Among all cyclic thermodynamic processes , the Carnot cycle has a special theoretical value and practical application. Often he is called unsurpassed, great, ideal, etc. And for many, he generally seems to be something mysterious and incomprehensible. However, if all accents are correctly set, then all the simplicity, genius and beauty of this invention, which was discovered by the French scientist and engineer Sadi Carnot, will instantly be revealed. And it will become clear that there is nothing supernatural in the process he proposed, but there is only the most efficient use of certain laws of nature.
So what exactly is the famous and mysterious Carnot cycle? It can be defined as a quasistatic process based on bringing the thermodynamic system into thermal contact with a pair of thermostat tanks with constant and stable temperature values. It is assumed that the temperature of the first (heater) exceeds that of the second (refrigerator). The Carnot cycle consists in the fact that at first the thermodynamic system, initially having a certain thermal value, comes into contact with the heater. Then, by infinitely slow pressure reduction, a quasistatic expansion is caused in it, accompanied by the borrowing of heat from the heater and resistance to external pressure.
After this, the system is isolated, which again causes a quasi-static adiabatic expansion in it, until its temperature reaches the same values for the refrigerator. With this type of expansion, the thermodynamic system also performs some work of resistance to external pressure. In this state, the system is brought into contact with the refrigerator, and by continuously increasing the pressure, it is compressed to a certain point, as a result of which it then completely transfers to the second tank the thermal energy borrowed from the heater. The Carnot cycle is unique in that it is not accompanied by any heat loss. Theoretically, such a scheme can be called a perpetual motion machine. This is all because the thermal efficiency of the Carnot cycle, which depends solely on the temperature of a pair of tanks, will always be the maximum possible. However, so far no one has managed to create a machine whose thermal efficiency would exceed thirty percent of Sadi Carnot allowed by the cyclic process.
And this process is called ideal, because it is much better than other cycles capable of turning heat into useful work. On the other hand, due to difficulties in organizing and conducting isothermal processes, its use in real engines is extremely difficult. For maximum heat transfer efficiency, such a machine needs to be completely isolated from the external environment, which is practically impossible in reality.
The reverse Carnot cycle is the basis of the principle of the heat pump, which, unlike the chiller, should give as much energy as possible to any hot object, such as a heating system. Some of the heat is borrowed from an environment with a lower temperature, the rest of the necessary energy is released when performing mechanical work, such as a compressor.