Reversible and Irreversible process -
A reversible process is an ideal process that never occurs, whereas an irreversible process is a natural process that is commonly found in nature. When we tear a page from our notebook, we cannot replace and ‘un-tear’ it. This is an irreversible process. Whereas when water evaporates it can also condense as rain. This is a reversible process. Let us study more about these below.
Reversible process –
A thermodynamic process is reversible if the process can reverse in such a way that both the system and the surroundings return to their original states, with no changes elsewhere in the universe. This means that both the system and the surroundings return to their initial state at the end of the reverse process.
In the above figure, the system has changed from state 1 to state 2. Reversible processes can be completely reversed and there is no trace left to show that a thermodynamic change took place in the system. During a reversible process, all changes occurring in the system are in thermodynamic equilibrium with each other.
Intrinsically Reversible process –
If no irreversibility occurs within the boundaries of the system then the process is intrinsically reversible. In these processes, a system passes through a series of equilibrium states, and when the process is reversed, the system passes through the exact same equilibrium state when returning to its initial state.
Externally Reversible process –
In an externally reversible process, there is no irreversibility outside the boundaries of the system during the process. Heat transfer between a reservoir and a system is an externally reversible process if the surface of contact between the system and the reservoir is at the same temperature.
A process can be reversible only if it fulfills two conditions –
• Disruptive force should be absent.
• The process must take place in an infinitely small time.
In simple words, a process that can reverse completely is a reversible process. This means that the final properties of the system can be completely reverted to the original properties. The process can be completely reversible if the change in the process is infinitesimally small. Under practical circumstances it is not possible to detect these very small changes in a very short time, so a reversible process is also an ideal process. The changes taking place during a reversible process are in equilibrium with each other.
Irreversible process -
Irreversible processes result in deviating away from the curve, so the amount of overall work done is reduced. An irreversible process is a thermodynamic process that departs from equilibrium. In the context of pressure and volume, it occurs when the pressure (or volume) of a system is changed so dramatically and quickly that the volume (or pressure) does not have time to reach equilibrium.
A classic example of an irreversible process is when a certain amount of gas is allowed to escape into a vacuum. By releasing pressure on a sample and allowing it to occupy a larger space, the system and surroundings are not in equilibrium during the expansion process.
There is less work here. However, significant work is required, with an equal amount of energy dissipation as heat flows to the environment. This is to reverse the process.
Engineering archaism –
Historically, the term Tesla principle was used to describe (among other things) some of the reversible processes invented by Nikola Tesla. However, this phrase is no longer in traditional use. The theory stated that some systems could be reversed and operated in a complementary manner.
It was developed during Tesla’s research into alternating currents where the magnitude and direction of the current are varied cyclically. During the demonstration of the Tesla turbine, the disc rotated and machinery attached to the shaft was driven by the engine. If the operation of the turbine were reversed, the disc would act as a pump.
By Chanchal Sailani | January 17, 2023, | Editor at Gurugrah_Blogs.
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