THERMODYNAMICS
MECH2010 /2023 Summer
Prof. Fu-Lin Tsung
Thermodynamics, What is it
• From Greek
• therme:
• dynamis:
• “Thermo-dynamic” was first coined by Lord ________
• The science that deals with heat and work, and properties
of matter that relates to heat and work
• Thermodynamics formalize the relationship between heat,
work, and energy
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________ thermodynamics ... is the only physical theory of
universal content which I am convinced ... will never be
overthrown.
— Albert Einstein
Name another branch of thermodynamics
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Why Study Thermodynamics
It’s applicable to most branches of engineering
- aircraft/propulsion
- fossil fuel and nuclear power stations
- alternative energy systems
- Fuel Cells
- Geothermal
- Ocean thermal, wave, tidal wave power generation
- Wind
- Automobile
- Compressor/pumps (oil & gas, refrigeration, …)
- Electronics cooling
- Heating/ventilation, air-conditioning
- Steam/Gas turbines
- ….
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In everyday life
•
•
•
•
•
Hot Coffee and Ice cube
Hot noodle soup cooling
Shower w/ mix of hot/cold stream of water
Hair dryer
AC system in car, house, classroom
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Course Outline, test1
• Will refine as weeks go by
• Week 1-4, chapter 1-4
• basic concepts - system, properties, state, process
• First Law of Thermodynamics (closed system)
• heat, work, energy, energy balance
• Thermodynamic cycles
• Evaluating thermo properties
• Application of 1st Law to closed systems
• Ideal gas model, specific heats
• Application of 1st Law to open systems
• Test1
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Class Expectations
- Class participation
- This course is not just thermodynamics
- It’s engineering
- It’s professional development
- It’s life
- Go through syllabus
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HW/Test expectations
• Example problem/process
• A body with a mass of 1 kg is at rest at a height of 10m. The body is
dropped. Assume gravity is 9.81 m/s^2, neglect drag forces, find
• the time to reach the ground
• the kinetic energy as a function of time
• The potential energy as a function of time
• Plot the key results
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HW due by end of week 1
• Read Ch1
• Know Key Eng Concepts listed on pg 26
• Using Fig 8.1(a)
• Identify each subsystem as closed or open (control volume)
• Checking understanding: 1.11, 1.13, 1.16, 1.17, 1.21, 1.23
• Problems: 1.25, 1.27
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Learning Outcomes
►Explain several fundamental concepts used throughout this book including
closed system, control volume, boundary and surroundings, property, state,
process, the distinction between extensive and intensive properties, and
equilibrium.
►Identify SI and English Engineering units, including units for specific volume,
pressure, and temperature.
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Learning Outcomes, cont.
►Describe the relationship among the Kelvin, Rankine, Celsius, and Fahrenheit
temperature scales.
►Apply appropriate unit conversion factors during calculations.
►Apply the problem-solving methodology used in this book.
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System
System –
any region of space, or any selected amount of matter,
specified for study (i.e. anything you want)
S__________
(environment) – everything outside of the system
Control Surface (system b_______) – real / imaginary surface separating
the system from the surroundings
_______
System
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________
system
• System may be large or small, moving or stationary, rigid or deformable,
and are shown schematically separated from its surroundings (or
environment) by its boundary using dotted lines
• Clear identification of the system / system boundary is extremely
important. In doing an energy balance on the system, the energy
transfer to (and from) the system crossing the boundary must be clearly
identified
• Energy is transferred across the system boundary (in/out of the system)
in the form of w____ and h_____t________
What does a rigid system mean?
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Types of System
I______ system - neither energy (work and heat) nor mass crosses the
system boundary (i.e. fixed mass w/ no energy transfer)
C_____ System - only energy (_____ and ______) crosses system boundary
(i.e. no mass in/out)
O______ System (control volume) - both _______ and ______ cross system
boundary (focus is on region of space)
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Closed System
►A system that always contains the same
amount of matter.
►No transfer of _______ across its boundary
can occur.
►__________ system: special type of closed
system that does not interact in any way with
its surroundings.
Control Volume (Open System)
►A given region of space through which mass flows.
►Mass may cross the boundary of a control volume.
System
Given
Need
Hot coffee &
ice cube
Mcoffee, Mice,
T initial
Final
temperature
Hot noodle
soup cooling
Msoup, Tdesired, Heat_in/out
Tinitial
Shower
ṁhot, ṁcold
Tinitial
T_mixed
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system
Fig_1-1
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
Macroscopic vs Microscopic
In principle, can solve forces on molecule using Newton’s Laws determine
behavior
• 1 m^3 of gas at 1 atm and temperature -> ~2.4 x1025 molecules
• 6 eqns of motion for each molecule (3 for position, 3 for velocity) -> 1.4x1026
differential eqns to solve simultaneously
• Not possible. Desktop have RAM on the order of 109
• We can model the average behavior of molecules statistically
• We also use simple empirical relations to capture the statistical nature of
law.
