Transcript Fusion reactors

Fusion reactors
• Main problem is maintaining
the fusion material at high
enough T so that fusion
produces the bulk of the
energy (break even)
• Confined plasma via a
magnetic field so it does not
contact the container walls
(which would cool it and
quench the reaction)
• Not nearly as hazardous as
fission reactors, most studies
show severe failures to be
contained within the plants
themselves.
Barriers to fusion power
• Scientific feasibility of the reactions
• Economics
• Damage to reactor components due to large
flux of high energy neutrons
• Availability of materials to build the reactors
• Maybe in 50 years -but we have been saying
that for 50 years!
Planes, trains and automobiles
• 27% of the total national energy budget goes
into transportation
• Of this 27%, 35% is used by automobiles
• Autos are among the least energy efficient
modes of transportation (Bicycles are number
1)
• Rely in the internal combustion engine
What does it take to move a car?
• Four force terms need to be considered:
• Force needed to accelerate the vehicle
– Fa = ma
• Force needed to climb any hills
– Fh=msg, where s is the slope of the hill
• Force needed to overcome internal energy losses (tire flexure,
wheel bearings, friction with the road surface, etc)
– Fr = Crmv, where Cr is a constant term
• Force needed to overcome aerodynamic drag on the vehicle,
depends upon speed.
– Fad = CD Af v2 /370 where CD is the aerodynamic drag coefficient, Af is
the frontal area of the vehicle.
• So the total force required is the sum of these 4 terms:
– FT = Fa + Fh + Fr + Fad
Energy required
• The energy required will be equal to the work
done by the force over a given distance or
– E = W = Fd or
– E = Pt, where P is the power output and t is the
time the vehicle is operated or
– E = Fvt
• So to minimize energy, you need to minimize
the forces.
Making current cars more efficient
• Minimize the force required:
– ma+msg+ Crmv+CD Af v2 /370
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Make m small
Make Cr small
Make CD small
Make Af small
Make v small
Or any combination of reducing these values
Alternatives to the internal
combustion engine
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Flywheels
Electric batteries
Hybrids
Alcohol
Hydrogen
Flywheels
• Energy storage device
• Flywheel is spun up and the energy is stored as rotational energy to
be used at a later time
• Designed to resist losses of rotational energy due to friction, etc
• Energy stored is given by
• Ek = Iω2
where I = moment of inertial of the flywheel, and ω is the angular
velocity.
• The moment of inertial is a function of the mass and the distance
from the center of rotation
• So the structure of the flywheel and the rotational rate determine
the amount of energy stored.
• Ultimate limit on the energy storage is the strength of the flywheel.
Spin it too fast, and it will tear itself apart.
Flywheel vehicles
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Could extract energy from braking-rather than waste the energy into frictional
heating of brakepads, reverse the engine and spin up the flywheel.
Need to be recharged on the power gird, saves gas, but drains electricity
The big implementation problem is materials which can withstand the stress
needed to spin the flywheel fast enough to make this a worthwhile alternative.
Prototype mass transportation vehicles have been built (In Sweden and by
Lockheed)
Used in Formula 1 racing to recover energy lost in braking and along with a
continuously variable transmission to improve Formula one car acceleration.
Also used in the incredible hulk roller coaster at Universal Islands of Adventure in
Orlando, Fl.
– Ride starts with an uphill acceleration, rather than a gravity drop.
– Flywheels are used to provide the initial energy impulse, otherwise the park would brown out
the local energy grid everytime the ride began.
Hybrids
• Still use gasoline powered engines, but combine them with (usually)
batteries to achieve better fuel economy.
• Different from a flex-fuel vehicle:Flexible fuel vehicles (FFVs) are designed
to run on gasoline or a blend of up to 85% ethanol (E85).
• no loss in performance when operating on E85.
• FFVs typically get about 25-30% fewer miles per gallon when fueled with E85.
• Idea is to use as small as possible a gasoline engine, and only when it can
be run at peak efficiency.
• Use excess power to recharge the battery (no need to tap the power grid)
• Use energy from braking (regenerative braking) to also charge the battery
• Work best in stop and go driving.
• Major initiative in the auto industry right now.
• Result in using less gas-stretching our fossil fuels
• In 2011, there will be 39 different models of hybrids available
Pure electric vehicles
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Powered by an electric motor, rather than a gasoline engine
Needs batteries – current generation of batteries have 520 times less energy
density than gasoline.
Need to be charged from the power grid
If all the vehicles in the US were converted to electric cars, it would triple the
current electric energy generation
Recharging electric vehicles takes time- several hours, whereas it takes minutes to
refill your gas tank
Batteries have a finite lifetime, need to be replaced every 2-3 years at a current
cost of $1000.00
Limited range (less than 100 miles before recharging is needed)
Ultimate limit is current battery technology-current lead acid batteries have not
changed much in 100 years.
Environmental effects from the disposal of lead acid batteries
No new promising battery technologies on the horizon to substantially help
electric cars