What is a carnot engine ? Derivee an expression for efficiency of carnot engine . On what factors does it depend?
Answers
Answer:
Explanation:
A Carnot engine is an idea, used to reason about heat engines. You cannot build one; it’s just a thought experiment.
Essentially, Carnot was trying to work out the practical limitations of steam engines, but his work is applicable to any engine that converts heat into work, whether that’s by boiling water externally to make steam, by burning fuel directly in a cylinder fitted with a piston, or by using mass flow to turn a turbine, as in a jet engine.
A Carnot engine considers how heat can be used to perform work, without considering practical real-world losses. It assumes that a mechanical arrangement could be made to extract work from heat with no friction, heat losses to the surroundings, pumping losses, or any other annoying snag that afflicts anything you could build. It then looks as the maximum work such an engine could theoretically obtain based on first principles; namely, the Laws of Thermodynamics.
The results are not encouraging in many respects. A key finding is that the output of any engine is essentially in proportion to the ratio of the temperature at the start of the cycle and the temperature at the end. Because of that, perfect efficiency could only be achieved if the ‘exhaust’ temperature after doing work was absolute zero.
η=1−TC/TH×100%
This is a very important result from Carnot’s work. Efficiency is 1 - the ratio of hot to cold ‘reservoirs’, being the temperatures at the start and end of a piston’s stroke, for example.
Since engine exhausts are not even cool, let alone as cold as absolute zero, the inefficiency of a real-world heat engine is plain for anyone to see. In addition, real engines have a variety of additional losses not considered by Carnot, so they will always be worse than Carnot’s theoretical engine.