Enthalpy of air / vapor mixture 2

[vroma]

Hi everyone,

I'm out of my depth with this area and I'm hoping you can help. I'm trying to determine the enthalpy of air with some moisture at around 600 degrees Fahrenheit and atmospheric pressure. Would I do this by adding the enthalpy of dry air to the enthalpy of superheated steam at 600 deg F (weighted by the masses of air and water, respectively)?

Thanks,
vroma

 

[Latexman]

Yes.

Good luck,
Latexman

 

[vroma]

Great! Thanks, Latexman. Are you aware of any good online resources for the air and superheated steam enthalpies at around 600 deg F? Ideally, in a tabular format.

Thanks again,
vroma

 

[Latexman]

http://webbook.nist.gov/

has enthalpies for nitrogen, oxygen, and water.

Good luck,
Latexman

 

[DickRussell]

Keep in mind that enthalpy is not an absolute quantity, such as temperature or pressure, but always is relative to some base condition. Typically, the enthalpy is anchored to zero for the ideal gas state at a very low temperature, such as zero absolute. In an earlier version of the API Technical Data Book, Petroleum Refining, the basis was zero for the liquid at -200 F, except for 10 light gases. In most (all?) steam tables, the base is zero for liquid water at 0 C.

Since only enthalpy differences have any usefulness, there is no problem with having components in a mixture use different zero enthalpy basis - until you have a change in composition due to reaction (eg. combustion). Then you must use caution, and not use enthalpy differences between input and exhaust as heat of reaction.

 

[Feric]

Hi there:

Here is a URL contaning a free online calculator for air:

http://members.aol.com/engware/calc1.htm

Thanks,

Gordan

Gordan

http://engware.i-dentity.com

 

[25362]

Table A-5 of Holman's Heat Transfer, McGraw-Hill, gives the thermophysical properties for air at atmospheric pressure.