air properties over 400F
air properties over 400F
(OP)
Hi, can anybody help me ?
I am facing to following problem:
I'd need to calculate air properties over 400F and 5bar
May I understand that traditional formulas that I can find in ashrae handbook cannot be utilized ?
May I understand taht at these conditions there is no more water in the air, because of this temperature, therefore it is a nonsense to consider relative humidity ?
can anybody give me a link where to find formulas for calculating these properties ?
Many thanks
I am facing to following problem:
I'd need to calculate air properties over 400F and 5bar
May I understand that traditional formulas that I can find in ashrae handbook cannot be utilized ?
May I understand taht at these conditions there is no more water in the air, because of this temperature, therefore it is a nonsense to consider relative humidity ?
can anybody give me a link where to find formulas for calculating these properties ?
Many thanks





RE: air properties over 400F
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RE: air properties over 400F
rmw
RE: air properties over 400F
But please, can anybody tell me where to find the formulas to calculate the air properties in these conditions ?
many thanks
RE: air properties over 400F
RE: air properties over 400F
The fact is there can be an infinite quantity of water per pound of dry air becaust the temperature is above the saturation temperature of water at 5 bar. You need to determine the water content one way or another but you cant assume "saturated conditions"
RE: air properties over 400F
And please, apologizes for not being so clear.
Anyhow my current problem is:
how to determine this properties.
In usual air conditioning and refrigeration conditions, humid air can be considered as an ideal gas.
My question is:
at the conditions of 400F and 5bar can humid air still be considered an ideal gas or shall we take into consideration different factors ?
Many thanks
RE: air properties over 400F
rmw
RE: air properties over 400F
Industrial Research Service's
Psychrometric Tables and Charts
by
Zimmerman and Lavine
Second Edition
This has high temp air tables and charts.
Something else that also works is an excel add-in called "@air". It is found on at:
http://www.techwareeng.com/prodAA.htm
It works great on superheated air. The only suggestions I could give you for formula to develop your own application is maybe something from a flue gas book or a boiler vendor.
That's the best help I can give.
RE: air properties over 400F
http://www.engineering-4e.com/calc1.htm
http://www.engineering-4e.com
RE: air properties over 400F
As a matter of fact I am going deeper into this problem, and new questions are presenting.
Indeed, if I consider the water saturation pressure at air temperature, this is higher than ambient pressure.
Does it make sense to define a relative humidity in this conditions ?
To mr. UtilityLouie
in this condition the suggested software doesn't work
to Mr.FOURe
unfortunately I have to consider moist air !
Many thanks for your help
RE: air properties over 400F
Does it make sense to define a relative humidity in this conditions ?"
NO.
There can be an infinite quantity of water per pound of dry air because the temperature is above the saturation temperature of water at 5 bar. Relative humidity is (actual water / maximum water) = (anything / infinity) = 0 independantly of actual water content. Not a very usefull concept is it?
RE: air properties over 400F
RE: air properties over 400F
Formulation of High-Temperature Properties for Moist Air. Nelson and Sauer. HVAC&R Research Vol 8, No. 3. July 2002.
RE: air properties over 400F
Mr KiwiMace, I bought that article.
Just to integrate my question with two new - sorry for delay -.
Since at described condition do not exist saturation conditions,
does it make sense to define a dew point ?
Would air at this condition dehumidify if getting in contact with a colder surface ?
many thanks