Huh

[telophase]

So I've got that little travel humidifier running in my office. I also have a fan on, because the water vapor mostly falls down to the ground and makes me feel like it's just getting the carpet wet (it vanishes into the air a foot away from the humidifier; it's probably fine), but with teh fan on I get a vague sense that it's blowing into the air. :D

Something I noticed though - the fan is turned away from me because my hair blowing around annoys the fool out of me. The humidifier is offset from it, not in the direct airstream but next to it, and the water vapor coming from the thing gets pulled sideways and back before getting into the airstream. Huh.

Can anyone tell me the physics of this? I assume there's an area of low pressure alongside the stream of air from the fan, which pulls the water vapor in?



The top two pics are with the fan on, one from the front and one from the top where you can better see the water vapor being pulled into the airstream. The last picture is one when the fan is not on, so you can see what the vapor normally does.



P.S. The stains on the desk are water stains, caused before I realized that some amount of the water vapor condensed on the unit and ran down to puddle underneath it. Hence the paper towel it's sitting on now. Although since I started using the fan with it, I haven't had that problem.

Comments

[lnhammer]

Not alongside: in the stream of air from the fan. In general, a moving stream of compressible fluid such as air will be at a lower pressure than the surrounding fluid, and will pull in fluid from its surroundings as a result.

You can demonstrate this by taking two pieces of paper and holding them by the top an inch or two apart, and then blowing down between them: the papers are drawn together, because of the low pressure your breath creates.

---L.

[lnhammer]

(signed, former physics TA who had fun demonstrating this and other consequences in lab sections)

[telophase]

:) Thanks!

[plasticchimera.livejournal.com]

Yeah, moving air (or any substance, works with water too) has a lower pressure than still air. It's how airplanes fly.

[telophase.livejournal.com]

Fly, little humidifer! Fly!

[lady-noremon.livejournal.com]

:D

[inkblot14.livejournal.com]

I remember this from Mr. Wizard. Bernoulli's Principle. It's the same basic idea behind perfume atomizers. The fast moving air across the opening of the mister draws the water vapor out into the stream and helps disperse it.

[telophase.livejournal.com]

Thanks!

[tprjones.livejournal.com]

I don't think Bernoulli's principle would specifically account of the rearwards motion of the mist. I would guess the reason it goes back towards the fan instead of just straight sideways into the air stream probably has to do with the airflow on the side of the fan being gently backwards, as the rear of the fan draws air into it from along the wall.

disclaimer: I am not a physicist, but I play on on the internet.