Definitions Of Terms Used In Mechanical Industry

ISHAN TOPRE · 2011-04-12T15:22:42+00:00

Let us start something like defining terms of hard core mechanical industry. I will set the ball rolling. Reynolds number: It is defined as the ratio of inertia force of a flowing fluid and the viscous force of the fluid. Inertia force= Mass*Acceleration of the flowing fluid.= ρ*V*velocity. where ρ=density of fluid and V is volume. Viscous force= Shear stress*Area= τ*a By definition of Reynolds number R=VL/ν. Where ν=μ/ρ. Or R=ρVd/μ Then there is also Reynolds model law It is a law in which models are based on Reynolds number. These models include 1.Pipe flow problems 2.Resistance experienced by submarines, airplanes, fully immersed bodies etc.

Definitions Of Terms Used In Mechanical Industry

ISHAN TOPRE
@ishan-nohePN

Updated: Apr 12, 2011

Views: 1.5K

Let us start something like defining terms of hard core mechanical industry. I will set the ball rolling.

Reynolds number: It is defined as the ratio of inertia force of a flowing fluid and the viscous force of the fluid.

Inertia force= Mass*Acceleration of the flowing fluid.= ρ*V*velocity.

where ρ=density of fluid and V is volume.

Viscous force= Shear stress*Area= τ*a

By definition of Reynolds number R=VL/ν.

Where ν=μ/ρ. Or

R=ρVd/μ

Then there is also Reynolds model law It is a law in which models are based on Reynolds number. These models include
1.Pipe flow problems
2.Resistance experienced by submarines, airplanes, fully immersed bodies etc.

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jhbalaji

Member • Apr 12, 2011

BottleNeck - Process that Consumes more time
Through Put Rate - Output Rate for a period of time

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ISHAN TOPRE

Member • Apr 13, 2011

Froude number:

Froude number is the ratio of roots of inertia force of a flowing fluid to the gravity force.

Mathematically it can be expressed as F= Square root(Fi/Fg)= V/square root( L*g)

Where V=Volume=L*L*L.

Froude's model law:

It is the situation when the models are based on Froude's number. We can apply this model only when the only dominant force is the force due to gravity on system. Consider the following examples in which it is generally used.
1.Free surface flows
2.Fluids of different densities flowing over each other.
3.Flows where waves are formed etc.

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ISHAN TOPRE

Member • Apr 13, 2011

Euler's number: It is the ratio of square roots of flowing fluid to the pressure force exerted by fluid.

mathematically it can be stated as Fe= Square root(Fi/Fp)=V/square root(p/ρ)

Where Fp=intensity of pressure*Area and Fi=ρAV*V

Euler's model law: When the models are based on Euler's number then we use this model law.
When the pressure forces alone are applicable that time only we use Euler's model law.

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ISHAN TOPRE

Member • Apr 15, 2011

Model Analysis:

Now many must be wondering what a model analysis is. 😀 A model is a prototype of actual structure. I would rather say that it is even a previous version of a prototype It is quite important as far as the fluid flow is concerned. I have noted a few advantages of model analysis which I want to share it here with you.

1. We can predict the merits of alternative designs with this model testing.

2. The tests performed on models can be used for obtaining the performance of prototypes only if a complete similarity exists between model and the prototype.

3.The performance of hydraulic system can be predicted in advance.

4.We can use dimensional analysis as a tool for establishing relations between variable factors.

Hello friends, not so technical. But I think for buddying engineers it might be useful when they begin the model analysis. It may give them an insight of the real problem.

What say crazyengineers? 😁

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ISHAN TOPRE

Member • Apr 15, 2011

Dynamic similarity:

Dynamic similarity is said to exist, between model and the prototype if the ratios of corresponding forces acting at corresponding points are equal. Also their directions should be same.

In simple terms it means similarity of forces between model and prototype. 😀

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yadavundertaker mohit

Member • Apr 15, 2011

dynamic similarity and model analysis together are used to find the performance of turbines before actually installing them. they are the most powerful tools in fluid machinery and fluid dynamics.

