Chapter 1: introduction and
basic concept
Prepared by: Dr. Khalad AlMuhaysh
LEARNING OBJECTIVES
By the end of this lecture, students will be able to:
• Define thermodynamics and energy using precise engineering language.
• Explain the principle of conservation of energy conceptually.
• Distinguish between the First and Second Laws at a qualitative level.
• Define system, surroundings, and boundary.
• Distinguish between closed systems, open systems, and isolated systems.
• Classify properties as intensive or extensive.
• Define state and equilibrium.
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What Is
Thermodynamics?
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THERMODYNAMICS AND ENERGY
• Thermodynamics: The science of energy.
• Energy: The ability to cause changes.
• The name thermodynamics stems from the Greek
words therme (heat) and dynamics (power). [which
describe the conversation of heat into power]
• Principle of energy conservation:
Energy can change from one form to another but the
total amount of energy remains constant.
• What is the thermodynamics science ?
• It is the science that deals with all aspects of energy
and energy transformations, including power
generation, refrigeration, and relationships among the
properties of matter.
THERMODYNAMICS AND ENERGY
• The first law of thermodynamics: An expression of the conservation of energy
principle.
• The first law asserts that energy is a thermodynamic property.
• The second law of thermodynamics: It asserts that energy has quality as well as
quantity, and actual processes occur in the direction of decreasing quality of
energy.
• Classical thermodynamics: A macroscopic approach to the study of
thermodynamics that does not require a knowledge of the behavior of
individual particles. It provides a direct and easy way to the solution of
engineering problems and it is used in this text.
• Statistical thermodynamics: A microscopic approach, based on the average
behavior of large groups of individual particles.
Applications of
thermodynamics
DIMENSIONS AND UNITS
Secondary or
derived units
Quantity
Standard unit
Symbol
Area
Square meter
𝑚2
Volume
Cubic meter
𝑚3
Velocity
Meter per second
𝑚/𝑠
Acceleration
Meter per second square
𝑚/𝑠 2
Angular velocity
Radian per second
𝑟𝑎𝑑/𝑠
Derivation
formula
Angular acceleration Radian per second square
𝑟𝑎𝑑/𝑠 2
Density
Kilogram per cubic meter
𝑘𝑔/𝑚3
Force
Newton
Pressure
Newton per square meter
𝑁/𝑚2
Torque
Newton meter
𝑁. 𝑚
Work, energy, heat
Joule
𝐽
𝑁. 𝑚
Power
Watt
𝑊
𝐽/𝑠
𝑁
𝑘𝑔 𝑚/𝑠 2
SI and English Units
• Metric SI system: A simple and logical system based on a decimal relationship between the
various units.
• English system: It has no apparent systematic numerical base, and various units in this
system are related to each other rather arbitrarily.
Work = Force × Distance
1 J = 1 N∙m
1 cal = 4.1868 J
1 Btu = 1.0551 kJ
Dimensional homogeneity
• All equations must be dimensionally homogeneous. Thus, all the terms in an equation must
have the same unit.
• All non-primary units (secondary units) can be formed by combinations of primary units.
Force units, for example, can be expressed as
• They can also be expressed more conveniently as unity conversion ratios as:
• Unity conversion ratios are identically equal to 1 and are unitless, and thus such ratios (or
their inverses) can be inserted conveniently into any calculation to properly convert units.
Thermodynamics systems
• In thermodynamics the term system is used to
identify the subject of the analysis.
• 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.
• boundary of a system can be fixed or movable.
• Working fluid: The gas or liquid that actuates the
system. Like Freon in refrigeration cycles and steam in
power plants and the gas inside the piston cylinder
system shown.
Types of Systems
• Closed system: A fixed amount of mass (working fluid), also known as a control mass).
• That is, no mass can enter or leave But energy, in the form of heat or work, can cross the
boundary.
• If, as a special case, even energy is not allowed to cross the boundary, that system is called
an isolated system.
Types of Systems
• An open system, or a control volume, as it is often called, is a properly selected region in
space. It usually encloses a device that involves mass flow such as a compressor, turbine, or
nozzle.
• Flow through these devices is best studied by selecting the region within the device as the
control volume.
• Both mass and energy can cross the boundary of a control volume.
• Control surface: The boundaries of a control volume. It can be real or imaginary.
Types of Boundaries
Type of boundary
Open
Closed
Semi-permeable
Rigid
Isolated
Interactions
All interactions possible (Mass, Work, Heat)
Matter cannot enter or leave
Only certain species can enter or leave
Mechanical work cannot be done
No interactions are possible (Mass, Work, Heat)
Properties of a System
• Any characteristic of a system is called a property.
• Some familiar properties are pressure P, temperature T,
volume V, and mass m.
• Properties are considered to be either intensive or
extensive.
• Intensive properties are those that are independent of
the size or mass of a system, such as temperature,
pressure, and density.
• Extensive properties are those whose values depend on
the size of the system. Total mass, total volume, and total
energy are some examples of extensive properties
• An Extensive properties per unit mass are called specific
properties. Some examples of specific properties are
specific volume (v =V/m) and specific total energy(e =
E/m).
Properties of a System
• Density is mass per unit volume.
• Specific volume is volume per unit mass.
• Specific gravity: The ratio of the density of a substance to the density of some standard
substance at a specified temperature (usually water at 4°C).
• Specific weight: The weight of a unit volume of a substance.
State
• State is a set of properties that completely describes the condition of the system.
• At a given state, all the properties of a system have fixed values.
• If the value of one property changes, the state will change to a different one
equilibrium
• The word equilibrium implies a state of balance.
• A system in equilibrium experiences no changes when it is isolated from its surroundings.
• Types of equilibrium in Thermodynamics:1. Thermal Equilibrium: the temperature does not change with time.
2. Mechanical Equilibrium: the pressure does not change with time.
3. Phase Equilibrium: the mass does not change with time.
4. Chemical Equilibrium: the chemical composition does not change with time (no chemical
reactions occur).
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