Basic Thermodynamic
Basic Thermodynamic
Basic Thermodynamic
by
Sharan Shegedar & Laxmikanth S G
Depatment of Mechanical Engineering
Engineering & Technology
Faculty of Co-Education
12/16/2019 1
12/16/2019 2
12/16/2019 3
FUNDAMENTAL CONCEPTS , DEFINITIONS , WORK AND HEAT
Thermodynamic definition and scope, Microscopic and Macroscopic
approaches. Some practical applications of engineering thermodynamic
Systems. Thermodynamic systems and control volume with examples.
Thermodynamic properties, states, processes and cycles, reversible and
irreversible process, quasi-static process. Thermodynamic equilibrium;
definition, mechanical equilibrium; diathermic wall, thermal equilibrium,
chemical equilibrium, Zeroth law of thermodynamics, Temperature;
concepts, scales, international fixed points and measurement of
temperature, simple problems on temperature concept.
Mechanics, definition of work and its limitations. Thermodynamic
definition of work; examples, sign convention, Point and path function.
Displacement work in quasi static process, other modes of work , Heat
Transfer and Compression of heat and work.
12/16/2019 5
Module-1 Fundamental Concepts , Definitions , Work and Heat
(10 hours)
Thermodynamic definition and scope, Microscopic and Macroscopic
approaches. Some practical applications of engineering thermodynamic
Systems. Thermodynamic systems and control volume with examples.
Thermodynamic properties, states, processes and cycles, reversible and
irreversible process, quasi-static process. Thermodynamic equilibrium;
definition, mechanical equilibrium; diathermic wall, thermal equilibrium,
chemical equilibrium, Zeroth law of thermodynamics, Temperature;
concepts, scales, international fixed points and measurement of
temperature, simple problems on temperature concept.
Mechanics, definition of work and its limitations. Thermodynamic
definition of work; examples, sign convention, Point and path function.
Displacement work in quasi static process, other modes of work , Heat
Transfer and Compression of heat and work.
12/16/2019 5
Thermodynamic definition and scope
Thermodynamics is the branch of science which deals with energy transfer and its effect
on the physical properties of the system.
It is based upon the observation of common experience which have been formulated into
thermodynamic laws. It is mainly study of 3E’s , i.e Equillibrium, Energy and Entropy.
Thermodynamics is concerned with the ways
energy is stored within a body or system and how energy transformations, including those
which involve heat flow and work done on or by the system, may take place. Another partial
definition: “The study of the laws that govern the conversion of energy from one form to
another, the direction in which heat will flow, and the availability of energy to do work...”
Thermodynamics is a branch of physics concerned with heat and temperature and their relation
to energy and work. It defines macroscopic variables, such as internal energy, entropy, and
pressure, that partly describe a body of matter or radiation. It states that the behavior of those
variables is subject to general constraints, that are common to all materials, beyond the peculiar
properties of particular materials. These general constraints are expressed in the four laws of
thermodynamics [including the Zeroth Law]. Thermodynamics describes the bulk behavior of
the body, not the microscopic behaviors of the very large numbers of its microscopic
constituents, such as molecules.
12/16/2019 6
Define thermodynamics ?
The subject of this course is classical macroscopic
thermodynamics TD (i.e., not microscopic statistical
thermodynamics).
What is Thermodynamics?
12/16/2019 10
THERMODYNAMIC SYSTEMS AND CONTROL VOLUME WITH EXAMPLES
A Thermodynamic (TD) System is a quantity of matter or region in space chosen for study. It
is bounded by a real or imaginary surface called the boundary, which separates the system
from its surroundings.
A system with no movement of mass into or out of it (such as a sealed tank) is called
a closed system with fixed mass (aka control mass). Energy in the form of heat or work may
move in and out, and the real or imagined boundary and enclosed volume may move.
If energy as well as mass is not allowed to move in or out, the closed system is also
isolated. [Apparently the volume of an isolated system can change.] An isolated system is a
general system of fixed mass (thus a closed system) where no heat or work may cross the
boundary. It is a closed system with fixed mass and also with no energy crossing its boundary.
An isolated system is often a collection of systems (aka subsystems) contained within an
overall boundary, including a main system and surrounding systems all within the overall
boundary that are exchanging mass and energy among themselves but none exchange mass or
energy outside the overall boundary.
A system with fixed volume which allows mass (and energy) to enter or exit is
called an open system with a fixed volume (aka control volume) — it is enclosed within a real
or imagined control surface. Energy and mass may move in and out and the boundary, which is
usually fixed (but may move in some systems). Examples of control volume devices include
compressors and turbines. Under steady-flow conditions, instantaneous mass and energy
12/16/2019 11
contained in the volume are often constant.
A thermodynamic system is defined as a quantity of matter or a region in space upon which
attention is concentrated in the analysis of a problem. Everything external to the system is
called the surroundings or the environment(shown in fig below). The system is separated
from the surroundings by the system boundary. The boundary may be either fixed or
moving. A system and its surroundings together comprise a universe.
