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Buoyancy-Driven Two Phase Flow and Boiling Heat Transfer in Narrow Vertical Channels CFD Simulation of Two Phase Channel Flow Karl J.L. Geisler, Ph.D.

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Presentation on theme: "Buoyancy-Driven Two Phase Flow and Boiling Heat Transfer in Narrow Vertical Channels CFD Simulation of Two Phase Channel Flow Karl J.L. Geisler, Ph.D."— Presentation transcript:

1 Buoyancy-Driven Two Phase Flow and Boiling Heat Transfer in Narrow Vertical Channels CFD Simulation of Two Phase Channel Flow Karl J.L. Geisler, Ph.D. http://www.menet.umn.edu/~kgeisler

2 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler2 CFD Model  2-D FLUENT VOF multiphase simulation of channel flow  Evaluate convective enhancement mechanism  Estimated bubble parameters at selected operating point  T sat = 12.3°C D b = 0.78 mm f = 59.3 Hz = (16.9 ms) -1  g = 4.2 ms N / A = 96354 1/m 2

3 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler3 5 mm channel liquid liquid phase volume fraction vapor time in seconds each frame = 5 ms

4 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler4 0.7 mm channel liquid liquid phase volume fraction vapor time in seconds each frame = 5 ms

5 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler5 0.3 mm channel liquid liquid phase volume fraction vapor time in seconds each frame = 5 ms

6 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler6 CFD Observations and Conclusions  Unconfined boiling heat flux nearly 50% due to enhanced convection Disruption of thermal boundary layer by bubble motion ≈3x single phase natural convection  Narrow channels show higher mass flux, enhanced single phase convection below nucleation site  Sensible heat rise in 0.3 mm channel yields reduced heat flux compared to 0.7 mm channel  Maximum enhancement observed for 0.7 mm channel 0.7 mm channel only 20% better than unconfined  0.7 mm experiment 50–150% better  0.3 mm experiment 150–500% better  Enhanced liquid convection likely NOT dominant enhancement mechanism

7 CFD Background and Additional Results For details, see: http://www.menet.umn.edu/~kgeisler/Geisler_PhD_Dissertation.pdf

8 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler8 Bubble Departure Diameter

9 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler9 Bubble Departure Frequency

10 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler10 Nucleation Site Density (1)

11 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler11 Nucleation Site Density (2)

12 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler12 Nucleation Site Density (3)

13 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler13 Latent Heat Contribution

14 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler14 2-D Bubble Volume

15 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler15 Vapor Generation Rate

16 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler16 Vapor Inlet Mass Flux

17 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler17 Boiling parameter predictions for saturated FC-72 at atmospheric pressure (101 kPa)

18 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler18 Mikic and Rohsenow (1969) bubble growth rate correlation

19 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler19 CFD Model Geometry

20 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler20 GAMBIT screen-shot of model geometry showing vertices, edges, and faces

21 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler21 GAMBIT screen-shot showing mesh details in vicinity of vapor inlet

22 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler22 Comparison of temperature results from single phase numerical simulations

23 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler23 Velocity results for initial steady-state single phase solution

24 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler24 Nucleation site mass flux profiles

25 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler25 Phase contour plots at 4 ms time steps from the beginning of the VOF simulation through the first four bubble generations

26 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler26 Phase contour plots at 4 ms time steps from the beginning of the VOF simulation through the first four bubble generations

27 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler27 Velocity contour plot at end of VOF simulation, 5 mm channel

28 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler28 Inlet and outlet mass flow rates as a function of time, 5 mm channel

29 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler29 Heater top and bottom heat flux as a function of time, 5 mm channel

30 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler30 Two Phase Simulation Temperature Results Comparison

31 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler31 Surface heat flux profiles for 5 mm channel single phase natural convection solution and VOF simulation results at t = 1.34 s

32 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler32 Surface heat flux profiles

33 Karl J.L. Geisler, Ph.D. January 2007 http://www.menet.umn.edu/~kgeisler33 CFD Simulation Results Summary


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