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Thread: fans

  1. #1
    Low Bitrate LudeAtude's Avatar
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    fans

    is it better to have them push air in or pull air out.
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  2. #2
    Maximum Bitrate eCarô's Avatar
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    No. It's better to have them pull air in, and push air out.

  3. #3
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    yes what he said.. if you only can use one.. i'd say pull the car out as close to your cpu as you can get
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    Maximum Bitrate binary.h4x's Avatar
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    Yup, by only having an exhaust fan, you are creating a lower pressure in the case than outside, thus running cooler. If the pressure was greater in the case than outside of it, then the inside of your case would turn into an oven.
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  5. #5
    Maximum Bitrate eCarô's Avatar
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    Quote Originally Posted by binary.h4x
    Yup, by only having an exhaust fan, you are creating a lower pressure in the case than outside, thus running cooler. If the pressure was greater in the case than outside of it, then the inside of your case would turn into an oven.
    Can you explain this to us laymen?

  6. #6
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    Personally I like it running pulling air in. Dust is less of an issue since you can put a filter on it that way. As long as you have a good airflow going, it won't make that much of a difference.

  7. #7
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    ohh boy....the infamous "push/pull" question...

    I have seen this raised on several PC related forums. Some people have strong opinions both ways. Every time I have read about someone actually TESTING a theory, it seems to make little to no difference.

    I personally *believe* that actual airflow is more important than the push/pull question. Your typical PC case is far from airtight, so it's not going to develop much of a pressure differential, even IF you had several 120mm fans all pushing (or pulling) in the same direction.

    Some fans get better CFMs in a 'push' configuration, while others are better in a 'pull'. The manufacturer might be able to tell you if you knew where to look, but most likely you'll just have to try it out both ways and see.

    Of course, I'm assuming that you only want to have 1 or 2 fans (as in most car PC applications). It can get really complicated with more fans.

    If someone knows of any comprehensive testing with reasonable techniques and data, I'd love to see it!

  8. #8
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    Quote Originally Posted by LudeAtude
    is it better to have them push air in or pull air out.
    Both.

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  9. #9
    Maximum Bitrate eCarô's Avatar
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    Quote Originally Posted by eCarô
    No. It's better to have them pull air in, and push air out.
    Maybe it's better if they are sucking air out, or cramming air in. Or maybe blowing air thru.

  10. #10
    FLAC samc's Avatar
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    what I do is always put 1 for in, 1 for out. but I've never really thought about air flow..etc.. so I could be way off.
    Mine needs to be updated.

  11. #11
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    Quote Originally Posted by samc
    what I do is always put 1 for in, 1 for out. but I've never really thought about air flow..etc.. so I could be way off.
    This is correct because the CPU fan needs air to cool the CPU. On a desktop PC airflow is key, please note that it has been documented(i dont want to find it) that it is possible to have too many fans in a case. Again for a desktop PC you want both intake and exhaust, intake on the bottom front and exhaust on the top rear(hot air rises).

    In a CarPC many of the same practicies can apply. However I think that for a one fan case it is better to have it blow air in and across the components then suck air out because again it needs the air to transfer the heat too, the less air there is the less heat it can take away. However that being said in most cases its going to not make ANY noticible difference.
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  12. #12
    Maximum Bitrate eCarô's Avatar
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    Quote Originally Posted by eCarô
    Maybe it's better if they are sucking air out, or cramming air in. Or maybe blowing air thru.
    Oooh. Try jamming the air all up in the casizzle.

  13. #13
    Maximum Bitrate binary.h4x's Avatar
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    Quote Originally Posted by eCarô
    Can you explain this to us laymen?
    I can try
    Ok, my proof for this is called the Pressure Law(easy enough ). The Pressure Law states that pressure is directly proportional to temperature. P=kT . k is a constant, its just so your equations work right, but dont affect the proportion. So taking from that equation, if P increases, then T will increase, and if P decreases then T will decrease.

    When you have one fan blowing in, yes, you get more air in, but when it tries to get out of all those little cracks in your case, the air will start to pressurize. But with one fan pulling air out, the fan will suck air in through all those same cracks, but yes, the air draw is slow, but results in a lower pressure in your case.

    I hope that helped

    BTW you CAN have too many fans. Once you have too many, the air will form a "freeway" of sorts for the fresh cool air. And the cool air will just stay on this "freeway" until its out of the case, and what turns out happening is that pockets of hot air will be trapped against your motherboard, cards, or devices because the hot air can "cross" the freeway.
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  14. #14
    Maximum Bitrate eCarô's Avatar
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    Quote Originally Posted by binary.h4x
    I can try
    Ok, my proof for this is called the Pressure Law(easy enough ). The Pressure Law states that pressure is directly proportional to temperature. P=kT . k is a constant, its just so your equations work right, but dont affect the proportion. So taking from that equation, if P increases, then T will increase, and if P decreases then T will decrease.

    When you have one fan blowing in, yes, you get more air in, but when it tries to get out of all those little cracks in your case, the air will start to pressurize. But with one fan pulling air out, the fan will suck air in through all those same cracks, but yes, the air draw is slow, but results in a lower pressure in your case.

    I hope that helped
    Well, that sounds pretty good. But once you do the math, you'l realize that the Pressure Law is insignificant.

    First of all, case fans are made to move air. They are not designed to compress air. They simply could not increase the pressure by much (much less than 1 psi). So the amount of heat that you created while pressurizing the air in your case wouldn't be much. And after you've compressed it, you've made all your heat. The heat is not continuously created while you hold the pressure, it's a one shot deal. So, if anything you are warming your rig quicker when you first turn it on (pressurizing air), but then you are only compressing whatever air it takes to replace what escapes out of the "cracks" in your case.

    Plus I was kind of assuming that anyone that only has one fan, would also have an intake or exhaust vent on the other side of the case. Actually, I should have said this "first of all" because it make the debate about pressure meaningless.

    BTW you CAN have too many fans. Once you have too many, the air will form a "freeway" of sorts for the fresh cool air. And the cool air will just stay on this "freeway" until its out of the case, and what turns out happening is that pockets of hot air will be trapped against your motherboard, cards, or devices because the hot air can "cross" the freeway.
    If you have designed in (on purpose or by accident) an "air freeway" for the air to flow thru your case, without going across the MB, RAM, HD, etc., reducing the airflow will reduce it to an "air footpath" (or whatever). The location of the fans is just as important as the amount of air they are moving.

    BTW, when I can think of a simple way to explain it, I'll set you guys straight on the push/pull thing. Maybe I can just throw out a hint or two, and someone can run with it.

    How does the fan know if it is pushing air into your case, or pulling it out? If it doesn't know, how can it reduce the airflow for one of the directions?

    Why don't fan manufacturer's list two different airflows (push and pull)?

  15. #15
    Maximum Bitrate tom2112's Avatar
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    You guys have GOT to be kidding me. A fan that is specifically better at pushing than pulling? Yeah right.

    As far as the fan is concerned, pushing and pulling are the same thing. That's like saying that the fan will perform better if it is facing north. Due to the very nature of a fan, it will always PUSH and PULL. A fan always pushes air out the front and pulls it in the back. That's what the angled spinning blades do. The air displaced by the spinning blades is then replaced by the vacuum created by the displacement of the air that was pushed, thereby pulling in more air to be displaced. It is a matter of our perspective (not the fan's) which we call it - push or pull.
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