Evaluation of Metal Oxide Whiskers Grown on Screens for Use as Aerosol Filtration Media
Titel:
Evaluation of Metal Oxide Whiskers Grown on Screens for Use as Aerosol Filtration Media
Auteur:
Brewer, James M. Goren, Simon L.
Verschenen in:
Aerosol science and technology
Paginering:
Jaargang 3 (1984) nr. 4 pagina's 411-429
Jaar:
1984
Inhoud:
Metal oxide whiskers grown on commercially available screens were evaluated as new filter media. The screens were woven from phosphor bronze wire of diameter Dwire = 114 μm in a square mesh with fraction open area ε = 0.303. Whiskers' diameters are remarkably uniform for the chosen growth conditions, averaging about 0.6 μm. Whisker lengths are much more variable, and whiskers over 20 μm long can be grown. Pressure drop ΔpN and aerosol penetration PN through TV 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 μm. 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 η computed as follows: η = (1 - P1/NN)/(1 - ε). 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, η was successfully correlated with a Stokes number Stk = ρPD2PCPU/18μDwire. However, the un-oxidized screens also required accounting for the variation of the Reynolds number Re = ρDwireU/μ. The influence of whiskers on η increases as the average whisker length increases or as Stk decreases, and increases for η of 10 to 50-fold, relative to unoxidized screens, have been measured. To compare the advantage of lower penetration with the disadvantage of higher pressure drop, a figure of merit Nη/ΔpN was computed. For DP = 1.0 μm, whiskers are advantageous relative to unoxidized screens over the entire range of velocity; for DP = 2.0 μm, whiskers are advantageous for U < 2 m/s; and for DP = 4.6 μm, whiskers are advantageous for U < 0.5 m/s.
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