Presentation is loading. Please wait.

Presentation is loading. Please wait.

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.

Similar presentations


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.

2 Karl J.L. Geisler, Ph.D. January 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 = /m 2

3 Karl J.L. Geisler, Ph.D. January mm channel liquid liquid phase volume fraction vapor time in seconds each frame = 5 ms

4 Karl J.L. Geisler, Ph.D. January mm channel liquid liquid phase volume fraction vapor time in seconds each frame = 5 ms

5 Karl J.L. Geisler, Ph.D. January mm channel liquid liquid phase volume fraction vapor time in seconds each frame = 5 ms

6 Karl J.L. Geisler, Ph.D. January 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:

8 Karl J.L. Geisler, Ph.D. January Bubble Departure Diameter

9 Karl J.L. Geisler, Ph.D. January Bubble Departure Frequency

10 Karl J.L. Geisler, Ph.D. January Nucleation Site Density (1)

11 Karl J.L. Geisler, Ph.D. January Nucleation Site Density (2)

12 Karl J.L. Geisler, Ph.D. January Nucleation Site Density (3)

13 Karl J.L. Geisler, Ph.D. January Latent Heat Contribution

14 Karl J.L. Geisler, Ph.D. January D Bubble Volume

15 Karl J.L. Geisler, Ph.D. January Vapor Generation Rate

16 Karl J.L. Geisler, Ph.D. January Vapor Inlet Mass Flux

17 Karl J.L. Geisler, Ph.D. January Boiling parameter predictions for saturated FC-72 at atmospheric pressure (101 kPa)

18 Karl J.L. Geisler, Ph.D. January Mikic and Rohsenow (1969) bubble growth rate correlation

19 Karl J.L. Geisler, Ph.D. January CFD Model Geometry

20 Karl J.L. Geisler, Ph.D. January GAMBIT screen-shot of model geometry showing vertices, edges, and faces

21 Karl J.L. Geisler, Ph.D. January GAMBIT screen-shot showing mesh details in vicinity of vapor inlet

22 Karl J.L. Geisler, Ph.D. January Comparison of temperature results from single phase numerical simulations

23 Karl J.L. Geisler, Ph.D. January Velocity results for initial steady-state single phase solution

24 Karl J.L. Geisler, Ph.D. January Nucleation site mass flux profiles

25 Karl J.L. Geisler, Ph.D. January 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 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 Velocity contour plot at end of VOF simulation, 5 mm channel

28 Karl J.L. Geisler, Ph.D. January Inlet and outlet mass flow rates as a function of time, 5 mm channel

29 Karl J.L. Geisler, Ph.D. January Heater top and bottom heat flux as a function of time, 5 mm channel

30 Karl J.L. Geisler, Ph.D. January Two Phase Simulation Temperature Results Comparison

31 Karl J.L. Geisler, Ph.D. January 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 Surface heat flux profiles

33 Karl J.L. Geisler, Ph.D. January CFD Simulation Results Summary


Download ppt "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."

Similar presentations


Ads by Google