Mechanical Engineering - Steam Nozzles and Turbines - Discussion

ENTROPY remains constant is called an isentropic process.

It an adaibatic process.

Because heat transfer zero.

What is entropy?

There is no any change in entropy during flow in nozzle.

Entropy is the rate of randomness of the molecules of fluid.

ds = dq/dt, q heat, t temperature.

While considering flow through a tube, if the flow is very gradually compressed (i.e. Area decreases) and then gradually expanded (i.e. Area increases), the flow conditions are restored (i.e. Return to its initial position).

So, such a process is a reversible process. According to the Second Law of Thermodynamics, whenever there is a reversible flow, constant value of entropy is maintained. Engineers classify this type of flow as an isentropic' flow of fluids. Isentropic is the combination of the Greek word "iso" (which means - same) and entropy.

As a gas is forced through a tube, the gas molecules are deflected by the walls of the tube. If the speed of the gas is much less than the speed of sound of the gas, the density of the gas remains constant and the velocity of the flow increases. However, as the speed of the flow approaches the speed of sound we must consider compressibility effects on the gas.

The density of the gas varies from one location to the next. Considering flow through a tube, as shown in the figure, if the flow is very gradually compressed (area decreases) and then gradually expanded (area increases), the flow conditions return to their original values. We say that such a process is reversible. From a consideration of the second law of thermodynamics, a reversible flow maintains a constant value of entropy.

Entropy means molecular disorderness of any system.