Explain the working of heat engine and derive the expression for its efficiency?
Answers
Heat Engine
A heat engine involves a thermodynamic process that converts the heat supply in it into mechanical work. Let’s look at the types of heat engines.
The efficiency of Heat Engine
The efficiency ‘η’ of the heat engine is the ratio between its output of work to the heat supply of the heat engine. Let us derive an expression for the efficiency of a heat engine.
η =W/Q1
where, W is the work done by the engine and Q1 is the heat absorbed from the source. After each cycle, the engine returns to its original state so that it does not affect its internal energy.
ΔU =0
W = Q1−Q2
Hence the engine efficiency is:
η =(Q1−Q2)/Q1
η = 1−Q2/Q1
so here efficiency will be 100% but in actual, this is not possible because there will be some loss of energy in the system. Hence for every engine, there is a limit for its efficiency. Gasoline and diesel engines, jet engines, and steam turbines that generate electricity are all examples of heat engines.