multiphasenucleate-boiling

1、Tutorial: Modeling Nucleate Boiling Using FLUENTIntroductionThe purpose of this tutorial is to demonstrate the modeling of forced convection nucleate boiling using the Eulerian multiphase model. The solution of this problem requires the use of user-defined functions (UDFs).This tutorial demonstrates

2、 how to do the following:Read the mesh file in FLUENT.Generate a single phase flow solution and use the fully-developed outlet as inlet in- formation for the multiphase calculation.Compile a set of user-defined functions (UDFs) for modeling mass, heat, and momen- tum transport in boiling flow.Define

3、 solution-dependent material properties as piecewise-linear functions of temper- ature.Use outlet profiles from one simulation as inlet conditions for another simulation. Set up the Eulerian multiphase model to predict boiling.Hook the compiled UDFs to the solution in order to model phase change due

4、 to boiling.Run the calculations until a steady-state solution is obtained. Postprocess the resulting data.PrerequisitesThis tutorial assumes that you are familiar with the menu structure in FLUENT and that you have a good understanding of the basic setup and solution procedures. Some basic steps in

5、 the setup and solution procedure will not be shown explicitly.Problem DescriptionIn this tutorial, you will consider upward, vertical flow in a pipe with a heated wall. The flow domain is shown schematically in Figure 1. The pipe is 15.4 mm in diameter and 2 m in length. The wall provides heat to t

6、he fluid at the rate of 345.6 kW/m2. As the wall1c Fluent Inc. March 1, 2007Modeling Nucleate Boiling Using FLUENTtemperature rises above the fluid saturation temperature, steam bubbles are formed and they migrate away from the wall. Since the bulk flow is subcooled, the bubbles condense near the ce

7、nter of the pipe.Axis of symmetryOutletHeated Wall 5 mm thick Stainless Steelq = 345.6 kW/m22 mrr = 7.7 mmInletV = 1 m/s T = 200o CP = 45 atmFigure 1: Schematic of the ProblemThis tutorial will guide you through the complete problem setup in FLUENT. Outlet profiles of velocity magnitude and turbulen

8、ce quantities generated for a simulated flow field without boiling will be used as inlet information to the boiling simulation. This is done to ensure a fully-developed profile of these quantities at the inlet. Finally, the results of the boiling simulation will be compared with available experiment

9、al data.Preparation1. Copy the files, boiling-conjugate.msh and boiling-rpi-model.c to your working folder.2. Start the 2D, double precision (2ddp) version of FLUENT.2c Fluent Inc. March 1, 2007Modeling Nucleate Boiling Using FLUENTSetup and SolutionSingle Phase FlowStep 1: Grid and Units1. Read the

10、 mesh file (boiling-conjugate.msh).Case.As the mesh file is read FLUENT reports the progress in the console.2. Check the grid.Check3. Display the grid.Grid.4.Customize the display.Views.Click the Camera. button to open the Camera Parameters panel.(a)Select Up Vector from the Camera drop-down list. S

11、et the vector (X, Y, Z) to (1, 0, 0).Click Apply and close the Camera Parameters panel.The graphics window now displays the pipe in the vertical position. setting only controls the display of the mesh and/or solution. This(b)(c)(d)The camera is a displayfeature only and does not affect the calculati

12、ons. In this case, the flow is still in the x-direction.Select axis from the Mirror Planes selection list. Click Apply.Click Save to save the view.The saved view, view-0 is now visible in the Views list.Close the Views panel.(e)(f)(g)(h)(i)Zoom and pan in the graphics display window to familiarize y

13、ourself with the mesh (Figure 2).3c Fluent Inc. March 1, 2007DisplayDisplayGridReadFileModeling Nucleate Boiling Using FLUENTFigure 2: Grid Display near the Inlet5.Change the units of pressure to atmospheres.The operating pressure for this problem is known to be 45nience, change the units of pressur

14、e to atmospheres.atmospheres. For conve-Units.(a) Select pressure from the Quantities selection list and atm from the Units selection list.The pressure unit is now set to atmosphere.(b) Close the Set Units panel.4c Fluent Inc. March 1, 2007DefineModeling Nucleate Boiling Using FLUENTStep 2: Models1.

