MIXING LIQUID HOLDING TANKS FOR UNIFORM CONCENTRATION*

Achieving uniform concentration within liquid holding tanks can often times be a difficult task for the nuclear chemical process industry. This is due to the fact that nuclear criticality concerns require these tanks to be designed with high internal aspect ratios such that the free movement of fluid is greatly inhibited. To determine the mixing times required to achieve uniform concentra- tion within these tanks, an experimental program was conducted utilizing pencil tanks, double-pencil tanks, and annular tanks of varying geometries filled with salt-water solutions (simulants for nitric acid actinide solutions). Mixing was accom- plished by air sparging and/or pump recirculation. Detailed fluid mechanic mixing models were developed—from first principles—to analyze and interpret the test results. These nondimensional models show the functionality of the concentration inhomogeneity (defined as the relative standard deviation of the true concentration within the tank) in relationship to the characteristic mixing time—among other variables. The results can be readily used to scale tank geometries to sizes other than those studied here.