Fundamentals of thermodyamics, fluid mechanics and heat transfer

thermo fluids ppt gives you the overview of thermodynamics, fluid mechanics and heat transfer fundamentals. It provides you more informative and easy understand concepts. This will help you during the exam preparation

1. Thermo-fluids Prepared by Dr. K. Balaji Associate Professor Department of Mechanical Engineering Amrita School of Engineering Coimbatore Source: Thermodynamics by Cengel & Boles Internet sources Fluid Mechanics by Cengel & Cimbala Heat Transfer by Cengel & Ghajar

2. Thermodynamics Properties of ideal and real gases, pure substance Closed, open and isolated system Properties, state, equilibrium, process, and cycles Zeroth, first, second, and third law of Thermodynamics Energy, entropy, and exergy balance Fluid Mechanics Properties of fluids Classification of fluid flow Static and Buoyancy Fluid Kinematics Fluid Dynamics mass Momentum Energy Heat Transfer Conduction governing equation and boundary condition Convection Heat transfer coefficient Radiation emissive power Overview of Thermo-fluids

3. Thermodynamics

4. Continuum Model continuous, homogeneous matter with no holes, that is, a continuum The continuum idealization allows us to treat properties as point functions To assume the properties vary continually in space with no jump discontinuities Knudsen number ,  K n  = λ /  L, λ is the mean free path  L  is the characteristic length – diameter of the molecule Usually when K n > 0.01, the concept of continuum does not hold good Beyond this critical range of Knudsen number, the flows are known as slip flow (0.01 < K n  < 0.1), transition flow (0.1 < K n  < 10) and free-molecule flow (K n  > 10) It describes the degree of departure from continuum Actual Fluid Continuum Model K n < 0.01 Mean free path is inversely proportional to the density

5. Greatest Minds of Thermodynamics

6. Thermodynamics – Therme + Dynamis Heat Low grade energy High grade energy Power

7. IC Engines Power Plant Gas Turbine Engine Water Dam Refrigerator Air-conditioner Food processing unit Submarines Aircraft Spacecraft Automobiles Human System Applications of Thermodynamics

8. Approaches in Thermodynamics

9. Thermodynamics Working Substance Single phase – Solids, liquids & gases – ideal & real Two-phase – water & refrigerant System Closed system Open system Isolated system Properties Intensive Extensive Cycles Gas Power Cycle Vapour Power Cycle Process Isochoric Isobaric Isothermal Isentropic Adiabatic Laws of Thermodynamics Zeroth law First Law Second Law Third Law Thermodynamic Balance Energy Balance Entropy Balance Exergy Balance

10. Ideal Gas

11. B B B B Universal gas constant U PV = m R T Mass Gas constant P v = R T Specific Volume K B – Boltzmann constant   28g 44g

12. At high temperature/low pressure – density is low Ideal vs Real Gas Behavior At low temperature/high pressure – density is high

13. Phases of a Pure Substance At  room temperature and pressure, copper is a solid , mercury is a liquid , and nitrogen is a gas The two phases of H 2 O Photographic triple point of water. Reflections at Masku Riviera, Finland. The three phases of H 2 O Solid - copper Liquid - mercury Gas - Nitrogen

14. Phase-change Processes of Pure Substances Compressed liquid Saturated liquid Saturated liquid and vapour Saturated vapour Superheated vapour v

15. Types of Systems System: A quantity of matter or region in space chosen for investigation

16. Boundary Surrounding Anything outside the system is considered as surrounding Immediate surroundings refer to the portion of the surroundings that is affected by the process Environment refers to the region beyond the immediate surroundings whose properties are not affected by the process at any point A surface that separates the system from its surroundings the contact surface shared by both the system and the surroundings Mathematically speaking, the boundary has zero thickness It can neither contain any mass nor occupy any volume in space

17. Properties of a system: Any characteristic of a system is called a property

18. State: A set of properties that completely describes the condition of the system The State Postulate The state of a simple compressible system is completely specified by two independent, intensive properties . Simple compressible system - in the absence of electrical, magnetic, gravitational, motion, and surface tension effects

