The ASME steam tables are developed with much highend mathematics, and all of the formulas are given within that publication, but in my view, far too complicated unless you need answers that are really accurate.
If you have access to EXCEL, there is a graphing feature, you plot several points of interest, then tell EXCEL to fit the curve, you can try polynominals, exponentials, etc. and usually a second or third order polynominal will be accurate enough. EXCEL will also display the formula iff you specify this feature.
When fitting thermodynamic properties I usually select a general equation form:
Y = A + B * ( X  Xo ) ^ Alpha
Playing with the constants you can usually arrive at a function that is better than the functions EXCEL is preprogrammed for, but it does take some time, fiddling with A, B, Xo, and Alpha. I usually write MACROs to step the constants up and down, it makes finding the right constants much faster. The "Goal Seek" feature in EXCEL also often works well, searching constants to make the least squares error becoming Zero.
For example, saturation temperature (F) as a function of saturation pressure (PSIA), in the vicinity of atmospheric pressure up to several hundred PSIA:
T = 117.17 * P ^ .22322
And a much more crude approximation of the saturation curve, yet doable with a $3 calculator, pressure is BarA, temperature is C:
P = ( T / 100 )^4
Just a little question: why is this post in "Non Engines and Boilers"?
