Atmospheric Triple Point
 

Can anyone advise of the pressure (or equivelant Pressure Height) in the atmosphere whereafter water exists in 2 states only, ice or water vapour, with no liquid state between?

I had it in my notes some years ago when I was doing some University lectures on Aerodynamics, but lent it to one of the students who permanently borrowed it.

enicalyth, your name comes to mind as a possible source of all wisdom regarding atmospheric water vapour.

Thanks in advance,

Smokey

Old Smokey,

I believe the pressure is 6.1mb.

I make that ~19km up assuming a gradient layer to ~11km and an isothermal above that.

Out of interest, the Martian atmospheric pressure is about 6.8mb which is, of course, why any water there wouldn't hang about for long.

:ok:

PS: Edited coz I'm a dummy and can't get my units right.

I dunno sometimes about you OS; all you had to do is make a phone call or an email... :p

http://www.sciencebyjones.com/triple...nt%20curve.gif

Triple point for water: T= 273.16 K and P= 0.612 kPa

SR71 & MkVIII,

Two very closely matching responses in such a short time, thank you sincerely to both of you.

I'd always kept the figure "in my back pocket" as it may have had aircraft icing considerations, after considering the Pressure Height, maybe not a consideration for current transport aircraft. I'll leave that zone for the high flyers like SR71.

MkVIII, your tone in this and other posts sounds familiar, so too is that diagram. You weren't the Uni student who nicked my notes were you?

Thank you,

Old Smokey (aka Old Grumpey)

Nope, not me your Honour! :}

Yup I make it 34.4 kilometres...

At 112800ft the ISA atmospheric pressure is 12.766 lb per square foot. (It is 2116.22 lb per square foot at ISA sea-level).

At this point I believe water goes ice to vapour (or back again) without liquid in between. Anything that goes from solid to vapour without a liquid phase is "sublime". Diagrams look fine.

Now let's suppose M0.77, aspect ratio 8.4, L/D about 20... and 60 tonnes weight.

(Sips a sublime gin and tonic)... It needs 80,000sq ft wing area, a wingspan of 820ft with a Lift/Drag of 19.77 and a speed of 460kts and engines burning 0.65lb fuel per hour for every lb of drag to cut along at 106.2 nautical air miles for every 1000lb of fuel. Assuming I can light the kerosine-air engines that is.

I'll let Sir Richard Branson go there. Now if Captain Claret has a bottle handy...

enicalyth,

I think that this has to be a Pprune record, 3 respondants agreeing with each other within very small tolerances, and no dissidents!

I can see now why I put the information in my back pocket, I'll leave the flights there to the more adventurous.

Thanks to all,

Smokey

Well, ya could've asked Francis Gary Powers! :p :p :p