Heat Engine | Working, Efficiency [Brief Explanation]

By | February 11, 2019

What is a Heat engine?

A heat engine is a device which operates in a cyclic process to generate work from the supplied heat.

Below diagram shows working of a heat engine

Heat Engine

Where:

Th: Temperature of source

Tc: Temperature of sink

Qh: Heat supplied to the engine

Qc: Heat rejected by the engine

W: Work output of the engine

Given: Th > Tc

From the above diagram we can easily figure out that

Work output of heat engine

W = Qh – Qc

Efficiency of heat engine

η = Work output/ Heat input

η = (Qh – Qc)/ Qh

η = 1 – Qc/ Qh

From the second law of thermodynamics we know that Qc can never be equal to zero. Which means that efficiency of a heat engine can never be 100%. Even in the ideal case.

Kelvin-Plank statement of second law

It is impossible for a heat engine to produce net work in a cycle if it exchanges heat only with bodies at a single fixed temperature.

Also read:

What is first law of thermodynamics?

What is thermodynamic equilibrium?

What is a thermodynamic system?

What is two property rule in thermodynamics?

What is dead state of a thermodynamic system?

Image source: By P.wormer – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=12404233

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