There are three classes of systems: (a) closed system, (b) open system and (c) isolated system.
The closed system (Fig. ) is a system of fixed mass. There is no mass transfer across the
system boundary. There may be energy transfer into or out of the system. A certain quantity
of fluid in a cylinder bounded by a piston constitutes a closed system.
12/16/2019 12
The open system (Fig. 1.3) is one in which matter crosses the boundary of the system. There
may be energy transfer also. Most of the engineering devices are generally open systems, e.g.,
an air compressor in which air enters at low pressure and leaves at high pressure and there are
energy transfers across the system boundary. The isolated system (Fig. 1.4 ) is one in which
there is no interaction between the system and the surrounding. It is of fixed mass and energy,
and there is no mass or energy transfer across the system boundary.
If a system is defined as a certain quantity of matter, then the system contains the same
matter and there can be no transfer of mass across its boundary. However, if a system is
defined as a region of space within a prescribed boundary, then matter can cross the
system boundary. While the former is called a closed system, the latter is an open
system.
12/16/2019 13
For thermodynamic analysis of an open system, such as an air compressor (Fig. 1.5),
attention is focused on a certain volume in space surrounding the compressor, known as the
control volume, bounded by a surface called the control surface. Matter as well as energy
crosses the control surface.
A closed system is a system closed to matter flow, though its volume can change against a
flexible boundary. When there is matter flow, then the system is considered to be a volume
of fixed identity, the control volume. There is thus no difference between an open system
and a control volume.
12/16/2019 14
THERMODYNAMIC PROPERTIES, STATES, PROCESSES AND CYCLES,
Every system has certain characteristics by which its physical condition may be
described, e.g., volume, temperature, pressure, etc. Such characteristics are called
properties of the system. These are all macroscopic in nature.
When all the properties of a system have definite values, the system is said to
exist at a definite state. Properties are the coordinates to describe the state of a
system. Or
State : It is the condition of the system at an instant of time as described or
measured by its properties or each unique condition of the system is called a
state
Any operation in which one or more of the properties of a system changes is
called a change of state.
The succession of states passed through during a change of state is called the
path . or
It is a series of state through which a system passes during a process is called
path of the process
12/16/2019 15
When the path is completely specified, the change of state is called a process, e.g. a
constant pressure 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 iss known
as thermodynamic process.
A thermodynamic cycle is defined as a series of state changes such that the final state is
identical with the initial state (Fig. 1.6).
while a system consisting of more than one phase is known as a heterogeneous system.
Examples: Cereal in milk, Vegetable soup, Pizza, Blood ,Gravel, Ice in soda, Salad dressing, Mixed nuts
,Bowl of colored candies and Soil
12/16/2019 17
In mechanics, equilibrium means a condition of balance maintained by an
equality of opposing forces.
Thermodynamic Equilibrium
A system is said to exist in a state of thermodynamic equi1ibrium when no
change in any macroscopic property is registered, if the system is isolated from its
surroundings.
An isolated system always reaches in course of time a state of thermodynamic
equilibrium and can never depart from it spontaneously. Therefore, there can be no
spontaneous change in its any macroscopic property, if the system exists in an
equilibrium state. Thermodynamics studies mainly the properties of physical systems that
are found in equilibrium states.
12/16/2019 18
In the absence of any unbalanced force within the system itself and also
between the system and the surroundings, the system is said to be in a state of
mechanical equilibrium. If an unbalanced force exists, either the system alone or
both the system and the surroundings will undergo a change of state till mechanical
equilibrium is attained.
12/16/2019 19
When the conditions for any one of the three types of equilibrium are not satisfied,
a system is said to be in a non-equilibrium state. If the non-equilibrium of the state is due
to an unbalanced force in the interior of a system or between the system and the surrounding,
the pressure varies from one part of the system to another. There is no single pressure that
refers to the system as a whole. Similarly, If the non-equilibrium is because of the
temperature of the system being different from that of its surroundings, there is a non-
uniform temperature distribution set up within the system and there is no single temperature
that stands for the system as a whole. It can thus be inferred that when the conditions for
thermodynamic equilibrium are not satisfied, the states passed through by a system cannot be
described by thermodynamic properties which represent the system as a whole.
Thermodynamic properties are the macroscopic coordinates defined for, and significant to,
only thermodynamic equilibrium states. Both classical and statistical thermodynamics study
mainly the equilibrium states of a system.
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. A quasi-equilibrium process can be viewed as 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.
12/16/2019 20
Let us consider a system of gas contained in a cylinder (Fig. 1.7). The system initially is in
equilibrium state, represented by the properties p 1 , v 1 , t 1 The weight on the piston just
balances the upward force exerted by the gas. If the weight is removed, there will be an
unbalanced force between the system and the surroundings, and under gas pressure, the
piston will move up till it hits the stops. The system again come to an equilibrium state,
being described by the
properties, p 2 , v 2 , t 2,
12/16/2019 21
12/16/2019 22
REVERSIBLE AND IRREVERSIBLE PROCESS
The reversible process is the ideal process which never occurs, while the irreversible
process is the natural process that is commonly found in nature.
