Project:-Impulse Water Turbine

Project:-Impulse Water Turbine 

MATRAIL & EXPENDITURE ON PROJECT

DC MOTOR=Rs120/-

LED BULB =Rs10/-

GUN GLUE=Rs150/-

GUN GLUE STICK=Rs15/-

PUMP =Rs140/-

NOZZLE =Rs10/-

CONTAINER=50/-

PLY STAGE=

SHAFT BOX=

WIRING PVC PIPE=Rs15/-

PUMP PIPE =Rs15/-

FEVI KVIC=Rs5/-

SPOON =Rs5/-

M-SHEEL=20/-

1.Introduction

The Pelton wheel is an impulse-type water turbine. It was invented by Lester Allan Pelton in the 1870s. The Pelton wheel extracts energy from the impulse of moving water, as opposed to water's dead weight like the traditional overshot water wheel. Many variations of impulse turbines existed prior to Pelton's design, but they were less efficient than Pelton's design. Water leaving those wheels typically still had high speed, carrying away much of the dynamic energy brought to the wheels. Pelton's paddle geometry was designed so that when the rim ran at half the speed of the water jet, the water left the wheel with very little speed; thus his design extracted almost all of the water's impulse energy—which allowed for a very efficient turbine.

Heard about electricity generation by hydropower plants, know what makes them so efficient that they are lightening up our houses. Yeah that’s the whole effort we have put-in to design our turbines, and make them more and more efficient. Now days an efficient turbine can utilize up-to 90% of the water’s potential energy. Although there are various types of impulse turbines available, but Pelton wheel turbine is the most widely used impulse turbine. We can generate maximum up-to 200 MW of electricity from a Pelton wheel turbine, where we have water head (height of stored water), as high as one thousand meter.

We know about the potential of water, a very long time from now, when it was used to grind wheat into flour by converting the energy of flowing water into rotational energy through large water wheels. Since then till now let’s see how much we have advanced and changed to use the water’s potential energy in more efficient way

2. History Of Impulse Turbine

Lester Allan Pelton was born in Vermillion, Ohio in 1829. In 1850, he travelled overland to California, to take part in the Gold Rush. Pelton worked by selling fish he caught in the Sacramento River.[3] In 1860, he moved to Camptonville, a center of placer mining activity. At this time many mining operations were powered by steam engines which consumed vast amounts of wood as their fuel. Some water wheels were used in the larger rivers, but they were ineffective in the smaller streams that were found near the mines. Pelton worked on a design for a water wheel that would work with the relatively small flow found in these streams.[4]

By the mid 1870's, Pelton had developed a wooden prototype of his new wheel. In 1876, approached the Miners Foundry in Nevada City to build the first commercial models in iron. The first Pelton Wheel was installed at the Mayflower Mine in Nevada City in 1878.[4]. The efficiency advantages of Pelton's invention were quickly recognized and his product was soon in high demand. By the mid-1880s, the Miners Foundry could not meet the demand, and in 1888, Pelton sold the rights to his name and the patents to his invention to the Pelton Water Wheel Company in San Francisco. The company established a factory at 121/123 Main Street in San Francisco.[5]

The Pelton Water Wheel Company manufactured a large number of Pelton Wheels in San Francisco which were shipped around the world. In 1892, the Company added a branch on the east coast at 143 Liberty Street in New York City. By 1900, over 11,000 turbines were in use. In 1914, the company moved manufacturing to new, larger premises at 612 Alabama Street in San Francisco. In 1956, the company was acquired by the Baldwin-Lima-Hamilton Company, which ended manufacture of Pelton Wheels.

3. Principle of Impulse turbine

Impulse turbine works on the basic principle of impulse. When the jet of water strikes at the turbine blade with full of its speed, it generates a large force which used to rotate the turbine. The force is depends on the time interval and velocity of jet strikes the blades. This turbine used to rotate the generator, which produces electric power. Impulse turbine works on the basic principle of impulse. When the jet of water strikes at the turbine blade with full of its speed, it generates a large force which used to rotate the turbine. The force is depends on the time interval and velocity of jet strikes the blades. This turbine used to rotate the generator, which produces electric power.





