BASIC COCEPT OF THERMODYNAMICS Prof kiran gore Thermodynamics

BASIC COCEPT OF THERMODYNAMICS Prof. kiran gore

Thermodynamics Greek word Theme – Heat Dynamics – Motion Thermo” refers to released heat during combustion “ Dynamics” refers to mechanical action for doing work “ Definition “Thermodynamics is the science which deals with energy transfer & effect of energy transfer on the properties of substance. ”

Thermodynamic system, boundary , surrounding

Thermodynamic system

Types of system 1. Closed system 2. Open system 3. Isolated system

Closed system (Control mass)

Example of closed system Food items in pressure cooker

Example of closed system • Gas trapped within a piston & cylinder device stopper P I S T O N C Y L I N D E R

Example of closed system • Hot coffee in a cup Heat flows in the direction of decreasing temperature.

Example of closed system • Bulbs & lamp

Open system (control volume)

Example of open system WATER BOILER

Example of open system Nozzle

Example of open system Reciprocating air comp

Example of open system Internal combustion engine

Adiabatic system

Example of isolated system Thermos

Units & Dimension q Mass – The basic unit of mass is Kg. for larger masses units of mass is Tone. 1 Tone = 1000 Kg. or 103 Kg. q Volume The space occupied by the matter is called as volume. Unit = m 3 or Liter 1 Liter= 10 -3 m 3

Units & Dimension q Weight – Weight of the body is the force exerted on it’s mass due to gravity. Weight (W) = m. g Where m= mass of the body in Kg. g= acceleration due to gravity.

Units & Dimension q Force. The product of mass & acceleration is called as force. Force = mass X acceleration = Kg X m/s 2 =N

Units & Dimension q Density -mass per unit volume of a substance. q. Specific volume -volume per unit mass of a substance.

Units & Dimension q Specific gravity The ratio of the density of a substance to the density of water.

Units & Dimension Which shoes create the most pressure?

Units of Pressure The most common unit for pressure is bar 1 bar = 105 pa = 105 N/ m 2 = 102 K pa Force Pressure = Area = N/ m 2 = Pascal

Atmospheric pressure, absolute, gauge

Units & Dimension q. Temperature – Temperature can be define as measure of hotness or coldness. Ø The temperature of a body is measured in Celsius (o c), Kelvin (K), Fahrenheit (o f). Ø Their relation is 1 o c = 273 K

Energy • Energy is defined as capacity to do work. • Any one form of energy can be converted into another form. • Energy can be stored in different forms. • The different forms are as 1. Potential energy 2. Kinetic energy 3. Internal energy

Potential energy of the system is the energy stored in the system due to its position in a gravitational field. d(P. E. ) = m. g. (Z 2 –Z 1) Kinetic energy of a system is the energy which arises from the motion of a mass. d(K. E. ) = 1/2. m. (V 2 2 –V 1 2 )

Internal energy (U) It is the energy arising in the form motions of molecules & atoms. Total energy The total energy of the system is the summation of potential energy, kinetic energy, & internal energy. Total energy (E) = P. E. + K. E. +U

Heat • It is the transfer form of energy that flows between two system (or a system & its surrounding ) by virtue of the temperature difference between them. Surroundings System Heat

Heat transfer rate (Q) The quantity of heat transfer in unit time is called as heat transfer rate. Q = Q/ dt KJ/s or KW Heat transfer (q) The heat transfer per unit mass of the system is denoted by q & it is expressed as q = Q/ m k. J/ kg

Relation between Q & q Q = 30 k. J m = 2 kg t = 5 s Q = 6 k. W q = 15 k. J/kg

Specific heat (C) • The specific heat of a substance is define as the quantity of heat required to raise the temperature of unit mass of substance through unit degree temperature difference. C = 1/m (d. Q/d. T) k. J/kg. K ØLiquids & solids have only one specific heat. ØGases have two specific heat (Cp or Cv). Cp = specific heat at constant pressure Cv = specific heat at constant volume

Work The work like heat is also form energy in transit. It is defined as the energy transfer associated with force acting through a distance. Surroundings System Work q. Mechanical work – Work done = Force X displacement =NXm = Joule Heat

Moving boundary work Pext V 2 Pint V 1

Sign Conventions U = q - w +w System -w +q -q engineering

Units & Dimension q Powerpower. The rate of doing of work is called as = N. m/ s = J/s =Watt (W)

Enthalpy (H) • The sum of internal energy (U )& the product of pressure (P) & volume (V) appears frequently in many thermodynamic analyses. Enthalpy (H) = U + p V • It is measured in units of Kj. • The enthalpy per unit mass system is referred as specific enthalpy & is denoted by h (Kj/Kg).

