Flywheels: Kinetic into Potential Energy Kinetic into Potential Energy.

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Flywheels: Flywheels: Kinetic into Kinetic into Potential Energy Potential Energy

Transcript of Flywheels: Kinetic into Potential Energy Kinetic into Potential Energy.

Flywheels:Flywheels: Kinetic into Potential Kinetic into Potential

EnergyEnergy

• Ultracapacitors: – Stores energy as a charge across two plates– High power, low energy

• Flywheels:– Energy stored in a high velocity composite wheel. When

desired, energy is transferred to the axle via clutch • Batteries:

– Electrochemical reaction creates electricity as long as reactants exist in closed containers (closed system)

• Fuel Cells:– Electrochemical reaction creates electricity as long as fuel

and oxidant are supplied (open system)

Alternative Vehicle Energy Storage

Vehicle Power RequirementsPower (W,J/s) = Energy (mass*velocity2) (J, Ws) /Time (s)

• Small passenger vehicles = 70-90hp (50-65kW)

• SUV or truck = 120-180hp (90-135kW)

• Only 10-25hp when cruising (I.e. not accelerating)

• Electric Vehicles (EV’s) must store-release ALL this power/energy

• Hybrid Vehicles (HEV’s) only need recoup-release small portion of this power/energy to supplement IC engine

Flywheels

© on original matter only, Charles E. Bakis, 1999

Flywheel: Electromechanical System

Motor/Generator• Supply and remove energy via electricity

Housing• Containment (for safety in case of burst)• Vacuum (prevent heating, reduce losses)

Bearing(s)• Allow free rotation of rotor• Maintain orientation of rotor

Rotor (complete rotating assy.)• Rim (primary spinning mass)• Hub (connects rim and shaft)• Shaft (connects m/g to bearings, hub & rim)

Suspension• Shock & vibration isolation• Anchorage

Rim/Hub/Shaft Assembly

Toray Composites (America)

“Cogged” Hub Design (GS Hub)

DesignsDesigns

Ball Bearings

Source: The Barden Corp.

Ball

Outer RaceInner Race

Cage

Groove

StatorRotor

Source: Revolve, Inc. http://www.revolve.com

Magnetic Bearings

Bearings

Rotor DesignObjective: Maximize energy per unit mass

Assume: Thin rim flywheel of radius r and mass m

Energy: K = ½ I2, where = rotational velocity (rad/s) and polar moment of inertia I = mr2

K = ½ mv2 = ½ mr22

where rim velocity v = r

•Want high strength, low density & high velocity

Flywheel Pros & Cons

Pros• High round-trip efficiency in short-

term use (80-95%)

• Potentially long product life (measured in tens of years)

• Low toxicity of constituents • High power per unit mass (fast,

equal charge & discharge times)

• Easy to determine state of charge

Cons• Developing technology

• Currently expensive

• Potentially low energy per unit mass (due to bulky containment)

• Uncertain safety in a burst event:– fragmentation & ejection of

material– sudden release of energy

Source: T. Michaelis, NASA GRC, 10/99

Speed ofSound in

air (1 atm,20°C)

Concorde AssaultWeapon

KalashnikovAK-102

Carbon FiberRotor

344 m/s 688 m/s 850 m/s @muzzle

1000 m/s @rim OD

Mach 1 Mach 2.0 Mach 2.5 Mach 2.9

Perspectives

• High speed flywheel must spin in vacuum

University of Texas Center for Electromechanics

• High speed fossil-fuel powered train w/ comparable acceleration as all-electric train

• 3 MW turbine-alternator to overcome rolling and aerodynamic losses at 150 mph

• 600 MJ (165 kWh) flywheel capable of delivering an additional 3 MW for acceleration, speed maintenance on grades, and recovery of braking energy