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Author Topic: How do Trees Really lift Water to their Leaves?  (Read 244849 times)

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #200 on: 29/10/2008 09:26:07 »
BTW, Andrew, a competent Engineer would know how any black box he uses will work because he couldn't risk it failing to perform as he expects when tested. You have been using a black box all the time but have no idea what is going on inside. You're no Engineer. There goes another group of workers who you have denigrated.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #201 on: 29/10/2008 10:23:47 »
Sophie You are forgetting one very important observation which you must consider.

The flow from one vessel to another both at ground level therefore at = pressures, yet clearly visible in the Brixham video as being far superior to the flow rates observed in trees. Adhesion as you state is responsible for sticking the water to the inside of the tube, Cohesion evident in the flow from one vessel to another is clearly not relying on adhesion. Once the bead of water is severed by cavitations the water flows from the tube ends and empties it if they are removed from the water at ground level. Adhesion clearly is not as important for suspending the water. When the water bead collapses and the tube endings remain in the water at ground level. The water falls back to the 10 metre level. The space above it being vacuum as was shown in the original problem of the pump by Galileo and co.

Your last post appears to be stating the obvious again regarding adhesion in the tube and this is where I fear we may have had crossed lines. I was relating to your capped end tube all along. I see no point in stating the obvious. One could go on to argue that the cord used to raise the rope exerts a constricting pressure and the downward pulling on the cord over a pulley block exerts an upward motion to the tube and the airÖÖ. pressure exerts a positive pressure outside the tube and on the water in the reservoirís at ground level. Why complicate a simple successful experiment when all this is obvious to the observer? This may be required for a patent application, but surely not for a simple tubular experiment?

Nevertheless. I melted the end of a 130 CM length of the same tubing used in the Brixham experiment, Blew down so the molten end formed a bulb as you suggested, filled it with tap water making sure no bubble were present, held it up and noted that water did not flow out of the end as expected. Applied a very moderate centrifugal force by holding the closed end and gently rotating it to find with little to no force water flowed from the end as expected.

Next: Repeated the same with previously boiled / degassed water and found that there may have been slight (if any) increase in resistance to the bead of water failing. The tube was at no point rotated the tube differently to force the bead of water to break and the tension could not have been any where close to that observed in the Brixham Experiment at 24 meters. One could argue that the air flowing passed the open end increased the tension on the water inside the tube, but trust me on this, I did the experiment to see for myself if adhesion could support the water in a 6 mil bore nylon tube, not to make it fail but to try to make it work.

Again I must state that there is little to no point repeating the same experiment with a longer length of tubing as the force exerted by the column of suspended water will easily cause the water to be pulled from the tube.

It may interest you to know that when the U tube is performed lower than 10 metres and the ends of the tubes are removed from the water, the water flows out and will not remain in the tubes. I look forward very much to your comment on this observation too.
 
Andrew K Fletcher

Albert Einstein
One had to cram all this stuff into one's mind for the examinations, whether one liked it or not. This coercion had such a deterring effect on me that, after I had passed the final examination, I found the consideration of any scientific problems distasteful to me for an entire year.
« Last Edit: 29/10/2008 10:45:28 by Andrew K Fletcher »
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #202 on: 29/10/2008 10:44:40 »
If you were a thinker instead of a sheep you would engage your brain before opening your mouth. Again you attack me. It is I that has trashed the bull that you have been teaching not you that has trashed my experiments. Worth remembering that don't you think?
Any moron can keep churning out the same written literature without questioning it.

Albert Einstein
Humiliation and mental oppression by ignorant and selfish teachers wreak havoc in the youthful mind that can never be undone and often exert a baleful influence in later life.


BTW, Andrew, a competent Engineer would know how any black box he uses will work because he couldn't risk it failing to perform as he expects when tested. You have been using a black box all the time but have no idea what is going on inside. You're no Engineer. There goes another group of workers who you have denigrated.

