A Rankine cycle with reheat uses water as its working fluid. Superheated vapour enters the high-pressure turbine at 10 MPa and 440oC. The steam expands through this high-pressure turbine to 0.7 MPa and is then reheated to 400oC. The steam then expands through the low-pressure turbine to 6 kPa before entering the con-denser. The mass flow rate of water through the cycle is 600 kg/s.The temperature of the water at the pump inlet is 30oC.
The isentropic efficiency of the pump is 65%. The isentropic efficiency of the high-pressure turbine is 92% while that of the low-pressure turbine is 87%.
The turbine and pump can be treated as adiabatic. The pressure drops of the work-ing fluid as it flows through the boiler and through the condenser are negligible. Kinetic and potential energy effects can also be ignored. For your analysis use the state point numbering scheme indicated in the following schematic:
Here is a picture of the problem as well as the schematic,
- Determine quality of steam at 2
- Determine quality of steam at 4
- Calculate the net power produced in the cycle
- Calculate the back work ratio of the cycle
- Calculate the thermal efficiency of the cycle
I am using these steam tables
x = ( sout - sf[P] ) / sfg[P]
h = hf[P] + x*hfg[P]
Wnet = Sum of Power
BWR =( -Wc/m ) / Wt/m
neff = Wt / Qin
The Attempt at a Solution
Here is what I have done so far,
I am stuck on how I am supposed to find the net power and I am not 100% sure what I have done so far is correct.
For finding the newt power produced I think I know how to determine the turbine power, but for the pump power I have,
Wp = m ( h5 - h6 )
I am not sure how to find the h values and my data for state 5, T = 30 oC and P = 6 kPa doesn't seem to work with any of the steam tables.
edit: After working some more I noticed that it states that in state 5 it is water, so liquid. From here if I assume my pressure of 6 kPa is wrong and ignore it I can continue on and obtain my h5 also I can use the entropy from state 5 to interpolate my enthalpy in state 6 since I know it is an adiabatic pump.
Updated picture of my work, last 3 answers in bottom right,