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If a pressure difference exists along a pipe, the flow will accelerate to compensate that pressure. In that case, what is the requirement of a convergent nozzle, which also does the same job?

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If local pressure gradients exist how would someone control how much the velocity of the flow should be and what should be the direction? Convergent nozzles gives a user precise control over the characteristics of the fluid flow i.e, velocity and direction.

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    $\begingroup$ To add, pressure difference isn't always accompanied by acceleration. In steady flow through a uniform pipe, pressure difference exactly balances viscous forces and thus each fluid element has constant velocity. Then to increase fluid ejection velocity we must reduce the cross-section, which is what a nozzle does. $\endgroup$
    – Deep
    Sep 14, 2018 at 7:25
  • $\begingroup$ Thank you very much for your replies. But the question is based on an assumption that, there exists a large pressure difference to accelerate the flow. In that case, is precise control (and less loss) the only extra advantage of a nozzle ? $\endgroup$
    – Ashok
    Sep 14, 2018 at 8:42
  • $\begingroup$ To answer that with clarity it would entirely depend on what the particular setup is considered. And control of the flow parameters externally by a user would encompass almost all of the potential requirements one could have. Ashok, is there any particular example that you are thinking of where the advantages aren't clear enough? $\endgroup$ Sep 14, 2018 at 10:14

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