Bernoulli's Equation and liquid density

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SUMMARY

The discussion centers on applying Bernoulli's Equation to calculate the pressure difference between two points in a fluid flow scenario. Given a liquid density of 1200 kg/m³, fluid speeds of 7.5 m/s at point A and 11 m/s at point B, the correct approach to find the pressure difference PB – PA involves rearranging Bernoulli's Equation. Participants clarify that neglecting the constant in the equation leads to incorrect assumptions, emphasizing the importance of maintaining the equation's integrity to arrive at accurate results.

PREREQUISITES
  • Understanding of Bernoulli's Equation
  • Knowledge of fluid dynamics principles
  • Familiarity with pressure and velocity relationships in fluid flow
  • Basic algebra for rearranging equations
NEXT STEPS
  • Study the derivation and applications of Bernoulli's Equation in fluid mechanics
  • Learn about the implications of fluid density on pressure calculations
  • Explore examples of pressure difference calculations in horizontal pipe flow
  • Investigate the effects of neglecting constants in fluid dynamics equations
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Students of fluid mechanics, engineers working with fluid systems, and anyone involved in calculating pressure differences in fluid flow applications.

physkid1
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1. The density of the liquid flowing through the horizontal pipe in the drawing is 1200 kg/m3. The speed of the fluid at point A is 7.5 m/s while at point B it is 11 m/s. What is the difference in pressure, PB – PA, between points B and A?
2. Bernoulli's Equation P1 + 1/2 pv1^2 + pgy1 = P2 + 1/2 pv2^2
3. ok to find P is it possible to make P1 = 1/2 pv1^2 + pg (y1 can be neglected) then do the same with P2 then subtract the two values to work out the pressure ? or am i way off ?
 
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physkid1 said:
Bernoulli's Equation P1 + 1/2 pv1^2 + pgy1 = P2 + 1/2 pv2^2

to find P is it possible to make P1 = 1/2 pv1^2 + pg (y1 can be neglected) then do the same with P2 then subtract the two values to work out the pressure ?

While you would arrive at the correct final answer, your working would not be quite right.
You would be saying that P1=0.5 p v12 but that's not right. You are disregarding the constant in Bernoulli's Equation; in effect, equating it to zero.

It is better to rearrange Bernoulli's Equation to give the pressure difference, viz., P2 - P1 and that way the constant vanishes and your working will be correct all the way through and no more complicated.
 

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