Slope of efficiency curves

[glenncof]

I have been looking at various FF filter media and am wondering about the slope of the efficiency curve. I have NO practical experience, I’m just trying to evaluate claims by various manufactures as they relate to the media and, subsequently, relative load-up characteristics in operation.

Just as reference I have been looking at Donaldson Synteq, Fleetguards Stratapore & Microglass, various blends such as FRAM Triad (Extend. Guard), M1, and cellulose (with/without phenolic-resin).

From what I understand, first order effect is pore size distribution. Glass/synthetic seems it could achieve tight distribution leading to a sharp efficiency cutoff relative to particle size. Cellulose may be much harder to control pore size distribution resulting in a less-sharp curve.

But if I have a perfect distribution of 8-10um pores the media (I guess) would be loaded relatively quickly. This leads to the layered (aka depth) concept where larger particles are filtered at higher levels from the fine pore surface within media. I can’t guess the effect on pore distribution since this probably relates to the fabrication process.

My problem arises from partial & different data points (only one or two) on filters beta or particle efficiency provided by most manufactures. My sense is the more glass/synth, the more brittle and costs go up. That’s why I’m trying to compare efficiency of various media, then I can look at filter cost.

First, is basic understanding heading in right direction ?
Second, is there any “rule of thumb” on the slope of these curves relative to media (and fab process) ?

 

[Gary Allan]

Good questions. I wish I knew how to even reason them ..and having the answers.

My one (or two, maybe) dimensional view is in terms of beta ratio and holding capacity. The rest magically configures itself in the background totally with my ignorance of the process

How that integrates into what you're trying to achieve here ...got me swinging.

It should make for an interesting discussion if some higher end members chime in.

 

[427Z06]

Here's something else you may want to consider.

There are five basic mechanisms by which any filter can remove particles from a fluid. These mechanisms are: (1) direct interception, (2) inertial impaction, (3) gravitational deposition, (4) motile-particle deposition, and (5) electrostatic attraction. For these mechanisms there are dimensionless indexes that indicate which measurable characteristics of the filter, the particles, and the flow, affect the intensity of particle capture. By comparing the magnitudes of these indexes it is possible to determine the main mechanism a filter is using to capture particles.

Not rocket science, but like everything else, it's more involved than one would imagine.

 

[GeorgeCLS]

Another aspect of glass media filters is how the filter is laid up. i.e. several layers of a course micron material, followed by many layers of a medium micron, followed by a final ultra fine layer. Thus, how many of each of these various size layers are in a filter element can greatly affect its loading characteristics. Then put in the equation the dynamics of varying flow rates, vibrations both fluid and mechanical and all laboratory work can go down the drain.
This is exactly what took place a few years ago when CAT tackled their electronic fuel injector erosion issues. The lab indicated that a 6 micron beta 200 filter would effectively eliminate the wear issues caused by abrasives in the diesel fuel. Sooo, CAT immediately switched from a 30 micron filter to a 6 micron beta 200 filter. Problems did not go away..... On further study it was found that on the functioning engine the backfeed pulses from the engine were actually causing a cleansing affect on the filter element and had to reduce to a 2 micron beta 200 to effectively achieve a 6 micron beta 200 in the real world....

The same is true for many vehicle applications where steady state lab testing does not relate to real world application.. There simply are no steady flow applications!
George Morrison, STLE CLS

 

[427Z06]

Quote:

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Then put in the equation the dynamics of varying flow rates, vibrations both fluid and mechanical and all laboratory work can go down the drain.

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For those who want to read more, here's a brief article on the topic.

http://www.filterelement.com/DFE.pdf

 

[glenncof]

"What do you get when you multiply six by nine? - In base 13." Uhhh...42?

427Z wrote, "By comparing the magnitudes of these indexes it is possible to determine the main mechanism a filter is using to capture particles."

I thought direct interception IS the main mechanism in FF filters and that's why its tested and reported (advertised).

DFE results look like an approximation of static ones but leads one to consider the pore consistancy and vertical structure of the media. Gravity (or centripal) and electrostatic...I dont see these in playing a big part in FF's.

But I'm not trying to design or solve a filter problem. I'm just trying to crudely compare various media approaches to see if I might place value on higher cost FF filter solutions.