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August 20, 2015, 05:54 
Multiphase heat transfer

#1 
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pkladisios
Join Date: Jul 2015
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Greetings!
I'm having considerable trouble thermally simulating a airwater tank (80% filled with water, rest is air). I have already run simulations for a tank completely filled with a single fluid (water). By adding a second fluid, i have no heat transfer inside the fluid domain!!! What i have done so far: FLUID DOMAIN Basic settings Reference pressure>1 atm Buoyancy model>buoyant>x:0 y:9.81 z:0 m/s2 Buoyancy reference density>1000 kg/m3 Fluid models Multiphase> free surface > standard Heat transfer>fluid dependent Fluid specific models Heat transfer>Thermal energy (both for air and water) Fluid pair models Interphase transfer>free surface Heat transfer>heat transfer coefficient>10 W/m2K (estimation) Initialization Cartesian velocity components>U=V=W=0 m/s Relative pressure>1 atm Temperature>25 oC Volume fraction>0.8 water/0.2 air SOLID DOMAIN Solid models Heat transfer>thermal energy Initial conditions Temperature>25 oC DEFAULT FLUID SOLID INTERFACE Additional interface models Heat transfer>Conservative heat flux DEFAULT FLUID SOLID INTERFACE SIDE 1 Boundary details Heat transfer>Conservative heat flux DEFAULT FLUID SOLID INTERFACE SIDE 2 Boundary details Heat transfer>Conservative heat flux Using the settings above, heat transfer stops at the outer solid exterior. What is weird is that volume fraction diagrams show up quite reasonable. It is most certain that i' m doing something wrong. Any help will be greatly appreciated. Thank you in advance! Last edited by pkladisios; August 20, 2015 at 05:59. Reason: correction 

August 20, 2015, 06:46 

#2 
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Glenn Horrocks
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Location: Sydney, Australia
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You should be able to take the working single phase case, replace the fluid with a multiphase fluid and keep all the solid heat transfer stuff the same and it should work.
Can you post some images of what you are seeing and your CCL. 

