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October 11, 2010, 10:55 
Simulation of a Silo

#1 
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Attesz
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Hi CFX users,
I'm going to simulate a silo full of corn, with hot air blowing in. The main problem is the material properties of the corn My first idea is model the corn as a porous domain (i've never done such a thing). The main goal is to determine the temperature distribution in the silo, so actually the temp.dist of that 6 tonns of corn. Thanks in advance for any suggestions! Attila 

October 11, 2010, 18:07 

#2 
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Glenn Horrocks
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Does the corn move? Then maybe a fluidised bed. If the corn is still then a porous domain approach makes sense. In the preview version of CFX V13 I think you can couple the porous material temperature with the air temperature and that is probably important for this  so talk to CFX support to get the latest preview version.


October 12, 2010, 03:03 

#3 
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Attesz
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Hello Glenn,
the corn is still, and it fills up the silo. Thank you, Attila 

October 12, 2010, 15:40 

#4 
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Michael P. Owen
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Glenn is correct, to do the CHT in the porous domain, you will either have to get R13 Preview 3, or you will have to do is yourself using CEL, sources, and an Additional Variable.


October 12, 2010, 15:49 

#5 
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Attesz
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Hi Michael,
we have research license at the university, can we download the R13 in this case? If not, doing it myself is difficult? Is there good documentations in the topic? Thanks. 

October 12, 2010, 16:01 

#6  
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Michael P. Owen
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October 12, 2010, 16:22 

#7 
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Attesz
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Okay, thanks for your reply. I will need documentations in simulation of porous domains, and heat transfer(i think the tutorials will be not enough to learn these topics). The parameters of the corn is more problematic. Anyway, it is a little bit difficult for me, but that's the challange of CFD.
Thanks again, Attila 

October 12, 2010, 16:43 

#8 
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Michael P. Owen
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Also, FYI R13 Preview 3 officially ended back in August, so you are probably out of luck trying to get a copy.


October 12, 2010, 16:48 

#9 
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Michael P. Owen
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You may be in luck. It turns out from the world's largest coincidence that I now have to implement this in R12.1 by tomorrow for a client. If I get it working, I'll tell you how I did it.


October 12, 2010, 17:35 

#10 
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Michael P. Owen
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Ok, it only took me 45 minutes.


