Page 82 - Mechanical Engineer's Data Handbook

APPLlED MECHANICS 71

Example The power of an ongine is 100 kW at a mean
speadof250nvmin-'.Theencrgy to beabsorbed by
the flywheel between maximum and minimum speeds
is 10% of the work done per revolution.
Calculate the required moment of inertia for the
flywheel if the spad fluctuation is not to cxaed 2%.
2x x 250 = 26.2 rad S- '
r
where: K = -. K, 10.02, KB=O.l, UJ~,,, =- 60
L
If K is under about 0.3, it is accurate enough to use Energy per revolution E = looooo = 24 OOo J
254)
only the first two terms containing B in each formula.
z4-2 nywfmds

Flywheels are used for the storing of enesgy in a Values of1 and k (radius of gyration)
rotating machine and to limit speed fluctuations.
Formulae are given for the calculation of the moment Solid disk:
of inertia of flywheels and for speed and energy
fluctuation. Mass m=Hb
r
Angular velocity o==2nN Radius of gyration k=-
Angular acceleration a = - fi
(02-01)
mr2 pxr4b
t Moment of inertia I = mk2 = - -
=
Acceleration torque T=la 2 2
where: I=mk2.
102
Energy stored E = -
2
Calculation of I for given speed jluctuation

If P = power,
P
Energy from engine per revolution=-
N
Cafficitnt of speed fluctuation

Example For flywheel in previous example
(J = 175 kg-m*. If the flywheel is a solid disc with
thickness of the diameter, and the density is
Coefficient of energy fluctuation 7000 kgm-3, determine the dimensions.

KEE
Required moment of inertia I=
KNOL
Thus: diameter D= 1088mm, thickneas 6- 181 mm.