Short Answer:

Hydraulic efficiency in reaction turbines is the ratio of the useful power developed by the runner (turbine blades) to the power supplied by the water at the inlet. It tells how effectively the turbine converts the water’s energy into mechanical energy.

Higher hydraulic efficiency means that less energy is lost due to friction, turbulence, or improper flow inside the turbine. It is a key factor in determining the overall performance of a reaction turbine and is usually expressed as a percentage.

Detailed Explanation:

Hydraulic efficiency in reaction turbines

Hydraulic efficiency is an important performance measure for reaction turbines. It represents how efficiently the energy of flowing water is converted into useful mechanical energy by the turbine runner. In simple terms, it compares the actual energy used by the turbine to turn the shaft with the total energy available in the water entering the turbine.

Mathematically, hydraulic efficiency is expressed as:

Hydraulic Efficiency (ηₕ) = Runner Power / Water Power at Inlet

Where:

• Runner Power is the energy delivered to the runner blades that actually produces motion.
• Water Power at Inlet is the total potential and kinetic energy of the water entering the turbine.

This efficiency is always less than 100% because some energy is lost due to fluid friction, turbulence, leakage, and eddies inside the turbine casing and runner.

How it works in reaction turbines

Reaction turbines, such as Francis and Kaplan turbines, operate using both pressure and velocity energy of water. Unlike impulse turbines where all energy is converted before striking the blades, in reaction turbines, water remains under pressure while passing through the runner.

Here’s how hydraulic efficiency applies in this case:

• As water flows over the curved blades of the runner, its pressure and velocity change.
• If the blade design is good and water flows smoothly, more of the water’s energy is captured and used.
• If there are energy losses due to bad blade shape, improper angle, or rough surfaces, the efficiency drops.

A well-designed reaction turbine with proper water flow direction and minimal loss can achieve high hydraulic efficiency, often above 90%.

Factors affecting hydraulic efficiency

1. Blade Design: Efficient, smooth, and properly curved blades help in reducing energy loss.
2. Water Flow Direction: Proper angle of water entry ensures better energy transfer.
3. Turbulence and Friction: Rough surfaces and sharp turns create turbulence, lowering efficiency.
4. Leakage Losses: Water escaping through small gaps reduces useful power output.
5. Operating Conditions: Efficiency changes with load, speed, and flow rate.

Importance in turbine performance

Hydraulic efficiency is directly related to the overall performance of the turbine. A turbine with high hydraulic efficiency produces more mechanical power from the same amount of water, reducing energy wastage and improving plant output.

It also affects other efficiencies like mechanical and overall efficiency. Hence, engineers focus on improving hydraulic efficiency during design and operation for better performance and energy savings.

Conclusion:

Hydraulic efficiency in reaction turbines measures how well the turbine converts water energy into mechanical power. It is calculated by comparing the runner power to the total water energy at the inlet. High hydraulic efficiency means better energy conversion and less wastage, making it essential for the effective working of reaction turbines.