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. At this point the gas is in the same state as at the start of step 1.Second law of thermodynamics is stated in two different ways, called –Īccording to Kelvin Plank statement, second law of thermodynamics is stated as – During this step, the surroundings do work on the gas, increasing its internal energy and compressing it, causing the temperature to rise to T 1. Isentropic compression of the gas (isentropic work input). (4 to 1 on Figure 1, D to A on Figure 2) Once again the mechanisms of the engine are assumed to be thermally insulated. (This is the same amount of entropy absorbed in step 1, as can be seen from the Clausius inequality.Ĥ. ɧ =$\left( $ to flow out of the gas to the low temperature reservoir. If Q 1 is the amount of heat absorbed from the source and Q 2 be the heat rejected to the sink, then the efficiency of the heat is given as This engine consists of a cylinder fitted with the piston.Ī heat engine with 100% efficiency is only a theoretical possible: The petrol engine was developed by Otto in 1877 and hence it is also called Otto engine. (iii) In reversible process, the sum of entropies of system and surrounding remains constant but in an irreversible the total entropy of the system and surrounding increases. (ii) The net entropy of the universe in any natural process always increases and tends to acquire maximum value. (i) All spontaneous process is irreversible in nature. The second law also states that the changes in the entropy in the universe can never be negative.įollowing are the statements of second law of thermodynamics: The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time.