Are you running a simulation? or doing it experimentally?

Also does it stay constant at 10psi after 7 minutes?

I'm doing a experiment.

It keep growing after 7.

https://www.sciencedirect.com/search?qs=pressure%20drop%20of%20porous%20media&show=25&sortBy=relevance

Hi Washim, thanks for the references on how to calculate pressure drop. However do any of these explain the "increase over time" feature of my confusion?

Hi Feichen

A likely cause for this is migration of loose particles within the porous medium, blocking downstream pores. Make sure the water is free from suspended fine particles, including colloidal ones, since these could also block the pores. Of course, check whether the pressure gages are working fine.

Pecanha should be right. In a second experiment I would invert the flow direction in the porous medium.

Feichen, comments above are the most likely answer to your problem, this also happens in real life and most times until TIF occurs. Filtration might be able to fix the problems as suggested, should be at least 2 microns for your experiments or lower. Fluid-rock interaction will be the second thing to look at if your pressure drop continues to increase. I hope it helps

Hi y'all,

Thank you so much for your answers. I tried using a 1 um filter to filter my water, it still happened. Also, my porous media is a annealed fibrous media with no loose particles. It is very frustrating at this point.

Hi Feichen and all.

OK: no loose particles migration and pore blocking. Then, the porous medium itself could be undergoing compression during experiment, thus reducing its permeability (Cf. Darcy’s Law). In this case, a constant flow rate would give what you getting: an increasing pressure drop. Try a constant very small flow rate. It will give a very small pressure drop, hopefully not enough to compress the medium and the pressure drop will be constant. If that is the case, you’re dealing with very compressible porous medium. If it is unavoidable to deal with this medium, for a given flow rate, you will need a large cross section so as to have low velocity and low pressure drop.

Hi Pecanha, I feel like this is the most likely hypothesis. Any idea how I could use experiments to confirm?

Hi Feichen

As I suggested, try very small constant flow rates. If the porous medium does not compress under flow, the associated pressure drop will remain constant (gage indication). For each flow rate you try, give the system a little time to guarantee a steady condition. If you increase the flow rate slowly, you may detect the critical flow rate above which the fiber porous medium will undergo compression.

Another possibility will be to pack firmly the fiber porous medium by mechanical means, before the flow test. This could reduce a lot, perhaps eliminate, the compression it will undergo during flow.

Feichen, I think Mr. Pecanha above is correct about compression of the filter media, perhaps you should try a bit of modelling of the permeability of the fibrous media(or DP). It can be done with the basic Kozeny-Carman work and look at the relationship between "voidage" and "permeability". Consider using Rushton et al 1977, it is well explained by Johnston P. "Fundamentals of Fluid Filtration" 2nd Edition. Please note that in the O&G industry certain filters are rated on compression level to suit certain particle size range, has been done for a long time. I hope it helps.

Hi Feichen, I agree with answers/suggestions by others above.

1. What material is your annealed fibrous medium made from?

2. Is there a tendency to generate some kind of heat (a slight temperature increase) by equipments during the actual running of the experiment? If so, this might have some effect on the porosity of the medium. Take temperature reading to confirm. Good luck.

Journal of Materials Science November 2013, Volume 48, Issue 22, pp 7827–7836| Compressibility of electrospun fiber mats

Journal of Membrane Science Volume 451, 1 February 2014, Pages 111-116, Permeability of electrospun fiber mats under hydraulic flow

Let me add an approach apart from those suggested by others. One could speculate that very fine particles are present in water and the slow deposition on the filter material leads to what is observed. In order to eliminate or confirm this possibility, the first experiment that should be done/should have been done would be to use certified "ultra clean water" and see if the problem persists. My predication is that the water you have used in "not clean". Otherwise, why would you use a filter anyway?

Hi yang,

As per said by Pro. Mukunda, First you have to analyse the kind of impurities present in water. If impurities size larger than mesh size then it will restrict your flow and continues rises Pressure.

Particle precipitation is not very likely, considering the observation made with a 1um filter in place and the short time within the pressure drop is increasing. To exclude this assumption, crosscheck the long term pressure drop increase at low mass flows.

The filter compression proposal of Peçanha does only work, if the porosity of the porous media (annealed fibers) becomes very small. At high porosities, the pressure drop should hardly depend on the porosity.

Could you please specifiy the porosity of your porous media? Do you know the compressibility/Young modulus of your porous media?

Following above last comment which I believe is correct, I have seen measurements of compaction under water injection in the laboratory for grannular filter media, also measured DP from production wells. The results indicate a moderate drop in porosity and permeability (27% to 23%) for various levels of pressure differentials. Also showed a level of dilatancy (increase in DP), all way below grain crushing pressures. I hope it helps.

What is the direktion of flow over the bed? Upside down or from below up? Use later one to lift the particles and avoid packing.