Question

Steam at 15 bar, 540 °C, 60 m/s enters an insulated turbine operating at steady state and exits at1.5 bar, 89.4 m/s. The work developed per kg of steam flowing is claimed to be (a) 606 kJ/kg, (b)765.9 kJ/kg. Can either claim be correct? Explain. textbook

Answer 1

Both can be correct is steam exits as superheated steam.

Step-by-step explanation:

The model for the turbine is created by using the First Law of Thermodynamics:

`w_(out) = h_(in)-h_(out) + (1)/(2)\cdot (v_(in)^(2)-v_(out)^(2))`

Specific enthalpies for both states are presented below:

State 1 (Superheated Steam)

`h = 3562.10\,(kJ)/(kg)`

State 2 (Saturated Vapor)

`h = 2693.10\,(kJ)/(kg)`

The specific work of turbine is:

`w_(out) = 3562.10\,(kJ)/(kg) - 2693.10\,(kJ)/(kg)+(1)/(2)\cdot [(60\,(m)/(s) )^(2)-(89.4\,(m)/(s) )^(2)] \cdot ((1\,kJ)/(1000\,J) )`

`w_(out) = 866.803\,(kJ)/(kg)`

Both can be correct is steam exits as superheated steam.