Francis Turbine

The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts.

A Francis turbine comprises mainly the four components:

• Spiral casing,
• Guide or Stay vanes,
• Runner blades,
• Draft tube.

Spiral Casing :

 Most of these turbines have vertical shafts although some smaller turbines of this type have horizontal shaft. The fluid enters from the penstock to a spiral casing which completely surrounds the runner. This casing is known as scroll casing or volute. The cross-sectional area of this casing decreases uniformly along the circumference to keep the fluid velocity constant in magnitude along its path towards the guide vane. This is so because the rate of flow along the fluid path in the volute decreases due to continuous entry of the fluid to the runner through the openings of the guide vanes or stay vanes. 

 Guide or Stay vane:

The basic purpose of the guide vanes or stay vanes is to convert a part of pressure energy of the fluid at its entrance to the kinetic energy and then to direct the fluid on to the runner blades at the angle appropriate to the design. The guide vanes impart a tangential velocity and hence an angular momentum to the water before its entry to the runner. The guide vanes are also known as wicket gates.

Runner blades:

The flow in the runner of a Francis turbine is not purely radial but a combination of radial and tangential. The flow is inward, i.e. from the periphery towards the centre. The height of the runner depends upon the specific speed. The height increases with the increase in the specific speed. The main direction of flow change as water passes through the runner and is finally turned into the axial direction while entering the draft tube.

Draft tube:

The draft tube is a conduit which connects the runner exit to the tail race where the water is being finally discharged from the turbine. The primary function of the draft tube is to reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet.

Ultrasonic Machining

Ultrasonic machining is an unconventional machining process. Ultrasonic machining is a method of grinding that uses an abrasive liquid rather than direct tool contact.

 
Principle

In ultrasonic machining, a liquid filled with abrasive material flows through over the work piece, and the work tool vibrates against the abrasives. The abrasive materials affect the work piece and remove material. For vibration we use a piezoelectric material, which vibrates on providing an emf.

Construction

The basic mechanical structure of USM is very similar to that of drill machine, howevee it can also be used on brittle materials also. The workpiece is mounted on a vice, which can be located at the desired position under the tool using a 2-axis table. The table can further be lowered or raised to accommodate work of different thickness.

 The basic elements of a USM are:

• Slurry delivery and return system,
• Feed mechanism to provide a downward feed force on the tool during machining,
• The piezoelectric material, which generates the ultrasonic vibration,
• The horn or concentrator, which mechanically amplifies the vibration to the required amplitude of 15-50 microns and accommodate the tool at its tip.

Working

In an ultrasonic machining, a tool of desired shape is vibrates at an ultrasonic frequency of 19-25 kHz with an amplitude of around 15-50 microns over the workpiece. Generally the tool is pressed downward with a feed force, F. Between the tool and the workpiece, the machining zone is flooded with hard abrasive particles generally in the form of water based slurry. As the tool vibrates over the workpiece, the abrasive particles acts as indenters and indent both the workpiece and the tool.

Pelton Turbine

Pelton wheel turbine is a high efficiency water turbine.  Water turbines are used to make electricity and serve as industrial power sources. The Pelton wheel works by extracting energy from the forward momentum of the water. It is an impulse turbine. It was invented by Lester Allan Pelton in 1870.

A Pelton wheel consists of two basic parts, the turbine and the penstock. The turbine is shaped like a wheel. The rim of the wheel is covered with buckets shaped like spoons. As water hits these spoons, it changes direction. Most of the energy in the water is transferred to the wheel, which causes it to turn. The wheel is attached to a shaft and the shaft is connected to a generator, which converts the rotational energy into electricaenergy.

The penstock is the apparatus that brings water to the wheel. The penstock has a nozzle with an opening smaller than the width of the pipe. Nozzle contains a spear which helps to increase the velocity of water and also regulate the amount of water striking the buckets, the spear is controlled by handle in either outward or inward direction. As water is forced through this smaller opening, the water pressure decreases, but the speed at which the water moves is increased.

For the Pelton wheel to reach maximum efficiency, the water must be moving twice as fast as the buckets. 

Steam Turbine

A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. 

Steam turbines utilize the principle of allowing pressurized steam to expand in controlled stages. Each turbine can be composed of a number of impulse and reaction turbines, each of which allows the steam to expand and turn the blades, or buckets, within the device. Most steam turbines employ both of these variations in concern, with the impulse turbines operating under high pressure, and low pressure being utilized for the reaction turbines. The difference between the two is that the impulse turbine uses a nozzle to introduce high velocity steam into the rotors, while the rotors in reaction turbines are themselves a type of nozzle.

