BuoyancyDriven Two Phase Flow and Boiling Heat Transfer
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 Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. u
CFD Model o o o 2 -D FLUENT VOF multiphase simulation of channel flow Evaluate convective enhancement mechanism Estimated bubble parameters at selected operating point n DTsat = 12. 3°C n Db = 0. 78 mm n f = 59. 3 Hz = (16. 9 ms)-1 n tg = 4. 2 ms n N/A = 96354 1/m 2 Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 2
liquid 5 mm channel liquid phase volume fraction vapor time in seconds each frame = 5 ms Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 3
liquid 0. 7 mm channel liquid phase volume fraction vapor time in seconds each frame = 5 ms Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 4
liquid 0. 3 mm channel liquid phase volume fraction vapor time in seconds each frame = 5 ms Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 5
CFD Observations and Conclusions o Unconfined boiling heat flux nearly 50% due to enhanced convection n n Disruption of thermal boundary layer by bubble motion ≈3 x single phase natural convection o Narrow channels show higher mass flux, enhanced single phase convection below nucleation site o Sensible heat rise in 0. 3 mm channel yields reduced heat flux compared to 0. 7 mm channel o Maximum enhancement observed for 0. 7 mm channel n 0. 7 mm channel only 20% better than unconfined o o o 0. 7 mm experiment 50– 150% better 0. 3 mm experiment 150– 500% better Enhanced liquid convection likely NOT dominant enhancement mechanism Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 6
CFD Background and Additional Results For details, see: http: //www. menet. umn. edu/~kgeisler/Geisler_Ph. D_Dissertation. pdf Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. u
Bubble Departure Diameter Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 8
Bubble Departure Frequency Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 9
Nucleation Site Density (1) Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 10
Nucleation Site Density (2) Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 11
Nucleation Site Density (3) Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 12
Latent Heat Contribution Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 13
2 -D Bubble Volume Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 14
Vapor Generation Rate Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 15
Vapor Inlet Mass Flux Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 16
Boiling parameter predictions for saturated FC-72 at atmospheric pressure (101 k. Pa) Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 17
Mikic and Rohsenow (1969) bubble growth rate correlation Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 18
CFD Model Geometry Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 19
GAMBIT screen-shot of model geometry showing vertices, edges, and faces Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 20
GAMBIT screen-shot showing mesh details in vicinity of vapor inlet Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 21
Comparison of temperature results from single phase numerical simulations Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 22
Velocity results for initial steady-state single phase solution Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 23
Nucleation site mass flux profiles Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 24
Phase contour plots at 4 ms time steps from the beginning of the VOF simulation through the first four bubble generations Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 25
Phase contour plots at 4 ms time steps from the beginning of the VOF simulation through the first four bubble generations Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 26
Velocity contour plot at end of VOF simulation, 5 mm channel Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 27
Inlet and outlet mass flow rates as a function of time, 5 mm channel Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 28
Heater top and bottom heat flux as a function of time, 5 mm channel Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 29
Two Phase Simulation Temperature Results Comparison Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 30
Surface heat flux profiles for 5 mm channel single phase natural convection solution and VOF simulation results at t = 1. 34 s Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 31
Surface heat flux profiles Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 32
CFD Simulation Results Summary Karl J. L. Geisler, Ph. D. January 2007 http: //www. menet. umn. edu/~kgeisler 33
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