Maximum efficiency

Ideal engine has a maximum efficiency,

If a heat engine goes through fixed thermodynamics stage of a specificed process,



four main parts:η

  • Insulated – non conducting stand (the transfer of energy is not possible )
  • Hot reservoir– heat capacity should be infinite.

Because , After taking  any energy from it, the temperature of reservoir should be constant .

  • The reservoir in which infinite heat capacity will be conducting at high temperature is called to be cold reservoir.
  •  Cylinder  should be kept for working substances .

Cylinder wall should be non-conductive so that heat transfer is impossible .but base should be conducting .


For this , first place the cylinder on the hot reservoir since the temperature of reservoir is higher than the temperature of gas, the heat flows from the heat reservoir to the gas .Due to which the gas start to expands .

Since due to heat transfer gas is expanding therefore the temp of gas remain constant

This process is called Isothermal expansion.

as the gas expand , the volume of gas increase and pressure decrease .

In next step , take off the cylinder from the hot reservoir and place it on the insulating stand , when doing so, the gas is confined to the non-conducting wall.

Now let piston rise slowly upward .

Due  to which the gas continue to expand .But this time the gas is not getting any heat to expand .such expansion called Adiabatic expansion.

Since this expansion is taking place without heat .

The temperature of gas starts to decrease .Due to this expansion ,the volume of gas also increase and pressure decrease

In next step, lift the cylinder from the stand and place it on the cold reservoir , now pressure the piston downwards which causes compression of gas.

In this way the gas compresses at the same constant temperature .this called Isothermal compression

Due to this compression the volume of gas decreases and pressure increase

In final stage , cylinder keep on stand again and pressure piston downward

But now there is no cold reservoir to absorbs the heat getting produced extra.

Therefore , the temperature of gas start increase . this compression is called Adiabatic compression .

Pressure the piston until the temperature of gas rises back to equal that of the hot reservoir . This decrease the volume of the gas and increase the pressure

At the end of this step , the gas return to its initial stage .

This complete cycle is called the carnot cycle .The engine work on it ,is called carnot engine.

η =1-T1/T2

The efficiency depend on the temperature of both reservoir.

If  T1 is  ∞ kelvin and  T2 is 0 kelvin

Either rise the temperature of hot reservoir to ∞ kelvin or low down the temperature of reservoir to 0 kelvin .

In both cases,the efficiency will be 100%.



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