Impulse Turbine: Definition, Types, Component, Working Principle, Application, Advantages, Disadvantages [Notes & PDF]

what is impulse turbine ?

An impulse turbine is a type of steam turbine or hydraulic turbine that operates based on the principle of impulse. It is designed to convert the kinetic energy of a high-velocity fluid jet into mechanical work. This type of turbine is commonly used in hydroelectric power plants and certain types of steam power plants.

The working principle of an impulse turbine involves the conversion of the fluid’s kinetic energy into rotational motion. It consists of a set of stationary nozzles or blades called guide vanes or nozzles and a set of moving blades known as impulse or rotor blades. The fluid, either steam or water, is directed through the guide vanes, which accelerate the fluid to a high velocity. The high-velocity fluid then strikes the impulse blades, causing them to rotate.

The key feature of an impulse turbine is that the pressure drop occurs entirely in the nozzles or guide vanes, and the moving blades only experience a high-velocity fluid jet. This design allows for a simplified turbine construction and higher efficiency compared to reaction turbines, which have both pressure drop and velocity change in the moving blades.

The rotational motion produced by the impulse blades can be used to drive a generator or any other machinery connected to the turbine. The efficiency of an impulse turbine depends on factors such as the fluid velocity, blade design, and overall turbine construction. Engineers carefully optimize these parameters to achieve maximum power output and efficiency for a given application.

In summary, an impulse turbine is a type of turbine that converts the kinetic energy of a high-velocity fluid jet into mechanical work through a set of stationary nozzles and moving blades. It is commonly used in hydroelectric and steam power plants to generate electricity or drive machinery.

impulse turbine parts

The impulse turbine comprises several essential components that collaborate synergistically to facilitate the conversion of the kinetic energy of a high-velocity fluid jet into mechanical work. These components include the runner, buckets, nozzle, spear, casing, penstock, and potentially a braking jet.

The runner, as a fundamental part of the turbine, serves as the rotatable element that houses the carefully designed buckets or blades. These buckets, meticulously crafted curved surfaces, are securely affixed to the runner and play a pivotal role in effectively capturing the energy of the fluid jet and transforming it into rotational motion.

On the other hand, the nozzle, a stationary component, assumes the responsibility of directing and regulating the fluid flow onto the buckets. Its primary function involves accelerating the fluid to a significant velocity before it impinges upon the buckets, thus optimizing the efficiency of energy transfer.

To ensure the stability and precision of the fluid flow, a spear, commonly a small rod or pin, is typically positioned at the center of the nozzle. This spear aids in stabilizing and guiding the fluid jet, enabling it to strike the buckets with accuracy and consistency.

The casing, encompassing the turbine, assumes a critical role in providing structural support while maintaining the desired flow path of the fluid. Within the casing, various components, including the nozzles, buckets, and other internal parts of the turbine, are securely housed, ensuring proper alignment and optimal functionality.

Furthermore, the penstock, functioning as a conduit, facilitates the delivery of high-pressure fluid to the turbine. Acting as a channel or pipe, it effectively transports the fluid from its source, be it a dam or a steam generator, to the turbine’s nozzles where the energy conversion occurs.

In certain impulse turbines, an additional component known as a braking jet may be incorporated. This braking jet typically assumes the form of an extra nozzle and serves the purpose of directing a high-velocity fluid stream against the runner. By doing so, it introduces resistance, enabling control over the rotational speed of the turbine as necessary.

Collectively, these components seamlessly integrate to enable the efficient conversion of fluid energy into mechanical work within the impulse turbine. Through meticulous design optimization and meticulous calibration of these constituent parts, engineers strive to maximize turbine performance, ultimately achieving the desired power output and operational effectiveness.

working principle of impulse turbine

The impulse turbine operates based on Newton’s second law of motion, which states that the rate of change of momentum of an object is directly proportional to the force applied. In simpler terms, force is equal to the product of mass and acceleration (F = m * a).

In the case of an impulse turbine, the working principle revolves around two main factors: the mass of the flowing water or fluid and the change in velocity of the flow as it enters the turbine and exits after impact.

