Pressure vs speed for liquids ?

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Discussion Overview

The discussion revolves around the relationship between pressure and speed in liquids flowing through a horizontally positioned pipe with varying cross-sectional areas. Participants explore concepts related to fluid dynamics, specifically focusing on the implications of fluid speed and pressure in a scenario where a fluid flows from a wider section of a pipe to a narrower section.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions whether the speed of a fluid particle increases as it moves from a wider to a narrower section of the pipe and how this relates to pressure.
  • Another participant introduces the principle of conservation of mass for incompressible fluids, leading to the conclusion that fluid velocity increases in narrower sections.
  • A participant expresses surprise at the conclusion that fluid flows faster in the narrow section, indicating a shift in their understanding.
  • One participant suggests using Bernoulli's equation to analyze the situation, seeking clarity on the pressure difference involved.
  • Another participant posits that the pressure difference is what causes the fluid to flow faster in the narrower section of the pipe.
  • A later reply emphasizes that applying Bernoulli's equation reveals that the increase in velocity head corresponds to a drop in static head, indicating a relationship between speed and pressure.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between pressure and speed, with some advocating for the use of Bernoulli's equation while others are still grappling with the implications of the conservation of mass. The discussion remains unresolved regarding the precise nature of the pressure-speed relationship.

Contextual Notes

Participants acknowledge assumptions such as incompressibility and constant density, but the implications of these assumptions on the pressure-speed relationship are not fully resolved. There is also a lack of consensus on how to interpret the pressure differences in the context of fluid flow.

furkang
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pressure vs speed for liquids ? :(

Think of a pipe positioned horizontally.

Some fluid is flowing from left to right.(e.g. water)

Right side of the pipe is well narrower than left side.

Is the speed of a fluid particle at the right greater than the speed of a particle at the left?
What about their pressures?

(Perfect world no energy loss)
OR


perhaps I can NOT make such a comparison without considering any value constant.

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I am really confused please help , basically I am looking for an example which prooves inverse proportion of speed and pressure of LIQUIDS. Can you give me an example like mine? Thank you for your help...
 
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Let's assume an incompressible fluid - the density does not change - and apply conservation of mass.

[itex]\rho_1 * V_1 * A_1 = \rho_2 * V_2 * A_2[/itex]

for incompressible flow [itex]\rho_1 = \rho_2 = \rho[/itex]

which then leaves [itex]V_1 * A_1 = V_2 * A_2[/itex]

So what does the say about the relationship between fluid velocity (speed) and area?
 
ok that's well ...

that means fluid flows faster in the narrow section. That is completely different from my thought.
 
Is it the same if we use Bernoulli's equation to see that?

I could't see where is the pressure difference
 
Considering the fluid is incompressible, helps by making density constant. Is it the pressure difference, that causes the fluid to flow faster at the place where the pipe narrows?
 
You should take it the other way round(you should obviously apply Bernoulli's equation), that static head drop occurs due to increase in velocity head.
 

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