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Old   June 26, 2014, 06:23
Default some problems about radiation model
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wangruixing
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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...............
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Old   June 26, 2014, 12:51
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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,
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Old   July 21, 2014, 23:35
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Quote:
Originally Posted by Opaque View Post
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,
FLOW: Flow Analysis 1
&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
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Old   July 21, 2014, 23:39
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Quote:
Originally Posted by Opaque View Post
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,
thanks very much for your help,the CCL is above,and the radiation model ccl
is as follows


LIBRARY:
CEL:
&replace EXPRESSIONS:
Tclip = Tmax * step((T-Tmax)/ 1.[K]) + T * step((Tmax-T) / 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 = 4.74E-05 [K^-1]
b22 = 7.19E-05 [K^-1]
b23 = -7.41E-05 [K^-1]
b24 = -4.52E-05 [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
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Old   July 22, 2014, 05:53
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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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