[pkladisios]

Greetings!

I'm having considerable trouble thermally simulating a air-water 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!

[ghorrocks]

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.

[pkladisios]

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 2014.11.14-23.10-133146

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.E-4
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.

[pkladisios]

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)...

[Opaque]

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?

[ghorrocks]

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?

[pkladisios]

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.

[Opaque]

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

[urosgrivc]

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