anpopla.blogg.se - Second law of thermodynamics simple

See numerical problems based on this article.The second law of thermodynamics is an expression of the universal law of increasing entropy, stating that the entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium. Hence, there is no change in its internal energy.īy the first law of thermodynamics we have –

The working substance returns to its initial state after completing each cycle.

The efficiency of a heat engine is defined as the ratio of net work done by the engine in one cycle to the amount of heat absorbed by the working substance from the source.

The obtained work done ( W ) in each cycle is transferred to the environment by mechanical arrangement to get mechanical energy.

The remaining amount of heat ( Q_2 ) is then released into the sink at temperature ( T_2 ).

Then it converts a part of this heat energy into mechanical work ( W ).

The working substance absorbs heat ( Q_1 ) from the source at temperature ( T_1 ).

Freon or Ammonia is the working substance in a refrigerator or air conditioner.Ī heat engine works in four steps in every cycle of operation.

Petrol or diesel is the working substance in an internal combustion engine.

It can be a solid, a liquid or a gaseous substance.It is a substance which performs mechanical work when heat is supplied to it.It has infinite thermal capacity such that any amount of heat can be added to it and there will be no rise in temperature.It is a heat reservoir at a lower temperature ( T_2 ).It has infinite thermal capacity such that any amount of heat can be drawn from it and there will be no drop in temperature.It is a heat reservoir at higher temperature ( T_1 ).051401 WORKING OF A HEAT ENGINEĪ typical heat engine is represented in figure. Heat engine is a mechanical device which continuously converts heat energy into mechanical energy in a cyclic process. The coefficient of performance of a refrigerator can never be infinite.Maximum efficiency is achieved by a thermodynamic cycle which is a reversible cycle called Carnot cycle.The efficiency of a heat engine can never be 100 \%.Second law of thermodynamic puts a fundamental limit on the working performance of a heat engine or a refrigerator.( W ) is the work input to the heat pump.īased on the statements for second law of thermodynamic it is concluded that –.( Q_1 ) is the heat released to the hot sink at temperature ( T_1 ).( Q_2 ) is the heat absorbed from cold reservoir at temperature ( T_2 ).

This law is applicable for heat pumps or refrigerators.It is impossible for a machine to work without the help of any external agency which transfer heat extracting from a cold reservoir and releasing it to a sink at higher temperature. ( Q_2 ) is the heat released to the cold sink at temperature ( T_2 )Īccording to Clausius statement, second law of thermodynamic stated as –.( Q_1 ) is the heat absorbed from hot reservoir at temperature ( T_1 ).This law is applicable for heat engines.It is impossible to construct an engine which will produce no effect other than extracting heat from a hot reservoir and converting it into an equivalent amount of work. Second law of thermodynamics is stated in two different ways, called –Īccording to Kelvin Plank statement, second law of thermodynamics is stated as –