15、 Select the Pressure Based, Implicit, Axisymmetric solver with Steady time formulation.Solver.2. Enable the Energy Equation.Energy.3. Select the renormalization group k-epsilon turbulence model.Viscous.(a)Select k-epsilon (2 eqn) from the Model group box.The Viscous Model panel expands to show addit

16、ional options.Select RNG from the k-epsilon Model group box. Click OK to close the Viscous Model panel.(b)(c)Step 3: MaterialsMaterials.1. Copy the material water-liquid from the FLUENT materials database.2. Click the Fluent Database. button to open the Fluent Database Materials panel.(a) Select wat

17、er-liquid (h2o) from the Fluent Fluid Materials selection list.Click Copy to add the selected material to the current case setup.(b)(c) Close the Fluent Database Materials panel.3. Define density as a piecewise-linear profile of temperature.(a) Select piecewise-linear from the Density drop-down list

18、 to open the Piecewise-Linear Profile panel.(b) Set Points to 2.This tells FLUENT that you will be defining the linear profile using two data points.(c) Set Point to 1 in the Data Points group box.5c Fluent Inc. March 1, 2007DefineModelsDefineModelsDefineModelsDefineModeling Nucleate Boiling Using F

19、LUENT(d) Enter 473.15 K and 864.7 for Temperature and Value, respectively.(e) Set Point to 2 in the Data Points group box.(f) Enter 543.15 K and 770.6 for Temperature and Value, respectively.(g) Click OK to close the Piecewise-Linear Profile panel.Similarly, define piecewise-linear profiles for Cp,

20、Thermal Conductivity, and Viscosity as shown in Table 1.4.Table 1: Physical Properties of water-liquidClick Change/Create and close the Materials panel.5.6c Fluent Inc. March 1, 2007PointsPoint 1Point 2Temperature(k)ValueTemperature(k)ValueCp (j/kg-k)2473.154494543.155067Thermal conductivity (w/m-k)

21、2473.150.664543.150.5928Viscosity (kg/m-s)2473.151.339e-04543.159.995e-05Modeling Nucleate Boiling Using FLUENTStep 4: Operating ConditionsOperating Conditions.1. Enter 45 for Operating Pressure (atm).Enable Gravity.The panel expands to show additional inputs.(a) Enter -9.81 m/s2 for Gravitational A

22、cceleration in the X direction.This indicates that the gravity vector is opposed to the direction of flow.(b) Enter 503.15 K for Operating Temperature.3. Click OK to close the Operating Conditions panel.2.Step 5: Boundary ConditionsBoundary Conditions.1. Verify that the Type for the axis zone is set

23、 to axis.2. Select water-liquid from the Material Name drop-down list for the fluid zone.3. Define the boundary conditions at the inlet.(a) Retain the default selection of Magnitude, Normal to Boundary as the Velocity Specification Method.(b) Enter 1 m/s for Velocity Magnitude.7c Fluent Inc. March 1

24、, 2007DefineDefineModeling Nucleate Boiling Using FLUENT(c) Select Intensity and Hydraulic Diameter from the drop-down list for Turbulence Specification Method.(d) Enter 4% and 0.0154 mfor Turbulence Intensity and Hydraulic Diameter, respec- tively.(e) Click the Thermal tab and enter 473.15 K for Te

25、mperature.(f) Click OK to close the Velocity Inlet panel.4. Define the boundary conditions at the outlet.(a) Retain the default value of 0 atm for Gauge Pressure.(b) Retain the default Backflow Direction Specification Method.(c) Select Intensity and Hydraulic Diameter in the drop-down list for Turbu

26、lence Spec- ification Method.(d) Enter 4% and 0.0154 m for Backflow Turbulence Intensity and Backflow Hydraulic Diameter, respectively.Click OK to close the Pressure Outlet panel.The backflow conditions should be set to a reasonable value in order to instructFLUENT to introduce fluid through an outl

27、et if necessary.5. Close the Boundary Conditions panel.(e)Step 6: Single Phase Solution and Outlet Profile1. Set the solution control parameters.Solution.(a) Retain the default settings.(b) Click OK to close the Solution Controls panel.2. Specify residual monitor settings.Residual.(a) Enable the plo

28、tting of residuals.(b) Reduce the Convergence Criterion for continuity to 1e-08.(c) Click OK to close the Residual Monitors panel.3. Initialize the solution using the values at the inlet.Initialize.4. Request 500 iterations.Iterate.The solution converges in around 320 iterations.8c Fluent Inc. March

