2 replies to this topic

[NestorMadeo]

Hi, I need the formula to calculate the pressure of LPG in their various mixtures, with the temperature and density.
For example: 100% propane at -42 ° C to pressure you.
Thank you ... regards
Nestor

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[ankur2061]

Your query is not very clear. I am assuming that you are looking for the vapor pressure of LPG at various temperatures. Basically this requires the Antoine equation for the individual components which has the following general form:

log₁₀P_i = A - B/(t+C)

where:

P_i = vapor pressure of the i_th component, mmHgA

A = constant 1 for i_th component
B = constant 2 for i_th component
C = constant 3 for i_th component
t = reference temperature, °C

Vapor pressure of mixture

Pmix = Σx_i*P_i

where:

Pmix = VP of mixture, mmHgA
x_i = mole fraction of the component
P_i = VP of the i_th component, mmHgA

A vapor pressure calculator for pure compounds is available on "Cheresources" at:

http://www.cheresour...h&fromMainBar=1

Hope this helps.

Regards,
Ankur.

[MrShorty]

As Ankur suggests, using Raoult's law is certainly the easiest method for calculating the vapor pressure of mixtures. And, if I assume as suggested by your chart that LPG to you means "mixtures of C2-C4 aliphatic hydrocarbons," then Raoult's law is probably good enough for most applications. I would check it against your chart to see how much error this "ideal" computation has.

If you want to get really excited, you can incorporate activity and/or fugacity coefficients into your calculation. Computational difficulty goes up quite quickly, though. Only you can judge if, in your case, the improved accuracy is worth the extra effort.