Measuring Stagnation Pressure with a Manometer

In summary, a manometer is a device used to measure stagnation pressure, which is the total pressure of a fluid flow that includes the effects of both static and dynamic pressure. It consists of a U-shaped tube filled with a liquid, typically mercury, and connected to the fluid flow. The difference in the liquid levels in the two arms of the tube indicates the stagnation pressure. The manometer is a simple and accurate tool for measuring stagnation pressure and is often used in industries such as aviation and fluid dynamics research.
  • #1
krlss26
7
0
Hello.

We use a manometer to measure the pressure of an air tunnel. The connection of the manometer has to be changed as sometimes water enters the manometer and contaminates the fluid inside.

I have attached a picture in which I am showing the now and before of the connection. My question is: will this change in connection affect the reading in my manometer? (the black rectangles). If so, what will change in the equations? Now, the fluid is literally pushed inside the manometer, in the past it wasn't as the connection was attached the bottom of the tunnel. I have tried relating it to a Pitot tube reading, but I do not know how accurate this is, and some doubts have really gotten to me with the parameters.

Please let me know if I did not explain myself very well.

Thank you so much in advance.
 

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  • #2
krlss26 said:
Hello.

We use a manometer to measure the pressure of an air tunnel. The connection of the manometer has to be changed as sometimes water enters the manometer and contaminates the fluid inside.

I have attached a picture in which I am showing the now and before of the connection. My question is: will this change in connection affect the reading in my manometer? (the black rectangles). If so, what will change in the equations? Now, the fluid is literally pushed inside the manometer, in the past it wasn't as the connection was attached the bottom of the tunnel. I have tried relating it to a Pitot tube reading, but I do not know how accurate this is, and some doubts have really gotten to me with the parameters.

Please let me know if I did not explain myself very well.

Thank you so much in advance.

Why not go to an electronic pressure transducer?
 
  • #3
Quantum Defect said:
Why not go to an electronic pressure transducer?
I only have a manometer which gives me a pressure Reading in mmH20. I can connect it the way I desire, but I have to calculate the speed of air in the tunnel. It currently reads the static pressure, but I do not know how to go from there to a determination of the velocity of the air.

Maybe if I connect it in a way one of the ends is in the same direction of the fluid and the other determines the static pressure, I´ll be able to calculate this simulating a pitot tuve. What do you think?
 
  • #4
krlss26 said:
I only have a manometer which gives me a pressure Reading in mmH20. I can connect it the way I desire, but I have to calculate the speed of air in the tunnel. It currently reads the static pressure, but I do not know how to go from there to a determination of the velocity of the air.

Maybe if I connect it in a way one of the ends is in the same direction of the fluid and the other determines the static pressure, I´ll be able to calculate this simulating a pitot tuve. What do you think?
tube*
 
  • #5
I think this will reduce moisture into manometer to some extent. But if the air has too much moisture content and its temperature is not less then dew point of moisture your problem may persist. To measure air velocity you may need a venturi/ orifice or some other flow measuring instruments. Also to measure air flow correctly you may also have to give attention to requirement of any flow measuring instrument you will use.
 
  • #6
You answered your own question in the title: the new configuration gives the stagnation pressure whereas the old gave you the static pressure.
 
  • #7
You can homebrew a pitot tube with manometer connected for air speed and flow rate measurement. Russ is to the point...
 
  • #9
You new configuration will be measuring dynamic pressure (well, stagnation pressure since the air will stagnate at the fluid column). The old configuration would have been reading hydrostatic pressure minus whatever pressure drop you'd get due to the venturi effect. Since hydrostatic pressure is negligible for your old configuration you should get similar readings.

See:
http://en.wikipedia.org/wiki/Venturi_effect
 
  • #10
krlss26 said:
I have to calculate the speed of air in the tunnel. It currently reads the static pressure, but I do not know how to go from there to a determination of the velocity of the air.

Maybe if I connect it in a way one of the ends is in the same direction of the fluid and the other determines the static pressure, I´ll be able to calculate this simulating a pitot tuve. What do you think?

Based on your picture the "Now" setup is measuring the difference between the tunnel total pressure (assuming you are out of the boundary layer) and the atmospheric pressure outside the tunnel. If you want to get the tunnel speed you can connect your reference end of the tube (the end open to atmosphere) to the wall of the wind tunnel so that it measures the static pressure in the wind tunnel. This way your manometer will give you the dynamic pressure which you can use to calculated velocity.
 
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Related to Measuring Stagnation Pressure with a Manometer

1. What is a manometer?

A manometer is a scientific instrument used to measure pressure, particularly in gases and liquids. It consists of a U-shaped tube filled with a fluid, and the difference in height of the fluid in the two sides of the tube indicates the pressure difference between the two points.

2. How does a manometer measure stagnation pressure?

A manometer measures stagnation pressure by using the principle of Bernoulli's equation, which states that the sum of static and dynamic pressure in a fluid is constant. By measuring the difference in height of the fluid in the two sides of the manometer, the static pressure at the stagnation point (where the fluid flow velocity is zero) can be determined.

3. What are the units of measurement for stagnation pressure on a manometer?

The units of measurement for stagnation pressure on a manometer can vary, but are typically in units of pressure such as pascals (Pa), pounds per square inch (psi), or inches of mercury (inHg).

4. What factors can affect the accuracy of measuring stagnation pressure with a manometer?

There are several factors that can affect the accuracy of measuring stagnation pressure with a manometer, including the type and accuracy of the manometer itself, the fluid used in the manometer, the temperature and density of the fluid, and any external factors that may impact the fluid flow.

5. How is the reading on a manometer affected by changes in altitude?

The reading on a manometer can be affected by changes in altitude due to the change in atmospheric pressure. As altitude increases, the atmospheric pressure decreases, which can result in a lower reading on the manometer. To compensate for this, a correction factor can be applied to the reading to account for the change in altitude.

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