Entropy

Equality of temperature Hot system TRANSFER OF HEAT Cold system

Example of Equality of temperature

Zeroth low of thermodynamics “It states that when two system are in thermal equilibrium with third system then they are thermal equilibrium with each other”. System (s 1) A D I A B T I C W A L L System (s 3) System (s 2)

Thermodynamic Properties • Any measurable & observable characteristics of a system is called as “thermodynamics property”. Properties: • Temperature • Pressure • Volume • Internal energy • Entropy System

Classes of properties • Intensive – TEMPERATURE – PRESSURE – DENSITY NOT ADDITIVE OVER THE SYSTEM. Intensive properties: Those that are independent of the mass of a system, such as temperature, pressure, and density. • Extensive – MASS – VOLUME – ENERGY ADDITIVE OVER THE SYSTEM. Extensive properties: Those whose values depend on the size—or extent—of the system.

Criterion to differentiate intensive and extensive properties.

Thermodynamics State, path, process & cycle

Thermodynamics State The thermodynamic state is the condition of the system as characterized by certain thermodynamic properties like pressure, temperature specific volume etc.

Thermodynamic process • The transformation of the system from one fixed stats to another state is called as a process.

Thermodynamic path • A locus of series of state thorough which a system passes between initial state and final states is called path.

Thermodynamic cycle A thermodynamic cycle is a sequence of processes that begins & ends at the same state.

Point function When a system undergoes a change from one state to another, the properties of the system also change, which depends only on the end states & not on the path followed between these two stats. Therefore, these properties are called state function / point function. E. g. Temperature, pressure, volume.

Path function Ø A quantity whose value depends upon on the particular path followed during the process is called as a path function. Ø It requires a particular path & direction to represent the quantity on any plot. Ø E. g. heat , work.

Types of process Process- The transformation of the system from one fixed stats to another state is called as a process. • Types of process 1. 2. 3. 4. 5. Isobaric process Isochoric process Isothermal process Adiabatic process Polytrophic process

Isobaric process (constant=P) The process in which pressure of the system is kept remain constant is called as isobaric process.

Isochoric process (const=V) The process in which volume of the system is kept remain constant is called as isochoric process

Isothermal process (const =T) The process in which Temperature of the system is kept remain constant is called as Isothermal process.

Adiabatic process (pv√) The process in which entropy is kept constant during a process is called as adiabatic process. in these process heat neither leave nor enters the system.

Gas Laws BOYLES CHARLES GAY-LUSSAC’s

Boyle’s Law It states that if unit mass of gas is maintained at constant temperature, then the volume of gas is inversely proportional to the absolute pressure of gas. Robert Boyle P V ά 1/P PV = k V

Boyle’s Law

Charles’ Law It states that if unit mass of gas is maintained at constant pressure, then the volume of gas is directly proportional to the absolute temperature of gas. Jacques Charles V T

Charles’ Law

Gay-Lussac’s Law It sates that, the absolute pressure of unit mass of gas varies with it’s absolute temperature, when the volume of gas is kept constant. Gay-Lussac’s P T

D. Combined Gas Law P V PV PV = k T P 1 V 1 P 2 V 2 = T 1 T 2 P 1 V 1 T 2 = P 2 V 2 T 1

Ideal gas equation p. V = m. RT • Where, P = pressure in N/m 2 or pa, V = Volume in m 3, m = Mass of gas in kg, T = absolute temperature in K & R = Gas constant in J/kg. K = 0. 287 k. J/kg. K

Low of conservation of energy It states that the “ the energy can neither created nor be destroyed, but whenever there is change in the state of a system there is only transformation of one form of energy in to another.

First law of thermodynamics The statement of first low of thermodynamics in different forms can be stated as Ø When system undergoes in cyclic change, then the algebric sum of work delivered to the surrounding is directly proportional to the algebric sum of heat taken from the surrounding. i. e. Ф dw α

THERMODYNAMICS AND ENERGY • Thermodynamics: The science of energy. • Energy: The ability to cause changes. • The name thermodynamics stems from the Greek words therme (heat) and dynamis (power). • Conservation of energy principle: During an interaction, energy can change from one form to another but the total amount of energy remains constant. • Energy cannot be created or destroyed. • The first law of thermodynamics: An expression of the conservation of energy principle. • The first law asserts that energy is a thermodynamic property. Energy cannot be created or destroyed; it can only change forms 75 (the first law).

Example • Imagine a brick resting on window ledge 3 meters high. As the brick rests on the ledge it has potential energy. • If you knock the brick out of the ledge, the potential energy is converted to kinetic energy( the brick accelerated towards the ground). • When the brick hits the ground the kinetic energy converted to light energy (sparks), Sound energy and chemical energy (the brick breaks).

