NASA format
 

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

Re: NASA format
 

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

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.

I think you are confusing the NASA format (at least as used by CHEMKIN and ANSYS CFX) with the JANAF format

Guidance About calculation of Nasa Coefficient
 

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.

Can you please guide me how to calculate the NASA coefficient.

NASA coefficients are computed by curve-fitting discrete data to the specific polynomial form.

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).

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.

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.

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.