Experimental Investigation On Resuspension Of Deposited Particles On Cloth Surface By Strike

Resuspension of deposited particles contributes to indoor particulate pollution and then causes a serious threat to human health.Research findings in reverse traceability indicated that particle resuspension from surfaces was a result of external disturbance.If the external disturbance was large enough to overcome the adhesive force between the deposited particles and adhered surfaces,the resuspension of deposited particles might occur.The hardness,roughness,and electric charges of the adhered surfaces were the major factors on the adhesive force.Recent studies on the adhered surfaces were primarily concerned with hard materials such as glass,steel,wood,silicon and so on,while the soft and deformable fabrics or cloth was considered less.Therefore,the mechanisms of deposited particles detaching from the soft surface of the cloth such as cleanroom garments and filters are far from being fully understood until now.The study experimentally explored the detachment and resuspension of deposited particles on cloth surface by strike.The aerosolized ultrafine Arizona test dust(ATD)was delivered into a glass enclosure,and one side of the cloth surface was uniformly deposited with the ATDs due to the gravitational settling.The dimensions of the cloth segment were 130 mm(horizontal)×100 mm(vertical).The vertical edges of a cloth segment were clamped to the frame of the test rig.Because the vertical edges of the cloth segment were covered by the clamps with 15 mm in each side,the dimensions of the cloth segment exposed to the air were 100 mm×100 mm.The rod was a hollow cylinder,with a length of 130 mm,an inner diameter of 120 mm,and an outer diameter of 20mm.The rod was against a spring and then suddenly released when pulling out the stop plug.The elastic coefficient of the spring was 0.557 N/m.The strike direction was perpendicular to the cloth surface and the center of the striking rod coincided with the center of the cloth.The vibrating motion of the cloth segment was recorded by a micro laser distance sensor.Tracer smoke generated by a smoke pen was used to observe turbulent airflow induced by the moment of the cloth.A high-speed camera was used to photograph the dynamic processes of the particle detachment from the cloth segment and the vibrating motion of the cloth segment and the induced airflow after the strike.The initial mass of the ATDs adhered on the cloth segment before an experimental test and the residual particle mass after the strike were weighed by a digital precision balance.The ratios of the resuspended,landed,and residual particles from the cloth after striking were calculated.The relationship between the relative light intensity of the image of residual particles and the textile elongation or curvature of the cloth was analyzed.Moreover,the impacts of the strike strength(energy)of the rod,the initial surface dust load on the cloth segment,and the textile type on the particle detachment were compared.It was found that a mechanical strike to a fastened cloth segment could induce strong vibration of the cloth surface.When the cloth was squeezed by the striking rod to the maximum displacement,the reverse acceleration of the cloth was increased to the maximum value.When it reached the threshold(i.e.,192.5 m/s~2 for polyester twill),the adhesion particles were separated by inertia.Turbulent vortices caused by the cloth movement led to the detachment particles decelerate and converged into granular clouds.The central region of the cloth in contact with the striking rot has the lowest elongation and the smallest particle detachment rate during the striking process.When the cloth was squeezed by the striking rod,the unfixed sides bent,causing the granular layer to break up and form large cluster of particles,which promoted the separation of the particles.The increase in the impact strength caused up to 90%of the particles to detach from the cloth surface.The thicker the particle layer was,the easier it was to break up,so when the impact strength reached a value(i.e.,20J/m~2 in the experiment),it was more efficient to clean the cloth with thicker granular layer than thinner granular layer by striking.The surface of the cotton cloth was disorderly and rough,so it was difficult to remove the particles in the gap,resulting in the residual particle mass of the cotton cloth being about 20%more than the polyester cloth.