Impulse and reaction turbines are types of hydraulic turbines used for converting water energy into mechanical energy to generate electricity. Here are five main differences between impulse and reaction turbines:
Water Flow Path:
Impulse Turbine: In an impulse turbine, the water flow path is not restricted by the runner. High-velocity jets of water are directed onto the buckets or blades of the turbine, causing the runner to rotate due to the impulse (change in momentum) of the water.
Reaction Turbine: In a reaction turbine, the water flow path is partially or fully enclosed by the runner. The water pressure decreases as it flows over the blades, and the turbine extracts energy from both the kinetic energy and pressure energy of the water.
Pressure Change:
Impulse Turbine: Impulse turbines operate at atmospheric pressure. Water pressure remains constant as it passes through the turbine, and the energy is derived from the velocity of the water jets.
Reaction Turbine: Reaction turbines operate at varying pressures. As water flows over the blades, both pressure and velocity change, allowing the turbine to extract energy from both kinetic and pressure components of the water.
Blade Design:
Impulse Turbine: Impulse turbine blades are typically flat or slightly curved. They are designed to efficiently capture the kinetic energy from the high-velocity water jets.
Reaction Turbine: Reaction turbine blades are curved to efficiently utilize the pressure energy of the water. The shape of the blades allows for a gradual pressure drop as water flows over them.
Runner Rotation:
Impulse Turbine: Impulse turbines have an open runner, and the rotation is due to the impact of high-velocity jets of water on the blades. Pelton turbines are a common example of impulse turbines.
Reaction Turbine: Reaction turbines have a closed or partially enclosed runner. The rotation is a result of both the kinetic energy and pressure energy of the water acting on the blades. Francis and Kaplan turbines are examples of reaction turbines.
Applications:
Impulse Turbine: Impulse turbines are well-suited for high head (vertical drop) applications where a single jet of water can be directed onto the turbine blades. They are commonly used in mountainous regions with high-altitude reservoirs.
Reaction Turbine: Reaction turbines are suitable for low to medium head applications where a larger quantity of water can be directed onto the blades. They are widely used in river-based hydropower projects and can accommodate a range of head and flow conditions.
In summary, the key differences between impulse and reaction turbines lie in their water flow paths, pressure changes, blade designs, runner rotations, and applications. The choice between impulse and reaction turbines depends on factors such as the available head, flow rate, and specific site conditions in hydropower projects.