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1 EK 04: Energy and Thermodynamics Lectures Professor i Lin Course Page: linx@bu.edu; Phone: (67) 58-47

2 Textbook Lecture Notes and Problem Sets Fundamental of Engineering Thermodynamics 6 th edition By Michael J. Moran and Howard N. Shapiro ISBN Lecture notes and problem sets will be available online in pdf format at within one day after the class. Problem sets are due one week after assignment at 5:00 pm of the day No points if overdue unless with special permissions from the teacher

3 Grading Problem sets: 0% Two labs: 5% (required*) Mid term (closed book): 5% Final (closed book): 50% Class and discussion sections participation: 0% Ask questions; all questions are good questions * No final grades if missing labs

4 Lecture I What Is Temperature? 4

5 Objective To answer: what is thermodynamics all about? 5

6 Thermodynamics is the science that examines the effects of energy and mass transfer on macroscopic materials systems. Einstein: E M*c 6

7 Thermodynamics: Origin and Modern Development Thermodynamic laws were developed phenomenologically in the 9 th century. Statistical mechanics First-principles atomic interpretation of thermodynamics Bridge between macroscopic observables and averages of corresponding microscopic properties 7

8 What can and can t thermodynamics tell us? 8

9 Thermodynamics predicts whether a process will occur or not driving force for the process 9

10 Thermodynamics does not predict how fast a process will occur mechanism of the process Kinetics 0

11 Thermodynamics is the science that examines the effects of energy transfer on macroscopic materials systems. Thermodynamics predicts whether a process will occur given long enough time driving force for the process Thermodynamics does not predict how fast a process will occur mechanism of the process

12 Definitions System: the portion of the universe that is to be examined Surroundings: the rest of the universe Boundary: the invisible and infinitesimally thin surface that separate the system from the surroundings

13 System Surroundings and Boundary: Examples Milky way Cosmic microwave background radiation by Wilkinson Microwave Anisotropy Probe (WMA) satellite NASA

14 Definitions Continued Isolated system: cannot exchange energy or matter with the surroundings Closed system: can exchange energy but not matter with the surroundings Open system: can exchange both energy and matter with the surroundings Adiabatic system: can exchange work but not heat or matter with its surroundings Control volume: fixed boundary 4

15 Isolated System: Examples 5

16 Closed System: Examples 6

17 Open System: Examples Kids in general love their house being an open system at least once a year 7

18 Adiabatic System: Examples Decoupling of electronic and nucleus motions: M nucleus > 0 M electron 8

19 Definitions Continued Property of a system: a macroscopic characteristic of the system Extensive property: value is additive and quantity of matter (examples: total mass total volume total energy) Intensive property: value independent of quantity of matter (examples: density pressure temperature: if you put two identical objects of temperature T together the assembly has temperature T instead of T) 9

20 State: collection of all relevant properties Steady state: all property values independent of time Equilibrium: all property values independent of time even if isolated from surroundings Ar gas atoms Non-equilibrium states Now stir it any way you like and wait Equilibrium state Vacuum outside insulating box (the constraint) Vacuum outside 0

21 Non-equilibrium or transient: any other condition of the system weapon designers: e.g. shockwave Non-equilibrium property Non-equilibrium state Equilibrium property Equilibrium state C4 thermodynamics product gas thermodynamics focuses on studying equilibrium state and properties

22 A very useful picture: the equilibrium plane Non-equilibrium states State space approaching equilibrium on a transient path equilibrium states Starting from any non-equilibrium state the system will eventually approach a point on the equilibrium plane. Starting from an equilibrium state if the constraints are fixed one will stay at that equilibrium state (point) forever by definition.

23 What if the constraints are altered? The not-so-nice way The nice way

24 In system s state space: transient process or irreversible process path b path quasi-static process or reversible process a Quasi-static means very slow system s equilibrium plane 4

25 It turns out there is a fundamental difference between quasi-static paths (solid line stays on the equilibrium plane) and transient paths (dash line not always on the equilibrium plane): The former conserves the total entropy of the universe; while the latter causes the total entropy of the universe to increase. The above assertion provable in statistical mechanics (or at least made extremely intuitively convincing) is taken as an axiom in thermodynamics (second law). 5

26 Units of Mass Length Time and Why are units for? Force 6

27 English Units 7

28 International System of Units (SI) Only 7 base units!!! 8

29 Definitions Continued Specific volume of a system: inverse of density Pressure: force per area SI Unit: pascal N/m Temperature: Uhmm 9

30 State Variables State variables Set of sufficient and necessary properties that specifies the state of the system Examples Pure gases or liquids: P and V Magnetic solids: M and H Magnetic gases: M H P and V 0

31 The 0 th Law: Law of Thermal Equilibrium If both (system I and system III) and (system II and system III) are in thermal equilibrium (system I and system II) must be in thermal equilibrium.

32 Temperature from the 0 th Law ( ) ( ) 0 f F ( ) ( ) 0 g F ( ) ( ) g f

33 Temperature from the 0 th Law: Continued ( ) ( ) g f ( ) 0 F But according to 0 th law: Therefore we must have: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) b a t g b a t f + +

34 4 Temperature from the 0 th Law: Continued ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) b a t g b a t f + + ( ) ( ) g f and ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) t t b a t b a t + +

35 5 Temperature from the 0 th Law: Continued ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) b a t g b a t f + + ( ) ( ) ( ) t a b Define: ( ) ( ) ( ) t t t and because

36 Temperature from the 0 th Law: Continued ( ) t ( ) t ( ) t This implies the existence of a property of ( ) t. Whenever systems reach thermal equilibrium such property will be equal. This property is called temperature. 6

37 Units for Temperature SI: Kelvin (K) T > 0 K always! Celsius ( C) T ( C) T (K) -7.5 Fahrenheit ( F) T ( F).8T ( C) + 7