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Thread: air cooling with a venturi

  1. #1
    jeallen0's Avatar
    jeallen0 is offline Member
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    ok i had this idea. my pop was telling me bout his days in the army in germany and how they had these aircons that cooled portable hospitals and other portable buildings, called a venturi. all they did was to blow air through a tunnel that was tappered at the end down to a slightly smaller hole speeding up the air and cooling it at the same time. i was thinking how the same technoledgy could be applied to a, say, HS with a 12cm fan or some other fan that is able to move ALOT of air. so heres a diagram that i drew up im bout 2 min.
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  2. #2
    amd_man2005's Avatar
    amd_man2005 is offline Senior Member
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    Theoritically, it sounds good, but i think you would have to have a very powerful fan, and since it flows right out fo the fins, id think it would be harder to get it very much compressed. Also it seems that if ya did that, air would only blow onto the center of the heatsink, or where the naroow area is located, possibly lessening cooling capabilities. I could be wrong though, just how it seems to me

  3. #3
    Darthtanion's Avatar
    Darthtanion is offline Senior Member
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    Sorry, but I wouldn't put too much faith in this idea. Let me explain why:

    - You speak of a 12cm fan to be used in this cooling methodology. Since there aren't any heatsinks using this large a frame, you're going to have to perform this narrowing down of the airflow and also reduce the bottom mouth of the constricting device. This will leave you in the same boat as others who have made reducers for HSF combinations. This narrowing of the mouth causes a considerable amount of turbulence. This causes the forced air to lose its direction and become ineffective airflow... not cooling for squat.

    - When your dad was using the constricting airflow idea, it was most likely not having any sort of blocking device in front of the airflow. In the case of your cooling idea, you have the heatsink sitting right at the exit of the (hopefully) more rapidly moving air. Again, you are going to have more turbulence causing ineffective airflow.

    Sorry, but I just don't see it working unless you can come up with some means to combat the turbulence that you would be creating.
    Old age and treachery will overcome youth and skill
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  4. #4
    Tomi_s is offline Member
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    I agree with Darthtanion... :rolleyes: :rolleyes: :)

  5. #5
    sleet01 is offline Junior Member
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    Venturii have been used for a number of cooling applications through the years for one good reason: they cause the flow rate to increase _at_ the choke point. Unfortunately, they do not increase the total flow rate: Assuming your inlet and outlet are the same size, total in will be equal to (actually, because of friction, a little bit higher than) total out.

    Basically, as air flows into the choke point (technically, this point is the venturi), its pressure increases. This causes it to heat up due to compression, but it _also_ causes its flow rate to increase (since outflow = inflow).

    So here's what you do: Say you want to cool your CPU with a venturi. One way to do it would be to cut a large (120mm) hole in the bottom of your case. Make a venturi that scales down to an 80mm choke point; mount your fan in that choke point. Build the whole thing so that the fan mounts right below your heatsink (assuming you've got a vertical mount mobo). Then make a vent through the top of your case, et voila. This would really only increase cooling efficiency slightly, as venturii reduce turbulence and you would be drawing cooler air from the bottom of the case.

    Alternatively, you could mount a 120mm fan at the bottom; this would push more air. According to the exhaustive cooling guide <a href=http://www.7volts.com/heatguide.htm><font color=blue>here,</font></a> the total gain from doubling CFM is only around 30%-40% more cooling, though, so you might want to think twice about that setup.

    Another alternative is probably closest to the one your grandfather talked about: use the venturi to increase cooling on a water-cooling radiator. This is how a lot of older Army equipment is set up. This would be handy, say, for mounting a venturi/radiator outside of the computer, like in an auto stereo bass 'bazooka'. An added benefit is that is allows the use of large, low-RPM fans at lower noise than smaller, higher-speed fans.

    The original uses of venturi have generally been replaced with compressor-driven cooling tech, but they still have the advantage of being simpler and less costly to manufacture. Current uses of venturi include aircraft (pitot tubes, ducted external radiators), some large ventilation fans, and pressure-reduction pipe couplings.

