Efficiency of Real Heat Engines
Carnot realized that in reality it is not possible to build a thermodynamically reversible engine, so real heat engines are less efficient than indicated by Equation (1). Nevertheless, Equation (1) is extremely useful for determining the maximum efficiency that could ever be expected for a given set of thermal reservoirs.
Although Carnot's cycle is an idealisation, the expression of Carnot efficiency is still useful. Consider the average temperatures,
at which heat is input and output, respectively. Replace TH and TC in Equation (1) by <TH> and <TC> respectively.
For the Carnot cycle, or an equivalent, <TH> is the highest temperature available and <TC> the lowest. For other less efficient cycles, <TH> will be lower than TH, and <TC> will be higher than TC. This can help illustrate, for example, why a reheater or a regenerator can improve the thermal efficiency of steam power plants — and why the efficiency of combined-cycle power plants (which incorporate gas turbines operating at even higher temperatures) exceeds that of conventional steam plants.
According to the second theorem, "The efficiency of the carnot engine is independent of the nature of the working substance".
- See also: Heat engine (efficiency and other performance criteria)
Read more about this topic: Carnot Heat Engine
Famous quotes containing the words efficiency, real, heat and/or engines:
“I’ll take fifty percent efficiency to get one hundred percent loyalty.”
—Samuel Goldwyn (1882–1974)
“The spring is here, young and beautiful as ever, and absolutely shocking in its display of reckless maternity; but the Judas tree will bloom for you on the Bosphorus if you get there in time. No one ever loved the dog-wood and Judas tree as I have done, and it is my one crown of life to be sure that I am going to take them with me to heaven to enjoy real happiness with the Virgin and them.”
—Henry Brooks Adams (1838–1918)
“As in hoary winter’s night stood shivering in the snow,
Surprised I was with sudden heat which made my heart to glow;
And lifting up a fearful eye to view what fire was near,
A pretty Babe all burning bright did in the air appear;”
—Robert Southwell (1561?–1595)
“America is like one of those old-fashioned six-cylinder truck engines that can be missing two sparkplugs and have a broken flywheel and have a crankshaft that’s 5000 millimeters off fitting properly, and two bad ball-bearings, and still runs. We’re in that kind of situation. We can have substantial parts of the population committing suicide, and still run and look fairly good.”
—Thomas McGuane (b. 1939)