Quantyfing mixing in a convective boundary layer

Abstract

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.

The phenomenon of penetrative convection in a stably stratified fluid has been reproduced in laboratory employing a tank filled with water and subjected to heating from below. The goal in the experiment is predicting the mixing layer growth as a function of initial and boundary condition and describe the fate of a tracer dissolved in the fluid phase. The equipment employed is suitable for simultaneously providing temperatures inside the domain through thermocouples (sensitivity less than 0.1 °C) and Lagrangian particle trajectories obtained by using a 2D image analysis technique named Feature Tracking. The field of view is illuminated through a thin light sheet with a suitable optical equipment. The mixing layer growth is detected both employing temperature data and statistics of the velocity field, i.e. the vertical velocity component variance. Concerning the transport feature of the phenomenon under investigation, the velocity spatial correlation allows the plume horizontal dimension to be determined. This information coupled to the knowledge of the mixing layer height allows the spatial extension of the convective region to be fully described.