SOLUTION TO: Warm Air

Alright, I was in class thinking today, we all know (or many of us) that when air expands...it cools drasticly.
EDIT: think canned air coming out...makes the air near freezing (just like phase change...but this isn't that extreme)
This can be shown by making a small hole w/ ur lips...and blowing air out, even though the air inside your mouth is HOT...if u put ur hand up to ur lips 1-2 inches away..it's very cool.

SO HERES MY IDEA!

Take a fan...and make a very steep conversion duct for it.

SEE IMAGE BELOW (couldn't get the text drawing to space right)

OK now this isn't exactly the steepness of how the duct would be...but it's a good idea of it. SO what happens...is even if you have warm air coming IN, you get quite cool air coming OUT

Application 1

Now I know there is a big disadvantage...much smaller space for air to come of of...and lower CFM....BUT I think if something like this can be applied to say a small HS, or intake fan (chipset...video card....another sort of fan intake) it can prove good if not great results. Remember, even if warm air is being intaken, the air coming out will be cool...so this can even be applied INTERNALLY (air from inside case hitting something side case...instead of it coming from outside case)


Application 2

What could be done...for those a lil more "needy", you could take a large window fan (those square box fans...~mid tower size) and make a large duct, same principle...for the CPU HS...therefore the exaust of the fan would be ~120mm or 92mm (perfect for HS obviously) and the air would be very cool....even w/ warm intake air

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So what does everyone think? I'm hoping to test this w/ a case fan of mine...making a makeshift duct...and testing to see if unducted or ducted air is cooler.

Sry for the image size...don't normally do this stuff.

Sounds great!

I'd like to know how this turns out.

I think that this will not be as good as a normal fan. The pure CFM of a normal fan is going to more than make up for this I think. Also, I am not sure of the math of this but where does the heat go?

squasher said:

I think that this will not be as good as a normal fan. The pure CFM of a normal fan is going to more than make up for this I think. Also, I am not sure of the math of this but where does the heat go?

Click to expand...

Good point w/ the higher CFM, more heat...vs. lower CFM, less heat.

Heat is just motion of atoms isn't it? (MAY BE WRONG...I'm in Highschool so yeah)

Yeah but the air would move over slower. Like let's say you put a small fan over your northbridge, and have a duct thing like that. Air that comes out may be "cooler", but it'll come out at a smaller rate, which'll make the hot air inside the duct be "trapped" and thus warming up the northbridge even more.

Also, the little hole of cool air isn't enough to cool much of the surroundings. So even if you have a duct around your case fan, the output of air will be pretty low, I highly doubt that little amount of "cooler" air will do much. It's better to probably better to just do it simple and have all air in your case moving in one direction, ie. front to back or back to front.

Great idea though.

jcw122 said:

Heat is just motion of atoms isn't it?

Click to expand...

To be correct: Heat is the energy of atoms.
But the energy causes motion.

i think the scale is wrong.
ever played with canned air? thats decompression-style cooling...

you could use an air compressor and a tiny tiny nozzle, but tool compressors tend to heat the air....
but then the other guy has a point too, with compression and heat... think diesel engines...

skotti said:

To be correct: Heat is the energy of atoms.
But the energy causes motion.

Click to expand...

Gotcha, thanks for the clarification.

Heat is the average kinetic energy of the atoms.

orionlion82 said:

i think the scale is wrong.
ever played with canned air? thats decompression-style cooling...

you could use an air compressor and a tiny tiny nozzle, but tool compressors tend to heat the air....
but then the other guy has a point too, with compression and heat... think diesel engines...

Click to expand...

What do u mean u think the scale is wrong? BTW that pic isn't supposed to be dead accurate for the ratios and sizing needed.

and I dunno bout deisel engines so please explain

And yeah, I know canned air does that...that would have been a better example but o well.

i was talking higher - much higher pressures than a fan, and smaller, much smaller then a hole in cardboard would be sensible. like a pinhole...

diesel engines work by compressing air, till it gets HOT then spraying fuel in. then you get BOOM and rotation...no spark pluge required.

orionlion82 said:

i was talking higher - much higher pressures than a fan, and smaller, much smaller then a hole in cardboard would be sensible. like a pinhole...

diesel engines work by compressing air, till it gets HOT then spraying fuel in. then you get BOOM and rotation...no spark pluge required.

