Air in Mercury & Sprengel Pump Explained

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Discussion Overview

The discussion revolves around the mechanics of the Sprengel pump, specifically how it utilizes falling mercury to trap air and evacuate a chamber. Participants explore the principles behind the pump's operation, including the behavior of air in the presence of mercury and potential alternatives to mercury as a fluid in similar applications.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions why trapped air does not rise back to the top of the mercury, likening it to air bubbles from a diver's mask.
  • Another participant explains that the small diameter of the capillary tube and the high surface tension of mercury contribute to the trapping of air, suggesting an equilibrium of forces at play.
  • A different participant inquires about the possibility of using other fluids instead of mercury, linking the discussion to the concept of Coulomb force.
  • Another response indicates that finding a suitable alternative fluid would be challenging due to mercury's high density and its non-wetting properties with glass, which are advantageous for the pump's function.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of using alternative fluids to mercury, with some acknowledging the unique properties of mercury that make it effective while others explore the idea of alternatives.

Contextual Notes

The discussion does not resolve the question of alternative fluids, and the limitations of the proposed alternatives are not fully explored. The role of forces involved in the trapping mechanism is mentioned but not detailed.

Who May Find This Useful

Individuals interested in fluid dynamics, vacuum technology, or the mechanics of pumps may find this discussion relevant.

cragar
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I was reading about the sprengel pump , And it uses falling mercury to trap air to evacuate a chamber to get the air out of it , http://en.wikipedia.org/wiki/Sprengel_pump you can look at the diagram of the pump , my question is when the mercury traps the air and pushes it down , why doesn't the air just rise back to the top like air bubbles coming out of a divers mask back to the surface of the ocean.
 
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It tries, but the diameter of the capillary tube is so small, and mercury surface tension so large, that air is trapped. It is just a matter of equilibrium of forces involved.
 
sweet thanks for the answer , is there any other fluid that i could use besides mercury so that i could make my own , so this has a lot to do with the coulomb force.
 
Will be difficult. Mercury is very good for two reasons - it has a very high density (hence can "suck" air much stronger than lighter liquids) and doesn't wet glass surface (which means it can't flow around the bubble on the glass walls).
 

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