Calculate the pressure of propane in a vessel 9

[poseilus]

Is there an equation from where I can calculate the pressure of propane inside a tank if I know the temperature of the liquid?

This pressure is constant, when the vapour and liquid phase come in equilibrium.

 

[israelkk]

http://webbook.nist.gov/chemistry/fluid/

 

[Montemayor]

poseilus:

israelkk deserves Kudos for directing you to the best and most effective site you could expect to obtain a direct answer to your query.

At this free and authoritative site you can gather, view, and download all the thermodynamic properties for 34 compounds.

To answer your specific question, you can go to this website, select Propane as your compound and key in the units that you desire for the information you seek as well as identifying that you have a saturated compound at temperature increments. The program will generate all your results in tabulated HTML format that is easily copied and pasted onto a spreadsheet like Excel. You can then take the tabulated temperature – pressure results and regress them (“curve-fit”) into a usable analytical equation. I do this all the time with an excellent program I acquired some years ago called “DATAFIT”. For Propane, I obtain the following vapor pressure equation that has a maximum error of 1.118% error at the lowest temperature (-50 oF) that I regressed. I could get more extreme accuracy if I wanted to regress to a polynomial equation of the 9th order – but I think this is sufficient to make my point and obtain useful engineering data.

Y = A*X5 + B*x4 + C*x3 + D*x2+E*x + F
where,

Y = Propane Vapor Pressure in psia
X = Propane Temperature in oF
A = 1.234630790E-10
B = -1.817499989E-08
C = 1.929167768E-05
D = 0.005658595
E = 0.750256651
F = 38.366301800

Try out this equation and you’ll see how accurate it is as compared with the NIST data. You and others can do the same, developing your own analytical equations which you can then employ, for example, in your own computer subroutines and programs that you write for your own applications and problems in the future.

I hope this resolves your query. ¡Feliz Año Nuevo y Prosperidad!


Art Montemayor
Spring, TX

 

[poseilus]

This very good idea.

I guess I can do that with other physical properties like viscosity?


Thank you.

 

[israelkk]

For a shareware and excelent curve fitting program you can use the the CurveExpert program at

http://curveexpert.webhop.biz/

it has a 30 days evaluation period.

 

[Montemayor]

poseilus:

You got it. You can use the technique for all those values that are continuous and "reressable".

Art Montemayor
Spring, TX

 

[pennpoint]

Montemayor

"reressable". What's ("reressable").
Oh! it's New Years Eve...
Wishing all the best this coming year

pennpoint

 

[Montemayor]

pennpoint:

I was trying to key in "regressable", but this damn, half-empty bottle of Cristero Reserve Tequila keeps getting in the way of my keyboard. I'm going to have to concentrate on regressing back to some better Tequila - one without so much vapor pressure. (you've probably already noted that I forgot to key in the exponential sign on the powers of "X" in my vapor pressure equation. Sorry.....)

Happy New Year Everyone!

Art Montemayor
Spring, TX

 

[pennpoint]

Montemayor
Oh ya sure...I cought all of that too! Between my gin martinis but I did'nt want to point it out. Huh?

Hope your New Year brings the best

ppennpoint

 

[mbeychok]

.
Poseilus:

In addition to the excellent advice that you got from Art Montemayor, you can also use the Antoine equation to calculate vapor pressures. The Antoine equation is:

Log P₁₀ = A - [B/(T + C)]

where:
P = vapor pressure of the liquid
T = temperature of the liquid
A, B, and C are constants obtained by regression

Lists of the Antoine constants for various liquids are available in many publications. For example, "Properties of Gases and Liquids" (a book by R. C. Reid, J. M. Praunitz, and B. E. Poling) provides the Antoine equation constants for hundreds of liquids.

When using published Antoine constants, make sure to determine the pressure and temperature units that were used in obtaining the constants. Also, make sure to determine whether the logarithm used was Log₁₀ or Log_e.

Milton Beychok
(Contact me at www.air-dispersion.com)

 

[25362]

Depending on the exactness needed of the data, the well- known COX chart tells us that for many compounds, and in particular for paraffinic hydrocarbons, a plot of lnP^sat vs. 1/T generally yields a line that is nearly straight.

Thus the equation lnP^sat=A-B/T, where A and B are constants for any given species, provides an excellent basis for interpolation between reasonable spaced temperature values.

The Antoine equation set of constants -as mentioned by mbeychok- is valid only inside the specified temperature range. There are, of course, more accurate representations covering the whole range from triple point to critical point, as shown by Mr Montemayor, such as the Wagner equation that expresses the reduced vapor pressure as function of the reduced temperature using four constants.

 

[Latexman]

poseilus,

Excellent advice from all responders!

I would add one warning to the advice given above though. Do not extrapolate the equation you fit beyond the data used to create it, especially the polynomial! Outside of the data range used to create the equation, it can deviate from the real data not used (or the general trend) quite quickly. With a polynomial, the higher the order the worse it can do this.

If you absolutely have to extrapolate past the real data, I'd recommend you use an equation that has some theoretical basis to it and verify that it doesn't deviate from the general trend past the real data.


Good luck,
Latexman

 

[israelkk]

NIST have a computer program for PC that gives you the ability to calculate Propane and other gases properties. The old version was called MIPROPS which if I am not mistaken was free. A newer one was called "NIST Thermophysical Properties of Pure Fluids Database"

 

[poseilus]

Thank you all for your help.

I know now a lot of ways to determine the pressure of propane.

About Antoine equation i am trying to find out those constants on the web without any good result. There is also wagner equation that I will try to figure out how it works.

 

[mbeychok]

.
Poseilus:

(1) Go to this web site:

http://webbook.nist.gov/chemistry/

(2) Click on "Name" which takes you to another page
(3) Enter the name "Propane", select "SI" units, select "Phase change" data and then click on "Search" which will take you to another page
(4) Scroll down until you see the Antoine equatation constants for three different temperature ranges. Choose the constants that cover your desired temperature range.

Follow the same procedure for Butane.

Hope this helps you and Happy New year,


Milton Beychok
(Contact me at www.air-dispersion.com)