19. Types of Thermodynamic Process Isochoric or constant volume Isobaric or constant pressure Isothermal or constant temp. Reversible adiabatic Polytropic Free expansion Process: Any change that a system undergoes from one equilibrium state to another is called a process Path: the series of states through which a system passes during a process is called the path of the process

20. Types of Thermodynamic cycle Cycle: A system is said to have undergone a cycle if it returns to its initial state at the end of the process Gas Power Cycle Vapour Power Cycle IC Engine Power Plant

21. Heat transfer : the form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature difference Heat Transfer Mechanisms

22. Work transfer : Any form of energy transfer other than temperature difference between system and its surroundings is called work transfer

23. Types of work Mechanical Work Non-mechanical Work Electrical work Electromagnetic work Polarization work Moving Boundary work Non-moving Boundary work Spring work Surface tension work Constant volume work Constant pressure work Constant temperature work Adiabatic work Polytrophic work Shaft work

24. Similarities between heat and work transfer Both are recognized at the boundaries of a system as they cross the boundaries. That is, both heat and work are boundary phenomena. 2. Systems possess energy, but not heat or work. 3. Both are associated with a process, not a state. Unlike properties, heat or work has no meaning at a state. 4. Both are path functions (i.e., their magnitudes depend on the path followed during a process as well as the end states). Point and Path functions Depends on the state Depends on the path it follows Exact differential Inexact differential Denoted by d Denoted by  All properties are point function Heat and work are path function dP = P B – P A  W W 2 – W 1  Q Q 2 – Q 1

25. Energy & its interactions Static Form (Total Energy) Dynamic Form Macroscopic Microscopic Kinetic Energy [ velocity] Potential Energy [elevation] Internal Energy Sensible Latent Nuclear Chemical Heat Work Mass Molecular Translation Molecular Rotation Electron Translation Molecular Vibration Electron Spin Nuclear Spin Flow Energy [pressure] Open System First Law of Thermodynamics

26. 70 o C 10 o C 25 o C 70 o C 10 o C 25 o C Surrounding (C) (A) (B) (B) Laws of Thermodynamics Zeroth law of thermodynamics Concept of thermal equilibrium You must play the game First law of thermodynamics Concept of change in energy ( E ) You can’t win the game Third law of thermodynamics Concept of absolute entropy You can’t quit the game Second law of thermodynamics Concept of change in entropy ( S ) You can’t break even in the game

27. Open System – Steady flow devices Hair dyer Water heater Air compressor Shower mixer Ceiling fan Water pump condenser Shower mixer

28. Introduction to the Second Law of Thermodynamics The use of the second law of thermodynamics is not limited to identifying the direction of processes. The second law also asserts that energy has quality as well as quantity. The first law is concerned with the quantity of energy and the transformations of energy from one form to another with no regard to its quality. Preserving the quality of energy is a major concern to engineers, and the second law provides the necessary means to determine the quality as well as the degree of degradation of energy during a process.

29. The Second Law of Thermodynamics Kelvin–Planck Statement It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work. A device that violates the Kelvin–Planck statement of the second law. Clausius Statement It is impossible to construct a device that operates in a cycle that transfers heat from a lower-temperature body to a higher-temperature body without any external agency. A device that violates the Kelvin–Planck statement of the second law.

30. Equivalence of the Two Statements

31. Carnot Cycle   The Carnot Principles 3 4 1 2 For any reversible process

32. Heat Engine Refrigerator Heat Pump Heat Pump Heat Pump Heat Pump

33. For any process, the Clausius inequality gives   ; a quantity whose cyclic integral is zero depends on the state only and not the process path, and thus it is a property. Clausius realized in 1865 that he had discovered a new thermodynamic property, and he chose to name this property entropy   Entropy Entropy can be viewed as a measure of molecular disorder, or molecular randomness

34. According to 2 nd law of Thermodynamics, A process can occur in a certain direction only, not in any direction, and entropy is always generated during the process. Low entropy generation High entropy generation Entropy in everyday life Entropy is a non-conserved property, and there is no such thing as the conservation of entropy principle. Entropy generation is a measure of the magnitudes of the irreversibilities during that process

