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June 26, 2014, 05:23 
some problems about radiation model

#1 
New Member
wangruixing
Join Date: Dec 2013
Posts: 5
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hi,
i have some problems about cfx, if i use multigray model in radiation model, cfx will apparance error as fllow: Prefix error in variable 'CH4.molf' referenced in parameter 'Absorption Coefficient' in object '/FLOW:Flow Analysis 1/DOMAIN:combustor/FLUID MODELS/THERMAL RADIATION MODEL/SPECTRAL MODEL/GRAY GAS:Gas 4'. The prefix 'CH4' is not recognised in domain 'combustor' in flow 'Flow Analysis 1'. but ch4 has been add in cfx. every boday who can help me............... 

June 26, 2014, 11:51 

#2 
Senior Member
Join Date: Jun 2009
Posts: 458
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ANSYS CFX is case sensitive, CH4 and ch4 are different materials.
w/o looking at the command file, it is difficult to tell if fluid prefix is also needed for your case, i.e. Mixture.CH4.molf to be explicit about the fluid and the component the expression is referring to. Hope the above helps, 

July 21, 2014, 22:35 

#3  
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wangruixing
Join Date: Dec 2013
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Quote:
&replace DOMAIN: combustor Coord Frame = Coord 0 Domain Type = Fluid Location = CREATED_MATERIAL_17 BOUNDARY: combustor Default Boundary Type = WALL Create Other Side = Off Interface Boundary = Off Location = AIRIN,CEMIAN,DIMIAN,GASIN,HUOJUTONG,HUOJUTOU,OUT BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Adiabatic END MASS AND MOMENTUM: Option = No Slip Wall END THERMAL RADIATION: Diffuse Fraction = 1. Emissivity = 1. Option = Opaque END WALL ROUGHNESS: Option = Smooth Wall END END END DOMAIN MODELS: BUOYANCY MODEL: Option = Non Buoyant END DOMAIN MOTION: Option = Stationary END MESH DEFORMATION: Option = None END REFERENCE PRESSURE: Reference Pressure = 1. [atm] END END FLUID DEFINITION: f Option = Material Definition MATERIAL DEFINITION: Option = Reacting Mixture END MORPHOLOGY: Option = Continuous Fluid END END FLUID MODELS: COMBUSTION MODEL: Eddy Dissipation Model Coefficient A = 4.0 Eddy Dissipation Model Coefficient B = 1.0 Option = Eddy Dissipation Reactions List = Methane Air WD2,WD2 Methane Oxidation,Reaction 1,WD2 CO Oxidation END COMPONENT: CH4 Option = Transport Equation END COMPONENT: CO Option = Transport Equation END COMPONENT: CO2 Option = Transport Equation END COMPONENT: H2O Option = Transport Equation END COMPONENT: H2S Option = Automatic END COMPONENT: N2 Option = Constraint END COMPONENT: O2 Option = Transport Equation END COMPONENT: SO2 Option = Automatic END HEAT TRANSFER MODEL: Option = Thermal Energy END THERMAL RADIATION MODEL: Option = Discrete Transfer Radiation Transfer Mode = Participating Media SCATTERING MODEL: Option = None END SPECTRAL MODEL: Option = Weighted Sum of Gray Gases GRAY GAS: Gas 1 Absorption Coefficient = abscoef1 Option = Expression Weight = weight1 END GRAY GAS: Gas 2 Absorption Coefficient = abscoef2 Option = Expression Weight = weight2 END GRAY GAS: Gas 3 Absorption Coefficient = abscoef3 Option = Expression Weight = weight3 END GRAY GAS: Gas 4 Absorption Coefficient = abscoef4 Option = Expression Weight = weight4 END END END TURBULENCE MODEL: Option = k epsilon END TURBULENT WALL FUNCTIONS: Option = Scalable END END END END 

July 21, 2014, 22:39 

#4  
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wangruixing
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Quote:
is as follows LIBRARY: CEL: &replace EXPRESSIONS: Tclip = Tmax * step((TTmax)/ 1.[K]) + T * step((TmaxT) / 1.[K]) Tmax = 2400 [K] abscoef1 = (k1 * (H2O.molf + CO2.molf + CO.molf) + kHC1 * CH4.molf) * pabs abscoef2 = (k2 * (H2O.molf + CO2.molf + CO.molf) + kHC2 * CH4.molf) * pabs abscoef3 = (k3 * (H2O.molf + CO2.molf + CO.molf) + kHC3 * CH4.molf) * pabs abscoef4 = (k4 * (H2O.molf + CO2.molf + CO.molf) + kHC4 * CH4.molf) * pabs b11 = 0.364 b12 = 0.266 b13 = 0.252 b14 = 0.118 b21 = 4.74E05 [K^1] b22 = 7.19E05 [K^1] b23 = 7.41E05 [K^1] b24 = 4.52E05 [K^1] k1 = 0. [m^1 atm^1] k2 = 0.69 [m^1 atm^1] k3 = 7.4 [m^1 atm^1] k4 = 80. [m^1 atm^1] kHC1 = 3.85 [m^1 atm^1] kHC2 = 0. [m^1 atm^1] kHC3 = 0. [m^1 atm^1] kHC4 = 0. [m^1 atm^1] weight1 = b11 + b21 * Tclip weight2 = b12 + b22 * Tclip weight3 = b13 + b23 * Tclip weight4 = b14 + b24 * Tclip END END END 

July 22, 2014, 04:53 

#5 
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wangruixing
Join Date: Dec 2013
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I have find the solution to the problem，because i haven‘t add radiation model in
material.if I add radiation model in reacting mixture，it will be right。。。。。 

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