Definitions Of Terms Used In Mechanical Industry
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
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. Posted in: #Mechanical
Through Put Rate - Output Rate for a period of time
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)
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.
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.
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? 😁
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. 😀
Image source: Google Image Result for https://www-mdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/fprops/dimension/dsim.gif
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:
high head ,impulse turbine and axial flow.
medium head ,reaction turbine.
low head ,high discharge reaction turbine.
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.
Image credit: Google Image Result for https://saba.kntu.ac.ir/eecd/ecourses/instrumentation/projects/reports/Flowmeter/orifice_files/DP_OrificePlate_cal.gif
1.Distorted models and 2. Undistorted 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.
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. 😀
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.
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=ρVd/μ) 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. 😀
image credit : https://www.google.com/imgres?imgurl...e=2&ndsp=8&ved=1t:429,r:1,s:9&biw=888&bih=467
image credit: Google Image Result for https://4.bp.blogspot.com/_gQen9AZHznw/TI1G3SQjAWI/AAAAAAAAB2Y/qytKZJDi9ig/s320/expZ-radialSink-230.png
Pr = v / α (1)
Pr = Prandtl's number
v = momentum diffusivity (m2/s)
α = thermal diffusivity (m2/s)
The Prandtl number can alternatively be expressed as
Pr = μ cp / k (2)
μ = 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.
Image source: Google Image Result for https://www.argentumsolutions.com/images/tutorials/heat/BoundaryLayers.gif
g = acceleration due to gravity
β = volumetric thermal expansion coefficient
Ts = source temperature
T∞ = quiescent temperature
L = characteristic length
ν = 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.
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
ν = kinematic viscosity
ρ = fluid density
Ca = concentration of species a
T = constant temperature
p = constant pressure
Article Source: Grashof number: Definition from Answers.com
It is given by
Now try to observe this image and understand Nusselt number
Image source: Google Image Result for https://easycalculation.com/physics/fluid-mechanics/images/nusselt-number.gif
Google Image Result for https://www.thermal-wizard.com/tmwiz/convect/forced/fd-tube/fd-tube.gif
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
Image source: Google Image Result for https://www.hitachi-metals.co.jp/e/prod/prod06/img_p06/16_1.gif
Image source: Google Image Result for https://www.tpub.com/content/draftsman/14276/img/14276_161_1.jpg
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.
Image source: Google Image Result for https://img.tfd.com/ggse/af/gsed_0001_0008_0_img1813.png
Here the holes are designed as per the shaft. This is difficult practice. Rarely used as per my knowledge.
Transition fit: Exactly the same shape.
Interference fit: very tight fit.
Image source: Google Image Result for https://www.mech.uq.edu.au/courses/mech2110/standard_fits/types_of_fits.gif
For example see hydraulic actuator:
Image source: Google Image Result for https://www.tpub.com/content/doe/h1013v2/img/h1013v2_166_1.jpg
For example see the pneumatic actuator
Image source: Google Image Result for https://openticle.com/images/modul%204%20figure%2034%20pneumatic%20actuator.GIF
Vacuum pressure: The pressure in a vacuum condition is called is called vacuum pressure.
Atmospheric pressure: Pressure of air around us.
Image source: https://www.google.com/imgres?imgurl...&page=1&ndsp=8&ved=1t:429,r:1,s:0&tx=89&ty=38
Image source shows a suction pyrometer.
Image source: Google Image Result for https://www.chec.kt.dtu.dk/upload/institutter/kt/chec/checlabpix07/suction_pyrometer.jpg
It is expressed in mm of water column.
Image source: Google Image Result for https://images-mediawiki-sites.thefullwiki.org/11/2/8/8/0981215960866399.png
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.
Image source: Google Image Result for https://info.lu.farmingdale.edu/depts/met/met205/cquenchtemp.JPG
Image source: Google Image Result for https://metallurgyfordummies.com/wp-content/uploads/2011/02/Tempering.gif
Source: Austempering - Wikipedia
Image source: Google Image Result for https://info.lu.farmingdale.edu/depts/met/met205/martempering.JPG
Image source: Google Image Result for https://www.plinthandchintz.com/mambo/images/stories/DesignSpeak/fillet.jpg
Image source: Google Image Result for https://www.wellnitz.com/_images/8x8x16_1.75Chamfer.JPG
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: 30°, pitch: 1 mm, profile angle: 90°. Object's diameter: 24 mm, material: aluminium (silver anodised).
Source: Knurling (Wikipedia)
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.
In quenching the metal is cooled rapidly in cold water. It is used to increase the toughness of the metal or alloys.
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.
Image source: Google Image Result for https://www.gearshub.com/gifs/gear-hobbing-process.jpg
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.
Image source: Google Image Result for https://www.tankpressure.com/wp-content/uploads/2009/10/pressureVessel.jpg
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.
Image source: Google Image Result for https://www.owlnet.rice.edu/~ceng402/ed1projects/proj00/lear/pipe.gif
This is heat transfer due to external agencies whether cooling or heating.
This figure shows heating of water by forced convection.
Image source:Google Image Result for https://www.physics.arizona.edu/~thews/reu/Convection.bmp
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.
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.
Torque or Turning Force:
It is the total amount of force which is required to create acceleration on moving substance.
Two forces those acts on equally,parallely & oppositely on two separate points of same material.
It is the amount of moving effect which is gained for action of turning force.
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.
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.
First i go with some documentary terms which was used extensively in mechanical industry audits,
PPAP- Production part approval process
FMEA-Failure mode and effect analysis
DFMEA- Design Failure mode and effect analysis
PFMEA-Process Failure mode and effect analysis
MSA- Measurement system analysis
GR&R- Gauge repeatability and reproducibility
SPC -Statistical process control
PC chart- Process control chart
FO report- First off report
PSW- Part submission warrant
CAPA- Corrective actio nad preventive action
GD&T- Geometric dimensioning and tolerancing
RPN- Risk priority number