Thermodynamics & Heat
Engines
Prof. Dr. Hamada Mohamed Abdelmotalib
Mechanical Power & EnergyEngineering Dep.
Faculty of Engineering, Minia University
Course Syllabus
1.
Introduction and basic concepts
2.
Properties of pure substance
3.
First law of thermodynamics
4.
Second law of thermodynamics
5.
Thermal Power Plants
6.
Rankine Cycle
7.
Gas turbines
8.
Modification of gas turbine
9.
Short Notes on Internal Heat Engines
2
Dr. Eng. Hamada M. Abdelmotalib
Introduction
 Thermodynamics can be defined as the science of energy. Energy can be viewed as the
ability to cause changes. The name thermodynamics stems from the Greek words
therme (heat) and dynamis (power).
 Thermodynamics is commonly encountered in many engineering systems and other
aspects of life. Many ordinary household utensils and appliances are designed, by using
the principles of thermodynamics. Some examples include the electric or gas range, the
heating and air-conditioning systems, the refrigerator, the humidifier, the pressure
cooker.
 Some SI and English Units
In SI, the units of mass, length, and time are the kilogram (kg), meter (m), and second
(s), respectively. The respective units in the English system are the pound-mass (lbm),
foot (ft), and second (s). The pound symbol lb is actually the abbreviation of libra,
which was the ancient Roman unit of weight.
3
Dr. Eng. Hamada M. Abdelmotalib
System and control volumes
 A system is defined as a quantity of matter 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.
 Systems may be considered to be closed or open, depending on
whether a fixed mass or a fixed volume in space is chosen for study.
 A closed system (also known as a control mass) consists of a fixed
amount of mass, and no mass can cross its boundary. But energy, in
the form of heat or work, can cross the boundary; and the volume of
a closed system does not have to be fixed. If, as a special case, even
energy is not allowed to cross the boundary, that system is called an
isolated system.
 An open system, or a control volume,, is a properly selected region
in space. It usually encloses a device that involves mass flow such
as a compressor, turbine, or nozzle. Both mass and energy can cross
the boundary of a control volume.
 In general, any arbitrary region in space can be selected as a control
volume.
 The boundaries of a control volume are called a control surface
4
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 mass
of a system, such as temperature, pressure, and 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.
Equilibrium
 Thermodynamics deals with equilibrium states. The word equilibrium
implies a state of balance. In an equilibrium state there are no
unbalanced potentials (or driving forces) within the system.
 a system is in thermal equilibrium if the temperature is the same
throughout the entire system.
 Mechanical equilibrium is related to pressure, and a system is in
mechanical equilibrium if there is no change in pressure at any point
of the system with time.
 A system is in chemical equilibrium if its chemical composition does
not change with time, that is, no chemical reactions occur.
5
Dr. Eng. Hamada M. Abdelmotalib
Process and cycles
 Any change that a system undergoes from one equilibrium
state to another is called a process, and the series of states
through which a system passes during a process is called the
path of the 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.
 If the piston is moved slowly, the molecules will have
sufficient time to redistribute and there will not be a
molecule pileup in front of the piston. As a result, the
pressure inside the cylinder will always be nearly uniform
and will rise at the same rate at all locations. It should be
pointed out that a quasi-equilibrium process is an idealized
process and is not a true representation of an actual process.
But many actual processes closely approximate it, and they
can be modeled as quasie quilibrium with negligible error
 An isothermal process, is a process during which the temperature T remains constant; an
isobaric process is a process during which the pressure P remains constant; and an
isochoric (or isometric) process is a process during which the specific volume v remains
constant.
Dr. Eng. Hamada M. Abdelmotalib
6
 A system is said to have undergone a cycle if it returns to its initial state at the end of the
process. That is, for a cycle the initial and final states are identical.
 The term steady implies no change with time. The opposite of steady is unsteady, or
transient. The term uniform, however, implies no change with location over a specified
region.
 A large number of engineering devices operate for long periods of time under the same
conditions, and they are classified as steady-flow devices. Steady-flow conditions can be
closely approximated by devices that are intended for continuous operation such as
turbines, pumps, boilers, condensers, and heat exchangers or power plants or
refrigeration systems.
 when a body is brought into contact with another body that
is at a different temperature, heat is transferred from the
body at higher temperature to the one at lower temperature
until both bodies attain the same temperature. At that point,
the heat transfer stops, and the two bodies are said to have
reached thermal equilibrium.
