Question

Problem 2 (50 pts): You are interning at a power-plant engineering company that is in the process of designing a new steam cycle. Your manager asks you to help in estimating the turbine work output for 2 different operating conditions:

i) Water enters the turbine at 600 °C and 17.5 MPa and exits at 20 kPa as a saturated mixture with a quality of 0.95.

ii) Same inlet conditions as (i), but exits at 20 kPa as a saturated mixture with a quality of 0.85.

a) Calculate the turbine work output per unit mass of water for conditions (i) and (ii). (35 pts)

b) Comment on the difference in the turbine work output between conditions (i) and (ii). (5 pts)

c) Show the process across the turbine for conditions (i) and (ii) on the same T–v diagram. (10 pts)

Answer 1

Griven that i initial conditions Piz. Gooc , P,= 17.5MPa from super heated steam table to wales at P: 17.5mpo =) Tsub= 354.6°c. To bouc > Tsul Hence steam exists as superheuled vapoor at inicial condition at P=175mpu .T,= 6052 =) The 356+ 4b k g | given that wiler exits top bine as saturated mixture with quality (n) = 0.95 at P 20KpQ from saluruled steary table of water by Pressure at P: zokupa as he= 251.4 kiling 3 - 26 08 15 KS Y. heg= 2357.55 kilky : h₂= hfta (hy-he) anft nx heg : 2357.55 . = 251.470.95x R SS Tha= 2379.089 kJ/kg

Turbine work out put (ar)= h, he = 3561.40-2379.089 I alt 1182.37 0.85 | inilet conditions sume, but walor exite al colpa as saluraled mi tore with quality i h₂= het uhey - 251.4 + 0.85% 2357 55 1 The= 2255.3175 kilkyl - 3561-46-2955.175 2 - 1 (NT), 1306. 1425 kuling o if keep all other parameters changing the quality se . of steam from constanst by reducing Quality 0.95 to 0.85

Turbine work out put is increasing if we decrease the Qual: r, ам диҳо - А heat rejection is decreased! Hence work is incrouse 0.95 1. QR 0.85 . А водат оn Q«екол Qrej t => in a even though it is increased decreuted more wole particles in steam that will lead Turbine blades by erosion. if Quality is are available to damage of Ad TN Og5 095 797