Fundamentals ofThermodynamics
Introduction to Thermodynamics
what is Thermodynamics ??
Thermodynamic is a branch of science which deals with energy transfer and its effect on the system.
why study thermodynamics ?
Study of Thermodynamics is very useful in following fields
(A) power Developing devices like IC Engines, External combustion engines, Nuclear power plant.
(B) Power consuming devices like refrigerator, AC, pumps etc.
(C) Other utility systems like Heat exchangers, Chemical Power plant.
PURE SUBSTANCE
First We learn Working Substance
Pure substance is defined as the substance which remainshomogeneous and its chemical composition does not change,even through, it undergoes change of phase.
For example: A system of ice, water and steam as molecular structure of all three phases remains the same.
SYSTEM & SURROUNDING
System: A quantity of matter or a region in a space chosen for study.
Surrounding: The Mass or region outside the system.
Boundary: it is real or imaginary surface that separates the system from its surroundings.
Universe: System and surrounding together is called as Universe.
Types of Systems
Following are types of systems
1)Closed System
2)Open System
3) Isolated System
Closed System
In closed System there is no mass transfer across the boundaries but there is transfer of energy.
Open System
In open System Mass Transfer as well as heat and work transfer both take place across the boundaries.
Isolated System
In isolation system there is no mass or energy transfer across the boundaries.
Properties
Property can be defined as an observable characteristics of System
Types of Properties
1) Extensive Property
2) Intensive property
Extensive Property:
The property Which are dependent on mass called as Extensive property. Example: Volume and Energy
Intensive Property:
The property which are independent of mass are called as intensive property.
Example: Pressure, Temperature, Specific volume
Thermodynamic State
• State may be define as or describe by some observable quantities such as volume, pressure, temperature, density etc.
• All such quantities are called as thermodynamics properties.
• Minimum two properties are required to define state of system. state defines the actual condition of working substance.
• In below figure point 1 and 2 represent initial and final state of working substance respectively .
Thermodynamic cycle
• When Number of processes are performed on system, in such a way that final state is identical with initial state then it is called thermodynamic Cycle or Cyclic Process.
• In other word when system comes to original state after passing through a sequence of processes then it is known as cyclic process OR Thermodynamic cycle.
• In figure 1-A-2 and 2-B-1 represent thermodynamic processes Whereas 1-A-2-B-1 represents a thermodynamic cycle.
Energy
The Energy can be defined as capacity to do work.
The Energy posses by system is of two types
1) Stored Energy
2) Transient Energy
Stored Energy
The stored Energy is energy possessed by system within its boundaries.
Examples of stored Energy
1) Potential Energy
2) Kinetic Energy
3) Internal Energy
Examples of stored Energy
1) Potential energy: the energy possessed by a body or a system by virtue of its position in a force
field.
P.E. = Wz
= mgz
Where, W= Weight of body
m= mass of body
g = Acceleration due to gravity
z= Distance above the ground level
2) Kinetic Energy: It is energy possessed by a body by virtue of its mass and velocity of motion.
K.E.= 𝟏
𝟐 mc2 Where, m= mass of body
c= velocity of body
3) Internal energy: It is energy possessed by body due to its molecular arrangement and motion of molecules. & it is denoted by U.
4) Total Energy: It is sum of above three types of energies.
E= P.E.+K.E.+U
Transient Energy
Transient energy is defined as the energy which is capable of crossing boundaries.
For Example:
1) Heat
2) work
Examples of Transient Energy
1) Heat: Heat the energy transferred without transfer of mass across the boundaries due to an
intensive property difference ( temperature difference) between the system and surrounding.
Sign convention for heat
During the passage of fluid through a system, Fluid can have heat interaction specified below.
a) Heat Added to system then Q +ve
b) Heat rejected to system then Q –ve
c) If Heat neither added nor rejected
then Q=0
2) Work
In thermodynamics work is defined as The energy transferred without transfer of mass across the
boundaries due to an intensive property difference between system and surrounding.
Sign convection for work
a) If work done by system then W +ve
b) If External work required or Work Consumed
then W –ve
c) If No Work done then W=0
Some Basic Terms
1) Pressure: Pressure is defined as Force per Unit Area.
It is measured in N/m2 or Pascal or Bar.
2) Temperature: Temperature is a Thermodynamic property which shows the degree of hotness or heat intensity of a body.
Units: Kelvin, Fahrenheit.
3) Density: Density is the ratio of mass to the volume.
Units: kg/ m3
4) Specific Weight: Specific Weight is the weight of gas having unit volume.
Some Basic Terms
5) Enthalpy: • We already know about enthalpy. Enthalpy is related to the amount of energy that is lost or gained by a system during a normal chemical process. • Enthalpy is defined as sum of internal energy (U) and product of pressure and volume.