When water or fluid flows into the turbine, it possesses both mass and velocity. The nozzles or guide vanes of the turbine accelerate the fluid, converting its pressure energy into kinetic energy. This increase in velocity leads to a change in momentum of the fluid.

As the high-velocity fluid jet strikes the moving blades or buckets of the turbine, there is an impulse force exerted on the blades. According to Newton’s second law, this force is directly proportional to the change in momentum experienced by the fluid.

The change in momentum is a result of the difference in velocity of the fluid before and after impact with the blades. By transferring its momentum to the rotating blades, the fluid experiences a change in velocity, and the blades start to rotate.

The force exerted by the fluid on the blades causes the rotor to spin, and this rotational motion can be utilized to generate electricity or perform mechanical work.

Therefore, the working principle of an impulse turbine is based on the concept of imparting a change in momentum to the fluid by accelerating it and then transferring that momentum to the rotating blades, resulting in the generation of rotational motion and the conversion of fluid energy into mechanical work.

how does impulse turbine works

The working principle of an impulse turbine involves the conversion of the kinetic energy of a high-velocity fluid jet into mechanical work. Here’s a step-by-step explanation of how an impulse turbine works:

1. Fluid Acceleration: The process begins with the fluid, such as water or steam, entering the turbine through stationary nozzles or guide vanes. These nozzles or guide vanes are designed to control the flow and accelerate the fluid to a high velocity. The pressure energy of the fluid is converted into kinetic energy during this stage.
2. High-Velocity Jet: Once the fluid passes through the nozzles or guide vanes, it emerges as a high-velocity jet. The high-velocity fluid jet then enters the region where the moving blades or buckets of the turbine are located.
3. Impulse Transfer: As the high-velocity fluid jet strikes the moving blades or buckets, it transfers its momentum to the turbine’s rotor. The impact of the fluid on the blades causes them to change their direction, resulting in a change in momentum. According to Newton’s third law of motion, the change in momentum of the fluid produces an equal and opposite reaction, causing the rotor and the blades to rotate.
4. Rotational Motion: The rotational motion of the blades and rotor is driven by the impulse transfer from the high-velocity fluid jet. The rotating blades are connected to a central shaft, which transfers the rotational energy to the generator or the machinery being powered by the turbine.
5. Fluid Exhaust: After the fluid imparts its momentum to the blades, it exits the turbine and is typically discharged into a lower-pressure environment, such as a tailrace in a hydroelectric power plant or an exhaust system in a steam power plant. The fluid’s pressure and velocity are reduced, and it is then either reused or discharged from the system.
6. Energy Conversion: The rotational motion of the turbine’s rotor is converted into mechanical work, which can be used to generate electricity through an attached generator or drive other machinery connected to the turbine.

In summary, an impulse turbine works by accelerating a fluid to a high velocity through nozzles or guide vanes. The high-velocity fluid jet impacts the moving blades, transferring its momentum and causing the rotor to rotate. The rotational motion is then utilized to generate power or drive machinery. The conversion of fluid energy into mechanical work is the fundamental principle behind the operation of an impulse turbine.

Types of Impulse Turbine

There are several types of impulse turbines, each with its own unique design and characteristics. Here are some of the common types of impulse turbines:

