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September 16, 2015, 12:01 
Evaporation Condensation in Heat Pipe

#1 
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G. S.
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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 # CFX14.0 build 2011.10.1023.01 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*(LiqHty)*LiqVF0.79 [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 = 1LiqVF 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.E4 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 

September 16, 2015, 12:53 

#2  
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September 16, 2015, 13:20 

#3 
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G. S.
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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...


September 16, 2015, 22:24 

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September 17, 2015, 11:36 

#5 
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G. S.
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Tags 
condensation, evaporation, heat, multiphase, pipe 
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