August 20, 2015, 07:05 

#3 
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pkladisios
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Thank you for your answer. In order to save space, this is only the Fluid analysis part of my CCL:
# State file created: 2015/08/20 13:00:14 # Build 16.0 2014.11.1423.10133146 FLOW: Flow Analysis 1 SOLUTION UNITS: Angle Units = [rad] Length Units = [m] Mass Units = [kg] Solid Angle Units = [sr] Temperature Units = [K] Time Units = [s] END ANALYSIS TYPE: Option = Transient EXTERNAL SOLVER COUPLING: Option = None END INITIAL TIME: Option = Automatic with Value Time = 0 [s] END TIME DURATION: Option = Total Time Total Time = 60 [s] END TIME STEPS: Option = Timesteps Timesteps = 10 [s] END END DOMAIN: fluid_domain Coord Frame = Coord 0 Domain Type = Fluid Location = B15 BOUNDARY: Default Fluid Solid Interface Side 1 Boundary Type = INTERFACE Location = F10.15,F8.15,F9.15 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = No Slip Wall END WALL CONTACT MODEL: Option = Use Volume Fraction END END END DOMAIN MODELS: BUOYANCY MODEL: Buoyancy Reference Density = 1000 [kg m^3] Gravity X Component = 0 [m s^2] Gravity Y Component = 9.81 [m s^2] Gravity Z Component = 0 [m s^2] Option = Buoyant BUOYANCY REFERENCE LOCATION: Option = Automatic END END DOMAIN MOTION: Option = Stationary END MESH DEFORMATION: Option = None END REFERENCE PRESSURE: Reference Pressure = 1 [atm] END END FLUID DEFINITION: air Material = Air at 25 C Option = Material Library MORPHOLOGY: Option = Continuous Fluid END END FLUID DEFINITION: water Material = Water Option = Material Library MORPHOLOGY: Option = Continuous Fluid END END FLUID MODELS: COMBUSTION MODEL: Option = None END FLUID: air FLUID BUOYANCY MODEL: Option = Density Difference END HEAT TRANSFER MODEL: Option = Thermal Energy END END FLUID: water FLUID BUOYANCY MODEL: Option = Density Difference END HEAT TRANSFER MODEL: Option = Thermal Energy END END HEAT TRANSFER MODEL: Homogeneous Model = Off Option = Fluid Dependent END THERMAL RADIATION MODEL: Option = None END TURBULENCE MODEL: Homogeneous Model = Off Option = Laminar END END FLUID PAIR: air  water INTERPHASE HEAT TRANSFER: Heat Transfer Coefficient = 20 [W m^2 K^1] Option = Heat Transfer Coefficient END INTERPHASE TRANSFER MODEL: Option = Free Surface END MASS TRANSFER: Option = None END MOMENTUM TRANSFER: DRAG FORCE: Drag Coefficient = 0.44 Option = Drag Coefficient END END SURFACE TENSION MODEL: Option = None END END INITIALISATION: Option = Automatic FLUID: air INITIAL CONDITIONS: Velocity Type = Cartesian CARTESIAN VELOCITY COMPONENTS: Option = Automatic with Value U = 0 [m s^1] V = 0 [m s^1] W = 0 [m s^1] END TEMPERATURE: Option = Automatic with Value Temperature = 25 [C] END VOLUME FRACTION: Option = Automatic with Value Volume Fraction = 0.2 END END END FLUID: water INITIAL CONDITIONS: Velocity Type = Cartesian CARTESIAN VELOCITY COMPONENTS: Option = Automatic with Value U = 0 [m s^1] V = 0 [m s^1] W = 0 [m s^1] END TEMPERATURE: Option = Automatic with Value Temperature = 25 [C] END VOLUME FRACTION: Option = Automatic with Value Volume Fraction = 0.8 END END END INITIAL CONDITIONS: STATIC PRESSURE: Option = Automatic with Value Relative Pressure = 1 [atm] END END END MULTIPHASE MODELS: Homogeneous Model = Off FREE SURFACE MODEL: Option = Standard END END END DOMAIN: solid_domain Coord Frame = Coord 0 Domain Type = Solid Location = B11 BOUNDARY: Default Fluid Solid Interface Side 2 Boundary Type = INTERFACE Location = F10.11,F8.11,F9.11 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END END END BOUNDARY: adiabatic_bottom Boundary Type = WALL Location = F13.11 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Adiabatic END END END BOUNDARY: convection Boundary Type = WALL Location = F12.11,F14.11 BOUNDARY CONDITIONS: HEAT TRANSFER: Heat Transfer Coefficient = 50 [W m^2 K^1] Option = Heat Transfer Coefficient Outside Temperature = 40 [C] END END BOUNDARY SOURCE: SOURCES: EQUATION SOURCE: energy Flux = 800 [W m^2] Flux Coefficient = 20 [kg s^3 K^1] Option = Flux END END END END DOMAIN MODELS: DOMAIN MOTION: Option = Stationary END MESH DEFORMATION: Option = None END END INITIALISATION: Option = Automatic INITIAL CONDITIONS: TEMPERATURE: Option = Automatic with Value Temperature = 25 [C] END END END SOLID DEFINITION: steel Material = Steel Option = Material Library MORPHOLOGY: Option = Continuous Solid END END SOLID MODELS: HEAT TRANSFER MODEL: Option = Thermal Energy END THERMAL RADIATION MODEL: Option = None END END END DOMAIN INTERFACE: Default Fluid Solid Interface Boundary List1 = Default Fluid Solid Interface Side 1 Boundary List2 = Default Fluid Solid Interface Side 2 Interface Type = Fluid Solid INTERFACE MODELS: Option = General Connection FRAME CHANGE: Option = None END HEAT TRANSFER: Option = Conservative Interface Flux HEAT TRANSFER INTERFACE MODEL: Option = None END END PITCH CHANGE: Option = None END END MESH CONNECTION: Option = Automatic END END OUTPUT CONTROL: RESULTS: File Compression Level = Default Option = Standard END TRANSIENT RESULTS: Transient Results 1 File Compression Level = Default Option = Standard OUTPUT FREQUENCY: Option = Every Timestep END END END SOLVER CONTROL: ADVECTION SCHEME: Option = High Resolution END CONVERGENCE CONTROL: Maximum Number of Coefficient Loops = 10 Minimum Number of Coefficient Loops = 1 Timescale Control = Coefficient Loops END CONVERGENCE CRITERIA: Residual Target = 1.E4 Residual Type = RMS END TRANSIENT SCHEME: Option = Second Order Backward Euler TIMESTEP INITIALISATION: Option = Automatic END END END END COMMAND FILE: Version = 16.0 END Temperature and volume fraction distribution along to cross section cuts of the tank, respectively: In the meantime, i' ll look into your suggestion about replacing the working fluid. Last edited by pkladisios; August 20, 2015 at 07:42. Reason: adding images 

August 20, 2015, 10:26 

#4 
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pkladisios
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I'm really sorry but, when you write "replace the fluid with a multiphase fluid" what exactly do you mean? My only though is to define a fixed composition mixture, but unfortunately it only allows a single phase for both materials (air, water)...


August 20, 2015, 11:03 

#5 
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As Glenn suggested, you can take the single fluid case and add another fluid (as you seem to have done).
Then, you initialize the volume fraction to be 1 for the previous fluid, and 0 for the newer fluid. The solution should be identical barring the ANSYS CFX solver has no problems dealing with 0 volume fraction for the new fluid. Once you pass that point, you know the heat transfer setup is consistent and start to increase the presence of the new fluid. What do you think? 

August 20, 2015, 19:37 

#6 
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Glenn Horrocks
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Your pictures seem to show this is a homogenous multiphase simulation because it looks like a distinct interface between air and water. But you are not using the homogeneous multiphase options. Why are you doing that?


August 21, 2015, 04:03 

#7 
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pkladisios
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Opaque, i' ll most certainly try your suggestion.
ghorrocks, i' ve tried turning on and off homogenous option both for heat transfer and multiphase to no avail. I' ve seen tutorials for multiphase flows without heat transfer taken into consideration and single fluid flows with heat transfer. It' s really annoying that i can' t combine both. 

August 21, 2015, 10:38 

#8 
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You definitely can run multiphase flows with heat transfer. I have seen simulations much more complex than those (including multicomponent phases with mass exchange between phases)
Something must be off in the setup 

June 7, 2016, 02:41 

#9 
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urosgrivc
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Hello
Can someone please explain >Flux Coefficient< I use source in the interface region in my simulations, and i dont have any problems understanding flux or total source. But the flux coefficient is bugging me because i dont know exactly what it means. And what is its unit? example from pkladisioss post : Flux Coefficient = 20 [kg s^3 K^1] Thank You 

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cfx, heat, multiphase, transfer 
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