THERMODYNAMICS

1. THERMODYNAMICS 1

2. MODULE-I 1.INTRODUCTION To Thermodynamics 2

3. What is Thermodynamics ? • The word thermodynamics comes from the Greek words therme (heat) and dynamis (power). • Thermodynamics is both a branch of physics and an engineering science. • Thermodynamics can be defined as the science of energy. 3

4. What is Thermodynamics ? • Thermodynamics is the science of energy transfer and its effects on the physical properties of the substances 4

5. Application Areas of Thermodynamics All activities in nature involve some interaction between energy and matter;thus, it is hard to imagine an area that does not relate to thermodynamicsin some manner.

7. Applications of Thermodynamics • Turbine, compressor, pumps, fans • Auto mobile engines • Refrigeration systems • Air-conditioning systems • Power plants 7

8. Macroscopic & Microscopic Approaches There are two views in the study of thermodynamics. • Macroscopic approach (2) Microscopic approach 8

9. Macroscopic Approach • The macroscopic approach to thermodynamics is concerned with the gross or overall behavior. This is sometimes called classical thermodynamics. 9

10. Macroscopic Approach • This macroscopic approach to the study of thermodynamics that doesn’t require knowledge of the behavior of individual particles. It is the overall behavior approach. It is also called as classical thermodynamics. It provides direct and easy way to the solution of engineering problems 10

11. Microscopic Approach • The microscopic approach to thermodynamics, known as statistical thermodynamics, is concerned directly with the structure of matter. 11

12. Microscopic Approach • A more elaborate approach based on the average behaviour of large groups of individual particles is called microscopic approach. This is also called as statistical thermodynamics. It is essential for applications involving high speed gas flows, very low temperature etc. 12

13. System:A quantity of matter or a region in space chosen for study. Surroundings:The mass or region outside the system Boundary:The real or imaginary surface that separates the system from its surroundings. System, Surrounding & Boundary 13

14. System, Surrounding & Boundary • The boundary of a system can be fixed or movable. 14

15. Types of system Based on the mass transfer and energy transfer across the boundary the systems are divided in 3 types. • Closed system or control mass system. • Open system or control volume system. • Isolated system 15

16. Closed system • Closed system (Control mass):A fixed amount of mass, and no mass can cross its boundary. 16

17. Open system • Open system (control volume):A properly selected region in space. • A control volume can be fixed in size and shape or it may involve a moving boundary as shown in figure. • Most control volume however have fixed boundaries and thus don’t involve any moving boundaries. • Example : Compressor, turbine, IC engine, nozzle, boilers 17

18. Isolated System • There is neither energy transfer nor mass transfer occurs the boundaries which is shown in Figure. • Example: Ice cube in a thermos flask, hot gases in a perfectly insulated closed chamber. 18

19. Equilibrium States • An equilibrium state is one in which the properties of the system do not change with time. • In many cases, an equilibrium state has intensive variables which are uniform throughout the system. • A non-equilibrium state may contain intensive variables which vary in space and/or time. • An equation of state is a functional relationship between the state variables; e.g. if P,V and T are the state variables, then the equation of state has the form f(P, V, T) =0. • In 3-dimensional P-V-T space, an equilibrium state is represented by a point, and the equation of state is represented by a surface. 19

20. Property:Any characteristic of a system. Some familiar properties are pressure P, temperature T, volume V, and mass m. Properties are considered to be either intensive or extensive. PROPERTIES OF A SYSTEM 20

21. A property is a macroscopic characteristic of a system such as mass, volume, energy, pressure, temperature, entropy etc. It is measurable characteristics describing the system. Measureable characteristics are temperature, pressure, Volume etc. Properties are classified into two categories Extensive property Intensive Property PROPERTIES OF A SYSTEM

22. PROPERTIES OF A SYSTEM • Intensive properties:Those that are independent of the mass of a system, such as temperature, pressure, and density. • Extensive properties:Those whose values depend on the size or extent of the system. • Specific properties:Extensive properties per unit mass. 22

23. Extensive property A property is called extensive if its value for an overall system is the sum of its values for the parts into which the system is divided. Extensive properties depend on the size or extent of a system. Example: Mass, volume, energy etc. Intensive Property Extensive property & Intensive Property Intensive properties are not additive in the same previously considered. Their values are independent of the size or extent or mass of a system and may vary from place to place within the system at any moment. Thus intensive property may be function of both position and time where as extensive properties vary at most with time. 23

24. State of a system • A set of properties that completely describes the condition of a system is called the state of the system. 24

25. State • At a given state, all the properties of a system have fixed values. If the value of even one properties changes, the state will change to a different one. • At any instant of time the state is described by its properties such as pressure, temperature, volume etc. 25

26. State • Properties when taken on axis to draw a graph they are termed as thermodynamic co-ordinates. • At state (1) pressure and volume is (P1,V1)and state (2) Pressure & volume is (P2, V2)as shown in Fig 26

27. Steady state • If a system exhibits the same values of its properties at two different times i.e. the properties are not changing with time but may be different at different points or positions, then the system is said to be at steady state. 27

28. Path When a system undergoes change in its state the line joining the series of intermediate states through which the system has passed is known as path as shown in Fig. 28

29. Process When any of the properties of a system change, the state changes and the system is said to have undergone a process. A process is a transformation from one state to another as shown in Fig 29

