What is the Difference Between Kaplan and Francis Turbine?

The main differences between Kaplan and Francis turbines are as follows:

1. Flow direction: In a Kaplan turbine, the water flows in axially and out axially, while in a Francis turbine, it flows in radially and out axially.
2. Efficiency: The efficiency of a Kaplan turbine is higher than that of a Francis turbine.
3. Cross-section and rotational speed: A Kaplan turbine has a smaller cross-section and lower rotational speed than a Francis turbine.
4. Runner blades: A Kaplan turbine has fewer runner blades than a Francis turbine.
5. Friction losses: Friction losses in a Kaplan turbine are less than those in a Francis turbine.
6. Shaft orientation: The shaft of a Francis turbine is usually vertical, while a Kaplan turbine's shaft is always vertical.
7. Specific speed: A Francis turbine's specific speed is medium (60-300 RPM), while a Kaplan turbine's specific speed is lower.

Both Kaplan and Francis turbines are reaction-type water turbines, meaning they require both kinetic and pressure energy for operation. Francis turbines are older water turbines, while Kaplan turbines are an upgraded version with improved efficiency and performance. Kaplan turbines are suitable for low head hydro sites and high flow conditions, while Francis turbines are better suited for medium specific speeds.

Comparative Table: Kaplan vs Francis Turbine

Both the Francis and Kaplan turbines are reaction-type water turbines that convert the kinetic energy and potential energy of water into rotational mechanical energy. However, there are several differences between them, which can be summarized as follows:

The Francis turbine is an older design, while the Kaplan turbine is an upgraded version of the Francis turbine, addressing some of its limitations. The Kaplan turbine is more efficient than the Francis turbine and is suitable for a wider range of water heads and flow rates.