Using capillary action to raise water (Is perpetual flow possible?)

  • #1

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I know there have been a number of posts relating to capillary action but after reading through them I cannot find an obvious answer to my query. Although capillary action can be used to explain the properties of 'wicking' materials that can raise water vertically I am unsure as to whether it is possible to collect that water at a point higher than it started. To illustrate I have done a number of common experiments such as a paper napkin or paper towel siphon from one glass to another. (see images attached). Eventually the water level in each glass will equate. If you then raise one end out of the glass will it continue to drip? Everything I have read would suggest no, in order to do this the surface tension would have to break (as I understand) and it is suggesting a continuous flow of water may be possible. However in this article http://drspark.com/idea001.php" [Broken] the author claims to have set up an experiment where water can be sucked up a capillary tube into a wicking material and leave at a higher point than it started. This would seem to me to break the rules of energy conservation and therefore not be possible unless there is something I am missing. I would be really grateful for any comments, I am an architecture student looking into the properties of wicking materials for the design of a pavilion that could provide evaporative cooling and thermal mass. As it is a short theoretical project I don't have enough time to fully explore but for my own interest I would like to understand whether this potential for perpetual water flow is possible or not?
 

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  • #2
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No, it isn't. There are many threads on this, I'll try to dig it up.
 
  • #3
NascentOxygen
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Something dodgy about that video. Trees move water up to the leaves by capillary action, where most of it evaporates from the leaves. It's the evaporation that draws up more. So long as you are content for the liquid to be evaporated, capillary action allows you to raise it up higher-that's what a wick does. The tree trunks are full of very very thin pipes in which the water rises. On a hot day, it is said that a microphone placed on the trunk of a tall tree can hear the pings (or reverberations) as the thread of water in individual pipes regularly breaks when the "suck" exceeds the force of attraction between the water molecules and a vapour lock momentarily forms, then repairs itself.
 
  • #4
Thanks for your replies, I agree that the video doesn't look quite right. I found a further reply by the author suggesting that the wick they hung from the top of the capillary tube was long enough so that a drop forming on the bottom of the wick would just touch the surface of the water below which would then draw out the water from the wick. However I am not sure that it is even possible for drops to form at the end of the wick. What I was initially planning was an experiment where water could be wicked from one bottle to another above (see attached image), this would be repeated up the structure however I believe some form of pump will be needed in the end.
@NascentOxygen - I think the evaporation could really help, however I would also be interested in the effects of temperature differentials and pressure differentials however this starts to look more at fluid dynamics and bernoulli's equations. I would be really interested to look at more detail on the tree structures to see if that sound can actually be heard?
 

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  • #5
NascentOxygen
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Flying right off at a tangent: you can have a perpetual fountain in a superfluid rising through a capillary. There is a video of a fountain that never stops. http://www.youtube.com/watch?v=kCJ24176enM"
 
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  • #6
NascentOxygen
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Your two bottle demo may appear to cause water to move upwards. The mechanism might be that a small amount of the vapour is captured in the upper bottle and condenses back into water. Is the condensate red or clear? What percentage of the loss from the lower bottle is captured in the upper bottle? You could try wrapping plastic tape around the exposed wick, or enclose it in sealed plastic tubing, to eliminate evaporation losses and see what happens. :smile:
 
  • #7
Trees move water up to the leaves by capillary action, where most of it evaporates from the leaves. /QUOTE]

This is not true. Water rises up trees due to active molecular pumping. (I have a degree in biology and was taught this.)

Capillary action is limited to 30 feet in theory, less in practice.
 
  • #8
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Hi, Interesting topic. I agree with Nascent Oxygen. Take trees, wrap a plastic bag around a few of the leaves and you will find water in the bag after a few hours. While it is true that capillary action , like atmospheric pressure is restricted to about 30 ft, what about valves. Since the variation in atmospheric pressure would be slight even up to a hundred metres or so, each time a valve closes it would be like making a new start going upwards!
 
  • #9
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Flying right off at a tangent: you can have a perpetual fountain in a superfluid rising through a capillary. There is a video of a fountain that never stops. http://www.youtube.com/watch?v=kCJ24176enM"
I'm pretty sure that fountain has not been proven to never stop. Even superfluids have a nonzero viscosity.
 
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  • #10
Hi, Interesting topic. I agree with Nascent Oxygen. Take trees, wrap a plastic bag around a few of the leaves and you will find water in the bag after a few hours. While it is true that capillary action , like atmospheric pressure is restricted to about 30 ft, what about valves. Since the variation in atmospheric pressure would be slight even up to a hundred metres or so, each time a valve closes it would be like making a new start going upwards!

That might work, but that is not how plants do things.
 
  • #11
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Patrick
I haven't ascertained whether plants use valves in their system but animals do, I should think. So you never know! Granted that this is your subject, I am just musing as it were.Given that a tree trunk must have an enormous number of capillaries running through it, it is possible, hypothetically speaking for water to start rising in one of the systems, with the valves closing behind it, till the water reaches a leaf and evaporates and the whole cycle could start again. Even a molecular pump sucking several tons of water upto heights exceeding a hundred metres during the course of a single night, must require some help from capillary action and atmospheric pressure. Maybe you could explain the working of the molecular pump in more detail ?
 
