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Since87 I suspect that what Bill was saying was along the lines of 'Don't expect to get more than half an axial fan's free air flowrate spec when using it with a 2" heatercore.' (I don't really know though since I don't know what article you are referring to.)
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More or less, mostly less. Apparently some of the popular 'silent' fans really fall off badly. The 38mm 120's were the best of the bunch, but even they weren't that good. Alot of what I got was from reading his graphs that showed airflow at certain static pressures, and attempting to map that back onto the fan PQ charts.
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I agree that stacking heatercores is not a good way to go, mainly because the fan noise required to get good performance is too high. Even if the air flowrate only drops to 85% (of single HC flowrate) with two heatercores stacked, (and reasonably quiet fans) the air will be heated so much by the first HC that the second HC won't be able to dump much heat.
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Exactly, the second core won't dump much heat, and I'm not even convinced that the amount of heat dumped by the second core would make up for the overall loss of cooling from reduced airflow. It would depend on just what the exact setup was.
The other issue is that the goal of cooling to ambient is an asymptotic curve, and increasing cooling comes at astronomically increasing cost. A 2-342 sized core has so much cooling capacity potential to start with that I would not expect much additional cooling from any further reasonable increase in rad size. I decided to go with a heater core very early on in my planning, so I haven't paid a great deal of attention to the commercial WC rad options. However, I've gathered the impression that a 2-342 has 2-4x the surface of most popular commercial rads, lower flow resistance, and better thermal transfer ability, so it seems like I already have far more than average performance potential.
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It's certainly possible to get improved performance with stacked HC's, just not worth the noise to me.
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I agree. I also suspect that the space penalty associated with stacking and getting improved performance is more than most people would anticipate.
I believe that it is possible to get reasonable flow through a 2" core by mounting fans on just the suction side. I also think that if one wants acceptable performance and tolerable noise, a duct is vital. The duct specs I've seen say that a fan needs at least 1.5" of free air space on each side to get optimal flow and reduced noise. This means that a 38mm (or 1.5") thick fan will require a minimum 4.5" of clear space for good airflow, 6.5" if one includes the core.
IMHO, to get reasonable flow through a 4" core a push-pull fan setup is indicated. If one assumed 4.5" on each side, plus the core, then it would take 13" of free space to fit the rad! That's more space than most cases have... Even with my monster sized cube case, I had a real squeeze to get just my 2" core mounted with the fans on ducts and preserving the space it needs.
Gooserider