Fusion reactors

1
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.

2
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!

3
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

4
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
• Fhmsg, 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

5
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.

6
Making current cars more efficient

• Minimize the force required
• mamsg CrmvCD Af v2 /370
• Make m small
• Make Cr small
• Make CD small
• Make Af small
• Make v small
• Or any combination of reducing these values

7
Alternatives to the internal combustion engine

• Flywheels
• Electric batteries
• Hybrids
• Alcohol
• Hydrogen

8
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 I?2
• where I moment of inertial of the
  flywheel, and ? 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.

9
Flywheel vehicles

• 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.

10
Hybrids

• Still use gasoline powered engines, but combine
  them with (usually) batteries to achieve better
  fuel economy.
• Different from a flex-fuel vehicleFlexible 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

11
Pure electric vehicles

• 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