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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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.