OpenFOAM Nucleate Boiling
2 likes1,270 views
This document details a project analyzing thrust generated by a water tank heated by radiative heat flux, employing 3D computational fluid dynamics through OpenFOAM. The study included preliminary system-level analysis and investigations of boiling modeling alongside sensitivity studies to optimize tank exhaust configurations. Key accomplishments include developing a hybrid analysis methodology and validating CFD solver performances against existing research while noting limitations in computational power and modeling accuracy.
OpenFOAM Nucleate Boiling
- 1. Thermal Radiation Steam Thrust Final Results Mihai Pruna ME632 For reference use only
- 2. Objectives Develop analysis methodology to determine the thrust obtained from a water tank heated by a radiative heat flux (solar concentrator or laser), with a small opening for vapor to escape. • System-level analysis system for preliminary design. coupled with • 3D Computational Fluid Dynamics analysis. •Add boiling modeling to OpenFOAM 2.3.1 Determine optimal configuration for tank exhaust (that produces most thrust for the fixed heat flux). For reference use only
- 3. Review Tank Boiling Water Parabolic Solar Collector Insulated surface Converging Nozzle Accelerating Steam Exhaust Radiation->Heat Flux Water boiled by solar concentrator Problem Definition Preliminary System-level Analysis in Excel /VBA For reference use only
- 4. Tank overall dimensions (m) For reference use only
- 5. • The open source CFD Toolbox OpenFOAM was used. • A solver that can model phase changes (mainly used for cavitation), interPhaseChangeFoam has been selected to model the problem. • The solver was modified to account for the temperature field and thus be able to model boiling, based on the work by Andersen(2011) CFD Solver Additional Equations: • Transport Equation to Model Temperature: Eqn 4 Andersen(2011) • Where DT is the Thermal Diffusivity: Eqn 3 Andersen(2011) • Roche-Magnus formula to get sat. pressure as a function of temp.(K) Eqn 5 Andersen(2011) • Phase change rate modeled with Kunz (1999) formulas, already implemented in OpenFOAM How do we pick the right Cc and Cv coefficients for our problem? Eqn 1 and 2 Andersen (2011) CFD Analysis Method For reference use only
- 6. Liquid volume fraction from system analysis Alpha water from system analysis sensitivity study Volumetric phase ratio at 0.15 seconds for Baseline case For reference use only
- 7. 0.984 0.986 0.988 0.99 0.992 0.994 0.996 0.998 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 Kunz phase change model sensitivity study Alpha Value from System Analysis Alpha water from CFD analysis sensitivity study Volumetric phase ratio at 0.15 seconds for Baseline case Alpha water versus Kunz coefficients Moving average trendline Settled on Cc and Cv=0.69 Increasing Cc and Cv beyond 0.8 has shown rapid increase in the phase change rate and increase in Courant number to unphysical values. For reference use only
- 8. Boundary conditions Mesh size reduction: ¼ of the tank is modeled Symmetry Plane Symmetry Plane Mesh Refinements near Walls And Exit Plane For reference use only
- 9. Boundary conditions Wall Outlet P=Patm Initial conditions (inside the tank) Heated bottom wall T=377.86K Calculated from radiation heat flux, on next slide T (K) 373.15 Static pressure (Pascals) 101325 Alpha liquid 1 Transport Properties (assumed constant for T around 373.15K) Thermal Diffusivity 0.000023m²/s Surface Tension 0.07N/m² Liquid Kinematic Viscosity 9.00E-07m2/s Density 1000kg/m3 Vapor Kinematic Viscosity 4.27E-04m2/s Density 0.02308kg/m3 For reference use only
- 10. Determining the bottom wall temperature Equation 10.5 in Incropera DeWitt (2002) • Radiative heat flux prescribed: 14739 W/m2 from El Ouederni et all (2009) • Calculate wall temperature Ts with the system analysis spreadsheet: • The surface temperature remains fairly constant through the iterative process, so the average value can be used as a boundary condition in OpenFOAM: 377.8645K Plot of Prandl Number vs Time from System Analysis • Fluid properties remain constant due to the system achieving equilibrium pressure and temperature almost immediately. 1.749 1.74905 1.7491 1.74915 1.7492 1.74925 1.7493 1.74935 0 0.05 0.1 0.15 0.2 0.25 Prandl Number (liquid) / timeFor reference use only
- 11. Water volume fraction animation, 0 to 1s. 1 Frame=0.01s Video at 5FPS X=0 cut For reference use only
- 12. Nozzle velocity animation, 0 to 1s. 1 Frame=0.01s Video at 5FPS X=0 For reference use only
- 13. Validation (Baseline Configuration) Figure 11 in Son,Dhir and Ramanujapu (1999) Bubble diameter with time for wall superheat of 7.0K Bubble departure timeline from CFD Results – at the wall Time between frames is 0.01s: 0 0.01 0.02 0.03 0.04 0.05 Bubble departure diameter from CFD results. Wall superheat is 4.7K • Data was not available for the wall superheat determined from the prescribed solar heat flux. • The bubble departure time should decrease with temperature difference increase. • Overall the CFD solver appears to capture the phenomena of bubble generation with sufficient accuracy. For reference use only
