Mixing in Water Storage Tanks. I: No Buoyancy Effects

Abstract

The results of extensive experiments on jet-induced mixing in water storage tanks are reported in two papers. The experiments were conducted on three styles of storage tanks using a newly developed three-dimensional laser-induced fluorescence (3DLIF) system that can measure the whole field of tracer concentrations in the tanks and its temporal evolution through the mixing process. Various inlet geometries were tested for each tank style. In this paper, the results of experiments with no buoyancy effects are given. The 3DLIF technique enabled complex flow patterns to be observed such as a donut-shaped dead zone that inhibited mixing in ground-level cylindrical tanks. Values of dimensionless mixing times are presented that enable comparisons of the mixing efficiency of different inlet configurations and allow prediction of mixing times in prototype tanks. For cylindrical tanks, the dimensionless mixing time increases with increasing depth-to-diameter ratio. Vertical nozzles at the bottom mixed most efficiently. If a single vertical nozzle is used, placing it near a sidewall is preferred. Mixing becomes somewhat more rapid as the number of nozzles increase. Mixing times for rectangular tanks are generally similar to cylindrical tanks. The use of a tube intended to enhance mixing actually inhibited mixing in standpipe tanks.