Mechanical Engineering - Steam Nozzles and Turbines - Discussion

Among the given statements:

"The expansion of steam in a nozzle follows Rankine cycle." - This statement is incorrect. The expansion of steam in a nozzle does not follow the Rankine cycle. Nozzles are typically used for isentropic (or adiabatic) expansion of steam, and this process is different from the Rankine cycle, which involves various processes like isentropic expansion, heat addition, and heat rejection in a steam power plant.

"The friction in the nozzle increases the dryness fraction of steam." - This statement is incorrect. Friction in a nozzle does not increase the dryness fraction of steam; it actually tends to decrease the dryness fraction by converting some of the kinetic energy into internal energy (sensible heat). This can result in a slight increase in temperature and moisture content in the steam.

"The pressure of steam at the throat is called critical pressure." - This statement is incorrect. The pressure of steam at the throat of a nozzle is not referred to as critical pressure. The critical pressure is a specific thermodynamic condition for a pure substance (such as water) where the distinction between the liquid and vapor phases disappears. It is a well-defined property and occurs at a specific temperature for a given substance.

So, None of the above statements is correct.

Please give explanation for option 1.

The correct answer is option (b).

Critical pressure ratio give velocity of steam at throat and which is equal to velocity of sound.

Only, option b is the correct answer.