Flow Characteristic in Corrugated Pipe

Raincoat? What do you mean missing a raincoat? How exactly did you get around to missing a raincoat under the circumstances?

That said, what exactly is your thought about why the water flow behaves that way? I have performed research and mathematical analysis on this subject many years ago and so I too hav some thoughts on why it actually happens. So I am curious what you have observed. The answer actually is in an old textbook which I will tell you after you tell us yours.

"I typically will drape the tubing over the edge of the sink in a U shaped fashion and connect the one end to a faucet while holding the other end ~2-3" below the faucet outlet to direct the tubing discharge water into the sink basin. When I stop the flow of rinse water through the tubing it stops running into the basin; however, when I go to disconnect the tubing at the faucet, it spews water around the room and onto me."

My best guess here is that the flow from the open end stops, with water held in the 2-3" higher section at the inlet side by atmospheric pressure. Because the tube is corrugated, the weight of the water stretches it to hold a greater volume of water than the internal volume of the empty tube. Disconnecting at the faucet (UK tap) allows the water to flow round the tube and start discharging - reducing the weight of water in the tube, and allowing it to contract. This effect continues as the volume remaining in the tube decreases and it springs back to its undeformed state - resulting in the water spraying around.

Just my two-penneth...

I have indeed observed that there is some streching of the tubing when there is the additional weight of water in it and I would be in agreement with your explanation except for the fact that the water spews out at the tap to tubing connection.

I am somewhat surprised that the water prefers to discharge (at least initially) at that elevated location rather than at the lower end of the pipe. This would suggest to me that there is some sort of vacuum caused at (or near) the tap. This is confusing to me since I would expect the tubing to preferentially discharge at the lower elevation site unless something is forcing it back to the tap (source) [eg. some sort of vacuum is formed near the source end]. Could, perhaps, the flow of water into the tubing at the tap end cause localized formation of vacuum pockets (ie: via an aspiration effect)?

Hmm...

Out of interest, are the corrugations in the form of a stack of circles, or helical? (don't know how to express it better).

Helical.

Stack of circles.

Now you have your answer or answers. When liquid flows through a corrugated tube, donut-shape circulating flows occurs in the regions of bigger diameter, and while the tap is on forces yet another spiraling flow in the axial direction. However, the donut-shape circulation is preferentially backwards. So when the tap is turned off and the spiraling flow stops only the backward circulation donut-shape flow exists hence the aggregate backflow towards the tap.

ref: Boundary Layer Theory, by Schlichting (sp ?)

I do not remember the page, but I leveraged the concept in reactor designs many years back.

I suspect it has to do with a pressure differential created by the variation in diameter of the tube between the minimum at the corrugations and the maximum diameter between them. It could also be a radial flow caused by the corrugations, creating a whirlpool effect, but fluid dynamics is not my strong suit - in fact, it isn't even a hobby...

Some actions have been explained to my mind by other posters already.

The reason that the flow is so low is due to the corrugations. This cause eddys that really slow the flow down. I saw this on my caravan many years ago where the makers had used cheap flexible electrical conduit for the waste water. It could actually "support" a large weight of water with BOTH ends open....I replaced all with smooth flexible plasic pipe and the flow was much improved and it never blocked again either without a "mechanical" reason.

Thank you posters for your interesting and insightful comments.

Agua_doc

Hello aqua doc,

So if I discern this correctly you have two different actions causing your blow back.

One is the annular eddy at each corrugation causing a reverse flow and restricting the waters path. This causes the pressure in the corrugated tube to increase with a gradient to the input.

Two is the elasticity of the corrugated tube. The pressure and the weight expand the tube like a bellows storing energy.

When you disconnect the input the spinning eddies still have momentum and the elastic of the tube stores the pressure which has a lower pressure at the intake vs the exit that acts like a partial one way valve.

Releasing the intake allows a pressure drop to expel the built up water.

Just picturing it in my head from the others input.

Brad

Part of that could be verified by waiting a while (10 mins?) 'til the water in the tube was in equilibrium - and it was unlikely that any spinning eddies etc. remained.