EN-202

Fall 2024

Dr. Farrukh Khalid

School of Energy Science and Engineering
IITG
The analysis of energy systems requires a solid
understanding of
- energy conversion processes
- transformation between various forms of energy
- ways of defining efficiencies of energy systems
We review fundamental concepts of
- thermodynamics
- heat transfer
- fluid mechanics
- thermochemistry
- power plants
- refrigeration systems
Thermal-fluid sciences (Thermal sciences): The physical
sciences that deal with energy and the transfer,
transport, and conversion of energy
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Application Areas of Thermal-Fluid
Sciences
 Designing a solar collector
involves
thermodynamics: the
determination of the amount of
energy transfer
heat transfer: the determination
of the size of the heat exchanger
fluid mechanics: the
determination of the size and
type of the pump

The design and analysis of

renewable energy systems, such as
this solar hot water system, involves
thermal sciences.
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Problem-Solving Technique 1

• Step 1: Problem Statement

• Step 2: Schematic
• Step 3: Assumptions and Approximations
• Step 4: Physical Laws
• Step 5: Properties
• Step 6: Calculations
• Step 7: Reasoning, Verification, and Discussion
Problem-Solving Technique 2

• A step-by-step approach can • The assumptions made while solving

greatly simplify problem solving. an engineering problem must be
reasonable and justifiable.
Problem-Solving Technique
• The results obtained from an • Neatness and organization are
engineering analysis must be highly valued by employers.
checked for reasonableness.
Problem-Solving Technique 4

• Engineering Software Packages • An excellent word-processing program

does not make a person a good writer; it
• All the computing power and the
simply makes a good writer a more
engineering software packages
efficient writer.
available today are just tools, and
tools have meaning only in the hands
of masters.
• Hand calculators did not eliminate
the need to teach our children how to
add or subtract, and sophisticated
medical software packages did not
take the place of medical school
training.
• Neither will engineering software
packages replace the traditional
engineering education. They will
simply cause a shift in emphasis in
the courses from mathematics to
physics.
Problem-Solving Technique 6

• A Remark on Significant Digits • A result with more significant digits than

that of given data falsely implies more
• In engineering calculations, the precision.
information given is not known to
more than a certain number of
significant digits, usually three digits.

• Consequently, the results obtained

cannot possibly be accurate to more
significant digits.
• Reporting results in more significant
digits implies greater accuracy than
exists, and it should be avoided.

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THERMODYNAMICS
Thermodynamics: The science of
energy and entropy.
Conservation of energy principle:
During an interaction, energy can
change from one form to another, but
the total amount of energy remains
constant.
Energy cannot be created or destroyed.
The first law of thermodynamics: An
expression of the conservation of
energy principle.
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. 10
Heat and other forms of energy

Energy can exist in numerous forms such as

✓ thermal
✓ mechanical
✓ kinetic
✓ potential
✓ electrical
✓ magnetic
✓ chemical
✓ nuclear
Their sum constitutes the total energy of a system.
Internal energy: The sum of all microscopic forms of
energy
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Internal energy: May be viewed as the sum of the
kinetic and potential energies of the molecules.

Sensible heat: The kinetic energy of the molecules.

Latent heat: The internal energy associated with

the phase of a system.

Chemical (bond) energy: The internal energy

associated with the atomic bonds in a molecule.

Nuclear energy: The internal energy associated with

the bonds within the nucleus of the atom itself.

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In the analysis of systems
that involve fluid flow, we
frequently encounter the
combination of properties u
and Pv.
Enthalpy: The combination u
+ Pv is defined as enthalpy
h = u + Pv
The internal energy u
Flow energy: The term Pv
represents the microscopic
represents the flow energy
of the fluid. energy of a nonflowing fluid,

It is also called the flow whereas enthalpy h

work. represents the microscopic
energy of a flowing fluid. 13
Specific Heats of Gases, Liquids, and Solids

Ideal gas
relation
Specific heat: The energy required to
raise the temperature of a unit mass of
a substance by one degree
Two kinds of specific heats:
✓ specific heat at constant volume cv
✓ specific heat at constant pressure cp Figure 2-3
Specific heat is the energy
At low pressures all real gases approach required to raise the
ideal gas behavior, and therefore their temperature of a unit mass of
specific heats depend on temperature a substance by 1 degree in a
only. specified way.

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The specific heat of a substance
changes with temperature.

