Can Branching Capillary Increase Water Height?

  • Context: Undergrad 
  • Thread starter Thread starter Medicago
  • Start date Start date
  • Tags Tags
    Capillary
Click For Summary

Discussion Overview

The discussion centers around the effects of bifurcating a capillary on its ability to raise water height, specifically whether a bifurcated capillary can draw water to a height greater than that of a single capillary. Participants explore the implications of capillary forces, meniscus formation, and the physical limitations of water transport in relation to tree height.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant proposes that bifurcating a capillary creates an additional meniscus, which could intuitively increase the capillary force and allow for a greater height of water to be drawn up.
  • Another participant argues that the height of water raised is determined solely by the diameter of the capillary, suggesting that bifurcation does not increase the height but may allow for more water volume.
  • A later reply clarifies that the question pertains to a single capillary that bifurcates, asking if it can draw up more water than a non-bifurcating capillary of the same height.
  • Some participants assert that having two menisci would not double the height of water that can be raised, citing the limitations of capillary action and the cohesive forces of water.
  • One participant discusses the concept of maximum height limits in trees, suggesting that cavitation and the balance of forces play a role in limiting water transport, which relates to their project on water transport in trees.
  • Another participant emphasizes the importance of pressure differences at the meniscus and argues that the force is not simply additive across the entire column of water.
  • Some participants express uncertainty about the validity of the bifurcation model, noting that faculty members did not provide a definitive answer, and mention finding references that lack explanation.

Areas of Agreement / Disagreement

Participants generally disagree on whether bifurcating a capillary can increase the height of water raised. Multiple competing views remain, with some asserting that it can lead to a greater height and others arguing that it cannot.

Contextual Notes

Participants mention various assumptions regarding the behavior of water in capillaries, the role of pressure differences, and the physical limitations of water transport, but these assumptions remain unresolved within the discussion.

Who May Find This Useful

This discussion may be of interest to those studying fluid dynamics, capillary action, and biological transport mechanisms, particularly in relation to plant physiology and tree height limitations.

Medicago
Messages
14
Reaction score
0
Say I have a single capillary that can raise water to height H.

If I split the capillary to make another meniscus, say δ distance from the top, and both branches are of the same radius as before, will I be able to bring water up higher (i.e. could I add another H-δ high column of water to the bottom of the tube)?

If I understand correctly, the capillary force is per meniscus, so adding another meniscus should, intuitively, add more force and be able to draw up more water.


Thanks!
 
Physics news on Phys.org
No, the height just depends on the diameter of the capillary at this point.
You can have more water inside, but you need more water for the same height with multiple capillaries.
 
Not multiple capillaries.

ONE capillary that bifurcates at the top. Can it draw up more water than a non bifurcating capillary of the same height?
 
If it bifurcates, it has two branches at the top.
See my previous post.
 
Well then I don't understand your answer.

I'll try to rephrase my question. I have a capillary that can draw water to height H. I bifurcated it near the meniscus to form two menisci. Can my new bifurcated capillary draw up 2H of water? Considering the radii of the two menisci are the same as the radius of the original meniscus.
 
Can my new bifurcated capillary draw up 2H of water?
Grammar indicates an amount of water, the definition of H is a height?

No, you cannot increase the height.
 
Yes, a 2H column of water.

Why not? If I have another meniscus, wouldn't the force be doubled?
 
Medicago said:
Yes, a 2H column of water.

Why not? If I have another meniscus, wouldn't the force be doubled?

Generalizing your question, if you are correct then using a porous or fibrous object with many branch points would then lead to an arbitrarily large column height- since it doesn't, there is a flaw in your reasoning.
 
Well the water will fail at some point. Water has a high tensile strength due to the cohesive forces between the molecules, but for some capillary height the water should give into the tug of war between gravity and capillary forces and cavitate (or evaporate), so an infinite column of water is not possible.

I believe this is the reason why trees have a maximum height limit. Really all of this revolves around a project I'm doing on water transport in trees, and the model I propose is based on the question above.

Taking this into consideration, would you change your answer?
 
  • #10
Medicago said:
Why not? If I have another meniscus, wouldn't the force be doubled?
The force where?
Force is not a magical universal number of a system.

In addition, I think you mean a pressure difference. This will not be doubled.


I believe this is the reason why trees have a maximum height limit.
It is a bit more complicated, but it is the basic concept.
 
  • #11
A pressure jump at the meniscus causes a force at the surface. It exists only at the surface, not along the entire column (obviously it is transferred throughout the column, but the pulling source is at the meniscus surface).


I believe this is the prime reason for the maximum height of trees. Turgor may also be involved, and also low flow velocities. Some researchers have put the height at about 120 meters tree height. If hope to show through my furcation model that water will yield when the tree is about 120 meters tall. For this I need to assume that a furcating capillary will draw up more water.
 
  • #12
I asked some faculty members (mechanical engineering) and no-one gave me a straight answer, but nobody said it was not valid.

Also I found it being used in an article but without explanation or reference so I guess it's trivial.

Anyway if anyone has any other ideas, I'd love to hear. thanks
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 1 ·
Replies
1
Views
4K
  • · Replies 18 ·
Replies
18
Views
3K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 2 ·
Replies
2
Views
12K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K