In the Other Words-

The potential energy of the water is converted into kinetic energy by passing it through a nozzle. Once we have high speed water jet, we can use its impact to rotate a turbine.

Or we can say, it works on Newton’s second law of motion, that it depends on two main factors, mass of water flowing in-to turbine, and change in the velocity of the flow coming in-to turbine to that of going out of turbine after impact. As the mass of water entering into the turbine is same as the water going out of turbine after impact, but with a considerable decrement in its velocity. And the intensity of impact depends upon the time taken by velocity to change from maximum (jet velocity) to minimum. Thus impulse turbine only uses the kinetic energy of water to get its power.
4.Components of Impulse Turbine

1. Runner

It is a solid circular-disc with cylindrical shaft in the center. The shaft and the runner both are made from high strength stainless steel where load on the turbine is considerably high. Runners are also made from cast iron where available water head is a bit low, thus force on turbine is not that high.

2. Buckets

Buckets are cup type hollow hemispherical structures, bolted on the periphery of the runner. Jet strikes these buckets to rotate the runner. Their design plays a vital role in deciding the efficiency of a turbine. . These are made either from stainless-steel or cast iron

3. Nozzle and Spear

Nozzle directs the flow of water to the buckets, with an increased velocity coming from a high head. Spear is a conical structure which is moved in and out of nozzle to regulate the flow of water striking the buckets.

4. Casing

Casing of an impulse turbine is a preventive shielding over the turbine, usually made of cast iron. It also prevents the water from splashing, and also guides it to the spill way

4. Working of Impulse Turbine

As we discussed impulse turbine works on basic principle of impulse. Its working can be describe in following points.

* High pressure water flow form dam (high head) to nozzle (low head).

* This water flows through divergent nozzle where it’s all pressure energy change into kinetic energy. It forms a water jet.

* The water jet strikes the blade at high speed which rotates the rotor.

* It transfers all kinetic energy of water to the rotor, which further use to rotate the generator.

* After transferring energy, water flows to the tail race.

* This process run continuously until sufficient power generates. For better understanding watch the video given below on working of impulse turbine.

In the Other Words:-

Water stored at a height is passed through a nozzle, situated almost at ground level or ever below ground level. Thus converting the energy of stored water into high speed jet. This high speed water jet strikes the buckets or blades attached to the runner, forcing runner to rotate at its own axis. Thus converting the energy of high speed-jet into rotational energy. This rotational movement of turbine shaft is used to produce electricity through generator.

Spear is moved in and out of nozzle to regulate the flow of water, according to the load on turbine. To get maximum power output from a turbine the velocity of jet striking the buckets should be as much as twice the speed of rotating buckets. So velocity of water-jet is regulated according to the load or rpm of turbine in such a way that we can keep turbine running in its most efficient range.

Moreover, practically we use 3 to 4 nozzles instead of one. This is done to deal with the high loads on turbine and to increase the power output capability of a turbine. Power is also regulated by closing few nozzles when load on the turbine is low.

When the load on the turbine decreases suddenly, and spear could not act fast enough to regulate the flow of water-jet, the rpm of turbine will keep on increasing and could damage the turbine. To prevent this from happening we use deflector which deflects the flow of water jet away from the turbine buckets. Thus keeping turbine under safe limits.

