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lolito_fr · 01-03-2004, 09:20 AM

Been thinking about this. I see your point BigBen2k, about the equivalent hydraulic diameter being too small. Makes sense actually, seeing as the (predominant?) friction losses arise from contact between the fluid and the pipe walls. (hydraulic diameter is defined as four times the ratio of cross section to wetted surface)

However, the equivalent hydraulic diameter is only used to determine the pipe losses. In this case, the "pipe" is the length of insertion of the needle in the cup. At roughly 1.5mm, this constitutes a very short pipe, IMO. (even if the hydraulic diameter is only 1.8-1.25=0.55mm)
I haven't worked out the theoretical losses (any volunteers?), but I should imagine that they would be considerably lower than the head loss due to the nozzles themselves.
Therefore I don’t believe that the head loss due to this "restriction" would impact the overall flow rate a great deal and I can't see how this is suddenly going to stop the jet from impacting the base of the cup

So yes, in theory maybe the cups are too narrow. In practice though, I wouldn’t like to use smaller diameter jets (my fingers are too big!?).
The other option would be to increase the cup diameter. (dumb technical considerations include drill size here…) This would reduce the density of the nozzle array, and the velocity of the water rising out of the cups would suffer, reducing the secondary cooling effects.

Edit: Impact of extra losses due to cups, and other obstructions on the water return path was determined (approximately) here :
http://forums.procooling.com/vbb/sho...4&postcount=20

01-03-2004, 09:20 AM	#51
lolito_fr Cooling Savant Join Date: Dec 2003 Location: France Posts: 291	Been thinking about this. I see your point BigBen2k, about the equivalent hydraulic diameter being too small. Makes sense actually, seeing as the (predominant?) friction losses arise from contact between the fluid and the pipe walls. (hydraulic diameter is defined as four times the ratio of cross section to wetted surface) However, the equivalent hydraulic diameter is only used to determine the pipe losses. In this case, the "pipe" is the length of insertion of the needle in the cup. At roughly 1.5mm, this constitutes a very short pipe, IMO. (even if the hydraulic diameter is only 1.8-1.25=0.55mm) I haven't worked out the theoretical losses (any volunteers?), but I should imagine that they would be considerably lower than the head loss due to the nozzles themselves. Therefore I don’t believe that the head loss due to this "restriction" would impact the overall flow rate a great deal and I can't see how this is suddenly going to stop the jet from impacting the base of the cup So yes, in theory maybe the cups are too narrow. In practice though, I wouldn’t like to use smaller diameter jets (my fingers are too big!?). The other option would be to increase the cup diameter. (dumb technical considerations include drill size here…) This would reduce the density of the nozzle array, and the velocity of the water rising out of the cups would suffer, reducing the secondary cooling effects. Edit: Impact of extra losses due to cups, and other obstructions on the water return path was determined (approximately) here : http://forums.procooling.com/vbb/sho...4&postcount=20 Last edited by lolito_fr; 01-03-2004 at 01:48 PM.