Meg 201 Lecture i & II
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Transcript of Meg 201 Lecture i & II
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In Science a type of question often asked is how much? How big? In order to answer such questions it is
important to have systems of measurement which are consistent and understood by all.
DIMENSIONS
Dimension is a property that can be measured such as distance, time, mass, temperature, speed, e.t.c
AUNIT
A unit is a basic division of a measure quantity and it enables one to say how much of the quantity we have.
FUNDAMENTALUNITS
A set of Fundamental Unit is a set of units for physical quantities from which every other unit can begenerated. There are seven basic fundamental Units in the field of Science and Engineering. The units are
listed below;
DERIVEDUNITS
Derived Units are units that are defined by reference to combinations of the Fundamental units.
DIMENSIONS & UNITS
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FUNDAMENTAL UNITS
There are seven basic fundament units in the field of Science and Engineering.:
Physical Quantity Unit
Length(l) Meter(m)
Mass(m) Kilogram(KG)
Time(t) Seconds(s)
Temperature(T) Kelvin (K)
Electric Current (I) Ampere (A)
Luminous Intensity Candela(cd)
Amount of Substance (n) Mole(mol)
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A system of unit is a set of Fundamental units defined for the purpose of measuring all necessary
physical quantities.
There are two major systems of units
1. Metric System
2. British Imperial System
S.I. unit will be used throughout in this course. S.I. unit is The International System of Units.
Adopted by the General Conference of weight and measures in 1960 and consequently endorsed
by the International Organization for Standardization. It is aCoherent System In a Coherent
System, all derived unit quantities are formed by the product or quotient of other unit quantities.
SYSTEM OFUNITS
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FUNDAMENTAL CONCEPTS
The following Fundamental Thermodynamic Concepts to be considered in
this course at this level are:
Systems
Control Volume
Properties and State of a System
Thermodynamic Process
Heat
Work
Pressure
Temperature
Zerothe Law
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THERMODYNAMIC SYSTEM
A system may be defined as a region
in space containing a quantity of
matter whose behaviour is being
investigated. This quantity of matter
is separated from its surrounding by a
boundary which may be a physical
boundary e.g. wall of a vessel.
A system may be defined as a collection
of matter within a prescribed and
identifiable boundary.
The boundaries are not necessarily
inflexible while surrounding is restricted
to those portion of matter external to the
system which are affected by change
occurring within the system
Boundary
Surroundings
Systems
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Boundary
Classification of Thermodynamic Systems
Thermodynamic systems can be classified into two basic: Closed System and
Open System
. Closed System
It is one in which there is no mass
transfer across the boundaries. e.gCombustion chamber of an Internal
combustion engine. It is a system of
fixed mass and identity whose
boundaries are determined by the
space of the matter occupied in it.
. Open System
An open system is one in which there is atransfer of mass of the working substance
across the boundaries. e.g. In a gas
turbine.
Turbine
Outlet
Inlet
Turbine
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CONTROL VOLUME
A control volume is defined as a fixed region in space where
one studies the masses and energies crossing the boundaries
of the region.
The concept of a control volume is very useful in analyzing
fluid flow problems.
Control Volume
1 2
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PROPERTIES & STATE OFA SYSTEM
Properties of a System
All the quantities that identify the State of a system are called Properties.
It is classified into two general groups; Extensive and Intensive Properties
Extensive Properties
The Properties of the system, whose
value for the entire system is equal to
the sum of their values for the
individual parts of the system are
called extensive properties, e.g. total
volume, total mass and total energy of
a system are its extensive properties.
Intensive Properties
The Properties of the system, whose
value for the entire system is not
equal to the sum of their values for
the individual parts of the system are
called intensive properties, e.g.
temperature, pressure and density
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State of a SystemIn all problems in Applied Thermodynamics we are concerned with energy transfers to or
from a system. Thestate of a system (when the system is in thermodynamic equilibrium) is
the condition of the system at any particular moment which can be identified by the statementof its properties, such as pressure, volume, temperature e.t.c. The number of properties
required to describe the system depends upon the nature of the system.
Path of Change ofState
When a system passes through the
continuous series of equilibrium states
during a change of state (from the initial
state to the final state), then it is known as
thepath of change of State.
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THERMODYNAMIC PROCESS
When a system changes its state from one equilibrium state to another equilibrium
state, then the path of successive state through which the system has passed is
known as thermodynamic process.
Thermodynamic or CyclicP
rocessWhen a process or processes are performed on a system in such a way that the
final state is identical with the initial state, it is known as a thermodynamic cycle or
cyclic process.
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HEAT
Heat is a form of energy which is transferred from one body to another body at a lower temperature , byvirtue of the temperature difference between the bodies.
Surroundings
For example when a body A at a certain temperature, say 50C, is brought into contact with a body B at a hightemperature, say 55C, then there will be a transfer of heat from B to A until the temperature of A are equal.
When the temperature of A is the same as the temperature of B, no heat transfer takes place between the bodies andthey are said to be in thermalequilibrium.
Heat is a form of transient energy which can be identified only when it crosses the boundary of a system. It exist
only during transfer of energy into and out of a system.
Heat can never be contained in a body or possessed by a body.
The heat flowing into a system is considered aspositive and heat flowing out of a system is considered negative
Heat can be transferred in three distinct ways, i.e. conduction, convection and radiation
S.I unit for heat is the Joule.
A BThermal
Insulator
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WORK
Mechanical work is defined as theproduct of a force(F) and the distance (l)
moved in the direction of the force.
W = F x l
Work done by the system on its surrounding is considered aspositive work,
while work on the system by its surrounding is considered as negative work.
Work is observed to be energy in transition. It is never contained in a body or
possessed by a body.
S.I unit of work is Nm = 1J
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CONTROL VOLUME
WORKDONE Work done by the fluid on the piston is givenby;
dW = F x dl
= P x A x dl
where A is the area of the piston
A x dl = dv
dW = Pdv
work done by the expanding fluid is;
W (+ve)
System
W(-ve)
Q(+ ve) Q(- ve)
Surrounding
F FFF
dv
Work done at moving boundary in a
Piston-Cylinder
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Quasi-Static or Quasi-equilibrium Process
When the process is carried out in such a way that at every instant, the system derivation from the
thermodynamics equilibrium is infinitesimal, then the process is known as Quasi-Static or Quasi-equilibrium
Process and each state in the process may be considered as an equilibrium state.
iv. Work done at constant volume
V1 = V2 = V
W = 0
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Quiz(10mins)
(1) State four thermodynamic processes (2) Give four similarities between Heat andWork
Solution
1) Thermodynamic Processes are;
Cyclic Process
Isobaric Process
Isothermal Process
Isochoric Process
Polytropic Process
Isentropic Process
Adiabatic Process
2) Similarities between Heat & work
i) Heat and Work are both transient phenomena.The systems do not possess heat or work.
ii) Heat and Work are boundary phenomena .They are observed at the boundary of thesystem.
iii) Heat and Work represent the energy crossingthe boundary of the system.
iv) Heat and Work are path function and hencethey are inexact differentials. They are writtenas Q and W
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Things to read-up
Temperature
Pressure