It is used for engineering students

1. Thermodynamic Process
When the system undergoes change from one thermodynamic state to final state due change in
properties like temperature, pressure, volume etc, the system is said to have undergone thermodynamic
process. Various types of thermodynamic processes are: isothermal process, adiabatic process,
isochoric process, isobaric process and reversible process.
1) Isothermal process: When the system undergoes change from one state to the other, but its temperature
remains constant, the system is said to have undergone isothermal process.
For instance, in our example of hot water in thermos flask, if we remove certain quantity of water from the
flask, but keep its temperature constant at 50 degree Celsius, the process is said to be isothermal process.
2) Adiabatic process: The process, during which the heat content of the system or certain quantity of the
matter remains constant, is called as adiabatic process. Thus in adiabatic process no transfer of heat between
the system and its surroundings takes place. The wall of the system which does not allows the flow of heat
through it, is called as adiabatic wall, while the wall which allows the flow of heat is called as diathermic wall
3) Isochoric process: The process, during which the volume of the system remains constant, is called as
isochoric process. Heating of gas in a closed cylinder is an example of isochoric process.
4) Isobaric process: The process during which the pressure of the system remains constant is called as isobaric
process. Example: Suppose there is a fuel in piston and cylinder arrangement. When this fuel is burnt the
pressure of the gases is generated inside the engine and as more fuel burns more pressure is created. But if the
gases are allowed to expand by allowing the piston to move outside, the pressure of the system can be kept
constant.

2. Thermodynamic State Point
• The state is specified or described by the properties.
• The state point can be indicated on a thermodynamic coordinate system.
• Thermodynamic coordinate system includes pressure volume diagram, temperature volume diagram,
temperature entropy diagram, enthalpy entropy diagram, pressure enthalpy diagram
Process:
• Whenever one or more of the properties of a system change we say that a change in state has occurred.
• For ex: in a piston and cylinder arrangement, if weight is removed from the piston rises and change in
state occurs in which pressure decreases and specific volume increases.
• The path of succession of states through which the system passes is called process.
• the transformation of a system from one fixed state to another state is called a process.
Path: Path is the complete series of states through which the system passes during a change from one
given state to other state.

4. The thermodynamic processes that are commonly met within engineering practice are
1) Constant pressure process (Isobaric)
2) Constant volume process(Isochoric)
3) Constant temperature process( Isothermal)
4) Reversible adiabatic process (Isentropic process)
5) Polytropic process
6) Throttling process.

5. Quasi – static process (very slow process) :
Quasi – meaning almost, static meaning infinite slowness. Thus quasi-static process is infinitely slow
transition of a system. Infinite slowness is the characteristic feature of a quasi-static process. A quasi-static
process is a succession of equilibrium states. It is a reversible process.
Cycle: It is a process whose initial and final states are same. Thus at the end of a cycle all the properties of
a working fluid have the same values as they had in the initial states.
There are 2 types of cycles.. thermodynamic cycle and mechanical cycle.
Thermodynamic cycle:
It is one in which the working substance is recirculated. Ex: water that circulates through steam
power plant and refrigerant that passes through refrigeration plant are the examples of thermodynamic
cycle. There is change of phase during the process but the end states do not change
Mechanical cycle:
In case of a mechanical cycle the working substance is not re circulated. In an IC engine air and fuel
are burnt in the engine, converted into the products of combustion and are then exhausted into the
atmosphere. Hence this type of cycle is called mechanical cycle.

6. Thermodynamic Properties
Property: It is defined as any quantity that depends on the state of the system and is independent of the path ( i.e. the
prior history) by which the system arrived at the given state. Conversely the state is specified or described by the
properties and later we will consider the number of independent properties a substance can have, i.e, the minimum
number of properties that must be specified to fix the state of a substance.
Thermodynamic properties can be divided into 2 general classes: intensive and extensive properties:
Intensive property: An intensive property is independent of mass; thus intensive property value remains same even if
the matter is divided into two equal parts. Ex: pressure, temperature, density etc.
Extensive Property: The value of an extensive property varies directly with the mass, i.e. if a quantity of matter in
given state is divided into 2 equal parts, the properties will have the half the original values. Ex: mass, total volume,
total enthalpy, total energy etc.

