Question

Air at 1 kg/sec enters into an insulated blower at 300 K. The inlet and outlet velocities of air are 60 m/s and 100 m/s respectively. If the blower consumes 40 kW power then the exit temperature of air is closest to $(c_p$ of air is equal to 1 kJ/kgK)

• A. 347 K
• B. 340 K
• C. 335 K
• D. 337 K

Answer 1

The correct option is D 337 K

By using steady flow energy equation,

$m_1[h_1+\frac{V_1^2}{2}]+\dot{Q}=m_2[h_2+\frac{V_2^2}{2}]+\dot{W}$

$m_1[c_p{T}_1+\frac{V_1^2}{2000}]=m_2[c_p{T}_2+\frac{V_2^2}{2000}]+\dot{W}$

$m_1=1kg/s,T_1=300k,V_1=60m/s,V_2=100m/s,\dot{W}=-40kW$

$1[1\times 300+\frac{{60}^2}{2000}-\frac{{100}^2}{2000}]+40=1\times T_2$

$T_2=336.8K$