Question

Air initially at 15 psla and 60 F is compressed to 75 psia and 400 F. The power input to air under steady state condition is 5 hp and heat loss of 4 Btu/lbm occurs during the process. If the change in Potential energy and kinetic energles are neglected, what will be the mass flowrate in lbm/min.?

Answer 1

Answer:$\dot{m}=3.46lbm/min$

Explanation:

Initial conditions

$P_1=15 psia$

$T_1=60 F^{\circ}$

Final conditions

$P_2=75 psia$

$T_2=400F^{\circ}$

Steady flow energy equation

$\dot{m}\left [ h_1+\frac{v_1^2}{2}+gz_1\right ]+\dot{Q}=\dot{m}\left [ h_2+[tex]\frac{v_2^2}{2}+gz_2\right ]+\dot{W}$

$\dot{m}\left [ c_pT_1+\frac{0^2}{2}+g0\right ]+\dot{Q}=\dot{m}\left [ c_pT_2+\frac{0^2}{2}+g0\right ]+\dot{W}$

$\dot{m}c_p\left [ T_1-T_2\right ]+\left [ -5hp\right ]=\dot{W} -5\times 746\times 3.4121$

$-4\dot{m}-\dot{m}\times 0.24\times \left [ 400-60\right ]$

$-81.6\dot{m}-4\dot{m}=-4.949 BTU/sec$

$\dot{m}=0.057821lbm/sec$

$\dot{m}=3.46lbm/min$