- 1. Basic concepts (I)How do you define energy?
2. Energy: definition related to physical forces Definition of energy: in physics, energy is thework that a force can or could do. Forces are: gravitational (due to interaction between mass and energy concentrations) electric (attraction and repulsion of charged particles) magnetic (attraction and repulsion of magnetic objects) chemical (driving chemical reactions: electro-magnetic) nuclear (binding nuclei together or breaking unstable apart) mechanic (impact of one moving object on another) 3. Force of Gravity On earth, we are constantly under the forceof gravity. What types of energy does gravityproduce? Acceleration of falling objects Altitude and depth pressure gradients of theatmosphere and the seas Part of the fusion of the earths core F 4. Mechanical Force Mechanic forces are when one object hitsanother. What type of energy does thisproduce? Acceleration / deceleration of interacting objects Heat dissipation within the objects Change of shape of objects vv v v 5. Electric & magnetic forces Cause electrons to be attracted to nuclei inatoms -> basis for chemistry Cause charges (electric current) to flow inelectric circuits -> basis for energy used inelectronics, lights, appliances Cause needle of compass to point north 6. Energy: definition, continued Energy is can also be inherent in a system,without any forces acting on it. Types of inherent energy are: In a steadily moving particle: mass x velocity2 In a mass: mass x (speed of light)2 = mc2 In a body at a certain temperature:(heat capacity of body) x temperaturefor water, heat capacity is, 1 calorie per gram perdegree Celsius or Kelvin In a chemical compound:2 H2 + O2 -> 2 H2O , Enthalpy released = -571.6 kJ/mol 7. Forms of energy Energy can take many forms kinetic (movement of a mass) electric, magnetic (movement of charges or electromagnetic fields radiating) Electricity Radiation (light) chemical (molecules with internal energy) heat (thermal) (statistical expression of kinetic energy of many objects in a gas, liquid or solid - or even radiation) potential (water above a dam, a charge in an electric potential or a battery)Other examples? 8. SI units for energy The SI unit of energy is a Joule: 1 kg*m2/s2 =1 Newton*m (Newton is the unit of Force) mass * velocity 2 mass * g * height (on earth, g = 9.81 m/s2 ) for an ideal gas = cvkBT (cv =3/2 for a monatomic gas) Power is energy per time: 1 Watt = 1 Joule/s= 1 kg*m2/s3 most commonly used in electricity, but also for vehicles in horsepower (acceleration time) 9. Other common energy units http://www.onlineconversion.com/energy.htmEnergy conversion Unit Quantity to Note 1calorie= 4.1868000 Joule 1kiloWatthour=kWh=3600000 Joule Apowerof1kWforadurationof1hour. ItisaisaunitofenergyusedinNorth1BritishThermalUnit=btu 1055.06JouleAmerica. It is the rounded-off amount of energy that1tonoilequivalent=1toe 4.19E+010 Joulewould be produced by burning onemetric ton of crude oil.1toncoalequivalent2.93E+10Joule Barrel 1tonoilequivalent=1toe 1/7.33 or1/7.1or1/7.4... ofoil1cubicmeterofnaturalgas3.70E+07Joule orroughly1000btu/ft31000Wattsforoneyear3.16E+010 Joule forthe2000Wattsociety1000Wattsforoneyear8.77E+006 kWh forthe2000Wattsociety 1horsepower7.46E+002 Watts 10. PrefixesOrders of magnitude Name Quantity Prefix thousand1E+03kilo million 1E+06 mega billion 1E+09giga trillion1E+12tera quadrillion 1E+15peta quintillion 1E+18exasextillion 1E+21 zettaseptillion 1E+24 yotta 11. How to do energy conversions(quick reminder) Given E = 5 kWh, what is value in MJ? From table, 1 kWh = 3.6 MJ 5 kWh x (3.6 MJ / kWh) = 18 MJ In other direction: 5 MJ = ? kWh 1 MJ = 0.28 kWh 5 MJ x (0.28 kWh / MJ) = 1.4 kWh 12. Basic concepts (II)How do you use energy? 13. What is energy for?How do you use energy?Examples of: Kinetic Electro-magnetic Electricity Radiation (light) Chemical Potential Heat (thermal)? 14. Practical energy: what is it for?Energy in daily life: we use it to ... stay alive (food, oxygen: chemical) move faster (transportation fuel: chemical) keep warm (heating fuel: chemical) almost everything else (keep cold, preserve food, light and ventilate spaces, cook, run machines, communicate, measure, store data, compute,...): electricityIn industrial processes: we use it to Extract (mechanical), refine (chemical), synthesize (chemical), shape (heat, mechanical), assemble (mechanical): produce 15. Properties of energy In any process, energy can betransformed but is alwaysconservedFuel + oxygen: heat, light + new compoundsMoving objects collide: heat + work on objectsFalling water+turbine: electricity + heat 16. Basic concepts (III)Energy conversion, conversion efficiency 17. Energy conversion Energy conversion: from one type to another Examples: Chemical to kinetic Chemical to electric Potential to electric Thermal to electric Chemical to thermal Radiation to chemical Radiation to electric