Efficiency -definition

[grahamatraynor]

Hi there,
is the efficiency defined normally using the heat absorbed in the hot
end, or the energy used creating the heat source (fuel values etc)?

for Stirling engines, what happens to heat energy not converted to
mechanical work? Is it all sunk to the cold end, or what portion
(roughly) is sunk to the cold end? What happens to the rest?
Im assuming that friction, etc only ends up as heat anyway.

Thanks!

[stan.hornbaker]

All thermal energy transferred to the hot end gas is either converted to mechanical energy (output) or rejected to the cooling water or atmosphere at the cold end.

The Carnot efficiency is <or = 1 - Tcool/Thot where the temperatures are on the absolute scale. Actual value will be less than the calculated value.

[grahamatraynor]

Thanks for the quick answer!
So, lets say the max Carnot efficiency is 80%, and a Stirling motor converts 50% of that energy, then the overall efficiency is 40%. Does the other 60% go to the coolant, or only the 50%?
Reason Im asking, is that sometimes you see advertisments with efficiencies posted for elec. and thermal. Presuming the cooling load is useful energy, then the efficiency would always be 100%. They never quote that.

[stan.hornbaker]

May I suggest that you look at some of Dr. Izz/s material at:

and the Second Law of Thermodynamics at:


Also refer to the article on Sadi Carmot and "Towards the second law"



A serious condideration of this material should clarify your thinking and understanding of the solution of your inquiries.