Albert Einstein
Education is what remains after one has forgotten everything he learned in school.
« Last Edit: 29/10/2008 10:49:00 by Andrew K Fletcher »
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #203 on: 29/10/2008 11:34:20 »
I have just read your last outburst, which I will ignore.
I was about to post the following reply when I read it.You will notice that I am trying to be constructive.:

Quote
I see no point in stating the obvious
It may appear obvious to you but nothing is 'just obvious' in Science. If you have an incomplete model in your mind of what is going on then you can't explain this.
The reason that you don't explain it must be because you can't.
You are doing to me exactly what you claim that Science teaching is doing to children.
What you are saying. effectively, is "You just have to accept this obvious fact". If it isn't obvious to me then are you going to shout at me as if I were a naughty / thick child or are you going to try to help me with my obvious misconception?
Which should I do if I were trying to get an idea across to a child who didn't get what I was saying?

Some comments:
Quote
Cohesion evident in the flow from one vessel to another is clearly not relying on adhesion
Do you have a cohesion meter and an adhesion meter to tell you this? What justification for this statement? (we are not dealing with a chain or wire made up of a solid substance)

Quote
I was relating to your capped end tube all along.
But I was, 'all along', asking you to draw a distinction between the two situations - yours and mine.

Quote
One could go on to argue that the cord used to raise the rope exerts a constricting pressure

Precisely. The weight of the rope will pull down on the pulley. The rope is a solid and, despite being able to distort a little (become a bit narrower and longer), the 'constricting pressure' is balanced by the molecular forces which are there - the properties of a solid. If you were to hang a length of chewing gum (a very plastic substance) over the pulley the gum would stretch and get thinner because it would flow. Water flows, too, but more easily, so you would expect the same if you didn't provide the tube outside it which could provide some extra forces.

Quote
I melted the end of a 130 CM length of the same tubing used in the Brixham experiment
Well, you did try.  It worked as expected.  During your whirling phase, it is not surprising that water flowed out - the tube could flex and bubbles would have been admitted into the bottom, allowing air in.  Also, the opening at the bottom would not have been horizontal so there would have been a pressure differential (Hydrostatic - not atmospheric) across the inverted surface of water - that would start a water flow - you can see this happen with an inverted bottle of water, too where the water flows (gloops)  out quicker if the bottle is not exactly vertical. If you had suspended the tube motionless and tapped the sides I would expect the same sort of thing to happen. It was worthwhile trying but you were not in a position to see what was actually going on inside the tube. If you were to try the same thing with your U tube, I think the water would fly out even quicker with such rough handling (see the last comment on this post for the reason).

Quote
Again I must state that there is little to no point repeating the same experiment with a longer length of tubing as the force exerted by the column of suspended water will easily cause the water to be pulled from the tube.
That presupposes your original ideas are correct and that the inside of the top of the tube was as smooth as the top of the looped U tube.
There are many problems associated with implementing the closed tube experiment and I can see how the continuous loop provides both a much smoother surface and a better chance of eliminating bubbles. That is a practical and not a fundamental difference between the two experiments. Very easy to draw the wrong conclusions about the actual mechanisms at work.

Quote
It may interest you to know that when the U tube is performed lower than 10 metres and the ends of the tubes are removed from the water, the water flows out and will not remain in the tubes
That is precisely what I should have expected to happen. It's an unstable situation. Unless the two arms of the tube are precisely the same length then there will be a hydrostatic pressure differential across them causing water to flow. Once it has started, the difference increases further and the flow will increase.  If the tubes are kept in small reservoirs, such as in your original videos, the levels will self-adjust. This, of course, explains why, when you added a more dense liquid to one side, the levels started to change; the hydrostatic pressures are not equal. If you were to raise the side with the salt in, you would find a new position in which the flow would be zero. (Until diffusion of the salt solution into the freshwater side started to change things).

To sum up, I can see nothing in your last post which proves or justifies further you explanations. Half way through you, yet again, beg the whole question by making the assumption all over again.
All you have described fits in perfectly with conventional theory.
I think I have identified the crux of our differences  enough times. Are you really not capable of answering my one small point about the way the molecules must be working 'at the top' IN BOTH CASES?

 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #204 on: 29/10/2008 12:33:10 »
It was Einstein not me that wrote those quotes attacking his own experience in the education system.

