FLuid Flow through a Divergent Section

  1. Hi,
    Can Someone Elaborate the fluid(water) Characteristics Such as Velocity n pressure When it passes through a divergent Part. Actually The Fluid is pumped Out from A 0.5HP Centrifugal Pump and then made to pass through a Divergent Part.
     
  2. jcsd
  3. Bobbywhy

    Bobbywhy 1,908
    Gold Member

    astronautnandu, Welcome to Physics Forums!

    For fluid flow through a divergent part please see question 3.4 in:
    http://www.efm.leeds.ac.uk/CIVE/CIVE1400/Examples/eg3_ans.htm

    Also, see page 12 of 25 (p. 123 of book), section 7.4.2: Loss with gradual change of area.
    Divergent pipe or diffuser, equations (7.28) through (7.32) and Fig. 7.13
    http://www.scribd.com/doc/9712922/Introduction-to-Fluid-Mechanics-Ch07

    If these references don’t satisfactorily answer your question, please return here to Physics Forums and post your doubt or question. Please be as clear and exact as possible when describing your scenario.

    Cheers,
    Bobbywhy
     
  4. Due to conservation of mass (continuity), the mass flow rate before the divergent section = the mass flow rate after the divergent section. The mass flow rate at any section=ρUA. So if the flow area increases (as in a diverging section), the velocity has to decrease to satisfy continuity (for a fluid of constant density such as water).

    If the velocity of a fluid decreases, the pressure associated with the kinetic energy of the fluid continuum, known as the dynamic pressure, decreases. Thus in accordance with Bernoulli, the static pressure increases.

    It is the opposite for a converging section.
     
  5. Look up Bernoulli's Law.

    Depending on your situation, can could assume inviscid fluid to simplify things.

    You also have to be careful that the divergence of the section isn't too extreme. If it is the assumption that the velocity is uniform throughout a particular cross section will not be valid.
     
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