basic mechanical engineering definitions

BASIC MECHANICAL ENGINEERING DEFINITIONS 

THERMAL ENGINEERING :

Boiler/Steam
Generator:
          It is a clossed 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 funtion 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 cros-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.Superchargeris driven by a belt from engine crakshaft. It is installed in intake system.

Turbocharging:
          Turbocharging is similar to the supercharging. But in that case tubocharger 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.

Governeor:
          Its function is to regulate mean speed of engine when there are variation in the load. If load incrases on the engine, then engine's speed must decrease. In that case supply of working fluid have to increase. In the otherway, if load decrease on the engine, then engine' speed must increase. In that case supply of working fluid have to decrease.Governor automatcally, 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 releasesenergy 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.

FLUID MECHANICS AND HYDRAULIC MACHINERY DEFINITION:

Adhesion :

             The attraction between the molecules of a liquid and molecules of a solid boundary surface in contact with liquid.

Cohesion :

           The  inter-molecular attraction between molecules of the same liquid.

TURBINE:
        A turbine is defined as the hydromachine which convert the hydraulic energy to mechanical energy and then this mechanical energy is converted into electrical energy when it is connected to generator.
Different types of turbine are:
PELTON turbine
high head ,impulse turbine and axial flow.

KAPLAN TURBINE
medium head ,reaction turbine.
FRANCIS TURBINE
low head ,high discharge reaction turbine.

Hydraulic Machine:
Turbine,Pump,Compressor etc.

Capillarity :

          It is defined as the phenomenon of rise (or)fall of aliquid surface in a small tube relative to the adjacent general level of liquid.when the tube held verticallyin the liquid capillarity rise(or)fall is due to the combined effect of adhesion and cohesion.

Vortex :

         In fluid dynamics a vortex is aregion in afluid in which the flow revoles around the axis line,which may be straight (or) curved example : smoke rays ,wind revolving around dust  

Buoyancy principle:

       When a body is immersed in a liquid, it is lifted up by a force equal to weight of liquid displaced by the body. The tendency of liquid to lift up an immersed body is buoyancy. The upward thrust of liquid to lift up the body is called buoyancy force.Bernoulli's Equation:
P/γ +V²/2g +Z = Constant

Where, P = pressure,

V = velocity,

Z = Datumn Head

Devices for fluid:

Venturimeter:     It measures discharge of fluid.

Piezometer   :    It measure pressure rate of fluid.
Notches       :    It measures discharge of fluid.
Orifice meter: It measures discharge of fluid.
Pitot tube     : It measures velocity of fluid.

Fluid discharge/Fluid flow:
Quantity of fluid flowing per second.

(through a section of pipe/ through a section of channel)

Q=AV

where, V= velocity of fluid,A= cross-sectional area of pipe/channel
Note: 1m³ = 1000 L1 cusec = 1 ft³/sec1 ft = 0.3048 m

Hydraulic Machine:
Turbine,Pump,Compressor etc.

Draft tube:
           It attaches with reaction turbine . Its function is to reduce energy loss from reaction turbine & it also reduce pressure at outlet which is must blow the atmospheric pressure.

Specific Weight:
Weight per unit volume of the fluid.

Specific Volume:
Volume per unit mass of the fluid.

Specific Gravity:
            It is the ratio of specific weight of required substance to specific weight of pure water at 4 degree centigrade temperature.

Specific heat:
            The amount of heat required to increase 1 unit temperature of 1 unit mass.
Viscosity:
Dynamic Viscosity:
The amount of resistance of one layer of fluid over other layer of fluid.Kinematic Viscosity:
It is the ratio of dynamic viscosity to density.

Surface tension :

          It is caused by the force of cohesion at the free surface (or) surface energy per unit volume of the liquid.

Archimedes principle :

        It is the physical law of the buoyancy discoved by the ancient greek mathematician and inventor Archimedes stating that any body completely(or) partially submerged in a fluid (gas(or) liquid) at rest is acted upon by an upward as buoyant force the magnitude of which is equal to the weight of the fluid.

HEAT TRANSFER :

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-ConductionConvectionRadiation

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

Mach Number:
          It is the ratio of the velocity of fluid to the velocity of sound.
M=1 ----------------- Sonic flow
M> (1-6) ----------- Super-Sonic flow
M>6 ---------------- Hyper-Sonic flow

Heat Treatment:
          Operation involving heating and cooling of a metal in solid state for obtaining desirable condition without being changed chemical composition.Its object-increase hardness of metal.increase quality of metal ( heat, corrosion,wear resistance quality )improve machinability.

MACHINE TOOLS :
Machine Tool:
          It is the power driven tool. It cut & form all kinds of metal parts.

