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Originally Posted by Cathar
Larger jets with more fully developed convectional activity at the base of the cup comes at the expense of larger cups. The further the walls move away from the jet (in a ratio sense) results in a increase of the ratio of "conduction distance to convectional surface area". i.e. the net convectional efficiency may get improved at the base of the cup, but we lose out double time on the walls as the water velocity there will be slower, and the heat has to move further up the walls to engage the same convectional area.
So again there's the balance. The principle of the Cascade somewhat sacrifices maximum convectional efficiency at the base of the cup, but attempts to make up for this by placing the jets at a distance that maximises the Nusselt number in the stagnation region immediately under the jet. This (smallish) loss then gets made up in the cup walls. The smaller the cups (and the smaller the jets as a result) the less distance the heat needs to travel up the cup walls. The smaller the cups in comparison to the jets (to a point) the greater the walled surface area that gets engaged for the same vertical distance from the CPU, and the greater the rate of convection due to increased water velocity (which decreases with radial distance from the jet).
That's the basics of the "constrained jet behavior" that I've been looking at. It does have some similarities to free-jet behavior, but overall I feel that they are actually quite different in terms of what configurations work best for either.
Still, this won't stop me from trying this second, more easy to machine prototype based upon more standard free-jet principles, but while using slightly larger jets, this actually leads to a significantly more restrictive block due to significantly less jets (which is not desirable except for those with well-above-average pumps), and indeed to shrink the free-jet design down to a point where the walls are effectively working in a similar fashion to the Cascade approach, the jets are now even smaller than they would have been on the Cascade, leading to an super-restrictive block.
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I can't believe it. Your actually getting close. Keep thinking. There is away and it has to do with the cups. Think about making this "secondary impingement effect" last longer within the cup. I would venture to say, the cups in your cascade are less than optimal but your limited in design choices being that small. This is something I'v been working on for the past year and a half trying to get it right with my limited machining , money(kids gotta eat). Your WWW is what got me thinking about a pure impingement block. But as you stated in your post, being restrictive has been the problem for me. The performance is shocking though paired with a strong pump. There is one more step beyond that can aid convection even more that was discussed between us last year. Making it practical is the challenge but it does work well.