THERMODYNAMICS [PC-ME 301]
INTRODUCTION
Thermodynamics is the science that deals with heat and work transfer and their
effect on the physical properties of substances.
Thermodynamic system
A thermodynamic system is defined as a quantity of matter in space or a region in
space chosen for study. The mass or region outside the system is called the
surroundings. The real or imaginary surface that separates the system from its
surroundings is called the boundary. The boundary of a system can be fixed or
movable. The system and surroundings together make the universe.
There are three types of thermodynamic
system exists in the universe.
For a closed system, also called control mass system, there is no mass or matter
transfer (i.e mass constant) but energy may transfer through the system boundary.
Example – the stored gas in a closed cylinder.
Both mass and energy can cross the system boundary in case of an open system.
Open system is also called control volume as the mass is not constant for this type
of system but the volume always remains constant. When the amount of mass
entering and leaving the system are equal, the system is called a steady flow
system. Otherwise it is called an unsteady flow system. Example – a steam turbine,
a gas turbine etc.
SHG/MODULE-1 & 2/PC-ME301 1
,THERMODYNAMICS [PC-ME 301]
Neither mass nor energy can cross the system boundary for an isolated system.
Example – a closed system with perfect thermal insulation throughout its
boundary.
A system can also be classified on the basis of phase. A phase is defined as a
quantity of matter that is homogeneous throughout. Accordingly we have, (a)
homogeneous system (b) heterogeneous system.
A homogeneous system consists of single phase, like ice, water, dry steam etc. But
a heterogeneous system consists of more than one phase, like mixture of ice and
water, solution of immiscible liquids etc.
Thermodynamic property
Thermodynamic property of a system can be defined as any quantity by which the
physical condition of the system is characterized. Example – pressure,
temperature, density etc.
Intensive properties are those that are independent of the mass of a system, such
as temperature, pressure, density.
Extensive properties are those whose values depend on the size or extent of the
system. Total mass, total volume and total momentum are some examples of
extensive properties.
Extensive properties per unit mass are called specific properties. Such as specific
volume, specific total energy (e = E/m).
State, path, process & cycle
The state of a system may be identified by certain observable, macroscopic
properties such as pressure, temperature and density. Whenever one or more of
the properties of a system change, the system undergoes a change of state. If a
system undergoes a change of state, the route taken by the system from one state
to another state is called the path of the change of state.
The path of succession of states through which the system passes is called the
process. When a system in a given initial state goes through a series of changes
of state or processes and finally returns to its initial state, the system has
undergone a thermodynamic cycle.
1-2 is a process and 1-2-1 is a cycle.
SHG/MODULE-1 & 2/PC-ME301 2
, THERMODYNAMICS [PC-ME 301]
Thermodynamic equilibrium
A system is said to be in thermodynamic equilibrium if it does not tend to
undergo any spontaneous change in macroscopic property, whenever the system
is isolated from its surroundings.
A system will be in a state of thermodynamic equilibrium, if all the following
three types of equilibrium are simultaneously satisfied:
(i) Mechanical equilibrium
(ii) Chemical equilibrium
(iii) Thermal equilibrium
Mechanical equilibrium is the equilibrium in thermodynamic pressure, chemical
equilibrium is the equilibrium in species concentration and thermal equilibrium is
the equilibrium in temperature.
Quasi – static process
A system in thermodynamic equilibrium will no longer be in a state of
equilibrium, whenever it is subjected to some disturbances, and the system is
supposed to be in a non-equilibrium state. The departure of state of the system
from thermodynamic equilibrium will be infinitesimally small if the disturbances
are also likewise. Consequently the process becomes infinitely slow and the final
state of the system will almost be in thermodynamic equilibrium. Such a process
is known as a 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.
As shown in the above figure, if the weights on the piston are removed at once,
the prevailing thermodynamic equilibrium will be lost. Instead, if the weights are
taken off one by one the deviation from thermodynamic equilibrium will be
infinitesimal and all the states the system passes through during the entire
process may be considered as equilibrium states.
