PRINCIPLE OF OPERATION OF SIMPLE IMPULSE TURBINE

It consists of one set of nozzle followed by one set of moving blades. A rotor is mounted on a shaft. The moving blades are Attached to the rotor.

The steam from the boiler at high pressure and low velocity enters the nozzle which is fitted in the casing. The steam expands in the nozzle where the pressure drops to p1 and velocity increases to V1. This high velocity steam jet impinges over the blades mounted on the rotor attached to the shaft. This causes the rotation of the turbine shaft and thus useful work is obtained. It is noted that the pressure of the steam when it moves over the blade remains constant but the velocity decreases.

The upper portion shows the longitudinal section of the upper half of the turbine. The middle portion shows the development of the nozzles and blading. The bottom portion shows the variation of velocity and pressure of the steam during which it passes through nozzles and blades.

DISADVANTAGES OF SIMPLE IMPULSE TURBINE :

* Since all the kinetic energy of the high velocity steam has to be absorbed in only one ring of moving blades, so the velocity of the turbine is too high i.e, up to 30000 rpm for practical purposes. Such high rotational speeds can only be utilized to drive generators with only large reduction gearing arrangements.

* The Velocity of Steam at exit is sufficiently high thereby resulting in a kinetic energy loss called "Carry over loss " or " leading velocity loss ". This loss is so high.

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THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The object to be checked is place

Advantages And Disadvantages Of Air Refrigeration System :

Advantages Of Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content.

Mechinopedia For Mechanical Engineers

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