airspirit,
What you are missing is that convection in a radiator is nothing more than the integral of h(x) * delta-T(x) * dA. Nowhere does time enter into the calculation of heat transfer.
Some time ago there was a post about water being in the radiator for ten seconds versus a total loop cycle time of 60 seconds. Gee, so the water is in the radiator 1/6 of the time. So what happens if the loop gets longer (ignoring added flow resistance for the moment)? Now the water is in the radiator 1/12 of the time. Does this change the radiator performance? No.
The simple fact is that a radiator has to pass heat from fluid to solid, through the solid, and from solid to air. It is entirely possible that the fluid to solid portion of this is the dominant effect. If so, increasing the water velocity (and consequently DECREASING the time the water spends in the radiator) will result in greater heat transfer.
By your argument we could slow our flow to a crawl in the radiator and all would be wonderful. Yeah, that's right, let the water sit in there for a couple of days. It'll be good and cool by the time it gets out. Yes, slower flow will result in higher fluid to air delta-T but at what cost? If the radiator is capable of getting down to within a couple degrees of ambient, then the only way to increase delta-T is to increase the inlet temperature to the radiator. Is this what you want?
I am not arguing that a radiator is more "efficient" with a higher delta-T. I am merely telling you that more efficient radiator performance does not necessarily equal lower chip temperatures. In fact more efficient radiator operation requires higher chip temperatures. Efficiency within the radiator gets progressively worse the nearer the fluid temperature gets to the air temperature.
If none of this makes sense to you, there is no point in my continuing. I simply don't have the time to rehash a semester of basic heat transfer everytime someone doesn't get it. What I would ask is that people don't rely merely on instinct alone in these matters. Instinct can be a wonderful thing, but there's no way of knowing when your instinct is wrong. This is why they offer classes on stuff, including heat transfer.
And don't forget what I've said all along. Parallel should do better for the vast majority of water coolers given the typical radiators that we use. But to say it's better 100% of the time would be inaccurate.
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