On Oct 24, 4:22*am, Smitty Two wrote:
In article ,

*bq340 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.

Sounds like you are envisioning a fiberglass filter, not the fan-fold
paper ones.

Well, if you really believe that's what I'm envisioning, then you
haven't followed this thread very closely.



If you have a fan-fold one that has 1" thick folds then we will
arbitrarily say it has 2000 tiny holes in it (although it really *has
more, obviously). Now if we make the pleats 2" thick we now have twice
as many holes in it, allowing twice as much air to pass thru it.

Snake oil. Those holes are placed at a steeper angle to the direction of
flow, reducing the effective size of each hole. And there's a lot more
"not hole" material in the path of the air, too, creating additional
friction.



Good grief. Let's say the holes are randomly oriented, which is
obviously a lot closer to how a real filter of the type under
discussion is going to behave. So now we have twice as many randomly
oriented holes in the 2" pleated filter as in the 1" pleated filter.
Which one is going to have less pressure drop across it and allow air
to flow through easier?







The outside dimensions stay the same, but the thickness of the filter
paper pleats (surface area) is doubled.- Hide quoted text -

- Show quoted text -