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yadavundertaker mohit

Member • Apr 15, 2011

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.

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ISHAN TOPRE

Member • Apr 15, 2011

Orifice plate or Orifice meter:

It is basically used to measure fluid flow through a pipe. It can be used as a replacement for Venturimeter. Though the efficiency in measuring fluid flow by orifice plate is quite low mostly 0.55.

Orifice meter is nothing but a flat circular plate which has a circular sharp edged hole. this plate is kept concentric with the pipe. The hole diameter is usually half the diameter of orifice plate.

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ISHAN TOPRE

Member • Apr 15, 2011

Models can be classified as

1.Distorted models and 2. Undistorted models.

1.Distorted models:
A model is distorted if it is not geometrically similar to prototype. In other words, in case of distorted model, we take different scales. In case of fluid flows like rivers and reservoirs two types of scale ratios are taken viz; Horizontal and linear are taken. Hence the river models are Distorted models.

2.Undistorted models:
If the scale of linear dimensions of model and its prototype is same then we call the model as distorted model.

I just want to ask now, is anyone having first hand experience of models? Can you tell us more? Then this is the right place to share. 😀

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ISHAN TOPRE

Member • Apr 16, 2011

Laminar flow:

In case of laminar flow, the fluid particles move in a straight line path in layers or laminae hence the name. The path of individual fluid flow do not cross each other. This type of flow is ideal and not seen in day to day cases. the velocity of flow should be very low.

In case of a model, a flow is said to be laminar only if the Reynold's number (R=ρVd/μ) is less than 2000.

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ISHAN TOPRE

Member • Apr 16, 2011

Turbulent flow:

Whenever the velocity of fluid flow is more or the quantity of fluid moving is less then we consider it as a case of turbulent flow.
In turbulent flow Reynold's number (R=ÏVd/Î¼) is less more than 4000 in case of a pipe flow.

Laminar flow changes to turbulent flow when any one or more of these condition prevail to increase Reynold's number greater than 4000:
1.Velocity of laminar flow is increased
2.Viscosity is decreased
3.Diameter of pipe is decreased.

It should be noted that there is a change from turbulent to laminar flow and vice versa as the fluid passes from different cross-section of same pipe, depending upon the existing conditions. However, practically we see only turbulent flow. 😀

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ISHAN TOPRE

Member • Apr 16, 2011

Sink flow: It is a type of flow in which the direction of flow of fluid is radially inwards towards the point where it disappears at a constant rate. This is opposite to the source flow where the fluid flow emanates from a certain source.

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ISHAN TOPRE

Member • Apr 17, 2011

The Prandtl Number is a dimensionless number . It is the ratio of momentum diffusivity (kinematic viscosity) and thermal diffusivity and can be expressed as

Pr = v / Î± (1)

where

Pr = Prandtl's number

v = momentum diffusivity (m2/s)

Î± = thermal diffusivity (m2/s)

The Prandtl number can alternatively be expressed as

Pr = Î¼ cp / k (2)

where

Î¼ = absolute or dynamic viscosity (kg/m s, cP)

cp = specific heat capacity (J/kg K, Btu/(lb oF))

k = thermal conductivity (W/m K, Btu/(h ft2 oF/ft))

The Prandtl Number is used in heat transfer and free and forced convection calculations.

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ISHAN TOPRE

Member • Apr 17, 2011

The Grashof number: is a dimensionless number in fluid dynamics which approximates the ratio of the buoyancy force to the viscous force acting on a fluid. It is named after the German engineer Franz Grashof.

where
g = acceleration due to gravity
Î² = volumetric thermal expansion coefficient
Ts = source temperature
Tâˆž = quiescent temperature
L = characteristic length
Î½ = kinematic viscosity
The product of the Grashof number and the Prandtl number gives the Rayleigh number, a dimensionless number that characterizes convection problems in heat transfer.
There is an analogous form of the Grashof number used in cases of natural convection mass transfer problems.

where

and
g = acceleration due to gravity
Ca,s = concentration of species a at surface
Ca,a = concentration of species a in ambient medium
L = characteristic length
Î½ = kinematic viscosity
Ï = fluid density
Ca = concentration of species a
T = constant temperature
p = constant pressure

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ISHAN TOPRE

Member • Apr 17, 2011

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ISHAN TOPRE

Member • Apr 18, 2011

Nusselt number (Nu): It is defined as the ratio of convection heat transfer to fluid conduction heat transfer under the same conditions. Consider a layer of fluid of width L and temperature difference.

