3 replies to this topic

[DANA-IF]

HI friends

I'd like to know about the RVP

As I know  vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system .

 

On the other hand , reid vapor pressure (RVP) is a common measure of the volatility of gasoline. It is defined as the absolute vapor pressure exerted by a liquid at 100 °F (37.8 °C) as determined by the test method ASTM-D-323. The test method applies to volatile crude oil and volatile nonviscous petroleum liquids, except liquified petroleum gases.

 

My question , why they said the RVP is defined as the absolute vapor pressure exerted by a liquid because vapor pressure is  the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases ?

Thanks a lot 

[PingPong]

It is not clear to me what exactly your question is.

 

The RVP of a liquid is simply the outcome of a standardised test. Is is not exactly the True Vapor Pressure, but there are graphs to convert one into the other.

[DANA-IF]

I mean on definitions they indicate :the reid vapor pressure is the pressure  exerted by liquid  while vapor pressure is  the pressure exerted by a vapor 

Edited by N.BH, 03 February 2014 - 10:11 AM.

[PingPong]

This is a silly discussion, mainly due to the way wikipedia states things.

 

The vapor pressure of a liquid is the equilibrium pressure of a vapor above that liquid.

 

The difference betwen TVP and RVP is only that RVP is measured in a closed container whereby a small part of the original liquid vaporizes. As a consequence the remainling liquid is slightly heavier than the original liquid, so the measured RVP is really the TVP of that slightly heavier liquid, not the TVP of the original liquid composition. Therefor the RVP is not quite the same value as the TVP.