Reservoir Destratification via Mechanical Mixers

Abstract

Destratification techniques are often used to improve water quality in reservoirs. The majority of investigations have concentrated on the use of bubble aerators; however, an interesting alternative is the use of mechanical mixing systems consisting of a large propeller immersed in the water column. A laboratory study of such a system was used to examine the efficiency of energy conversion from mechanical energy to buoyancy flux as a function of impeller diameter, the speed of rotation, and the degree and type of stratification. The results were shown to depend on a generalized Froude number with the peak efficiency of energy conversion as high as 12%. A direct scaling mechanism enabling the results found in the laboratory model to be applied to a prototype situation was achieved via the application of derived scaling parameters. A simple design methodology for prototype versions of mechanical mixing systems based on this study is suggested.