Problem # p026

 In a steam power plant the flow of super-heated steam into a section of the main-turbine is to be controlled. This is achieved by placing a constriction (throttle) inside the pipe through which the steam flows such that the pressure before the constriction (state 1) is at 10 MPa and 600 oC and behind (state 2) at 8 MPa. The constriction does not contain any moving parts and heat losses to the environment and changes in kinetic and potential energy can be neglected.
Superheated steam at 10 MPa
T [oC]   u [kJ/kg]   h [kJ/kg]   s [kJ/(kg K)]
600 3242 3625 6.9029
Superheated steam at 8 MPa
T [oC]   u [kJ/kg]   h [kJ/kg]   s [kJ/(kg K)]
520 3103 3448 6.7871
560 3179 3545 6.9072
600 3254 3642 7.0206
640 3330 3738 7.1283

Use the equation for the conservation of mass and for the conservation of energy plus the property data provided in the two tables above and linear interpolation to determine :

1. The temperature T2 of the steam downstream of the constriction.

2. The change in entropy. Should the entropy increase or decrease ?