Quote:
Originally posted by ozzy7750
ok, i need a little bit more clarification on this 'sucking out' issue.
is the ratio i need to work out the outlet area:inlet area, or hydraulic diameter outlet:hydraulic diameter inlet?
if it is the latter, how do i calculate the hydraulic diameter of the outlet?
i have 3.5mm cups, with 3/32 tubes (2.38mm od, 1.67mm id)
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I had to dig pretty deep, to get some answers to some questions, including that one.
As has been pointed out, the hydraulic diameter can be calculated using the formulae for an annular duct, as found here:
http://www.lmnoeng.com/PipeDuct.htm
What it boils down to, is that the hydraulic diameter of the annular duct is equal to the gap between the outside of the jet tube, and the cup wall.
So... if that gap is smaller than the jet tube's ID, then the flow speed is higher as the coolant exits the cup, and that's the "sucking" effect that I'm talking about, which would significantly reduce the jet effect.
As for the distance of the jet's outlet, from the cup's bottom, I believe that there was a reference made to where it needs to be somewhere between 3 to 5 times the jet's ID. I could be off though.
[edit] I found it.
Quote:
By Cathar
Jets develop fully over about a 4d distance. Less than this and what tends to occur is a concentrated "mash" of turbulent water striking the base.
Also, while the jet travelling down will lose a small amount of power due to the distance travelled, it also becomes more turbulent (or so it is hypothesised in scientific papers) and this leads to greater thermal efficiency. Again, search through google. There are many studies of the jet distance vs efficiency effect, and every single scientific paper I read found that getting less than 4d in height results in a performance drop off, hitting a peak plateau between 4-5d (different papers differ on the exact best distance) and then dropping off after that.
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Also, some references here:
http://forums.procooling.com/vbb/sho...=&postid=81386
[/edit]
JD: I found a pic of the baseplate to the "
Cascade", and I'm reposting it here, because I needed to show you something:
There's a fine balance in the gap, between the cups. If it's too small, then there's not enough heat rravelling up the fin (aka gap). If the gap is too large, then the mass is too large, and accumulates heat. Cathar describes it, in his thread:
http://forums.procooling.com/vbb/sho...&threadid=6666