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Fan cooling , qualitative assessment

Discussion in 'Electronic Design' started by N Cook, Aug 23, 2007.

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  1. N Cook

    N Cook Guest

    Without having to learn about pneumatics
    For an existing product with a 12V fan with ducted area across fan ie minus
    the central motor area, of about 6 square inches and current consumption of
    ..2 amps.
    As it stands this fan would seem to waste a lot of power and increase in
    noise, blowing through a set of 14 slots in the case of total air-vented
    area 1.5 sq ins.
    If most of this grill section was totally cut away , fared off, and an
    external wire grill added would that allow the use of .1 amp fan for
    more, or less air throughput and a bonus of less audible noise.
  2. John Larkin

    John Larkin Guest

    That all makes sense. One ROT is that the grille area should be at
    least as big as the fan area, so 4:1 will seriously restrict flow.

    Extech makes a nice, inexpensive air flow + temperature meter that
    lets you quantify things like this. Air flow can be counter-intuitive,
    and mere mortals can't afford to purchase or learn worthwhild airflow
    simulation software.

  3. Jim Thompson

    Jim Thompson Guest

    A really sharp M.E. that I worked with at GenRad from '77 to '87 had a
    smoke generator that he used to examine airflow.

    He would build a mock-up of the equipment with foam board, place
    cardboard obstacles shaped like components, add fans and observe the

    Then move things around and/or add baffles to shape the airflow.

    ...Jim Thompson
  4. John Larkin

    John Larkin Guest

    Incense, joss sticks, work fine.
    Right. A wood/plastic/cardboard/duct tape mockup can be done in an
    hour or two and is enormously instructive. You can also clamp some of
    those metal-case power resistors onto candidate heat sinks, crank in
    some power, and see what their operating temps will really be, and get
    an idea of how noisy the mess will be.

    It's fun to test cardcages with fan trays, or PC enclosures. You'll
    often get dead spots directly above fan trays, or air flowing
    leisurely in the opposite direction to where high-velocity flow was
    expected. Air is funky stuff, and there's an incredible amount of
    really bad thermal designs, or rather "designs", around.

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