fan location for control panel .

Discussion in 'General Electronics Chat' started by t00t, May 26, 2015.

  1. t00t

    Thread Starter Member

    Jan 22, 2015
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    Hi guys, I have a control panel which has a small transformer inside it . I have put a fan in the top left hand corner of the control panel to cool the transformer .

    The question is where do I put the air outlet for air to flow out . Should I put it at the top right corner ? Or should I put it at the bottom right corner ?

    This is because hot air flows up right ? So I was thinking maybe I should put the air outlet at the top right just opposite of my inlet air fan .

    The transformer is somewhere is the middle of the control panel .

    Thank you .
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    IMO..Have fan exhaust out and intake in the furthest opposite lower corner.. (filter over the intake and sized properly..which is typically larger than the fan exhaust..50%)
     
    Last edited: May 26, 2015
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    In many enclosures the fan brings air in through a filter, (Positive pressure) which ensures clean cool air entering, also much depends on the type of environment.
    Max.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Its best to place heat producers and fans down low with exhaust on top..
    Then fan blowing in if you have cool/dry/clean air outside the enclosure.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I generally follow the opposite the common practice of heat producers at the top, Transformers, power supplies etc.
    Heat producers down low result in heating everything above them.
    Max.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    It depends on the types of components, other restrictions in the air path, etc., but I generally agree with Max about placements.

    As for that whole "hot air rises" thing - no. Convection pressure is tiny compared to just about any fan on the planet.

    If you have control over *all* of the air openings in the cabinet, then you orient the fan as an exhaust fan. Doing this keeps the heat of the fan motor out of the equipment cabinet, but there also is a potential for the fan to suck in dirt through every tiny hole or gap. Generally speaking fans usually are set up as intakes for positive pressure ventilation. Among other things, this gives you more control over dust and dirt entering the cabinet because you know where to put the filter.

    ak
     
  7. wayneh

    Expert

    Sep 9, 2010
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    True, but you don't want to actively fight convection with extra fan speed. Working with convection gives a gain, however small.

    The important thing is that your heat producer isn't sitting in an un-ventilated corner, hidden from air flow.
     
  8. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    It seems counter-intuitive but, on tall enclosures, fans at the top blowing in with exhaust vents at the bottom often provides the most effective cooling. There are two advantages with this approach 1) the turbulence created by forcing air in distributes cool air throughout the enclosure, and 2) the top of the enclosure does not become significantly hotter than the bottom. Convection has no influence in the matter.

    If the heat is exhausted at the top of the enclosure (which, on the face of it seems logical), the equipment in this location will always run relatively hot.
     
  9. AnalogKid

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    Did some rack mount air-cooled gear for a Class I clean room, 6 kW per chassis. The room provided 2000 CFM of cold air per rack out of ceiling ducts, down through the racks to an evacuated elevated floor. Despite the size, one of the easiest thermal jobs because the room did all the work.

    ak
     
  10. MaxHeadRoom

    Expert

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    On one installation where an enclosure had to be kept sealed but cooled, it did not warrant a AC unit, so I constructed a heat exchanger from a 4ft length of sealed Finned HS mounted on the top exterior of the cabinet with a fan inside the cabinet blowing into the HS and exhausting back into the cabinet, it worked well.
    Max.
     
  11. AnalogKid

    Distinguished Member

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    For fully sealed projects, we get better fin density and heatsink performance with folded fin arrays bonded with thermally-conducting epoxy to both sides of an aluminum plate. We have two fin-folders on speed dial.

    ak
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    Convection is irrelevant when you use forced air cooling.

    Just have an intake and an exhaust (one of which has the fan) and the bit that gets hot somewhere between the two.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    That's often true, but only when there is much more air forced, specifically when the Reynolds number squared is much greater than the Grashof number. If the Re^2 is roughly equal to or less than Gr, convection cannot be ignored.

    In other words, with a small fan that doubles airflow relative to natural convection, the natural component matters. In a computer where the fans move >100X what would happen by natural convection, the natural component is nearly irrelevant.

    The TS said "small transformer", which tells us little about the power dissipation required except that it's likely ~10W, give or take an order of magnitude. We are also told he has a fan, with no specs. We don't know what the air path looks like or how it might be restricted at the inlet or outlet. I think blanket suggestions without the facts are prone to go one assumption too far.
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
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    A famous quote from the legendary R.J. Mitchell; "if it looks right - it'll probably fly".

    His Spitfire fighter flane certainly looked right, and it certainly did fly.
     
  15. t00t

    Thread Starter Member

    Jan 22, 2015
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    1
    Thank guys , I have put it at the bottom right corner and it seems cool enough .

    Thanks so much for the help :)
     
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