1. Pelton Turbine: The Pelton turbine is one of the most widely used impulse turbines in hydroelectric power plants. It consists of a set of spoon-shaped buckets or cups mounted on the circumference of a rotating wheel, known as the runner. High-pressure water jets are directed onto the cups, causing the water to be deflected and creating a high-velocity jet. The jet strikes the curved surfaces of the cups, transferring its momentum to the runner and causing it to rotate.
2. Turgo Turbine: The Turgo turbine is a variation of the Pelton turbine and is often used for medium head applications. It features a runner with double-cupped buckets that are more open and have a slightly different shape compared to the Pelton turbine. This design allows for greater water flow through the turbine and increased power output. The Turgo turbine is known for its high efficiency and suitability for moderate head and higher flow rate conditions.
3. Crossflow Turbine: Also known as Banki-Michell or Ossberger turbines, crossflow turbines are commonly used in low-head hydroelectric power plants. They have a vertical axis and utilize the flow of water across a set of fixed guide vanes and moving blades to generate power. The water flows tangentially over the guide vanes, creating a swirling motion that strikes the blades, causing them to rotate. Crossflow turbines are compact, easy to install, and can operate efficiently at low flow rates.
4. Multiple-Jet Turbine: The multiple-jet turbine, as the name suggests, uses multiple jets of fluid to drive the turbine. It consists of multiple nozzles that direct the fluid onto the turbine’s blades. This design allows for a distributed and balanced flow of fluid, resulting in improved efficiency. Multiple-jet turbines are commonly used in applications where a large flow rate of fluid is available, such as in high-capacity hydroelectric power plants.
5. Hollow Jet Turbine: The hollow jet turbine is a specialized type of impulse turbine designed to extract energy from low-velocity, high-volume flows of water. It features a hollow jet nozzle that allows the water to flow through the center of the turbine, rather than striking the blades directly. The water passing through the turbine creates a suction effect that draws in additional water, increasing the overall flow rate and power generation capability.

These are just a few examples of the types of impulse turbines. Each type has its own unique design features and is suited for specific operating conditions, such as varying head, flow rate, and fluid properties. The selection of the appropriate impulse turbine type depends on factors such as the available resource, site conditions, power requirements, and efficiency considerations.

application of impulse turbine

Impulse turbines have various applications in both hydroelectric and steam power plants. Here are some common applications of impulse turbines:

1. Hydroelectric Power Generation: Impulse turbines are widely used in hydroelectric power plants where they convert the kinetic energy of flowing water into mechanical energy. The turbines are placed in the path of high-velocity water streams, such as those found in dams or rivers, and the force of the water striking the turbine’s blades causes them to rotate. This rotational motion is then used to generate electricity through connected generators.
2. Steam Power Plants: Impulse turbines are also used in certain types of steam power plants. In these plants, high-pressure steam is directed through nozzles or guide vanes, which accelerate the steam to a high velocity. The high-velocity steam then strikes the impulse blades of the turbine, causing them to rotate. The rotational energy is used to drive generators and produce electricity.
3. Marine Propulsion: Impulse turbines can be employed in marine propulsion systems, particularly in high-speed vessels such as hydrofoil boats. By using a high-pressure water jet, impulse turbines convert the energy of the water flow into rotational motion, which propels the vessel forward. This application is commonly found in waterjet propulsion systems for fast boats, ferries, and military vessels.
4. Compressed Air Systems: Impulse turbines are also utilized in compressed air systems, where they convert the energy of high-pressure air into mechanical work. Compressed air is directed through the nozzles of the turbine, creating a high-velocity air jet that strikes the impulse blades, causing them to rotate. This rotational motion can be used to power machinery or drive air compressors.
5. Wind Power: While most wind turbines operate on the principle of lift or drag, there are also impulse turbines specifically designed for use in high-velocity wind environments. These turbines capture the kinetic energy of the wind by directing it through a nozzle or guide vanes, which accelerate the air flow. The high-velocity wind then strikes the impulse blades, generating rotational motion that drives an electrical generator.

These are just a few examples of the applications of impulse turbines. The versatility and efficiency of these turbines make them suitable for various industries where the conversion of fluid energy into mechanical work is required.

advantages of impulse turbine

Impulse turbines offer several advantages compared to other types of turbines. Here are some of the key advantages of impulse turbines:

