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coppice:

--- Quote from: TimFox on October 29, 2023, 09:55:03 pm ---Although dictionaries may differ on this, I was taught that "steam" was the visible material that included water vapor and droplets, as seen in a teakettle or steam locomotive, but that "water vapor" was invisible.
Humidity, however, can contain both water vapor and water droplets.

--- End quote ---
The usual terms, like your find in books about steam engines and turbines, are wet steam and dry steam. Wet steam. which is visible. is a mix of gas and fine droplets. When there are no droplets left its called dry steam, and is a true gas.

TimFox:
Besides dry (saturated) and wet (unsaturated, the most common type) steam, steam-plant engineering also defines superheated steam and supercritical water.
https://www2.tlv.com/steam-info/steam-theory/steam-basics/types-of-steam

Nominal Animal:

--- Quote from: helius on October 29, 2023, 09:48:58 pm ---
--- Quote from: Nominal Animal on October 29, 2023, 09:34:43 pm ---Ultrasonic aerosolizers/nebulizers/atomizers/etc. do not convert the liquid to vapor (gas): there is no phase transition.  They only mechanically chop the liquid up into tiny little droplets.  There is basically no temperature change, and only very little energy spent in the mechanical chopping action.

--- End quote ---
Ultimately there must be a phase transition, because it increases the humidity of the air in the environment.
--- End quote ---
Don't forget: even if you have absolutely dry air and expose liquid water, you'll get some water vapor in the air.  See vapour pressure of vapour.  The ambient air, water vapor, and water (both in vessels and in droplets) are in (well, tend towards) thermodynamic equilibrium.  (Analogously, you do get some water vapour from warm water even if it is not boiling hot.)

The energy for these state transitions are provided by the temperature of both the water and the ambient air.
This happens independently of the aerosolizer/nebulizer/atomizer/etc., with the tiny droplets having huge surface area compared to one liquid blob of water.
You can get the same humidity effect by having running water in the same room.

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