How does the wall of the diffusion cloud chamber affect performance?

Abstract

This chapter describes the results of two-dimensional treatment of the mass and energy transfer processes that occur during operation of the thermal diffusion cloud chamber (TDCC). It examines the effect of wet and dry walls and the aspect ratio— diameter to height— on the supersaturation and nucleation rate profiles. It also examines the effects of pressure, temperature, and background gas on the stability of chamber operation. The TDCC is a commonly used tool in the investigation of nucleation phenomena. It shows the results of a two-dimensional analysis of the mass and energy transport within the diffusion cloud chamber, which specifically accounts for the presence of the chamber wall, which can be dried by heating or wetted from condensation of the vapor. The effect of the two different operating conditions on the chamber interior appears negligible. A far greater influence on the interior conditions is the aspect ratio. A minimum aspect ratio of 7.5 is required to ensure the validity of the one-dimensional transport approximation. The analysis also showed that under certain operating conditions, density minima occur near the wall. These minima can lead to buoyancy driven convection, which in turn affects the nucleation rate in the center of the chamber.