Steam at 4 MPa and 400ºC flows through a 2-cm-diameter pipe. If the mass flux is 2 kg/min, the average velocity is nearest:

A) 10.8 m/s
B) 9.8 m/s
C) 8.8 m/s
D) 7.8 m/s


D) 7.8 m/s

When analyzing control volumes, V represents velocity. It’s difficult to use a different symbol in equations. Besides, when working problems involving control volumes, the actual volume is seldom encountered so V most often represents velocity. The exception is the volume flow rate, represented by V. The definition of the mass flux allows:





The units should be obvious. Make sure m2 is used for area, seconds for time, and kg/m3 for

density. The units will then check out.

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