A steam turbine operates with 1.6 MPa and 350°C steam at its inlet and saturated vapor at 30°C at its exit. The mass flow rate of the steam is 21.4 kg/s, and the turbine produces 12,350 kW of power. Determine the rate at which heat is lost through the casing of this turbine. The enthalpies are h1 = 3146 kJ/kg and h2 = 2555.6 kJ/kg.

Respuesta :

Answer:

[tex]\dot Q_{out} = 104.56\,kW[/tex]

Explanation:

The steam turbine is modelled after the First Principle of Thermodynamics. Changes in potential and kinetic energy are negligible:

[tex]-\dot Q_{out} -\dot W_{out} +\dot m \cdot (h_{in}-h_{out}) = 0[/tex]

The heat rate is:

[tex]\dot Q_{out} = \dot m \cdot (h_{in}-h_{out})-\dot W_{out}[/tex]

From steam and saturated tables, specific enthalpies at inlet and outlet are found:

Inlet - Superheated vapor

[tex]P = 1600\,kPa[/tex]

[tex]T = 350^{\textdegree}C[/tex]

[tex]h = 3146.0\,\frac{kJ}{kg}[/tex]

Outlet - Saturated vapor

[tex]T = 30^{\textdegree}C[/tex]

[tex]P = 4.2469\,kPa[/tex]

[tex]h = 2555.6\,\frac{kJ}{kg}[/tex]

The loss rate is:

[tex]\dot Q_{out} = (21.4\,\frac{kg}{s} )\cdot (3146.0\,\frac{kJ}{kg}-2555.6\,\frac{kJ}{kg} )-12350\,kW[/tex]

[tex]\dot Q_{out} = 104.56\,kW[/tex]