What Is the Impact of Throat Velocity on Pressure According to Bernoulli's Law?

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Discussion Overview

The discussion revolves around the impact of throat velocity on pressure as described by Bernoulli's Law. Participants explore the implications of high throat velocities, particularly in relation to negative absolute pressures and the physical meanings behind these concepts.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that Bernoulli's law indicates a direct relationship between pressure drop and fluid velocity at the throat.
  • One participant suggests that increasing throat velocity could imply an increase in pressure before the throat, referencing a rearrangement of Bernoulli's equation.
  • Another participant challenges the notion of negative absolute pressure, stating that it is nonsensical since absolute pressures cannot be negative.
  • A later reply introduces the idea that the maximum velocity at the throat is limited to sonic velocity, suggesting a boundary condition for the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the implications of high throat velocities and the concept of negative absolute pressure, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

The discussion does not clarify the assumptions underlying the application of Bernoulli's law in this context, nor does it resolve the mathematical interpretations presented by participants.

gerdsmit
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According to Bernouilli's law there is a direct relation between pressure drop and fluid's velocity at the throat. What would be the physical meaning of a high value negative absolute pressure that theoretically can be achieved by increasing fluid's throat velocity.
 
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It would probably mean that the pressure experienced before the throat is increased,

In the eq P1 + 1/2DV1^2 = -P2 + 1/2DV2^2,
bring _p2 to the other side

=>P1+P2 + 1/2DV1^2 = 1/2DV2^2

(D=density,P1 = initial press.,P2=final pressure,same for V1 and V2)

implying that the original pressure is increased...
Hope you understand what I am trying to say...(good question though)
 
gerdsmit said:
According to Bernouilli's [equation] there is a direct relation between pressure drop and fluid's velocity at the throat. What would be the physical meaning of a high value negative absolute pressure that theoretically can be achieved by increasing fluid's throat velocity.

It is nonsensical since absolute pressures cannot be negative.

CS
 
Absolute limit of velocity in any throat is going to be sonic velocity. There's your limit right there.
 

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