What happens when vacuum is applied to an elastic tube filled with tap water?

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Discussion Overview

The discussion focuses on the effects observed when applying vacuum to an elastic tube filled with tap water, including phenomena such as water brimming over the open end and the formation of air bubbles. The context involves exploring the behavior of the system under varying vacuum levels, specifically around -0.9 atm, and the implications of tube elasticity and water composition.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that applying vacuum causes water to brim over the open end and questions why this occurs, alongside the formation of an air bubble inside the tube.
  • Another participant suggests that the presence of trapped gases in tap water may contribute to the bubble formation, referencing the behavior of gases escaping from water when exposed to lower pressures.
  • The same participant explains the relationship between gas volume and pressure using the ideal gas law, indicating that the bubble's size increases as pressure decreases.
  • Concerns are raised about the collapse of the elastic tube, with a suggestion that using a stiffer hose could mitigate this issue.
  • A follow-up question seeks clarification on whether only a specific part of the tube needs to be stiffer to prevent collapse, which is confirmed by another participant.

Areas of Agreement / Disagreement

Participants generally agree on the potential causes of the observed phenomena, such as gas bubble formation and the effects of tube elasticity. However, the discussion includes varying perspectives on the specifics of these effects and the best approaches to address them, indicating that multiple views remain.

Contextual Notes

There are unresolved assumptions regarding the behavior of trapped gases in tap water and the specific mechanics of the tube's collapse under vacuum conditions. The discussion does not fully explore the implications of different tube materials or configurations.

Who May Find This Useful

This discussion may be of interest to individuals studying fluid dynamics, material science, or those involved in experimental setups that utilize vacuum systems with elastic materials.

JohnGe
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First of all, I want to ask for your understanding for my not well English.
I want to discuss all the effects will take place if we begin applying vacuum to the following system http://www.inkline.gr/temp/Vacuum-ElasticTube.gif .
Data:
The tube is elastic (squeezable)
The chamber is rigid
The tube contains tap water and it's closed at the right end
The final vacuum supposed to be about -0.9 atm (the water don't boil in this pressure at ambient temperature)

When I apply vacuum to the actual system happens a strange thing: the water brim over the open end. Why? After a bit an air bubble is formed inside the tube (the bubble is about 1/10 of the total tube volume). Why?
When I apply a vacuum about 0.75 atm the above effects are 10 times less.
 
Last edited by a moderator:
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Tap water has a lot of trapped gas in it. Fill a glass with tap water and let it sit on a table over night. You should see a lot of bubbles form on the glass. Some of the bubbles are a result of exposure to the air while sitting on your table while others are causesed by gases trapped within the water escaping. That could be the cause of your gas bubble. To help eliminate this you can draw a vacuum on the water to remove all air bubbles before use. This sort of thing shows itself when working with silicone molding gels or with epoxies.

The size of the bubble is a function of the ideal gas law. Remember, an ideal gas at a volume of V at some pressure will become a volume of kV at some lesser pressure (k being some constant) and that is why the bubble grows as you reduce pressure.

[tex]V\uparrow=\frac{\overrightarrow{nRT}}{P\downarrow}[/tex]

Next the brimming: You say you are using a soft hose. The brimming is probably due to a) the gas bubble formation and expansions along with b) the collapse of your hose. Get a stiffer hose and remove the trapped gases from your tap water.

Good luck.
 
Last edited:
Just one more question. To eliminate the collapse of the tube: according to my understanding, only the green part of the tube needs to be stiffer http://www.inkline.gr/temp/Vacuum-ElasticTube2.gif , am I right?
 
Last edited by a moderator:
Yes, you are correct.
 

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