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# Boiling Point at altitude?

06/01/2007 6:26 PM

I need to know a formula to calculate the boiling point of water at various altitudes. I can find some info for lower altitudes on the net but I need temps up to 50,000 feet altitude. The standard pressure for this altitude is 3.424641 inHga or 1.682 PSIA. I am programming a data system that will compute and display a realtime boiling point of water based on outside pressure. Part of this test includes heating a large quantity of water and this info is for safety just in case the test would experience a rapid decompression. I have some tables that show a few points above 20,000 feet but I would prefer an equation. My table says that the standard pressure at 50,000 feet is 120 DegF. Can anybody help me?

It would be great if this equation was tracable to a text book or scientific reference book for documentation.

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#1

### Re: Boiling Point at altitude?

06/02/2007 12:31 AM

Hi Flighttest,

Here is a chart of BP vs Vapor Pressure for Water:

This is based on the Antoine equation.

The Antoine equation solved for Vapor Pressure is:

where:

VP = vapor pressure in mmHg

A = 4.65430

B = 1435.264

C = -64.848

T = BP in ÂșC

If you can relate an altitude to atmospheric pressure (in this case the vapor pressure), you can then relate the BP to an altitude.

Hope this helps,

Mike

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#4

### Re: Boiling Point at altitude?

06/03/2007 7:28 AM

Great Info Mikerho.

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#7

### Re: Boiling Point at altitude?

06/04/2007 12:35 PM

Thanks for the help. I did finally work thru the info and posted a surprising result. When I plot altitude vs. boiling point of water, the relationship is basically linear.

jim

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#2

### Re: Boiling Point at altitude?

06/02/2007 11:39 PM

"The Properties of Steam" by Keenan & Keyes provide the data you seek up to a point.

Try Google and Dogpile for "boiling point of water vs. altitude" and similar terms. You should find several sources.

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#3

### Re: Boiling Point at altitude?

06/03/2007 3:46 AM

ou need data that relates pressure and temperature to fluid state. Such data sets are called phase diagrammes.

Get a friend that knows a bit about physics to explain to you what a phase diagramme is and how the boiling point of water relates to water vapour pressure when water changes its nature from a liquid to a gas.

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#5

### Re: Boiling Point at altitude?

06/04/2007 3:37 AM

Check out "The Thermodynamic Properties of Steam", by Mayhew & Rogers. Inside it is a table giving the International Standard Atmosphere, giving pressure versus altitude. Earlier in the publication is a table giving boiling temperature versus pressure. This lot should be all that is needed.

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#6

### Re: Boiling Point at altitude?

06/04/2007 9:21 AM

I was able to use the equation that Mikerho provided. Using the Antoine equation lead, I was able to find another equation that seems to work very well. The interesting thing is that the boiling point becomes a linear relationship when plotted against altitude instead of pressure. I was not expecting this but it was a pleasant surprise. Somehow, these are more directly related. This was educational!

Again, I appreciate the help.