Destratification by Mechanical Mixers: Mixing Efficiency and Flow Scaling

Experiments have been performed to assess the efficiency of mechanical mixers in destratifying water bodies. The effects of Reynolds number, physical scale, and Richardson number were all considered. The results demonstrated that the variation of mixing efficiency with Richardson number was well described by two different power-law regimes. At low Richardson numbers, the efficiency increased with increasing Richardson number. Above a critical value, however, the efficiency decreased rapidly with further increases in Richardson number. The experiments further showed that, over the range of Reynolds numbers considered, the results collapsed fairly well. Finally, experiments at different physical scales showed reasonable agreement. The main conclusion of the present technical note is that the destratification efficiency of mechanical mixers can be well parameterized by an overall Richardson number. The results, however, are specific to the particular geometric configuration studied. It is hoped that the present technical note will help to guide future studies of destratification systems in small lakes and reservoirs and fluid mixing in the chemical and process industries. DOI: 10.1061/ ASCE 0733-9429 2008 134:12 1772 CE Database subject headings: Stratified flow; Reservoirs; Stratification; Water quality; Turbulence; Mixing.