Measurement of rate of flow of fluids , Direct weighing , Orifice meter , Equation

Methods :

-  Direct Weighing or Measuring  .

- Hydrodynamic methods .

1. Orifice meter 

2. Venturi meter

3. Pitot tube 

4. Rota meter 

Direct weighing or measuring  :

- The liquid flowing through a pipe is collected for a particular period of time at any point and weighed .

- Rate of flow can be calculated  .

- Impracticable 

Orifice meter :

- It is a device used for measuring the rate of flow of a fluid flowing through a pipe . it works on the principle of pressure differential .

- Measure the variation in the pressure across a fixed construction placed in the depth of flow consisting of a constant area .

-  An Orifice in pipeline is shown in the figure with a manometer for measuring the drop in pressure ( differential  ) as the fluid passes through the orifice  . the minimum cross sectional area of the jet is known as the "vena-contracta."

- As the fluid approaches the orifice the pressure increases slightly and then drops suddenly as the orifice is passed .

- It continues to drop until the "vena contracta " is reached and then gradually increases in downstream a maximum pressure point is reached that will be lower than the pressure upstream of the orifice .

- The Pressure drop across the orifice increases when the rate of flow increases , when there is no flow there is no differential .

- The Differential pressure is proportional to the square of the velocity it therefore follows that if all other factor remain constant then the differential is proportional to the square of the rate of flow  .

Equation :

Q = Cd*A*SQRT( 2hg )

SQRT =  square root .

A  = cross sectional orifice 

h = Pressure Heads

g = gravity

Cd = Coefficient of discharge 

Q =  volumetric flow rate .