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  • SharkyForums.Com - Print: need help with fan air flow physics in case!

    need help with fan air flow physics in case!
    By lokiju October 16, 2001, 10:21 PM

    ok, will this setup work, or will it produce more problems than what it's worth? i have 3 fans exhausting the back, one on the power supply, one under it on the wall, and one as a pci card item. i have a fan intake on the bottom front of the case, and will be adding a 5.25 bay fan pretty soon as another front intake. my question is, if i add a blowhole fan modded on the side panel intaking onto the hsf, and a blowhole exhaust on top, will this be productive, or is there too many crossing air currents to be any good? i need a good physicist...or even a meteorologist!

    By hobbes2112 October 17, 2001, 01:44 AM

    Skip the blowhole on the top...

    fans over the pci area blowing in are good, front fan is really good...back fans are essential.

    By azngqvo October 17, 2001, 03:04 AM

    hmm...i'm no physicist, but i heard that it is best to have the same rate of airflow entering and exiting your cpu...this way there will be less stress on your fans and less noise.

    So, if you were going to add an exhaust on top and an intake on the side, i would suggest adding another intake on the side probably somewhere over the pci slots.

    Personally, I like the exhaust on the top because it made my cpu's temp lowered.

    By LouIII October 17, 2001, 03:07 AM

    If you can get a good front-to-back airflow, you'll be in business. A PSU with a good exhaust fan, and another exhaust fan at the rear is all you should need (maybe a small front fan, but I heed AMD's advice about avoiding them). Of course, a good hsf on your CPU is essential. Rounded IDE cables will open things up to improve airflow. If the interior of your case is free of obstructions and you have the above-mentioned fans, but your CPU is still running too hot, it's time to crank down the overclocking a few notches.

    By GB_Cobber October 17, 2001, 01:33 PM

    Ya dont need a physicist to know that when you put an inlet fan with no diffuser in the case,the air from the fan will interupt the designed air path of the case.

    Some of the hot air that would ussually get sucked out the nearest outlet will more likely be blown around inside the case in the turbulance caused by the inlet.
    This results in a higher overall case tempurature and actually very little more air volume passing through the case than having just the exhausts.

    Two fans in series do little more than aid each other and can not possibley increase air volume by more than a few%
    On the other hand, two fans in parrallel can deliver twice the volume if the inlet holes are big enough.
    So in this sence,inlet fans dont do much.

    From another point of view,Axial fans,due to their high blade surface area/back preasure ratio are much better at pulling air rather than pushing it.EI: a fan with a restriction to airflow in front of it will move more air than if that same restriction were behind it.
    Scroll fans have a much lower Blade surface area to backpreasure ratio and are much better for pushing air though a positive preassue environment,but in this case they would just stir the air up more.
    Scroll fans would make exellent cooler fans.
    Just duct them onto the cooler through a rubber boot from the outside of the case.that way you can guarrenty only cold air gets to you CPU.

    So just cut out all the finger guards,take out the inlet fans,make front inlet holes bigger,Put another exhaust in the top if you like and I'll put money on your case temp coming down.

    By shasha October 17, 2001, 09:06 PM

    I have to agree about the intake fans being a little over rated. I have tried them with several rigs and found that a good intake hole and strong exhaust works best and is less noisey. The secret is to make sure that there are no leaks for the exhaust fan to "cheat" with, i.e. little vent holes in the back. Think of it as a vacuum, the tighter the seal, the better the suction. Make the case draw cool air from the intake and force the hot air out.

    I just built a new 1.4G Athlon and it was a space heater. I used the case, unmodded and added a couple of decent fans. An 80mm intake and a 120mm exhaust. Almost 50C at idle. I removed the intake fan, about 48C. I opened up the intake and exhaust holes, taped off all air leaks anywhere and its 41-42C idle. A lot quieter than a lot of other rigs as well. I am not done, but I am headed in the right direction

    By lokiju October 17, 2001, 10:03 PM

    wait shasha, you said that you have NO fans now except for the power supply? just that and your heat sink fan? that doesn't make sense! maybe i misunderstood? you can't be at those low temps by taking fans away?

    By carpenoctem23 October 17, 2001, 10:52 PM

    If I were to have a good air flow setup, I would want two 80mm intake in the front of the case, one 120mm intake blow hole on the side over the CPU, one 92mm exhaust beneath the PSU, and one 92mm exhaust blow hole on the top. It would be loud though...

    By LouIII October 17, 2001, 11:28 PM

    quote:Originally posted by shasha:
    I have to agree about the intake fans being a little over rated. I have tried them with several rigs and found that a good intake hole and strong exhaust works best and is less noisey. The secret is to make sure that there are no leaks for the exhaust fan to "cheat" with, i.e. little vent holes in the back...
    I agree about the counterproductivity of front fans. On AMD's Web site, they discuss fan use and say that front fans often confuse the situation. I don't have the URL, but if you can find it, you'll see that they make a lot of sense.

    I think the fan thing got big when Lian Li and other manufacturers of hairy-chested cases started selling their cases with two front fans. It seems that all these fans are primarily about the affectation of high performance and are therefore aesthetic (at the expense of airflow, and needlessly drawing power from the PSU). If you want to do something for the looks of a system, you can add a window and light, clean up the interior wiring, etc. And you'd still have money left for a new game or a couple of CD's.

    By shasha October 18, 2001, 01:27 AM

    NO, if it was just the PSU fan, it would probably be a glob of melted plastic and metal. I have the 120mm fan in there, I just got some serious airflow form opening up the hole and throwing a wire gril over it, rather than the stamped grill of the case.

    By GB_Cobber October 18, 2001, 10:33 AM

    Thanks Shasha. Ive been waiting for someone to agree with me on this issue.I know it works but Its seems almost impossible to tell people their front fans are heating up their system without a long and drawn out explaination.Just like telling 64Mb MX owners they got ripped.
    I cant do all the work around here by myself

    By lokiju October 18, 2001, 05:59 PM

    yeah, i think i may drill some big holes in the front to help with airflow, to add to that small slot the case companies think willl draw in air from. that should triple the intake at least.


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