1. High Efficiency: Impulse turbines are known for their high efficiency in converting the kinetic energy of fluid into mechanical work. Since the pressure drop occurs primarily in the nozzles or guide vanes, the moving blades experience a high-velocity fluid jet, resulting in minimal energy losses. This design allows impulse turbines to achieve high levels of efficiency, making them ideal for power generation applications.
2. Simplicity of Design: Impulse turbines have a relatively simple design compared to reaction turbines. They consist of a set of stationary nozzles or guide vanes and a set of moving blades. The absence of pressure drop in the moving blades simplifies the construction and maintenance of impulse turbines, reducing complexity and potential failure points.
3. Wide Operating Range: Impulse turbines have a wide operating range, meaning they can efficiently operate under varying flow rates and pressure conditions. They can adapt to different operating conditions without significant loss in performance, making them versatile for use in various applications.
4. Suitable for High-Speed Applications: Impulse turbines are well-suited for high-speed applications due to their ability to handle high-velocity fluid jets. They can effectively harness the energy of fast-moving fluids, such as high-velocity water streams or high-pressure steam, making them suitable for use in power plants or marine propulsion systems requiring high rotational speeds.
5. Robustness and Reliability: The simplicity of impulse turbine design contributes to their robustness and reliability. With fewer moving parts and a more straightforward construction, impulse turbines are less prone to mechanical failures and require less maintenance compared to more complex turbine designs. This reliability is especially important for continuous operation in power generation facilities.
6. Ability to Handle Particles and Debris: Impulse turbines are generally more tolerant of particles and debris in the fluid compared to some other turbine types. The high-velocity fluid jet in impulse turbines can handle small particles without significant damage or performance degradation, making them suitable for applications where the fluid may contain impurities.

Overall, the high efficiency, simplicity of design, wide operating range, suitability for high-speed applications, robustness, and ability to handle particles make impulse turbines advantageous for various industries. Their reliability and efficiency make them a preferred choice for power generation, hydroelectric plants, steam power plants, and other applications where the conversion of fluid energy into mechanical work is essential.

disadvantages of impulse turbine

While impulse turbines offer several advantages, they also have certain disadvantages to consider. Here are some of the key disadvantages of impulse turbines:

1. Limited Pressure Drop: One of the limitations of impulse turbines is that they can only utilize the kinetic energy of the fluid, as the pressure drop occurs primarily in the nozzles or guide vanes. This means that they are not able to efficiently harness the energy from the pressure of the fluid itself. As a result, impulse turbines may not be as suitable for applications where the pressure drop in the fluid is significant.
2. Higher Speed Requirements: Impulse turbines typically require high fluid velocities to operate effectively. This means that they may require a higher flow rate or pressure to achieve the desired rotational speed and power output. In certain applications where high fluid velocities are not readily available, impulse turbines may not be the most practical choice.
3. Limited Operating Range: While impulse turbines have a wide operating range compared to some other types of turbines, they still have certain limitations. They may not perform optimally under extreme variations in flow rates or pressure conditions. Impulse turbines are generally more efficient at specific operating conditions and may experience reduced efficiency outside of those ranges.
4. Potential for Erosion: The high-velocity fluid jet in impulse turbines can lead to erosion of the blades over time. The constant impact of the fluid on the blades can cause wear and tear, especially if the fluid contains abrasive particles. This erosion can gradually degrade the turbine’s performance and efficiency, necessitating periodic maintenance and blade replacement.
5. Complexity of Nozzle Design: While impulse turbines have a simpler overall design compared to reaction turbines, the design and optimization of the nozzles or guide vanes can be complex. The shape, size, and arrangement of the nozzles greatly impact the turbine’s efficiency and performance. Achieving optimal nozzle design may require detailed engineering analysis and testing.
6. Lower Starting Torque: Impulse turbines typically have lower starting torque compared to reaction turbines. This means that they may require external starting mechanisms or additional devices to bring them up to the desired operating speed. In applications where a high starting torque is essential, impulse turbines may not be the most suitable choice without supplementary systems.

It’s important to consider these disadvantages alongside the advantages when selecting a turbine for a specific application. The choice of turbine type should be based on the specific requirements, operating conditions, and trade-offs that best align with the intended purpose.

difference between impulse and reaction turbine

Here’s a table outlining the key differences between impulse and reaction turbines:

It’s important to note that while the table highlights some general differences between impulse and reaction turbines, there may be variations and specific characteristics within each type of turbine depending on design variations and specific applications.

Reference : https://www.sciencedirect.com/topics/engineering/impulse-turbine