View Factor Orientation (or View factor or shape factor) plays an important role in radiation heat transfer. View factor is defined as, "fraction of radiation leaving surface 'i' and strike 'j' ". Summation Rule (View Factor) If there is are similar surfaces 'i' and 'j' , then: Blackbody Radiation Exchange Radiation Exchange between Opaque, Diffuse, Gray surfaces in an Enclosure 1. Opaque 2. Surfaces 3. Two surface enclosure Radiation Shield It is used to protect surfaces from radiation act like a reflective surface. References: Material from Class Lectures + Book named Fundamentals of Heat and Mass Transfer by Theodore L. Bergman + My knowledge. Photoshoped pics are developed. Some pics and GIF from Google. Videos from YouTube ( Engineering Sights ).
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Flywheel
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Flywheel
It is defined as, "a machine element which serves as reservoir which stores energy during the period when energy supply is more than the requirement and releases it when energy is less than requirement".
Used in IC, reciprocating (compressors or pumps) engines, presses, etc.
Excess energy is stored in flywheel and release to crankshaft during other strokes in which no energy is developed.
If space is small ↠ use small diameter and solid flywheel.
If space is not limited (like for presses, crushing machine, hammering machine) ↠ use large diameter and hollow flywheel.
Purpose of flywheel is to:
reduce amplitude of speed fluctuation (sinusoidal) for constant power output.
reduce maximum torque required.
energy stored and release when needed during cycle.
Parts of flywheel are
Rim ↠ outer portion of flywheel (which is like a wheel).
Hub ↠ center part which is installed on shaft.
Arms or Needle ↠ rods joining rim to hub.
Parameter that effects rotation of flywheel (centrifugal force) are:
Diameter of flywheel
Mass of flywheel (which can increase energy).
Coefficient of Fluctuation of Speed
Difference between maximum and minimum speeds during cycle is called Maximum Fluctuation of Speed.
Max. fluctuation of Speed = ΔN = N1 - N2
Ratio of maximum fluctuation of speed to the mean speed is called Coefficient of Fluctuation of Speed.
Some noteworthy points are:
Coefficient of Speed Fluctuation is a limiting factor in design of flywheel and depends on the nature of machine to which flywheel is employed.
The reciprocal of coefficient of speed of fluctuation is known as Coefficient of Steadiness (m).
The greater the forces applied, the higher the Cs.
Fluctuation of Energy
The fluctuation of energy is determined by turning moment diagram for one complete cycle of rotation. Consider a turning moment diagram for a single cylinder double acting steam engines.
Double acting engine ↠ which gives 2 stroke in each rotation of shaft (power and compression strokes).
To convert sinusoidal wave output into constant output (area under aAFe), we have following steps:
Step # 01
Work done by the engine when crank moves from point a to p. Energy required is equal to area under aABp. Less work is done by engine (by area aAB) than requirement.
Step # 02
Work done by the engine when crank moves from point p to q. Energy required is equal to area under pBbCq. More work is done by engine (by area BbC) than requirement which is stored in flywheel and its speed increases.
Step # 03
Work done by the engine when crank moves from point q to r. Energy required is equal to area under qCcDr. Less work is done by engine (by area CcD) than requirement.
Step # 04
Work done by the engine when crank moves from point r to s. Energy required is equal to area under rDdEs. More work is done by engine (by area rDEs) than requirement which is stored in flywheel and its speed increases.
Step # 05
Work done by the engine when crank moves from point s to e. Energy required is equal to area under SEFe. Less work is done by engine (by area EFe) than requirement.
Fluctuation of Energy
The variations of energy above and below the mean resisting torque line is called Fluctuation of Energy. The areas are BbC, CcD, DdE, aAB, EFe.
Max. Speed of Engine → At q and s, flywheel absorbs energy while the crank moves from p→q and r→s.
Min. Speed of Engine → At p and r, flywheel given out some energy when crank moves from a→p and q→r.
The difference between maximum and minimum energies is known as Maximum Fluctuation of Energy.
Maximum Fluctuation of Energy
Consider turning moment diagram for a multi-cylinder engine.
Coefficient of Fluctuation of Energy
It is the ratio of max.fluctuation of energy to the work done per cycle.
Energy Stored in a Flywheel
Let,
The radius of gyration is equal to mean radius of the rim (R) because thickness of rim is very small as compared to the diameter of rim.
Stresses in Flywheel
Consider a small element of rim. So, volume of small element is given by:
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Projection: The term Projection is defined as: Presentation of an image or an object on a surface. The principles used to graphically represent 3-D objects and structures on 2-D media and it based on two variables: Line of Sight. Plane of Projection. Line of Sight & Plane of Projection: Line of sight is divided into 2 types: Parallel Projection Converging Projection & A plane of projection is an imaginary flat plane upon which the image created by the lines of sight is projected. Orthographic Projection: When the projectors are parallel to each other and perpendicular to the plane of projection. The lines pf sight of the observer create a view on the screen. The screen is referred to as the Plane of Projection (POP). The lines of sight are called Projection lines or projectors. Rules of Orthographic Projection: Edges that are parallel to a plane of projection appear as lines. Edges that are incl...
Gear Forming by Machining Formation of gear through machining consists of following methods: Form Milling by Disc Cutter Form Milling by End Mill Cutter Shaper, Planner and Slotter Broaching 1. Form Milling by Disc Cutter It is defined as, " Tooth is cut one by one by plunging the rotating cutter into the blank " . Each gear needs a separate cutter. 8 - 10 standard cutters are available for producing 12 - 120 teeth gears. Used for big spur gears of large pitch. 2. Form Milling by End Mill Cutter It includes the cutting of tooth at a time and then indexed for the next tooth space for cutting. For a small volume production of low precision gears. Set of 10 cutters ↠ 12 - 120 teeth gears . Used for teeth of large gears/module. To reduce cost, same cutter is often used for multiple sized gears resulting in profile errors . Characteristics: Use of Hardened stainless steels (HSS) form milling cutters. Use of Ordinary milling machines. Low production rate (need of indexing...
If you use a flywheel with greater mass, will it vibrate more?
ReplyDeleteFrom my knowledge, vibrations increase with the increase in rotating mass.
DeleteGenerally, journal bearings are used for keeping flywheel at its place. For a greater mass flywheel, vibration dampers are used to reduce vibrations.