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I have a Li-Po battery charger that comes with its own cooling fan which, like most of the cooling fans, blows hot air out of the charger to cool the charger down.

I have a spare fan and I was wondering whether it should blow ambient air towards the charger or draw the hot air away from it?

It will be an external fan outside the casing of the charger. Charger itself is roughly the size of a normal Wi-Fi Adapter and the auxiliary fan has ben taken from a computer casing.

I know it does not really make much of a difference but was just curious as to which setup will perform better in order to dissipate the heat generated a little better.

Supplementary question:

If I had 2 extra fans would it be better if one was blowing air towards the charger and other was drawing away or both should be doing the same thing?

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migrated from physics.stackexchange.com Oct 24 '16 at 13:53

This question came from our site for active researchers, academics and students of physics.

  • $\begingroup$ Would Engineering be a better home for this question? $\endgroup$ – rob Oct 24 '16 at 13:50
  • $\begingroup$ @Rob It certainly appears so now that I have visited that to assess. Should I ask a new question there and close this one or it can be moved from here? $\endgroup$ – Hanky Panky Oct 24 '16 at 13:52
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The air coming out of the fan will be highly turbulent, wheras the air being sucked into the fan is less so. Hence blowing at the target will increase heat transfer. On the other hand, if you are looking at a casing, a fan blowing into the case will also blow dust into the case. A fan blowing out of the case will typically suck in less dust, as the fluid velocity at the opening of the case will typically be lower than directly next to the fan.

Finally, the choice of two fans in serial (one blowing, one sucking) or parallel (both blowing or sucking) depends on what you are trying to achieve (i.e. the system curve of the device to be cooled). Two fans in series will increase the total pressure you can build up, and is a good idea if you need to overcome a high pressure loss. Two fans in parallel will increase your flow rate if the pressure loss of your system is relatively low.

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I think it would depend on the enclosure. In an open environment, it would be better to blow cool air at the target. For closed cases, it seems more common to blow hot air out if there are not fans in both directions.

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  • $\begingroup$ Thanks!. If i had two fans would it be better if one was blowing and other was drawing air on the other side? Its a standard room environment. This room's temperature is around 25 C usually $\endgroup$ – Hanky Panky Oct 24 '16 at 13:46
  • $\begingroup$ That makes sense to me intuitively, but if it's really important, you should get a thermometer and test different configurations. $\endgroup$ – EL_DON Oct 24 '16 at 20:25
  • $\begingroup$ The charger itself has an internal thermometer and it displays the temperature on screen. For routine temperatures like 27-28C the fans the configuration is not really making a difference but i will have to increase the Amps to get to upper 40's range to see if the fans make a difference. Not that they are important but just for some knowledge :) $\endgroup$ – Hanky Panky Oct 25 '16 at 7:22
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There is a big difference in the resulting flow during blowing and suction. Blowing creates a reasonably well directed jet of air, while suction pulls air from all around. Therefore blowing is better if you want to cool a small region or object (which is your case), because you can direct the flow there.

In the case of two fans, I am not sure what the best configuration would be. Again since the object to be cooled is small and in the open, it makes sense to blow on them. Perhaps keeping the fans side by side and blowing them in the same direction is a good idea, but I can't be sure.

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  • $\begingroup$ Thanks! That makes sense and is the first thing i tried and it seems to work fine $\endgroup$ – Hanky Panky Oct 25 '16 at 5:45

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