Mathematically, H= U+PV
Units: Joules or kilo-Joules
6) Specific Enthalpy:
It is the enthalpy of gas having mass 1kg.Mathematically,
h= u+pv
Where, u = Specific internal energy
v= Specific volume
p = Pressure
Units : J/kg
Some Basic Terms
7) Entropy: • Entropy is defined as a thermodynamic property of working substance which increase with addition of heat and decreases with removal of heat.
• Entropy is a property of system that is depend on initial and final states of system and independent of path followed due that entropy is a point function. • It is denoted by S
• its unit: J/kg k or Kj/kg k.
Characteristics of Entropy
• Entropy increases, when heat is supplied, irrespective of the fact, whether temperature changes or not.
• Entropy Decreases, when heat is removed, irrespective of the fact that, whether temperature changes or not.
• During all adiabatic frictionless processes, heat transfer is zero. Therefore entropy remains constant and change in entropy is dS=0.
Law of Conservation of Energy
It states that energy can neither be created nor be destroyed through
it can be transformed from one form to another form.
Thermodynamic Equilibrium: • Thermal Equilibrium
• Mechanical Equilibrium
• Chemical Equilibrium
All types of Equilibriums includes in Thermodynamic Equilibrium.
Zeroth Law of Thermodynamics
Thermal Equilibrium:
• When two bodies having different temperature are brought in contact with each other then after some time we observe that both bodies are at same temperature. When this states equal temperature attained then two bodies are said Thermal equilibrium.
Zeroth Law of Thermodynamics
For Example:
Where system A is in Thermal equilibrium with system C atthe same time system B is also thermal equilibrium withsystem C.
According Zeroth’s law of thermodynamicsystems A and B are also in Thermal equilibrium with eachother and with system C. Thus, all three systems are in thermal equilibrium.
First Law of Thermodynamics
Statements of first Law:
1) Heat And work are mutually convertible that is when closed system undergoes a change then the net heat transfer is equal to the net work transfer.
2) Energy can Neither be created nor be destroyed through it can be converted from one form to another form.
3) It is possible to construct a perpetual motion machine of I st kind (PMM-I)
4) For closed system heat transfer is equal to sum of work transfer and change in stored energy,
dQ = dW + dE
Where, stored Energy (E) =K.E.+P.E.+I.E.
By mathematically,
Q = W + d(K.E.+P.E.+I.E.)
Q = W + d(K.E.) + d(P.E.)+ d(I.E.)
If changes in K.E. and P.E. are Neglected and change in Internal Energy is written as
Q = W + U
For analysis we consider the small Element the equation are modified as
dQ = dW + dU
Perpetual Motion Machine of First kind (PMM-I)
• PMM-I is Defined as a Machine which produces work energy without consuming an equivalent amount of another energy from any source.
• It is Impossible to construct machine because no machine can produce energy of its own.
• PMM-I violates the Law of conservation of Energy.
Limitations of First law of
Thermodynamics
1) First law does not specify the direction of flow of heat and energy.
2) This law could not specify the grade of Energy.
3) First law does not give the idea about reversible and irreversible processes.
Second law of Thermodynamics
Second law of Thermodynamics is defined in two ways
1) Kelvin Plank Statement:
It state that It is impossible to construct heat engine working on a cyclic process whose sole aim is convert the heat energy supplied into an equivalent amount of work.
2) Clausius Statement:
It states that it is impossible for a machine to transfer heat from a body at low temperature to a body at high temp without supply of external work.
Perpetual Motion Machine of second kind
(PMM-II)
PMM-II can be defined by two ways
1) PMM-II is defined as a device which converts total amount of heat supplied into equivalent amount of work. Since output is exactly equal to input. Efficiency of PMM-II is 100%. However this is impossible in actual practice. Therefore PMM-II violates Kelvin Plank statement.
Perpetual Motion Machine of kind II (PMM-II)
PMM-II is defined as a devicewhich can transfer heat from coldbody to hot body without supplyof external work.PMM-II violates the Clausius statement.
Classification of Thermodynamic
Processes
All Thermodynamic Processes are classified as in two types
1) Flow Processes: The process occurring in open system which permit the flow of mass of working substance across the boundaries to and from the system are known as flow processes.
It is classified in two types
a) Steady flow
b) Unsteady flow
2) Non flow Processes: -A process is said to be non flow in which a fixed mass undergoes a change of state within the defined boundary of system.
Steady Flow Energy Equation (SFEE)
Following are the assumption made for deriving SFEE
1) The mass flow rate throughout the system remains constant.
2) The heat transfer rate and work transfer rate also remain constant throughout system.
3) The chemical composition of fluid remains same.
4) Potential Energy, Kinetic Energy, Internal Energy and flow work energies are considered. Other forms like electrical, chemical energies neglected.
5) Only heat and work interaction between system and surrounding.
Steady Flow Energy Equation (SFEE)
Consider an open system through which the working substance flow at a steady rate.
Where,
P1 = Pressure substance entering the system
C1 = velocity of substance entering the system
Z1 = Height above the datum level for level
VS1= specific volume substance entry system
u1 = Specific internal energy
Q = Heat Supplied
W = Work done