To sum up:

1 the experiments at Brixham were roughly handled over a relatively prolonged period of time, due to the person at the top of the cliff lowering the tube rather than holding it steady, yet the bead of water remained intact as shown in the unedited actual time footage. More experiments have been done many times and recorded showing this bead of water to be a lot more robust than you are imagining it to be. I knew you would argue that gently rotating the smaller capped tube would not represent the longer tube. But surely you can comprehend how much tension there is in a u tube suspended to 78 feet = two columns of water pulling on each other. The tension BTW should be the same throughout the water column, because as you state each moecule must act on it's neighbouring molecules. A further experiment was conducted at a greater height than 24 metres. The water inside the tube was observed to boil without heat.






I have just read your last outburst, which I will ignore.
I was about to post the following reply when I read it.You will notice that I am trying to be constructive.:

Quote
I see no point in stating the obvious
It may appear obvious to you but nothing is 'just obvious' in Science. If you have an incomplete model in your mind of what is going on then you can't explain this.
The reason that you don't explain it must be because you can't.
You are doing to me exactly what you claim that Science teaching is doing to children.
What you are saying. effectively, is "You just have to accept this obvious fact". If it isn't obvious to me then are you going to shout at me as if I were a naughty / thick child or are you going to try to help me with my obvious misconception?
Which should I do if I were trying to get an idea across to a child who didn't get what I was saying?

Some comments:
Quote
Cohesion evident in the flow from one vessel to another is clearly not relying on adhesion
Do you have a cohesion meter and an adhesion meter to tell you this? What justification for this statement? (we are not dealing with a chain or wire made up of a solid substance)

Quote
I was relating to your capped end tube all along.
But I was, 'all along', asking you to draw a distinction between the two situations - yours and mine.

Quote
One could go on to argue that the cord used to raise the rope exerts a constricting pressure

Precisely. The weight of the rope will pull down on the pulley. The rope is a solid and, despite being able to distort a little (become a bit narrower and longer), the 'constricting pressure' is balanced by the molecular forces which are there - the properties of a solid. If you were to hang a length of chewing gum (a very plastic substance) over the pulley the gum would stretch and get thinner because it would flow. Water flows, too, but more easily, so you would expect the same if you didn't provide the tube outside it which could provide some extra forces.

Quote
I melted the end of a 130 CM length of the same tubing used in the Brixham experiment
Well, you did try.  It worked as expected.  During your whirling phase, it is not surprising that water flowed out - the tube could flex and bubbles would have been admitted into the bottom, allowing air in.  Also, the opening at the bottom would not have been horizontal so there would have been a pressure differential (Hydrostatic - not atmospheric) across the inverted surface of water - that would start a water flow - you can see this happen with an inverted bottle of water, too where the water flows (gloops)  out quicker if the bottle is not exactly vertical. If you had suspended the tube motionless and tapped the sides I would expect the same sort of thing to happen. It was worthwhile trying but you were not in a position to see what was actually going on inside the tube. If you were to try the same thing with your U tube, I think the water would fly out even quicker with such rough handling (see the last comment on this post for the reason).

Quote
Again I must state that there is little to no point repeating the same experiment with a longer length of tubing as the force exerted by the column of suspended water will easily cause the water to be pulled from the tube.
That presupposes your original ideas are correct and that the inside of the top of the tube was as smooth as the top of the looped U tube.
There are many problems associated with implementing the closed tube experiment and I can see how the continuous loop provides both a much smoother surface and a better chance of eliminating bubbles. That is a practical and not a fundamental difference between the two experiments. Very easy to draw the wrong conclusions about the actual mechanisms at work.

Quote
It may interest you to know that when the U tube is performed lower than 10 metres and the ends of the tubes are removed from the water, the water flows out and will not remain in the tubes
That is precisely what I should have expected to happen. It's an unstable situation. Unless the two arms of the tube are precisely the same length then there will be a hydrostatic pressure differential across them causing water to flow. Once it has started, the difference increases further and the flow will increase.  If the tubes are kept in small reservoirs, such as in your original videos, the levels will self-adjust. This, of course, explains why, when you added a more dense liquid to one side, the levels started to change; the hydrostatic pressures are not equal. If you were to raise the side with the salt in, you would find a new position in which the flow would be zero. (Until diffusion of the salt solution into the freshwater side started to change things).

