[wissal]

Hello everybody

I'm trying to simulate the condensation process in a pipe. The coolant flows around the pipe in a cooling annulus. ==> (Multiphase flow in the pipe + CHT)
* 3 Domains: cooling annulus, condenser pipe and steel pipe.

the unsteady simulations haven't worked so far (convergence problems). The steady ones gave odd results. It seems there is no flow inside the pipe, even y+ isn't defined in the domain where condensation is supposed to find place.
It would be of great help if anyone of you guys can see where the problem is.

In the attachement u'll find the results for the velocity.
Here is my setup for the Condenser domain:

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 = Steady State
EXTERNAL SOLVER COUPLING:
Option = None
END
END
DOMAIN: Condenser
Coord Frame = Coord 0
Domain Type = Fluid
Location = B38
BOUNDARY: Default Fluid Solid Interface Side 1
Boundary Type = INTERFACE
Location = F47.38
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
WALL ROUGHNESS:
Option = Smooth Wall
END
END
END
BOUNDARY: Inlet
Boundary Type = INLET
Location = InletCondenderTube
BOUNDARY CONDITIONS:
FLOW DIRECTION:
Option = Normal to Boundary Condition
END
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 145.3 [C]
END
MASS AND MOMENTUM:
Mass Flow Rate = 0.0166861111 [kg s^-1]
Option = Bulk Mass Flow Rate
END
TURBULENCE:
Option = Medium Intensity and Eddy Viscosity Ratio
END
END
FLUID: Humid Air
BOUNDARY CONDITIONS:
COMPONENT: H2O GAS
Mass Fraction = 0.8524
Option = Mass Fraction
END
VOLUME FRACTION:
Option = Value
Volume Fraction = 1
END
END
END
FLUID: Liquid
BOUNDARY CONDITIONS:
VOLUME FRACTION:
Option = Value
Volume Fraction = 0
END
END
END
END
BOUNDARY: Outlet
Boundary Type = OUTLET
Location = F39.38
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Option = Average Static Pressure
Pressure Profile Blend = 0.05
Relative Pressure = 0 [Pa]
END
PRESSURE AVERAGING:
Option = Average Over Whole Outlet
END
END
END
BOUNDARY: Symmetry_Condenser
Boundary Type = SYMMETRY
Location = F43.38,F46.38
END
DOMAIN MODELS:
BUOYANCY MODEL:
Buoyancy Reference Density = 0.46 [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 = 413.1 [kPa]
END
END
FLUID DEFINITION: Humid Air
Material = Gas Mixture
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID DEFINITION: Liquid
Material = Liquid
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END

[Opaque]

Unfortunately, you are setting up the problem the most difficult way to solve it.

Your simulation should be setup as a single phase flow in each fluid domain, plus a solid domain for the pipe.

However, to do so you must enable beta features and disable the Constant Domain Physics. Unfortunately, you must be careful from here on as the software does not do a bunch of physics checks for you.

[wissal]

Thank you Opaque for your reponse

I actually did that. I defined 3 domains: Condenser is where condensation takes place (with a subdomain for condensation and another one for evaporation), Cooling Jacket where the coolant flows, and a solid domain for the Tube.
So Condenser is the only Multiphase domain. The setup I attached is only for Condenser.

What bothers me is that it seems that the fluid doesn't even flow through the pipe (picture CFD post). The results for velocity are weird. Y+ is Undefined in this domain (why??). Something is sooo wrong and I can't figure out the problem.

[Opaque]

Perhaps you have already done the following, but good to point out anyways.

Since a beta feature is being used, I would step carefully in the model setup. Have you already run the single phase flow case ? That is, coolant fluid in the coolant jacket domain, and say "humid mixture" in the "condenser/evaporator" domain w/o any thermodynamic phase change active ? No need for multiphase flow anywhere.

Once that case is running properly, I would move into the next level of complexity.

Also, have you used the equilibrium phase change model already ? It is meant for condensation using a single phase fluid. No need for multiphase flow.

[wissal]

I will try that out!

Thanks a lot for your help