NOZZLE HIGHLIGHTS

NOZZLE HIGHLIGHTS 

  1. It  converts pressure into kinetic energy.
  2. No work done in a nozzle.
  3. There is no energy transfer in a nozzle.
  4. Nozzle is considered horizontal unless otherwise stated i. e. Z1 = Z2
  5. Convergent nozzle is used in industry as spray nozzles.
  6. All air crafts use convergent nozzles.
  7. Steam turbines use convergent –divergent nozzles.
  8. Convergent –divergent nozzles are used in super-sonic air crafts.
  9. Velocity at the inlet is neglected as compared to the velocity at the outlet.
  10. Pressure decreases with decrease of area.
  11. Velocity increases with decrease of area.
  12. Flow is considered 1-dimensional.
  13.  Properties of the flowing fluid change only in the direction of flow.
  14. Steady flow energy equation is applied in the analysis.
  15. Flow is considered isen-tropic unless otherwise specified.
  16. The minimum area in a nozzle is called throat.
  17. Velocity is sub –sonic or sonic in the convergent portion and becomes super-sonic in the divergent portion.
  18. For liquids, specific volume is constant over a wide range of pressure and temperature. Therefore only convergent nozzles are used for liquids.
  19. The ratio pressure at inlet to pressure at the section of sonic velocity is called the critical pressure ratio.
  20. At the critical pressure ratio, mass flow rate is maximum.  Then it is said that the nozzle is chocked.
  21. If the pressure at exit is higher than the designed pressure, it is an under expansion. It will cause a loss in thrust or power produced.
  22. If the pressure at exit is lower than the designed pressure, it is an over expansion. It will cause a gain in thrust or power produced.
  23. Angle of convergence is much greater than the angle of divergence.
  24. The length of convergent portion is much smaller than that of the divergent portion.
  25. Steam is a vapor. Its properties are known from the enthalpy entropy chart (Mollier chart). These can also be found from the steam tables.