24 巻 (1987) 4 号 p. 233-239
The adhesion force of a particle on a flat plate and on a cylinder was measured by centrifugal and air-drag methods. Then it was compared with van der Waals force.
Glass beads (dp=20-70μm) and zinc particles (dp=5-10μm) were used as test particles, and acrylic and brass plates were used as wall materials in the experiments. The detached fraction of the particles normal and tangential to the attached plane was measured at different centrifugal effect, and detachment force of a particle was then evaluated. The detachment force normal to the attached plate increased proportionally to particle size and agreed with the trend of van der Waals force. For the case of detachment in the tangential direction, the force required for the detachment was about one fiftieth of that in the normal direction, and it was expressible by the product of the frictional coefficient of the particle and the summation of the normal directional detachment force and particle weight.
In the air-drag method, the detachment of the glass beads (dp=15-720μm) from enamel (df=176μm) and stainless steel (df=815μm) wires was measured. Particles detached from a wire about 10m/s, and no significant difference was observed in the attached angle. This suggests that the reentrainment of captured particles may not take place frequently under the ordinary filtration condition of an air filter at several tens cm/s. The detachment of fine particles on a wire can be explained by the balance between fluid drag and van der Waals force. Based on the experimental evidence, it can be concluded that collected particles do not detach from a fiber surface under ordinary filtration conditions unless they do not form an unstable agglomerate on the fiber.