Evaluation of Metal Oxide Whiskers Grown on Screens for Use as Aerosol Filtration Media

Abstract

Metal oxide whiskers grown on commercially available screens were evaluated as new filter media. The screens were woven from phosphor bronze wire of diameter D, , = 114 pm in a square mesh with fraction open area E = 0.303. Whiskers' diameters are remarkably uniform for the chosen growth conditions, averaging about 0.6 pm. Whisker lengths are much more variable, and whiskers over 20 pm long can be grown. Pressure drop Ap, and aerosol penetration P , through N identical screens in series were measured. N varied from 1 to 10. The aerosols were dioctylphthalate droplets of diameter Dp equal to 1.0, 2.0, or 4.6 pm. The face velocity U was varied from 0.15 to 5 m/s. Capture efficiency was expressed in terms of a single-wire capture efficiency q computed as follows: q = (1 -Pk/N)/(l -E ) . For a given screen, the single-wire efficiency was found to be an increasing function of both particle size and face velocity, suggesting that capture is dominated by impaction. For each screen, q was successfully correlated with a Stokes number S t k = p p~j~p~/ 1 8 p D , , , . However, the unoxidized screens also required accounting for the variation of the Reynolds number Re = pD,,+,,U/p. The influence of whiskers on q increases as the average whisker length increases or as Stk decreases, and iucreases for q of 10 to 50-fold, relative to uunxidized screens, have been measured. To compare the advantage of lower penetration with the disadvantage of higher pressure drop, a figure of merit Nq/Ap, was computed. For Dp = 1.0 pm, whiskers are advantageous relative to unoxidized screens over the entire range of velocity; for Dp= 2.0 pm, whiskers are advantageous for U < 2 m/s; and for Dp = 4.6 pm, whiskers are advantageous for U < 0.5 m/s.

Bactericidal Hollow S-NiCo2O4 Nanoneedles for Air Purification

“…Meanwhile, the doping process due to the Kirkendall effect transforms the nanoneedles into a hollow structure, which enhances the local electric field strength. Meanwhile, the nanoneedle arrays can better improve the filter collection efficiency (bacterial contact efficiency) and reduce the pressure drop variation at the appropriate pore size and flow rate by combining this oxygen vacancy-rich “hollow nanoneedle” with electric field sterilization technology. − The instantaneous inactivation rates of E. coli and S.…”