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The influence of particle shape on the penetration through fibrous filters
J. Aemsol Sci. Vol. 29. Suppl. I, pp. S 1163-S I1 64.1998 0 1998 Published bv Elsevier Science Ltd. All rights reserved Printed in Great Britain 0021-8502/98 $19.00 + 0.00
Pergamon
THE INFLUENCE OF PARTICLE SHAPEON THE PENETRATIONTHROUGH FIBROUSFILTERS I.L. TUINMAN, L. STEENWEG TNO-PML, Lange Kleiwegl37,228OAA Rijswijk, The Netherlands KEYWORDS aerosol filtration, particle shape Aerosols encountered in reality often differ with respect to shape and size from test aerosols used to certify tilters. Because of this a study has been performed to test respiratory protective equipment with aerosols of varying shapes and to determine the intluence of particle shape on the penetration through some fibre filters. With a Condensation Monodisperse Aerosol Generator, CMAG, aerosols with several shapes besides the standard spherical oil-particles have been produced: 1) rod-shaped caffeine particles, 2) angular urea particles, 3) plate-like eicosanoic acid particles, and 4) needle-shaped arachidic acid particles. The aerosols are generated in the way described by Vaughan (1990). First an aerosol consisting of NaCl nuclei (* 40 nm in diameter) is produced with a nebulizer and dried in a diffusion dryer. The flow is then passed through hot vapour of a certain compound and when the flow cools down aerosol particles are formed by condensation of the vapour on the NaCl nuclei. The particle shape is determined by the condensing compound’s crystal structure. The particle size depends on the number of nuclei and the amount of condensing vapour, hence on the vapour temperature. The particle size distribution as a function of the temperature of the compound under production was determined with a DMA (TSI 3071) and for larger particles also with an AI’S (TSI 3320). The penetration of these aerosols through different particle filters has been compared with the penetration of standard oil aerosols (Durasyn 164) with an equivalent particle size distribution. The penetration decreases from spherical particles via angular particles and rods to a lowest penetration for plates. The reduction in penetration is shown in figure 1 (top) for a Drager P2 ftlter challenged with caffeine particles. The results match the Sndiis of Willeke et al. (1996) for rod shaped bacteria with approximately the same aspect ratio (about 4.5) as the caffeine particles have. The caffeine rods seem to form an extra filter layer with a relatively high pressure drop. When filters tested with caffeine are subsequently tested with oil droplets they show higher efficiencies than new filters. Eicosanoic acid more or less clogs the filters within a few minutes (depending on the generation conditions). New tilters show a penetration of eicosanoic acid which is about 10 times lower than that of oil droplets; for used filters the penetration decreases by another factor of 10. Urea shows a penetration comparable to that of NaCl. Thus the penetration is slightly lower than that of oil droplets, an effect which is much more pronounced when electrete filters are tested. S1163
Abstracts
s1164
of the 5th international
Aerosol
Conference
1998
P2 penetration spheres vs. rods spheres: oil droplets diamants: caffeine rods 0.80% f 0.70% -0.60% -g 0.50% -0 g 0.40% --
0
200
400
600
dp (nm) Aerosol generated (volume base) oil droplets (spheres) caffeine rods (diamants) 2E+l3
-
2E+13
--
4E+i2
--
2E+l2
-I
0
400
600
800
dp (nm) fig , 1 Comparison of the penetration of caffeine rods and spherical oil droplets(top) through a Drtiger P2jlter as a function of particle size determined with a DikL-4 (bottom).
REFERENCES N.P. Vaughan (1990), The generationofmonodispersefibers of caffeine,J. Aeros Sci.21, pp. 453-462 K. Willeke, Y. Qian, J. Donnely, S.Grinshpun, V. Ulevicius(1990), Penetrationof airbornemicroorganisms through a surgicalmask and a dust mist respirator,Am. Ind. Hyg. Ass.J. 57,348-355
Pergamon
THE INFLUENCE OF PARTICLE SHAPEON THE PENETRATIONTHROUGH FIBROUSFILTERS I.L. TUINMAN, L. STEENWEG TNO-PML, Lange Kleiwegl37,228OAA Rijswijk, The Netherlands KEYWORDS aerosol filtration, particle shape Aerosols encountered in reality often differ with respect to shape and size from test aerosols used to certify tilters. Because of this a study has been performed to test respiratory protective equipment with aerosols of varying shapes and to determine the intluence of particle shape on the penetration through some fibre filters. With a Condensation Monodisperse Aerosol Generator, CMAG, aerosols with several shapes besides the standard spherical oil-particles have been produced: 1) rod-shaped caffeine particles, 2) angular urea particles, 3) plate-like eicosanoic acid particles, and 4) needle-shaped arachidic acid particles. The aerosols are generated in the way described by Vaughan (1990). First an aerosol consisting of NaCl nuclei (* 40 nm in diameter) is produced with a nebulizer and dried in a diffusion dryer. The flow is then passed through hot vapour of a certain compound and when the flow cools down aerosol particles are formed by condensation of the vapour on the NaCl nuclei. The particle shape is determined by the condensing compound’s crystal structure. The particle size depends on the number of nuclei and the amount of condensing vapour, hence on the vapour temperature. The particle size distribution as a function of the temperature of the compound under production was determined with a DMA (TSI 3071) and for larger particles also with an AI’S (TSI 3320). The penetration of these aerosols through different particle filters has been compared with the penetration of standard oil aerosols (Durasyn 164) with an equivalent particle size distribution. The penetration decreases from spherical particles via angular particles and rods to a lowest penetration for plates. The reduction in penetration is shown in figure 1 (top) for a Drager P2 ftlter challenged with caffeine particles. The results match the Sndiis of Willeke et al. (1996) for rod shaped bacteria with approximately the same aspect ratio (about 4.5) as the caffeine particles have. The caffeine rods seem to form an extra filter layer with a relatively high pressure drop. When filters tested with caffeine are subsequently tested with oil droplets they show higher efficiencies than new filters. Eicosanoic acid more or less clogs the filters within a few minutes (depending on the generation conditions). New tilters show a penetration of eicosanoic acid which is about 10 times lower than that of oil droplets; for used filters the penetration decreases by another factor of 10. Urea shows a penetration comparable to that of NaCl. Thus the penetration is slightly lower than that of oil droplets, an effect which is much more pronounced when electrete filters are tested. S1163
Abstracts
s1164
of the 5th international
Aerosol
Conference
1998
P2 penetration spheres vs. rods spheres: oil droplets diamants: caffeine rods 0.80% f 0.70% -0.60% -g 0.50% -0 g 0.40% --
0
200
400
600
dp (nm) Aerosol generated (volume base) oil droplets (spheres) caffeine rods (diamants) 2E+l3
-
2E+13
--
4E+i2
--
2E+l2
-I
0
400
600
800
dp (nm) fig , 1 Comparison of the penetration of caffeine rods and spherical oil droplets(top) through a Drtiger P2jlter as a function of particle size determined with a DikL-4 (bottom).
REFERENCES N.P. Vaughan (1990), The generationofmonodispersefibers of caffeine,J. Aeros Sci.21, pp. 453-462 K. Willeke, Y. Qian, J. Donnely, S.Grinshpun, V. Ulevicius(1990), Penetrationof airbornemicroorganisms through a surgicalmask and a dust mist respirator,Am. Ind. Hyg. Ass.J. 57,348-355