 View Question
Q: Boiling point of water vs pressure > 1 bar ( Answered ,   3 Comments ) Question
 Subject: Boiling point of water vs pressure > 1 bar Category: Science Asked by: ivandelsol-ga 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``` Request for Question Clarification by maniac-ga on 01 Aug 2003 18:43 PDT ```Hello Ivandelsol, It may be easier to recommend - an Excel add in OR - another application that would calculate the thermodynamic properties of water / steam at a range of pressures. If this would be acceptable, please let us know. If so, please also indicate the type of computer / OS you would be using. --Maniac``` Subject: Re: Boiling point of water vs pressure > 1 bar Answered By: haversian-ga on 26 Aug 2003 19:16 PDT Rated: ```Hello ivandelsol-ga, 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 non-linear 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.phy-astr.gsu.edu/hbase/Kinetic/watvap.html#c1 For more information about the The Clausius-Clapeyron 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 Clausius-Clapeyron equation -Haversian```
 ivandelsol-ga rated this answer: ```Well done. The only thing missing is the EXCEL spread sheet. But I can do that, no problem. Thank you.``` ```I found a table that shows the vapor pressures (boiling point) [mm HG] of water at various temperatures in 20-degree 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.```
 ```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.```
 ```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). ```````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` ```````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` ``````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` 