dpb wrote:

Smitty Two wrote:
...
The part I'm having trouble with is the completely unjustified and
unsubstantiated claim that doubling surface area doubles (or improves by
any factor) air flow, given the same cross-sectional area of duct.
...
I think the problem is folks aren't looking at the whole picture.
Assuming a fixed media fractional area for flow, doubling the total area
does indeed double the open area. If that were all, it would be an
improvement. Unfortunately, what they're leaving out is that the
structural material doubles as well.

Hence, I think as you -- initially there may be little _added_ pressure
drop but the only potential real advantage may be that of the loading as
somebody mentioned could, possibly, extend lifetime somewhat.

I've not done a full dynamics analysis at all, but I can't see any other
major effect not covered by those very basic geometrical arguments.

I did send off a request for data from a pleated filter manufacturer who
published some pressure drop data for their 1" filters and also make 2",
4" and 5" filters of the same type for comparative data. If they
respond, I'll post their answer.

A moderate search found no published comparative data of value, only
single numbers and much uninstructive babble as here.

--

Ya don't need "a full dynamics analysis" Do a freaking "thought
experiment" -- would you DECREASE or INCREASE air resistance by adding
filter after filter after filter etc across a duct ???? Of course you'd
INCREASE air resistence. Geesh people!