Question

0.70 kg/s of air enters the compressor with a specific enthalpy of 390 J/kg and leaves it with a specific enthalpy of 550\ J/kg. Velocity at inlet and exit are 8 m/s and 1 m/s respectively. Assuming adiabatic process, what is power input to the compressor?

• A. 80 W
• B. 85 W
• C. 90 W
• D. 95 W

Answer 1

The correct option is C 90 W

$m=0.70kg/s$

$h_1=390J/kg$

$h_2=550J/kg$

$V_1=8m/s;V_2=1m/s$

Using SFEE

$h_1+\frac{V_1^2}{2}=h_2+\frac{V_2^2}{2}+\frac{W}{m}$

$390+\frac{8^2}{2}=550+\frac{1^2}{2}+\frac{W}{0.7}$

$W=-89.95W\simeq -90W$

Negative sign indicates work is done in the system