The first stage, isothermal reversible expansion process, the system absorbs heat from high temperature heat source; In the second stage, adiabatic reversible expansion process, the system temperature drops from high to low; The third stage, isothermal reversible compression process, the system releases heat to the low temperature heat source; The fourth stage, adiabatic reversible compression process, the system temperature rises from low.
We can draw a conclusion through the related theorem of thermodynamics that the efficiency of Carnot cycle is ηc= 1-T2/T 1. It can be seen that the efficiency of Carnot cycle is only related to the thermodynamic temperatures of two heat sources. If the temperature of high-temperature heat source T 1 is high and the temperature of low-temperature heat source t2 is low, the efficiency of Carnot cycle is high. Because there is no high-temperature heat source of T 1→∞ or low-temperature heat source of T2=0K(-273℃), the efficiency of Carnot cycle is necessarily less than 1.
Reversible thermodynamic cycle consisting of two isothermal processes and two adiabatic processes (see thermodynamic process). Carnot cycle was put forward by French engineer S Carnot in19th century, hence its name. Carnot cycle is divided into positive cycle and negative cycle. In the pressure-volume (p-V) diagram and temperature-entropy (T-S) diagram (see figure), ι-b-c-d-ι is a normal Carnot cycle, ι-b is a reversible isothermal endothermic process, and the working medium absorbs heat from a high-temperature heat source at the same temperature at T 1 B-c is a reversible adiabatic process, and the working fluid temperature drops from T 1 to T2. C-d is a reversible constant-temperature exothermic process, and the working medium releases heat Q2 to a low-temperature heat source at the same temperature at T2 temperature. D-ι is a reversible adiabatic process. The temperature of the working medium rises from T2 to T 1, completing a reversible cycle and doing net work W. The reverse Carnot cycle is opposite to the above-mentioned forward cycle, along the direction of ι-d-c-b-ι, so Q2 is the heat absorbed by the working medium from a low-temperature heat source (commonly known as refrigeration capacity), and q/kloc-.
Carnot theorem defines the limit of heat engine efficiency and points out the direction of improving heat engine efficiency (increasing T 1, reducing T2, reducing irreversible losses such as heat dissipation, air leakage and friction, and making the cycle as close as possible to Carnot cycle). It becomes the theoretical basis of heat engine research and the limit of heat engine efficiency. The research on the irreversibility of actual thermodynamic process and its relationship leads to the establishment of the second law of thermodynamics. The absolute thermodynamic temperature scale based on Carnot's theorem has nothing to do with the materials and properties of temperature measurement, which makes the temperature measurement based on an objective basis. In addition, the relationship between surface tension, saturated vapor pressure and temperature, as well as the electromotive force of reversible batteries can be studied by applying Carnot cycle and Carnot theorem. It should also be emphasized that Carnot's abstract and universal theoretical research, which puts aside specific devices and specific working fluids, runs through the whole study of thermodynamics. Cano's research has many meanings. His work pointed out the direction for improving the efficiency of heat engine; His conclusion already contains the basic idea of the second law of thermodynamics, but he failed to fully explore the final answer to the question because of the concept of heat and mass. Because of Kano's untimely death, his works were soon forgotten. Later, due to the re-study and development of French engineer Claperon (B.P.E.Clapeyron, 1799- 1864) in 1834, Kano's theory was noticed by people. Clapper used "pressure (force)-volume (product) diagram" to represent Carnot cycle, and proved that the work done by Carnot heat engine in a cycle is exactly equal to the area enclosed by the cycle curve. Claperon's work created conditions for the further development of Carnot's theory.