1 -12 Bomb Calorimeter Used to Determine Energy Content of Food (Fig. 1 -53)

E. Pressure • Barometer – measures atmospheric pressure Aneroid Barometer Mercury Barometer

E. Pressure • Manometer – measures contained gas pressure U-tube Manometer Bourdon-tube gauge

B. Charles’ Law V T

10 miles 4 miles Sea level 0. 2 atm 0. 5 atm 1 atm

As P (h) increases V decreases

1 -7 Compressed Process P-V Diagram (Fig. 1 -31)

1 -8 Absolute, Gage, and Vacuum Pressures (Fig. 1 -36)

1 -9 The Basic Manometer

1 -10 Temperature Scales Comparison (Fig. 1 -48)

1 -27 Chapter Summary • The absolute temperature scale in the SI is the Kelvin scale, which is related to the Celsius scale by

1 -28 Chapter Summary • In the English system, the absolute temperature scale is the Rankine scale, which is related to the Fahrenheit scale by

1 -29 Chapter Summary • The magnitudes of each division of 1 K and 1 0 C are identical, and so are the magnitude of each division of 1 R and 10 F. Therefore, and

• The second law of thermodynamics: It asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy. • Classical thermodynamics: A macroscopic approach to the study of thermodynamics that does not require a knowledge of the behavior of individual particles. • It provides a direct and easy way to the solution of engineering problems and it is used in this text. • Statistical thermodynamics: A microscopic approach, based on the average behavior of large groups of individual particles. • It is used in this text only in the supporting role. Conservation of energy principle for the human body. Heat flows in the direction of decreasing 92

Application Areas of Thermodynamics 93

IMPORTANCE OF DIMENSIONS AND UNITS • Any physical quantity can be characterized by dimensions. • The magnitudes assigned to the dimensions are called units. • Some basic dimensions such as mass m, length L, time t, and temperature T are selected as primary or fundamental dimensions, while others such as velocity V, energy E, and volume V are expressed in terms of the primary dimensions and are called secondary dimensions, or derived dimensions. • Metric SI system: A simple and logical system based on a decimal relationship between the various units. • English system: It has no apparent systematic numerical base, and various units in this system are related to each other rather arbitrarily. 94

• Open system (control volume): A properly selected region in space. • It usually encloses a device that involves mass flow such as a compressor, turbine, or nozzle. • Both mass and energy can cross the boundary of a control volume. • Control surface: The boundaries of a control volume. It can be real or imaginary. An open system (a control volume) with 95

PROPERTIES OF A SYSTEM • 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. • 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 Criterion to differentiate properties per unit mass. intensive and extensive properties. 96

Thermodynamic Systems Air Water Sediment

Types of Systems Isolated System Closed System Open System

Terms Phases Surroundings System quartz Water Ca. O • CO 2 Components Si. O 2 H 2 O Calcite wollastonite Ca. O • Si. O 2

Equation of State Intensive Variables P = Pressure T = Temperature Extensive Variables V = Volume n = moles

First Law Internal Energy work heat

Entropy Second Law S°ice < S°water < S°steam Measure of disorder of a phase S° of a pure crystalline solid = 0 at 0 K Third Law

Enthalpy Heat content of a substance at constant pressure

Heat Capacity

1 -1 Applications of Thermodynamics The human body Air-conditioning systems Car radiators Airplanes Power plants Refrigeration systems

Isolated System • Closed system where no heat or work (energy) may cross the system boundary – typically a collection of the a main system (or several systems) and its surroundings is considered an isolated system Isolated system boundary work Surr 1 system heat Surr 2 mass Surr 3

Total Energy of a System • Sum of all forms of energy (i. e. , thermal, mechanical, kinetic, potential, electrical, magnetic, chemical, and nuclear) that can exist in a system • For systems we typically deal with in this course, sum of internal, kinetic, and potential energies E = U + KE + PE E = Total energy of system U = internal energy KE = kinetic energy = m. V 2/2 PE = potential energy = mgz

Properties • Any characteristic of a system in equilibrium is called a property. • Types of properties – Extensive properties - vary directly with the size of the system Examples: volume, mass, total energy – Intensive properties - are independent of the size of the system Examples: temperature, pressure, color • Extensive properties per unit mass are intensive properties. specific volume density v = Volume/Mass = V/m r = Mass/Volume = m/V

State & Equilibrium • State of a system – system that is not undergoing any change – all properties of system are known & are not changing – if one property changes then the state of the system changes • Thermodynamic equilibrium – “equilibrium” - state of balance – A system is in equilibrium if it maintains thermal (uniform temperature), mechanical (uniform pressure), phase (mass of two phases), and chemical equilibrium

Processes & Paths • Process – when a system changes from one equilibrium state to another one – some special processes: • isobaric process - constant pressure process • isothermal process - constant temperature process • isochoric process - constant volume process • isentropic process - constant entropy (Chap. 6) process • Path – series of states which a system passes through during a process

1 -7 Compression Process

1 -6 Quasi-Equilibrium Processes • System remains practically in equilibrium at all times • Easier to analyze (equations of state can apply) • Work-producing devices deliver the most work • Work-consuming devices consume the least amount of work

State Postulate & Cycles • State Postulate – The thermodynamic state of a simple compressible substance is completely specified by two independent intensive properties. • Cycles – A process (or a series of connected processes) with identical end states P 2 Process B Process 1 A V