It is typically represented by a piston that is in a quasistatic state where the gas inside is expanded by a heat source, and then a heat sink is used to slowly remove the heat from the piston. Basically the Carnot Cycle is a theoretical heat engine that has two Isothermal processes and two adiabatic processes. It is stated that nothing in real life can be more efficient then the Carnot Cycle.
The Carnot Cycle is one of the most widely used ideal and reversible cycles. If something has be permanently deformed it will not release the same amount of energy that was used to deform it. Finally, another example of an irreversibility is an inelastic deformation. An example is a hot liquid that cools in air, the heat will not readily go back into that liquid, so the process cannot be reversed. Heat transfer can also cause irreversibility. Friction causes heat, which is lost energy from the system that cannot be reversed. Another common irreversibility is friction. This in turn results in unrestrained expansion, which can actually cause a pressure difference within the cylinder that the gas is expanding, or be compressed in. In real life, however, it’s not practical for a process to happen slow enough to be quasistatic. So what causes a process to have irreversibility’s? Well first most reversible processes assume that a process is quasistatic. If your irreversible process provides better results than your reversible process, then you either calculated your reversible process wrong, or something is wrong with your measurements. Basically the reversible process is a theoretical limit for its corresponding irreversible process. You can use those results and compare them to the results from an actual process that has been measured. Also, if you solve the reversible process, which is an ideal process. An irreversible process can have unknowns that can’ t be accounted for. So why do engineers focus on reversible processes instead of irreversible processes? They do this because a reversible process is much easier to analyze. Irreversible processes are real processes.
Any process that cannot return to it original state is an irreversible process. The opposite of a reversible process is an irreversible process. Reversible processes do not occur in nature, but instead are ideal processes. In other words the process can always be returned to its initial state. The definition of a reversible process is a process that can be reversed without leaving traces of the process on the surroundings. When studying thermodynamics the processes that are talked about are almost always reversible processes.