Numerical investigation of the motion of a growing droplet in a thermal diffusion cloud chamber

The evolution of spherical droplets resulting from the homogeneous condensation of vapor phase diluted in a background gas has been studied numerically. The model was compared with experimental data of dioctylphthalate (DOP) droplets in binary gaseous mixture of DOP-helium and of DOP-hydrogen in a thermal diffusion cloud chamber (TDCC). The motion of droplets due to thermodiffusiophoresis as obtained from numerical predictions is in agreement with the experimental results. Two-dimensional droplet dynamics involving the effect of convection, thermodiffusiophoresis, gravity and condensation has been examined in details for two flow configurations depending on the cloud chamber geometry. When the height of the TDCC is increased, the isothermal patterns and streamlines are similar to those obtained in the case of Rayleigh-Benard instabilities, leading a notable alteration of the droplet behavior. While the thermodiffusiophoresis forces govern the drop motion at low thermal Rayleigh numbers (in conductive regime), the behavior of the droplet is mainly driven by the drag force when the TDCC operates in convective regime (at high Rayleigh numbers). (C) 2003 Elsevier Ltd. All rights reserved.