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If a Cannot engine is independent of the working substance, then perhaps realengines should be similarly independent, to a certain extent. Why then, for real engines, are we so concerned to find suitable fuels such as cola, gasoline, or fissionable material? Why not use stones as fuel?

If a Cannot engine is independent of the working substance, then perhaps realengines should be similarly independent, to a certain extent. Why then, for real engines, are we so concerned to find suitable fuels such as cola, gasoline, or  fissionable material? Why not use stones as fuel?

Grade:11

1 Answers

Aditi Chauhan
askIITians Faculty 396 Points
8 years ago
Carnot engine is a reversible engine. All thermodynamic processes involved in the operation of the engine are reversible, which means that no dissipative processes such as turbulence and friction and no irreversible heat transfers can be present. One thing is clear: we will lose something if the real engines contain devices in which there is friction. The best real engine will be a frictionless engine. The loss of energy due to the friction, viscosity and insufficient combustion will reduce the efficiency of a heat engine from its ideal value.
We assume, then, the same idealization that we did when we studies the conservation of energy; that is, a perfectly frictionless engine. We must also consider the analog of frictionless motion, “frictionless” heat transfer. If we put a hot object at a high temperature against a cold object, so that the heat flows, then it is not possible to make that heat flow in a reverse direction by a very small change in the temperature of either object. But when we have a practically frictionless machine, if we push it with a little force the other way, it goes the other way.
The fuels used by real engines like coal, gasoline or fissionable material are all free from friction. These fuels in the working substance will maintain a reversible process in the working substance. That is why; for real engines, we are concerned to find suitable fuels such as coal, gasoline or fissionable material. But in the case of stones as a fuel, it will not free from friction. That is why; we cannot use stone as a fuel in the real engine

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