  • #12
Patrick
I haven't ascertained whether plants use valves in their system but animals do, I should think. So you never know! Granted that this is your subject, I am just musing as it were.Given that a tree trunk must have an enormous number of capillaries running through it, it is possible, hypothetically speaking for water to start rising in one of the systems, with the valves closing behind it, till the water reaches a leaf and evaporates and the whole cycle could start again. Even a molecular pump sucking several tons of water upto heights exceeding a hundred metres during the course of a single night, must require some help from capillary action and atmospheric pressure. Maybe you could explain the working of the molecular pump in more detail ?
It has been 38 years, but essentially living things have tremendous nanotechnology and do things molecule by molecule. It's very efficient.

Animals have circulatory values, and plants maybe use capillary action to some degree in the xylem and phloem. To say more I'd have to start searching for keywords.
 
  • #13
NascentOxygen
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  • #14
sophiecentaur
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This would seem to me to break the rules of energy conservation and therefore not be possible unless there is something I am missing. I would be really grateful for any comments, ?
There is no need for energy conservation to be violated. There is a constant supply of thermal energy from the room which can provide the Latent Heat of Evaporation for the water and any other energy needed to lift (select) a small proportion of 'energetic molecules' inside the column. I suspect that, if you conducted the same experiment in a sealed, insulated container with no light or other radiant energy admitted, the phenomenon would slow down or even stop once the humidity gets high.

I wonder if anyone ever studied (and found) a temperature gradient on a column like the one in the picture.

Btw, that 'syphon' is a very common phenomenon. If you hang a cloth over the lip of a bucket, nearly full of water, it will often just empty the bucket, dripping onto the floor, if the initial ' lift' is not too high and starts off the syphon action.
 
  • #15
NascentOxygen
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Water rises up trees due to active molecular pumping. (I have a degree in biology and was taught this.)

Capillary action is limited to 30 feet in theory, less in practice.
Quite. I should have used a phrase different from "capillary action" since that has a specific definition in science. Perhaps "capillary transport" would be a good fit, coupled with what I said about it being powered by evaporation from the leaves.
 
  • #16
sophiecentaur
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Capillary action is limited to 30 feet in theory, less in practice.
That, surely, only refers to a closed capillary tube. A porous medium does not have a varying hydrostatic pressure operating at different levels. Atmospheric pressure is acting at all levels because it has holes in the sides all the way up, through which evaporation can take place. That would imply no limit to column height, wouldn't it?
 
  • #17
Sorry I haven't been on here for a while. Thank you to everyone for all your help. There are some very interesting themes here that I will continue to explore when I get a chance however my architectural proposals began to move into a different direction and I left the vertical transportation of water. Perhaps something to pick up in the future.
 
  • #18
As was mentioned on other parts of the forum it is the evaporation, or rather the "hole" caused by evaporation at the top of the column that causes the water to rise in trees. In Physics as you know there are many explainations for phenomena, but some seem to be better than others. One could use the "smug" explaination of "wetting" to explain this action. or someone who realizes that "holes" in these columns are like the "holes" in semiconductors could turn the whole theory into something that most of us are more comfortable with, a semiconductor theory of capillary action. One way to create the holes is to use thermal energy to draw the water up, on a hot day in spring, if a tree is cut, it bleeds profusely, that is how much water can be drawn up by the heat, enough to see a flow. Can other fluids such as metals be drawn up tubes by other sizes of photons, can elementary particles be drawn up by interaction of other sorts at the top of the column vertex, perhaps a path integral theory of capillary action. that is where recent physics has to be, it has to deal with the real miracle of capillary action, not with the old wetting theory, or chemical bond theory.
 
  • #19


Has anyone tried doing this with the help of very thin glass tubes?
 
  • #20
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As was mentioned on other parts of the forum it is the evaporation, or rather the "hole" caused by evaporation at the top of the column that causes the water to rise in trees.
As an aside has anyone seen a video of a tomato plant injected with red or blue food die.
I can't find one on U-tube, it's quite interesting to watch.I remember injecting a plant in the base of the main stem many years ago and was stuned to see the liquid shoot up the plant with great force and speed.
 
  • #21
NascentOxygen
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I seem to recall people placing a stick of celery in ink to show water transport.
 
  • #22
Bobbywhy
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“Transporting water to the tops of trees”
N. Michele Holbrook and Maciej A. Zwieniecki
January 2008 Physics Today

“Trees are solar driven evaporative pumps that wick water up from the soil using capillary forces. But their ability to operate in a metastable state makes them unique among both natural and human-engineered transport systems.”

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=12&ved=0CHkQFjAL&url=http://www.fluid.dtu.dk/upload/fluid.dtu/articles09/missy_holbrook/pt_quickstudy0108[1].pdf&ei=vU0wUcvLCZTW8gSN3oHABg&usg=AFQjCNFZBdsWAFDUIz5CwiezLbcXtQNIVw&sig2=72lYfkZHBfkVy-tNTfHc3w

and: http://www.scientificamerican.com/article.cfm?id=how-do-large-trees-such-a [Broken]

and: http://en.wikipedia.org/wiki/Xylem

Finally, cavitation does occur in plants and trees under some conditions and is detected using an acoustic transducer as high frequency “pings” or “pops”. See http://5e.plantphys.net/article.php?ch=&id=395

Cheers, Bobbywhy
 
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  • #23
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I seem to recall people placing a stick of celery in ink to show water transport.
Sure that's interesting but not the same as injecting ink into the main stem of a tomato plant.
It does not creep up over time it literaly shoots up the stem in an instant, strange but true.
 

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