water vapor at high temp, low pressure

[mjw55]

Hello,

I've been trying to wrap my head around an application at a new job.

Currently running a hydrogen atmosphere counter-flow furnace. We are measuring the dew point of the atmoshpere before preheating/entering the furnace and we are debating measuring it just before (or after) it leaves the furnace.

Upon exit the atmoshpere it at 1800°F. The pressure throughout the H2 gas loop is around 0.5"H20 so it is close to atmospheric and always greater than.

I feel I have gathered an understanding of humidity/dew point/etc for sub-boiling temperatures but I have found little information on higher temperature environments. Especially an atmosphere where the temperature is above the critical point on the water phase diagram (although the pressure is not.)

Are the "The International Association for the Properties of Water and Steam" 1997 equations that I find frequently mentioned valid up to these temperatures?

I've been using the spread sheet from here:

http://www.bekktech.com/noteRH.html.

I get numbers but I am hesitent to accept them without understanding that they are still valid for my temperature range.

If anyone could give an explination or point me to a web resource I would be very appreciative.

Best Regards,

MJ