DRAWING PROPERTY DIAGRAMS

[penpusher33]

Hi,

Im trying to draw a T-S Diagram for Water (Basic Diagram).


Using the "Thermodynamics and Transport properties of Fluids" Publication by G.F.C RODGERS and Y.R.MAYHEW I have managed to draw the T-S Curve on Graph paper. But im having problems putting on Constant Pressure lines.

I am "visually" aware of how the graph should look and i can draw the pressure lines in the super heated region and then they follow constant temperature through the T-S curve. But how do i plot the rest of the pressure lines? the point at which the pressure line goes from being constant temperature and reduces in Entropy and temperature?

The pressure lines should "part away" from the "saturated liquid lines" but when i plot them they "follow" the saturated liquid line.

WHY!!!

Many thanks
Pete

 

[UmeshMathur]

There is an excellent and exhaustive discussion by the maestro, Professor T.F. Daubert of Penn State Univ. in his book "Chemical Engineering Thermodynamics" (McGraw-Hill, 1985) on how to perform the computatations required for drawing thermodynamic diagrams. Prof. Daubert is the primary editor of the API Technical Data Book, the authoritative reference for hydrocarbon systems.

 

[mtaffish]

Hey penpusher33

Drawing T-s diagrams can be very confusing and hard on graph paper , i would suggest you use EES[engineering equation solver] or more specifically REFPROP its can draw T-S diagrams P-h diagrams w.r.t to water and other fluids.

regards
taffish

 

[UmeshMathur]

penpusher33:

I believe that the likely explanation for the problems you reported is that the sources, assumptions, or numerical methods used in your thermodynamic calculations are flawed. If you want to do this kind of work yourself, understanding the fundamentals is essential. For water, I would use the IAPWS equations. Daubert (cited by me earlier) recommends use of the Lee-Kesler equation of state for hydrocarbons and light gases.

Numerical coding of these equations and iterative procedures is not for novices, however, as a fairly sophisticated knowledge of iterative numerical methods and algorithms would be required.

The REFPROP package mentioned by mtaffish performs these computations for you (all algorithmic details being obscured). Using the EES or other similar solver package will still require you to set up the computational algorithms yourself, as explained by Daubert for example, to build the cases required to plot each line on the final diagram.