30. Thermodynamic cycle A thermodynamic cycle is a sequence of processes that begins and ends at the same state. At the conclusion of a cycle all properties have the same values they had at the beginning. 30

31. Reversible Process Reversible Process: It is a process in which a system returns to its initial state along the same path without leaving any traces of its being happened on the surrounding. A reversible process is always a quasi-static process. 31

32. Irreversible Process Irreversible process: A process is irreversible of a system passes through a series of non equilibrium states i.e. if the irreversible process is made to reverse the path it will not restore to its initial state. 32

33. HOMOGENEOUS AND HETEROGENEOUS SYSTEMS • A quantity of matter homogeneous throughout in chemical composition and physical structure is called a phase • Every substance can exist in any one of the three phases,i.e.,solid,liquid and gas • A system consisting of a single phase is called a homogeneous system, while a system consisting of more than one phase is known as a heterogeneous system. 33

34. Thermodynamic Equilibrium • A system is said to exist in a state of thermodynamic equilibrium when no spontaneous change in any macroscopic property is observed as the system is isolated from its surroundings. • Equilibrium means the state of balance of a system within itself and between system and surroundings. Thus for attending a state of thermodynamic equilibrium following three types of equilibrium states the system must achieve. • Thermal Equilibrium • Mechanical Equilibrium • Chemical equilibrium 34

35. Thermal Equilibrium A system is in thermal equilibrium if the temperature is same throughout the system i.e. the system involves no temperature differential, which is the driving force for heat flow. 35

36. Mechanical Equilibrium • It is related to pressure and a system is in mechanical equilibrium if there is no change in pressure at any point of the system with time • However, the pressure may vary with in the system with elevation as a result of gravitational effects. But there is no imbalance of forces • The variation of pressure as a result of gravity in most thermodynamic systems is relatively small and usually disregarded 36

37. Chemical equilibrium • A system is in chemical equilibrium if no chemical reaction or transfer of matter from one part to another within the system takes place either through diffusion or any other chemical process. • Chemical composition of the system doesn't change with time. 37

38. Criteria for an equilibrium

39. Quasi-Static Process • When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times, it is called a quasi-static or quasi-equilibrium process • It is a sufficiently slow process that allows the system to adjust itself internally so that properties in one part of the system do not change any faster than those at other parts 39

40. Quasi-Static Process 40

41. Pressure • Pressure:A normal force exerted by a fluid per unit area 41

42. 68 kg 136 kg Afeet=300cm2 0.23 kgf/cm2 0.46 kgf/cm2 P=68/300=0.23 kgf/cm2 PRESSURE The normal stress (or “pressure”) on the feet of a chubby person is much greater than on the feet of a slim person. Some basic pressure gages.

43. Absolute pressure: The actual pressure at a given position. It is measured relative to absolute vacuum (i.e., absolute zero pressure). Gage pressure: The difference between the absolute pressure and the local atmospheric pressure. Most pressure-measuring devices are calibrated to read zero in the atmosphere, and so they indicate gage pressure. Vacuum pressures: Pressures below atmospheric pressure. Throughout this text, the pressure Pwill denote absolute pressureunless specified otherwise.

44. Pascal’s law: The pressure applied to a confined fluid increases the pressure throughout by the same amount. The area ratio A2/A1 is called the ideal mechanical advantageof the hydraulic lift. Lifting of a large weight by a small force by the application of Pascal’s law.

45. The Manometer It is commonly used to measure small and moderate pressure differences. A manometer contains one or more fluids such as mercury, water, alcohol, or oil. Measuring the pressure drop across a flow section or a flow device by a differential manometer. The basic manometer.

46. Other Pressure Measurement Devices • Bourdon tube: Consists of a hollow metal tube bent like a hook whose end is closed and connected to a dial indicator needle. • Pressure transducers: Use various techniques to convert the pressure effect to an electrical effect such as a change in voltage, resistance, or capacitance. • Pressure transducers are smaller and faster, and they can be more sensitive, reliable, and precise than their mechanical counterparts. • Strain-gage pressure transducers:Work by having a diaphragm deflect between two chambers open to the pressure inputs. • Piezoelectric transducers: Also called solid-state pressure transducers, work on the principle that an electric potential is generated in a crystalline substance when it is subjected to mechanical pressure.

47. THE BAROMETER AND ATMOSPHERIC PRESSURE • Atmospheric pressure is measured by a device called a barometer; thus, the atmospheric pressure is often referred to as the barometric pressure. • A frequently used pressure unit is the standard atmosphere, which is defined as the pressure produced by a column of mercury 760 mm in height at 0°C (Hg = 13,595 kg/m3) under standard gravitational acceleration (g = 9.807 m/s2). The length or the cross-sectional area of the tube has no effect on the height of the fluid column of a barometer, provided that the tube diameter is large enough to avoid surface tension (capillary) effects.

48. Temperature Temperature is defined as the degree of hotness or coldness of a body measured on a definite scale. Temperature is the driving force or potential for heat transfer. 48

49. Temperature • It is a measure of mean K.E. of the molecules of the system. A change in temperature of a system accounts for change in molecular motion and the K.E and the molecule. • Temperature is a parameter which determines whether or not a system is in thermal equilibrium with another system. 49

50. Temperature • When work or heat is supplied to a system it is not mandatory that the temperature of the system will increase. It may or may not increase until the molecular K.E. increase. • Example: - Temperature of a gas in a container doesn‟t increase when we put the container in a train. 50