Mechanical Engineering - Steam Nozzles and Turbines - Discussion

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.

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.

Nozzles are often analyzed under the assumption that the flow is isentropic, meaning it is both adiabatic (no heat exchange) and reversible.

This assumption simplifies the calculations and is valid for many practical applications, especially in high-speed flows such as those in turbines, jet engines, and rocket nozzles.

Here, it is not mentioned that the nozzle is convergent or divergent.

So however discharge or flow is constant in nozzle. And no heat transfer is taken place. So constant isentropic process.

It is both adiabatic and reversible. That is no heat is added and no energy transformation occurs.

Entropy is the change in the state of the system. Disorder is known as entropy.

Entropy is known as randomness and disorderness in molecules of the system.

Entropy is measure of degree of randomness of molecules of system.

Entropy is the probability of occurrence of an energy state.

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