Where Bill is getting at here is matching the PQ curve of the fan to the air-flow vs efficiency curve of a radiator.
If people looked at the thread earlier where someone asked about putting two radiators in air-flow series and I munched the math, it was pretty clear that this was a bad idea. Two radiators in air-flow series is essentially the same as a single double-thickness radiator.
The issue was that the fan was unable to sustain adequate air-flow through the thicker radiators to the point where the extra core rows weren't doing much of anything at all (in fact they were contributing almost nothing).
With a piss-weak fan (and most axial fans are piss-weak) something like a large orificed area single-row cored heater-core, or a tranmission oil style cooler, will be a better match.
2-row heater-cores are designed to typically be matched up with their blower-fans that are pushing 1+ inH2O of air-pressure, which is an easy thing to do for an automotive heater-core blower where at full chop they will easily do ~3inH2O of air-pressure at quite staggering flow rates (in comparison to similarly sized axial fans). Heater-core blowers also tend to sit somewhere where the bulk of their real noise is muffled very heavily, so they don't sound quite as annoying as they really are.
Given a certain sized orifice area and a good bit of nouse, one could easily design a more efficient solution than what we presently have, and still be using fairly quiet fans and getting very good cooling performance. Of course brute-force will always win, but we're talking quiet and efficient here.
Current heater-cores, by my estimate, are perhaps 3-4x more restrictive than what is ideal for a quiet low-pressure fan to work really well with. Ideally we want our fan to be pushing something like 75-80% of its rated air-flow, instead of the 30-40% that we see today with today's dual-row cores. Of course with a more "open" core, the efficiency for air-flow will drop away, but when air-flows are fairly low, this is less significant than one would think.
Something like a 15x15cm cored area heater-core, that was single-row (~ 1/2" to 5/8" thick), with a nice 10-15 degree angled shroud leading into the 12cm low-speed fan that is pulling, and had a fin density around 10-12FPI with ~8mm or so spacing between the tubes would likely perform quite a deal better than a BIX when matched with the same fan.
As you stick on more and more powerful fans, the BIX will come into its own over our low-speed-fan optimised core, but then you're paying for it with noise.
The lessons are there given all the testing that Bill has published in the past for those who are prepared to munch the math.
|