Phase Diagram

[qazinasir]

Hello,
I want to know is there any good book who teach me how to calculate dew point and Bubble point of hydrocarbon mixture , or you have any matlab program or any notes which help me how to calculate Dew point and Bubble, its a method giving in some books about calculating Trial and error way of calculating the results
but I when i make a program on Matlab , the answer never converges to a solution so I need more help regarding this , kindly do let me know ..
I am waiting
Regards

Qazi Nasir

[carlo.stenali]

many textbooks about thermodynamics do include the details of these procedures, see for example Walas, Daubert etc.
You need to solve a set of nonlinear equations so you can do as follows
a) estimate the dew (or bubble) temperature (or pressure)
b) calculate the fugacities of vapor and liquid phases, you should use an equation of state (Peng Robinson, Soave Redlich Kwong etc.)
c) calculate K values of each component Ki=Fli/Fvi
d) solve for equilibrium temperature (or pressure), this is easy with Newton or equivalent method, for example for dew point
SUM(Wi/Ki) = 1 then in Newton f = SUM(Wi/Ki) - 1
e) iterate to obtain the desired accuracy

To verify the results you may use a library which works in both Excel and Matlab

"http://www.prode.com/en/phaseenvelope.htm"

hoping this helps

[qazinasir]

thanks for the valueable information , I have problem making a phase envelope , rest of them I have done it but don't know about hows to make a phase envelope . 2ndly my results are not getting immpropiate may be i have problem some where thats why i am looking for some reference example or a book . if you have any please could you able to email me so i will provide my email to you .

[carlo.stenali]

to calculate a dew point (or bubble point) line up you can utilize the procedure previously described for calculating a dew (or bubble) point and at each step use as starting point the dew (or bubble) point composition previously calculated, the trick is to decide between a temperature or pressure step, you can evaluate the slope dp/dt (i.e. (p2-p1)/(t2-t1) where t1,p1 and p2,t2 are the calculated dew or bubble points) and do a temperature (or pressure step) depending from this value.
This procedure permits to calculate a phase envelope and estimate the position of critical point (as intersection of dew and bubble line).
Commercial software as the above mentioned Prode Properties do include a Newton solver (or minimizer) and derivatives vs. temperature, pressure, composition, these can improve both speed and reliability in retrograde region where a simplified procedure may fail.
For details about these procedures (quite complex) you may look for papers and books from Michelsen and other authors.

[qazinasir]

Thanks for such a valuable information , Could you have any solved example of bubble point / dew point calculation for reference of understand or you can refer me to any book where is there any example of calculating the phase envelope and also bubble and dew point , as for I have search some of thermodynamic books I Couldn't find any solved example of so ... , I need a solved example ... theory i can read from books like above I know all about it but i need to mathematically calculate it for this i need an example for reference , hope you could assist me in that.
regards,

[paolomaldini]

Thanks

[qazinasir]

Can you have a download version of 'Michelsen' book. Please do sent me a link if you have one.

[carlo.stenali]

there are several important contributes presenting different methods for phase envelope construction, in addition to the papers of Michelsen you may consider the work of Nichita, Pedersen and others

don't underestimate the work required, it's a really difficult task,
there could be many different phases in equilibria,

-vapor+iquid
-vapor+liquid+liquid
-vapor+solid
-liquid+solid
-....

there is an example of VLL described in Prode operating manual

'http://www.prode.com/docs/pppman.pdf'