Carnot engine is a theoretical thermodynamic cycle proposed by Leonard Carnot. It gives the estimate of the maximum possible efficiency that a heat engine during the conversion process of heat into work and conversely, working between two reservoirs, can possess. In this section, we will learn about the Carnot cycle and Carnot Theorem in detail.
Carnot Theorem:
According to Carnot Theorem:
Any system working between two given temperatures T1 (hot reservoir) and T2 (cold reservoir), can never have an efficiency more than the Carnot engine working between the same reservoirs, respectively.
Also, the efficiency of this type of engine is independent of the nature of the working substance and is only dependent on the temperature of the hot and cold reservoirs.
Carnot Cycle:
A Carnot cycle is defined as an ideal reversible closed thermodynamic cycle in which there are four successive operations involved, which are isothermal expansion, adiabatic expansion, isothermal compression and adiabatic compression. During these operations, the expansion and compression of substance can be done up to the desired point and back to the initial state.
Carnot Cycle
Following are the four processes of the Carnot cycle:
In (a), the process is reversible isothermal gas expansion. In this process, the amount of heat absorbed by the ideal gas is qin from the heat source, which is at a temperature of Th. The gas expands and does work on the surroundings.
In (b), the process is reversible adiabatic gas expansion. Here, the system is thermally insulated, and the gas continues to expand and work is done on the surroundings. Now the temperature is lower, Tl.
In (c), the process is reversible isothermal gas compression process. Here, the heat loss qout occurs when the surroundings do the work at temperature Tl.
In (d), the process is reversible adiabatic gas compression. Again the system is thermally insulated. The temperature again rises back to Th as the surrounding continue to do their work on the gas.
So, the expression for net efficiency of carnot engine reduces to:
Netefficiency=1−T2/T1