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March 24, 2014, 13:46 
Water in stewpot

#1 
New Member
onder
Join Date: Mar 2009
Posts: 15
Rep Power: 9 
Hello
I am trying to simulate stewpot on cookstove. I did analysis. When I check the result, I notice that water density in stewpot is constant. Therefore no flow and turbulance being in stewport. And the tepreture spread is not correct. Teperature is rising only near of fire border stewport. When you look the photo of result you will see. I have done little research on the internet and the forum I found table of water density depend on temperature of water. Then I wrote lineer equation. I dont have any problem with equation but I could not manage to write expression. I tried many ccl but cfx didnot accept them. İf someone write the right structure of expression which is for density depend on water temperature. Thanks , regards. At analysis there is one air domain , one water domain and one stewpot domain. http://postimg.org/image/jmld71jgd/ 

March 24, 2014, 17:33 

#2 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,395
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Have a look at the buoyant flow examples in the CFX tutorial manual. You will have missed something you need. To do a buoyant flow you need:
* A gravity vector defined * Either a boussinesq buoyancy model (incompressible fluid, buoyancy force applied as a source term proportional to temperature) or a density versus temperature model (eg ideal gas or variable properties fluid) * Something to drive a temperature gradient * Enough time to allow a temperature gradient to form. 

March 24, 2014, 17:54 

#3 
New Member
onder
Join Date: Mar 2009
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When I wrote exprssion in material properties>equation of state > densiyt = function 1 (T)
Function 1 (T) is table water density at temperatures like 0 997 20 996 40 995 like this. when start run solver gives this error PROBLEM ENCOUNTERED WHEN EXECUTING CFX EXPRESSION LANGUAGE     The CFX expression language was evaluating:   Density     The problem was:   Value below interpolation range     FURTHER INFORMATION     The problem was encountered in executing the expression for:   densty   The complete expression is:   Function 1(T )   The error occurs on subexpression:   ction 1(T     BACKGROUND INFORMATION     The error was detected at one location. The same problem may be   present at other locations  that has not been investigated.   The following values are for the first location which has the   problem.       END OF DIAGNOSTIC OUTPUT FOR CFX EXPRESSION LANGUAGE When I wrote the expression in precfx it gives this alert Material 'Water at 25 C': Table generation controls are not set for this material. Please ensure that the default pressure and temperature tabulation ranges are appropriate for your setup. 

March 24, 2014, 18:22 

#4 
New Member
onder
Join Date: Mar 2009
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I write another expression for densty
999[kg m^3]((T273[K])/1[K])*0.385[kg m^3] with this expression I start the solver İt gave this eror Domain Group: water1 domain Buoyancy has been activated. The absolute pressure will include hydrostatic pressure contribution, using the following reference coordinates: ( 8.58744E06, 0.00000E+00, 1.55602E+00). Domain Group: water2 domain This is a transient run with at least one compressible fluid and no boundary pressure set. The pressure level is set through the transient term in the continuity equation. To accelerate convergence, the pressure level will also be shifted dynamically to satisfy global mass conservation. ++  ****** Notice ******   This is a multiphase simulation with a compressible phase.   Total pressure (used for postprocessing or if total pressure   is specified at a boundary) is calculated assuming all phases   are incompressible.  ++ ++  ****** Notice ******   This is a multiphase simulation in a closed system.   A global correction will be applied to the volume fractions to   accelerate mass conservation.  ++ Domain Group: water2 domain Buoyancy has been activated. The absolute pressure will include hydrostatic pressure contribution, using the following reference coordinates: ( 4.15488E02,2.40000E02, 1.64800E+00). Fatal bounds error detected  Variable: water.Density Locale : ++  ERROR #001100279 has occurred in subroutine ErrAction.   Message:   Stopped in routine ENFORCE_BOUNDS            ++ ++  An error has occurred in cfx5solve:     The ANSYS CFX solver exited with return code 1. No results file   has been created.  + 

March 24, 2014, 18:49 

#5 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,395
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Yes, that is another problem with your approach  if the domain is sealed then you will have problems with the density going bezerk as the system heats up.
To start off I recommend you use the simple incompressible fluid buoyancy model. You do not need to define a density versus temperature relationship for this which simplifies things. Have a look in the CFX tutorials for examples of how to set this sort of simulation up. Also  this error message says this is a multiphase model. You did not mention you are doing a multiphase model! You have not got the basic buoyancy driven flow working yet so you should remove the multiphase bit and just get the buoyant flow working on pure water. Once you can model a pot full of water successfully then you can add the multiphase bits  which I presume are the meat and veges (yummy). 

March 27, 2014, 15:03 

#6 
New Member
onder
Join Date: Mar 2009
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Thankyou so much ghorrock. I am working on it, I solved densty problem but still there are something wrong I willfix in soon time.


September 19, 2014, 09:46 
density variation

#7 
New Member
pavan
Join Date: Sep 2014
Posts: 1
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Hi mztcu
How u have solved density problem. How u have varied density with temperature using user function. I am also getting same error please help i have got stuck in my project 

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