DESIGN OF FLY WHEELAn Alternate way to store Energy

What is Flywheel?• A rotating mechanical device that is used to store rotational

energy.• It acts like a reservoir and stores the energy in mechanical form

• It Supply energy when required.• Releases it when it is more then required.

• Energy is stored by the formulaE = ½ Iω2

• Where “I” is the moment of inertia and it can vary for different shapes of wheels. For solid disk the “I=Mr2/2”.

• “ω” is the rotational velocity and it is in (rad/sec).

Functions and Operation

• Fly wheel smoothen out variations in the speed of a shaft

caused by torque fluctuations if source of driving torque is

fluctuating.

• It is also used to provide continuous energy in system.

• It is also used to supply intermittent pulses of energy at

transfer rates that exceed the abilities of its energy source.

How to Design Flywheel?Design Approach:-There are two stages for it• The degree at which energy is required to smoothen and its

moment of inertia.• The geometry of flywheel.Design Parameters:-• It depend upon acceptable changes in the speed.Speed fluctuation:-• The change in the shaft speed during a cycle is called the speed

fluctuation and it is given byFl =ωmax−ωmin

Design of FlywheelDesign Equation:-

IS

where “Cf” is the co-efficient of speed fluctuation and “Ek”is the kinetic energy and “avg” is the average rotational motion.Torque Variation and Energy:-

The required change in kinetic energy Ek is obtained from the known torque time relation or curve by integrating it for one cycle and it is given by

d =Ek

Geometry of Flywheel

• It can be a solid cylindrical disc.

• It can be like conventional wheel design.

• But energy requirements and size of the flywheel increases the geometry

changes to disc of central hub and peripheral rim connected by webs and

to hollow wheels with multiple arms.

Geometry of FlywheelStresses in Flywheel:-• Flywheel being a rotating disc, centrifugal stresses acts upon its

distributed mass and attempts to pull it apart.• Its effect is similar to those caused by an internally pressurized cylinder.

σ =ω2- )γ = material weight density.ω= angular velocity in rad/sec. ν= Poisson’s ratio, is the radius to a point of interestri and ro are inside and outside radii of the solid disc flywheel.

ApplicationsTypical applications for flywheels include;• Dynamic balancing of rotating elements.• Energy storage in small scale electricity generator sets.• Automotive applications such as clutches.

Advance and Modern Flywheel• Advanced flywheels are also now used for protecting against

interruptions to the national electricity grid.• The flywheel provides power during period between the loss of utility

supplied power and either the return of utility power or the start of a sufficient back-up power system

• Flywheels have also been proposed as a power booster for electric vehicles. Speeds of 100,000 rpm have been used to achieve very high power densities.

• Modern high energy flywheels use composite rotors made with carbon-fibre materials. The rotors have a very high strength-to-density ratio, and rotate at speeds up to 100,000 rpm. in a vacuum chamber to minimize aerodynamic losses.

Benefits in AerospaceFlywheels are preferred over conventional batteries in many aerospace applications because of the following benefits:

• 5 to 10+ times greater specific energy• Lower mass / kW output• Long life. Unaffected by number of charge / discharge cycles• 85-95% round trip efficiency• Fewer regulators / controls needed• Greater peak load capability• Reduced maintenance / life cycle costs

Use of Flywheel in NASANASA use the flywheel for deep space propulsion

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