What is the difference between a Francis and Kaplan turbine?

What is Francis Turbine?

A Francis turbine is a type of water turbine designed for medium to high head applications in hydroelectric power plants. It has a radial flow runner, where water enters the turbine axially and flows radially through the runner blades. Blades are usually adjustable to control flow and optimize performance for different conditions. Francis turbines are well suited for locations with significant elevation changes in the water source.

What is Kaplan Turbine?

A Kaplan turbine is a type of water turbine designed for low to medium head applications in hydroelectric power plants. It has an axial flow runner, allowing water to flow parallel to the axis of rotation. Kaplan turbine blades are capable of adjusting both pitch and angle, enabling efficient operation over a wide range of flow rates and head conditions. Kaplan turbines are typically used in locations where the water height is relatively low and the flow rate is high, such as slow-moving rivers or tidal power installations.

Difference between Francis and Kaplan Turbine

The main difference between Francis and Kaplan turbine are listed step by step below.

Francis Turbine Runner Design

Runner design is an important aspect that differentiates Francis and Kaplan turbines. The main differences in runner design between Francis and Kaplan turbines are:

Radial flow:

The Francis turbine has a radial flow runner design. This means that water enters the runner axially (along the axis of rotation) and then reverses direction to flow radially (toward the outer edges of the runner).

Curved Blade:

The runner blades in a Francis turbine are curved, similar to buckets. These curved blades are designed to effectively capture the kinetic energy of the water as it changes direction and flows through the runner.

Adjustable Blade:

Many Francis turbines have adjustable blades. Adjustability allows control of water flow through the runner, allowing optimization for different operating conditions.

Suitable for medium to high heads:

Francis turbines are typically used in applications with medium to high head conditions, where the height of the water source is significantly reduced.

Kaplan Turbine Runner Design

Axial flow:

A Kaplan turbine has an axial flow runner design. This means that the water flows parallel to the axis of rotation as it passes through the impeller. There is no change in flow direction from axial to radial within the runner.

Adjustable Blade:

The prominent feature of the Kaplan turbine is the presence of adjustable blades. Both pitch (angle of attack) and blade angle can be changed. This adjustment is important to optimize performance under varying flow conditions.

Propeller like blades:

Kaplan runner blades are often similar to propeller blades. These blades are designed to effectively capture the kinetic energy of the water as it passes through the runner, similar to a ship’s propeller.

Suitable for short to medium heads:

Kaplan turbines are specifically designed for low to medium head applications, making them suitable for locations with relatively low head drops and high flow rates.

In summary, the key differences are in the direction of flow within the runner (radial for Francis, axial for Kaplan), blade shape, and suitability for different head conditions. Francis turbines are well suited for medium to high heads, while Kaplan turbines are best for low to medium head applications.

Operating Condition for Francis and Kaplan Turbine

The operating conditions of Francis and Kaplan turbines vary based on their design characteristics and the hydraulic conditions for which they are optimized. The main differences in the operating conditions of Francis and Kaplan turbines are:

Operating condition of Francis Turbine

Head Range:

Francis turbines are suitable for medium to high head conditions. They work effectively in situations where the height of the water source is significantly reduced, usually from a medium to high head.

Flow range:

Although Francis turbines can handle a range of flow rates, they are generally more efficient in moderate to high flow rate conditions. The design allows for efficient energy conversion in situations where the water flow is not unusually fast.

Operation speed:

Francis turbines generally operate at higher speeds than Kaplan turbines. Higher rotational speeds are well suited for moderate to high head applications.

Blade Adjustment:

Francis turbines often have adjustable blades that can be controlled to optimize efficiency under different flow conditions. This adjustment is particularly useful in maintaining performance in different operating scenarios.

Operating condition of Kaplan Turbine

Head Range:

The Kaplan turbine is designed for low to medium head conditions. They are particularly suitable for locations where there is relatively little drop in water height.

Flow range:

Kaplan turbines perform best in high flow rate conditions. Their axial flow design allows efficient operation in rivers and other water bodies with high flow velocities.

Operation speed:

Kaplan turbines can operate at lower speeds than Francis turbines. Adjustable blade and axial flow designs contribute to the ability to adapt to varying flow conditions, making them effective for low to medium head applications.

Blade Adjustment:

A special feature of Kaplan turbines is their adjustable blades in terms of both pitch and angle. This adjustment is important to improve flow rate and performance over a wide range of heads.

In summary, Francis turbines are well suited for medium to high head conditions with moderate to high flow rates, while Kaplan turbines are designed for low to medium head conditions with high flow rates. The synchronization of adjustable blades in both turbine types allows them to operate efficiently within their specified head and flow limits.

