Mechanical Engineering Basic Terms - 3

Calorific Value of fuel:

It us the total amount of heat obtained from burning 1 kg solid or liquid fuel.

Boiler/Steam 

Generator:

It is a closed vessel which is made of steel. Its function is to transfer heat to water to generate steam.

Economiser:

It is a part of boiler. Its function is to heat feed water which is supplied to boiler.

Superheater:

It is a part of boiler. Its function is to increase temperature of steam into boiler.

Air-Preheater:

It is a part of boiler. Its function is to preheats the air to be supplied to furnace and it recover heat from exhaust gas.

Boiler Draught:

It is an important term for boiler. It is the difference of pressure above and below the fire grate. This pressure difference have to maintain very carefully inside the bolier. It actually maintaind the rate of steam generation. This depends on rate of fuel burning. Inside the boiler rate of fuel burning is maintained with rate of entry fresh air. If proper amount of fresh air never entered into the boiler, then proper amount of fuel inside the boiler never be burnt. So, proper fresh air enters into the boiler only by maintaining boiler draught.

Nozzle:

Nozzle is a duct of varying cross-sectional area. Actually, it is a passage of varying cross-sectional area. It converts steam's heat energy into mechanical energy. It is one type of pipe or tube that carrying liquid or gas.

Scavenging:

It is the process of removing burnt gas from combustion chamber of engine cylinder.

Supercharging:

Actually, power output of engine depends on what amount of air enter into the engine through intake manifold. Amount of entry aiy if increased, then must be engine speed will increased. Amount of air will be increased by increasing inlet air density. The process of increasing inlet air density is supercharging. The device which is used for supercharging is called supercharger. Superchargers driven by a belt from engine crankshaft. It is installed in intake system.

Turbocharging:

Turbocharging is similar to the supercharging. But in that case turbocharger is installed in exhaust system whereas supercharger is installed in intake system. Turbocharger is driven by force of exhaust gas. Generally, turbocharger is used for 2-stroke engine by utilizing exhaust energy of the engine, it recovers energy otherwise which would go waste.

Governor:

Its function id to regulate mean speed of engine when there are variation in the load. If load increases on the engine, then engine's speed must decrease. In that case supply of working fluid have to increase. In the other way, if load decrease on the engine, then engine' speed must increase. In that case supply of working fluid have to decrease.Governor automatically, controls the supply of working fluid to the engine with varying load condition.

Flywheel:

It is the one of the main parts of the I.C. engine. Its main function id to store energy in the time of working stroke or expansion stroke. And, it releases energy to the crankshaft in the time of suction stroke, compression stroke & exhaust stroke. Because, engine has only one power producing stroke.

Rating of fuel:

S.I. Engine:

Octane number. Octane number indicates ability of fuel to resist knock.

C.I. Engine:

Cetane Number. Cetane number indicates ability of ignition of diesel fuel. That means, how much fast ignites diesel fuel.

Stoichiometric ratio:

It is the chemically correct air-fuel ratio by volume. By which theoretically sufficient oxygen will be gotten to burn all combustible elements in fuel completely.

Heat Transfer:

It is a science which deals with energy transfer between material bodies as a result of temperature difference.There are three way to heat transfer such as - Conduction, Convection & Radiation

Thermal Conductivity:

It is the quantity of heat flows between two parts of solid material by conduction. In this case following consideration will be important fact-

Time------ 1 sec

Area of that solid material-------- 1 m²

Thickness of that solid material------ 1m

Temperature difference between two parts of that material------ 1k

Heat Exchanger:

It is one type of device which can transfer heat from one fluid to another fluid. Example- Radiator, intercooler, preheater, condenser, boiler etc.

Refrigeration and Air Conditioning 

Refrigeration:

It is the process of removing heat from a substance. Actually, extraction of heat from a body whose temperature is already below the temperature of its surroundings.

1 tonne of refrigeration:

It is amount of refrigeration effect or cooling effect which is produced by uniform melting of 1 tonne ice in 24 hours from or at 0 degree centigrade or freezing 1 tonne water in 24 hours from or at 0 degree centigrade.

Humidification:

It is the addition of moisture to the air without change dry bulb temperature.

Dehumidification:

It is the removal of moisture from the air without change dry bulb temperature.