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For a subsonic airflow, air passing through a divergent duct:
  • A
    decreases in pressure and velocity.
  • B
    increases in velocity and decreases in pressure.
  • C
    decreases in velocity and increases in pressure.
  • D
    increases in pressure and velocity.

Refer to figure.

The attached figure shows the principle of divergent ducts, where energy is neither being added nor taken away, but where the gaseous energy is being converted from velocity to pressure and temperature. There is a velocity decrease as air flows from a small inlet to a larger outlet. As velocity decreases, dynamic pressure (Pd) also decreases. Since no energy is added or subtracted from the system, total pressure (Pt) for the air remains constant and static pressure (Ps) increases. One way of viewing this is that the dynamic pressure is converted to static pressure; thus, a static pressure rise is seen as air flows through a divergent duct and is compressed. A temperature rise is also noticed since compression is a heating process.

  • In simple words, when moving through a Divergent Duct the velocity of the air decreases but pressure and temperature increase.

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