental data except for outliers which deviated by a maximum of 24% from the experimental data. The correlation yielded similar results for the larger aerosol aerodynamic particle size of 10 nm and increased flow rates of 56 to 112 L/min. For these conditions, the model deviated from the experimental data by less than 10% with one outlier which deviated by 20% for the coarse sandpaper pipe at a flow rate of 1 12 L/min. The correlation was used to show that the transport lines should be removed for cleaning or replacement once the pressure drop has exceeded 7.5 mm Hg. The experimental data has shown that the aerosol penetration decreases below 85% for an internal roughness comparable to this pressure drop limit. The correlation for aerosol penetration in transport lines with internal roughness presented should be a beneficial engineering tool for predicting the aerosol losses in sampling systems where roughness is a concern. The correlation should be a useful sub-model for aerosol penetration prediction computational tools as well.