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Modding Water Cooling Radiator Shoot-Out

Discussion in 'Article Discussion' started by Guest-16, 23 May 2008.

  1. DannyDirect

    DannyDirect New Member

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    Hello guys, great article. Anyhow I have a small question.

    I have the Lian Li PC-P80 case and have now got water cooling, where is the best place to put the radiator in such a case?
     
  2. E.E.L. Ambiense

    E.E.L. Ambiense Acrylic Heretic

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    Isn't it obvious? :hehe:

    Depending on how much cooling power you require, and if you wanted it internally, you can mount a single 120mm rad on the exhaust, or single, dual or triple 120mm rad up in front. Or get even more creative.
     
  3. Djayness

    Djayness phwupupupup

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    I would have liked to have seen if a fan shroud made any difference at all to temps, in addition to this, if pull or push is better and what about fans on both sides of the radiator.


    Please! These things I must know!
     
  4. E.E.L. Ambiense

    E.E.L. Ambiense Acrylic Heretic

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    It's been documented before many times on many forums. Fan shrouds may make a difference of a degree or so; nothing drastic. Push or pull is quite debatable (and is, daily!); in my personal experience on all the WCed rigs I've done for others or myself, pull is better for more silence and efficiency. Having fans on both sides of the rad only maintains pressure; again, not a drastic difference in temps if at all for the added noise.

    The truth is, try it out for yourself, and whatever works for you, works for you!
     
  5. EmJay

    EmJay New Member

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    Thanks for the review! Wish I had the money to tinker with water cooling... maybe some day.
     
  6. Marquee

    Marquee Mac Pro Modder

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    I have not fully read a review for a while. But this review really hocked me and kept me reading word for till the end. Great review I really enjoyed it.
     
  7. Hamish

    Hamish New Member

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    go lower, some of us like silence ;)

    i run 3 of these on my PA120.3 hooked up to a rheobus
    i run them at about 5v at night, they're barely spinning but its still enough to keep a 3.5ghz yorkfield and a 3870 plenty cool :)
    <3 thermochill :D
     
  8. Orlix

    Orlix New Member

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    I really liked this review. I had not seen one on rads and I have been looking for one for a while.

    From what I gathered the rads in the tests are supposed to be the best. Could you throw in a Thermaltake TMG in there? It would be interesting to see if the cheaper rads would hold their ground... for example a system with TMG1 and TMG2 (120+240 rad) vs any 240 on the review. The Big water 745 is an all in one and costs €100 and includes the TMGs. Maybe is it worth it for a beginner to start with this and add a good CPU block and work the way up from there as experience and funding increases?

    I have been interested in water cooling, but it has always been too expensive :S
     
  9. pdf27

    pdf27 New Member

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    NO!!!!!!
    Trying to do this starts to break the laws of thermodynamics all over the place (not to mention ones like conservation of energy!). The rule

    power = mass flow rate x Cp x temperature difference​

    will always apply no matter how much heat you're dumping into the system. Since Cp is a physical constant (1010 J/kg for dry air) and mass flow rate is set by your pump or fan (depending on whether you're looking at the water side or air side - the formula applies to both) that means temperature difference must be directly proportional to power *.

    If you have two systems, one of which can dissipate 75W and the other 95W for an identical set of mass flows and temperatures, then for that same mass flow/temperature combination the temperature difference between the water and atmospheric temperature will be 27% higher at 25W heat load for the 75W radiator. If you aren't seeing this then you have problems with your temperature measurement system.
    It is entirely possible that this temperature difference may not be a problem in practice, but you can't just wave your hands and pretend it doesn't exist.

    * Note: I'm assuming we're operating at the low temperatures of a typical watercooling setup here - as the temperature rises radiation cooling becomes a lot more important, and this is proportional to (temperature)^4.
     
  10. Da Dego

    Da Dego Brett Thomas

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    Hey PDF27,

    You are DEAD on that this is the proper thermodynamic theory. The problem comes in theory != practice. In reality, the closer you get to the outer thermal dissipation, the more that the difference you explained becomes apparent.

    It's much like a power supply. Theoretically, at 80% load and 20% load there really shouldn't be a difference in efficiency. However, that's patently untrue, because the basic theory does not account for current leak, minimums held by the capacitors, and various other inefficiencies that come from an imperfect system.

    If you test a 240mm radiator and a 360mm radiator both with X heat where X is less than about 40% of load, you'll find they're fairly constant even though the 360mm rad can dissipate considerably more heat with the same fan speed and flow rate. That's cause you'll only be able to get the temperature down to an equilibrium, which at load there will be X amount of heat being dumped in so you can dissipate Y amount of it. It's the part where theory doesn't quite mesh with practice, and if you have a small enough spare system you can see that the same applies to a 120 vs. a 240mm rad.

    Basically, yes, a 95w dissipating system should be more efficient across the board than a 75w dissipating system, no matter what the input power. However, in practice there's a point where things just stay cool. :) If both systems can keep the fluid at ambient, nothing is going to make the 360mm radiator cool any "better" than the 240mm. You'll just be able to volt down your fans more and still maintain the same temperature.

    Where the theory breaks off, basically, is the allowance for ambient temps. The fluid simply cannot go below that in any passive system. So if you can cool 75W of heat, the system requires about 33% of its overall ability to hit ambient, whereas with 95W it only needs 26%. It is 27% more EFFICIENT at reaching the SAME temperature. Bottom line, your temps don't change until the system is under enough load that one system can't dissipate it all and the other still can, which is what I was trying to illustrate.

    Don't forget, we're also talking about CPU temps - which are an equilibrium between CPU and block and fluid. So if fluid is being kept at roughly ambient (which it can't go lower) then CPU temps just plain don't notice a difference. :) Which is the point I'm trying to get to. :D
     
  11. pdf27

    pdf27 New Member

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    Neither system will ever be able to keep the fluid at ambient unless they have a heat pump fitted. For there to be any heat transfer, there must be a temperature difference - for it to be otherwise (absent Rankine's Daemon or similar) is a violation of the Zeroth Law of Thermodynamics.
    I'm quite willing to accept that the performance difference between two radiators is too small to measure with the equipment you're currently using. I sometimes do thermal testing for a living, and know exactly how hard it is to get decent data (and how bad manufacturer's data often is).

    You what? If the 360mm radiator can use a lower mass flow of air per fan for the same air-water temperature difference then by definition it is cooling better and hence for the same mass flow of air per fan will keep the water cooler (closer to the ambient air temperature).

    This is the one that I really object to. If the max thermal dissipations are defined for the same mass flows of air and water, and the same temperature difference between air and water inlets then they simply cannot reach the same temperature - that would be a violation of the zeroth law again.

    Now we're getting somewhere. If you're going by CPU diode temperatures then the chances of you noticing temperature differences of the magnitude we're dealing with here are minute.
    Incidentally, how long did you run each test before you took temperatures?
     
  12. K20

    K20 New Member

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    Anyway PDF27, thanks for opening up an interesting discussion about something which had confused me. What is your Penguin writing?
     
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