In the Other words:-

Nozzles direct forceful, high-speed streams of water against a series of spoon-shaped buckets, also known as impulse blades, which are mounted around the outer rim of a drive wheel—also called a runner (see photo, 'Old Pelton wheel..'). As the water jet hits the blades, the direction of water velocity is changed to follow the contours of the blades. The impulse energy of the water jet exerts torque on the bucket-and-wheel system, spinning the wheel; the water jet does a "u-turn" and exits at the outer sides of the bucket, decelerated to a low velocity. In the process, the water jet's momentum is transferred to the wheel and hence to a turbine. Thus, "impulse" energy does work on the turbine. Maximum power and efficiency are achieved when the velocity of the water jet is twice the velocity of the rotating buckets. A very small percentage of the water jet's original kinetic energy will remain in the water, which causes the bucket to be emptied at the same rate it is filled, (see conservation of mass) and thereby allows the high-pressure input flow to continue uninterrupted and without waste of energy. Typically two buckets are mounted side-by-side on the wheel, with the water jet split into two equal streams; this balances the side-load forces on the wheel and helps to ensure smooth, efficient transfer of momentum from the water jet to the turbine wheel.

Because water is nearly incompressible, almost all of the available energy is extracted in the first stage of the hydraulic turbine. Therefore, Pelton wheels have only one turbine stage, unlike gas turbines that operate with compressible fluid

5. Construction of Impulse Turbine

Blades:

The number of blades is situated over the rotary. They are concave in shape. The water jet strikes at the blades and change the direction of it. The force exerted on blades depends upon amount of change in direction of jet. So the blades are generally concave in shape.

Rotor:
Rotor which is also known as wheel is situated on the shaft. All blades are pined into the rotor. The force exerted on blades passes to the rotor which further rotates the shaft.

Nozzle:

A nozzle play main role of generating power from impulse turbine. It is a diverging nozzle which converts all pressure energy of water into kinetic energy and forms the water jet. This high speed water strikes the blades and rotates it.

Casing:
Casing is the outside are which prevent the turbine form atmosphere. The main function of casing is to prevent discharge the water from vanes to tail race. There is no change in pressure of water from nozzle to tail race so this turbine works at atmospheric pressure.

Braking nozzle:
A nozzle is provided in opposite direction of main nozzle. It is used to slow down or stop the wheel.

6. Advantages of Impulse Turbine

Advantage:

1. It can works at low discharge or at low flow rates.

2. This turbine has high efficiency.

3. Impulse turbine is flexible according to the load condition. At higher load more than one nozzle are used.

4. They work at atmospheric pressure so no problem of leakage.

5. It is easy to assemble.

7. Disadvantages of Impulse Turbine

Disadvantages:

1.Large size compare to others.

2.Efficiency decreases with time.

3.It required high head witch is hard to control.

4. It is costly to install.

8.Applications Of Impulse Turbine

It is used worldwide to produce electrical energy in a number of hydro-power plants.

Turbochargers in automobiles uses the pressure energy of exhaust gases through impulse turbine. Where hot and pressurized gases coming out of exhaust are converted into high velocity jet by passing them through nozzle.

It is also used in reverse osmosis plant, where waste water jet velocity is used to run turbine, thus acts as an energy recovery system.

In the Other Words:-

Pelton wheels are the preferred turbine for hydro-power where the available water source has relatively high hydraulic head at low flow rates. Pelton wheels are made in all sizes. There exist multi-ton Pelton wheels mounted on vertical oil pad bearings in hydroelectric plants. The largest units - the Bieudron Hydroelectric Power Station at the Grande Dixence Dam complex in Switzerland - are over 400 megawatts [1]. The smallest Pelton wheels are only a few inches across, and can be used to tap power from mountain streams having flows of a few gallons per minute. Some of these systems use household plumbing fixtures for water delivery. These small units are recommended for use with 30 metres (100 ft) or more of head, in order to generate significant power levels. Depending on water flow and design, Pelton wheels operate best with heads from 15–1,800 metres (50–5,910 ft), although there is no theoretical limit.

9. Design rules of Impulse Turbine

The specific speed parameter is independent of a particular turbine's size.

Compared to other turbine designs, the relatively low specific speed of the Pelton wheel, implies that the geometry is inherently a "low gear" design. Thus it is most suitable to being fed by a hydro source with a low ratio of flow to pressure, (meaning relatively low flow and/or relatively high pressure).