It is given by

Now try to observe this image and understand Nusselt number

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ISHAN TOPRE

Member • Apr 18, 2011

Coefficient of Thermal expansion(Linear) : The linear coefficient of thermal expansion a (Greek letter alpha) gives the degree of a material as to how much will it expand for each degree of temperature increase, as given by the formula:

Î±=(dl/dt)/L

Where dl = the change in length of material in the direction being measured
l = overall length of material in the direction being measured
dT = the change in temperature over which dl is measured

Its unit is per kelvin or per degree celsius

As an exercise Try this. Try to configure what is being explained in this image

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ISHAN TOPRE

Member • Apr 20, 2011

Countersunk: To be simple, it is a conical hole in any object.

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ISHAN TOPRE

Member • Apr 21, 2011

Hole basis system:

The shaft are designed as per the existing holes. This is the prevalent system in any industry because it is easy to design a shaft that to vary diameter of a hole.

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ISHAN TOPRE

Member • Apr 21, 2011

Shaft basis system:

Here the holes are designed as per the shaft. This is difficult practice. Rarely used as per my knowledge.

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ISHAN TOPRE

Member • Apr 21, 2011

Clearance fit: Some clearance is left.

Transition fit: Exactly the same shape.

Interference fit: very tight fit.

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ISHAN TOPRE

Member • Apr 21, 2011

Hydraulics: Any machine which works on fluids other than Air. The science of that is called hydraulics.

For example see hydraulic actuator:

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ISHAN TOPRE

Member • Apr 21, 2011

Pneumatics: Any machine which works on Air as a working fluid its science of that is called pneumatics.

For example see the pneumatic actuator

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ISHAN TOPRE

Member • Apr 21, 2011

Gauge pressure: Pressure with respect to ambient air temperature or temperature of surroundings.

Vacuum pressure: The pressure in a vacuum condition is called is called vacuum pressure.

Atmospheric pressure: Pressure of air around us.

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ISHAN TOPRE

Member • Apr 21, 2011

Pyrometer: A type of temperature measuring device adopted for measuring super high temperatures.

Image source shows a suction pyrometer.

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ISHAN TOPRE

Member • Apr 21, 2011

Draught in a chimney: The pressure difference required for free flow of flue gases in a plant containing chimney is called draught.

It is expressed in mm of water column.

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ISHAN TOPRE

Member • Apr 21, 2011

Tempering:

It is a heat treatment process. It is used to make metals tough. It is done by heating steel at a temperature range of about 150 to 250 Degree centigrade. Then it is cooled at a slow rate.

This makes the hard steel to get soften.

See this diagram.

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ISHAN TOPRE

Member • Apr 21, 2011

Quenching: It is a hardening process. The steel transforms in to martensite. It is similar to tempering with only difference that we have rapid cooling.

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PraveenKumar Purushothaman

Member • Apr 21, 2011

Austempering is an isothermal heat treatment that is applied to ferrous metals, most notably steel and ductile iron. In steel it produces a lower Bainite microstructure whereas in cast irons it produces a structure of acicular ferrite and high carbon, stabilized Austenite known as ausferrite. It is primarily used to improve mechanical properties. Austempering is defined by both the process and the resultant microstructure . Typical austempering process parameters applied to an unsuitable material will not result in the formation of Bainite or ausferrite and thusly the final product will not be called austempered. both microstructures may also be produced via other methods. for example, they may be produced as-cast or air cooled with the proper alloy content. These materials are also not referred to as austempered.

