Question

| carnot
engine
diagram ​

Answer 1

Explanation:

The Carnot cycle when acting as a heat engine consists of the following steps:

1. Reversible isothermal expansion of the gas at the "hot" temperature, TH (isothermal heat addition or absorption). During this step (1 to 2 on Figure 1, A to B in Figure 2) the gas is allowed to expand and it does work on the surroundings. The temperature of the gas does not change during the process, and thus the expansion is isothermic. The gas expansion is propelled by absorption of heat energy Q1 and of entropy from the high temperature reservoir.
2. Isentropic (reversible adiabatic) expansion of the gas (isentropic work output). For this step (2 to 3 on Figure 1, B to C in Figure 2) the piston and cylinder are assumed to be thermally insulated, thus they neither gain nor lose heat. The gas continues to expand, doing work on the surroundings, and losing an equivalent amount of internal energy. The gas expansion causes it to cool to the "cold" temperature, TC. The entropy remains unchanged.
3. Reversible isothermal compression of the gas at the "cold" temperature, TC. (isothermal heat rejection) (3 to 4 on Figure 1, C to D on Figure 2) Now the gas is exposed to the cold temperature reservoir while the surroundings do work on the gas by compressing it (such as through the return compression of a piston), while causing an amount of heat energy Q2 and of entropy T_to flow out of the gas to the low temperature reservoir. (This is the same amount of entropy absorbed in step 1.) This work is less than the work performed on the surroundings in step 1 because it occurs at a lower pressure given the removal of heat to the cold reservoir as the compression occurs (i.e. the resistance to compression is lower under step 3 than the force of expansion under step 1).
4. Isentropic compression of the gas (isentropic work input). (4 to 1 on Figure 1, D to A on Figure 2) Once again the piston and cylinder are assumed to be thermally insulated and the cold temperature reservoir is removed. During this step, the surroundings continue to do work to further compress the gas and both the temperature and pressure rise now that the heat sink has been removed. This additional work increases the internal energy of the gas, compressing it and causing the temperature to rise to TH. The entropy remains unchanged. At this point the gas is in the same state as at the start of step 1.

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Answer 2

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.