[bobkoure]

Originally Posted by joeyek

Did you mean the deep shroud is more effective in a fans' pushing setup than the pulling one?

Yes, that's what I observed.

When the factor of the rebounded air by the rad is taken into account, the situation could be different.

I only have a few data points. Absolutely, the situation could be different if you are doing something different than I was - for instance, if you have a more-powerful fan, although I suspect (as in guess) that it would actually be more pronounced in this case.

More space can avoid the dead zone of the axial fan, but at the same time the force is weaker.

I don't presume to understand exactly what the air movement is doing. It'd be interesting to get an array of different rads, fans, and clear shrouds and use smoke to see what was actually happening. Failing that kind of data I don't know what's going on in there - and I'd suspect you don't either.

Like aircooling, a weak fan cannt blowing the air deep enough to the hottest base of a heatsink.

This is actually quite a different situation and one I do know a bit about as I did a certain amount of race bike work in the 70's. Air cooling a heat sink is very like air-cooled motor cooling in that you are trying to force airflow down between fins and then out to one side or the other. Directed pressure is important here as you otherwise end up with a standing wave (higher pressure, if you will) at the root of the fin and air only penetrates to the point where the two forces balance. (And yes, we did testing with smoke - come to think of it, there were some mirrors involved as well to allow simultaneous filming of several areas, so it really was "smoke and mirrors" ) Anyway, without appropriate ducting (including ducting an exit path to a low pressure area) longer, tighter fins, often could mean a hotter motor. When I got to talking to one of my aviation friends about this, he explained that this was very old news, so it's not like we discovered any new principles or anything.