Thanks Rich,

I've been doing filter validation for 20 years, so yes, I know of what
you speak. Now, show me either of:

A spun depth filter with "a 0.000000000002 micrometer" absolute
porosity,
OR

ANY spun filter with any absolute porosity rating.

The point is, you were wildly exaggerating, and I was pointing that out.
If you *could* create a filter of the listed porosity, the surface
tension alone would create such a high pressure you'd never get any flow
at all. As you obviously know.

Oh, and you might want to reconsider statements about "differential
pressure is SOLEY due to the absolute viscosity" of the liquid. Never
had the fun of filtering thixotropic products eh?

Keith Hughes


RichH wrote:

ummmmmmm yourself

Bubble point is related to retention efficiency ---- ONLY.

If your were filtering a 60/40 mixture of isopropyl alcohol and water
your statement would have (some) validity .... but ONLY if your were
using uniform porosity polymeric *membranes* at retention levels below
0,45uM. It is a mathematical/physical impossibility to consider 'bubble
point' for such fixed media (fiberous) and comparatively HUGE retention
sizes. If you know what a bubble pointg is, then you also know that such
fixed fibrous media has inconsistant porosity and permeability - ie. a
2uM media will have 'pores' approaching 50 or 100uM!!! Bubble point is
simply not applicable.
For yourself I respectfully suggest that you look up the filtration
regimes as defined by the ASTM "OSU F-1 protocols"

Operating differential pressure is SOLEY due to the absolute viscosity
of the fluid!!!!

Bubble point is a nondestructive CORELATION or a bacterial (specified
test organism) challenge (or latex spheres) ... to a plugging situation
using specific test organisms on MEMBRAWES. Oil filters use a fiberous
media ... where bubble point is totally nonapplicable: 1. non uniform
media, 2. retention matrix larger than 1uM. Tell me where on this
planet that one can do a 'bubble point' (or forward flow diffusion) on
the media type used in fuel oil filters? - is fiberous and non-uniform
in permeability; and thus, are unable to be tested via bubble point as
the contact wetting angle of surface tension vs. the media is
nonuniform. Bubble point is ONLY perfomed on MEMBRANES of ?0.45uM used
in filtration .... not on fiberous nonuniform porosity media.

Differential pressue of a CLEAN filter is SOLELY due to the absolute
viscosity (viscous shear) of the fluid being filtered. Surface tension
is irrelevent with respect to viscous shear/?P. Changing the surface
tension (wetting angles) will ONLY affect the *retention* ability under
varying intrusion pressures ... ie:. modifying the van der walls
absorbtive attraction at the BET surface of the media or membrane.
Differential pressure affects the internal velocity of the fluid THROUGH
filter media/membrane AND those media with high ?P will have/approach
insufficient contact or residence time for absorbtion mechanism of
capture; thus, leaving only mechanical means of 'captu'seiving',
direct interception and inertial impaction. You can matematically
predict by the (area1/area2)E1.66 = (velocity2/velocity1)E1.66 =
((Q/deltaP1)/(Q/deltaP2))E1.66 ...as a LIFE performance predictor (the
exponential varies between 1 for high viscosity non-newtonian fludis to
approx 1.666 for newtonian fluids.... no surface tension/wetting angles
involved.