Quote:
Originally Posted by rattlsnak
Bernoulli's principle.. This will cause lower pressure but more velocity (in that section) -- up until the point where its back to normal sizing.. Then it's not going to matter.
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From the picture it looks like the duct is flattened without increasing the width (maintaining overall volume).
If the ducting is over-sized and can flow more than the fan puts out with minimal restriction, then it'll be fine. But if the ducting is sized correctly for the fan, the restriction will reduce flow.
If that is the case and it is a true reduction in cross-sectional area, then he pressure will INCREASE right before the restriction, which will increase pressure, which will increase velocity. But the flow will be decreased.