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# basics of thermodynamics

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### basics of thermodynamics

1. 1. The fascinating world of Thermodynamics Instructor Dr. Madhusree Kundu
2. 2. Thermodynamics Lecture # 1
3. 3. Thermodynamics (from the Greek thermos meaning heat and dynamis meaning power) is a branch of physics. It relates heat and work It deals with the effect of imposition of energy on the physical properties of substances. The foundation of thermodynamics is based on experimental observations.
4. 4. The observations have been formalized in to four thermodynamic laws. Thermodynamics may be broadly defined as a framework for viewing and correlating the behaviour of the system Historically, thermodynamics developed out of the need to increase the efficiency of early steam engines.
5. 5. The first and second laws of thermodynamics emerged simultaneously in the 1850s, primarily out of the works of William Rankine, Rudolf Clausius, and William Thomson (Lord Kelvin). Classical thermodynamics derives from physicist Robert Boyle’s 1662 postulation.
6. 6. The first thermodynamic textbook was written in 1859 by William Rankine, a civil and mechanical engineering professor at the University of Glasgow Lord Kelvin coined the term thermodynamics in his 1849 publication ‘An Account of Carnot's Theory of the Motive Power of Heat’.
7. 7. Thermodynamic efficiency In thermodynamics, thermodynamic efficiency, symbolized by (e), is defined as: e=W/Q where W is the absolute value of work done in one thermodynamic cycle. Q is the absolute value of the change in heat.
8. 8. Thermodynamic systems A thermodynamic system is defined as that part of the universe that is under consideration. A real or imaginary boundary separates the system from the rest of the universe, which is referred to as the environment or surrounding.
9. 9. Isolated Systems – matter and energy do not cross the boundary. Adiabatic Systems – heat does not cross the boundary. Diathermic Systems - heat crosses boundary. Closed Systems – matter does not cross the boundary. Open Systems – heat, work, and matter may cross the boundary.
10. 10. A control volume is a volume in space of interest for a particular study or analysis. The surface of this control volume is called the control surface. Control volume  The size and shape of control volume are arbitrarily chosen to suit our analysis.
11. 11. Mass as well as heat and work can cross the control surface, and the mass in the control volume (as well as its properties) change with time. The boundary may be fixed, or it may move (expand or contract).
12. 12. Control volume is an open system massin massout control volume Consider a tank with a piston and one inlet, and one outlet. Through the inlet mass comes in and through the outlet it goes out.
13. 13. Control Mass No exchange of mass is allowed, it resembles a closed system  As a control mass undergoes a change of state, energy may cross the boundary as either heat or work.
14. 14. Microscopic Approach Microscopic point of view is based on molecular level study to explain the behaviour of a system. A huge number of variables are required to specify the condition of a system Statistical thermodynamics is based on microscopic approach
15. 15. Macroscopic approach Macroscopic point of view is based on gross or time-averaged effects of many molecules. In this approach the condition of system can be specified by only measurable quantity like P, V, T and the number of variables to be dealt with are quite few. These effects can be perceived by human senses and measured by instruments.
16. 16. Statistical thermodynamics is a branch of thermodynamics concerned with the study and analysis of actual phenomena with full interpretation, explanation, and evaluation of microscopic, i.e. statistical energy-level atomic and molecular details.
17. 17. It is a branch of thermodynamics concerned with the study and analysis of actual phenomena with avoidance of full interpretation, explanation, and evaluation of microscopic, i.e. statistical energy-level atomic and molecular details. Generally, phenomenological thermodynamics, being synonymous with classical thermodynamics. Phenomenological thermodynamics
18. 18. Thermodynamic properties These are the attributes that can characterize the system by P, V, T, density, specific heat etc. Extensive property: It depend on the system size or the amount of material in the system. Mass, volume, entropy, energy (Internal energy and enthalpy) are examples of it.
19. 19. Intensive Property: is the physical property of the system that does not depend on the system size or the amount of material in the system. The examples are temperature, pressure, and density.
