Experimental Study of Impulse Resuspension with Laser Doppler Vibrometry

Abstract

Particle resuspension due to mechanical impulse was studied for spherical polymethylmethacrylate (pmma) particles ranging from 1.7 to 14.4 µm in diameter on titanium dioxide (TiO 2 ) and silicon dioxide (SiO 2 ) wafers. Dry powders were dispersed, electrostatically neutralized, and allowed to deposit under the influence of gravity. Contaminated surfaces were then mechanically excited with a 5 MHz piezoelectric transducer where surface accelerations (∼10 6 m/s 2 ) and resuspension ratios were quantified with laser Doppler vibrometry (LDV) and digital microscopy, respectively. For TiO 2 , experiments were performed over a broad range of relative humidity (25 to 95%) to assess the effects of capillary condensation. Resuspension was a monotonically decreasing function of relative humidity. Existing theories were used to separate data into two adhesion regimes based on capillary bridge formation: van der Waals (vdW) and capillary dominated adhesion. For relative humidity above 60%, resuspension forces were nondimensionalized by the theoretical capillary force. Resuspension data for all particle sizes and relative humidity were described by a single sigmoid function dependent on the dimensionless resuspension force. Below 60% relative humidity, resuspension forces were nondimensionalized by the vdW force calculated with Johnson-Kendall-Roberts adhesion theory. The experimental work of adhesion (pmma-TiO 2 ) was optimized such that the dimensionless resuspension curves, for capillary and vdW forces, had equivalent dimensionless resuspension forces at 50% resuspension. The calculated value, 0.047 J/m 2 , was within the range of values expected from other published works. Resuspension was not observed for particles on SiO 2 substrates. This result was attributed to electrostatic surface charge patches where particle charge and surface resistivities were measured to analyze the relative influence of electrostatic adhesion forces.

Effects of relative humidity and particle and surface properties on particle resuspension rates

“…In particular, high RH can lead to capillary condensation between a particle and a surface strongly enhancing adhesion and suppressing particle resuspension Hubbard et al 2012). Ibrahim et al (2004) showed that the threshold velocity to detach 50% of the 70 mm stainless steel spheres on glass surfaces in a wind tunnel was increased from 3.6 m/s to 13.4 m/s as humidity increased from 18% to 67%.…”

“…Ibrahim et al (2004) showed that the threshold velocity to detach 50% of the 70 mm stainless steel spheres on glass surfaces in a wind tunnel was increased from 3.6 m/s to 13.4 m/s as humidity increased from 18% to 67%. Likewise, resuspension of 1.7 -14.4 mm poly(methyl methacrylate) (PMMA) spheres from TiO 2 surfaces by mechanical impulse force (vibration) decreased monotonically with increasing RH (Hubbard et al 2012).…”

“…These studies show that in addition to RH, capillary force strength is influenced by surface chemistry and geometry (Jones et al 2002), especially the nanoscale roughness of both the particles and the surfaces Hubbard et al 2012). These roughness studies are important, because most particles found in the environment are not smooth at the nanoscale (Goldasteh et al 2012).…”

Monolayer and Multilayer Particle Deposits on Hard Surfaces: Literature Review and Implications for Particle Resuspension in the Indoor Environment

“…Full-scale walking-induced resuspension studies have reported resuspension from both monolayer (Karlsson et al 1999;Tian et al 2011) and multilayer deposits Kubota et al 2009;Tian et al 2011;Shaughnessy andVu 2012, Kubota andHiguchi 2013) on hard flooring. Gomes et al (2007) found aerodynamic removal forces associated with airflow disturbances generated by human walking to be the primary mechanism for particle resuspension from flooring, although surface vibrations, mechanical abrasion, and electrostatic forces can contribute to resuspension (Gomes et al 2007;Hu et al 2008;Qian and Ferro 2008;Hubbard et al 2012). Several studies investigated the airflow generated by foot motions.…”

Vocal fold vibration measurements using laser Doppler vibrometry

“…7 This method has been used for non-contact vibration measurements within the automotive, aerospace, biomedical, and acoustics industries. [8][9][10] For vocal fold velocity measurements, LDV can measure the inferior-superior vibrations and has advantages over standard and high-speed videoendoscopy. It yields online quantitative data, in contrast with qualitative video data that require further image analysis.…”