In: Physics
Show that, for a Carnot engine operating between reservoirs at temperatures T1 and T2 (T1 > T2), the thermal efficiency is given by
Eta sub R = T1-T2/T1
The Carnot engine cycle is represented by the diagram below.
The Carnot engine has two thermal reservoirs -- one at high temperature T1 and the other at low temperature T2. The engine consists of a reversible isothermal expansion from state 1 to 2, reversible adiabatic expansion from state 2 to 3, a reversible isothermal compression from state 3 to 4 and lastly a reversible adiabatic compression to state 1.
During processes 2-3 and 4-1, there is no heat interaction as they are adiabatic. Heat exchange in process 1-2 is
Heat exchange in process 3-4 is
Net heat interaction = Net work done
W =
The processes 2-3 and 4-1 are reversible, adiabatic and hence
V2/V3 = V1/V4 or V2/V1 = V3/V4
Then efficiency = Work done / heat input =