An Experimental Study of Plane Plumes in Cold Water

The peculiar density variation of water with temperature makes the Boussinesq approximations invalid in the vicinity of density extremum conditions. The buoyancy force reversals which often arise from the density extremum have been studied in many recent investigations. The formulation of an accurate density relation has resulted in a simplified analysis for many convective motions. Two such analyses have dealt with the flow generated above a heated line source in cold water, around the extremum point. We present an experimental investigation of such flow. Temperature measurements have been carried out for ambient temperatures, t_∞ ≥ t_m, the temperature of density extremum, for pure water at atmospheric pressure. These measurements are in satisfactory agreement with the analyses. As the ambient temperature is successively increased above the density extremum temperature, the transformation of the flow behaviour from non-Boussinesq to Boussinesq is very clearly observed. Velocity measurements have been made at t_∞=4°C, the extremum temperature. For t_∞<t_m, very complex flow patterns exist, due to the bidirectional buoyancy force. These patterns have been visualized. The influence of a bounding impermeable surface below the plume source has also been examined.