Steam leaves the boiler of a power plant at 7 MPa, 500 degree C as shown in Figu
ID: 1718048 • Letter: S
Question
Steam leaves the boiler of a power plant at 7 MPa, 500 degree C as shown in Figure P3.8. As the steam passes to the turbine, there is a small pressure drop due to friction in the pipe and the temperature drops due to a heat loss through the pipe's insulation. The surface temperature of the pipe insulation is 45 degree C. Because of these effects, the steam enters the turbine at 6.93 MPa, 493 degree C. The steam then passes through an adiabatic turbine and exits at 10 kPa. The turbine an isentropic efficiency of 85% and is delivering 600 MW of power. Determine the following: Heat transfer rate from the pipe connecting the boiler to the turbine (in MW). Entropy generation rate associated with the heat loss from the pipe (kW/K).Explanation / Answer
(a) at P1 = 7 MPa and T1 = 500 C
h1 = 3411.25 kJ/kg
at P2 = 6.93 MPa and T2 = 493 C
h2 = 3395.086 kJ/kg
at P3 = 10 kPa
h3 = 2583.9 kJ/kg
heat transfr through pipe = h1 - h2 = 16.164 kJ/kg
work done by turbine = 600 * 10^6 = m * 0.85 * (3395.086 - 2583.9)
m = 870.18557 kg/s
heat transfer through pipe = 870.18557 * 16.164 = 14.065 MW
Entropy generation = 14065 / (273 + 45) = 44.231 kW/K