What is a carnot engine?

1 Answer
Aritra G.
Jan 10, 2017

A Carnot's engine is an idealised engine whose working is perfectly reversible. This engine uses an ideal gas as the working substance and performs a 4-stroke process to complete one cycle.

It draws heat (say #Q_1#) from source and rejects heat (say #Q_2#) to sink thereby performing an amount of work #W = Q_1 - Q_2#

Explanation:

The Carnot's engine is a reversible engine working between two temperature limits.

The complete cycle incorporates -

1) Isothermal expansion of ideal gas at the temperature of the source #T_1# drawing an amount of heat #Q_1#

2) Adiabatic expansion of ideal gas. In this process, the temperature of the ideal gas falls from source temperature #T_1# to sink temperature #T_2#.

3) Isothermal compression of ideal gas at sink temperature #T_2#. In doing so, it rejects heat #Q_2# to the sink.

4) Adiabatic compression of ideal gas where the temperature naturally raises from #T_2# to #T_1# and thus the working substance returns to its original state completing the cycle.

The efficiency is given as

#eta =# Work done #/# Heat input

Thus, #W = Q_1 - Q_2# and heat input is obviously #Q_1#

This gives, #eta = W/Q_1 = 1 - (Q_2)/(Q_1)#

It may be shown thermodynamically that #(Q_2)/(Q_1) = (T_2)/(T_1)#

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