Why Does Misting Fan Cool Air?

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Discussion Overview

The discussion revolves around the cooling effect of misting fans, specifically focusing on the principles of evaporative cooling and the energy dynamics involved when water evaporates into the air. Participants explore the relationship between the energy levels of water in different states and the resulting temperature changes in the surrounding air.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes evaporative cooling as the process where evaporating water takes energy from its surroundings, leaving both the water and the air cooler.
  • Another participant argues that in a misting fan, the mist evaporates and takes energy from the air, yet questions why the air feels cooler despite the overall energy level of the system remaining the same.
  • A later reply suggests that while the energy of liquid water and water vapor may be similar, the temperature decreases due to the increase in potential energy of water molecules when they evaporate, which comes at the expense of the kinetic energy of surrounding air.
  • One participant challenges the notion of "same entropy," indicating that this statement is incorrect.
  • Another participant raises a question about whether water vapor is cooler than the liquid water it evaporates from, and discusses the change in kinetic energy during the transition from liquid to vapor.
  • A participant explains that the energy required to separate water molecules into vapor form reduces the kinetic energy of surrounding air molecules, leading to a decrease in air temperature.

Areas of Agreement / Disagreement

Participants express differing views on the energy dynamics of evaporative cooling and the relationship between temperature and energy states of water in liquid and vapor forms. The discussion remains unresolved, with multiple competing explanations presented.

Contextual Notes

There are limitations in the assumptions made about energy levels and entropy, as well as the definitions of temperature and kinetic energy in the context of phase changes. These aspects remain open for further clarification.

hacillunation
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So, as far as I know evaporative cooling is when the top layer of a material (lets say water) evaporates- taking energy with it leaving the rest of the material cooler. Also leaving the air, which transported some heat to it, cooler.

But in a misting fan, the mist evaporates, takes energy from the air, and then- it just remains there.
So the overall energy level of the system should be the same, no? Same entlapy, same entropy.

Then why when this mixture of air and evaporated water droplets blows- even that you suposedly get a system with the same energy level as before, it cools you down?

Thx.
 
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hacillunation said:
So, as far as I know evaporative cooling is when the top layer of a material (lets say water) evaporates- taking energy with it leaving the rest of the material cooler. Also leaving the air, which transported some heat to it, cooler.

But in a misting fan, the mist evaporates, takes energy from the air, and then- it just remains there.
So the overall energy level of the system should be the same, no? Same entlapy, same entropy.

Then why when this mixture of air and evaporated water droplets blows- even that you suposedly get a system with the same energy level as before, it cools you down?

Thx.
The energy liquid water may have the same as the energy of the water vapour but the temperature has decreased. The water mixing with the air results in an increase in potential energy of the water molecules. This potential energy comes at the expense of the kinetic energy of the surrounding air. So the temperature of the surrounding air decreases.

The potential energy of water molecules in vapour comes from the fact that water molecules are polar - in liquid and solid form they stick together and it takes energy to separate them.

AM
 
Thank you for the succint answer.

That raises another question then...
So, youre saying that water vapor is cooler than the water it escapes from?
But when water evaporates, doen't it increase its particle speed?
 
The mist is liquid not vapor. That's why it is visible.

Also when you said "same entropy", the statement is wrong.
 
hacillunation said:
Thank you for the succint answer.

That raises another question then...
So, youre saying that water vapor is cooler than the water it escapes from?
But when water evaporates, doen't it increase its particle speed?
It is a bit complicated because the water molecules in liquid form are stuck together and have vibrational kinetic energy. When they separate into individual molecules (vaporization) they no longer vibrate against each other but have translational kinetic energy. The average translational kinetic energy of those water molecules can be less than the original liquid water but because they are not stuck to other water molecules they stay in vapour form. The energy required to separate the molecules is at the expense of the kinetic energy of the surrounding air molecules. So the temperature of the air decreases as more water is vaporized.

AM
 

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