Starting a siphon ?

[gaber]

I am looking for an idea related to a siphon mechanisms that has been puzzling me for a while. I am doing a small research on a natural (karst) spring, that has a cyclic (intermitent) behaviour. The low-flow discharge of the spring is in the range of few litres per second, during outbursts it rises up to 500 l/s. The total volume discharged during the outburst is about 1000 m^3. The frequency of outbursts ranges between few hours and few weeks, depending on the amount of precipitation which determines the recharge to the system. Note, that we do not know the geometry of the system; we have an access to the spring pool and we expect a natural reservoir which empties by siphon action through the conduit feeding the spring during the outburst. The usual interpretation of such spring is a siphon mechanism, which I agree. However, my problem is a high contrast between the low flow and the high flow.

Imagine a simple system with a reservoir with inflow of few L/s, emptying through a looping conduit/pipe to a lower position. How can a siphon effect be triggered in such system with such low inflow, if the same conduit drains 500 L/s during the outburst. Am I getting something wrong to see the problem here ? So, I am looking for possible geometries and mechanisms which could occur in nature (no valves, switches, constant geometry…), that enables cyclic siphoning of a system with maximal discharge - recharge ratio in the range of two orders of magnitude. I could post this to earth science section, but I consider this a rather mechanical problem.

[studiot]

Have you looked at your toilet lately?

 

Does it not also have the same extended low rate inflow plus intermittent high outflow characteristics?

[gaber]

Have you looked at your toilet lately?

 

Does it not also have the same extended low rate inflow plus intermittent high outflow characteristics?

1. Yes, latest this morning .

2. No. Empirical facts: Even with relatively high steady inflow there is no intermittent action.

[studiot]

 

intermittent action.

 

 

But you have a mechanical valve in the cistern. If that failed would ther not be overflow?

 

Have you never seen the situation where the flush does not terminate but continues at the reduced rate of the inflow?

[michel123456]

Have you looked at your toilet lately?

 

Does it not also have the same extended low rate inflow plus intermittent high outflow characteristics?

In a toilet there is a mechanism triggered by your hand. The siphon at the bottom has nothing to do with the flush.

 

If I understand clearly the question is "what triggers the discharge ?"

 

I guess some gas must be involved, I cannot figure triggering a discharge only with a constant geometry and a regular flow.

[gaber]

In a toilet there is a mechanism triggered by your hand. The siphon at the bottom has nothing to do with the flush.

 

If I understand clearly the question is "what triggers the discharge ?"

 

I guess some gas must be involved, I cannot figure triggering a discharge only with a constant geometry and a regular flow.

Exactly that is the problem: how to trigger "high discharge" siphoning with constant low discharge inflow into the reservoir, without any man made mechanisms. I was having air locks or some other role of air in mind, but still, this is a rather general idea. I have put some conceptual picture on https://www.dropbox.com/sh/qp12m1d313sqeq8/fZ_IYcXrWg.

The question is how to fill the tube (or get the air out) to start siphoning. Any hint, link to literature is most wellcome.

Thanks for thinking my problem.

[studiot]

What's so difficult?

 

This sketch is a very simple way for a self discharging siphon to work. I would have to know considerably more about the strata to work out anything better. I have shown pipe like voids, but is more likely to be be faults / fractures or other features since it is natural, although natural clay filled 'pipes' do occur. and the 'void' may be a pocket of pervious rock, rather than an actual chamber.

 

Of course, the siphon may simply be formed from the local folding of a thin pervious layer, sandwiched between two impervious ones, that gets recharged when it rains, until there is enough water in it to drive the siphon over the top of the anticline, thus starting the siphon until the aquifer is drained. It may then issue forth as a spring on the other side of the anticline at a local fault.

 

The water may be entering not directly but along the interface between to layers ot strata.

 

There are just oodles of possibilities.

 

go well

Edited September 27, 2013 by studiot

[ewmon]

Explore it as Jacques Cousteau did (and others continue to do) at the Fontaine de Vaucluse in southern France, whose operation, I believe, continues to remain a mystery.

