Friday, 28 February 2014

Humidity and temperature

There's a good table of the absolute humidity and temperature here at Transport Information Services, if anyone is intereste.

For a range of temperatures and relative humidities, at five-degree and ten-percent intervals, It shows the absolute humidity and dew point. The absolute humidity is grammes of water per cubic metre of air. The dew point is the temperature the air must drop to if water is going to start precipitating from it, or the temperature the air must not drop to if you don't want condensation. 

The issue of humidity and temperature is in fact very complex, since you're looking at the properties of droplets of water that are behaving like a gas. More information in general is available here on wikipedia

Also, you get forums like this one with lines like "We all know the ideal gas law, PV = nRT. But the number of moles, n, can be written as m/M where m is the mass of gas, and M is the molecular weight in g/mol. Then PV = (m/M)*RT."

If you do know that, then there are plenty of forums out there, and a great deal of physics. In the meantime, I'll stick to relative humidity doubling with every ten degree temperature drop, or use the table if I need more precision.