Secrets behind Choked flow in pipes


Choked Flow:
  • Choked flow is a fluid dynamic condition associated with the Venturi effect. When a flowing fluid at a given pressure and temperature passes through a constriction (such as the throat of a convergent-divergent nozzle or a valve in a pipe) into a lower pressure environment the fluid velocity increases.
The basic liquid sizing equation tells us that the liquid flow rate through a control valve is proportional to the square root of pressure drop. 
This linear relationship does not always hold true. As the pressure drop is increased the flow first reaches a point where increasing pressure drop only produces a small increase in flow, and then very soon after that, no matter  how much the pressure drop is increased, the flow does not increase at all.
When this happens, we say that the flow has become choked. The pressure drop at which flow becomes choked (the dividing line between the non-choked and the choked portions of the graph) is called delta P sub T, T stands for “terminal” or the end. Another term that is sometimes used for the same thing is delta P allowable or “the allowable pressure drop.”
Possibilities behind Chocked flow:

  1.  Change in diameter of pipe throughout the system linings.
  2.  Presence of Orifice in between the system linings.
Effects over the output due to choked flow:
  1. It will lead to the decrease in flow rate(m3/hr) through the system lining which will affect the Kv value for the system and ultimately leads to less Kv value. (Kv=Flow coefficient m3/hr).
  2. Also it may lead to cavitation and hence slow damage to the system. 


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