Understanding Reaction Turbines and Flow Types

Reaction turbines are a type of hydraulic turbine that operates under pressure, where the water's pressure changes as it moves through the turbine and gives up its energy. There are different classifications of reaction turbines based on how the water flows through them.

Let's analyze each pair provided in the question:

Analyzing Pair 1: Francis Turbine - Mixed-Flow Turbine

The Francis turbine is one of the most common types of hydraulic reaction turbines. It is designed for medium head and medium discharge. In a Francis turbine, the water enters radially towards the runner's center and then flows axially out. This combination of radial and axial flow makes it a mixed-flow turbine.

Thus, the pairing of the Francis turbine with mixed-flow is correct.

Analyzing Pair 2: Kaplan Turbine - Radial Flow Turbine

The Kaplan turbine is a propeller-type turbine with adjustable blades. It is used for low head and high discharge. Water flows through a Kaplan turbine axially, meaning the water flow is parallel to the axis of rotation of the runner.

A radial flow turbine, like the original Fourneyron turbine, involves water flowing predominantly radially, either inwards or outwards. The Kaplan turbine does not operate based on radial flow.

Therefore, the pairing of the Kaplan turbine with radial flow is incorrect. Kaplan turbines are axial-flow turbines.

Analyzing Pair 3: Propeller Turbine - Axial Flow Turbine

A propeller turbine is a type of reaction turbine where the runner has a shape similar to a boat propeller. Water flows axially through the runner, parallel to the axis of rotation. Propeller turbines are typically used for low head applications. The Kaplan turbine is a variation of the propeller turbine where the runner blades are adjustable.

Thus, the pairing of the Propeller turbine with axial flow is correct.

Summary of Pair Analysis

• Pair 1 (Francis turbine - Mixed-flow turbine): Correct
• Pair 2 (Kaplan turbine - Radial flow turbine): Incorrect (Kaplan is axial flow)
• Pair 3 (Propeller turbine - Axial flow turbine): Correct

Based on the analysis, only pairs 1 and 3 are correct.

Therefore, the correct option is the one stating that only 1 and 3 are correct pairs.