Water Boiling Question - Closed Cylinder

shreesha87 · March 25, 2014, 12:28

Hello everyone

I have a general question about thermodynamics/fluids. I did not know which forum should I post this so selected this forum.

Assume I have a perfectly sealed cylinder filled with water completely (no gaps whatsoever). I heat the cylinder from the outside
to 100 degrees C. So will the water boil?

Shree

fivos · March 26, 2014, 04:13

Your question is not correctly defined. First of all you should define the operating pressure (or lets say the initial pressure) of your water mass.

Assuming you begin with water at atmospheric conditions (p=1bar) then still you need more data about the exact heat you provided. The reason is that at 100C you may have saturated water, saturated steam, or steam and water mixture. You can also see here:
http://en.wikipedia.org/wiki/File:TS...dampf_engl.png

Here you can see the T-s diagram for water. For pressure of 1bar there are infinite possible conditions corresponding to T=100C, all under the saturation curve (the red one).

So, in order to get a definite answer it is essential to know the exact heat provided, through which you can find the enthalpic rise (see http://www.engineeringtoolbox.com/mo...ter-d_308.html). By having specified enthalpy and pressure you have defined a single point.

Note that in reality things are not simple because by heating water, it will expand. Since you perfectly constrain it, heating will pressurize it above the initial pressure. Thus, I think, that is safe to assume that at 100C the water would still be subcooled water, since its pressure will be higher than 1bar.

March 25, 2014, 12:28	Water Boiling Question - Closed Cylinder	#1
shreesha87 New Member Join Date: Oct 2013 Posts: 13 Rep Power: 12	Hello everyone I have a general question about thermodynamics/fluids. I did not know which forum should I post this so selected this forum. Assume I have a perfectly sealed cylinder filled with water completely (no gaps whatsoever). I heat the cylinder from the outside to 100 degrees C. So will the water boil? Shree

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March 26, 2014, 04:13		#2
fivos Senior Member Phoevos Join Date: Mar 2009 Posts: 104 Rep Power: 17	Your question is not correctly defined. First of all you should define the operating pressure (or lets say the initial pressure) of your water mass. Assuming you begin with water at atmospheric conditions (p=1bar) then still you need more data about the exact heat you provided. The reason is that at 100C you may have saturated water, saturated steam, or steam and water mixture. You can also see here: http://en.wikipedia.org/wiki/File:TS...dampf_engl.png Here you can see the T-s diagram for water. For pressure of 1bar there are infinite possible conditions corresponding to T=100C, all under the saturation curve (the red one). So, in order to get a definite answer it is essential to know the exact heat provided, through which you can find the enthalpic rise (see http://www.engineeringtoolbox.com/mo...ter-d_308.html). By having specified enthalpy and pressure you have defined a single point. Note that in reality things are not simple because by heating water, it will expand. Since you perfectly constrain it, heating will pressurize it above the initial pressure. Thus, I think, that is safe to assume that at 100C the water would still be subcooled water, since its pressure will be higher than 1bar.