The specific speed is the main criterion for matching a specific hydro-electric site with the optimal turbine type. It also allows a new turbine design to be scaled from an existing design of known performance.

(dimensioned parameter),

where:

= Frequency of rotation (rpm)

= Power (W)

= Water head (m)

= Density (kg/m3)

The formula implies that the Pelton turbine is geared most suitably for applications with relatively high hydraulic head H, due to the 5/4 exponent being greater than unity, and given the characteristically low specific speed of the Pelton.
11.Turbine physics and derivation

Energy and initial jet velocity:

jet In the ideal (frictionless) case, all of the hydraulic potential energy (Ep = mgh) is converted into kinetic energy (Ek = mv2/2) (see Bernoulli's principle). Equating these two equations and solving for the initial jet velocity (Vi) indicates that the theoretical (maximum) jet velocity is Vi = √2gh. For simplicity, assume that all of the velocity vectors are parallel to each other. Defining the velocity of the wheel runner as: (u), then as the jet approaches the runner, the initial velocity relative to the runner is: (Vi − u).[7] The initial velocity of jet is Vi

Final jet velocity:

Assuming that the jet velocity is higher than the runner velocity, if the water is not to become backed-up in runner, then due to conservation of mass, the mass entering the runner must equal the mass leaving the runner. The fluid is assumed to be incompressible (an accurate assumption for most liquids). Also it is assumed that the cross-sectional area of the jet is constant. The jet speed remains constant relative to the runner. So as the jet recedes from the runner, the jet velocity relative to the runner is: −(Vi − u) = −Vi + u. In the standard reference frame (relative to the earth), the final velocity is then: Vf = (−Vi + u) + u = −Vi + 2u.
Optimal wheel speed[edit]


We know that the ideal runner speed will cause all of the kinetic energy in the jet to be transferred to the wheel. In this case the final jet velocity must be zero. If we let −Vi + 2u = 0, then the optimal runner speed will be u = Vi /2, or half the initial jet velocity.

Torque:

By Newton's second and third laws, the force F imposed by the jet on the runner is equal but opposite to the rate of momentum change of the fluid, so

F = −m(Vf − Vi)/t = −ρQ[(−Vi + 2u) − Vi] = −ρQ(−2Vi + 2u) = 2ρQ(Vi − u),

where ρ is the density, and Q is the volume rate of flow of fluid. If D is the wheel diameter, the torque on the runner is

T = F(D/2) = ρQD(Vi − u).

The torque is maximal when the runner is stopped (i.e. when u = 0, T = ρQDVi). When the speed of the runner is equal to the initial jet velocity, the torque is zero (i.e. when u = Vi, then T = 0). On a plot of torque versus runner speed, the torque curve is straight between these two points: (0, pQDVi) and (Vi, 0).[7] Nozzle efficiency is the ratio of the jet power to the water power at the base of nozzle
Power[edit]

The power P = Fu = Tω, where ω is the angular velocity of the wheel. Substituting for F, we have P = 2ρQ(Vi − u)u. To find the runner speed at maximum power, take the derivative of P with respect to u and set it equal to zero, [dP/du = 2ρQ(Vi − 2u)]. Maximum power occurs when u = Vi /2. Pmax = ρQVi2/2. Substituting the initial jet power Vi = √2gh, this simplifies to Pmax = ρghQ. This quantity exactly equals the kinetic power of the jet, so in this ideal case, the efficiency is 100%, since all the energy in the jet is converted to shaft output.[7]

Efficiency:

A wheel power divided by the initial jet power, is the turbine efficiency, η = 4u(Vi − u)/Vi2. It is zero for u = 0 and for u = Vi. As the equations indicate, when a real Pelton wheel is working close to maximum efficiency, the fluid flows off the wheel with very little residual velocity.[7] In theory, the energy efficiency varies only with the efficiency of the nozzle and wheel, and does not vary with hydraulic head.[8] The term "efficiency" can refer to: Hydraulic, Mechanical, Volumetric, Wheel, or overall efficiency.


The End