Calculating Flow Rate w/ Manometer & Venturi Meter

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Discussion Overview

The discussion revolves around calculating the flow rate of air using a manometer and a Venturi meter. Participants explore the necessary parameters and equations involved in determining flow rates, particularly focusing on the differences between gases and incompressible fluids.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the method to calculate flow rate from a manometer connected to a Venturi meter, specifying the dimensions of the Venturi tube.
  • Another participant questions whether the fluid is a gas or an incompressible fluid, noting that temperature is necessary for calculating mass flow rate if it is a gas.
  • A formula for mass flow rate is provided, which includes variables for density, velocity, and cross-sectional area, along with a reference to Bernoulli's equation for calculating velocity.
  • A participant confirms that the fluid is air and expresses the need to convert manometer readings to volume flow rate.
  • A link to a calculator with relevant equations and explanations is shared for further assistance.

Areas of Agreement / Disagreement

Participants generally agree on the need for specific parameters to calculate flow rate, but there is no consensus on the exact method or equations to use, particularly regarding the treatment of air as a gas versus an incompressible fluid.

Contextual Notes

The discussion does not resolve the assumptions regarding the behavior of air as a gas and its impact on flow rate calculations, nor does it clarify the necessary conditions for applying the equations mentioned.

Who May Find This Useful

Individuals interested in fluid dynamics, particularly those working with flow measurement devices like manometers and Venturi meters, may find this discussion relevant.

serfinos
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Hi ,

Does anyone know , how to calculate the flow rate from a manometer ? there is a pipe attatch to the venturi meter, the inside tube of venturi is 32 mm and the outside 62 mm.
A fan is sucking the air, so flow rate is produced.

Thank You
 
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First off, is this a gas or another fluid which an be modeled as incompressible (e.g.water)?

If it is a gas you would need the temperature as well to find a mass flow rate. However, if all you needed was a volume flow rate you could get away with just the venturi tube.

Okay, so the mass flow rate of a fluid is as follows:

m_dot=rho*V*A

where V is fluid velocity and A is the area of whatever duct you are using and rho you can find in some reference, for an incompressible fluid we can assume that rho is pretty much constant.

A you can find by measuring and V can be calculated from bernoulli's equation, assuming no major changes in elevation.

V=sqrt(2*(P/rho));For a gas the density (rho) changes drastically with temperature so one would need to use the ideal gas law to find the correct density which would be a function of pressure and temperature.
 
It is a gas , assuming air is through the pipe, so i need to find the flow rate of the air.
I need to convert the number that the manometer is giving me to volume flow rate.
 
thanks a lot
 

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