Orifice plate :




  • A types of flow rate sensing devices which is known as OBSTRUCTION METER 
  • Orifice plate is one of the obstruction meter in flow rate devices. because an orifice plate acts as an obstruction (obstacle) in the flow meter. 
  • Obstruction means they are going to  restrict the fluid flow or flow is going to be changed, due to the obstruction pressure difference will generate  in fluid
  • Causing the change in fluid pressure which depends on the rate of flow
  • By measuring the difference in the flow before and after the obstruction using a differential pressure sensor, we can determine the flow rate of fluid
  • Orifice plate is an indirect method for flow measurement
  • Change in pressure is proportional to the flow rate
  • Orifice is a mechanical device 






Basic working principle of Orifice


  • When the orifice plate is placed in the pipe which carries the fluid, whose rate of flow is to be measured, the orifice plate causes a pressure drop which varies the flow rate.
  • The velocity of fluid will be maximum at the maximum restriction and the pressure will be minimum at such a point.
  • The pressure drop measure by the differential pressure sensor,  which is proportional to the fluid flow rate. 


Types of Orifice plate 

 Square Edged Concentric



  • These are most commonly used for flow measurement.
  • This has special features such as simple structures, high accuracy, and ease of installation & replacement.
  • The orifice plates are correctly finished to the dimensions, surface roughness, and flatness to the applicable standard.
  • These plates are recommended for clean liquids, gases & steam flow, when the Reynold number 7 ranges from 10000 to 10

        
        Eccentric


  • For liquids containing solid particles that are likely to sediment or for vapors likely to deposit water condensate, this orifice plate is used with its eccentric bore bottom flush with the bottom of the piping inside surface so that the sedimentation of such inclusions are avoided.
  • Likewise, for gases or vapors, it may be installed with its eccentric bore top flush with the ID of the piping to avoid stay of gas or vapor in its vicinity.


     Segmental


  • Segmental orifice plates are most useful where there is substantial entrained water or air and also if there is a suspension in the fluids.
  • This avoids build up in front of the orifice plate. The orifice hole is placed at the bottom for gas service and top for liquids.

     Quadrant Edge


  • The inlet edge of the bore of this orifice plate is rounded to a quarter circle. This orifice plate is usually used for viscous fluids & Reynolds number between 2000 to 10000.


      Conical Entrance


  • These conical entrance orifice plates are used for low Reynolds number in the range of 80 to 2000 and give more constant or predictable discharge coefficient.
  • At lower Reynolds numbers, the discharge coefficient of the square edge orifice plate may change by as much as 30%. These are more usable for viscous service.