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| | From:  Zurconium2 (Original Message) | Sent: 3/10/2006 4:50 PM |
Hello...Hope you can help with this question... What is the difference in temperature in the boiling point of water at normal atmospheric pressure (1 atm) and at a pressure of 1 bar? What precision do you need in the measurements in order to detect the difference? Not sure where to start? Thanks! |
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| | | From: ·Steve· | Sent: 3/10/2006 11:49 PM |
You can obtain the boiling point of water at different pressures using a table, such as the "Boiling Points of Water at Various Pressures" in the CRC Handbook, or with a Javascript boiling point calculator from the Internet.
In the calculator linked below, you have to enter the pressure in units of inches of Hg. When you hit "Calculate" it returns the temperature in °F and °C and the pressure in millibars.
1 atm = 1.01325 bar
1 bar = 0.986923 atm
1 atm = 760 mm Hg = 29.92126 in Hg
Convert 1 bar to inches of mercury and plug that value into the calculator to get the boiling point at 1 bar pressure. It's not much lower!
Steve
Water Base Boiling Point Calculator
http://www.csgnetwork.com/h2oboil2calc.html/(The calculator program assumes 1 atm = 29.92 in Hg instead of a more accurate 29.92126 in Hg. At 29.92126 in Hg, it gives the boiling point of water as 100.001°C instead of 100°C, a small error.)
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1 atm pressure is at sea level. The boiling point at 1 atm is 100 degrees celcius. As your altitude increased, the pressure decreased, and boiling point decreased too. Each 100 meter, 0.5 atm pressure decreased. You can search for the ratio of pressure vs boiling point. |
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| | | From: ·Steve· | Sent: 10/11/2006 5:07 AM |
>> Each 100 meter, 0.5 atm pressure decreased << But at that rate the pressure would be zero at 200 meters?  |
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I don't know how i happened to write such a comment. Sure the atmospheric pressure decreases by increasing altitude, but not skyrocket. It takes 5500 metres to become 0.5 atm in average conditions. With increasing altitude each 100 meters, air temperature decreases 0.5 degrees celcius in troposphere. |
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| | | From: ·Steve· | Sent: 11/27/2006 5:29 AM |
>> With increasing altitude each 100 meters, air temperature decreases 0.5 degrees celcius << Ahh, that's what you were thinking of... sounds reasonable. Just checked... Th = To �?nbsp; 0.0065° / m X h according to the Wikipedia article at http://en.wikipedia.org/wiki/Density_of_air (To = 298.15 K or 25°C). That would be a 0.65 degree decrease per 100 m of altitude. The article didn't say how accurate the formula is!  Steve |
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| | | From: ·Steve· | Sent: 11/27/2006 5:33 AM |
Forgot to mention, the pressure formula given there is a mess, not so clear-cut!  |
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