Etudes sur modèle réduit des dispositifs de dégazage dans les puits de mise en charge

Studies on a scale-model of the deaeration systems used in water pressure shafts

Société du Canal de Provence

Abstract

Water pressure shafts connecting the canals to the operational tunnels are to be found in several hydro-electric developments designed and executed by the Société du Canal de Provence. The water entering the shaft causes air emulsions which are driven to the bottom. However, it is absolutely necessary to prevent air bubbles from entering the tunnel in order to avoid a reduction in the volume of flow and hammering which can cause damage to the plant. The methods for deaerating the water, designed on a scale-model, depend on the energy content of the water entering the shaft and the extent of dissipation of energy within the shaft. The first example given is a shaft depth 47 m and diameter 10 metres with a rate of flow of 10 m3/sec and a maximum head of 27 metres. This shaft thus has a large capacity which ensures virtually complete dissipation of the energy of the jet and does not require a deaeration system. The second example given is a 19 m deep shaft whose diameter of six metres has been determined after having studied the velocity of a scent of bubbles. Tests performed on scale models have revealed that air emulsions entered the level at rates of flow of between 5 and 9 m3/ sec. The deaeration method adopted consisted of building a circular chamber five metres long and of the same diameter as the shaft at the entrance to the tunnel. The third example is a 13 m deep and 5 m diameter shaft, rate of flow 11 m3/sec. This facility has necessitated not only a deaeration chamber at the entrance to the tunnel but also a jet breaking floor installed in the middle of the shaft. The floor has made it possible on the one hand to break the energy of the fall and thus reduce the volume of air driven to the bottom of the shaft, and on the other, to prevent a vortex, which was occurring at maximum flow from reaching the tunnel. The tests undertaken revealed the need to install an additional deaeration chamber at the entrance to the tunnel to complete deaeration, which was not fully performed by the jet-breaking floor.