To sum up, I can see nothing in your last post which proves or justifies further you explanations. Half way through you, yet again, beg the whole question by making the assumption all over again.
All you have described fits in perfectly with conventional theory.
I think I have identified the crux of our differences  enough times. Are you really not capable of answering my one small point about the way the molecules must be working 'at the top' IN BOTH CASES?

By the way, bubbles being admited into the bottom of the whiling tube will not alter the adhesion at the top of the tube with a mere two rotations will it? How do those bubbles travel from the opend end to the top of the capped tube while it is generating centrifugal force towards the ends of the pipe? What really happens in the tube is that the weight of the water exerts too much force on the molecules stuck to the top of your domed capped tube ending.


« Last Edit: 29/10/2008 12:47:54 by Andrew K Fletcher »
 

Offline neilep

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Re: How do Trees Really lift Water to their Leaves?
« Reply #205 on: 29/10/2008 13:16:19 »
Glad to see everyone is being so cordial, courteous and gracious   ;) ;D

 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #206 on: 29/10/2008 14:13:24 »
Thank you Neil!
Andrew:
You need to refomat your post. The quote includes some of your own words at the bottom, I think.

Your original post did not discuss how the space at the top had formed. Are you suggesting that the gap at the top of the tube was a vacuum? In which case , when you removed your 'extra force', the water would have gone back up to the top (as Galileo et al have found). If the gap remained, then it was full of air. This air can only have got there as bubbles from the bottom, out of solution or via a leak in your 'sealed end.  It must have come from somewhere.
Quote
The tension BTW should be the same throughout the water column,
Just not true. If you take a chain (of finite mass) and hang it up. The tension between the bottom two links is equal to the weight of the bottom link. The tension between the top two links is equal to the weight of the whole chain - less the top link weight.  How can the bottom link 'know' how many links there are above it? If there were more  tension acting on the bottom link than its weight then  it would move upwards. (Newton's First Law of Motion applies, as always)

How can you pontificate about this topic if you make a simple error like that? Some serious rethinking is needed, I fear.

I wouldn't mind betting that Einstein made a point of learning, thoroughly,  all about Newtonian Physics before he started leading off that it was inadequate or wrong. He never treated anything as 'obvious'.
I can sympathise with him regarding his view that his education was lacking. HE, as it proved later, was actually very clever  and was probably frustrated at his teachers not even approaching him in ability and he never did suffer from an understated ego.  Andrew - you are no Einstein.
I am just a humble proponent of a system which seems to work very well and is very consistent (except at its esoteric edges) - because the people who have constructed it are are lot more clever than you or I. But I do my best to avoid skating around difficult points - unlike you, who still refuse to address one pivotal question which I need not repeat, surely.
 

Offline JimBob

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Re: How do Trees Really lift Water to their Leaves?
« Reply #207 on: 29/10/2008 15:07:25 »
Y
Glad to see everyone is being so cordial, courteous and gracious   ;) ;D


And we could always determine the outcome of this by, oh, say broadswords. No light sabers - this is an age of enlightenment.

 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #208 on: 29/10/2008 15:16:39 »
Keyboards at dawn, I think. Or any other time in the 24hr cycle.
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #209 on: 29/10/2008 15:16:54 »
Can you feel the tension?
 

paul.fr

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Re: How do Trees Really lift Water to their Leaves?
« Reply #210 on: 29/10/2008 15:54:37 »
Glad to see everyone is being so cordial, courteous and gracious   ;) ;D



Well im only reading this topic for the insults. Although i do find in upsetting when two grown men (ok, one may or may not be a woman..oh and i discount BC because he is a chemist) yadda yadda yadda...

Lokk, just get on with slagging eachother off, i have popcorn ready you know!
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #211 on: 29/10/2008 16:07:13 »
All I want is an answer and all will be clear folks.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #212 on: 29/10/2008 16:12:14 »
You know Sophie, you must be correct. I must be a complete idiot for showing you that water can be placed under tension when you refuted it. But where does that leave you?

Tension is brewing
Of course every molecule in the columns is under tension. Each and every single one of them. The downward pull from gravity on the water must also have an effect on the walls of the stiff nylon tubing, but not sufficient to account for the water springing up the tube when the ends are removed from the water container at ground level.

