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Note for Power Plant Engineering - PPE By Jitendra Pal

  • Power Plant Engineering - PPE
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PEME5409 POWER PLANT ENGINEERING Module 1: Section 3 Flow Through Nozzles Dr. Sudhansu S. Sahoo Assistant Professor Department of Mechanical Engineering C.E.T. Bhubaneswar, Odisha, India.

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Nozzles •A nozzle is a passage of smoothly varying cross-section by means of which the pressure Energy of working fluid is converted into kinetic energy. •The shape of the nozzle is designed such that it will perform this conversion of energy with minimum loss. Applications •Steam, water and gas turbines. •Jet engine s, rocket motors to produce thrust. •Artificial fountains. •Flow measurements. •Injectors for pumping feed water to the boilers and ejectors for removing air from the condensers. When a fluid is decelerated in a passage of varying cross section causing rise in pressure along the stream, then the passage is called a diffuser. These are extensively used in centrifugal compressors, axial flow compressors, ram jets etc. BPUT-CET_8th SEM_MECH_PPE 2

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Types of Nozzles i) Convergent Nozzle Cross section of the nozzle decreases continuously From entrance to exit ii) Divergent Nozzle Cross section of the nozzle increases continuously From entrance to exit iii) Convergent –Divergent Nozzle Cross section of the nozzle first decreases and then increases Specific volume of a liquid is almost constant over a wide range of pressure, therefore, Nozzles for liquids are always convergent, even at high exit velocities (e.g. a fire-hose) BPUT-CET_8th SEM_MECH_PPE 3

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Relationship between Area, Velocity and Pressure in Nozzle flow Applying mass conservation equation ρ AV = Cons tan t.................................(1) d ( ρ AV ) = 0 d ρ dA dV + + =0 A V ρ dA dV d ρ =− − ..................................(2) A V ρ Applying momentum conservation equation dp ρ + VdV + gdz = 0.............................(3) dp = − ρVdV dp dV = − ........................................(4) 2 V ρV BPUT-CET_8th SEM_MECH_PPE 4

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