This requires no addition of heat to the band because there is no work being done, and there is no internal energy to be changed. We put the band in an environment at T H , adjusting the applied force to keep the length constant. This requires no addition of heat to the band because there is no work being done, and there is no internal energy to be changed. Q in , of this engine in terms of T H and T C . Note that the efficiency, e , does not include the exhaust heat, Q out , because e is the ratio of what we get, the total work by the band, to what we have to give, Q in .
Exhaust heat comes for free.
The efficiency is identical to the efficiency of a Carnot engine. Uses ideal gas as working fluid. Uses reversible processes only. Employs adiabatic expansion. By using only reversible processes, we keep the entropy of the system plus environment constant.