Evaporative cooling is a technique used to cool air by using the evaporation of a liquid.

My google research on evaporative cooling shows a ubiquitous concept of forcing air through a pad/membrane/foam/sponge that holds water, and the air exiting the pad is colder to a degree that depends on the ambient humidity. Apparently the output can be 10C or more colder than the input.

Evaporative cooler
(Image from wikipedia.org)

As I understand, it's the evaporation of the water that causes the air to be cooled. And, as I take it, it's the heat from air at the input being absorbed by the water and causing a phase change that cools it.

What if the water is atomized by something such as an ultrasonic humidifier? Ultrasonic humidifiers use a "speaker" of sorts to vibrate water into a vapor. I can't find any mention of ultrasonic humidifiers being used to cool a room. At first it seemed to me that they would not cool the air, as water was simply atomized (instead of the heat from the air going in to a phase change).
But thinking about this another way: The atomized water particles would mostly evaporate in the air, which should thus cool it, right?

Do ultrasonic humidifiers cool air to the same degree that pad-based evaporative coolers do? (Assuming similar water volume used). If not, can ultrasonic humidifiers be used in a more elaborate system to cool the air?

  • $\begingroup$ The main driver for evaporation is the density difference between water vapor at the surface and vapor far away from the surface. If you make a mist of water, it would impede this density difference, resulting in less evaporation. I therefore think pad-based evaporators are more effective. $\endgroup$ May 28, 2019 at 22:21
  • $\begingroup$ en.wikipedia.org/wiki/Evaporative_cooler , has even ancient roots $\endgroup$
    – anna v
    May 29, 2019 at 4:19

1 Answer 1


What you propose has been in use for many years. It is called an air washer, which uses a pump to spray water through nozzles into a fine mist which is mixed with the incoming air stream and then passed through a trap that catches any unevaporated water droplets before the cooled air is distributed.

  • 1
    $\begingroup$ Interesting. But do they lower the temperature in a similar capacity as the pad-style evaporative coolers? I'm not seeing air washers marketed as temperature reducing. $\endgroup$
    – Bort
    May 29, 2019 at 2:04
  • $\begingroup$ they do. however, the pad types do not require high pressure pumps and have no nozzles to get clogged with minerals. $\endgroup$ May 29, 2019 at 15:38

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