PARTICLE FILTER BASED ON THERMOPHORETIC DEPOSITION FROM NATURAL-CONVECTION FLOW

We present an analysis of particle migration in a natural convection f low between parallel plates and within the annulus of concentric tubes . The flow channel is vertically oriented with one surface maintained at a higher temperature than the other. Particle migration is dominate d by advection in the vertical direction and thermophoresis in the hor izontal direction. From scale analysis it is demonstrated that particl es are completely removed from air flowing through the channel if its length exceeds L(c) = (b4g/24K v2), where b is the width of the channe l, g is the acceleration of gravity, K is a thermophoretic coefficient of order 0.5, and v is the kinematic viscosity of air. Precise predic tions of particle removal efficiency as a function of system parameter s are obtained by numerical solution of the governing equations. Based on the model results, it appears feasible to develop a practical filt er for removing smoke particles from a smoldering cigarette in an asht ray by using natural convection in combination with thermophoresis.