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Unread 02-20-2004, 10:26 AM   #79
WAJ_UK
Cooling Savant
 
Join Date: Oct 2003
Location: Sussex
Posts: 109
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Today I have too much time on my hands and I'm a hopeless addict I've been sitting around all day taking far too many temp measurements. I have 9 different combinations of blocks to test and I'm almost halfway, after pretty much a solid week of testing. I don't have any lectures at uni on a friday so I've spent all day sitting at the laptop updating my spreadsheets as my test continues.

There is a bit more to water jet impingement than whether or not the flow is turbulent. It is highly likely that the flow is turbulant anyway at lower reynolds numbers. You need quite a long, extremely smooth pipe for the flow to become turbulant as high as 4000. As soon as the jet exits into the surrounding water it will become increasingly turbulant the further it travels through the surrounding water. However the centerline velocity of the jet reduces the further the jet travels through the surrounding water.
These two elements (turbulence and centerline velocity) are the key ingredients to impingement cooling. So basically, the further the nozzle exit from the base plate, the greater the turbulence and the closer it is the greater the jet velocity. So it is a case of balancing the two components to give the optimum heat transfer.

But now I'm off to the pub

Typical student
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