Saturated vapor pressures of water

[MaxPlanck]

Hi all,

I have a question regarding the saturated vapor pressures inside a compressor dryer working at 8 bar(a).

For a calculation I need to know the satured vapor pressures of water at a temperature of 150 °C. I cannot find those numbers in tables in literature. They all stop at 100°C, which is logic otherwise you could have relative humidity higher than 100%.

If I have a dryer working at 8 bar(a) and a regeneration temperature of 150 °C, than I CAN have a relative humidity between 0 and 100 %, depending on the absulute moisture content in the air.
Is there a way to calculate the vapor pressures at these temperatures and pressures?

Many thanks in advance.
Sherpa

 

[MortenA]

Any desent steam table should tell you this - but anyway: 476 kPa (abs)

Best regards

Morten

 

[MortenA]

if you temperature at athomaspheric pressure is higher than 100ºC then you have superheated steam.

best regards

Morten

 

[MaxPlanck]

If I want to recalculate it to a pressure of 8 bar absolute, can I just divide it by 8?

Best regards,
Sherpa

 

[25362]

Saturation would mean about

4.76[÷]8 = 0.595 = 59.5% moisture in the vapor

 

[MortenA]

???

Its not easy to calculate saturated water vapour pressure - use a table.

If you wish to calculate the %humidity for a superheated steam then you must calculate the water content at your boiling point for the actual pressure and then at the superheated temperature and thats the relationship.

Just rememeber that if you got a "pot" boiling at atm. pressure it cant be any hotter than 100 deg C. If you wish to superheat it that must take place "downstream" the pot.

If this is serious work then i think its about time that you contact somebody who knows about steam - and fork out the consultancy fee if its not in-house.

Best regards

Morten

 

[dcasto]

are you injecting steam? and trying to dry it. a compressor dryer????? You can't have any more water at the compressor discharge than at the inlet and any gas will hold more water vapour at 150C and 8 bar than any inlet I know of.

 

[MaxPlanck]

Hi,

Thank you all for the input.
I found some interesting formulas in the 2005 ASHRRAE Handbook to calculate saturated vapor pressure in ranges from -100°C - 200°C.

I was just wondering if the working pressure of 8 bar would have an influence on this vapor pressure, but it seems to me that only the temperature of the water vapor has importance.
When you have water vapor at 8 bar and a temperature of 150°C, I don't think one can speak of steam, or am I wrong? At 8 bar, water starts to boil at +- 171°C.

So my ultimate question is: is it correct to say that the (saturated) vapor pressure does not change when pressured is raised. Total pressure would be:
P(total = 8 bar) = P(air) + P(water vapor)

So as long as I don't form steam, I can use vapor pressures.

Many thanks for all the replies.
Sherpa

 

[MortenA]

Max: To answeryour question directly: Yes

However i get the feeling that you may need more direct consultation with somebody how know this subject than what you can get here if this is used professionally.

Best regards

Morten