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FLOW MEASUREMENT, Electromagnetic flowmeter. (magnetic flowmeter or…

- - - - A orifice plate, metal discs with a hole in the middle is inserted into the pipe and placed perpendicular to the flow stream.
      - As the flowing fluid passes through the orifice plate, the restricted cross section area causes an increase in velocity and decrease in pressure.
      - The pressure difference before and after the orifice plate is used to calculate the flow velocity.
    - - Easy to use & cheap
      - Widely used
      - Can be obtained in wide range of diameter
    - - Impractical for system with low static pressure
      - Subject to damage by water hammer and foreign objects
      - High pressure loss
  - - - When a fluid flows through the venturi tube, it accelerates in the convergent section and decelerates in the divergent section, resulting a drop in the static pressure followed by a pressure recovery in the flow direction.
      - By measuring the difference in the pressures at an axial station up stream of the convergent section and at the throat, the volumetric flowrate can be estimated.
      - Widely used to measure the discharge through the pipe.
    - - Lower pressure loss
      - Can be installed vertically, horizontally or inclined
      - Higher accuracy
    - - High viscosity effect
      - Requires long laying length
      - Expensive & large in size
  - - - When the fluid enters the nozzle, it converges and due to this, its pressure keeps on reducing until it reaches the minimum cross section area called throat.
      - This pressure drop is measured using a differential pressure transducer and when calibrated, this pressure becomes a measure of flowrate.
    - - Very compact
      - High coefficient of discharge
      - Easy installation & cheap
    - - High in maintenance
      - Low pressure recovery
- - - - the increase in pressure and decrease in velocity
      - decrease in pressure and increase in velocity