# Tag Info

18

The surface of any fluid has an associated energy-per-unit-area, known as the surface energy, a.k.a. surface tension. This energy is not a property of the fluid alone, but of the fluid and the medium it is in contact with. In your case you would have associated surface energies for the water-air interface, $e_{wa}$, as well as for the water-paper interface, ...

6

Your problem is highly nontrivial. The theoretical tool to be used is the renormalization group, which extracts the relevant dynamics of the large scales of the system. But if we were able to use it "in a blind way", then we would have a technique to study the macroscopic dynamics of any microscopic system... and this would made a lot of my colleagues ...

5

The physics behind this is the same capillary action that causes water to move up narrow cylindrical channels. Tissue paper is extremely porous, but the pores are sufficiently narrow that the cohesion between water molecules (actually driven by the Coulomb interaction, since water molecules are polar) and adhesion between the water and the surfaces of the ...

5

You are right, these masks are almost useless as a protection against urban aerosols. With swine flu, there was a lot of discussion (example) that even the best masks cannot catch virus particles which are only 100 nm in size. The usual surgical masks are even less effective - they will hardly block anything smaller that 1 micron. Now, urban aerosols have ...

4

I would expect stimuli-responsive polymers to have what you're looking for, and the keyword "stimuli-responsive" may be a useful search term. The stimuli-responsive polymers undergo conformational changes in response to changes in their environment. The primary environmental control variables people use are temperature, pH, and ionic strength. But people ...

4

The credit should actually go to Slaviks for the wise suggestion of keywords to look for. Tunable porosity gives the following article: DOI:10.1002/ange.201201686 Prashant Tyagi et al. Dynamic Interactive Membranes with Pressure-Driven Tunable Porosity and Self-Healing Ability. Angewandte Chemie, 2012. ABA triblock copolymer (pictured above) ...

3

The keyword for porous flows is Darcy's flow, which is based on the Darcy law guiding the field of mass flux instead of velocity: $$\vec{q}=-K\nabla p$$ $\vec{q}:=\vec{u} \cdot \text{porosity}$, so it is equivalent to normal flow only for homogeneous media. This equation comes from averaging the NS over porous volume; however, as you can see, it is very ...

1

The previous answer tells you why the water moves up but doesn't explain where the energy comes from. In order for water to move up and thereby gain gravitational potential energy, you need to have some energy loss somewhere else to compensate. Some of the energy comes from the random molecular movement of heat which extends the edge of the water itself up ...

1

There are 3 kinds of mixtures in liquid... True Solution Colloids Suspension These three vary in between because of the size of the particle in them. see wiki. Now, the salt solution you were talking about comes under category "true solution" i.e. particle size less than 1 $nm$. Now we don't have sieve to filter out this particles of this dimension. ...

1

For the input parameters provided, your velocity estimate is reasonable but probably not accurate. Reason is that Darcy's law assumes Stokes (small Reynolds number) flow. For the parameters provided, together with a density of 1 kg/m3, and substituting a flow length scale of 0.001 m, the Reynolds number reaches a value around 10. This means that the flow ...

1

To start with, I'll say that my SPH knowledge comes from astrophysical/cosmological applications, but I think it's partly transferable. You're right that discretization limits the scale that can be resolved by the simulation. Any processes operating on scales below the resolution limit are... well... not resolved. I know of two possible remedies. The obvious ...

1

The porosity is needed if you are interested in the flow velocity within the porous medium. If you look at $Q/A$ this is also a velocity but with reference to the void or empty channel (this is also referred to as superficial velocity), as $A$ represents void and matrix. To get the velocity within the medium (in straight flow direction) one needs to correct ...

1

Situationes where Stokes (without Navier) rules, are well known, eg hydrogeology (ground water) or oil geology (secondary or tertiaty recovery) A word which might be usefull to search for: percolation.

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