Laser-induced natural convection and thermophoresis

The influence of axial laser volumetric heating and forced convection on the motion of aerosol particles in a vertical tube has been studied using the Boussinesq approximation. For constant wall temperature, an asymptotic case provides simple temperature and velocity profiles that determine the convection and thermophoretic motion of small aerosol particles. Laser heating induces upward buoyant motion neat the tube center, and when forced convection is downward, there may be an inflection in the velocity profile. For constant laser heating (a small absorption limit), a velocity profile may be found that will minimize the distance over which particles are deposited on the wall. Such an observation may have some bearing on the manufacture of preforms from which optical fibers are drawn.