35. Exergetic Efficiency   Exergy – maximum work potential that can be extracted from the given energy The actual work delivered by the system

36. Energy Balance Entropy Balance Exergy Balance Closed System Closed System Closed System Open System Open System Open System   Heat or Work     Heat     Heat or Work   Heat or Work or mass       Heat or mass     Heat or Work or mass              

37. Energy, Entropy, and Exergy transfer Heat Work Mass Energy Entropy Exergy Based on the energy balance equation Based on the type of process               Closed system   Open system  

38. Fluid Mechanics

39. Fluid : A substance undergoes deformation continuously when acted upon by shearing stress of any magnitude Solid Fluid Shear Stress  Shear Strain Shear Stress  rate of strain (A) (B)

40. Classification of Fluid Flow 1D Uniform Vs Non-Uniform

41. Fluid Properties Mass Weight Volume Density Specific volume Specific weight Specific gravity Temperature Pressure Compressibility factor Isothermal compressibility Coefficient of volume expansion Specific heat capacity Vapour pressure Internal energy Enthalpy Kinetic energy Potential energy Flow energy Dynamic viscosity Kinematic viscosity Surface tension

42. Mass, Weight, Volume & Density Mass (m): Quantitative measure of inertia . The inertial mass is a measure of an object's resistance to acceleration when a force is applied. i.e., resistance to a change in velocity. (kg) Weight (W): The weight of an object (W) is the magnitude of the force acting on the object due to Earth’s gravity field, i.e., the acceleration produced by gravity (N) Volume (V): It is the amount of space an object can takes up. (m 3 ) Density ( ) : It is a measure of how much matter occupies a given amount of space. It is quantified with the ratio of mass per unit volume.  = m / V (kg/m 3 )

43. Specific Volume, Specific Weight & Specific Gravity or Relative density Specific volume ( v ): It is defined as volume of a fluid occupied by a unit mass. In other words, it is the reciprocal of density. (m 3 /kg) Density Tower Specific Weight ( ): It is defined as the weight of the fluid per unit volume. (N/m 3 ) Specific gravity (SG): the ratio of a fluid’s density to that of a standard reference fluid (water for liquids/solids, air for gases) at STP.

44. Temperature & Pressure Temperature (T): It is the measure of degree of how hotness or coldness of an object is. In microscopic view, temperature is the average kinetic energy of the molecules. (K) Degree of coldness or hotness Pressure (P): It is defined as a normal, compressive and inward force exerted by a fluid per unit area. In microscopic view, pressure is the momentum transfer between the fluid and wall of the container. P = F / A (N/m 2 or Pa)

45. Absolute Pressure / Atmospheric Pressure/Gauge Pressure & Vacuum Pressure

46. 1 atm = 10.3 m of H 2 O 1 atm = 14.7 PSI 1 atm = 10 km of air 1 atm ~ 1 kgf/cm 2 ~ 10 5 Pa ~ 1 bar     Rough estimation Atmospheric Pressure 760 mm Hg or 0.76 mHg 10. 3 m H 2 O

47. Pascal Law: pressure at a point is equal in all directions Variation of Pressure with Depth P =  g h P x = P y = P z Pressure is independent of cross sectional area 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. Ratio A 2 / A 1 is called ideal mechanical advantage

48. Pressure Measurement Piezometer & Pitot Static Tube Simple U tube Manometer Differential Manometer Barometer Inclined manometer Bourdon tube Pressure Transmitter Pressure Transducer

49. Viscosity /Absolute Viscosity/Dynamic Viscosity/Coefficient of Viscosity Viscosity ( ) : The viscosity of a fluid is a measure of its resistance to the rate of deformation. (Pa.s = 10 Poise) The angular displacement or deformation (or shear strain) Linear Profile: u(y) = a + by (l) (l) Thus we conclude that the rate of deformation of a fluid element is equivalent to the velocity gradient du/ dy The rate of deformation (and thus the velocity gradient) is directly proportional to the shear stress Newton’s law of Viscosity:

50. Drag force: The force a flowing fluid exerts on a body in the flow direction. Drag Force & Pumping Power Pumping Power: This is the power required to overcome frictional force to move forward. It is also propulsive power. W p = F U The viscosity of a fluid is directly related to the pumping power needed to transport a fluid in pipe or to move a body through a fluid.

