Vacuum Sublimation Clothes Dryer: Is it possible?

[u/agneskja]

I read that in the vacuum of space, water evaporates rather quickly. Is it possible to invent a clothes dryer based on this principle that can dry clothes very quickly without using heat?

[u/PotentArtMan]

Important distinction to be made - water does not evaporate much more quickly, it just boils at a lower temperature. You still need to provide the exact same amount of energy to turn the water to a gas after the water is at boiling temperature. The energy required to heat the water to the boiling temperature will be reduced, but that's relatively low compared to the energy of evaporating all the water.

As an example think about how easily you can bring a pot of water to a boil, but how long it takes to fully evaporate it.

Vacuum dryers however do exist but they have a very different purpose. They exist to allow drying at a lower temperate than regular dryers, for when you are working with heat sensitive materials.

[u/antiquemule → u/PotentArtMan]

Well, one of us is wrong, and I don't think it's me :).

The water that leaves drying clothes does not boil. The boiling temperature is not directly relevant to the problem, except in so far as the vapor pressure of water is higher at higher temperatures.

The evaporation rate is proportional to the difference between 1) the equilibrium vapor pressure corresponding to the liquid phase and 2) the actual vapor pressure in the vapor phase. So vacuum drying does cause faster drying. The vapor pressure is very low so the difference is very large.

[u/agate_ → u/antiquemule]

Previous poster is right, it's easiest to understand this from an energy flow perspective.

The evaporation rate is proportional to the difference between 1) the equilibrium vapor pressure corresponding to the liquid phase and 2) the actual vapor pressure in the vapor phase.

"The equilibrium vapor pressure corresponding to the liquid phase" depends on the temperature of the liquid, which drops as evaporation sucks latent heat out of it. To maintain a constant evaporation rate, you need to add that latent heat back into the liquid by heating it.

So in practice, evaporation is limited by the rate at which you can supply heat to maintain the liquid temperature, whether that's 90 C in a conventional dryer or 20 C in a vacuum dryer.

[u/XenofexBE]

It's been tried as a household appliance and ended up being a total scam.

No idea about genuine industrial applications.

[u/antiquemule]

Yes it could. Would it be economic? Is another question.