[michel123456]

What's so difficult?

 

This sketch is a very simple way for a self discharging siphon to work. I would have to know considerably more about the strata to work out anything better. I have shown pipe like voids, but is more likely to be be faults / fractures or other features since it is natural, although natural clay filled 'pipes' do occur. and the 'void' may be a pocket of pervious rock, rather than an actual chamber.

 

siphon1.jpg

Of course, the siphon may simply be formed from the local folding of a thin pervious layer, sandwiched between two impervious ones, that gets recharged when it rains, until there is enough water in it to drive the siphon over the top of the anticline, thus starting the siphon until the aquifer is drained. It may then issue forth as a spring on the other side of the anticline at a local fault.

 

The water may be entering not directly but along the interface between to layers ot strata.

 

There are just oodles of possibilities.

 

go well

I don't understand.

 

I dared to stole your sketch. See below.

 

 

When level C has been reached, the 2 parts are acting as communicating vessels.

 

When drop O falls, then drop2 goes out.

 

Right or wrong?

[studiot]

#First let me apologise for the poor quality of my hasty sketch. This may have led you astray.

 

Start with the chamber or porous zone empty.

 

Water percolates in and the chamber collects until the level reaches B

 

Percolation continues, but the water still cannot escape until its level is such that it is enough to initiate the siphonic action, which I have shown as A.

 

In fact there will be a small discharge as soon as the level reaches the lower part of the outlet, you have shown as C.

 

Once the water between my A and B has been discharged the level will be too low to sustain siphonic action so only this water will exit. The water below B will remain.

 

Of course other factors which affect the discharge are the rate of influx and the available rate of eflux. A heavy rainshower, for instance, will rapidly charge up a finite chamber, but the outlet may be restricted so the eflux will occur in sudden heavy bursts.

 

As I said the most likely situation is that the collection is not in an open chamber but in porous material that is bent around an anticline (upfold).

 

Does this make it any clearer?

[michel123456]

This?

[studiot]

Thank you so much for the link, I got sidetracked by the pop pop boats. Ideal for some younger relatives!

 

The siphon is full immersed in the cup so completely empties it.

If the outlet is to one side and does not reach the bottom then it will not completely empty.

 

I should have noted that an anticline is tension dominated, whereas a syncline is compression dominated.

 

This is because the outer top is stretched in an anticline, leading to cracking and weakness in an otherwise impervious layer, allowing a route for water entry.

 

Edited September 28, 2013 by studiot

[gaber]

Explore it as Jacques Cousteau did (and others continue to do) at the Fontaine de Vaucluse in southern France, whose operation, I believe, continues to remain a mystery.

Good idea, but the diameters here are bit smaller (10-20 cm) than in Fintaine de Vaucluse; and iy is not a mystery anymore. Its genesis and action is now well understood.

What's so difficult?

 

This sketch is a very simple way for a self discharging siphon to work. I would have to know considerably more about the strata to work out anything better. I have shown pipe like voids, but is more likely to be be faults / fractures or other features since it is natural, although natural clay filled 'pipes' do occur. and the 'void' may be a pocket of pervious rock, rather than an actual chamber.

 

siphon1.jpg

Of course, the siphon may simply be formed from the local folding of a thin pervious layer, sandwiched between two impervious ones, that gets recharged when it rains, until there is enough water in it to drive the siphon over the top of the anticline, thus starting the siphon until the aquifer is drained. It may then issue forth as a spring on the other side of the anticline at a local fault.

 

The water may be entering not directly but along the interface between to layers ot strata.

 

There are just oodles of possibilities.