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Energy Transfer
Energy can be transferred to or from a given
mass by two mechanisms:
- heat transfer
- work
Heat transfer rate: The amount of heat
transferred per unit time.
Heat flux: The rate of heat transfer per unit
area normal to the direction of heat transfer.
Power: The work done per unit time.

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 SYSTEMS AND CONTROL VOLUMES
• System: A quantity of matter or a region in space chosen for study.
• Surroundings: The mass or region outside the system
• Boundary: The real or imaginary surface that separates the system
from its surroundings.
• The boundary of a system can be fixed or movable.
• Systems may be considered to be closed or open.
• Closed system (Control mass): A fixed amount of mass, and no
mass can cross its boundary

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• Open system (control volume): 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.
• Control surface: The boundaries of a control
volume. It can be real or imaginary.

A control volume can involve

fixed, moving, real, and imaginary
boundaries.

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The Steady-Flow Process
• During a steady-flow
• The term steady implies no process, fluid properties
within the control volume
change with time. The may change with position
opposite of steady is but not with time.

unsteady, or transient.
• 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 process: A process during which a
fluid flows through a control volume steadily.

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.
5

• Under steady-flow conditions, the mass and energy

contents of a control volume remain constant.
Temperature And The Zeroth Law Of
Thermodynamics 1

• The zeroth law of

thermodynamics: If two
• Two bodies reaching
bodies are in thermal thermal equilibrium
equilibrium with a third body,
they are also in thermal after being brought into
equilibrium with each other. contact in an isolated
• By replacing the third body
with a thermometer, the zeroth
enclosure.
law can be restated as two
bodies are in thermal
equilibrium if both have the
same temperature reading even
if they are not in contact.
Temperature And The Zeroth Law Of
Thermodynamics 2

• Temperature Scales
• All temperature scales are based on some easily reproducible states such as the
freezing and boiling points of water: the ice point and the steam point.
• Ice point: A mixture of ice and water that is in equilibrium with air saturated
with vapor at 1 atm pressure (0 °C or 32 °F).
• Steam point: A mixture of liquid water and water vapor (with no air) in
equilibrium at 1 atm pressure (100 °C or 212 °F).
• Celsius scale: Temperature in SI unit system
• Fahrenheit scale: Temperature in English unit system
• Thermodynamic temperature scale: A temperature scale that is independent
of the properties of any substance.
• Kelvin scale (SI) Rankine scale (E)
• A temperature scale nearly identical to the Kelvin scale is the ideal-gas
temperature scale. The temperatures on this scale are measured using a
constant-volume gas thermometer.
The First Law of Thermodynamics
First law of thermodynamics = Conservation of energy Principle: Energy can
neither be created nor destroyed during a process; it can only change forms.

The net change (increase or

decrease) in the total energy of
the system during a process is
equal to the difference between
the total energy entering and the
total energy leaving the system
during that process.

stationary simple
compressible systems

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 THE FIRST LAW OF THERMODYNAMICS
• The first law of thermodynamics (the conservation of energy
principle) provides a sound basis for studying the relationships
among the various forms of energy and energy interactions.
• The first law states that energy can be neither created nor
destroyed during a process; it can only change forms.

The First Law: For

all adiabatic
processes between
two specified states
of a closed system,
the net work done
is the same
regardless of the
nature of the closed
system and the
details of the
process.
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 The energy balance for any
system undergoing any process
in the rate form

Steady- flow process

In steady operation, the rate of energy

transfer to a system is equal to the rate
of energy transfer from the system. 27
 A closed system consists of a fixed mass.
Energy Balance for
Closed Systems The total energy E for most systems
encountered in practice consists of the
internal energy U.
This is especially the case for stationary
systems since they don’t involve any
changes in their velocity or elevation during
a process.

In the absence of any work

interactions, the change in the
energy content of a closed system
is equal to the net heat transfer.
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Energy Balance for Steady-Flow Systems
Control volume: A large number of engineering devices such as water heaters and
car radiators involve mass flow in and out of a system.
Most control volumes are analyzed under steady operating conditions.
Steady: No change with time at a specified location.
Mass flow rate: The amount of mass flowing through a cross section of a flow
device per unit time.
Volume flow rate: The volume of a fluid flowing through a pipe or duct per unit
time.

The mass flow rate of a fluid at a cross

section is equal to the product of the fluid
density, average fluid velocity, and the
cross-sectional area.
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Under steady conditions, the net rate of
energy transfer to a fluid in a control
volume is equal to the rate of increase in
the energy of the fluid stream flowing
through the control volume.

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References

• Powerpoint by Mehmet Kanoglu et al

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