Add a pinch of salt to one side and water is drawn up under tension. Not because of pressure changes either. 1 grain of salt will trigger this flow! How can you account for this in pressure changes?  Surely this flow is responsible for generating the pressures and not the other way around. What drives the circulation before a heart forms? Gravity is a good starting place! This is not the same as a siphon. I keep trying to explain that there is a huge difference between a siphon flow and a density flow. Thought experiment. Coloured salt solution added to upward flow side of a siphon in sufficient quantity to generate a density flow in the upward flowing side. Here we have a downward density flow in the same side as an upward flowing siphon flow. Seen it done it!

Do I have a laboratory and unlimited funds to go with my cohesion and adhesion measuring device? Perhaps an entire university behind me even as you do?

You avoid most of my questions and ignore most of my answers and concentrate on what is happening to the molecules inside the tube? I do not understand what you want from me other than for me to become a verbal punch bag that is?
 

Offline Bored chemist

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Re: How do Trees Really lift Water to their Leaves?
« Reply #213 on: 29/10/2008 19:16:13 »
Fascinating, but I'd sooner see you answer Sophie's question.
 
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #214 on: 29/10/2008 19:31:02 »
I did try to deal with all the issues in your last post. Did I avoid any of them?
I am surprised that you don't think the behaviour of molecules is relevant to the way substances behave. To my mind that is a crucial issue upon which all other things in this topic must hinge. Any explanation just has to include the molecular consideration or we are back in the middle ages.

Have you given some thought to my chewing gum idea? Is that not relevant to the situation with water?

One grain of salt will cause a flow? Of course it will. The solution around it is more dense and will drop through the fresh water, albeit quite slowly. It would be a real surprise if it stayed there or went up.

What is 'surely' about the flow generating the pressure? You can measure a pressure difference with out needing any flow. As I suggested, try raising the salty side and you will get a balance point (equalise the pressure difference) with no flow. Why do you muddle up cause and effect so often? What do you suppose started the flow in the first place? Everything needs energy from somewhere to make it happen. Where does the energy come from for your flow if not from the salt having been lifted, by some means or another and gaining Gravitational Potential.

How about my question regarding the space that you saw above the column of water? Did it stay there? Was it air? How did it get there?  There is an interesting practical question here.

The fact that an open-bottomed U tube doesn't stay full is very well explained in terms of small pressure difference. You have not replied to my general comments about your latest trials. I think they were mostly good-willed comments??

What is a "density flow"? It is not a term in common use.

I fully believe you saw what you saw but the girl saw the tooth fairy's money too. Was she right to believe in the tooth fairy? She could have found the real cause by the appropriate experiment - staying awake all night- or asking someone who knows.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #215 on: 31/10/2008 09:27:02 »
Ok let me ask you to state what you know about the Brixham experiment.
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #216 on: 31/10/2008 18:27:50 »
There's no point in going into too much detail but what it has actually 'proved', rather than what you have 'seen in it' is as follows. Water, under reduced pressure, will not boil instantly. It exhibits cohesion and adhesion. The forces of adhesion and cohesion, as a pair, sustain a siphon process when you increase the density of the liquid on one side of a U tube.
That, in itself, makes the Brixham Experiment well worthwhile having been done. It is a surprising result but reasonable with hindsight. There is, elsewhere, work which shows and measures the 'dynamic (temporary) tensile strength' of water under negative pressures.
You have not yet answered my objections /  questions regarding the results of your recent single tube experiment. They are the same questions that I would have asked myself if I had done the work myself - I was not trying to give you a hard time about it.

Your explanation and the undefined terms you use (such as density flow,  for instance) are not the only ones possible.

My explanation uses conventional and well tested ideas and tries to use as much of the existing knowledge as possible.

If you really had a convincing package of explanations for the phenomenon then you should be able to reconcile your ideas with such fundamental questions as mine regarding how the molecules behave at the top. You have still not managed to answer this in any depth. You just cannot ignore the problem or dismiss it as obvious - it isn't.