Click to expand...

First part, I dunno...try using ur mouth as I suggested before...even not blowing too hard it works...but I'm no scientist so I may be wrong...that's why I'm gonna test it w/ case fan of mine sometime.

2nd part...I had no idea diesels work like that...that's really intriguing...and a good point also, I wonder how it gets hot from compression.

orionlion82 said:

i was talking higher - much higher pressures than a fan, and smaller, much smaller then a hole in cardboard would be sensible. like a pinhole...

diesel engines work by compressing air, till it gets HOT then spraying fuel in. then you get BOOM and rotation...no spark pluge required.

Click to expand...

First part, I dunno...try using ur mouth as I suggested before...even not blowing too hard it works...but I'm no scientist so I may be wrong...that's why I'm gonna test it w/ case fan of mine sometime.

2nd part...I had no idea diesels work like that...that's really intriguing...and a good point also, EXCEPT the air coming out will not be compressed....it will be decompressing (cooling)

This is talking about expanding the air though, orion, which cools it down. The problem I can see with this is that the small end of the duct would have to be too far away to give a useful expansion effect. a pump would work but then you have to make sure the pump itself isnt heating the air up and then get cooling for the pump and by that point you might as well have got WC.

You'll have noticable airflow drop, especially if this thing is used with heatsink. It's due to duct turbulence and pressure that's needed to make air go between fins of heatsink. Such adapters ararely work as they should, but it seems that the longer adapter is, the better airflow it allows.

I can tell you that blowing warm air through a duct with a fan will not actually cool the air. If anything this will warm it slightly. It may feel cool on your hand, but thats because the air is mixing with the ambient air and conducting heat away from your hand. Try blowing 2 inches away from a thermometer and see what happens.

Look at the specifications of the max pressure of your fans. It is not anything near what it would take to create any density change. If you force air through a smaller duct, you will get higher velocities, not compressed air.

This one of the few times I will say don't even try it.


Now suppose you get a dozen 150mm fans lined up like a turbine and force the air through your duct, what will happen? You will get hot air. Yes compressing air makes it hot. What happens when it decompresses back to normal atmospheric pressure? It goes back to the inlet temperature. Nothing is gained at all.

When you say you feel cold air on your hand when you blow through a small hole the air itself isn't actually colder than blowing through a larger hole. The cooling you are feeling is the cooling of the air removing heat through forced convection (moving air) on your hand not a cooler air coming out of your mouth.

Forced convection has many parameters that will need to be considered. 2 of the main ones are velocity of the air and the surface area of the object (you hand).

When you close your lips you increase the velocity and decrease the area on your hand thus removing more heat.

This is a simple explination of what i belive you were feeling on your hand. There are certainly alot more parameters to be considered in forced convection.

Ven0m said:

You'll have noticable airflow drop, especially if this thing is used with heatsink. It's due to duct turbulence and pressure that's needed to make air go between fins of heatsink. Such adapters ararely work as they should, but it seems that the longer adapter is, the better airflow it allows.

Click to expand...

True. Great idea and I love it, but you would need ALLOT of static pressure to get this high velocity air thing to work. I tried something similar with 4 stacked box fans and a long trashbag duct to my heatsink. It failed miserably. Not even 4 stacked box fans had enough static pressure, then again box fans aren't noted very well for having good pressure.

rusauced said:

When you say you feel cold air on your hand when you blow through a small hole the air itself isn't actually colder than blowing through a larger hole. The cooling you are feeling is the cooling of the air removing heat through forced convection (moving air) on your hand not a cooler air coming out of your mouth.

Forced convection has many parameters that will need to be considered. 2 of the main ones are velocity of the air and the surface area of the object (you hand).

When you close your lips you increase the velocity and decrease the area on your hand thus removing more heat.

This is a simple explination of what i belive you were feeling on your hand. There are certainly alot more parameters to be considered in forced convection.

Click to expand...

Agreed, but it should have some sort of an effect. Having the air move through the heatsink at a higher velocity has the same effect of blowing it on your hand. The more air is compressed, in theory, it should get HOTTER. But in this case, that effect is minimal and the benefits of having higher velocity could actually be greater than just using a standard fan. Who knows, I say try it and see! I have tried tons of stuff. I have probably gone through about 5 pounds of cardboard just doing little cooling mods.