When we tear a page from our notebooks, we cannot change this and ‘un-tear’. This is an
irreversible process. Whereas when water evaporates, it can also be condensed in the form
of rains. This is a reversible process.
A thermodynamic process is reversible if the process can return back in such a that both
the system and the surroundings return to their original states, with no other change
anywhere else in the universe. It means both system and surroundings are returned to their
initial states at the end of the reverse process.
In the figure above, the system has undergone a change from state 1 to state 2. The
reversible process can reverse completely and there is no trace left to show that the system
had undergone thermodynamic change. During the reversible process, all the changes in
state that occur in the system are in thermodynamic equilibrium with each other.
Internally reversible process
The process is internally reversible if no irreversibilities occur within the boundaries of
the system. In these processes, a system undergoes through a series of equilibrium states,
and when the process reverses, the system passes through exactly the same equilibrium
states while returning to its initial state.
12/16/2019 23
Externally reversible process
In externally reversible process no irreversibilities occur outside the system boundaries
during the process. Heat transfer between a reservoir and a system is an externally
reversible process if the surface of contact between the system and reservoir is at the
same temperature.
A process can be reversible only when its satisfying two conditions
Dissipative force must be absent.
The process should occur in infinite small time.
12/16/2019 24
Irreversible Process
Irreversible processes are a result of straying away from the curve, therefore decreasing the
amount of overall work done. An irreversible process is a thermodynamic process that departs
from equilibrium. In terms of pressure and volume, it occurs when the pressure (or the volume)
of a system changes dramatically and instantaneously that the volume (or the pressure) do not
have the time to reach equilibrium.
In an irreversible process, finite
changes are made; therefore the
system is not at equilibrium
throughout the process. At the
same point in an irreversible
cycle, the system will be in the
same state, but the surroundings
are permanently changed after
each cycle. It is the difference
between the reversible work and
the actual work for a process as
shown in the following equation :
I = W rev - W a
12/16/2019 25
Thermodynamic equilibrium; definition, mechanical equilibrium; diathermic wall,
thermal equilibrium, chemical equilibrium,
12/16/2019 29
Pressure increases in a fluid with depth h, given simply by ΔP = ρgh provided ρ and g are uniform. (ρ
variation with depth is often negligible for virtually incompressible fluids over small height differences.)
If density varies with height or depth z, the differential dP = -ρg dz may be integrated to obtain ΔP,
which reduces to ΔP = ρgh for constant ρ.
12/16/2019 30
Heat energy is expressed in J or kJ. Heat may also be expressed in calories, where 1 cal =
4.1868 J exactly (but definitions vary). energy is given by British thermal unit Btu, where 1
Btu ≈ 1.0551 kJ depending on definitions. In TD, Heat is energy in transition as it crosses a
boundary, thus it might best be termed Heat Transfer.
Power is, “The rate at which work is done or energy is transferred [or used]. It is given as
energy per unit time with units Watts, where 1 W = 1 J/s and 1 kW = 1 kJ/s
12/16/2019 31
System
In thermodynamics, the system is defined as a definite space or area on which the
study of energy transfer and energy conversions is made.
Open system: System in which both mass and energy cross the boundaries of the
system.
Closed system: System in which mass does not cross boundaries of the system,
though energy may do so.
Isolated system: System in which neither mas nor energy crosses the boundaries of
the system.
Boundary
The system and surroundings are separated by a boundary.It may be fixed or movable
or imaginary. It will not occupy any volume or mass in space.
Surroundings
Anything outside the system which affects the behavior of the system is known as
surroundings.
12/16/2019 32
Heat
Heat is energy transferred between substances or systems due to a temperature difference between
them. As a form of energy, heat is conserved that means it cannot be created or destroyed. It can,
however, be transferred from one place to another. Heat can also be converted to and from other forms
of energy.
For example, a steam turbine can convert heat to kinetic energy to run a generator that converts kinetic
energy into electrical energy. A light bulb can convert this electrical energy to electromagnetic radiation
which, when absorbed by a surface, is converted back into heat. By convention, heat is given to a body
is taken as positive while that taken out of the body is taken as negative.
Sign conventions for heat in internal energy:-
ΔU is taken as positive if the internal energy of the system increases.
ΔU is taken as negative if the internal energy of the system decreases.
Work
In a process, the work done by the system or on the system depends not only on the initial and final
states of the system but also upon the path adopted for the process. Work is done when a force acting
on a system displaces the body in its own direction.Work ‘W’ done on or by a system is the product of
force and displacement.
For example, a man pushing a car may feel that he is doing a lot of work, but no work is actually done
unless the car moves. The work done is the product of the force applied by the man multiplied by the
distance through which the car moves. If there is no friction and the surface is level, then the car, once
set in motion, will continue rolling indefinitely with constant speed. The rolling car has a kinetic energy
of motion equal to the work required to achieve that state of motion.
12/16/2019 33