Short Answer:

Hydraulic efficiency is the ratio of the actual energy delivered by the fluid to the theoretical energy supplied to it by the pump or turbine. It shows how effectively the hydraulic machine converts energy between fluid and mechanical form. In simple terms, it measures the losses that occur due to friction, turbulence, and other hydraulic resistances inside the machine.

In pumps, hydraulic efficiency indicates how much of the mechanical energy is converted into fluid energy, while in turbines, it shows how much of the fluid energy is converted into mechanical power. It is usually expressed as a percentage and helps in judging the performance of hydraulic machines.

Detailed Explanation :

Hydraulic Efficiency

Hydraulic efficiency is one of the most important parameters used to evaluate the performance of hydraulic machines like pumps and turbines. It represents the efficiency with which energy transfer occurs between the fluid and the machine. In any hydraulic device, a part of the energy is lost due to friction, turbulence, and leakage within the fluid passages. Hydraulic efficiency helps to determine how much useful energy remains available after these losses.

In simple words, hydraulic efficiency can be defined as:

It expresses the effectiveness of the fluid flow through impellers, blades, or passages inside the machine. The higher the hydraulic efficiency, the better the machine performs, as it means less energy is wasted due to fluid friction and eddies.

Hydraulic efficiency varies depending on the type of hydraulic machine. For example:

• In pumps, hydraulic efficiency represents the ratio of the energy imparted to the fluid (in the form of head or pressure) to the energy actually supplied by the impeller.
• In turbines, hydraulic efficiency shows how much of the energy available in the water or fluid is converted into mechanical energy on the turbine shaft.

Mathematically, for a pump, hydraulic efficiency is given by:

where,
= hydraulic efficiency
= acceleration due to gravity
= manometric head
= velocity of whirl at outlet
= tangential velocity of the impeller at outlet

This expression shows that the efficiency depends on the energy actually transferred to the liquid compared to the energy theoretically available from the impeller.

Similarly, for turbines, hydraulic efficiency can be expressed as:

In both cases, it highlights the proportion of energy that is effectively used for performing useful work.

Factors Affecting Hydraulic Efficiency

1. Friction Losses:
   When the fluid flows through the impeller or turbine blades, friction occurs between the fluid particles and the surfaces of the blades. This causes energy loss and reduces hydraulic efficiency.
2. Leakage and Recirculation:
   Leakage through clearances in pumps or turbines reduces the actual discharge and increases energy losses, thereby lowering efficiency.
3. Turbulence and Eddy Formation:
   Poor design of flow passages or sharp turns in the flow path cause turbulence and eddy currents, which waste energy.
4. Blade Design and Angle:
   The efficiency depends largely on the shape, size, and angle of the blades. Properly designed blades ensure smooth flow and high hydraulic efficiency.
5. Operating Speed:
   If the machine does not operate at its designed speed, the flow pattern may become disturbed, leading to energy losses.
6. Fluid Properties:
   Viscosity, density, and temperature of the fluid influence friction and flow characteristics, thus affecting efficiency.

Importance of Hydraulic Efficiency

Hydraulic efficiency is very important in the design and operation of hydraulic machines for the following reasons:

• Performance Evaluation: It helps to compare the actual performance of a machine with its theoretical performance.
• Design Improvement: Engineers use efficiency data to improve impeller and turbine designs for better flow and reduced friction.
• Energy Saving: Higher hydraulic efficiency means less energy loss and more economical operation.
• Maintenance Planning: Low efficiency may indicate internal wear, cavitation, or blockage, which requires maintenance.

In a centrifugal pump, total efficiency () depends on three main efficiencies:

1. Mechanical Efficiency – related to bearing and shaft friction.
2. Volumetric Efficiency – related to leakage losses.
3. Hydraulic Efficiency – related to friction and fluid flow losses.

These efficiencies combine as follows:

Hence, improving hydraulic efficiency directly improves the overall efficiency of the pump or turbine.

Typical Values

In practical systems, hydraulic efficiency usually ranges between 70% to 90% for well-designed machines. Small pumps or turbines may have lower efficiency due to greater relative friction losses, while large machines are usually more efficient due to smoother flow paths and optimized design.

To increase hydraulic efficiency, smooth internal surfaces, gradual curvature in flow passages, and well-balanced impellers are used. Proper maintenance, avoiding cavitation, and operating near the design conditions also help to maintain high efficiency.

Conclusion :

Hydraulic efficiency defines how effectively a hydraulic machine transfers energy between the fluid and mechanical system. It indicates the proportion of useful energy available after accounting for losses like friction, leakage, and turbulence. A higher hydraulic efficiency means smoother flow and better energy conversion, leading to improved overall performance. Therefore, it is a vital factor in designing, selecting, and maintaining efficient hydraulic systems such as pumps and turbines.