Question

3. In a reheat cycle, steam leaves the boiler and enters the high-pressure turbine (HPT) at 6 MPa and 440 °C. After expansion in the high-pressure turbine to 500 kPa, the steam is reheated to 480 °C and then expanded in the low-pressure turbine (LPT) to 10 kPa. The end states of both the HPT and LPT fall in the liquid-vapor mixture region. Draw the cycle diagram and the T-s diagram, and determine the work done to the pump, total work done by the turbine, and the cycle efficiency. (25 points)

Answer 1

The TS chart is prepared and then enthalpy values at different states are obtained from the property tables. The total work will be the sum of work in high pressure turbine and the work in low pressure turbine. The work supplied by the pump is then calculated. The cycle efficiency will be the ratio of net work (i.e. turbine work minus the pump work) to the net heat supplied. The heat will be supplied before entering high pressure and before entering low pressure turbine.

GMPa 500 Kia = 713K T = 4408 7 = 4000 = 753K 3 6 K h = 27 3302.9 Kg 1kg. K s, = 6.722 Kg 1kg .k 2 75 + = 3431.1 S = s, = 6.722 = ff + Aty 6.722 = (1.85365) + (4-9737) 20-9788 hy = hq + rhify => 1 = (637.55) + (0-9788) 2109.55 h = 2702.42 Kiliky hy z = 8.018 KG lky K 3-4-8.018 = 8.018 = 10.6492) + , (7.4990) % = 0.9825 h = het 4 a hug h = (191-8) + (0.9825)* 2392-1 hy = 2542.18 Kg 1 kg. hg = hp = 191.8 kg 1 kg. h = ly = 1213.9 kg Ikg. eft my hig Total Work Done (h, hey) et (hy he) -> (3302-9- 2702.42) (3431-1 - 2542.18) - 1489.4 Kg 1 kg work suppliced to Pamp Cheahs) -> (1213-9 - 1918) = 1022.1 kg likg Cycle lifficiency => (Work Done) - (loor Supplied) (Heat Supplied) 47 = (1489.4 - 10221) (h, - hp) + (hz-he) (1489.4 - 1022:1) (3302-9-1213.9) +(3431.2 - 2702-42 2 116.58%