What is a heat engine? Explain its working with schematic diagram.

Explanation

Heat engine is a thermodynamics device which converts heat energy into mechanical energy (work).
Working of Cornot's engine:
Step 1: The working substance (ideal gas) is enclosed in a non-conducting wall and conducting bottom of a cyclinder fitted with air tight non conducting piston. This is placed on the source having in infinite thermal capacity at a steady temperature. The top surface is conducting and the rest non conducting. As a result, the gas expands isothermally. The work done by the system,
`W_1= mu RT_1 log.(V_2)/(V_1) ("Curve A B")`
Step 2: The working substance is now placed on a non conducting platform, as a result of which no heat exchange takes place between the system and the surroundings. The system expands adiabatically at the expense of its internal energy. The gas cools. The work done by the system,
`W_2(mu R)/(gamma -1)(T_1-T_2) ("Curve B C")`

Step 3: The working substance is now placed on the sink maintained at a steady low temperature `T_2 K.` The system undergoes isothermal compression at this temperature. The pressure of gas increases and volume decreases without any change in internal energy and specific heat of gas remain at infinity.
`W_3=mu RT_2 log((V_4)/(v_3)) ("Curve C A")`
Step 4 : The working substance is placed on a non-conducting platform. Under thermal isolation, the system undergoes change in its internal energy and its specific heat remains at zero. Adiable compression results in increase in the pressure and temperature at the expense of work being done on the system. The system is allowed to reach its initial state. This completes one cycle of operation. The area bounded by the curves gives the amount of heat converted into work.
`W_4=(-mu R)/(gamma-1)(T_1-T_2) ("Curve D A")`.
i.e., Net work done `= W= W_1+W_2+W_3+W_4`.
Work done `=mu R(T-T_2) log_e((V_2)/(V_1))`.