Zeroth law of thermodynamics
 The zeroth law of thermodynamics states that if two bodies are in thermal equilibrium
with a third body, they are also in thermal equilibrium with each other
7
Dr. Eng. Hamada M. Abdelmotalib
Temperature Scales
 The temperature scales used in the SI and in the English system today are the Celsius
scale and the Fahrenheit scale.
 On the Celsius scale, the ice and steam points were originally assigned the values of 0
and 100°C, respectively. The corresponding values on the Fahrenheit scale are 32
and 212°F.
 It is very desirable to have a temperature scale that is independent of the properties of
any substance. Such a temperature scale is called a thermodynamic temperature scale.
The thermodynamic temperature scale in the SI is the Kelvin scale. The lowest
temperature on the Kelvin scale is absolute zero, or 0 K.
8
Dr. Eng. Hamada M. Abdelmotalib
- Density is defined as mass per unit volume
- The reciprocal of density is the specific volume v, which is defined as volume
per unit mass. That is,
- The density of a substance, in general, depends on temperature and pressure.
The density of most gases is proportional to pressure and inversely proportional
to temperature. Liquids and solids, on the other hand, are essentially
incompressible substances, and the variation of their density with pressure is
usually negligible.
.
-Sometimes the density of a substance is given relative to the density of a wellknown substance. Then it is called specific gravity, or relative density, and is
defined as the ratio of the density of a substance to the density of some standard
substance at a specified temperature (usually water at 4C, for which ρH2O =
1000 kg/m3).
-The weight of a unit volume of a substance is called specific weight and is
expressed as
9
Dr. Eng. Hamada M. Abdelmotalib
Pressure
 Pressure is defined as a normal force exerted by a fluid per unit area. We speak of
pressure only when we deal with a gas or a liquid. The counterpart of pressure in solids
is normal stress, which is force acting perpendicular to the surface per unit area
 The pressure unit pascal is too small for pressures encountered in practice. Therefore,
its multiples kilopascal (1 kPa = 103 Pa) and megapascal (1MPa =106 Pa) are
commonly used.
 The actual pressure at a given position is called
the absolute pressure, and it is measured relative
to absolute vacuum (i.e., absolute zero pressure).
 Most pressure-measuring devices, however, are
calibrated to read zero in the atmosphere, and so
they indicate the difference between the absolute
pressure and the local atmospheric pressure. This
difference is called the gage pressure. Pressures
below atmospheric pressure are called vacuum
pressures
Dr. Eng. Hamada M. Abdelmotalib
10
Pressure measurement devices
The Barometer
-
Atmospheric pressure is measured by a device
called a barometer; thus, the atmospheric pressure
is often referred to as the barometric pressure.
where ρ is the density of mercury, g is the local
gravitational acceleration, and h is the height of the
mercury column above the free surface.
-Note that the length and the cross-sectional area of the
tube have no effect on the height of the fluid column of a
barometer
- Atmospheric pressure Patm changes from 101.325 kPa at sea level to 89.88,
79.50, 54.05, 26.5, and 5.53 kPa at altitudes of 1000, 2000, 5000, 10,000, and
20,000 meters, respectively.
11
Dr. Eng. Hamada M. Abdelmotalib
12
Dr. Eng. Hamada M. Abdelmotalib
Manometer
 A manometer is commonly used to measure small and moderate
pressure differences. A manometer mainly consists of a glass or
plastic U-tube containing one or more fluids such as mercury,
water, alcohol, or oil. To keep the size of the manometer to a
manageable level, heavy fluids such as mercury are used if large
pressure differences are anticipated. The differential fluid column
of height h is in static equilibrium, and it is open to the
atmosphere. Then the pressure at point 2 is determined directly
from Eq.
13
Dr. Eng. Hamada M. Abdelmotalib
Other Pressure Measurement Devices
Bourdon tube
When the tube is open to the atmosphere, the tube is
undeflected, and the needle on the dial at this state is
calibrated to read zero (gage pressure). When the fluid
inside the tube is pressurized, the tube stretches and
moves the needle in proportion to the applied pressure.
Pressure transducers
use various techniques to convert the pressure effect to an electrical effect such
as a change in voltage, resistance, or capacitance. Pressure transducers are
smaller and faster, and they can be more sensitive, reliable, and precise than their
mechanical counterparts. They can measure pressures from less than a millionth
of 1 atm to several thousands of atm.
Piezoelectric transducers,
also called solid-state pressure transducers, work on the principle that an electric
potential is generated in a crystalline substance when it is subjected to
mechanical pressure.
14
Dr. Eng. Hamada M. Abdelmotalib
15
Dr. Eng. Hamada M. Abdelmotalib
16
Dr. Eng. Hamada M. Abdelmotalib