Stpuid Question Pipe and Resistance with Fluids?! - Page 1
Forum section: electronics / general

author: Lord of nothing
author_rank: Super Contributor
timestamp: August 09, 2020, 11:14:04 am
content: HiWell I guess when a Fluid flow truth a Pipe the Pipe create some resistance since the Fluid sticks to the Wall. Is that rite? If its so there are thinks like the Lotus effect. So would a Pipe who is coated with that have less resistance since the Fluid dont stick to that?Thanks

author: tggzzz
author_rank: Super Contributor
timestamp: August 09, 2020, 11:29:47 am
content: Quote from: Lord of nothing on August 09, 2020, 11:14:04 amYour English is normally a bit better than that. Have you been taking something illegal?

author: Lord of nothing
author_rank: Super Contributor
timestamp: August 09, 2020, 11:44:51 am
content: No?!Its very hard to describe it.I just want transport a Fluid its will be Water over a longer way truth some Pipes and I would like to use a small pump for. It will flow 5 Floor up and down and that should be as efficient as possible. Its a closed System.

author: tggzzz
author_rank: Super Contributor
timestamp: August 09, 2020, 11:52:22 am
content: Draw a diagram.Use google translate to/from German

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 09, 2020, 12:17:34 pm
content: Friction is due to the boundary condition. Even if the pipe doesn't become wetted by the fluid (there is an air space between pipe and fluid), the fluid's surface is still held in place by the microscopic contact points which give rise to the lotus effect.Now, the surface is fluidic too, so it's not perfectly still. The boundary condition is more complicated. Parts of the surface (between contact points) can still move. That surface movement, in turn, shears against the air space, which is much less viscous so we can probably ignore it.Over a long time scale, I wonder if the effect is persistent. Consider: all gases have nonzero solubility in liquid. Slowly, the air space shrinks as its gas is absorbed by the fluid (being deposited elsewhere in the system). (Maybe this won't happen everywhere in a closed system, but at least somewhere.) For it to be persistent, it has to have so much energy in surface tension that an actual vacuum can be formed, filled only with the fluid's vapor. Which I suspect just can't happen with most fluids.It's not a useless question -- it's certainly possible with the right combination. Take mercury for example: it has so much surface tension, and so little surface energy, that it doesn't really stick to anything nonmetallic in the first place. Even smooth surfaces in vacuum. (On the other hand, it strongly wets most ordinary metals!)Also, we can test a continuum of surface energies down to zero, by heating any fluid towards its critical point, where surface tension disappears completely (gas and liquid densities become equal and phase separation ceases). So the question is, what combinations of what fluids, at what temperatures and pressures, and with what surfactants if any, can make use of this?Applications where it can benefit, assuming the boundary layer remains intact -- include viscous, viscoelastic or inhomogeneous fluids: if the bulk fluid has higher effective viscosity than the liquid surface, then there can be more shear right near the surface than in the bulk. That is, it has laminar flow but with a non-parabolic velocity profile due to a nonlinear shear property.Otherwise, if the fluid wets the pipe surface, it's just any other rough-pipe condition, and your surface treatment is at best wasted, or makes things worse.Surface roughness induces turbulence at somewhat lower velocities, so has a bit more drag than a smooth pipe. There is a length scale that goes with that: very small features diffuse energy rather than shed vortices. A nanoscale surface treatment might be effectively smooth for water, but not, say, for air. A rusty pipe might be effectively smooth for honey perhaps, but not water.Tim

author: Lord of nothing
author_rank: Super Contributor
timestamp: August 09, 2020, 01:03:43 pm
content: I found "Black 3.0" who is a cheap Blacker than Black, Black Paint who absorb almost all light.I thought thats the perfect stuff to coat some Copper, PVC Pipes and flush some Liquid (I would prefare Water since its not Toxic for the Most People and Animal out there) thruh to heat something up to a nice Temperature. Well I must check how many Heat it can absorb from Sunlight to check what I could heat with. Like "just" the Pool in Summer or maybe "preheat" the Water who back the the Central Heating System. If the get very efficient maybe support the Central Heating System in Summer. In Summer its quite Impossible to going on the Attic since the get so Hot.Maybe I could drive the Pump with some Peltier Elements one side is connect with the "cold" Side where the Water is rush into and the Hot Side is coming from the Black Painted Tubes. The Pool act as Heat Absorber.

author: Haenk
author_rank: Super Contributor
timestamp: August 09, 2020, 06:50:02 pm
content: (I hated "Strömungsmechanik" at university)Pipes and media is one of the basic topics: All media is slowed down by the boundary, which leaves you with a parabel-like speed of flow distribution (imaginary cut through the pipe), highest speed in the center of the pipe. The lotus-coating won't have a huge effect, probably next to none.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 09, 2020, 08:50:35 pm
content: Why is this in dodgy tech? It's not a scam/pseudoscience, should probably be in general.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: August 15, 2020, 05:50:08 am
content: Why not just use a slightly bigger pipe?

author: IanB
author_rank: Super Contributor
timestamp: August 15, 2020, 06:08:18 am
content: Quote from: Lord of nothing on August 09, 2020, 11:44:51 amYou really do need to draw a diagram.For instance, if you really want to pump water up five floors then friction will be the least of your worries. For that you have to worry about gravity, or "head" in engineering terms. The pump must generate enough pressure to overcome the weight of a column of water 5 floors high. If we suppose one floor is 3 metres, then 5 floors would be 15 metres. That would be give a pressure of about one and a half atmospheres, which is vastly greater than any resistance in a properly sized pipe over that distance.As to smoothness of pipe walls, it does have a small influence, but the major influence is the diameter of the pipe. The way to reduce resistance is to use a bigger pipe. Even if you had a miraculous pipe with perfectly smooth walls, there would still be nearly as much resistance as with less smooth walls.