saturation point 2

[kdashc]

Is it correct that if the saturation pressure is less than the partial pressure of a gas then that gas exists in a vapor state.

and if the saturation pressure is greater than the partial pressure tha that gas exists in a liquid state?

 

[speco]

Kdashc,

I don't think so. I believe it's the other way around.

Regards,

Speco

 

[Latexman]

If the saturation pressure is less than the partial pressure of a component, this is the same as the partial pressure of a component being greater than the saturation pressure and that component will be a mixture of vapor and liquid (condensation).

If the saturation pressure is greater than the partial pressure of a component, this is the same as the partial pressure of a component being less than the saturation pressure and that component will be a vapor.

If you are below the critical temperature of a component and the component is in a gaseous state, it is usually called a vapor.

If you are above the critical temperature of a component and the component is in a gaseous state, it is usually callled a gas.

Good luck,
Latexman

 

[ione]

Vapour pressure is by definition the pressure of a vapour which is in equilibrium with its liquid, or generally speaking non-vapour phase. The equilibrium could be intended in this way: the probability a molecule of vapour turns into liquid is the same as that a molecule of liquid turns into vapour. The higher the vapour pressure the lower the boiling temperature. So when the equilibrium is reached if you increase pressure part of vapour will turn into liquid. On the contrary if you reduce pressure part of the liquid will turn into vapour. Anyway there is a critical temperature above which the only state possible is gaseous whatever is the pressure applied.

 

[kdashc]

im sorry, i see now, i did have it backwards thanks.

if there are two gasses in a pressurizd container that reads 100 PSIA. and hypothetically we introduce both at once with one gas at a partial pressure of 70 PSIA and the other a partial presssure at 30 PSIA. and still hypothetically the first gas totally condenses into a liquid. would the second gas still be at a partial pressure of 30 PSIA or would it be at 100 PSIA?

 

[Latexman]

Hypothetically, what caused the first vapor to condense? Temperature reduction or magic?

Good luck,
Latexman

 

[kdashc]

im sorry that was a bad hypothetical.

say we have a typical aftercooler for a gas compressor.

and that the system is at 100 PSIA and the two gasses enter at 300F and are cooled to 100F, and the first gas condenses to a liquid at 200F.

would the second gas stay at 30PSIA and bring the entire operating pressure to 30PSIA or would it would it go to 100PSIA?

 

[Latexman]

If this is a closed system (no flow, fixed volume), the final operating pressure will be less than 30 PSIA. Since T decreases, P will decrease. Remember PV = nRT for the remaining gas.

If this is a flowing, operating system, it's going to depend on the controls.

Good luck,
Latexman

 

[kdashc]

does anyone have any experience on the above situation with an compressure producing a two gas mixtue at a certain pressure and temp then running through an aftercooler where one gas is condensed to a liquid.

specifically do you see constant pressure (neglecting inherent pressure drop of heat exchanger) or do you see an operating pressure inline with partial pressure of the uncondensed gas???

 

[Latexman]

Now we are getting down to the nitty gritty!

In a compressor system there is usually a control valve or process downstream that restricts flow so the inventory of the gas can build-up to the desired pressure. Again, remember PV = nRT. Inventory is the n part. Even if 70% condenses and the temperature is lowered, you can compress the remaining gas into a volume between the compressor and the restriction to get the pressure desired. There is no specific answer to you question. It depends on what pressure you want and the limitations of the compressor, pipe, and fittings.

A wise man once told me, "if you want the right answer, you have to ask the right question".

Good luck,
Latexman

 

[CH5OH]

boiling point:temperature at which a liquid boils (pressure is kept constant,temperature is raised)
vapour pressureressure at which a liquid boils (temperature is kept constant,pressure is lowered)
consider the pressure in the cooler:
if the heat removal in the cooler is kept constant then you can have 3 cases:
both gasses remain super heated:the pressure is the sum of the partial pressures (high gas flow)
one gas superheated,the other is partial condensed:the pressure is about equal to the superheated partial pressure (medium gas flow)
one gas superheated, the other completely condensed:the pressure is lower than the superheated partial pressure
(low gas flow)