1. Recall that we wrote the First Law of Thermodynamics as:
The above only applies for a STEADY FLOW process, I.e. a process where none of the properties inside the control Volume (C.V.), including energy, are changing with time.
The turbine problem is an example of a steady process. If the process is unsteady, i.e. transient, the total amount of energy inside the system (or CV) can change.
The First Law for such a process is given by:
Where dECV/dt is the rate of change in the total energy of the Control Volume.
First law-ex-1