steam turbine eff calculation

Thermodynamics.

Efficiency is the ratio of [power output / power input].

The input power is calculated from the difference in energy enthalpies between the inlet & exhaust steam conditions of the steam i.e the pressure & temperature at inlet & exhaust conditions need to be known and the enthalpy is obtained from steam tables. You also need the steam flow rate.

Output power would be obtained from measuring / calculating the power that the turbine performs e.g when driving an electrical generator, the output is generally measured, when driving a pump, the hydraulic power can be calculated. In both these instances allowances must be made for:

1. the efficiencies of the generator [85% ?] and the pump [65% ??]

2. frictional losses in bearings etc.

You can get quite fancy and make allowances for heat loss from the casing & piping, steam losses from leaks and blow vents..... It would depend on the accuracy that you are after and the boundary limits that have been set.