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Research Papers: Flows in Complex Systems

Comparison of Experiments to Computational Fluid Dynamics Models for Mixing Using Dual Opposing Jets in Tanks With and Without Internal Obstructions

[+] Author and Article Information
Robert A. Leishear

 Savannah River National Laboratory, Aiken, SC 29808Robert.Leishear@srnl.doe.gov

Si Y. Lee

 Savannah River National Laboratory, Aiken, SC 29808Si.Lee@srnl.doe.gov

Mark D. Fowley

 Savannah River National Laboratory, Aiken, SC 29808Mark.Fowley@srnl.doe.gov

Michael R. Poirier

 Savannah River National Laboratory, Aiken, SC 29808Michael.Poirier@srnl.doe.gov

Timothy J. Steeper

 Savannah River National Laboratory, Aiken, SC 29808Timothy.Steeper@srnl.doe.gov

J. Fluids Eng 134(11), 111102 (Oct 24, 2012) (21 pages) doi:10.1115/1.4007536 History: Received September 14, 2011; Revised July 18, 2012; Published October 24, 2012

This paper documents testing methods, statistical data analysis, and a comparison of experimental results to computational fluid dynamics (CFD) models for blending of fluids, which were blended using a single pump designed with dual opposing nozzles in an 8-foot-diameter tank. Overall, this research presents new findings in the field of mixing research. Specifically, blending processes were clearly shown to have random, chaotic effects, where possible causal factors, such as turbulence, pump fluctuations, and eddies, required future evaluation. CFD models were shown to provide reasonable estimates for the average blending times, but large variations—or scatter—occurred for blending times during similar tests. Using this experimental blending time data, the chaotic nature of blending was demonstrated and the variability of blending times with respect to average blending times was shown to increase with system complexity. Prior to this research, the variation in blending times caused discrepancies between CFD models and experiments. This research addressed this discrepancy and determined statistical correction factors that can be applied to CFD models and thereby quantified techniques to permit the application of CFD models to complex systems, such as blending. These blending time correction factors for CFD models are comparable to safety factors used in structural design and compensate variability that cannot be theoretically calculated. To determine these correction factors, research was performed to investigate blending using a pump with dual opposing jets, which recirculate fluids in the tank to promote blending when fluids are added to the tank. In all, 85 tests were performed both in a tank without internal obstructions and a tank with vertical obstructions similar to a tube bank in a heat exchanger. These obstructions provided scale models of vertical cooling coils below the liquid surface for a full-scale, liquid radioactive waste storage tank. Also, different jet diameters and different horizontal orientations of the jets were investigated with respect to blending. Two types of blending tests were performed. The first set of 81 tests blended small quantities of tracer fluids into solution. Data from these tests were statistically evaluated to determine blending times for the addition of tracer solution to tanks, and blending times were successfully compared to computational fluid dynamics (CFD) models. The second set of four tests blended bulk quantities of solutions of different density and viscosity. For example, in one test, a quarter tank of water was added to three quarters of a tank of a more viscous salt solution. In this case, the blending process was noted to significantly change due to stratification of fluids and blending times increased substantially. However, CFD models for stratification and the variability of blending times for different density fluids were not pursued, and further research is recommended in the area of blending bulk quantities of fluids. All in all, testing showed that CFD models can be effectively applied if statistically validated through experimental testing, but, in the absence of experimental validation, CFD models can be extremely misleading as a basis for design and operation decisions.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Blending test results for a single nozzle (Grenville and Tilton [11-12])

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Figure 2

Tank geometry for species transport calculations

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Figure 3

CFD model for a single upward pointing jet used during tank blending

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Figure 4

Comparison of CFD results to experiment in a 0.5 -m (1.64-ft)-diameter tank for blending using a single jet angled with respect to the tank bottom (Patwardhan [13])

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Figure 5

Test schematic for acid, base, and dye additions

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Figure 6

Test schematic for blending due to external bulk transfers into the pilot-scale tank

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Figure 7

Tank cooling coil design

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Figure 8

Pilot-scale blending tank model scaled from full-scale tank, elevation

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Figure 9

Pilot-scale tank model, plan

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Figure 10

Modeled cooling coils and center column assembly with overhead stiffeners and lifting lugs

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Figure 11

Cooling coil assembly and center column

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Figure 12

Phase 1, pilot-scale tank without cooling coil models

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Figure 13

Phase 2, pilot-scale tank with cooling coil models installed

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Figure 14

Initial pilot-scale tee nozzle designs

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Figure 15

Initial tee nozzle design installation

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Figure 16

CW pump model cross section

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Figure 17

Final CW pump model operating in the pilot-scale tank

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Figure 18

Dye addition at C1 riser (Test 1)

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Figure 19

Raw pH data for analysis

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Figure 20

Concentration data for analysis

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Figure 21

Normalized concentration data for analysis

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Figure 22

Comparison of 95% blending to 99% blending (Test 21)

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Figure 23

Comparison of normalized hydrogen ion concentrations to measured sodium concentrations

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Figure 24

Diffusion following a base addition, coils installed (Test 6)

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Figure 25

Diffusion following an acid addition, coils installed (Test 7)

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Figure 26

Comparison of Phase 1 pilot-scale test results for a tank with or without cooling coils

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Figure 27

Typical blending time test results

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Figure 28

Inadequate blending (Test 22)

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Figure 29

Summary of blending time results

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Figure 30

Typical set of blending time data

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Figure 31

Velocity in a pilot-scale tank without coils at a vertical plane through upward-pointing nozzles (Tests 74–77)

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Figure 32

Velocity in a pilot-scale tank without coils at a horizontal plane through the horizontal centerline of the pump model (Tests 74–77)

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Figure 33

Typical cross section of the pilot-scale tank during blending (Tests 14–16, 25.4 mm (1 in.) above the tank floor)

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Figure 34

Model geometry for a tank without coils

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Figure 35

Model geometry for a tank with coils

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Figure 36

Model geometry for a tank with coils near the pump nozzles

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Figure 37

Comparison of CFD results to experiments for a tank with coils installed

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Figure 38

Comparison of CFD results to experiments for a tank without coils installed

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Figure 39

Data analysis [6]

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Figure 40

pH measurements for transfer of NaNO2 to water

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Figure 41

pH measurements for transfer of NaNO2 to NaNO2

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Figure 42

Interface between salt solution layers; transfer of water into a salt solution (Test 84)

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Figure 43

Waves at interface layer; transfer of water into a salt solution (Test 84)

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Figure 44

Interface layer; level changes during blending of a stratified salt solution; transfer of water into salt solution

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