 

go well

Thanks for the posts. We are dealing with conduits or solutionally enlarged fractures. Chambers in soluble rocks can be several milions cube meters large, so 1000 cube meters is no problem. So, we do not need low pervious and high pervious rocks (it wouldn't work in such a riforous manner in any case). The problem, however, still remains. For the siphon to act, you need to fill the outflowing tube completely (or almost completely). The tube in your picture will act as a simple overflow with free surface flow (a "weir") if your inflow is not large enlogh to fill it. If you look the funny fountain video, the recharge is colose to the siphoning discharge. In that case I see no problem. Try it with very small recharge, will it work than ?

[studiot]

 

The tube in your picture will act as a simple overflow with free surface flow (a "weir") if your inflow is not large enlogh to fill it.

 

 

The condition under which my diagram will act as a siphon or simply an overflow depend upon the inlet and outlet conditions.

 

I thought I had already explained that, did you not understand it?

The diagram was meant to be able to reproduce this stated behaviour, which it could do in suitable circumstances.

 

The frequency of outbursts ranges between few hours and few weeks, depending on the amount of precipitation which determines the recharge to the system.

 

Here is a modified drawing, exaggerated to demonstrate the point.

 

Water enters the initially empty chamber and fills it to level CC a total of volume 3

There is no outflow at this stage.

Further inflow fills the volume marked 2 plus the left hand pipe of the siphon.

When the water reaches level AA it starts to trickle out over what you have dubbed a weir.

So long as the inflow remains low it will trickle out over this weir.

 

However inflow is variable and a sudden influx of water equal only the the small additional volume 1 and taking the level to BB will initiate the siphonic action.

 

The siphon will now discharge through the outflow until the level falls to CC.

That is the whole of volumes 1 and 2 will discharge continuously in a sudden rush.

 

There will then be a dry period where volume 2 recharges, the duration will depend upon the size of volume 2 and the inflow rate.

 

The siphon is then reset ready for action.

 

Note that unlike the cup and straw siphon in the video the intake for the outlet is not at the bottom (though it could be) so volume 3 is never discharged once filled. The straw emptied the cup completely since one open end went to the bottom.

Note also that this mechanism is capable of providing a much larger temporary sudden discharge, plus a lower base rate flow, depending upon the geometry. All it requires is volume 1 to be much smaller than volume 2.

Edited September 29, 2013 by studiot

[John Cuthber]

It reminds me of one of these

http://en.wikipedia.org/wiki/Soxhlet_extractor

[gaber]

 

 

The condition under which my diagram will act as a siphon or simply an overflow depend upon the inlet and outlet conditions.

 

I thought I had already explained that, did you not understand it?

The diagram was meant to be able to reproduce this stated behaviour, which it could do in suitable circumstances.

 

I have no problems understanding all what you claim and you are right. My question was: can you foresee any settings where the high discharge (500 l/s) siphoning can be triggered (no valves or any moving parts) by low constant inflow (3 l/s) with Volume 2 in your scetch of 1000 m3 ?

[studiot]

 

My question was: can you foresee any settings where the high discharge (500 l/s) siphoning can be triggered (no valves or any moving parts) by low constant inflow (3 l/s) with Volume 2 in your scetch of 1000 m3 ?

 

 

Did I not mention high rate of discharge?

 

 

That is the whole of volumes 1 and 2 will discharge continuously in a sudden rush.

 

The outflow is controlled solely by the outflow geometry and configuration. Once the siphonic action is initiated the inflow exerts no control over the outflow, rather like the toilet flush I referred to in post2.

 

Do you understand this?

 

The inflow in not going to be constant, which you originally stated.

 

 

depending on the amount of precipitation

 

Of course perhaps this might be the only absolutely constant, naturally occurring flow, in existence.

 

As a matter of interest have you heard of Turloghs in the Burren in County Claire in Eire?

You should look these up.

[michel123456]

It reminds me of one of these

http://en.wikipedia.org/wiki/Soxhlet_extractor

I should have known the Pythagorean cup.

 

 

http://www.youtube.com/watch?feature=player_embedded&v=LLlwzlbY_OU

Edited October 8, 2013 by michel123456

[John Cuthber]

Shortly afterwards, the Pythagoreans invented the saucer.