Thermodynamics: Concepts, Definitions, and Laws

1. Chapter 2 • Some Concepts • Definitions

2. Definition of Thermodynamics • The science of energy and entropy • The science that deals with heat and work and those properties of substances that bear a relation to heat and work

3. Basis of thermodynamics • Experimental observations (findings) • Formalize into certain basic laws(zeroth, first, second, and third laws)

4. Objectiveof Student • To gain both • a thorough understanding of the fundamentals, and • an abilityto apply these fundamentals to thermodynamic problems

5. 2.1 Thermodynamic System and Control Volume • Thermodynamic System • It contains matter and device(s) in a control surface. • Itsboundaries may be closed (fixed mass/ control mass) or open ( involving a flow of mass), and may be movable or stationary. • It may have flows of energy in term of heat transfer and work across it.

6. Isolated system –No mass, heat, or work across the boundary.

7. Control Mass

8. Control Volume

9. 2.2 Macroscopic vs Microscopic Point of View • Macroscopic Point of View- concerned with the Gross or Average Effects of many molecules • Continuum • Microscopic Point of View- Classical and Statistical approach

10. 2.3Properties and Stateof a Substance • Definition of a Phase • Phase is a quantity of matter that is homogeneous throughout. • Phase of a Substance • Substance may exist in a different state which involves observable and macroscopic properties • It may be regarded as a function of some statei, therefore Phasej = f (statei) = f(Pi, Ti , Densityi,…, etc. ) • Factors, like Pi, Ti , Densityi,…, etc., are all properties of some statei.

11. Each property of a substance in a given state has only one(same) definite value. • Regardless of how the substance arrive at the state (path). • Thermodynamic EquilibriumEquilibrium is a state when system properties are invariable.

12. Intensive Property independent of mass, like P, T, and density Extensive Property varies directly with mass, like total volumeExtensive propertiesper unit mass are intensive(specific) properties. Thermodynamic Properties

13. 2.4 Processes and Cycles • Processes • Path of different states • Statei (Pi,Ti ,Di,.) to Statej (Pj,Ti ,Dj,.) , i≠j • Cycles • Path, i = j

14. Quasi-equilibrium process A quasi-equilibrium processis one in which the deviation from thermodynamic equilibrium is infinitesimal. Fig. 2.3

15. Quasi-equilibrium process • All the states the system passes through during a quasi-equilibrium process may be considered equilibrium states. • Many actual processes closely approach a quasi-equilibrium process and may be so treated with essentially no error.

16. 2.5Units forMass, Length, Time, and Force

17. 2.6 Energy • An Important Concept • Definition：the capability to produce an effect • From molecular view, it can be transferred and stored.

18. Potential energy in the coordinate system for a diatomic molecule Fig. 2.4

19. Heat transfer to water Fig. 2.5

20. 2.7Specific Volume and Density

21. ρ= The definition and continuum limit for the specific volume and (specific) density • Specific volume • Density

22. Density of common substances

25. 2.8 Pressure Fig. 2.8

26. Pascal ( Pa )1 Pa = 1 N/m2 bar1 bar = 1x105 Pa = 0.1 MPa atm1 atm = 101325 Pa Pressure Units

27. Terms used in Pressure Measurement

28. Pressure measurement - using a column of fluid

30. 2.9 Equality of Temperature Two bodies have equal temperature if, when they are in thermal communication, no change in any observable property occurs.

31. 2.10The Zeroth Law of Thermodynamics • When two bodies have equality of temperature with a third body, they in turn have equality of temperature with each other.

32. 2.11 Temperature Scales • Celsius scalesoC • Kelvin ScalesK • RelationK = oC +273.15