check image Steam enters a turbine with a pressure of 30 bar, a temperature of 4

Question

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Steam enters a turbine with a pressure of 30 bar, a temperature of 400 °C, and a velocity of 160 m/s. Saturated vapor at 100 oC exits with a velocity of 100 m/s. At steady state, the turbine develops work equal to 540 kJ per kg of steam flowing through the turbine. Heat transfer between the turbine and its surroundings occurs at an average outer surface temperature of 350 K. Neglect the change in potential energy between inlet and exit. a. Determine the heat transfer rate, CV for the turbine (-22.6 kJ/kg). b. Determine the rate at which entropy is produced within the turbine n kJ/kg K per kg of steam flowing, ocv /m CV Given: h 3230.9 kJ/kg, s1 6.9212 kJ/kg. K h2 2676.1 kJ/kg, s2 7.3549 kJ/kg K (vi V2) 30 bar 400°C 100°C

Explanation / Answer

everything is given to find part A. The only tricky part is units.

Q/mdot= 540000-(3230900-2676100)-(0.5*(160^2-100^2))

Q/mdot=-22600 J/kg → -22.6 kJ/kg

for part B im not 100% sure, but i'll give it a shot.

you have 0=Q/T+m(s1-s2)-sigma

(sigma/m)=(Q/m)/T+(s1-s2)

(sigma/m)= -(-22.6)/350-(6.9212-7.3549)

(sigma/m)=0.50 kJ/kg*K

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