UNIT-1
INTRODUCTION
Thermodynamics
Thermodynamics is the branch of physics that deals with the relationship
between heat and other forms of energy. In particular, it describes how
thermal energy is converted to and from other forms of energy and how it
affects matter.
Thermodynamic systems
The thermodynamic system may be broadly defined as a definite area or a
space where some thermodynamic processes is taking place. It is a region
where our attention is focused for studying a thermodynamic process. A
little observation will show that a thermodynamic system has its
boundaries, and anything outside the boundaries is called its surroundings.
These boundaries may be fixed like that of a tank enclosing a certain mass
of compressed gas; or movable like boundary of a certain volume of liquid
in a pipe line.
6
,The thermodynamic systems may be classified into the following three
groups:
1. Closed system
This is a system of fixed mass and identity whose boundaries are
determined by the space of the matter (working substance) occupied
in it.
7
, A close system is shown in figure. The gas in the cylinder is
considered as a system. The heat and work crosses the boundary of
the system during the process, but there is no addition or loss of the
original mass of the working substance. It is thus obvious, that the
mass of working substance, which comprises the system, is fixed.
2. Open system
In this system, the working substance crosses boundary of the
system. Heat and work may also cross the boundary.
The figure shows the diagram of an air compressor which illustrates
an open system.
3. Isolated system
A system which is completely uninfluenced by the surrounding is
called an isolated system. It is a system of fixed mass and no heat or
work crosses the boundary. An open system with its surroundings
(known as a universe) is an example of an isolated system.
Thermal Equilibrium
When there are variations in temperature from point to point of an isolated
system, the temperature at every point first changes with time. This rate of
change decreases and eventually stops. When no further changes are
observed, the system is said to be in thermal equilibrium.
8
, Equality of Temperature
Consider two bodies of the same or different materials, one hot and the
other cold. When these bodies are brought in contact, the hot body
becomes cooler, and the cold body becomes warmer. If these bodies remain
in contact for some time, a state reaches, when there is no further
observable change in the properties of the two bodies. This is a state of
thermal equilibrium, and at this stage the two bodies have the equal
temperatures. It thus follows that when two bodies are in thermal
equilibrium with each other, their temperatures are equal.
Laws of thermodynamics
1. Zeroth Law of Thermodynamics
This law states, “When two bodies are in thermal equilibrium with a
third body, they are in thermal equilibrium with each other.”
2. First Law of Thermodynamics
This law state, “The heat and mechanical work are mutually
convertible.”
This law may also be stated as, “The energy can neither be created nor
be destroyed though it can be transferred from one form to another.”
3. Second Law of Thermodynamics
This law states, “There is a definite limit to the amount of mechanical
energy, which can be obtained from a given quantity of heat energy.”
This law has been stated by Claussius in a slightly different form as, “It
is impossible for a self-acting machine working in a cyclic process, to
transfer heat from a body at a lower temperature, to a body at a higher
temperature, without the aid of an external agency.”
This law has also been stated by Kelvin-Planck as, “It is impossible to
construct an engine working on a cyclic process, whose sole purpose is
to convert heat energy into work.”
Meaning of Refrigeration
The term ‘REFRIGERATION’ may be defined as the process of removing
heat from a substance under controlled conditions. It also includes the
process of reducing and maintaining the temperature of a body below the
general temperature of its surroundings. In other words, the refrigeration
9
INTRODUCTION
Thermodynamics
Thermodynamics is the branch of physics that deals with the relationship
between heat and other forms of energy. In particular, it describes how
thermal energy is converted to and from other forms of energy and how it
affects matter.
Thermodynamic systems
The thermodynamic system may be broadly defined as a definite area or a
space where some thermodynamic processes is taking place. It is a region
where our attention is focused for studying a thermodynamic process. A
little observation will show that a thermodynamic system has its
boundaries, and anything outside the boundaries is called its surroundings.
These boundaries may be fixed like that of a tank enclosing a certain mass
of compressed gas; or movable like boundary of a certain volume of liquid
in a pipe line.
6
,The thermodynamic systems may be classified into the following three
groups:
1. Closed system
This is a system of fixed mass and identity whose boundaries are
determined by the space of the matter (working substance) occupied
in it.
7
, A close system is shown in figure. The gas in the cylinder is
considered as a system. The heat and work crosses the boundary of
the system during the process, but there is no addition or loss of the
original mass of the working substance. It is thus obvious, that the
mass of working substance, which comprises the system, is fixed.
2. Open system
In this system, the working substance crosses boundary of the
system. Heat and work may also cross the boundary.
The figure shows the diagram of an air compressor which illustrates
an open system.
3. Isolated system
A system which is completely uninfluenced by the surrounding is
called an isolated system. It is a system of fixed mass and no heat or
work crosses the boundary. An open system with its surroundings
(known as a universe) is an example of an isolated system.
Thermal Equilibrium
When there are variations in temperature from point to point of an isolated
system, the temperature at every point first changes with time. This rate of
change decreases and eventually stops. When no further changes are
observed, the system is said to be in thermal equilibrium.
8
, Equality of Temperature
Consider two bodies of the same or different materials, one hot and the
other cold. When these bodies are brought in contact, the hot body
becomes cooler, and the cold body becomes warmer. If these bodies remain
in contact for some time, a state reaches, when there is no further
observable change in the properties of the two bodies. This is a state of
thermal equilibrium, and at this stage the two bodies have the equal
temperatures. It thus follows that when two bodies are in thermal
equilibrium with each other, their temperatures are equal.
Laws of thermodynamics
1. Zeroth Law of Thermodynamics
This law states, “When two bodies are in thermal equilibrium with a
third body, they are in thermal equilibrium with each other.”
2. First Law of Thermodynamics
This law state, “The heat and mechanical work are mutually
convertible.”
This law may also be stated as, “The energy can neither be created nor
be destroyed though it can be transferred from one form to another.”
3. Second Law of Thermodynamics
This law states, “There is a definite limit to the amount of mechanical
energy, which can be obtained from a given quantity of heat energy.”
This law has been stated by Claussius in a slightly different form as, “It
is impossible for a self-acting machine working in a cyclic process, to
transfer heat from a body at a lower temperature, to a body at a higher
temperature, without the aid of an external agency.”
This law has also been stated by Kelvin-Planck as, “It is impossible to
construct an engine working on a cyclic process, whose sole purpose is
to convert heat energy into work.”
Meaning of Refrigeration
The term ‘REFRIGERATION’ may be defined as the process of removing
heat from a substance under controlled conditions. It also includes the
process of reducing and maintaining the temperature of a body below the
general temperature of its surroundings. In other words, the refrigeration
9