The arrangement of impulse and reaction turbines within a steam turbine can effectively make the system very efficient. By making use of both high and low pressure, and having the steam do work at each stage of its expansion, the process may remain highly isentropic. This simply means that the entropy that goes into the system is similar to that which comes out. The other benefit of the design is that the spinning of the turbines creates rotary motion, which can be ideal for both power generation and turning paddles or other drive mechanisms on ships.

The modern steam turbine was invented in 1884 by Sir Charles Parsons, whose first model was connected to a dynamo that generated 7.5 kW or 10 hp of electricity. 

 

parson's turbine

A number of other variations of turbines have been developed that work effectively with steam. The de Laval turbine invented by Gustaf de Laval accelerated the steam to full speed before running it against a turbine blade. De Laval's impulse turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam, but is considerably less efficient.

 

de laval turbine

Gas Turbine

A turbine is a machine used to deliver power and so gas turbine uses gas as its intake for power delievery.

A gas turbine is a rotary combustion engine that converts the potential energy in gas, plus the kinetic energy of moving air, into a massive amount of energy that turns an output shaft, performing actual work.

Fresh atmospheric air flows through a compressor that brings it to higher pressure. Energy is then added by spraying fuel into the air and igniting it so the combustion generates a high-temperature flow. This high-temperature high-pressure gas enters a turbine, where it expands down to the exhaust pressure, producing a shaft work output in the process. The turbine shaft work is used to drive the compressor and other devices such as an electric generator that may be coupled to the shaft. The energy that is not used for shaft work comes out in the exhaust gases, so these have either a high temperature or a high velocity. The purpose of the gas turbine determines the design so that the most desirable energy form is maximized.

 Gas turbines are used to power aircraft, trains, ships, electrical generators, or even tanks.There are many types of turbine engines, For example, a windmill is a classic, very simple turbine, and steam engines are turbine engines as well.

Turbo Engine

When we think about super cars and supersonic aircrafts, a question always comes in mind that how could these cars attains such a high speed, and the answer is just by using a turbo charged engine.

A turbo-compound engine is a reciprocating engine that employs a blowdown turbine to recover energy from the exhaust gases. The turbine is usually mechanically connected to the crankshaft, as on the DC-7B and the Super Constellation, but electric and hydraulic systems have been investigated as well. The turbine increases the output of the engine without increasing its fuel consumption, thus reducing the specific fuel consumption. The turbine is referred to as a "blowdown turbine" , as it recovers the energy developed in the exhaust manifold during blowdown, that is the first period of the exhaust process when the piston still is on its expansion stroke, this is possible since the exhaust valves open before bottom dead center.

Turbo-compounding was used on on several airplane engines after World War II, including the Napier Nomad and the Wright R-3350. The first aircraft engine to be tested with a power-recovery turbine was the Rolls-Royce Crecy, during WWII.

Turboprop Engines

Turboprop engines are gas turbine engines which is used in aircraft. The gas turbine is designed in such a manner that it drives aircraft propeller using a reduction gear. Turboprops have their origin in the first half of the 20th century.  Gvorgy Jendrassik is considered to be the father of the turboprop, with his first small scale design for the engine appearing in 1937.

The United Kingdom was the site of the production and sale of the earliest mass marketed turbo prop engines. The Rolls Royce Company developed and marketed the RB.50 Trent, considered by many to have set the standard for later developments in turboprop technology. Rolls Royce made use of the knowledge acquired during the development of the Trent and later produced a highly reliable turboprop engine known as the Dart. The design and function of the Dart was such that production of the engine continued for over fifty years.

Turboprop engines are generally used on small subsonic aircraft, but some aircraft outfitted with turboprops have cruising speeds in excess of 500 knots (926 km/h). Large military and civil aircraft, such as the Lockheed L-188 Electra and the Tupolev Tu-95, have also used turboprop power. The Airbus A400M is powered by four Europrop TP400 engines, which are the third most powerful turboprop engines ever produced, after the Kuznetsov NK-12 and Progress D-27.

The turboprop engine is a simple device that includes a turbine, intake, combustor, compressor, and a propelling nozzle. Air flow is processed by the intake and then passed to the compressor. Fuel is added to the compressed air as it passes into the combustor, creating the energy as the mixture passes into the turbine. It is within the turbine that the power used to drive both the propellers and the engine proper is created. A portion of the power keeps the compressor functioning and continuing to pass air into the combustor. The remainder is passed through the propelling nozzle and helps to create the thrust generated by the propeller.

Turboprops are very efficient at flight speeds below 390 knots (725km/h) because the jet velocity of the propeller and exhaust is relatively low. Due to the high price of turboprop engines, they are mostly used where high-performance short-takeoff and landing capability and efficiency at modest flight speeds are required.