Question

Steam enters a counterflow heat exchanger operating at steady state at 0.06 MPa with a quality of 0.9 and exits at the same pressure as saturated liquid. The steam mass flow rate is 1.3 kg/min. A separate stream of air with a mass flow rate of 100 kg/min enters at 30oC and exits at 60oC. The ideal gas model with cp = 1.005 kJ/kg·K can be assumed for air. Kinetic and potential energy effects are negligible. Determine the temperature of the entering steam, in oC. For the overall heat exchanger as the control volume, what is the rate of heat transfer, in kW.

Answer 1

Explanation:

$\begin{array}{ll}\1 & \2 \\P_{1}=0-\_{\text {mpa }} \text { Steam } & P_{2}=0.06 mpq \\x=0.9 & x=0 \text { (satunated liquid) }\end{array}$

a) Term of entering steam will be Tsaturated of corresponding pressure

   $so, At P =0.06 mpa , T_{s a t}=85.92^{\circ} C$

b)

    $\begin{aligned}Q &=m c_{p}\left(T_{0}-T_{i}\right) \\&=\frac{100}{60} \times 1.005(60-30)=50.25 W\end{aligned}$