Simulation Analysis for HB-Line Dissolver Mixing

Lee, S

Savannah River Site (S.C.)

关键词: Turbulent Flow;    Fluid Mechanics;    Flow Rate;    Mixers;    Positioning;   

DOI  :  10.2172/890219
RP-ID  :  WSRC-TR-2005-00528
RP-ID  :  DE-AC09-96SR18500
RP-ID  :  890219

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 90{sup o} apart and helical pitch agitator submerged in a flat tank containing dissolver baskets. The work is intended to determine maximum agitator speed to keep the dissolver baskets from contacting the agitator for the nominal tank liquid level. The analysis model was based on one dissolver basket located on the bottom surface of the flat tank for a conservative estimate. The modeling results will help determine acceptable agitator speeds and tank liquid levels to ensure that the dissolver basket is kept from contacting the agitator blade during HB-Line dissolver tank 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 four 90{sup o} pitched blades or three flat blades. Hydraulic conditions were fully turbulent (Reynolds number about 1 x 10{sup 5}). A standard two-equation turbulence model ({kappa},{var_epsilon}), was used to capture turbulent eddy motion. The commercial finite volume code, Fluent [5], 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. The nominal calculations and a series of sensitivity runs were made to investigate the impact of flow patterns on the lifting behavior of the dissolver basket. At high rotational speeds and low tank levels, local turbulent flow reaches the critical condition for the dissolver basket to be picked up from the tank floor and to touch the agitator blades during the tank mixing operations. This is not desirable in terms of mixing performance. The modeling results demonstrate that the flow patterns driven by the agitators considered here are not strong enough to lift up the dissolver basket for the agitator speeds up to 2500 rpm. The results also show that local velocity magnitudes for the three-blade flat plate agitator are at maximum three times smaller than the helical fourblade one. Table 5 and Table 6 summarize the results.