Question

Heat engine rejects some heat to the sink. This heat​

Answer 1

Heat engine rejects some heat to the sink. This heat is unavailable in the universe.

• According to Kelvin Plank statement and 2nd Law of Thermodynamics , a machine with 100% efficiency is impossible.

• Hence , a part of heat energy input is converted to work and the rest is lost to the sink.

• This loss of heat to sink is mainly due to restrictions in temperature difference between source and sink, and also due to friction between various moving parts of the engine.

• This heat loss is useless and is not available.

Efficiency of heat engine is given as :

$\boxed{ \sf{ \eta = \dfrac{work \: output}{heat \: absorbed} \times 100\%}}$

Answer 2

Heat engine rejects some heat to the sink . This Heat is  

Unavailable in the Universe.

Reason :

According to Kelvin - Planck Statement :

"No process is possible whose sole result is the absorption of heat from a reservoir and the complete conversion of heat into work."

Working substance[heat engine] will absorb the heat released by Source and converts some amount of heat into Work and releases some amount of heat to sink Which goes unavailable in the universe.

Hence a machine with 100% efficiency is impossible.