7. THERMODYNAMIC PROPERTIES
Thermodynamic properties are taken from a macroscopic perspective.
To dealing with quantities that can either directly or indirectly be measured and counted.
Mass, length and time are considered as fundamental physical quantities, they are related by
Newton's second law of motion.
i.e. F= m * a
Mass – kg Length – m Time – s
Energy: It is defined as the capacity to do work. It is also defined as the capability to produce an effect
When considered from molecular point of view, three general forms of energy become important.
1) Intermolecular potential energy. 2) Molecular kinetic energy 3) Intermolecular energy
Specific Volume: It is a macroscopic property and defined as the volume occupied by unit mass. It is reciprocal of density
and its unit is m3/ kg.
The specific volume of a system in a gravitational field may vary from point to point. Specific volume increases as the
elevation increases.
Thus the definition of specific volume involves the specific volume of a substance at a point in a system.

8. Pressure: The pressure in a fluid at rest at a given point is the same in all directions. We define pressure as the normal
component of force per unit area. Its unit is pascal or N/m2. When dealing with liquids and gases we ordinarily speak of
pressure. For solids we speak of stresses.
Two other units not part of international system continue to be widely used are
Bar = 105 Pa = 0.1MPa and standard atmosphere is 1 atm = 101325 Pa.
Patm = 1.01325 bar
Absolute zero pressure
A
Gauge
Pressure
Atmospheric
Pressure
Patm
(Pgauge)
(+ve preesure)
Absolute
Gauge
Pressure
(Pabs)
B
Vacuum gauge
Pressure
(-ve preesure)
Absolute
Gauge
Pressure
(Pabs)
Absolute Gauge Pressure
Patm + Pgauge
Patm - Pvacuum
Barometric pressure= 760 mm Hg=101.325 kPa

9. Temperature
Temperature is a measure of the molecular activity of a substance. The greater the movement of molecules, the
higher the temperature. It is a relative measure of how "hot" or "cold" a substance is and can be used to
predict the direction of heat transfer.
Temperature Scales
• The two temperature scales normally employed for measurement purposes are the Fahrenheit (F) and
Celsius (C) scales.
• These scales are based on a specification of the number of increments between the
freezing point and boiling point of water at standard atmospheric pressure.
• The Celsius scale has 100 units between these points, and the Fahrenheit scale has 180 units. The zero
points on the scales are arbitrary.
• The freezing point of water was selected as the zero point of the Celsius scale. The coldest
temperature achievable with a mixture of ice and salt water was selected as the zero point of the
Fahrenheit scale.
• The temperature at which water boils was set at 100 on the Celsius scale and 212 on the Fahrenheit
scale.
• The relationship between the scales is represented by the following equations.
°F = 32.0 + (9/5)°C
°C = (°F - 32.0)(5/9)

10. Temperature Scales
• It is necessary to define an absolute temperature scale having only positive values.
• The absolute The absolute temperature scale that corresponds to Celsius scale is called
Kelvin (K) scale and absolute scale that corresponds to the Fahrenheit scale is called the
Rankine (R) scale
• The zero points on both absolute scales represent the same physical state. This state is
where there is no molecular motion of individual atoms
• The relationships between the absolute and relative temperature scales are shown in
the following equations.
°R = °F + 460
°K = °C + 273

11. What is the Rankine equivalent of 80°C?
Solution: °F = (9/5) °C + 32 .
= (9/5)(80) + 32 = 176 °F
°R = °F + 460
= 176 + 460
= 636 °R
What is the Kelvin equivalent of 80°F?
Solution: °C = (5/9) (°F - 32)
= (5/9) (80 - 32)
= 26.7°C
°K = °C + 273
= 26.7 + 273
= 299.7 °K

12. Zeroth law of Thermodynamics:
It states that when two bodies have equality of temperature with the third body, they in turn
have equality of temperature with each other.
When a body A is in thermal equilibrium with body B and also separately with body C then B and C
will be in thermal equilibrium with each other.