A study on the removal of infinitesimal particles on a wall by high-speed air jet―Measurements of adhesive force and particle removal rate―

Abstract

We investigated the mechanism for the removal of fine particles from a solid wall using a high-speed impinging air jet. In general, it is difficult to remove fine particles of the order of micrometers by the impingement of simple air flow because they strongly adhere to the surface by van der Waals forces and remain immersed in the viscous sublayer. To overcome this, we developed high-speed air jet nozzles with triangular cavities that add strong velocity and pressure fluctuations to the high-speed air flow. The experimental results showed that the cavity nozzle enhances the removal performance for particles larger than 1 μm. The effect of the pressure fluctuation induced in the jet flow on the removal performance is discussed from the experimental results. First, the adhesive force was measured experimentally from the centrifugal force acting on particles with 5-25 μm diameters set on a rotating disk. Based on a simple theoretical consideration regarding the balance of moments acting on a particle, we estimated the effects of hydrodynamic removal forces such as drag, lift, and pressure gradient fluctuation against measured adhesive forces. The theoretical estimation showed that drag plays a major role, and the force of the pressure gradient could be effective for the removal of large particles. The proposed model is able to explain the experimental results indicating that the removal rates for 3-μm-sized particles are improved by the air flow velocity fluctuations generated by the cavity nozzle.