Why the Final Entropy in an Actual Turbine Process is Greater Than in an Isentropic Process

In a turbine, the final entropy in an actual process is greater than that of an isentropic process due to several key factors that introduce irreversibilities into the system. This article aims to provide an in-depth understanding of the reasons behind this phenomenon, supported by explanations, keywords, and a discussion of practical applications.

Irreversibilities

The primary cause for the increase in entropy in a real turbine process is the presence of irreversibilities. Irreversibilities are inherent to real systems and are caused by factors such as friction, turbulence, and heat transfer across finite temperature differences. These factors prevent the process from being perfectly reversible, which is a fundamental requirement for an isentropic process.

Non-ideal Fluid Behavior

Real fluids do not behave ideally under all conditions. Viscosity and compressibility can lead to energy losses and deviations from ideal behavior, resulting in increased entropy. These deviations can be significant, especially in turbines where the fluid dynamics are complex and the rate of compression and expansion is high.

Heat Losses

A real turbine will inevitably experience heat losses to the surroundings. These losses, caused by conduction, convection, or radiation, contribute to an increase in entropy. The second law of thermodynamics states that in an open system, the entropy of the universe increases over time, and this increase is directly related to the energy lost to the surroundings.

Mechanical Losses

Mechanical inefficiencies, such as bearing friction and flow separation, can also contribute to irreversibilities. These losses reduce the effective work output of the turbine, leading to an increase in the entropy of the system. Friction in bearings and losses due to flow separation, which can cause vortices and turbulence, are significant contributors to these inefficiencies and thus to the increase in entropy.

Flow Mixing

Another factor contributing to the increase in entropy is the mixing of different fluid streams. In a turbine, fluid streams from various stages of expansion can mix, leading to an increase in entropy due to the mixing of streams at different temperatures and pressures. This mixing can cause turbulent flow, which further increases the entropy of the system.

Conclusion

In summary, while an isentropic process is characterized by constant entropy, actual turbine processes experience various irreversibilities that result in an increase in entropy. This increase reflects the loss of available energy for work due to these inefficiencies. Understanding these factors is crucial for optimizing turbine performance and making accurate calculations in real-world applications.

The simple answer is that entropy increases in a real system due to real-world conditions such as friction, losses in the system, drag, gas losses over surfaces, turbulence, internal friction, and other losses. Isoentrope processes are merely an ideal simplifying assumption used in analysis to make calculations easier. In real-world scenarios, it is impossible to achieve a completely isentropic process due to the inherent inefficiencies and losses present in the system.