At cruise conditions, air flows into a jet engine at a steady rate of 60 lbm/s. fuel enters the engine at a steady rate of 0.58 lbm/s. the average velocity of the exhaust gases is 1535 ft/s relative to the engine. if the engine exhaust effective cross-sectional area is 3.3 ft2, estimate the density of the exhaust gases in lbm/ft3.

Explanation:

To deduce the density of the fluid we start from the concept related to the conservation of Flow. In which the mass of air and the mass of the fuel is equal to the total mass expelled.

In this way,

For definition we know that the mass flow is given by,

Where,

Density

A = Cross-sectional area

Average velocity

Replacing in the mass flow in the Exhaust:

We have that in our problem that

Replacing,

Therefore the denisty of the exhaust gases is