Page 9 - BASIC CONCEPTUAL OF THERMOFLUID

CHAPTER 1: CONCEPTUAL PRINCIPLE IN THERMOFLUIDS

During the reversible process, all the changes in state that occur in the system are in thermodynamic
equilibrium with each other.

Irreversible processes are a result of straying away from the curve, therefore decreasing the amount of overall
work done. An irreversible process is a thermodynamic process that departs from equilibrium. In terms of
pressure and volume, it occurs when the pressure (or the volume) of a system changes dramatically and
instantaneously that the volume (or the pressure) does not have the time to reach equilibrium.

Fig. 4: Irreversible process in thermodynamics

A classic example in Fig. 4 above showing of an irreversible process is allowing a certain volume of gas to
release into a vacuum. By releasing pressure on a sample and allowing it to occupy a large space, the system
and surroundings are not in equilibrium during the expansion process. Here little work occurs. However, there
is a requirement of significant work, with a corresponding amount of energy dissipation as heat flows to the
environment. This is in order to reverse the process. For example, both processes simply describe in Table 4
as below:

Table 4: Reversible and Irreversible Process

Reversible Process Irreversible Process

The process is carried out infinitely slowly It is carried out rapidly
Equilibrium may exist only after the completion of the
At any stage the equilibrium is not disturbed
process
It takes infinite time for completion It takes a finite time for completion
Work obtained in this process is maximum Work obtained in this process is not maximum

Thermodynamic cycle refers to any closed system that undergoes various changes due to temperature,
pressure, and volume, however, its final and initial state are equal. This cycle is important as it allows for
the continuous process of a moving piston seen in heat engines and the expansion or compression of the

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