Efficiency of Francis and Kaplan turbine

The efficiency and speed characteristics of Francis and Kaplan turbines are influenced by their design features and the specific operating conditions for which they are optimized. The main differences between efficiency and speed of Francis and Kaplan turbines are:

Efficiency of Francis Turbine

Francis Turbine is known for its high performance, especially in medium to high head applications. Their radial flow design and adjustable blades allow for efficient energy conversion over a range of operating conditions.

Efficiency of Kaplan Turbine

Kaplan turbines are also highly efficient, especially in low to medium head applications. Their axial flow design and adjustable blades contribute to efficient energy conversion, especially in high flow rate conditions.

Application of Francis and Kaplan turbine

Francis and Kaplan turbines are two types of water turbines with different characteristics that make them suitable for different hydropower applications. The main applications of Francis and Kaplan turbines are:

Francis Turbine Applications

Hydroelectric Power Plants:

Francis turbines are commonly used in hydroelectric power plants, especially in locations with medium to high head conditions. These turbines are well suited to convert the energy of falling water into electricity.

Hilly areas:

Areas with mountainous terrain often have rivers or springs with significant changes in elevation. Francis turbines are used in such areas to extract energy from water as it descends from high elevations.

Reservoir Based Hydropower:

Francis turbines can be used in reservoir-based hydropower systems where water stored in a reservoir is released to generate electricity. The adjustable blades of Francis turbines enable them to adapt to variable flow conditions.

Industrial Applications:

In some industrial settings, where there is a constant and substantial flow of water with moderate to high head, Francis turbines can be used for onsite power generation.

Kaplan Turbine Applications

Low Head Hydropower:

The Kaplan turbine is specifically designed for low to medium head conditions. They are often used in locations where the water source has a relatively low drop in height but a high flow rate, such as rivers and floodplains.

River and stream installations:

Kaplan turbines are suitable for installations in rivers and streams where the flow velocity is relatively high. Their axial flow design allows them to efficiently capture the energy of flowing water.

Tidal Power Plants:

In tidal power plants, Kaplan turbines can be used to capture energy from tidal flows. Adjustable blades are particularly useful in adapting to the variable and directional nature of tidal currents.

Run-off River Hydropower:

Kaplan turbines are well suited for run-of-river hydropower projects, where the objective is to generate electricity from the natural flow of a river without the need for significant reservoirs.

Offshore Hydropower:

In offshore installations, Kaplan turbines can be used to harvest energy from tidal waves, taking advantage of the axial flow design and adjustable blades to adapt to changing flow conditions.

See Also:

What is Turbine and its Function?

Frequently asked questions (FAQs)

Q1: What is Francis Turbine?

Ans: A Francis turbine is a type of water turbine used to generate hydroelectric power. It has a radial flow runner and is suitable for medium to high head applications.

Q2: Where are Francis turbines commonly used?

Ans: Francis turbines are commonly used in hydroelectric power plants, especially in mountainous areas where there are significant changes in the height of rivers.

Q3: What is the design principle of Francis turbine runner?

Ans: The runner of a Francis turbine has curved blades, and water enters the runner axially, changing direction to flow radially through the blades.

Q4: Why are Francis turbines suitable for variable flow conditions?

Ans: Francis turbines often have adjustable blades that can be controlled to optimize efficiency under different flow conditions, allowing them to adapt to changes in water flow.

Q5: How efficiently do Francis turbines operate under head conditions?

Ans: Francis turbines work effectively in medium to high head conditions, where the height of the water source is reduced significantly.

Q6: What is Kaplan Turbine?

Ans: The Kaplan turbine is a type of water turbine designed for low to medium head applications. It has an axial flow runner with adjustable blades.

Q7: Where are Kaplan turbines commonly used?

Ans: Kaplan turbines are typically used in low-head applications, such as rivers, tidal power plants, and locations where there is a relatively low head drop but high flow rates.

Q8: What is the design principle of Kaplan turbine runner?

Ans: Kaplan turbine runners have adjustable blades similar to propeller blades, and water flows parallel to the axis of rotation (axial flow).

Q9: Why are Kaplan turbines suitable for variable flow conditions?

Ans: Kaplan turbines have adjustable blades that can be changed in pitch and angle, allowing efficient operation over a wide range of flow rates and head conditions.

Q10: Over what range of head conditions do Kaplan turbines operate efficiently?

Ans: Kaplan turbines operate effectively in low to medium head conditions, where there is a relatively small drop in the height of the water source.

Q11: How are Francis and Kaplan turbine runner designs different?

Ans: The runner of a Francis turbine has a radial flow design, while the runner of a Kaplan turbine has an axial flow design with adjustable blades.

Q12: What is the main application difference between Francis and Kaplan turbines?

Ans: Francis turbines are used in medium to high head applications, while Kaplan turbines are used in low to medium head conditions with high flow rates.

Q13: Which turbine is more suitable for changing flow conditions?

Ans: Both Francis and Kaplan turbines may be acceptable due to adjustable blades, but Kaplan turbines are specifically designed for efficient operation over a wide range of flow conditions.