Abstract
The effect of the shapes of the inlet and outlet pipes on the displacement efficiency of old water in a cylindrical water supply tank was investigated. The flow structure in the tank was also visualized with a planar laser-induced-fluorescence (LIF) technique. The inlet water jet was marked with a laser-fluorescent dye, i.e., a fluorescent yellowish-green (aqueous solution of disodium fluorescence). The displacement efficiency of water inside the tank that has an inlet pipe with a diverging nozzle and an outlet pipe with a circular baffle plate is better than that of the other tank. The decrease in the displacement efficiency of old water in a tank that has inlet and outlet pipes the center of the tank without a diverging nozzle and a baffle plate is related to the large fluctuation of flow near the outlet pipe. The baffle plate is found to prevent the diffusion of old water. The displacement efficiency of old water which is different in temperature to new water in the tank is not better than that of the same temperature. The cause of the decrease in the displacement efficiency is the stay of old wtaer near the center of tank.
