[gerardosrez]

Hello colleagues,

I am setting up a simulation of a so called heat pipe....with the difference that mine has no adiabatic section....

I am using Homogeneous model for continuity and momentum, inhomogeneous for heat transfer/thermal phase change for evaporation condensation...

Also I defined a HBM (homogeneous binary mixture) formed by Liq Water and Vap Water, both substances are based in IAPWS IF97 data...

My question is...if I am modeling using steam tables data...should I use Thermal or Total Energy for solving energy equation?....

If so, should I use Total Energy for vap phase only? or for both phases...

This is my input file, and also I attached a picture of my domain

# State file created: 2015/09/16 11:27:25
# CFX-14.0 build 2011.10.10-23.01

LIBRARY:
CEL:
EXPRESSIONS:
CondTemp = if(Time<900 [s],316.7[K],if(Time<1800 [s],325.0 \
[K],if(Time<2700 [s],331.7 [K],if(Time<3600 [s],335.7 \
[K],if(Time<4500 [s],341.6 [K],if(Time<5400 [s],345.5 \
[K],if(Time<6300 [s],349.4 [K],if(Time<7200 [s],352.8 \
[K],if(Time<8100 [s],349.7 [K],if(Time<9000 [s],339.6 \
[K],if(Time<9900 [s],336.5 [K],if(Time<10800 [s],333.6 \
[K],if(Time<11700 [s],331.4 [K],if(Time<12600 [s],330.8 \
[K],if(Time<13500 [s],330.2 [K],if(Time<14400 [s],329.0 [K],328.3 \
[K]))))))))))))))))
EvapHeatInput = if(Time<900 [s],4361[W m^-2],if(Time<1800 [s],4387 [W \
m^-2],if(Time<2700 [s],4449 [W m^-2],if(Time<3600 [s],4501 [W \
m^-2],if(Time<4500 [s],4542 [W m^-2],if(Time<5400 [s],4563 [W \
m^-2],if(Time<6300 [s],4573 [W m^-2],if(Time<7200 [s],4589 [W \
m^-2],if(Time<8100 [s],4620 [W m^-2],if(Time<9000 [s],4630 [W \
m^-2],if(Time<9900 [s],4599 [W m^-2],if(Time<10800 [s],4589 [W \
m^-2],if(Time<11700 [s],4578 [W m^-2],if(Time<12600 [s],4568 [W \
m^-2],if(Time<13500 [s],4578 [W m^-2],if(Time<14400 [s],4563 [W \
m^-2],4527 [W m^-2]))))))))))))))))
HydroP = LiqDen*g*(LiqHt-y)*LiqVF-0.79 [bar]
LiqDen = 998 [kg m^-3]
LiqHt = 370 [mm]
LiqVF = if(y<LiqHt,1,0)
SurfTCoeff = a+b*Temperature+c*Temperature^2
a = 0.09805856 [N m^-1]
b = -0.00001845 [N m^-1 K^-1]
c = -0.00000023 [N m^-1 K^-2]
END
END
MATERIAL: LiqVapMix
Binary Material1 = Vapor Water
Binary Material2 = Liquid Water
Material Group = IAPWS IF97
Option = Homogeneous Binary Mixture
SATURATION PROPERTIES:
Option = IAPWS Library
END
END
MATERIAL: Liquid Water
Material Group = IAPWS IF97
Option = Pure Substance
Thermodynamic State = Liquid
PROPERTIES:
Option = IAPWS Library
END
END
MATERIAL: Vapor Water
Material Group = IAPWS IF97
Option = Pure Substance
Thermodynamic State = Gas
PROPERTIES:
Option = IAPWS Library
END
END
END
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 = Value
Time = 0 [s]
END
TIME DURATION:
Maximum Number of Timesteps = 200
Option = Maximum Number of Timesteps
END
TIME STEPS:
Option = Timesteps
Timesteps = 0.0005 [s]
END
END
DOMAIN: Fluid
Coord Frame = Coord 0
Domain Type = Fluid
Location = Assembly
BOUNDARY: MirrorFluid
Boundary Type = SYMMETRY
Location = mirror1
END
BOUNDARY: MirrorFluid2
Boundary Type = SYMMETRY
Location = mirror2
END
BOUNDARY: condenser
Boundary Type = WALL
Location = condsurface
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Fixed Temperature = CondTemp
Option = Fixed Temperature
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
END
END
BOUNDARY: evaporator
Boundary Type = WALL
Location = evapsurface
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Heat Flux in = EvapHeatInput
Option = Wall Heat Flux
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
END
END
DOMAIN MODELS:
BUOYANCY MODEL:
Buoyancy Reference Density = 0.5542 [kg m^-3]
Gravity X Component = 0 [m s^-2]
Gravity Y Component = -g
Gravity Z Component = 0 [m s^-2]
Option = Buoyant
BUOYANCY REFERENCE LOCATION:
Cartesian Coordinates = -1.53273 [m], 0.896652 [m], 0.0005 [m]
Option = Cartesian Coordinates
END
END
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
REFERENCE PRESSURE:
Reference Pressure = 1 [bar]
END
END
FLUID DEFINITION: Liq Water
Material = Liquid Water
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID DEFINITION: Vap Water
Material = Vapor Water
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
FLUID: Liq Water
FLUID BUOYANCY MODEL:
Option = Density Difference
END
HEAT TRANSFER MODEL:
Option = Thermal Energy
END
END
FLUID: Vap Water
FLUID BUOYANCY MODEL:
Option = Density Difference
END
HEAT TRANSFER MODEL:
Option = Total Energy
END
END
HEAT TRANSFER MODEL:
Homogeneous Model = Off
Option = Fluid Dependent
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = Laminar
END
END
FLUID PAIR: Liq Water | Vap Water
Surface Tension Coefficient = SurfTCoeff
INTERPHASE HEAT TRANSFER:
Option = Two Resistance
FLUID1 INTERPHASE HEAT TRANSFER:
Option = Zero Resistance
END
FLUID2 INTERPHASE HEAT TRANSFER:
Fluid2 Nusselt Number = 3.66
Option = Nusselt Number
END
END
INTERPHASE TRANSFER MODEL:
Interface Length Scale = 1. [mm]
Option = Mixture Model
END
MASS TRANSFER:
Option = Phase Change
PHASE CHANGE MODEL:
Option = Thermal Phase Change
END
END
END
MULTIPHASE MODELS:
Homogeneous Model = On
FREE SURFACE MODEL:
Option = None
END
END
END
INITIALISATION:
Option = Automatic
FLUID: Liq Water
INITIAL CONDITIONS:
TEMPERATURE:
Option = Automatic with Value
Temperature = 331.45 [K]
END
VOLUME FRACTION:
Option = Automatic with Value
Volume Fraction = LiqVF
END
END
END
FLUID: Vap Water
INITIAL CONDITIONS:
TEMPERATURE:
Option = Automatic with Value
Temperature = 331.45 [K]
END
VOLUME FRACTION:
Option = Automatic with Value
Volume Fraction = 1-LiqVF
END
END
END
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
STATIC PRESSURE:
Option = Automatic with Value
Relative Pressure = HydroP
END
END
END
OUTPUT CONTROL:
RESULTS:
File Compression Level = None
Option = Standard
END
TRANSIENT RESULTS: Transient Results 1
File Compression Level = Default
Include Mesh = No
Option = Selected Variables
Output Variables List = Absolute Pressure,Pressure,Velocity,Velocity \
u,Velocity v,Velocity w,Density,Liq Water.Density,Liq \
Water.Temperature,Liq Water.Velocity,Liq Water.Velocity u,Liq \
Water.Velocity v,Liq Water.Velocity w,Liq Water.Volume Fraction,Vap \
Water.Density,Vap Water.Temperature,Vap Water.Velocity,Vap \
Water.Velocity u,Vap Water.Velocity v,Vap Water.Velocity w,Vap \
Water.Volume Fraction
OUTPUT FREQUENCY:
Option = Timestep Interval
Timestep Interval = 10
END
END
END
SOLVER CONTROL:
ADVECTION SCHEME:
Option = High Resolution
END
CONVERGENCE CONTROL:
Maximum Number of Coefficient Loops = 100
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 = 14.0
END