October 12, 2010, 17:53 

#11 
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Michael P. Owen
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Here's the CCL for the model that does CHT for a porous domain (the mesh is just a tube with an inlet and an outlet):
The domain: FLOW: Flow Analysis 1 &replace DOMAIN: Porous Domain Coord Frame = Coord 0 Domain Type = Porous Location = B6 BOUNDARY: Inlet Boundary Type = INLET Interface Boundary = Off Location = F8.6 BOUNDARY CONDITIONS: ADDITIONAL VARIABLE: Solid Temperature Option = Zero Flux END FLOW REGIME: Option = Subsonic END HEAT TRANSFER: Option = Static Temperature Static Temperature = 25 [C] END MASS AND MOMENTUM: Normal Speed = 10 [m s^1] Option = Normal Speed END TURBULENCE: Option = Medium Intensity and Eddy Viscosity Ratio END END END BOUNDARY: Outlet Boundary Type = OUTLET Interface Boundary = Off Location = F9.6 BOUNDARY CONDITIONS: ADDITIONAL VARIABLE: Solid Temperature Option = Zero Flux END FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Option = Average Static Pressure Pressure Profile Blend = 0.05 Relative Pressure = 0.0 [Pa] END PRESSURE AVERAGING: Option = Average Over Whole Outlet END END END BOUNDARY: Porous Domain Default Boundary Type = WALL Create Other Side = Off Interface Boundary = Off Location = F7.6 BOUNDARY CONDITIONS: ADDITIONAL VARIABLE: Solid Temperature Additional Variable Value = 0 [C] Option = Transfer Coefficient Transfer Coefficient = 10 [m s^1] END HEAT TRANSFER: Option = Adiabatic END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END DOMAIN MODELS: AREA POROSITY: Option = Isotropic END BUOYANCY MODEL: Option = Non Buoyant END DOMAIN MOTION: Option = Stationary END MESH DEFORMATION: Option = None END REFERENCE PRESSURE: Reference Pressure = 1 [atm] END VOLUME POROSITY: Option = Value Volume Porosity = 0.7 END END FLUID DEFINITION: Fluid 1 Material = Air at 25 C Option = Material Library MORPHOLOGY: Option = Continuous Fluid END END FLUID MODELS: ADDITIONAL VARIABLE: Solid Temperature Kinematic Diffusivity = Thermal Diffusivity Option = Diffusive Transport Equation END COMBUSTION MODEL: Option = None END HEAT TRANSFER MODEL: Option = Thermal Energy END THERMAL RADIATION MODEL: Option = None END TURBULENCE MODEL: Option = k epsilon END TURBULENT WALL FUNCTIONS: Option = Scalable END END INITIALISATION: Option = Automatic INITIAL CONDITIONS: Velocity Type = Cartesian ADDITIONAL VARIABLE: Solid Temperature Additional Variable Value = 25 [C] Option = Automatic with Value END CARTESIAN VELOCITY COMPONENTS: Option = Automatic with Value U = 0 [m s^1] V = 0 [m s^1] W = 10 [m s^1] END STATIC PRESSURE: Option = Automatic with Value Relative Pressure = 0.0 [Pa] END TEMPERATURE: Option = Automatic with Value Temperature = 25 [C] END TURBULENCE INITIAL CONDITIONS: Option = Medium Intensity and Eddy Viscosity Ratio END END END POROSITY MODELS: LOSS MODEL: Loss Velocity Type = Superficial Option = Isotropic Loss ISOTROPIC LOSS MODEL: Option = Linear and Quadratic Resistance Coefficients Quadratic Resistance Coefficient = 650 [kg m^4] END END END SUBDOMAIN: Sources Coord Frame = Coord 0 Location = B6 SOURCES: EQUATION SOURCE: Solid Temperature Multiply by Porosity = No Option = Source Source = Solid Temperature Source Source Coefficient = Solid Temperature Source Coefficient END EQUATION SOURCE: energy Multiply by Porosity = No Option = Source Source = Energy Source Source Coefficient = Energy Source Coefficient END END END END END The Additional Variable: LIBRARY: &replace ADDITIONAL VARIABLE: Solid Temperature Option = Definition Tensor Type = SCALAR Units = [K] Variable Type = Volumetric END END The Expressions: LIBRARY: CEL: &replace EXPRESSIONS: Energy Source = Heat Transfer Coefficient*Volumetric Surface Area Density*(Temperature  Solid Temperature) Energy Source Coefficient = Heat Transfer Coefficient*Volumetric Surface Area Density Heat Transfer Coefficient = 100 [W m^2 K^1] Solid Density = 1000 [kg m^3] Solid Specific Heat Capacity = 100 [m^2 s^2 K^1] Solid Temperature Source = Energy Source/(Solid Specific Heat Capacity * Solid Density) Solid Temperature Source Coefficient = Energy Source Coefficient/(Solid Specific Heat Capacity * Solid Density) Solid Thermal Conductivity = 10 [W m^1 K^1] Thermal Diffusivity = Solid Thermal Conductivity/Solid Density/Solid Specific Heat Capacity Volumetric Surface Area Density = 100[m^2 m^3] END END END Solver Control: FLOW: Flow Analysis 1 &replace SOLVER CONTROL: Turbulence Numerics = First Order ADVECTION SCHEME: Option = High Resolution END CONVERGENCE CONTROL: Length Scale Option = Conservative Maximum Number of Iterations = 100 Minimum Number of Iterations = 1 Timescale Control = Auto Timescale Timescale Factor = 100 END CONVERGENCE CRITERIA: Conservation Target = 0.01 Residual Target = 1e6 Residual Type = RMS END DYNAMIC MODEL CONTROL: Global Dynamic Model Control = On END END END Be careful of the Solid Density, thermal conductivity, specific heat capacity; they are for the porous matrix itself, not the material it is made of. 

October 13, 2010, 11:30 

#12 
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Attesz
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Dear Michael,
thank you , it was very kind from you to help me so much! Additional variables, expressions are known for me, i was in trouble only with the theoretical background, but it seems to be getting clear now. Do you have any ideas how to set the thermal parameters for the porous domain if I would have the parameters of the corn? If i will lucky, there will be measures too, so I can validate the material properties. Thanks again, Attila 

October 13, 2010, 11:34 

#13  
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Attesz
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October 13, 2010, 11:51 

#14  
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Attesz
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These parameters will be hard to found out later...but the thermal setup is clear. Thanks again. 

October 13, 2010, 13:01 

#15  
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Michael P. Owen
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October 13, 2010, 13:02 

#16 
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Michael P. Owen
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By the way, what is this for? Research paper? Dissertation? Class project? Work?


October 14, 2010, 06:00 

#17  
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Attesz
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Thanks for your suggestions again, Michael! Attila 

October 14, 2010, 21:14 

#18 
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Michael P. Owen
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Assume the kernel is a sphere. Rectilinear. It's somewhere in between. Cad model it and measure it.


October 15, 2010, 07:01 

#19 
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Attesz
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Okay, it's a good idea.
Thanks! Best regards, Attila 

October 15, 2010, 07:52 

#20 
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Joshua Counsil
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If the heat input is very high, can we expect popcorn to form?


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