Low pressure, high velocity flow vs static pressure

• T C
In summary, the conversation discusses a scenario involving a compressible flow at 0.99 barA pressure and 300 m/s velocity being released into 1 barA pressure. The question is whether the flow can be released at 1 barA or not. It is argued that the static pressure may be lower than the release pressure, but the dynamic pressure is around 0.7 barA and when added to the static pressure, it exceeds the release pressure. The situation may require a divergent nozzle for the flow to exist. It is also mentioned that the static and dynamic pressures can be measured using standard temperature and density calculations.
T C
TL;DR Summary
I want to discuss an imaginary scenario here where we have a compressible flow flowing through a tube at 0.99 barA pressure and at 300 m/s velocity and that flow is released into 1 barA pressure. Is it possible or not.
In this scenario, we have a compressible flow at 0.99 barA pressure and flowing at 300 m/s velocity and is released into 1 barA pressure. Point is, whether the flow can be released at 1 barA or not at the release pressure is higher than the pressure of the compressible fluid inside the tube. And here is my thought in this regards. The static pressure of the flow may be lower than the release pressure, but it has another pressure and that's the dynamic pressure. At 300 m/s velocity, the dynamic pressure is around 0.7 barA and when that's added to the existing static pressure of the compressible fluid, the total pressure far exceeds the release pressure and the flow can be easily released. For the sake of simplicity, it has been assumed that the tube is frictionless and the static fluid at 1 barA pressure, where this flow is released, is the same and density difference is negligible.

Lnewqban
How are you measuring each of those pressures?

Is this supposed to be a steady state flow? How was the flow at the lower pressure established on the upstream side?

I don't see how your situation can exist unless there is a divergent nozzle at the tube exit.

russ_watters
Lnewqban said:
How are you measuring each of those pressures?
Static pressures are chosen and dynamic velocity calculators available on net. Let's consider the both the fluids at standard temperature. The density can be calculated easily and just put those values into the calculator and you can get the results.
Chestermiller said:
Is this supposed to be a steady state flow? How was the flow at the lower pressure established on the upstream side?
Can't understand what you want to mean.
Dullard said:
I don't see how your situation can exist unless there is a divergent nozzle at the tube exit.
Why a divergent section would be necessary?

In case of De Laval nozzle, the release pressure (mentioned as ambient pressure in the page) can be 2-3 times higher than the pressure at the exit of the nozzle. If that's true, that simply means a high velocity flow of lower pressure can easily enter at higher pressure if the gross i.e. total sum of static and dynamic is higher than the release pressure.

1. What is the difference between low pressure, high velocity flow and static pressure?

Low pressure, high velocity flow refers to a fluid moving at a high speed with a low pressure, while static pressure refers to the pressure exerted by a fluid that is not in motion.

2. When would low pressure, high velocity flow be preferred over static pressure?

Low pressure, high velocity flow is preferred in situations where the fluid needs to be moved quickly and efficiently, such as in ventilation systems or in jet engines. Static pressure is preferred in situations where a stable and consistent pressure is needed, such as in hydraulic systems.

3. How does low pressure, high velocity flow affect the surrounding environment?

Low pressure, high velocity flow can create turbulence and disturbances in the surrounding environment, which can be useful for mixing and dispersing fluids or particles. It can also cause noise and vibrations.

4. What are some common applications of low pressure, high velocity flow?

Low pressure, high velocity flow is commonly used in industries such as aerospace, automotive, and HVAC (heating, ventilation, and air conditioning) for tasks such as cooling, propulsion, and ventilation.

5. How is low pressure, high velocity flow measured and controlled?

Low pressure, high velocity flow can be measured using instruments such as pitot tubes or flow meters. It can be controlled by adjusting the flow rate or by using devices such as valves or dampers to regulate the pressure and velocity of the fluid.

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