A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical power when combined with a generator. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor.
Types of Turbines
There are two main types of hydropower turbines: reaction and impulse.
The type of hydropower turbine selected for a project is based on the height of standing water—referred to as “head”—and the flow, or volume of water over time, at the site. Other deciding factors include how deep the turbine must be set, turbine efficiency, and cost.
A reaction turbine generates power from the combined forces of pressure and moving water. A runner is placed directly in the water stream, allowing water to flow over the blades rather than striking each individually. Reaction turbines are generally used for sites with lower heads and higher flows. Reaction turbines develop torque by reacting to the fluid’s pressure or mass. The pressure of the fluid changes as it passes through the turbine rotor blades.
The pressure of Flowing Water:
- Definition: Pressure is the force per unit area exerted by the fluid on the surfaces it contacts. It is a scalar quantity and represents the intensity of the force exerted by the fluid.
- Units: Pressure is typically measured in Pascals (Pa), atmospheres (atm), pounds per square inch (psi), or other pressure units.
- Importance: Pressure is vital in fluid dynamics as it is responsible for pushing the fluid through pipes, valves, and other components of a hydraulic system. It plays a role in determining the direction of fluid flow and can be used to calculate the force applied by the fluid on surfaces.
- Control: Pressure can be controlled by regulating factors such as flow rate, fluid density, or the shape of the conduit. Pressure can also vary with depth in a fluid (hydrostatic pressure) and is affected by external forces like pumps or gravity.
Here’s a simplified explanation of how a reaction turbine works with respect to fluid pressure:
- Fluid Inlet: The high-pressure fluid (steam, water, or another fluid) is directed into the turbine blades.
- Blade Design: The turbine blades are designed to redirect the flow of fluid and harness the pressure energy of the fluid.
- Fluid Expansion: As the high-pressure fluid flows over and through the turbine blades, it undergoes a controlled expansion, releasing some of its pressure energy.
- Torque Generation: The pressure difference between the fluid’s inlet and outlet, combined with the change in flow direction, results in a force that causes the turbine blades to rotate. This rotation generates torque, which can be used to drive a generator or perform other mechanical work.
- Fluid Outlet: The now lower-pressure fluid exits the turbine and may be further processed or released.
The pressure of the fluid is a fundamental factor that drives the turbine’s operation by causing the fluid to flow through the turbine and exerting a force on the turbine blades. This process demonstrates the conversion of pressure energy into mechanical energy (torque) in a reaction turbine.
An impulse turbine generally uses the velocity of the water to move the runner and discharges at atmospheric pressure. A water stream hits each bucket on the runner. With no suction on the downside of the turbine, the water flows out the bottom of the turbine housing after hitting the runner. An impulse turbine is generally suitable for high-head, low-flow applications.
Velocity of Flowing Water:
- Definition: Velocity refers to the speed and direction of water flow in a specific direction. It indicates how quickly the water is moving and in which direction.
- Units: Velocity is typically measured in meters per second (m/s) or feet per second (ft/s).
- Importance: Velocity is crucial in fluid dynamics because it determines how fast fluid particles are traveling through a given cross-section of a conduit or pipe. It affects factors such as flow rate, discharge, and the kinetic energy of the fluid.
- Control: Velocity can be controlled or adjusted by changing the flow rate or altering the geometry of the flow path (e.g., using a nozzle to increase velocity).