

Subject:
Boiling point of water vs pressure > 1 bar
Category: Science Asked by: ivandelsolga List Price: $9.50 
Posted:
01 Aug 2003 16:28 PDT
Expires: 31 Aug 2003 16:28 PDT Question ID: 237993 
Can you give me an equation or graph, solving the boiling point of water for pressures increasing above one atmosphere. Particularly interested in solar water heaters which may have check valves between the city water supply and the solar water heater  


Subject:
Re: Boiling point of water vs pressure > 1 bar
Answered By: haversianga on 26 Aug 2003 19:16 PDT Rated: 
Hello ivandelsolga, A brief outline of the problem is as follows: The hotter a given body of water is, the more it wants to be a gas. However, the higher the pressure, the more the gas wants to condense into a liquid. Those two oppose each other, but not linearly. According to this page on nonlinear regression ( http://www.nlreg.com/boil.htm ), the formula for boiling point as a function of pressure is given by Clapeyron's Equation: Temperature = 3200 / log(Pressure/1700)  459.7 Temperature in degrees Farenheight; pressure in PSI For more information about the vapor pressure of water, and boiling: http://www.biggreenegg.com/boilingPoint.htm http://hyperphysics.phyastr.gsu.edu/hbase/Kinetic/watvap.html#c1 For more information about the The ClausiusClapeyron equation: http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch14/clausius.html http://theory.ph.man.ac.uk/~judith/stat_therm/node44.html http://www.tau.ac.il/~phchlab/experiments/iodine/clauclap.html Search strategy: boiling point of water at pressure boiling versus pressure Clapeyron equation ClausiusClapeyron equation Haversian 
ivandelsolga
rated this answer:
Well done. The only thing missing is the EXCEL spread sheet. But I can do that, no problem. Thank you. 

Subject:
Re: Boiling point of water vs pressure > 1 bar
From: atozxrodga on 01 Aug 2003 19:16 PDT 
I found a table that shows the vapor pressures (boiling point) [mm HG] of water at various temperatures in 20degree Celcius increments. It is on page 13 at the following URL: http://www.geology.fau.edu/course_info/spring03/GLY5243/5243LN03_S03.pdf This table could be used to estimate the boiling point of water by interpolation and unit conversion. For example, supposed you wanted to know the boiling temperature (vapor pressure) of water at 3.5 bar. Since the table is given in mm Hg, conversion of 3.5 bar is necessary. 1 bar is 700 mm Hg. Therefore 3.5 bar is 2400 mm Hg. From the table: the vapor pressure of water at 120 degrees C is 1489.14 mm Hg the vapor pressure of water at 140 degress C is 2710.92 mm Hg Therefore the temperature at which water boils (vapor pressure) at 2400 mm Hg is somewhere between 120 degrees Celsius (1489.14 mm Hg) and 140 degrees Celsius (2710.92 mm Hg). But where? *Assuming* a linear relationship between these two values, it can be found thus: The difference between 1489.14 and 2710.92 is 1221.78. The difference between 1489.14 and 2400.00 is 910.86. 910.86 is 74.5519 percent of 1221.78. Therefore, the temperature at which water boils at 2400 mm Hg (3.5 bar) will be 75.5519 percent of the difference between 120 and 140 degrees celcius. Since that difference is 20, and 75.5519 percent of that difference is 15.11, the temperature is 120+15.11, or 135.11. Hope this is helpful. 
Subject:
Re: Boiling point of water vs pressure > 1 bar
From: redhossga on 02 Aug 2003 06:12 PDT 
You may have a serious problem. If you do have a check valve installed between your water heater and the water main, you should have a thermal expansion tank in your system. The T&P valve on your water heater is not designed to operate on a daily basis. They are a safety valve only and should be inspected and replaced on a regular schedule. The thermal expansion tank allows the water in your system a volume to expand into when expansion occurs due to heating. Water heaters can explode with considerable force if there is no way to relieve the pressure. 
Subject:
Re: Boiling point of water vs pressure > 1 bar
From: gasserga on 24 Aug 2003 13:51 PDT 
This relationship requires a complex polynomial, but you can use the following simple formulae within the prescribed ranges. For 14.7 psi abs(1 atmos)  24 psi abs use: Y = 52.68logX + 70.3 For 24 psi abs  100 psi abs use: Y = 52.68logX + 0.19X + 65.8 X is steam pressure in psi absolute Y is steam temperature in degrees Fahrenheit Logarithms are natural(base e). ```````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` ```````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` ```````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` 
If you feel that you have found inappropriate content, please let us know by emailing us at answerssupport@google.com with the question ID listed above. Thank you. 
Search Google Answers for 
Google Home  Answers FAQ  Terms of Service  Privacy Policy 