[Antanas]

Originally Posted by gerardosrez

Hello colleagues,

I am setting up a simulation of a so called heat pipe....with the difference that mine has no adiabatic section....

I am using Homogeneous model for continuity and momentum, inhomogeneous for heat transfer/thermal phase change for evaporation condensation...

Also I defined a HBM (homogeneous binary mixture) formed by Liq Water and Vap Water, both substances are based in IAPWS IF97 data...

My question is...if I am modeling using steam tables data...should I use Thermal or Total Energy for solving energy equation?....

Total Energy equation differs from Thermal Energy in that it contains terms to account kinetic energy effects. Do you have such? Significant сompressibility effects, M>0.3 or not constant specific heats?

[gerardosrez]

No I don't have such a a case with the heat pipe....but...due to different temperatures I have different densities across the whole domain for each phase of water...

[Antanas]

Originally Posted by gerardosrez

No I don't have such a a case with the heat pipe....but...due to different temperatures I have different densities across the whole domain for each phase of water...

This don't have relationship to choice of energy equation type IMO.

[gerardosrez]

Originally Posted by Antanas

This don't have relationship to choice of energy equation type IMO.

Thanks Antanas,

So I understand that I am able to use thermal energy model with the density difference produced by temperature field without affecting the solution stability


Thanks again