Remember - you are the one who is introducing a new idea and rejecting the established one. The burden of proof lies with you. That is, if you want it to be taken seriously.
Are you still not prepared to discuss the molecular situation and the nature of the forces all through the water?
Rather than just getting upset that your ideas haven't been accepted without argument, you need to substantiate them better.
 

Offline _Stefan_

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Re: How do Trees Really lift Water to their Leaves?
« Reply #217 on: 01/11/2008 01:52:50 »
I'd really like to see Andrew answer whether the column of water would remain intact if the tube were removed.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #218 on: 01/11/2008 10:08:36 »
SophieCentaur.

Thank you for your reply

However, you have not stated anything I have not already stated other than mentioning the adhesion of water to the inside of the tube, which to me at least was obvious. In other posts, I have mentioned this, as soft walled tubes collapse when tension is applied. Again it is obvious that the water is still stuck to the tube and that the tension is pulling on those molecules which in turn pull on the tube. One could also argue that the adhesion inside the tube, coupled with the applied tension lowers the pressure inside a soft-walled tube to the point where atmospheric pressure pushes the tube in and that it does so because air molecules are in contact with the outside of the tube. I have also stated time and time again that the water resists the tendency to boil over the 10 metre mark, even adding when you take the experiment considerably higher than 24 metres the water boils as would expect it to. Even stating that adhesion in certain previous experiments was the reason for failure when cohesion in an unbroken column of water succeeds. Somewhere, I have also stated about my friend Adrian Van Sweden, a brilliant physicist, and former water engineer from South West Water sat on a step with his hands covering his face saying this is not possible after witnessing my experiments. He added water cannot exist in a negative pressure environment but here it is. Why have I not been taught this?

Remember what I said about working with a siphon over 10 metres
As you lower one vessel it stretches the water on the side that you are lowering causing cavitation and eventual failure. It does not induce a flow from one vessel to another. This is worth considering because had it ever have done so it would have been in the literature by now, as many engineers, plumbers, pipe fitters, boilermakers, fire fighters, irrigation experts, have all entertained this problem.

The spinning Z tube where water is injected at the centre of the Z causes the water to cavitate when sufficient tension has been applied. As water passes over the elbows of the Z tube rotating clockwise it induces tension that can be measured accurately.

Hindsight is an easy word to say after an event, but a difficult word to comprehend before an event.   

The 6 mil bore tubing capped and swung around gently caused the water to empty from the tube without any deliberate whipping or flexing in the tube. I wanted this experiment to succeed by the way as I have to admit there was a chance it could have, albeit slim. Even using degassed, pre-boiled water it made little to no difference. The spinning Z tube on the other hand confirms the huge tensile strength of water and as the Z tube is of a very small size, adhesion provides the stability of the injected water preventing it from necking. In a soft tube this necking is illustrated. In a solid walled tube not so obvious.

This is why IBT is important for varicose veins shrinking and oedema being drawn from the surrounding tissue back into the circulation. The density flow through the arteries induces the tension in the veins causing the fluids to pull the veins in as the pressure is relieved that causes them to bulge.

Studying trees on the other hand is more difficult due to the rigidity of the tubes, except in the stages of tube production just beneath the bark. This is where pressures and adhesion count in the liquids before they become solid tubes. The pressure in the liquid caused by the gravity induced downward flow resulting from solute free evaporation at the leaf enables a flow without tubes under a positive pressure, essential for maintaining the inside diameter of the forming tubular cells. And lignifications strengthen the walls around the flow by attracting and hanging on to the molecules of resin suspended in the sap. So here lies the answer to yours and Stefanís valid question about whether a flow can exist without tubes. In fact circulation in all creatures begins long before any tubes are formed.   

Andrew K Fletcher
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #219 on: 01/11/2008 10:52:12 »
Why do you bother to include comments about trees and IBT in your reply?
The fact that you can observe certain effects does not justify your explanations of one simple effect. You just cloud the issue.

You will notice a scattering of posts from other members amongst our dialogue. They all include the same basic question as mine regarding the basics of what happens at the surfaces of the tubes, in molecular terms.

I assure you that we are not all 'ganging up' on you about this. You should take it as a sign that the question really does need answering.

You keep doing exactly what you complain that teachers of Science do. You expect us to believe in something and refuse to look outside your particular model. Just consider, for a moment, that you could be wrong in this particular aspect of what you (think you) understand.