SHG/MODULE-1 & 2/PC-ME301 3
INTRODUCTION
Thermodynamics is the science that deals with heat and work transfer and their
effect on the physical properties of substances.
Thermodynamic system
A thermodynamic system is defined as a quantity of matter in space or a region in
space chosen for study. The mass or region outside the system is called the
surroundings. The real or imaginary surface that separates the system from its
surroundings is called the boundary. The boundary of a system can be fixed or
movable. The system and surroundings together make the universe.
There are three types of thermodynamic
system exists in the universe.
For a closed system, also called control mass system, there is no mass or matter
transfer (i.e mass constant) but energy may transfer through the system boundary.
Example – the stored gas in a closed cylinder.
Both mass and energy can cross the system boundary in case of an open system.
Open system is also called control volume as the mass is not constant for this type
of system but the volume always remains constant. When the amount of mass
entering and leaving the system are equal, the system is called a steady flow
system. Otherwise it is called an unsteady flow system. Example – a steam turbine,
a gas turbine etc.
SHG/MODULE-1 & 2/PC-ME301 1
,THERMODYNAMICS [PC-ME 301]
Neither mass nor energy can cross the system boundary for an isolated system.
Example – a closed system with perfect thermal insulation throughout its
boundary.
A system can also be classified on the basis of phase. A phase is defined as a
quantity of matter that is homogeneous throughout. Accordingly we have, (a)
homogeneous system (b) heterogeneous system.
A homogeneous system consists of single phase, like ice, water, dry steam etc. But
a heterogeneous system consists of more than one phase, like mixture of ice and
water, solution of immiscible liquids etc.
Thermodynamic property
Thermodynamic property of a system can be defined as any quantity by which the
physical condition of the system is characterized. Example – pressure,
temperature, density etc.
Intensive properties are those that are independent of the mass of a system, such
as temperature, pressure, density.
Extensive properties are those whose values depend on the size or extent of the
system. Total mass, total volume and total momentum are some examples of
extensive properties.
Extensive properties per unit mass are called specific properties. Such as specific
volume, specific total energy (e = E/m).
State, path, process & cycle
The state of a system may be identified by certain observable, macroscopic
properties such as pressure, temperature and density. Whenever one or more of
the properties of a system change, the system undergoes a change of state. If a
system undergoes a change of state, the route taken by the system from one state
to another state is called the path of the change of state.
The path of succession of states through which the system passes is called the
process. When a system in a given initial state goes through a series of changes
of state or processes and finally returns to its initial state, the system has
undergone a thermodynamic cycle.
1-2 is a process and 1-2-1 is a cycle.
SHG/MODULE-1 & 2/PC-ME301 2
, THERMODYNAMICS [PC-ME 301]
Thermodynamic equilibrium
A system is said to be in thermodynamic equilibrium if it does not tend to
undergo any spontaneous change in macroscopic property, whenever the system
is isolated from its surroundings.
A system will be in a state of thermodynamic equilibrium, if all the following
three types of equilibrium are simultaneously satisfied:
(i) Mechanical equilibrium
(ii) Chemical equilibrium
(iii) Thermal equilibrium
Mechanical equilibrium is the equilibrium in thermodynamic pressure, chemical
equilibrium is the equilibrium in species concentration and thermal equilibrium is
the equilibrium in temperature.
Quasi – static process
A system in thermodynamic equilibrium will no longer be in a state of
equilibrium, whenever it is subjected to some disturbances, and the system is
supposed to be in a non-equilibrium state. The departure of state of the system
from thermodynamic equilibrium will be infinitesimally small if the disturbances
are also likewise. Consequently the process becomes infinitely slow and the final
state of the system will almost be in thermodynamic equilibrium. Such a process
is known as a 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.
As shown in the above figure, if the weights on the piston are removed at once,
the prevailing thermodynamic equilibrium will be lost. Instead, if the weights are
taken off one by one the deviation from thermodynamic equilibrium will be
infinitesimal and all the states the system passes through during the entire
process may be considered as equilibrium states.
SHG/MODULE-1 & 2/PC-ME301 3