20. 20. The properties of the system can be described by an equation of state which specifies the relationship between these extensive and intensive parameters or variables. Thermodynamic properties are defined for, and significant to, only thermodynamic equilibrium states.
21. 21. Thermodynamic state The state of the thermodynamic system can be thought of as an optimal ensemble of thermodynamic parameters, namely temperature, pressure, density, composition, etc., which characterize the system. Neither its surroundings nor its history characterize the system.
22. 22. P V Gas
23. 23. P V Gas
24. 24. P V P1, V1 P2, V2 Gas
25. 25. For a system, each of the properties at a particular state has unique set of intensive properties regardless of the path, how the system has arrived to that particular state. State properties are path independent. Phase: A quantity of matter homogeneous throughout in chemical composition and physical structure is called a phase. Vapour, liquid and solid are the three phases.
26. 26. Thermodynamic Equilibrium A system is said to be in equilibrium, where there is no change in macroscopic property is registered, when the system is kept isolated from the surroundings. A system in equilibrium never changes to any other state spontaneously.
27. 27. At equilibrium the state properties do not change until and unless there is an energetic evolution from one to another state. The word equilibrium implies a state of balance. In an equilibrium state, there are no unbalanced potentials (or driving forces) within the system.
28. 28. The system is in equilibrium in three ways: Thermal equilibrium Mechanical equilibrium Chemical equilibrium Thermodynamics studies mainly the properties of physical systems that are found in equilibrium state.
29. 29. Mechanical equilibrium: In the absence of any unbalanced force within the system itself and between the system and surrounding, the system is said to be in mechanical equilibrium. Chemical equilibrium:If there is no chemical reaction or transfer of matter from one part of the system to another the system is said to be in chemical equilibrium
30. 30. Thermal equilibrium: When the system is separated from its surroundings by a diathermic ( means allows the heat to flow) wall and if there is no change in temperature of the system, the system is said to be in thermal equilibrium with the surroundings.
31. 31. Both classical and statistical thermodynamics study mainly the equilibrium states of a system. Non-equilibrium thermodynamics is a branch of thermodynamics concerned with studying irreversible transformations.
32. 32. Process The path of the succession of states through which the system passes is called the process. A thermodynamic process may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state.
33. 33. P V P1, V1 P2, V2 Gas
34. 34. Quasi equilibrium process: Such a process is the locus of all the equilibrium points through which the system passes. Infinite slowness is the attribute of the process. In quasi--static process the departure of the state of the system from the thermodynamic equilibrium state is infinitely small
35. 35. An isothermal process occurs at a constant temperature. An example would be to have a system immersed in a large constant- temperature bath. Any work performed by the system will loose equivalent amount of energy to the bath, but its temperature will remain constant.
36. 36. T V Isothermal Process
37. 37. An isobaric process occurs at constant pressure. An example would be to have a movable piston in a cylinder, so that the pressure inside the cylinder is always at atmospheric pressure, although it is isolated from the atmosphere.
38. 38. T V Isobaric Process
39. 39. An isochoric process is one in which the volume is held constant, meaning that the work done by the system will be zero. An isochoric process is also known as an isometric process. An example would be to place a closed tin can containing only air into a fire. To a first approximation, the can will not expand, and the only change will be that the gas gains internal energy, as evidenced by its increase in temperature and pressure.
40. 40. T V Isochoric Process
41. 41. A thermodynamic cycle is a series of thermodynamic processes which returns a system to its initial state. A B Cyclic Process P V
42. 42. Thermodynamic cycles often use quasi- static process to model the workings of actual devices to obtain maximum efficiency.
43. 43. Two primary classes of thermodynamic cycles are Power cycle Refrigeration cycle Power cycles are cycles which convert a heat input into a work output. e.g.,Internal combustion engine. Refrigeration cycles transfer heat from low to high temperatures using work input. e.g., refrigerator.
44. 44. A dimension is a physical variable used to specify the behavior or nature of the particular system. The length of a rod is a dimension of the rod.The gas temperature is a thermodynamic dimension of a gas. Units and Dimensions Units are needed to measure the dimension.
