Do you need to measure the porosity of the whole filter, or just the volume of the adsorbent it contains ? Porosity = 1 - d(porous system)/d(solid), where d(porous system) = mass(porous system) / V(porous system), and d(solid) is the skeletal density of the solid material from which the porous system is made (e.g. around 1.8 g/cm3 for grains of activated carbon). d is density, m mass and V volume, of course. This is the simplest way. If your filter is not based on carbon, you have find the density of the material from which it is made (e.g. cellulose, etc.).

Alain

Thanks Alain,

i know the procedure how do calculate.

I need simple experimental method. I have filter to find thev pososity for it.

how i can find the void volume.

for soil and stone: we can use the difference in volume by using a graduate cylinder.

filled the cylinder with soil upti certin level.

add water to find how much water added beforelevel in cylinder start changing.

is there any simple metode I can use it with using ethe equipment used for this purpose and we have got any one of them.

i need  a method we use it in the lab with simple measurement.

regards 

Faik,

You are describing pycnometry. Methods exist (helium displacement) for measuring the void fraction of an object.

But I sense that you also want to know how well the filter conducts a fluid across it - which is only weakly related to the void fraction (not all voids are connected to each other).

In which case a flow meter and a known pressure differential are needed to establish the flow rate that the filter can sustain. Then, with some assumptions about the flow regime and the geometry of the pores, you can deduce an effective cross-sectional area.

(note, the viscosity of air, like most liquids, varies with temperature)

I should think that the primary measurement of interest for automotive air filters would be the pressure drop at some flow or the flow at some pressure drop, either one of which would be fairly easy to measure with easily obtained equipment.

thanks James and Dudley,

I gave example in previous comment.

what I am looking for is:

I have filter. i need a simple method to measure (with some calculation) to find its porosity.

Dear Faik,

You might do the same as you have suggested for soil and stones, but instead of water I would use of fluid of much lower surface tension, to be sure that the elements of the filter are well impregnated by the fluid. An organic solvent with a few drops of non ionic surfactant should allow of good impregnation of the porosity. Vacuum may also help.

Alain

The information may be useful for your research

Electrospun Polymer nanofibers have a wide range ofapplications including automotive air filters. Largesurface area, small pores, flexible and adequate

porosity are widely recognized as importantparameters for improving the performance of thefilter media and therefore measuring the porosity of

the medium is extremely important. Porositymeasurement techniques such as density basedmethod, mercury porosimetry, capillary flowporometry, image analysis are relatively inaccurateand they have some disadvantages for measuring theporosity of the nano fibers. In the present studyporosity measurement for nanofiber mat usingpycnometer was explored. Pycnometer is generally

used to measure the density of the solids of havingvolumes upto 150 cc. Volume of the nanofiber wasmeasured by pycnometer and porosity is determined

as fraction of the void in total volume of the fiber.Total volume is calculated from FESEM imagethickness. Various advantages of pycnometry method

when compared to other techniques were discussedbased on the results of porosity measurements ofnanofiber mats

A Novel Method for Measurement of Porosity in Nanofiber Mat using Pycnometer in Filtration

Sudhakara Sarma Sreedhara, Narasinga Rao Tata, PhD

Journal of Engineered Fibers and Fabrics 132 Volume 8, Issue 4 – 2013

www.jeffjournal.org/papers/Volume8/V8I4(16)%20S.%20Seedhara.pdf

Faik,

Two ways to do it.

1) If you have access to a small but UHV vacuum chamber and an accurate pressure gauge (active Pirani or a Barotron) then you could simply pump down the filter, shut off the pumps, connect a known volume of air to the evacuated chamber and measure the resulting pressure.

If the chamber is sufficiently small (ie, six pieces of stainless steel brazed into a strong cube) then the pressure change will be entirely due to the solid fraction of the filter.

2) As per Alain's excellent suggestion. Known volume of low viscosity fluid (hexane, say), immerse filter, note volume change over time.

I agree with Dr James Garry .·