Explained: The Carnot Limit
Anytime engineers try to design a new kind of heat-based engine or improve on an existing design, they bump up against a fundamental efficiency limit: the Carnot Limit.The Carnot Limit “sets an absolute limit on the efficiency with which heat energy can be turned into useful work,” says MIT’s Jane and Otto Morningstar Professor of Physics Robert Jaffe, who co-teaches a course on the physics of energy. If engineers are faced with redesigning an engine that is 35 percent efficient, it makes a big difference whether the maximum possible efficiency of such an engine is 50 percent — in which case it may not be feasible to try to push it further — or 80 percent, in which case there is a significant margin for improvement.Nicolas Léonard Sadi Carnot, who was born in France in 1796 and lived for only 36 years, deduced this limit. His insights into the nature...