Question

Why is carnot cycle not practical for a steam power plant?

Answer 1

carnot cycle is a hypothetical cycle which is designed to theoritically calculate max efficiency of an engine working bw temperature T high and T low it uses isothermal and adiabatic processes which are ideal for an ideal gas

real engine has lower efficiency than carnot

Answer 2

It is impossible to make an steam power plant. The simple reason for the same is that the isothermal expansion 1-2 will have to be carried out extremely slow to ensure that the air is always at temperature T1, similarly the isothermal compression 3-4 Will have to be carried out extremely slow. But reversible adiabatic expansion 2-3 and reversible adiabatic compression 4-1 should be carried out as quickly as possible,in order to approach ideal adiabatic condition. We know that sudden changes in the speed of an engine are not possible in actual practice. Moreover, it is impossible to completely eliminate friction between the various moving parts of the engine, and also heat losses due to conduction , radiation etc. It is thus obvious that it is impossible to realise carnot's power plant in actual practice.