October 15, 2019, 08:08:39 PM
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Topic: Vapor Calculation Help  (Read 462 times)

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Offline LondonDis

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Vapor Calculation Help
« on: June 23, 2019, 12:39:03 PM »
Hi All (Posted in wrong forum so moved here)

I am new to this forum as this topic is somewhat out of my comfort zone so thought I would give here a try. I would like some help with what I imagine is going to be a fairly simple calculation for all in here:

I would like to work out the space alcohol vapour will occupy after evaporation. I know how many litres of ethanol will evaporate and the assumption will be there is no ventilation. I need to get to a point where I know how much cubic meters it will occupy.

Does anyone know the best way to approach this.
Cheers.

Offline chenbeier

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Re: Vapor Calculation Help
« Reply #1 on: June 23, 2019, 12:49:26 PM »
If you above the boiling point you can approach with ideal gas law to get a rough calculation.

Offline LondonDis

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Re: Vapor Calculation Help
« Reply #2 on: June 23, 2019, 01:32:47 PM »
If you above the boiling point you can approach with ideal gas law to get a rough calculation.

Hi, sorry I should have said this is simply ethanol at room temperature.

So 500 litres of ethanol evaporated in a fixed space with no ventilation. Let's call it 100m3 of space. I would like to work out what % of the m3 is now ethanol vapor.

I am assuming it isn't as simple as 0.5%. i.e 500L being half a cubic meter in the 100m3 space

Offline Borek

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Re: Vapor Calculation Help
« Reply #3 on: June 23, 2019, 04:25:33 PM »
You need to find what is the saturated vapor pressure of ethanol for room temperature (you should be able to google tables, or perhaps coefficients for Antoine equation).
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Offline Enthalpy

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Re: Vapor Calculation Help
« Reply #4 on: June 24, 2019, 04:28:37 AM »
Wiki has the equilibrium vapour pressure of ethanol
https://en.wikipedia.org/wiki/Ethanol
https://en.wikipedia.org/wiki/Ethanol_(data_page)#Vapor_pressure_of_liquid

The volumes of liquid and gaseous ethanol differ, so the proportion isn't between air and liquid ethanol. But the proportion of partial pressures equals the proportion of moles.

Two situations can occur, computed differently, depending on whether the air volume can contain all the ethanol as a vapour, or instead if it stops the evaporation before.

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