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Second Law of thermodynamics

Second Law of thermodynamic:

1) Kelvin Planck statement:

  • It is impossible for engine to convert all the heat energy into work without rejecting some energy to sink i.e. no engine will have 100% efficiency.
  • Presence of sink is essential for continuous conversion of heat into work.

2) Clausius statement:

  • It is impossible to absorb heat energy from cold body and reject to hot body without doing work on it i.e. self acting refrigerator is impossible.

Heat engine:

  • Any device which converts heat energy continuously into mechanical work
  • Its main parts are:

i)Source: A hot body at a constant high temperature (T1) from which the heat engine can draw heat (Q1).

ii)Sink: A cold body at a constant low temperature (T2) to which any amount of heat can be rejected.

iii)Working Substance: Working substance is an ideal gas which on being supplied with heat performs mechanical work.

Efficiency of heat engine:

  • External work obtained to the heat energy absorbed by the working substance from the source.
  • Denoted by ɳ
  • ɳ=%
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  • ɳ=%
  • ɳ=%
  • When heat engines are placed in series then sink of 1st engine act as source for 2nd engine and so on.
  • Efficiency of heat engine always less than 1 or 100%