Experiments on a vortex in a circular pipe with a closed end

There are many kinds of branch pipes connecting to the main coolant pipes of nuclear plants. Some of them are closed with valves during normal operation of the plants, and form deep cavities. The flow in the main pipes induces cavity flow in the branch pipes. Cavity flow and heat radiation form a thermal stratification in the pipe. We observed the structure of the cavity flow in a branch pipe with a closed end, and found there are one or two cellular vortices near the branch and a spiral vortex beyond them. We measured the distribution of the tangential velocity of the spiral vortex to get an experimental equation. We also measured velocity and temperature distributions near a thermal stratification to get the local Richardson number. The cavity flow deeply goes into the branch pipe, and its length depends on the local Richardson number given by the decay of the tangential velocity and the stability of the stratification. (author)