Radiation to thermal Electric to thermal Electric to chemical 18. Why is this important? Efficiency What is efficiency?Output / InputEnergy out / energy in for an energyconversion process?Energy out = energy in , so not veryusefulUseful energy out / energy inPhysical work / Heat content of fuelElectricity / physical workFood / Inputs to agriculture 19. Efficiencies (2)Source: Smil 1999 20. Efficiencies (3)Source: Smil 1999 21. More than one conversion process The total efficiency is the product of allconversion efficiencies: Etotal = E1 x E2 x E3 x E4 x E5 x E6 x Total losses can be (and are) tremendous Most losses are in the form of radiated heat,heat exhaust But can also be non-edible biomass or non-work bodily functions (depending on finalgoal of energy) 22. Chain of conversion efficiencies: Light bulb trt c eerEtotal=E1xE2xE3=35%x90%x5%=1.6%Source: Tester et al 2005 23. Example 2: diesel irrigationLosses:t t t,r t,m 24. Example 3: Drive power 25. Example 4: living and eating Need 2500 kcal/day = 10 MJ/day or 2kcal/min. 2200 for a woman, not pregnant or lactating,2800 for a man (FAO). EU: 3200 kcal/day. Equivalent to 4.75 GJ/year vegetable caloriesin a vegetarian diet (including 1/3 loss of foodbetween field and stomach) Equivalent to 26.12 GJ/year vegetable caloriesin a carnivorous diet (1/2 calories from meat) Vegetarians are 5.5 times more efficient interms of vegetable calories. 26. Efficiency of human-powered motionkcal/mile 27. EU Energy Label A, B, C ratings formany common appliances Based on EU standardmetrics for each appliance kWh / kg for laundry % of reference appliancefor refrigerators 28. Importance of consumer behavior/lifestyle EU energy label vs. temperature of washingkWhpercycle/EnergyRating ABCDEF 90Cwash1.22 1.46 1.59 1.72 1.85 1.98 60Cwash0.94 1.12 1.23 1.34 1.47 1.6 40Cwash0.56 0.67 0.74 0.79 0.85 0.91 29. USA EnergyGuide label EnergyStar ratingsexist, but are notA,B,C grades Instead, applianceshave EnergyGuidelabels (usuallywithout EnergyStarratings) 30. Basic concepts (IV)Thermodynamics and entropy 31. Conservation, but Energy is ALWAYS conserved However, energy is not always useful:dissipated heat is usually not recoverable. Useful energy is an anthropocentric conceptin physics: from study of thermodynamics Thermodynamics investigates statisticalphenomena (many particles, Avogadrosnumber = 61023): energy conversioninvolving heat. 32. 3+1 laws of thermodynamics If systems A and B are in thermalequilibrium with system C, A and B are inthermal equilibrium with each other(definition of temperature). Energy is always conserved. The entropy of an isolated system not atequilibrium will tend to increase over time. As temperature approaches absolute zero,the entropy of a system approaches aconstant. 33. Paraphrases of 2 laws ofthermodynamics You cant get something from nothing. You cant get something from something.1. Youcantgetanythingwithoutworkingforit. Themostyoucanaccomplishistobreakeven.2. Youevencantbreakeven. (economics)There is no such thing as a free lunch. 34. History of thermodynamics (2nd law)Nicolas Lonard Sadi Carnot (1796-1832) Theory of heat engines, reversible Carnot cycle: 2nd law of thermodynamicsLudwig Boltzmann (1844-1906) Kinetic theory of gases (atomic) Mathematical expression of entropy as a function of probability 35. EntropyThe entropy function S is defined asS = kB log (W) kB = Bolzmanns constant = 1.381023 =Joule/Kelvin W=Wahrscheinlichkeit= possible states Increases with increasing disorderFor instance: vapor, water, ice expanding gas burning fuel 36. 2nd law of thermodynamicsdS 0 entropy increases over time (definition of time)dtFor a system undergoing a change,S system 0 for an isolated systemS system + S environment 0 for an non - isolated system 37. 2nd law of thermodynamicsTotal entropy always increases with time.An isolated system can evolve, but only if its entropydoesnt decrease.A subsystems entropy can increase or decrease, but thetotal entropy (including the subsystems environment)cannot decrease.R. Clausius (1865):Die Energie der Welt ist konstant.Die Entropie der Welt strebt einem Maximum zu.Notion of heat death of the universe 38. Basic concepts (V)Applications of thermodynamics: heat engines, Carnot cycle, maximum and real efficiencies. 39. Performance of energy conversionmachines (Carnot cycle) Heat engine (cycle) Heat, cool engine fluid Diesel, internal combustion Reversible processes: Entropy remains constant Sc = - Sh Irreversible processes Real world Heat losses, no perfect insulator Heat leakage Pressure losses, friction 40. The Carnot Cycle (the physics) Idealcyclebetween isotherms(T=constant) andadiabats(S= constant).dE=dW-dQ where dW=PdV dQ=TdS LoopintegraloverdE=0.ThetotalworkfromonecycleoftheengineisTheheattakenfromthewarmreservoirisTheefficiencyis :theoreticalmaximalforheatengine. 41. Common types of heat engines Rankine cycle: stationary pow