# Minimum PDF Table Temperature

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 June 25, 2009, 21:02 Minimum PDF Table Temperature #1 New Member   James Macphee Join Date: May 2009 Posts: 4 Rep Power: 10 Hi all, I am modelling coal combustion using the PDF mixture fraction approach however as my job solves I have the following message appear at most iterations... Minimum PDF table temperature in 1023 cells on zone 10 ...the number of cells varies however it never seems to reduce down to zero. I have tried changing the number of enthalpy points and mean mixture fraction points when creating the PDF table however at present this does not seem to make any difference. Also the air entering my kiln is at 337K and ~1000K while I have set the minimum temperature as 298K Does anyone know what this message means....is it a problem and if so how do I fix it?? Thanks for anyones help.

 June 28, 2009, 10:06 #2 New Member   Graham Join Date: Apr 2009 Posts: 7 Rep Power: 10 in the text interface, define/models/species look for the expert option and decrease Maximum Heat Loss Fraction and then regenerate your table...

 October 11, 2011, 11:01 Minimum pdf table temperature in XXX cells #3 New Member   fabian diaz Join Date: Aug 2010 Posts: 2 Rep Power: 0 I had this problem in my simulation: Minimum pdf table temperature in XXX cells I solved it by changing the default values of viscosity and thermal conductivity that come with fluent. I used the next equations: Thermal conduc (W/m-K) = -1.049352E-12x3 - 8.863118E-09x2 + 8.105885E-05x + 7.183288E-04 Viscosity (Kg/m-s) = 1.139977E-15x3 - 1.051178E-11x2 + 4.567342E-08x + 4.878605E-06 Where x = temperature (K)

 August 14, 2013, 18:07 minimum pdf table temperature #5 New Member   fabian diaz Join Date: Aug 2010 Posts: 2 Rep Power: 0 The problem with the minimum pdf table temperature can be solved by lowering the under relaxation factor for energy even below 0.9. It's going to take more iterations to assure a low energy unbalance of the model but sometimes it is necessary.

 August 16, 2013, 16:40 #6 New Member   Clan McKenzie Join Date: Aug 2013 Posts: 7 Rep Power: 6 Hello, Thanks for all the replies. I was finally able to find the location where I could lower the Maximum Heat Loss Fraction! You were correct it is under "non-premixed-combustion-expert". Originally it was set to 0.66, I set it to 0.4 and ran the simulation again. Unfortunately this did not help fix the error. I still have "minimum pdf table temp" error occuring on every iteration and to many cells. I have also tried reducing the under relaxation factor for Energy to 0.6 and this did not help either. I have increased the mesh as well as increased the inlet temperature to 600K for the fuel and the oxide to no avail. I have noticed that my P1 residuals are acting strangely though. They are far below the other residuals. Any thoughts?

 August 17, 2013, 01:48 #7 New Member   Graham Join Date: Apr 2009 Posts: 7 Rep Power: 10 You really want all scalar, including energy and P1, URFs near 1. If your case diverges, try 0.99 for both energy and P1. Again, you need to re-generate the PDF after you lower the heat loss parameter. I would ignore this message if only a few cells are hitting the lower limit. But, you can lower the heat loss to 0.1 if it still bothers you.

January 27, 2015, 10:24
#8
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Nikolaos Babilas
Join Date: Nov 2014
Posts: 37
Rep Power: 4
Quote:
 Originally Posted by burritolover Hello, Thanks for all the replies. I was finally able to find the location where I could lower the Maximum Heat Loss Fraction! You were correct it is under "non-premixed-combustion-expert". Originally it was set to 0.66, I set it to 0.4 and ran the simulation again. Unfortunately this did not help fix the error. I still have "minimum pdf table temp" error occuring on every iteration and to many cells. I have also tried reducing the under relaxation factor for Energy to 0.6 and this did not help either. I have increased the mesh as well as increased the inlet temperature to 600K for the fuel and the oxide to no avail. I have noticed that my P1 residuals are acting strangely though. They are far below the other residuals. Any thoughts?
Where is the tab non premixed combustion expert? i couldn't find it at all. i try to reduce the maximum heat loss fraction because i have the same problem.

 March 9, 2015, 22:26 #9 Member   Join Date: Jun 2014 Location: Taiwan Posts: 89 Rep Power: 5 "Maximum Heat Loss Fraction" is here: /define/models/species> non-premixed-combustion-expert Probability Density Function for PDF Table (0 for double-delta 1 for beta) [1] Interpolation method for PDF Table (0 for linear 2 for polynomial) [2] Maximum Temperature to Adiabatic Flame Temperature Ratio [1] Maximum Heat Loss Fraction [0.667] 0.5 Maximum Heat Gain Fraction [0.25] Enable checking of PDF table temperature limits? [yes] Equilibrium Calculations at Inlets: 0:full-equilibrium 1:frozen-composition [1] -- What should I do when two error message "Maximum PDF table temperature in 4778 cells on zone 150097" and "Minimum PDF table temperature in 514 cells on zone 150097 " appear at the same time?

 November 16, 2015, 14:32 Rich flamability limit #10 New Member   Ahmad Jabbar Join Date: Sep 2015 Posts: 5 Rep Power: 4 I also had the same problem. The issue was resolved when I used secondary air stream. RFL value for secondary air should be=1.0 http://aerojet.engr.ucdavis.edu/flue...mit-tempadjust You can take a look on the user guide as well. Any further suggestions will be appreciated. Last edited by Ahmad134; November 17, 2015 at 22:25.

August 28, 2017, 05:23
#11
New Member

Join Date: May 2013
Posts: 11
Rep Power: 6
Quote:
 Originally Posted by burritolover Hello, Thanks for all the replies. I was finally able to find the location where I could lower the Maximum Heat Loss Fraction! You were correct it is under "non-premixed-combustion-expert". Originally it was set to 0.66, I set it to 0.4 and ran the simulation again. Unfortunately this did not help fix the error. I still have "minimum pdf table temp" error occuring on every iteration and to many cells. I have also tried reducing the under relaxation factor for Energy to 0.6 and this did not help either. I have increased the mesh as well as increased the inlet temperature to 600K for the fuel and the oxide to no avail. I have noticed that my P1 residuals are acting strangely though. They are far below the other residuals. Any thoughts?
I have experienced the "Minimum PDF table enthalpy exceeded" problem and it was solved changing the Maximum Heat Loss Fraction to a higher value than the default, i.e. I changed it from 0.66 to 0.9.
seems reasonable given the name of the parameter. to lower it as suggested earlier in the thread did not work

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