A 100 % non-cavitating liquid (not fluid, which includes gases) would be required to have vapour pressure equal to zero. Such a liquid doesn’t exist. I guess a polymer melt free of plasticiser (usually a mineral oil) would have a very low vapour pressure. The higher its molecular weight, the lower its vapour pressure. Mind you, such melts flow violating the no slip condition at solid walls.

Polymer... Maybe a polymer gel? That is not a "liqud", there should be some weak, molecular bonds... and that's OK for the purpose. It does not have to "flow". Jelly is fine.

No slip condition violation is OK too. This could be used as a lubricant for the end plates, in frictionless triaxial apparatus...

And for a "far fetched" experiment, which would allow me to increase dilative sand strength (undrained) to extreme levels.

At the moment, dilative undrained sand peak strength is limited by cavitation phenomenon in water. During undrained tests, the void volume is "locked" by water. As sand dilates - voids are held "locked" by water. But when cavitation pressure is reached - water "releases" the voids, causing pure plastic peak strength to be reached...

If there was a polymer that does not cavitate - that could allow us to make super-materials, something on the lines of "soft armor" - super resistant to impact loads, by harnessing the properties of void content in dilative sand.

The thing could be used for soil curing around turbines or earhquake zones... whatever. But I can't find a "liquid like" substance, which would have high "volumetric tension" resistance... going below -100kPa... pulling at 200 kPa in all principal directions... I'm not even sure how to describe it. Those type of tests don't seem to be common. Could be a new branch of testing is required. One where the material is "pulled apart" rather than consolidated under high pressure.

A gel is a two-phase system: dispersant/external phase is a solid and dispersed/internal phase is a liquid. Size of liquid particles range roughly from 1 to 1000 nm. The gel migth flow (non-newtonian fluid), depending on the relative proportion of phases. During flow, cavitation may occur, governed mainly by the liquid phase vapour pressure, which is highly dependent on temperature. Again, you’ll have to find/develop a gel using a liquid of very low vapor pressure, so as to minimize the chances of cavitation.

Hi All,

Adding on one of my research questions. If the pressure of a flowing water reaches negative pressure due to some restriction (say in the range of -88 kPa to -150 kPa at 45 deg C) does that mean there is presence of cavitation? Can you refer to any sources that give concrete relation between negative pressure and cavitation? (2) Also what is the relation between temperature of water and negative pressure of a fluid? Say at 45 deg C 9500 Pa is vapor pressure. At 45 deg C -ve _______(fill in) Pa is vapor pressure? Thanks.

The term you're probably looking for is "vapor pressure".

It's the pressure at which fluid (or even solid) water vaporizes. There's a table, you can find it here: https://en.wikipedia.org/wiki/Vapour_pressure_of_water

So, water will become "steam" (gas) at pressures below atmospheric pressure. The colder the water - the more vacuum it takes to make it into a gas... If you cool water into ice, then you can do this amazing thing - you can turn ice into vapor without entering the liquid state at all.

The fact remains, liquid water cannot reach -100kPa (absolute zero). For the same reason, you cant "suck" water 10m up a tube. You'll just end up sucking "vapor" at the other end. The tube above 10m limit will be full of gas, no liquid water. https://www.youtube.com/watch?v=HUmZrtiXDik

So, cavitation is unavoidable at pressures near absolute zero. You can't really reach below -100kPa without turning liquid into vapor. Maybe for a few nanoseconds or something, but that's nano mechanics... a different paradigm.

I find it very awkward that properties of water are not part of the standard geotechnical curriculum. So many engineers I've met, who have no idea about water stiffness, and yet design structures built in rivers and the sea... bizarre... water properties play a significant role in undrained - dynamic and impact load scenarios. They do these calculation where pore pressure reaches -400kPa... which is utter nonsense. That's pure plastic yielding at that point. And they do not notice, or do not care... That's very bad, and dangerous.

With the original question I'm hoping to find some polymer or whatnot, which has some "bonds" which make it a "gel" rather than fluid, thus, perhaps, leaving the ability to withstand negative pressure below -100kPa.

Hi Nagalingam and followers.

You should use “negative manometric pressure” rather than “negative pressure”. Cavitation analysis uses “absolute pressure” which is always positive. Cavitation is a very complex phenomenon involving simultaneous momentum, heat and mass transport in flowing liquids.

The answer to your question is yes. Cavitation is a phenomenon associated with liquid flow in passages constrained by solid walls, fixed or movable. Very shortly, it can be adequately broken down in a sequence of six stages: (1) liquid particles (finite conception!) move from a region A, where the absolute pressure is pA, to a nearby region B, where the pressure is pB, with pB < pv, the liquid vapour pressure at the flow temperature. (2) as a consequence, the liquid effectively boils at B, so that vapor bubbles (or cavities!) appear at B. (3) under the action of non equilibrated forces (weight, buoyancy and drag), bubbles move accelerated to a region C where pC > pv. (4) as a consequence, bubbles implode with liquid from all around accelerating towards C. (5) At C the incoming liquid particles from all space directions colide with each other, and their kinetic energy is converted to heat locally. A small part of this heat is transferred to the liquid surrounding C. However, the greater part of it expands the liquid at C against a great mass of cold incompressible liquid, increasing even more the local pressure at C. (6) Since pressure away from C are relatively low, C acts a source of pressure spherical waves that are sent throughout the liquid in three dimensions. These will eventually reach nearby solid walls with a regular hammering sequence, possibly removing small solid particles from it (cavitation pitting). Mind you, we are talking about local/spot temperatures and pressures near, respectively, 800 ºC and 1000 atm.

Look for NPSH (Net Positive Suction Head), a concept related to cavitation in pumps, in standard Fluid Mechanics books. Some of the variables affecting NPSH depend on temperature: liquid vapor pressure, viscosity and density. That’s the “relation” between cavitation and temperature, you looking for.