29、 1, 2007SolveInitializeSolveMonitorsSolveControlsSolveModeling Nucleate Boiling Using FLUENTFigure 3: Residual History of the Single-Phase Flow Solution5.Plot the fully developed outlet profile (Figure 4).XY Plot.(a) Set the Plot Direction (X, Y) to (0, 1).(b) Select Velocity. and Velocity Magnitude

30、 in the Y Axis Function drop-down lists.(c) Select outlet from the Surfaces selection list.(d) Click Plot and close the Solution XY Plot panel.9c Fluent Inc. March 1, 2007PlotModeling Nucleate Boiling Using FLUENTFigure 4: Fully-Developed Outlet Velocity Profile6.Write a data profile at the outlet.I

31、n this step, you will write a file containing selected flow solutioninformation onspecified surfaces. Later, you will use this information as inlet boundary conditions when the boiling model is enabled.Profile.10c Fluent Inc. March 1, 2007WriteFileModeling Nucleate Boiling Using FLUENT(a)(b)(c)Selec

32、t Define New Profile in the Options group box. Select outlet from the Surfaces selection list.SelectVelocityMagnitude,TurbulenceKineticEnergy(k), andTurbulentDissipation Rate (Epsilon) from the Values selection list.Scroll down the Values list to select Turbulence Kinetic Energy (k), and Turbulent D

33、issipation Rate (Epsilon).Click Write. to open the Select File panel.Enter f for File Name and click OK.This writes a profile file to the working folder. The profile file contains the solu- tion information that was requested in the Write Profile panel. This information is used to s

34、upply inlet information in the boiling calculation.Close the Write Profile panel.(d)(e)(f)7. Read the newly created profile into memory.After creating a profile, you need to read it into memory for the profile variables to be available as boundary conditions.Profile.FLUENT displays the progress of r

35、eading the profile, in the console.8. Savethecaseanddatafiles(boiling-single-phase.cas.gzandboiling-single-phase.dat.gz).Setup and SolutionBoiling FlowStep 1: Models1. Enable the unsteady solver.Solver2. Enable the Eulerian multiphase model.Multiphase.11c Fluent Inc. March 1, 2007ModelsDefineModelsD

36、efineReadFileModeling Nucleate Boiling Using FLUENT(a) Select Eulerian from the Model group box.Set the Number of Phases to 2.Click OK to close the Multiphase Model panel.An Information dialog box opens, reminding you that the available material prop- erties have changed. Click OK to continue.(b)(c)

37、3. Ensure that Mixture is selected from the k-epsilon Multiphase Model group box.Viscous.Step 2: Compile the UDF1. Compile the UDF, boiling-rpi-model.c.Compiled.(a) Click Add. in the Source Files section to open the Select File panel.(b) Select the source file boiling-rpi-model.c.(c) Click Build to

38、build the library.A Warning dialog box opens, asking you to make sure that the UDF source files are in the same folder that contains the case and data files. Click OK.FLUENT compiles the code. FLUENT shows the progress of the compilation in the console. Monitor the progress for compilation and linki

39、ng errors.(d) Click Load to load the newly created UDF library.2. Define function hooks.Function Hooks.12c Fluent Inc. March 1, 2007User-DefinedDefineFunctionsUser-DefinedDefineModelsDefineModeling Nucleate Boiling Using FLUENT(a) Select adjust for force for Adjust drop-down list.(b) Select heat flu

40、x from the Wall Heat Flux drop-down list.(c) Click OK to close the User-Defined Function Hooks panel.3. Increase the Number of User-Defined Memory Locations to 22.Memory.There are 22 user-defined memory locations (UDMs) that are used by the UDF. The number of locations needs to be specified in order

41、 that the UDF runs properly and that UDM quantities are available for postprocessing.Step 3: MaterialsMaterials.1. Enter additional properties for water-liquid.(a) Enter 18.0152 for Molecular Weight.(b) Enter 0 for Standard State Enthalpy.(c) Enter 533.15 K for Reference Temperature.(d) Click Change

42、/Create.2. Copy an additional fluid material (water-vapor) from the FLUENT materials database.(a) Click the Fluent Database. button to open the Fluent Database Materials panel.(b) Select fluid in the Material Type drop-down list.Select water-vapor (h2o) from the Fluent Fluid Materials selection list

