Originally posted by gsbaker:
[B]...If I find the magic number I'll post.[B]
Since this subject has been revived...

There is no "magic number" for reducing the area of ducting to increase the velocity in an optimal manner. However, there is an equation that requires measurements from flow meters and pressure sensors, but I don't believe anyone wants to go that far.

When I complained to my ME friend that this was becoming too complex for the weekend amateur he said, "Look at the end of a leaf blower. That's about right."

He also reminded us not to miss any hot surface area, e.g. if you can get to, say, 12 square inches of hot material you wish to cool, don't pinch the duct exit area down to less than that.

Now where is that leaf blower?

Gregg