You went to the trouble of experimenting with the single tube - that's good. But why don't you reply to my queries about experimental details? I am a pretty experienced experimenter and my points are valid.

Please stop repeating your anecdotes and answer the main question. I will then stop asking it.
« Last Edit: 01/11/2008 17:17:40 by sophiecentaur »
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #220 on: 01/11/2008 18:33:06 »
If you have something to add about molecular behaviour in tubes then spit it out man. You appear not to be asking a question but to be implying you know the answer to your own question so get on with it.

I mentioned the tubular growth in trees because I was asked how this flow system could be there without tubes. The reference to soft walled tubes was required to explain how a flow could cause tubes to form with the flow maintained inside them once they have formed.

Perhaps you would like to explain why water inside the tube does not conform to the phase diagram of water to people viewing this thread too?
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #221 on: 01/11/2008 21:44:53 »
I'll spit it out, 'man'.

If the water is to stay in contact with the top of your U tube or my single tube, the molecules at the very top must be attracted to the top or they will move away from it. They must behave in exactly the same way. How can they tell whether they are at the top of your tube or at the top of my tube? They have no brains and no eyes. The same forces must be acting on them. Can you suggest why they should behave any differently? Are you suggesting that no force is needed in your U tube where a force is needed in my tube?
The answer to this question must contain no mention of trees or sick people or how bad Science teaching is.

We can't get anywhere near your flow system until you justify  something far more fundamental.

You won't answer my perfectly understandable questions about your latest experiment. Why not? Does it threaten your integrity or don't you understand them?

I haven't mentioned your Xylem tubes for ages. I am not interested in your tubes until we get the first bit sorted out. Is it really too hard for you?

I have to explain nothing - you are the one who is making the claims.
I just need some valid justifications for your new opinion - not paranoia.

This is a Science Forum. Why don't you treat it as such? Please apply some logic.
 
« Last Edit: 01/11/2008 21:46:47 by sophiecentaur »
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #222 on: 01/11/2008 23:27:07 »
Andrew
I suggest you try reading through this article and some of the references in it.
www.lps.ens.fr/~caupin/fichiersPDF/CRPhys_2006_7_1000-1017.pdf

You may find it instructive. If you can read it and understand what it says, it will tell you a lot of what you need to know about trees, the conditions under which tension in water becomes relevant and how cavitation occurs.
Basically, some of your ideas work for trees but they won't work for firemen.
Before anyone thinks they have found something new, it is a good idea for them to trawl through the literature.
Your 'revolutionary' ideas are very fragmented and seem to contain a lot of half-understood notions. Your very worthwhile experiment on the cliffs has been a bit wasted because of your interpretation of the results.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #223 on: 02/11/2008 16:39:04 »
Sophie, before I read the link provided, I have gone back over the Siphon thread to try to understand what your problem with the Brixham Experiment is. Which incidentally is far from wasted! The results from the many experiments conducted, some of which I have not included in this forum, produce the results that they were intended to produce. The problem with being a lateral thinker is one tends to processes problems as a whole, and not segmented so that each can be understood.

You say water would move away from the inside of the tube. As water is already compressed by gravity, where is it going to move to? It can't move down the tube because it is linked to other molecules balancing the downward pull equally on the opposite side of the U tube. It canít flow out because this would require cavitations to form, again to break the cohesive bond. It canít flow up because of gravity, It canít collapse the tube because the wall is strong enough to resist the decompression. If molecules move away from the wall, more molecules must replace it because each molecule acts upon its neighbours. Cavitations will inevitably combine to form larger vapour bubbles and this will cause the water columns to fall back to the level at which atmospheric pressure can sustain them @ 10 metre mark, so although the molecules cannot determine which experiment they are in, we must take into account at all times that each molecule is linked to another inside the tube, so deciding the fate or purpose of a single molecule or groups of molecules that are part of a huge volume of molecules in the same experiment is a little difficult to consider to say the least.