43、. Click Copy to add the selected material to the current case setup.Close the Fluent Database Materials panel.(c)(d)(e)13c Fluent Inc. March 1, 2007DefineUser-DefinedDefineModeling Nucleate Boiling Using FLUENT3. Modify the properties of water-vapor.(a) Specify the properties as shown in Table 2.Tab

44、le 2: Physical Properties ofwater-vapor(b) Click Change/Create.4. Create the wall material (stainless steel) by modifying the properties of aluminum.(a) Select solid from the Material Name drop-down list.(b) Rename aluminum to stainless-steel and delete the entry for Chemical For- mula.(c) Enter the

45、 properties of stainless-steel as shown in Table 3.Table 3: Physical Properties of stainless-steel(d) Click Change/Create and click Yeswhen asked if you want to overwrite aluminum.5. Close the Materials panel.Step 4: Phase InteractionPhases.1. Define the primary (liquid) phase.(a)Select phase-1 from

46、 the Phase selection list and click the Set. button to open the Primary Phase panel.Enter liquid for Name.(b)14c Fluent Inc. March 1, 2007DefinePropertyValueDensity (kg/m3)8030Cp (j/kg-k)502.48Thermal Conductivity (w/m-k)16.27PropertyValueDensity (kg/m3)23.75Cp (j/kg-k)4221Thermal Conductivity (w/m-

47、k)0.0528Viscosity (kg/m-s)1.79e-05Molecular Weight18.0152Standard State Enthalpy0Reference Temperature533.15Modeling Nucleate Boiling Using FLUENT(c) Select water-liquid from the Phase Material drop-down list.(d) Click OK to close the Primary Phase2. Define the secondary (vapor) phase.panel.(a) Spec

48、ify vapor for Name and select water-vapor from the Phase Material drop-down list.(b) Select user-defined from the Diameter drop-down list to open the User-Defined Functions panel.(c) Select diameter and click OK.(d) Click OK to close the Secondary Phase panel.3. Define the interaction between the ph

49、ases.(a) Click the Interaction. button to open the Phase Interaction panel.(b) Click the Drag tab.15c Fluent Inc. March 1, 2007Modeling Nucleate Boiling Using FLUENTi. Select user-defined from the Drag coefficient drop-down list to open the User- Defined Functions panel.ii. Select drag and click OK.

50、Similarly, click the Lift tab and select lift from the Lift Coefficient drop-down list. Click the Heat tab and select ranz-marshall from the Heat Transfer Coefficientdrop-down list.Click the Mass tab and set the Number of Mass Transfer Mechanisms to 1.The panel expands to show additional inputs.(c)(

51、d)(e)16c Fluent Inc. March 1, 2007Modeling Nucleate Boiling Using FLUENTi. Select vapor and liquid from the From Phase and To Phase drop-down lists, respectively.It is important that vapor be selected for Fromfor To Phase. Otherwise, an error will result.Phase and liquid be selectedii. Select user-d

52、efined from the Mechanism drop-down list.iii. Select vaporisation condensation in the User-Defined Functions panel.iv. Click OK to close the Phase Interaction panel.4. Close the Phases panel.Step 5: Operating ConditionsOperating Conditions.1. Enable Specified Operating Density in the Variable-Densit

53、y Parameters group box.2. Enter 23.75 kg/m3 for Operating Density.3. Click OK to close the Operating Conditions panel.Step 6: Boundary ConditionsBefore setting the boundary conditions, you need to initialize the flow field. The reason for initializing the flow field is that there currently is only a

54、 single-phase flow solution in memory and later on you will be setting two-phase boundary conditions on the walls. If the solution is not initialized at this point, an error will result later on.Initialize.17c Fluent Inc. March 1, 2007InitializeSolveDefineModeling Nucleate Boiling Using FLUENTInitia

55、lize the flow field from the inlet zone.In order to maintain flexibility in multiphase problems, FLUENT allows the specification of separate boundary conditions for each phase. Boundary conditions for the mixture phase are required as well. This allows each phase to be treated differently at various surfaces. When multiphase flow is enabled, the Boundary Conditions panel shows a drop-down list containing the names of each phase.Boundary Conditions.Define the boundary conditions for the continuum zone (fluid).1.Set the boundary conditions for the mixture phase.(