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<misc> Re: Filters
Barry wrote:
>>
Scenario:
We have two filters that have about the same surface area available
for filtering. Both rely on a maze of fibers to trap particulates from
the airstream. Both are dry (no oil). One filter flows more than the
other. Let's call this filter 'Flow'. How does 'Flow' wind up being
the less restrictive of the two? Answer, it filters less. There are no
smoke or mirrors here (remember, the surface area is the same). It
has
to filter less. Either 'Flow' has a wider path between the fibers for
air to flow or the path is shorter for particulates to follow. Perhaps
both. Either way there is less filtration using 'Flow'.
> Is there any room for debate here?
I think so. You're leaving out the pattern of the fibers themselves. Imagine
that both filters have 100 layers of fibers. One filter randomly distributes
them, so sometimes the gap between two fibers in one layer is 'plugged' by a
fiber in the next layer. The other carefully aligns the fibers so that this
never occurs. I know absolutely nothing about air flow (although I can spell
laminar ;-) but it seems to me entirely possible that the *layout* of the
elements of the filter might have an effect on the volume of the air that
passes through.
Further, you assume that smaller particles must be getting past the 'high
flow' filter, despite the oil, because it achieves its rate of flow thanks
entirely to larger spaces between 'fibers', which also seems to ignore the
fact that real filters are composed of multiple layers.
I freely admit that all of the above is pure speculation, unburdened by data.
Simon Kennedy
'95 M3