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Fan direction

Discussion in 'Electronic Design' started by D Yuniskis, Dec 27, 2010.

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  1. D Yuniskis

    D Yuniskis Guest


    I rarely design anything that needs active cooling
    so when it comes to fans, my approach is largely
    inconsistent (read that as: "varies with day of week
    and phase of moon!).

    When it comes to *case* fans ("CPU"s, external disk
    drives, printers, etc.) I tend to opt to push air
    *into* the case drawing it through a filter, first
    (i.e., pulling air *out* usually results in drawing
    all sorts of dust and crud into the case from
    the area surrounding the device -- since most inlets
    are not filtered).

    Of course, that depends on what's inside the case
    "behind" the fan. As well as the roles of any other
    fans in the case.

    I'm adding a couple of (tiny) fans to some external
    disk enclosures and found myself facing this question,
    yet again. :-/

    So, can anyone offer a nice mnemonic / *rule* that I
    can just commit to memory and never have to waste time
    thinking about crap like this again?? :)

  2. mike

    mike Guest

    You're underthinking it.
    Fans are all about getting air where you want it.
    You need to control the airflow in and out to make sure
    the hot things get cooled.
    A general rule of thumb#1 is "plugged filters don't cool nuthin'".
    Rule of thumb#2 is "All filters get plugged".

  3. When one has a supply in a case that is to be mounted within a case,
    sometimes one will see the other circumstance.

    Typically, however, one wants positive pressure to keep the dust build
    up down and more controllably located.
  4. Push the air in, and as Paul pointed out, Laminar air flow for best
    Or Impingement cooling for pin fin heat sinks, see

    Also, inlet area should be 1/2 the outlet area.

  5. Cesar Rabak

    Cesar Rabak Guest

    Em 27/12/2010 23:21, Martin Riddle escreveu:
    Where in the Earth does this really happen? In order to decrease the
    air to heat sink resistance *turbulent* air flow must be insured.
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