Abstract

MUJAL I COLILLES, Anna; BATEMAN-PINZON, Alien  and  DE MEDINA-IGLESIAS, Vicente. Experimental study of mixing efficiency in water storage tanks. Tecnol. cienc. agua [online]. 2011, vol.2, n.3, pp.77-95. ISSN 2007-2422.

The phenomenon of mixing in drinking water storage tanks and reservoirs has a direct effect on the quality of outgoing water due to the creation of poor mixing zones and volume stratification, which can produce negative effects on public health. The design of a storage tank must consider the conditions of the inlets and outlets, as well as their orientation (vertical or horizontal) to prevent the formation of these zones. This article presents experiments done at a reduced-scale physical model with three different inlets (a pipe and two waterfalls) in order to determine which of these inlets achieved the best mixing efficiency. Moreover, the effects on mixing efficiency by columns that support the roof of the tank were studied. A digital image technique was conducted with qualitative results that show that the flow leaving through a pipe obtains better efficiency than that of waterfalls, in both the model and the prototype, because of the horizontal momentum that the former exerts on the flow. It is important to note that the time taken to mix the stored volume depends on the distance between the inlet and the opposite wall, as well as its orientation. In terms of columns, neglecting the viscous scale effects and taking into account the whole tank, the columns have a negative effect on mixing efficiency, even though they divide the flow and create zones of local turbulence since they absorb energy from the flow and generally decrease the mixing speed.

Keywords : mixing time; water supply storage tank; efficiency; jets; physical scaled model; Reynolds scale; image processing.