Cooling Fan direction question

[wintersdawn 178]

I've fitted a heatsink with cooling fan to the motor of my rc but am not sure which is the best way round to fit the fan regarding air flow.

At the moment I have the air generated by the fan facing down onto the motor but wondered if it should be the other way round so the hot air from the motor is sucked into the fan and pumped out above and away from the motor?  Cheers for any advice.

 

[Willy iine 18842]

What's important is having fresh air circulating around the heatsink (and motor) to make it efficient.  Depending on how the air is routed, fan could be set up either way.

[djmcnz 755]

It is true that it could go either way but you want to remove hot air, not cool hot air (which is far less efficient). As long as cool air can be drawn in from somewhere you should set it to extract hot air. Trying to force hot air out by blowing cold air in is also really inefficient.

[Juggular 5181]

From computer building videos, I learned a lot of interesting stuff.  I think you have it right.  

As it turns out, pushing air into it cools better.  Like you, I had thought, "heat rises, so pulling heat away from it is better."  But No.  You want to "push" air directly onto the hot thing.  

It made sense only after thinking about it for a while. 

Say that you are really hot.  If you have a big fan, would you want air blown at you, or would you try to have the heat taken away from you by sitting very close to the backside of the fan?  You just get more air molecules move around you if the fan's air hits you directly.  

Even in an enclosed box, pusher is better than puller, that's why most computers have a pusher fan on their CPU instead of a puller fan.  (Below blue fan pushes air onto the fins)  GPU fans also push air onto the chips.   

Electric motors with internal fans?  They often blow air to the motor so the air would sweep across the motor's cooling fins.   

The only 2 exceptions I can think of are motors for drills and central air.  Drill motors have a fan inside them. It blows air away. Because the motor is encased in a tube (plastic body of the drill), the cool air has to get sucked in from the front slit, pass over the motor and gets blown out to the side.  

 

Hot air rises.  If small amount of air gets moved like CPU fans, blowing down onto the chip works better.  But big central air pulls enough hot air to fill a soccer stadium in 24 hours. If all that heat were generated at once, it could lift up a hot air balloon.  

So if the AC fan were pushing down, that would go against the rising force. It would also re-circulate hot air around it, making the AC hotter and hotter.  

When that much air has to pass through the condenser, it's better to go with the rising flow.  By pulling, the AC will always get cooler air from the ground and hot air would be shot 50 feet up to the sky.  

So, aside from fans in drill motors and central ACs, you want to blow at the hot thing.  (That includes coffee.  If you have to drink hot coffee fast, blowing on it would be more efficient than trying to suck the steam away, even if your breath is hotter than ambient temperature.)   

 

[wintersdawn 178]

Thanks all for the replies and Juggular for the detailed reply, I understand it better now and am glad I don't have to change the fan around 😊