Process:

Source: <a href="https://en.wikipedia.org/wiki/Austempering" target="_blank" rel="nofollow noopener noreferrer">Austempering</a>

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ISHAN TOPRE

Member • Apr 22, 2011

MARTEMPERING is a term used to describe an interrupted quench from the austenitizing temperature of certain alloy, cast, tool, and stainless steels.

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ISHAN TOPRE

Member • Apr 22, 2011

Fillet: To cut a circular round groove.

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ISHAN TOPRE

Member • Apr 22, 2011

Chamfer: To cut a straight edge.

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PraveenKumar Purushothaman

Member • Apr 22, 2011

Knurling is conducted on a lathe, for getting a visually-attractive diamond-shaped (criss-cross) pattern by cutting or rolling into metal. This pattern allows hands or fingers to get a better grip on the knurled object than would be provided by the originally-smooth metal surface.

Close-up shot of a diamond-pattern knurling on a cylindric work piece. Knurling method: left/right with tips raised (DIN 82 name: RGE), spiral angle: 30Â°, pitch: 1 mm, profile angle: 90Â°. Object's diameter: 24 mm, material: aluminium (silver anodised).

Source: <a href="https://en.wikipedia.org/wiki/Knurling" target="_blank" rel="nofollow noopener noreferrer">Knurling</a>

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yadavundertaker mohit

Member • Apr 22, 2011

NORMALISING:

it is a heat treatment process which is used to relieve internal stresses and refining the grain size which improve the mechanical properties. In this process after heating the metal it is cooled in still air to room temperature.

QUENCHING:
In quenching the metal is cooled rapidly in cold water. It is used to increase the toughness of the metal or alloys.

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ISHAN TOPRE

Member • Apr 22, 2011

@ Yadavundertaker: By the way metals like steel gets hardened and not toughened by quenching. Correct me if I am wrong. 😀

Hobbing: It is a process of making gears and similar objects. It can be done on a standard milling machine or a special hobbing machine.

In our workshop practicals we used milling machine.

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ISHAN TOPRE

Member • Apr 22, 2011

Nowadays every one is talking about pressure vessels. So let us define pressure vessel

Pressure vessel is a cylindrical container to hold fluids at a high pressure. They are generally boilers or even cooking gas cylinders. It is as simple as that. 😀

Now see this big one.

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ISHAN TOPRE

Member • Apr 23, 2011

Natural convection:

It is the cooling or heating of an object without the aid of external agents i.e.; naturally.It is also called Free convection.

This figure shows cooling of heated pipe by free convection.

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ISHAN TOPRE

Member • Apr 23, 2011

Forced convection:
This is heat transfer due to external agencies whether cooling or heating.

This figure shows heating of water by forced convection.

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yadavundertaker mohit

Member • Apr 23, 2011

Why pressure vessels or gas cylinders are made cylindrical in shape?(mostly asked interview question)

because at sharp edges there will be a very high pressure concentration which result in explosion of the container. Thats why we have cylindrical shapes.

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Ramani Aswath

Member • Apr 30, 2011

ishutopre
Forced convection:
This is heat transfer due to external agencies whether cooling or heating. This figure shows heating of water by forced convection. IMG]https://www.physics.arizona.edu/~thews/reu/Convection.bmp[/IMG]

There seems to be some issue in this image. It shows a pan with presumably water kept on a gas flame. The bottom surface gets hot and heats the adjacent water layer. This expands, becomes lighter and floats up. The colder surrounding water moves in, gets heated in turn and the whole process repeats. This is the classic thermal syphon and is an example of natural convection. The heat transfer coefficient is small in this case and it takes time to heat the whole mass. There will be some stratification also.

On the other hand, If one puts in a spoon and stirs up the fluid, one 'forces' the thinning of the Prantl layer at the bottom thereby increasing the heat transfer coefficient. The added velocity convects away the heat faster from the point of generation. The image seems to miss out this 'forcing' of convection by an external velocity.

Bioramani

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