I have now read the lengthy paper you linked to and found it to be a report on the progress of science relating to cohesion, adhesion, tension, surface tension and cavitations in water and other various liquids, dealing with ancient science and more modern science approaches to the problems of cavitations in water. Most of which was familiar to myself, and some of which I have included in the two threads, including the spinning tubes, stretched water, etc.  Nevertheless, I have not seen this paper before and it does include at least two experiments that I have not heard of before. So thank you for posting the link and for taking the time to look at the experiments.

The terminology I use may not always be in accordance with writing a convincing academic argument and I agree with you on this at least, but if you compare what I have stated to what you have provided in the PDF file we are not far from the mark at all.

Throughout the paper you provided, there is no mention of timescales for cavitations to develop in degassed water, although nucleation is mentioned in relation to impurities in water, I suspect the main seed points are indeed between the water/tube interface. I cannot see another experiment that could show timescales for cavitations other than inside a living plant or tree. The U tube gives us prolonged stability of water under negative pressure and tension allowing us to see cavitations developing through the opaque tubing. There must be clearer tubing produced that could allow us to look more clearly at the forming cavitations.

Deionised water previously boiled will enable the Brixham experiment to easily exceed the 24 metre mark and give us prolonged stability.

I thought the inclusion of particles entering the experiment to cause the nucleation was interesting also. And had not considered this.



The following history event shows how a tiny bubble of gas causes the Huygens experiment, (similar to yours), fails from the paper you provided the link to.


4.1. Pull
A straightforward way to stretch a liquid is to pull directly on it. The pull can be generated by the own weight of the liquid. This is how Huygens made the first experimental observation of negative pressure in 1662, and published his work in 1672 [49]. A tube open at one end is filled with water purged of air, and inverted over a water bath. If the air above the bath is evacuated, water remains suspended in the inverted tube. The pressure at the top of the water column of height h is Psat − ρgh, where ρ is water density, and g the acceleration of gravity. As soon as a bubble of air is injected in the tube, it rises and the water column falls. This experiment was presented to the Royal Society of England, and repeated on water and mercury by several physicists, including the famous Hooke and Boyle,
who reached −0.2 MPa in mercury. The phenomenon was later re-discovered by Donny [23] and Reynolds [47,48]. Details are given by Kell [50]. As Reynolds used a 2.3 m-long tube wetted with water before being filled with mercury, he obtained the most negative pressure for water with this method: −0.3 MPa [48]. Hayward, who thought that the method was invented by Donny [23], re-used it to study different liquids [51]. Another way to pull a liquid is to mechanically increase its volume with a bellow for instance. One can also put the liquid under pressure before warming it up, and eventually releasing the pressure. These techniques have been widely used to make bubble chambers where high energy particles are detected because they trigger cavitation in the metastable liquid (see Ref. [53] for a review); however, volatile liquids with a low surface tension were preferred to water. But the bellow method was used by Hayward to design a water pump with a suction lift of 17 m, corresponding
to a pressure of −0.17 MPa [52]; much higher liquid columns exist in tall trees (see Section 7.1).
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #224 on: 02/11/2008 19:46:25 »
Saying that you are thinking laterally doesn't prove that you are right.
You have brought up many issues which are very interesting and have changed my views about the behaviour of water under negative pressure.
BUT  the model which is in your head is still flawed. It cannot hope to describe what is going on if you say, for instance, that you have negative pressure up there but gravity is still Pushing the water against the tube. How is that consistent?
A truly valid model has to deal with all the little nitpicking details which you choose to ignore. You cannot be so selective about what you do and don't accept about convention without total rigour. Your explanations for what happens in your experiment just would not extend to other situations - even to a single tube. Your brief experiment was not detailed enough. You won't even answer my reasonable queries about it. You are too confident of your model to submit it to scrutiny. Do you not see how important it is to make clear what was in the void at the top of the tube? If it is air then there must be a leak. If there is water vapor or a vacuum then the void would vanish when pressure increases again. What happened? Can you remember? It is NOT irrelevant if your interest is truly scientific. There is nothing glamorous about pressing on and ignoring these queries and objections.
I despair of ever getting answers to these and the other questions which I and others have asked. If you want to be groundbreaking you have to be totally thorough.
 

The Naked Scientists Forum

Re: How do Trees Really lift Water to their Leaves?
« Reply #224 on: 02/11/2008 19:46:25 »

 

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