Evaluation of the Effect of Thermal Stratification Strength on Artificial De-stratification Efficiency in Reservoirs

Thermal stratification and mixing can greatly change the water quality in a reservoir during a year. A conventional method to de-stratify the reservoir is using a bubble plume produced by an air diffuser system. If the aeration system designed properly, maximum efficiency can be achieved. In this paper a full three dimensional computational fluid dynamics model using ANSYS Fluent software employed to study the artificial de-stratification process in a laboratory tank. Because of some deficiencies in Fluent software and in order to produce more accurate results, UDF codes were written and added to the CFD model. Based on the results, stratification strength is a critical factor which controls the energy required for mixing the reservoir. It is also concluded that by reducing the amount of gas injected to the reservoir, less energy dissipates through turbulence. Therefore, the efficiency of de-stratification process will increase. According to the results, it is recommended that aeration system should be designed to work when plume number is around 400.