Agitator Mixing Analysis in a HB-Line Flat Tank

Lee, S.Y.

Savannah River Site (S.C.)

关键词: Flow Rate;    Mixers;    Density;    Radioactive Wastes;    Tanks;   

DOI  :  10.2172/799468
RP-ID  :  WSRC-TR-2002-00219
RP-ID  :  AC09-96SR18500
RP-ID  :  799468

美国|英语

来源: UNT Digital Library

【 摘 要 】

In support of the HB-Line Engineering agitator mixing project, flow pattern calculations have been made for a 45 degrees pitched three-blade agitator submerged in a flat rectangular tank. The work is intended to determine agitator speeds that provide acceptable mixing performance for various tank liquid levels based on flow rates past solids deposited on the bottom surface of the flat tank. The modeling results will help ensure the acceptable suspension of solid particles as a function of agitator speed and tank liquid level during precipitation operations. The numerical modeling and calculations have been performed using a computational fluid dynamics approach. Three-dimensional steady-state momentum and continuity equations were used as the basic equations to estimate fluid motion driven by an agitator with three 45 degrees pitched blades. Hydraulic conditions were fully turbulent (Reynolds number about 2x104). A standard two-equation turbulence model (k-e), was used to capture turbulent eddy motion. The commercial finite volume code, Fluent [7], was used to create a prototypic geometry file with a non-orthogonal mesh. Hybrid meshing was used to fill the computational region between the round-edged tank bottom and agitator regions. At high rotational speeds and low tank levels, a surface vortex can reach the agitator blades and allow air to be drawn into the solid-fluid mixing zone. This is not desirable in terms of mixing performance. The analysis results show that the lowest liquid level among the four considered, 4.5 inches, is higher than the critical liquid height for air entrainment for agitator speeds up to 600 rpm. All the analysis results demonstrate that about 600 rpm provides adequate solids mixing capability for various tank levels (12, 8.5, 7, and 4.5 inches) containing 20-micron solids with a specific gravity of 2.5.