Pressure theory applied to a Venturi tube

In summary, the pressure in the inlet/outlet of a Venturi tube is greater than in the throat due to the conservation of energy and Bernoulli's equation. As the tube narrows and the speed increases, the kinetic energy density also increases, resulting in a decrease in pressure. This is due to the pressure being a measure of energy per displaced volume.
  • #1
extricate
2
0
Hi,

I'm a little confused about the pressure in the inlet/outlet and the throat of a Venturi tube.

Why is the pressure in the inlet/outlet greater than in the throat? I thought that because air is needed to flow into a smaller space so the pressure has to be greater?

Pardon me. I've self-learning.

Thanks for your time.
 
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  • #2
welcome to pf!

hi extricate! welcome to pf! :smile:

it's conservation of energy (density) …

Bernoulli's equation is simply a conservation of energy (density) equation

(and pressure is energy density: pressure = work done per displaced volume = energy per displaced volume)

where the tube is narrower, the speed is faster, so the kinetic energy density is greater

so the pressure must be less :wink:
 
  • #3
Thanks a lot for the reply.
 

1. What is a Venturi tube and how does it work?

A Venturi tube is a device used to measure the flow rate of fluids in pipes. It consists of a converging section, throat, and diverging section. As the fluid flows through the converging section, its velocity increases and the pressure decreases. In the throat, the velocity is highest and the pressure is lowest. As the fluid flows through the diverging section, its velocity decreases and the pressure increases. This change in pressure can be measured and used to calculate the flow rate.

2. What is the principle behind the Venturi effect?

The Venturi effect is based on the principle of conservation of energy. As the fluid flows through a narrow section of the tube, its velocity increases and the pressure decreases. This is because the total energy of the fluid (kinetic energy + potential energy) must remain constant. Therefore, as the kinetic energy increases, the potential energy (pressure) must decrease.

3. How is the Bernoulli equation used in the pressure theory applied to a Venturi tube?

The Bernoulli equation, which states that the total energy of a fluid remains constant, is used to calculate the pressure difference between the converging and diverging sections of the Venturi tube. This pressure difference can then be used to determine the flow rate of the fluid.

4. What factors affect the accuracy of a Venturi tube measurement?

The accuracy of a Venturi tube measurement can be affected by several factors, including the shape and smoothness of the tube, the viscosity of the fluid, and the presence of any obstructions or disturbances in the flow. It is also important to ensure that the fluid is flowing in a steady, uniform manner.

5. How is a Venturi tube used in practical applications?

Venturi tubes are commonly used in various industries, such as aviation, chemical processing, and water treatment, to measure the flow rate of fluids. They are also used in carburetors of automobiles to control the air-fuel mixture. Additionally, Venturi tubes can be used in medical devices, such as inhalers, to regulate the flow of medication.

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