Recently came across the phenomenon that heating a room apparently decreases the humidity. If it was just that heating the space makes a lot of the water condense out of the air, eg onto window panes or other surfaces, then I could accept that. But the bit my brain can’t get around is that if it’s 80% humidity but 2celcius outside, and it’s say 70% humidity and 15celcius inside, why is it helpful to open a window? The warm air inside would be cooled, but surely the water in the air outside would diffuse in and raise the humidity in the room? I feel like I’m missing something really obvious here :/
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Temperature is how much the atoms are vibrating.
High temperature allows more mixing between air and water.
Imagine you are water and want to get in a room full of people that are air. If the people in the room are standing still shoulder to shoulder, you won’t get in. If those people start to dance song move around, you will find a gap. The more they dance the more gaps you have available. If they stop to dance you will be squeezed out of the room.
That’s how air absorbs water. If you take cold air it has very little water capacity, you heat it, it will have more room to let water in. That’s why to dry things we use hot air. The same air when cooled will release the water it can’t hold anymore.
The way we practically measure it is by relative humidity, the % of water relative to the max capacity at that temperature. It tells you how that air mass will behave, if it will have the tendency to dry things or damp things.
Absolute humidity is instead water mass vs air mass ratio. That’s used for technical calculations as it’s not related to temperature. For example, how much rain you can get from a storm is linked to absolute humidity. From absolute humidity it’s easier to calculate what pressure and temperature is needed to get to the dew point for example. “Today we have X absolute humidity, therefore we will have fog as soon as the temperature gets down to Y degrees”. Or “we have X absolute humidity so my compressor will get Y kg of condensation water to get rid of per hour of operation”.
It works the same for all the solutions. Dissolving sugar in water works the same way as dissolving water in air. Hotter water, more sugar can be dissolved. That’s why cooking pies involves a lot of temperature control, to ease or deter things from mixing or dissolving one in the other.
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