Sangeetha Pulapaka

A Carnot heat engine is a mechanical arrangement to convert heat into mechanical work. Sadi Carnot devised an ideal heat engine which was free from all imperfections of an ideal heat engine. '

It consists of mainly five parts - A cylinder with a working substance, source, sink and insulating pad. The cylinder consists of  insulating walls and conducting base.

It is fitted with an inslulating frictionless piston. The source has infinite thermal capacity. That means any amount of heat can be taken out of it, without changing the temperature of the source. The sink is at a lower temperature and has infinite thermal capacity. This means that any amount of heat can be added to it without changing its temperature. The working substance in the cylinder is an ideal gas which absorbs heat from the source. It does some mechanical work and rejects the  remaining amount of heat into the sink.

During the operation of the carnot cycle the working substance undergoes adiabatic expansion and adiabatic  compression. The cylinder is placed on an insulatiing pad which thermally isolates the working substance inside the  cylinder from the surroundings. To get continuous supply of work the working substance is taken through a series of operations called the carnot cycle.

PV diagram for a Carnot cycle, employing only reversible isothermal and adiabatic processes. Heat transfer  Q_{h} occurs into the working substance during the isothermal path AB, which takes place at constant temperature T_{h}. Heat transfer Qc occurs out of the working substance during the isothermal path CD, which takes place at constant temperature Tc. The net work output W equals the area inside the path ABCDA. Also shown is a schematic of a Carnot engine operating between hot and cold reservoirs at temperatures T_{h} and Tc. Any heat engine using reversible processes and operating between these two temperatures will have the same maximum efficiency as the Carnot engine.


This toy is an example of a carnot's engine.It was also used in an epsiode of Homer Simpson!

Vivekanand Vellanki

Very interesting question. I only wish you had said "the teacher drew a loop on the board".

The carnot engine is based on using the formula: PV = nRT; where P is the pressure exerted; V is the volume and T is the temperature.

I suggest you view this video to understand carnot cycle and carnot engine.