Size expansion vessel to reduce pressure loss

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SUMMARY

The discussion centers on the pressure dynamics of a 1000M3 pressure vessel filled with water at 8 bar, particularly when 20 liters of water is released. Without an expansion vessel, the pressure will drop significantly, potentially to zero, depending on the vessel's material properties. With an expansion vessel prepressurized to 8 bar, the pressure loss will also occur, but the presence of a vacuum breaker can mitigate vacuum formation, preventing collapse. The discussion highlights critical factors such as the modulus of elasticity of the vessel material and the implications of vacuum formation on pressure stability.

PREREQUISITES
  • Understanding of fluid dynamics and pressure systems
  • Knowledge of pressure vessel design and materials
  • Familiarity with vacuum formation and its effects on liquid systems
  • Basic principles of hydrostatics and pressure head calculations
NEXT STEPS
  • Research the effects of pressure loss in large-scale pressure vessels
  • Study the principles of vacuum breakers and their applications in pressure systems
  • Learn about the modulus of elasticity in materials used for pressure vessels
  • Explore the calculations for pressure head in liquid-filled vessels
USEFUL FOR

Engineers, pressure vessel designers, and safety professionals involved in fluid dynamics and pressure system management will benefit from this discussion.

RobinDeG
Hi all,

Given:
I have a pressure vessel of 1000M^3 filled with water with 8 bar pressure.
On this pressure vessel I have installed a valve and a expansion vessel on top of the pressure vessel.
The expansion vessel is prepressurized to 8 bar as well.

Question:
when I open the valve i lose 20 liters of water.
The decrease of water will result in a pressureloss in the vessel.

Question 1: what will the new pressure be (without an expansion vessel)
Question 2: What will the new pressure be with an expansion vessel

To make it easier: the expansion vessel will be filled with water also.
 

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If both vessels are liquid full then the pressure measured at the level of the outlet will be the combination of the 8 bar imposed pressure plus pressure head of the contained liquid. lf all vapor has been vented from the expansion vessel and the liquid is essentially incompressible then the 8 bar of imposed pressure will quickly drop to zero (the actual time will depend upon the vessel material's modulus of elasticity and pressure stress on the vessel).

If there is a vacuum breaker attached to the top of the expansion vessel, the pressure measured at the outlet level will then be a function of the pressure head of the draining liquid until the vessel is emptied to the outlet level.

If there is no vacuum breaker on the expansion chamber, once the initial 8 bar pressure reaches zero, the draining liquid will begin to develop a vacuum in the vessels' volume above the liquid level that is proportional to the increase in that volume. This vacuum will continue to increase until: 1) the vacuum is equal to the backpressure at the vessel's discharge point (assuming no air is drawn into the vessel through the draining discharge connection) or: 2) the vacuum reaches the vaporization pressure the liquid in the vessel; or, 3) at some point, the vacuum exceeds the buckling strength of the vessel and the vessel collapses.
 
How rigid is the tank? 20L is quite a small percentage of 1,000,000L.
 

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