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#1 |
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Hi,
I want to use the coefficients that describe the specific heat capacity outside CFX5.5. These coefficients are given in the MATERIALS file (/cfx551/etc/). However, they are stated in the "NASA-format": SPECIFIC HEAT CAPACITY: Option = NASA Format Temperature Limit List = 300 [K], 5000 [K], 1000 [K] NASA Coefficient List = \ 0.03697578E+02, 0.06135197E-02, -0.01258842E-05,\ 0.01775281E-09, -0.01136435E-13, -0.01233930E+05,\ 0.03189166E+02,\ 0.03212936E+02, 0.01127486E-01, -0.05756150E-05,\ 0.01313877E-07, -0.08768554E-11, -0.01005249E+05,\ 0.06034738E+02 END #SPECIFIC HEAT CAPACITY What exactly is this format. It isn't just a1+a2T+a3T^2+a4T^3+a5T^4+a6T^5+a7T^6, because this gives me a heat capacity of O2 of 6.11e+13 at 300K, which of course is not correct. Can anybody help me? Cujo |
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#2 |
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Hi, I found the answer myself: Only the first 5 coeffients are needed for the expression of the heat capacity. The first series of 5 coefficients in the CFX MATERIALS file are applicible for a temperature range of 300-1000[K]. The first 5 coefficients in the second block are for the range 1000-5000[K]. The heat capacity is obtained as: cp/Ru=a1+a2T+a3T^2+a4T^3+a5T^4 [J mol^-1 K^-1], with Ru the universal gas constant. Bye Cujo
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#3 |
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Sai Krishna
Join Date: May 2018
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In that last 2 coefficients a6 and a7 represents powers e-2 and e-1 for the temperature. Not e+6 and e+7.
Hope this helps you. |
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#4 |
Senior Member
Join Date: Jun 2009
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I think you are confusing the NASA format (at least as used by CHEMKIN and ANSYS CFX) with the JANAF format
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#5 |
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Arif Aziz
Join Date: Aug 2021
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Dear,
I have you are fine and doing well. I want to calculate the NASA Coefficient values for the Methanol, I have no Idea how to calculate it please guide me. |
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#6 |
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Arif Aziz
Join Date: Aug 2021
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Can you please guide me how to calculate the NASA coefficient.
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#7 | |
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Quote:
You can try the following links http://combustion.berkeley.edu/gri-mech/data/nasa_plnm.html http://combustion.berkeley.edu/grime...0/thermo30.dat From the two pages, and looking at a common material between the ANSYS CFX database and the page above, you can reverse-engineer the format (I once understood it, but) Hope the above helps, === Edit === Reviewing the different material databases in ANSYS CFX , I just noticed Methanol is listed by two formulas: CH3OH and CH4O (inappropriate).
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#8 |
New Member
Arif Aziz
Join Date: Aug 2021
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CH3OH L 8/88C 1H 4O 1 G 200.000 3500.000 1000.000
1.78970791E+00 1.40938292E-02-6.36500835E-06 1.38171085E-09-1.17060220E-13 -2.53748747E+04 1.45023623E+01 5.71539582E+00-1.52309129E-02 6.52441155E-05 -7.10806889E-08 2.61352698E-11-2.56427656E+04-1.50409823E+00 Dear, I am confuse about it that how I take it, I mean which value refer a1 and a7 for the upper interval and which value refers a1 and a7 for the lower interval, Your guidance will be highly appreciated. |
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#9 | |
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Quote:
From the two pages, and looking at a "common material" between the ANSYS CFX database and the page above, you can reverse-engineer the format (I once understood it, but) Just pick one material in both databases, and compare side by side.
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#10 |
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Arif Aziz
Join Date: Aug 2021
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Hello Dear,
I put the values but when I run my simulation I got the error. I do not know where I am making mistake. MATERIAL: CH3OH Material Group = Gas Phase Combustion,Interphase Mass Transfer Option = Pure Substance Thermodynamic State = Gas PROPERTIES: Option = General Material EQUATION OF STATE: Molar Mass = 32.04 [kg kmol^-1] Option = Ideal Gas END SPECIFIC HEAT CAPACITY: Option = NASA Format LOWER INTERVAL COEFFICIENTS: NASA a1 = 5.71539582E+00 NASA a2 = -1.52309129E-02 [K^-1] NASA a3 = 6.52441155E-05 [K^-2] NASA a4 = -7.10806889E-08 [K^-3] NASA a5 = 2.61352698E-11 [K^-4] NASA a6 = -2.56427656E+04 [K] NASA a7 = -1.50409823E+00 END TEMPERATURE LIMITS: Lower Temperature = 200 [K] Midpoint Temperature = 1000 [K] Upper Temperature = 3500 [K] END UPPER INTERVAL COEFFICIENTS: NASA a1 = 1.78970791E+00 NASA a2 = 1.40938292E-02 [K^-1] NASA a3 = -6.36500835E-06 [K^-2] NASA a4 = 1.38171085E-09 [K^-3] NASA a5 = -1.17060220E-13 [K^-4] NASA a6 = -25374.9 [K] NASA a7 = 1.45023623E+01 END These values I took from the link for the methanol which you have sent me. |
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