Question

What is heat engine. Explain its different parts with diagram and explain the efficiency of heat engine with the formula.
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Answer 1

In a heat engine a body is configured to do work when placed in alternating contact with hot and cold bodies so that heat can be supplied and absorbed. In simple terms heat engine is a device which converts thermal energy to mechanical energy.

Steam Engine

Basic Components : -

Working substance For Example: - a mixture of fuel vapour and air in a steam engine.

External Reservoir which is at higher temperature.

External Reservoir which is at lower temperature.

The reservoirs are at different temperature so that there is flow of energy from higher level to lower level.

Consider a hot reservoir having a temperature T1 and a cold reservoir having a temperature T2.

Heat engine takes heat Q1 from the hot reservoir it does some work Won the surroundings and remaining amount of heat Q2 is returned to cold reservoir

Example: - If we consider a steam engine, the work done by the engine on the surroundings is same as the mechanical energy which gets transferred to the wheels of the vehicle and as a result the vehicle moves.

The engine takes heat Q1 from a hot reservoir at temperature T1, releases heat

Q2 , to a cold reservoir at temperature T2 and delivers work W to the surroundings.

Efficiency of a heat engine:

Efficiency indicates how much useful work we get as an output by the engine by using the amount of heat energy as input.

It is denoted by η.

Mathematically :

η = W/Q1

where W= output and Q1 = input

By calculating

η = 1- Q2/Q1

Where

Q1=heat input in 1 cycle

Q2=work done in 1 cycle.

η = 1 – Q2/Q1

For 100% efficient η = 1 ( which means Q2/Q1=0)

There is always some heat is lost to the surroundings

Heat lost (Q2) = 0

There is no heat engine whose efficiency is 100%.There is always some of the losses associated with the heat engines.