- 14. Limitations Method • Diffuse Interface (A feature of the VOF method without interface sharpening) • Simulations on nucleate boiling require special treatment at the wall (micro region) Figure 2(a) in Yohei and Bojan (2011) • Thermal Diffusivity modeled as a constant • Phase change model more suitable for cavitation rather than temperature driven evaporation Computational Power / Time • Each simulation of 1s took 12 hours. Phenomena beyond 1s were not captured. • Mesh was rather coarse, finer mesh would help with a sharper interface and more accuracy, For reference use only
- 15. Geometry variations Baseline Wide nozzle intake Narrow nozzle exhaust For reference use only
- 16. Baseline Wide nozzle intake Narrow nozzle exhaust Nozzle velocity plots at 0.63s For reference use only
- 17. Thrust variation with nozzle geometry Baseline Wide nozzle intake Narrow nozzle exhaust 4.43*10-3N 4.06*10-3N 6.47*10-3N 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0.012 0.013 0.014 0.015 0.016 Thrust vs Avg. Nozzle Diam Thrust was averaged over the first second , ignoring the first tenth of a second, in order to allow the flow to adjust from the initial conditions to a more natural exhaust. For reference use only
- 18. Summary of project accomplishments Developed a hybrid analysis method for computing thrust of a nozzle-equipped vessel heated from below with a radiation flux. Iterative system analysis in Excel: • Radiative heat flux converted to temperature difference for easy application of CFD BC • Estimate of liquid volume fraction with time used to tweak CFD phase change model. CFD Analysis in OpenFOAM • Extended the work of Andersen(2011) to add evaporation to a newer version of OpenFOAM, 2.3.1 • Performed sensitivity studies to determine the best Kunz phase change model coefficients • Shared insights gained on the cfd-online.com forums so that others can continue to refine the solver • Determined the trend of thrust increasing with smaller overall nozzle dimensions. (more simulation runs for different configurations will help refine the trend) For reference use only
- 19. References • Hill, Philip G., and Carl R. Peterson. Mechanics and Thermodynamics of Propulsion. Reading, MA: Addison- Wesley Pub., 1992. Print. • Incropera, Frank P., and David P. DeWitt. Fundamentals of Heat and Mass Transfer. New York: Wiley, 2002. Print. • Brennen, Christopher E. Fundamentals of Multiphase Flow. Cambridge: Cambridge UP, 2005. Print. • Michta, Edouard. Modeling of Subcooled Nucleate Boiling with OpenFOAM. Master of Science Thesis. Royal Institute of Technology. Stockholm, Sweden, 2011. • CFD Online." CFD Online. N.p., n.d. Web. 10 Feb. 2015. cfd-online.com • El Ouederni A.R. , Salah M. Ben , Askri F. , Nasrallah M. Ben and Aloui F. Experimental Study of a Parabolic Solar Concentrator. Revue des Energies Renouvelables Vol. 12 N°3 (2009) 395 – 404 • "The OpenFOAM Foundation." OpenFOAM®. N.p., n.d. Web. 10 Feb. 2015.openfoam.org • Yohei Sato, Bojan Ničeno. A New Conservative Phase Change Model for Nucleate Boiling. Proceedings of the International Conference Nuclear Energy for New Europe. Bovec, Slovenia, 2011 • Andersen, Martin. CFD with OpenSource software. Chalmers University of Technology. Sweden, 2011. • Kunz, Robert F., Boger, David A., Chyczewski, Thomas S., Stinebring, David R. and Gibeling, Howard J. Multi-phase CFD Analysis of Natural And Ventilated Cavitation About Submerged Bodies. 3rd ASME/JSME Joint Fluids Engineering Conference. San Francisco, California, 1999. • Son, G., Dhir, V. and Ramanujapu, N. “Dynamics and Heat Transfer Associated With a Single Bubble During Nucleate Boiling on a Horizontal Surface”. Journal of Heat Transfer, Vol 121. Los Angeles, CA, 1999. For reference use only
- 20. Appendix 1: CFD Analysis Equation Details • Andersen (2011) eqn. 3: Thermal Diffusivity • Andersen (2011) eqns. 1 and 2 or Kunz and all (1999) eqn. 3: Evaporation / CondensationFor reference use only
- 21. Appendix 2: Auxiliary equations details Equation 10.5 in Incropera DeWitt (2002) Csf is the surface fluid combination; Cpl is the specific heat of the liquid. L suffix means liquid and v suffix means vapor; hfg is the latent heat of vaporization; Ts is the temperature of the heated surface ; Tsat is the temperature of saturated vapor. Prandl Number is the ratio of viscous diffusion rate to thermal diffusion rate Equation 6.46 in Incropera DeWitt (2002) For reference use only
- 22. Appendix 3: Determining thrust with Paraview Exhaust surface patch (top)Calculate thrust/area for each cell cell Integrate by multiplying with cell area and summing over surface For reference use only
- 23. Appendix 4: Thrust versus time (Baseline configuration) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0 0.2 0.4 0.6 0.8 1 1.2 Thrust(N) vs Time(s) for Baseline Averaging thrust over the first 0.7s (0.1-0.7 in 0.1s increments) appears to be sufficient to calculate a value. Thrust might decrease later on but a longer analysis will require computational resources currently unavailable. For reference use only