45. 45. C. G.S. F.P.S M. K. S S.I (System International) Basic Units  Derived units
46. 46. Basic units (S. I) Mass (M), kg Length (L), m Time (t), s Amount of substance, mole Temperature, K Electrical current, A Luminous Intensity, candela, cd Plane angle, rad
47. 47. Derived units (S.I) Force (F), N Energy (E), Joules, J, Nm Power, watt, W, J/s Pressure, pascal, Pa
48. 48. English Engineering unit system (Basic units) Length, ft Mass, lbm Time, s Amount of substance, lb mole Temperature, R Force (F), lbf
49. 49. The value of gc in SI and Engineering unit The unit of force is derived from Newton.s second law F m X a or F X C = m X a where ‘m’ is the mass and ‘a’ is the acceleration. In SI unit, m = 1 kg and a = 9.80665 m/s2 Then F = 9.80665 N 9.80665 N X C = 1 kg X 9.80665 m/s2 C=1 kg m/s2/N
50. 50. If we replace C by gc, the gravitational constant F= m a/ gc In SI unit, gc, = 1 kg m/s2/N = 1 In Engineering unit, F= 1 lbf , m= 1 lbm a=32.174 ft/ s2 Hence, 1 lbf X C = 1 lbm X 32.174 ft/ s2 C = 32.174 lbm ft/ s2/ lbf gc, = 32.174 lbm ft/ s2
51. 51. Energy Macroscopic mode of energy Microscopic mode of energy The two types of macroscopic mode of energies are, Kinetic Energy  Potential energy
52. 52. Molecular Kinetic energy: It is associated with the translational velocity of individual molecules. Microscopic mode of energy are of three types, Intermolecular potential energy: It is associated with the forces between the molecules and their position with respect to each other.
53. 53. Intramolecular energy: It is associated with molecular and atomic structure and related force Total Energy= Macroscopic energy + microscopic energy =Kinetic energy + Potential energy + Internal Energy
54. 54. Continuum From macroscopic point of view we deal with volumes which are very large compared to its molecular dimension. Within this volume span we can assume the substance to be continuous and can be divided infinite times disregarding the action of individual molecule.
55. 55. Continuum The continuum concept looses its validity when molecular mean free path of the molecules approaches the dimension of the vessel. e.g., In vacuum technology, in microchannel flow.
56. 56. Specific Volume and Density  The Specific Volume of a system in a gravitational field may vary from point to point. Specific Volume: volume per unit mass Specific Density: mass per unit volume Both are intensive properties v
57. 57. where is the smallest volume for which the mass can be considered a continuum. V m V v VV lim
58. 58. The specific volume and density are defined at a point in system. It may vary with elevation. But change in specific volume with elevation is not significant. So we can take one value of and Contd v
59. 59.  The specific volume and density may be given either on mass or on mole basis. Molal specific volume = Molal density =
60. 60. Pressure With liquids and gases: pressure, with solids: stresses It is defined as the normal component of force per unit area. A F P n AA lim where is the smallest area for which the fluid can be considered a continuum. A
61. 61. Units of Pressure Unit for Pressure in International System: force of one newton acting on a square meter area. Other units 2 /11 mNPa 5 2 1bar = 10 Pa = 0.1MPa 1atm = 101325Pa = 14.696lbf/in
62. 62. Ordinary pressure gauge .atmabs PPP Ordinary vacuum gauge absatm PPP .
63. 63. Measurement of pressure difference Fluid P A B Patm. = Po H Force acting at B 0 0P A mg P A AgH Force acting at A PA Pressure Difference: ghPPP 0
64. 64. Temperature  Because of difficulties in defining temperature, we define equality of temperature.  The two bodies have equality of temperature, if there is no change in any observable property occurs when they are in thermal communication.
65. 65. The Zeroth Law of Thermodynamics When two bodies have equality of temperature with a third body, they must have equality of temperature with each other.
66. 66. Thank You for Your patience