Cheap cool mist humidifier: I put in hot water in the reservoir. The output is a cool mist. Why isn't it a hot or warm mist?

[JEDI]

I have a $10 cool mist humidifier that holds a 1/2 gallon.
It's cold so i thought putting hot tap water in the reservoir would produce a hot or warm mist.
Nope.. the mist is cool.

Why is the mist cool when the water is hot?

 

[fralexandr]

The main contributor is likely pressure. the same reason a breath feels warm, but air blowing out of a pinched/pursed mouth feels cool.

Depending on how far from the humidifier you test the temperature, another significant factor could be heat loss due to surface area on contact with air.

 

[Dulanic]

It's the fact its a mist. Once the mist hits the air, it almost instantly becomes room temperature. You're giving the "water" more surface area to change temperature very quickly. In addition, evaporation has a "cooling" effect on your skin.

 

[BoomerD]

It's magic. It's a "cool mist humidifier." Inside the tubing, even boiling hot water would be instantly transformed into COOL MIST.

Everyone knows this.

 

[Paperdoc]

This actually is a result of Thermodynamics and the CHANGE of STATE for the water. Liquid water has a Thermal Capacity of 1 Calorie per gram per Celsius degree - in fact, that's really the basic definition of the Calorie, a unit for heat measurement. So to take one gram of liquid water from 0° C (freezing point) up to 100° C (Boiling point) will take 100 Calories. But at that point it is STILL liquid. THEN comes the change of STATE - converting the liquid into gas (steam) and this happens with NO change in temperature. But for the same one gram that still requires a huge 540 Calories to do that! Water molecules have a huge affinity for other water molecules, so they "prefer" to bond together, and it takes that much added energy to break that bond and free them to leave the liquid. AFTER that change of state, addition of MORE heat (IF the steam gas in confined to a closed container) can raise the GAS temperature by about 1 Celsius degree for every Calorie added.

So here is how this all plays out with a Cool Mist Humidifier. No matter what the temperature of the water in the unit starts out at, it is broken up into tiny droplets (mist) of LIQUID water and spread out into the air in a non-confined space. Each tiny droplet flying though the air will accept heat energy from the air molecules that bump into it, raising the energy of the water molecules near the surface of the droplet AND cooling the air molecules slightly. IF some of those droplets happen to hit your skin, they will happily gobble up energy from YOU, getting slightly warmer to match your skin temperature. You will feel that as a cooling of your skin because it gave away some of its heat energy. But most of the droplets will spread around your room, gathering heat from the air. As they do that, more and more of the molecules on the surface of the droplets achieve enough energy to escape from that liquid state and race off into the air as free molecules of water gas. NOTE that these droplets do NOT get hotter - they just lose some of their molecules as they escape into the gaseous state. This has the result also of lowering the temperature of the air just slightly. You do NOT see that as STEAM because the individual molecules are extremely small and separate. Even if a few of them happen to run into you, they amount of heat in a FEW gaseous water molecules is so extremely tiny that you do NOT experience any significant rise in your skin temperature. This is the same as how you feel in not-too-dry normal room air. In fact, that is exactly the situation you are in - a room with low to moderate Humidity in the air. Once the individual molecues of water are in the gas state they exchange energy with other air molecules and become the same temperature as other molecules, but they do not convert back to water in LIQUID state unless something removes all that gaseous-state energy to change to the liquid state.

A more extreme version of this process is the basis of what some call a "Swamp Cooler". This is a device that uses a fan to force a LOT of the room air through a fabric or mesh that is saturated with liquid water. The water grabs a lot of heat energy from the air to try to evaporate it into gaseous water, and that cools down the air and the room. Such devices are a cheap way to cool a room if the air is already very dry. But they don't work well if your air is already very humid, because much less water gas can be absorbed into the high-humidity air, so less cooling of the air is accomplished.

 

[JEDI]

It's magic. It's a "cool mist humidifier." Inside the tubing, even boiling hot water would be instantly transformed into COOL MIST.

Everyone knows this.

Not everyone is a crane operator who got hit on the head and turned Homer Simpson smart