51. Newtonian and Non-Newtonian Fluids Newtonian Fluid: Fluids which obeys Newton’s Law of Viscosity. Non - Newtonian Fluid: Fluids which does not obeys Newton’s Law of Viscosity. B = 0 & n = 1: Newtonian fluid B = 0 & n < 1: Pseudo-plastic B = 0 & n > 1: Dilatant B  0 & n = 1:Bingham plastic Newtonian fluid Non - Newtonian fluid Pseudo plastic Dilatant Bingham Plastic

52. B  0 & n = 1: Bingham plastic B  0 & n < 1 : Thixotropic B  0 & n > 1: Rheopectic B = 0 & n = 1: Newtonian fluid B = 0 & n < 1: Pseudo-plastic B = 0 & n > 1: Dilatant Bingham Plastic Viscoelastic Viscosity Constant when shear force is applied Viscosity Varies when shear force is applied

53. Temperature vs. Viscosity of Fluids Liquids Gases Cohesive forces between the molecules Molecular collisions between molecules At high temperature, the intermolecular force of attraction decreases At high temperature, the kinetic energy of molecules increases rapidly Energized liquid molecules can move freely – weak force of attraction Energized gas molecules freely collide with other molecules Viscosity of liquid decreases with increase in temperature Viscosity of gas increases with increase in temperature

54. Kinematic Viscosity In fluid mechanics and heat transfer, the ratio of dynamic viscosity to density appears frequently. For convenience, this ratio is given the name kinematic viscosity ( ) (m 2 /s ; cm 2 /s = 1 stoke) In general, the viscosity of a fluid depends on both temperature and pressure, although the dependence on pressure is rather weak. For liquids, both the dynamic and kinematic viscosities are practically independent of pressure, and any small variation with pressure is usually disregarded, except at extremely high pressures. For gases, this is also the case for dynamic viscosity (at low to moderate pressures), but not for kinematic viscosity since the density of a gas is proportional to its pressure . Dynamic viscosity, in general, does not depend on pressure, but kinematic viscosity does.

55. Surface Tension [Interfaces: Solid – liquid, liquid – liquid, liquid - gas ] Surface Tension (  s ) : The magnitude of the tension force per unit length. (N/m) Surface Energy (  s ) : The stretching work that needs to be done to increase the surface area of the liquid by a unit amount. (Nm/m 2 or J/m 2 ) Drop of blood forms a hump on a horizontal glass. Water droplets from rain A drop of mercury forms a near perfect sphere Dew hang from leaves of trees A soap released into air Liquid fuel injected into the engine Practical examples The tendency of liquid droplets to attain a spherical shape, which has the minimum surface area for a given volume. Pressure difference or Pressure jump Effect of Surface Tension It decreases with increase in temperature and becomes zero at the critical point The effect of pressure on surface tension is usually negligible chemicals, called surfactants, can be added to a liquid to decrease its surface tension Liquid Jet Droplet Soap Bubble      

56. Capillary Effect [Interfaces: Solid – liquid ] capillary effect: The rise or fall of a liquid in a small-diameter tube inserted into the liquid Practical examples: The rise of oil through a cotton wick The rise of water to the top of tall trees The curved free surface of a liquid in a capillary tube - meniscus contact (or wetting) angle ϕ : the angle that the tangent to the liquid surface makes with the solid surface at the point of contact wet the surface when ϕ < 90° not to wet the surface when ϕ > 90°

57. Hydrostatics – Fluids at rest No relative motion between adjacent fluid layers – no shear stress to deform it The only stress in fluid statics is the normal stress - due to pressure alone Variation of pressure is due to the weight of the fluid → fluid statics is relevant only in the presence of gravity fields Applications: Floating or submerged bodies, water dams and gates, liquid storage tanks, etc.

