NOZZLE HIGHLIGHTS

NOZZLE HIGHLIGHTS 

  1. There is conversion of pressure into kinetic energy.
  2. There is 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. Convergent nozzles are used in all aircrafts.
  7. Convergent –divergent nozzles are used in stream turbines.
  8. Convergent –divergent nozzles are used in super-sonic aircrafts.
  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. Velocity and other 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 isentropic 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 isconstant 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 and 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 which 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 which 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 the divergent portion.
  25. Steam is a vapour and its properties are known either from the enthalpy entropy chart (Mollier chart) or from the steam tables.