You are designing an industrial flywheel, a device for storing mechanical energy
ID: 1447336 • Letter: Y
Question
You are designing an industrial flywheel, a device for storing mechanical energy in the form of rotational kinetic energy (the stored energy can be harnessed by engaging a clutch). The design requirements are that the flywheel should store 250 kJ of energy when rotating at 1500 rpm, the radius of the flywheel should be 55 cm, and it is to be made from steel with a density of 7850 kg/m^3 .
(a) Find the required rotational inertia.
(b) If the flywheel is to be constructed as a simple disk, what will its mass need to be?
(c) How thick would the disk need to be?
Explanation / Answer
given
KE = 250 kJ
w = 1500 rpm = 1500*2*pi/60 = 157 rad/s
R = 55 cm = 0.55 m
rho = 7850 kg/m^3
a) Apply, KE = (1/2)*I*w^2
==> I = 2*KE/w^2
= 2*250*10^3/157^2
= 20.3 kg.m^2
b)
Apply, I = 0.5*M*R^2
==> M = 2*I/R^2
= 2*20.3/0.55^2
= 134 kg
c) Apply, mass = density*volume
M = rho*pi*R^2*t
==> t = M/(rho*pi*R^2)
= 134/(7850*pi*0.55^2)
= 0.018 m or 1.8 cm
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