Polynomial coefficient

[kaiserin98]

Hi Everyone,

Does anyone know where can I find a database for specific heat capacity curve-fit coefficients? My CFD code requires me to input 10 coefficients, 5 for low temperature and 5 for high temperature.

Thank you very much

Sing

 

[Tunalover]

I don't know where to find the database, but you could do it as follows using a table of Cp vs temperature (T):

Determine the coefficients in the two polynomials:
Cp=aT^4+bT^3+cT^2+dT+e for high temperature given five points
Cp=fT^4+gT^3+hT^2+iT+j for low temperature given five points

For each polynomial:
A. Graph a scatterplot using MS Excel
B. Ask for a smooth trendline going through each point
C. Ask that the interpolating polynomial be displayed on
the graph. Ask for a fourth order polynomial.

I may have a database for gas properties but it probably won't have the coefficients you want (only the Cp values).

Tunalover

 

[mirchee]

Are these coefficients required for pure components that are ideal gases? If so, you can obtain decent values from a recent book "Chemical Properties Handbook" by Professor Carl Yaws (McGraw-Hill, 1999).

Yaws provides coefficients for a fourth order polynomial, so you get 5 constants:

Cp = A + B T + C T^2 + D T^3 + E T^4, with T in Kelvins.

The Cp units are joule/(mole K). If your CFD package needs different units, you'll have to make the necessary conversions.

Most importantly, Yaws also provides the minimum and maximum limits of temperature for using these coefficients (typically, a very wide range from 298 to 1500 K).

You should be able to use the same coefficients throughout the range of interest, unless you are working with really hot or cold fluids and are outside Yaws' temperature range.

By the way, this book also has most of the other fluid properties needed for normal enginering work, so it's a GREAT BUY.