Jon, I was fooling around with your spreadsheet and I tried to figure out what the smallest amount of water that could be plugged in and get a livable temperature. Even at very, very low numbers (10^-24) the temperature still needs to 100C |

I'll check, but I think you are taking it outside the valid range. But the calculations are correct. I'll put a more complete answer together, hopefully today.

{ABE} I started on the full explanation, and figured out where you are going wrong. See the first word in cell B12. The pressure under consideration is normal atmospheric pressure (assumed due solely to oxygen and nitrogen and argon and a few trace gasses) **plus** the pressure due to water vapor in the atmosphere. (Actually it could be partly liquid, clouds, above the Earth's surface without affecting the result as long as it's all vapor at the Earth's surface).

The boiling point of water at 15 psi is 100 C. The boiling point of water at (15 + ε ) psi, where ε is small compared to 15 is 100 C within the precision we need here.

And we are looking at pure vapor. Vapor can obviously exist at temperatures lower than 100 C and pressure 15 psi, since humidity exists, but water can also exist; it depends on other factors. But for just vapor no matter what other factors you have to be in the vapor area.

A Pascal (Pa) is 6,895 psi and a Kelvin (K) (not *degrees* K, just K) is C + 273.15. The red dots are "critical points". The brownish area to the right of the liquid area is "supercritical fluid", both liquid-ish and vapor-ish. The point where all three phases touch is a "triple point" where the three phases are indistinguishable. The little blue X is standard temperature and pressure. If you move right from the blue X you get to the vapor/liquid line at (surprise) 373 K or 100 C.

It's clearer on a pressure-enthalpy diagram with lines of constant temperature, from STEAM P-H DIAGRAM:

The purple-bounded "bell" area is mixed liquid and vapor. To the left of the bell is liquid, to the right of the bell is vapor. The triple point is at the top of the bell Note that the lines of constant temperature are horizontal within the "bell". When a system is mixed water and steam, somewhere along one of those horizontal lines, the percentage of how far along that line it is is the "quality" of the steam. My spreadsheet is calculating the temperature where a line of constant pressure intersects the right edge of the "bell". That's the minimum temperature at which you *can* have pure vapor. Increase the temperature by the eentsiest bit or more and you *must* have pure vapor.

Clear as mud?

{ABE2}Cells A12, A13, and A14 should be set to display two figures to the right of the decimal point.

{ABE3} The C to F conversions are correct, multiplication and division take precedence over addition. See the online calculator at http://www.onlineconversion.com/temperature.htm.

*Edited by JonF, : No reason given.*

*Edited by JonF, : No reason given.*

*Edited by JonF, : No reason given.*

*Edited by JonF, : No reason given.*