Estimation of Air Velocity for Levitation of Microparticles for Air Quality Control

摘要

Using Newton's first law of motion and geometrical analysis, we performed an estimation of force balance on a microparticle to figure out the conditions for dust levitation and ventilation. The dust particle is assumed to be a sphere pushed by a uniform upward airflow. The gravitational force pulls it downward. The velocity-dependent drag force is assumed to be zero. The results show that the minimal speed of air is proportional to the square root of both the particle mass density and size. To visualize the formula, five samples of dust have been used involving hazardous PM2.5 dust. The minimal speed for PM2.5 dust at room temperature is similar to 22 cm/s, which is just 10% higher than the "breeze" speed of air commonly known in the industry. This analysis could be adopted to other more complex shapes of microparticles, such as ellipsoids and cylinders corresponding to various kinds of dust. The result could also help figure out optimal and effective ventilation and filtration systems toward saving energy in air quality control.