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Determining Vapour Pressure

Determining Vapour Pressure

Determining Vapour Pressure

(OP)
Under the new Pressure Equipment Directive it is necessary to classifiy the operating fluid as a gas or a liquid. The definition for each is that the fluid should be classed as a gas if the vapour pressure at the maximum temperature is above 0.5 BarG, else it is classed as a liquid.

The problem so many people are experiencing is determining the vapour pressure.

Does anybody know of any web sites that will hold data or explain the principles in determing the vapour pressure (especially from limited data).

Fawkes

RE: Determining Vapour Pressure

Fawkes:

Perry's Chemical Engineer's Handbook has pages filled with constants used to calculate the vapor pressure for tons of substances (231 to be precise).  Vapor pressure is a function of temperature and is given in Perry's as:

P(vap) = exp[C1+(C2/T)+C3*ln(T)+C4*T^(C5)]

As stated above, the constants (C1-C5) are given in Perry's.  You could also use the Antoine Equation:

log P = A - [B/(T+C)]

...but again, you would have to ge the constants (A,B, & C) for the specific compound from a source.

To get online information on vapor pressure, I would suggest you go to a search engine and type in "Vapor Pressure".  There is plenty of information out there.

jproj

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