Cyclic process

Before discussing about this concept, we take water for which in three states such as ice, water and vapour, after vapour state by decreasing temperature and pressure, again vapour state in turn to
solid state. This fact is explained in the matter triple point, i.e., water has cyclic process because it reaches to original state as ice after passing through different stages.
A process in which the system after passing through various stages returns to its initial state is called cyclic process. In a cyclic process, the change in the internal energy is zero.
According to first law of thermodynamics,
dQ=dU+dW
Since dU=0
dQ=dW

In cyclic process, the total heat absorbed by the system equals the work done by the system.
Obviously, the P-V diagram for a cyclic process will be closed curve.
The main application of cyclic process is that it is used in case of heat engines, refrigerators etc.