Physics 100 Lecture 24. Fusion Energy and Fuel Cells April 30, 2018

Transcription

1 1 Physics 100 Lecture 24 Fusion Energy and Fuel Cells April 30, 2018

2 2 Class quiz Chs 16-18: What is the key advantage of using biofuels? A. They are non-polluting. B. Burning them releases no CO 2 C. They are not fossil fuels. D. They produce energy and increase the food supply.

3 3 The binding energy per nucleon

4 4 Light Nuclear Particles In the hot plasma of nuclear fusion the electrons are all stripped from the atoms, leaving only the nuclei Hydrogen Deuterium Tritium H D T is a single proton is a proton + 1 neutron is a proton + 2 neutrons

5 5 Nuclear Fusion Heavy hydrogen (deuterium and tritium) nuclei combine to produce helium and release energy The energy source of the stars and our Sun Controlled fusion would produce nearly limitless energy with very little pollution and no long-lived radioactive waste.

6 6 Conditions for fusion A temperature of over K is required so that the nuclei collide with enough force to overcome electrical repulsion The hot plasma must be confined to keep density sufficiently high and to prevent contact with container walls. The apparatus must allow the energy to be harnessed as electricity, for example.

7 7 Fusion Experiments The tokamak is a doughnut-shaped device that uses magnetic fields to contain and isolate the hot fusion plasma

8 8 Fusion Experiments Inertial confinement reactors use pulsed lasers to initiate fusion in very short bursts

9 9 Problems with controlled fusion Temperatures of millions of kelvin are difficult to achieve Confinement of the hot plasma is very difficult 40+ years of effort failed to produce scientific breakeven the energy produced had always been less than the total energy input until October 7, 2013 (National Ignition Facility news release) ( but still no ignition yet)

10 10 Selected Fusion Efforts Magnetic Confinement Princeton National Spherical Torus Experiment Madison Madison Symmetric Torus and many others ITER Intl Thermonuclear Exptl Reactor EAST Experimental Advanced Superconducting Tokamak (China) Inertial Confinement (laser-induced fusion) LLNL National Ignition Facility Rochester OMEGA laser system LANL ICF testing and computer analysis

11 Madison 11 Symmetric Torus ITER Photos Univ. Rochester OMEGA laser system National Ignition Facility target chamber (LLNL)

12 12 ITER (France)

13 13 ITER 27 March 2018 Bioshield completed The concrete well for the Tokamak is now complete and the first installation activities can start on the inside. An initial group of "metrology nests" have been installed on the bioshield walls for alignment purposes. Photo: ITER Organization/EJF Riche 27 MARCH 2018

14 14

15 15 Compact Fusion Reactor efforts Lockheed Martin (TheDrive news article 3/26/2018) (Expert critique 10/16/2014) MIT SPARC (3/09/2018)

16 grams of every kg of deuterium fuel in a fusion reactor is converted into energy. How much energy is released? A J B J C J D J

17 grams of every kg of deuterium fuel in a fusion reactor is converted into energy. How much energy is released? A J E mc 2 B J kg m 2 s 2 C J D J J

18 18 Suppose we run a heat engine between a fusion plasma at K and the environment at 300 K. What is the maximum possible efficiency of the heat engine? A. 50% B. 80% C. 95% D %

19 19 Suppose we run a heat engine between a fusion plasma at K and the environment at 300 K. What is the maximum possible efficiency of the heat engine? A. 50% B. 80% C. 95% D % e T 300 K K cold max 6 Thot %

20 20 The hydrogen fuel cell (Ch. 10 pp , Ch. 17 p. 536)

21 21 The PEM fuel cell

22 22 Features of a fuel cell Sir William Grove invented the fuel cell in 1839 Hydrogen gas is fed to the negative terminal (the anode) A catalyst helps the hydrogen H 2 to split (by reducing the activation barrier), and send its electrons through an external circuit while the protons pass through the membrane 2H 4H 4e 2

23 23 Features of a fuel cell Oxygen combines with the electrons at the positive terminal (the cathode) and with protons to form water e 2 2 O 4 4H 2H O The overall reaction combines hydrogen and oxygen to produce electricity and water. 2H O 2H O 2 2 2

24 24 The proton exchange membrane (PEM) fuel cell Also known as polymer electrolyte membrane fuel cell Has a high power density and low operating temperature The electrolyte is a specially treated polymer (chemically related to Teflon) membrane that conducts only positive ions The membrane must be hydrated (7 water molecules for every proton conducted!) The membrane is poisoned by carbon monoxide

25 25 The proton exchange membrane fuel cell The anode-membrane-cathode assemblies are stacked for higher voltage

26 26 Fuel cell problems PEM cells: Hydration of the membrane requires careful water control and/or pressurization (adds weight, complexity). New membranes such as PBI may require less water. For all fuel cells, drawing large currents reduces performance Required catalysts are often expensive and rare metals like platinum

27 27 Fuel cell losses V I R Ohm s Law Applet

28 28 PEM Fuel Cell Stack 10 kw Fuel Cell Power Supply GENEPAC by PSA Puegot Citroën, France

29 29 Other types of fuel cells Phosphoric Acid Molten Carbonate Solid Oxide Alkali See comparison chart from the Department of Energy fuel cell site

30 30 Compare Fuel Cell Types

31 31 Which of the following statements is FALSE? A. Catalysts help fuel cells increase the gas transport rate to the electrodes. B. Fuel cells operate on the chemical reaction that combines hydrogen and oxygen. C. Fuel cells are like a battery with a continuous supply of chemical reactants. D. The only outputs of a fuel cell are water and electrical energy.