## The First Law of Thermodynamics

## Conservation of Energy

The principle of the conservation of energy states that __energy can neither be
created nor destroyed__. If a system undergoes a process by heat and work
transfer, then the net heat supplied, **Q**, plus the net work
input,** W**, is equal to the change of intrinsic energy of the
working fluid, i.e.

where **U1** and **U2** are intrinsic energy of the system at initial and final states, respectively. The special
case of the equation applied to a steady-flow system is known as steady-flow
energy equation. Applying this general principle to a thermodynamic cycle, when the system undergoes
a complete cycle, i.e. **U1 = U2**, results in:

where:

**Q= The algebraic sum of the heat supplied to (+) or rejected from (-) the system.**

**W= The algebraic sum of the work done by surroundings on the system (+) or by the system on
surroundings (-).**

Applying the rule to the power plant shown in figure below,

gives:

**Q = Qin - Qout **

**W = Win - Wout**

**Qin + Win - Qout - Wout = 0**

where,

**Qin** = Heat supplied to the system through boiler,

**Win** = Feed-pump work,

**Qout** = Heat rejected from the system by condenser,

**Wout** = Turbine work.

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