    Here's rather detailed <a href=http://www.efunda.com/formulae/fluids/venturi_flowmeter.cfm><font color=blue>flowmeter calculator</font></a>, but you'll need to look up most of the inputs yourself.

    Ta!
    --,-@
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  6. #6
    Frost's Avatar
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    Also, another proble to deal with is the "swirl" affect of air comming out of a fan. I have a case fan on the side of the computer directly above the CPU. Left on it's own it would swirl air all over inside the case and not get it to where I wanted it (the CPU HS/FAN). So I put a Burger King drink cup onto the inside of the van, and the cup is cut off to the point that it misses the top of the HS Fan on the CPU when I slide my side back on. The advantage is that it now directs the outside of the computer case air, directly to the CPU fan to be picked up and used by it.

    See: 500$ for an ATI 9700 Pro No Kiddin'

    I used to use a McDnoalds cup, but it was plain paper, and this Burger King cup is insulative Stryrofoam.:D Both are free.. just wash the cup when done.. LOL

    The ducting on the outside to draw in air that is as cold as possible, has been the ultimate idea. I've dropped my BARTON running overclocked to a mere 16 degrees C with this setup. Makes everything else inside the case cold as well. Also brings in nice fresh air inside the room and warms it 'slightly' before we get it. *S*
    "Former Nebraskan... fix it with bailin' wire."
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  7. #7
    pestilence is offline Junior Member
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    wow i must of drank too much and heard a refrence to pitot tubes on aircraft in a tweaktown form .. damn and i thought i could get away from work talk on here .. ( i am a F-15 crew chief ) well i will drink somemore and hope to forget i saw that .. :cheers:

    :thumbs do =

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  8. #8
    sleet01 is offline Junior Member
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    Yeah, well, my _computer_ sucks so I have to attempt to make up for it with a broad array of total bullcrap :)

    Next up, the problem of vortex formation and laminar flow with standard heatsink/fan combos... not :)

    :cheers: Cheers!

    __

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  9. #9
    Frost's Avatar
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    pestilence: Can you e-mail me a larger picture of that Avitar? I really like it!

    All things considered, remember.. the cooler the air.. the better the cooling. Now that's a bright idea isn't it??:D

    They should also make CPU heat sinks that have the clamp on either side of the middle and save the middle for the best part of heat dispersion. Now.. they have the slot there for the darn clamp.

    jenefarm@direcway.com for a picture.;)

    BTW 1 X 60mm intake fan directly over the CPU.
    1 X 60 mm fan on the HS for CPU
    2 X 90 mm fans on the powersuply (stock- standard)
    1 X 90 mm exhaust fan on the side of the case.

    5 fans total. about 3 fans too many at times!! LOL
    "Former Nebraskan... fix it with bailin' wire."
    Vern

    SYSTEM:
    MULTIBOOT -> Windows XP, ME and Mandrake 9.2 Linux

    Abit KV8-MAX3
    AMD 64 Clawhammer 3200+

    Kingston Hyper X 1GB DDR CAS 2 set agressively!
    Custom fan cooler for CPU
    USB 2.0 all onboard no card
    GeForce4 MX440 AGP 64MB DDR Video Card
    10/100 NIC 3Com onboard
    Leadtek TV 2000 XP video input card PCI
    160 GB ATA 133 Maxtor HD 8MB buffer
    350 W Enermax PS
    Toshiba DVD ROM drive
    Yamaha CD Burner
    Pioneer DVR-105 DVD Burner
    Logitec optical mouse on adapter
    DW 6000 Satellite 2-Way internet connection

    jenefarm@direcway.com

  10. #10
    pestilence is offline Junior Member
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    full size of my AV .. its there for your right clicking pleasure :spam:
    WIN XP SP1 + updates

    K8T800 MSI NEO FIS2R
    AMD 64 3200+
    SAPPHIRE 9800 PRO 128MB
    1x512 CORSAIR XMS 3200

    WD SATA 36.7GB RAPTOR
    WD ATA 80GB (STORAGE)

    ENERMAX EG651P-VE (FMA) N 550W PS
    +3.3=36A, +5=36A, +12=36A

    Xaser II case with 5 fans
    OEM CPU and video card fans
    viewsonic 22'' CRT

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