Buoyancy-Driven Two Phase Flow and Boiling Heat Transfer .ppt

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,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,2,CFD Model,2-D FLUENT VOF multiphase simulat

2、ion of channel flow Evaluate convective enhancement mechanism Estimated bubble parameters at selected operating point DTsat = 12.3C Db = 0.78 mm f = 59.3 Hz = (16.9 ms)-1 tg = 4.2 ms N/A = 96354 1/m2,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,3,5 mm channel,liquid liquid

3、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,4,0.7 mm channel,liquid 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,5,0

4、.3 mm channel,liquid 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,6,CFD Observations and Conclusions,Unconfined boiling heat flux nearly 50% due to enhanced convection Disruption of thermal boundary layer

5、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 on

6、ly 20% better than unconfined 0.7 mm experiment 50150% better 0.3 mm experiment 150500% better Enhanced liquid convection likely NOT dominant enhancement mechanism,CFD Background and Additional Results,For details, see: http:/www.menet.umn.edu/kgeisler/Geisler_PhD_Dissertation.pdf,Karl J.L. Geisler,

7、 Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,8,Bubble Departure Diameter,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,9,Bubble Departure Frequency,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,10,Nucleation Site Density (1),Karl J.L. Geisler

8、, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,11,Nucleation Site Density (2),Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,12,Nucleation Site Density (3),Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,13,Latent Heat Contribution,Karl J.L. Geis

9、ler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,14,2-D Bubble Volume,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,15,Vapor Generation Rate,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,16,Vapor Inlet Mass Flux,Karl J.L. Geisler, Ph.D. Janua

10、ry 2007 http:/www.menet.umn.edu/kgeisler,17,Boiling parameter predictions for saturated FC-72 at atmospheric pressure (101 kPa),Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,18,Mikic and Rohsenow (1969) bubble growth rate correlation,Karl J.L. Geisler, Ph.D. January 2007 htt

11、p:/www.menet.umn.edu/kgeisler,19,CFD Model Geometry,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,20,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,21,GAMBIT screen-shot showing m

12、esh details in vicinity of vapor inlet,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,22,Comparison of temperature results from single phase numerical simulations,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,23,Velocity results for initial steady-sta

13、te single phase solution,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,24,Nucleation site mass flux profiles,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

14、first four bubble generations,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,26,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,27,

15、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,28,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,29,Heater top and bottom

16、heat flux as a function of time, 5 mm channel,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,30,Two Phase Simulation Temperature Results Comparison,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,31,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,32,Surface heat flux profiles,Karl J.L. Geisler, Ph.D. January 2007 http:/www.menet.umn.edu/kgeisler,33,CFD Simulation Results Summary,