Page 131 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

c) Nozzle

A nozzle utilises a pressure drop to produce an increase in the kinetic energy of

the fluid.

Figure 3.2.7-3 Nozzle

The steady flow energy equation gives

  C 2 −C 2  
+
Q −W = m   (h 2 − h 1 )  2 1   ( + gZ 2 − gZ 1 )


  2  


Points to note :
i. The average velocity of flow through a nozzle is high, hence the fluid

spends only a short time in the nozzle. For this reason, it may be assumed

that there is insufficient time for heat energy to flow into or out of the fluid
during its passage through the nozzle, i.e. Q = 0.

ii. Since a nozzle has no moving parts, no work energy will be transferred to

or from the fluid as it passes through the nozzle, i.e. W = 0.
iii. Potential energy is generally small enough to be neglected.

Hence the equation becomes

  C 2 −C 2  
+
0 = m   ( − hh )   2 1  

 2 1  2   


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