Sinking cooling water plumes in a numerical model

Typ: Rapport
Serie: RHO 23
Författare: Jonny Svensson


Cooling water discharged from a power plant during winter conditions can form a mixture which is denser than the ambient cold water. The cooling water then sinks to the bottom. Such sinking plumes have been recorded during plume surveys outside power plants discharging in brackich or fresh waters.

A three- dimensional matematical numerical model is used to describe the sinking plume. The model runs show that the turbulence in the ambient water affects the sinking considerably. In rough weather conditions with strong turbulence the cooling water is well mixed from the surface to the bottom. A vertical wall (thermal bar) separates ambient water from cooling water. The warm water does not go very far from the outlet. During periods with low wind velocities (little turbulence in the ambient water) the model simulates both the initial floating plume, the sinking and the final spreading along the bottom.

Three runs are presented. One with straight coast and flat bottom. In this model configuration tests with different mixing coefficients were performed.The next run presented shows the small changes that occur when a simple bottom
topography is introduced in the model. The final case is one with a complicated coastline and bottom topography.

The model is shown to be a valuable tool in the process of judging the frequenecy and duration of sinking plumes and the size of bottom area outside a powerplant that will be affected by cooling water.