Example –

1. Lathe

2. Drill Press

3. Shaper Machine

4. Planer machine

5. Grinding

6. Miling

7. Broaching

8. Boring

Cutting Tool:
          Tool Materials for Cutting Tool:
1. High Carbon Steel

2. High Speed Steel (W+Cr+V)

3. Carbide (W Carbide+Ti Carbide+Co Carbide)

Indexing:

          It is the method of dividing periphery of job into equal number of division. Actually, it is the process of dividing circular or other shape of workpiece into equal space, division or angle.

Jig:
          It is one type of device which hold & locate workpiece and also guide & control cutting tool. It uses in drilling, reaming and tapping.

Fixture:
          It is one type of device which hold and locate workpiece. It uses in miling, grinding, planning & turning.

REFRIGERATION AND AIR CONDTIONING :

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.

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.

Critical temperature :

          Critical temperature of a substance is the temperature at and above which vapour of the substance cannot be liquidify no matter how much pressure is applied.

Critical temperature :oxygen-31.2 water -374 carbondioxide-31.2

Critical pressure :

          Critical pressure of a substance is the pressure required to liquidify a gas at its critical temperature.

 Critical pressure of oxygen-49.7 water-217.7 carbon-dioxide -73.0

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

Triple point :

          The triple point of the substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium.

Absolute temperature :

          It is also called as themodyamic temperature is the temperature of an object where 0(zero)is taken as absolute zero.it is taken in Kelvin scale,.

Humidification:
          It is the addition of moisture to the air without change dry bulb temperatur.

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

THERMODYNAMICS :

Themodynamics Law:

Zeroth Law:
          If two body are in thermal equilibrium with a third body then these two body are also in thermal equilibrium with each other.

First Law of Thermodynamics:
          In a closed system, work deliver to the surrounding is directly proportonal to the heat taken from the surrounding.And also, In a closed system, work done on a system is directly proportonal to the heat deliver to the surrounding.

Second Law of Thermodynamics:
          It is impossible to make a system or an engine which can change 100 percent input energy to 100 percent output.

Entropy:
          It is a thermodynamic property.

ds = dq/T

where, ds = change of entropy,

dq = change of heat,

 T = Temperature.

In adiabatic process, entropy can not change. Actually,lacking or mal-adroitness of tranfering energy of a system is entropy.

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

KINEMATICS OF MACHINERY :

Torque or Turning Force:
          It is the total amount of force which is required to create acceleration on moving substance.

Couple:
          Two forces those acts on equally,parallely & oppositely on two separate points of same material.

Moment:
          It is the amount of moving effect which is gained for action of turning force.

Stress:
          It is the force that can prevent equal & opposite force. That means, it is the preventing force. If one force acts on outside of a material, then a reactive force automatically acts to protest that force. The amount of reactive force per unit area is called stress. e.g. Tensile Stress, Compressive Stress, Thermal Stress.

Strain:
          If a force acts on a substance, then in that case if the substance would deform. Then the amount of deformation per unit length of that substance is called strain.

Spring:
It is one type of device which is being distorted under certain amount of load & also can also go to its original face after the removal of that load.

Its function:

v  To store energy.

v  To absorb energy.

v  To control motion of two elements.

Stiffness:
Load per unit deflection. The amount of load required to resist the deflection

Gear Train:
Meshing of two or more gear. It can transmit power from one shaft to another shaft.

MANUFACTURING TECHNOLOGY :

Ferrous Metal:
1. Cast Iron - (2-6.67)%C, Si, Mn, P, S

2. Steel - (0-2)%C

3. Wrought Iron - 99.5% Fe

Non-Ferrous Metal:
1. Brass - (Cu+Zn)

2. Bronze -

(Sn+Cu) ------ Tin Bronze

(Si+Cu) ------- Silicon Bronze

(Al+Cu) ------- Aluminium Bronze

Allowance:
          It is the difference between basic dimension of mating parts. That means, minimum clearance between mating parts that can be allowed.

Tolerance:
          It is the difference between upper limit of dimension. It is also the permissible variation above and below the basic size. That means maximum permissible variation in dimensions.

Clearance:
          It is the difference in size between mating parts. That means, in that case the outside dimension of the shaft is less than internal dimension of the hole.

Stiffness:
          It is the ability to resist deformation.

Toughness:
 `        It is the property to resist fracture.

Fatigue:
          When a material is subjected to repeated stress below yield point stress, such type of failure is fatigue failure.

Nuclear Fission:
          It is a nuclear reaction by which one big nucleous divided into two or more nucleous.

Nuclear Fussion:
          It is also a nuclear reaction by which one big nucleous will produced by adding two small nucleous.

Welding:
          It is the process of joining two similar or dissimilar metal by fusion.
Arc Welding -

* need D.C current

* produced (6000-7000) Degree Centegrade Temperature

Gas Welding -

* Oxy - acetylene flame join metals

* Oxygen & acetylene gas works

* produced 3200 Degree Centegrade Temperature