Understanding Parson Reaction Turbine Components

A Parson reaction turbine is a type of impulse turbine where the working fluid (like steam or water) expands and drops in pressure across both the stationary blades (also called nozzles or stator) and the rotating blades (rotor). This expansion means that the fluid exerts pressure on both sets of blades, causing the turbine to rotate.

Key Components of a Parson Reaction Turbine

The defining characteristic of a Parson reaction turbine's design is the arrangement of its blades:

• Fixed Blades (Stator): These blades are attached to the turbine casing. Their primary function is to direct the incoming fluid onto the moving blades at the correct angle and to cause some initial expansion of the fluid.
• Moving Blades (Rotor): These blades are attached to the turbine shaft. As the fluid flows through them, it expands further, dropping in pressure and velocity. This change in momentum and pressure difference across the moving blades generates torque, causing the shaft to rotate.

Crucially, these sets of fixed blades and moving blades are arranged alternately around the turbine shaft. The fluid passes through a set of fixed blades, then a set of moving blades, then another set of fixed blades, and so on. This alternating pattern allows for a gradual expansion of the fluid and efficient extraction of energy.

Analysis of Options

Let's examine the given options in light of the Parson reaction turbine's structure:

• Option 1: It is composed of only fixed nozzles. This is incorrect. A reaction turbine requires moving blades to extract energy from the fluid flow.
• Option 2: It is composed only of moving blades. This is also incorrect. Fixed blades (nozzles) are essential for directing the flow and initiating expansion.
• Option 3: It does not have any nozzles. This is incorrect. The fixed blades act as nozzles, guiding and expanding the fluid.
• Option 4: It is composed of moving blades (nozzles) alternating with fixed nozzles. This statement accurately describes the fundamental structure. The fixed blades function as nozzles, and they alternate with the moving blades (which also contribute to the reaction force due to fluid expansion). This alternating arrangement is key to the operation of a Parson reaction turbine.
• Option 5: This option is empty and therefore not applicable.

Therefore, the correct description highlights the alternating arrangement of fixed and moving blade sets, which is characteristic of a Parson reaction turbine.