58. Water stored in the dam – Dam design Stability of Immersed and Floating Bodies Fluids in rigid-body motion

59. A flat plate of uniform thickness h submerged in a liquid parallel to the free surface. Buoyant force acting on the plate is equal to the weight of the liquid displaced by the plate It is independent of distance (s) of the body from the free surface It is independent of the density of the solid body Buoyancy

60. Law of Floatation – Archimedes Principle Any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force, the magnitude of which is equal to the weight of the fluid displaced by the body.

61. A solid body dropped into a fluid will sink, float, or remain at rest at any point in the fluid, depending on its average density relative to the density of the fluid. The density of the water in the Dead Sea is about 24% higher than that of pure water. Therefore, people float much more easily (with more of their bodies above the water) in the Dead Sea than in fresh water or in normal seawater

62. Applications of Buoyancy

63. Stability of Immersed and Floating Bodies A floating body is stable if the body is (a) bottom-heavy and thus the center of gravity G is below the centroid B of the body, or (b) if the metacenter M is above point G. However, the body is (c) unstable if point M is below point G. An immersed neutrally buoyant body is (a) stable if the center of gravity G is directly below the center of buoyancy B of the body, (b) neutrally stable if G and B are coincident, and (c) unstable if G is directly above B. Stability is easily understood by analyzing a ball on the floor.

64. Lagrangian Description   Eulerian Description The mathematical tool material derivative is used to transformed from Lagrangian to Eulerian description System Approach   Control Volume Approach The mathematical tool Reynold’s Transport Theorem is used to transformed from System to Control volume approach Integral Analysis Differential Analysis Two Approaches in Fluid Mechanics Finite fluid element Infinitesimal fluid element

65. Types of Motion or Deformation of Fluid Elements A fluid element illustrating translation, rotation, linear strain, shear strain, and volumetric strain Translation Rotation Linear Strain Shear Strain Strain Rate Tensor in Cartesian Coordinates

66. Strain Rate Tensor in Cartesian Coordinates Rate of motion, rotation and deformation Volumetric Strain Rate /divergence   z   Incompressible flow  

67. Mass Energy Momentum Linear Momentum Angular Momentum T Kinetic energy correction factor

68. in W in m in Pa

69. Pump Turbine Pump-motor Turbine-generator

70. Linear and Angular Momentum Analysis T

71. Governing Equations Navier – Stokes Equation [NSE] x – momentum equation y – momentum equation z – momentum equation

72. Heat Transfer

73. Heat Transfer Conduction Radiation Heat Exchanger Convection Fourier Law Newton’s Law of Cooling Stefan- Boltzmann Law Types of Heat Exchanger Parallel Flow Counter Flow Cross Flow (Mixed and Unmixed) Shell and Tube (one or two shell with multiple tube pass) Method of Analysis LMTD -NTU

74. Conduction Heat Transfer Coordinate System Governing Equation n = for a plane wal l n = 1 for a cylinder n = 2 for a sphere Boundary Conditions Specified Temperature Boundary Condition Specified Heat Flux Boundary Condition Convection Boundary Condition Radiation Boundary Condition Interface Boundary Conditions Generalized Boundary Conditions Thermo - Physical Properties Thermal Conductivity Thermal Diffusivity Types of Problems 1D steady state using thermal resistance network Variable thermal Conductivity Heat generation in solids Critical radius of insulation Thermal contact resistance Enhancement of heat transfer – fins Transient heat conduction

75. 1D steady state using thermal resistance network Variable thermal Conductivity Heat generation in solids Critical radius of insulation Thermal contact resistance Enhancement of heat transfer - fins Transient heat conduction Fin Efficiency Fin Effectiveness

76. Governing Equations Forced Convection momentum mass energy Free Convection Heat Transfer Rate Pumping Power     Dimensionless Numbers Bulk Mean Temperature Film Temperature

77. Convection Problems Forced Convection Free Convection     Laminar Flow Turbulent Flow Flat Plate Cylinder Sphere Bank of Tubes Circular pipe non circular ducts Vertical Plate Vertical Cylinder Inclined Plates Horizontal Plate Horizontal cylinder Sphere   Internal Flow Laminar Flow Turbulent Flow

78. A i F ij = A j F ji

79. Thank You