• ________ Thermodynamics treats macroscopic effects only, ignore
microscopic impact of individual molecules
• Assume matter can be modeled as a continuum -> the limit in which
discrete changes from molecule to molecule can be ignored and distance
and time of interest is >> molecular scale
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Macroscopic vs Microscopic
When does continuum assumption fail?
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Property
• Macrosopic characteristics of a system to which a numerical value can
be assigned independent of history of the system
What are Examples of Property that can be used to describe the
system shown?
Gas
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State
► The condition of a system as described by its _________.
► Example: The state of the system shown is described by p, V, T,….
► The state often can be specified by providing the values of a sub____ of
its properties. All other properties can be determined in terms of these
few.
State: p, V, T, …
Gas
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Process
►A transformation from one ______ to another.
►When any of the properties of a system changes, the ____ changes, and
the system is said to have undergone a process.
►Example: Since V2 > V1, at least one p_____ value changed, and the gas has
undergone a process from _____ 1 to _____ 2.
State 1: p1, V1, T1, …
State 2: p2, V2, T2, …
Gas
Gas
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Extensive Property
► Depends on the size or extent of a system.
► Examples: mass, volume, energy.
► Its value for an overall system is the sum of its values for the parts into
which the system is divided.
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Intensive Property
►I________ of the size or extent of a system.
►Examples: _______, ________.
►Its value is not additive as for extensive properties.
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Equilibrium
►When a system is isolated, it does not interact with its surroundings;
however, its state can change as a consequence of spontaneous
events occurring internally as its intensive properties such as
temperature and pressure tend toward uniform values. When all such
changes cease, the system is at an ___________ state.
►Equilibrium states and processes from one equilibrium state to
another equilibrium state play important roles in thermodynamic
analysis.
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Equilibrium
Equilibrium: no observable changes in property (idealized, we never
totally achieve equilibrium)
►M_______ equilibrium – characterized by equal pressure
►T_______ equilibrium – characterized by equal temperature
►Chemical and phase equilibrium will not be covered in this class
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Relationships
• _______: any region of space, or any selected amount of matter,
specified for study
• _______: Macrosopic characteristics of a system to which a numerical
value can be assigned independent of history of the system
• _______: condition described by its thermodynamic properties
• _______: if a system undergoes a change from one thermodynamic
state to another thermodynamic state, it is said to have undergone a
process
• _______: if a system returns to its initial state after multiple process.
(thermodynamic “round trip”)
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Units
•
•
•
•
•
Mass: kg
Length: meter, m
Time: second, s
Temperature, Kelvin
Force, newton, N (= 1 kg-m / s^2)
slug (1 slug = 32.2 lbm)
ft
s
°R
lbf = 1 slug-ft / s^2
Tip of the day: for English system, Do NOT, ever, use lbm if force is involved. Always
convert lbm to slugs
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Density (r) and Specific Volume (v)
►From a macroscopic perspective, description of matter is simplified by
considering it to be distributed continuously throughout a region.
►When substances are treated as continua, it is possible to speak of
their intensive thermodynamic properties “at a point.”
►At any instant the density (r ) at a point is defined as
m
r = lim  
V →V '  V 
(Eq. 1.6)
where V ' is the smallest volume for which a definite value of the ratio
exists.
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Density (r) and Specific Volume (v)
►Density is mass per unit volume.
►Density is an _______ property that may vary from point to point.
►SI units are (kg/m3).
►English units are (slug/ft3). (if given in lbm, converted to slugs)
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Density (r) and Specific Volume (v)
►Specific volume is the reciprocal of density: v =
►Specific volume is volume per unit mass.
►Specific volume is an ______ property that may vary from point to
point.
►SI units are (m3/kg).
►English units are (ft3/slug). (if given in lbm, converted to slugs)
Specific volume is usually preferred for thermodynamic analysis when
working with gases that typically have small density values.
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Pressure (p)
► Consider a small area A passing through a point in a fluid at rest.
► The fluid on one side of the area exerts a compressive force that is normal
to the area, Fnormal. An equal but oppositely directed force is exerted on
the area by the fluid on the other side.
► The pressure (p) at the specified point is defined as the limit
F

p = lim  normal 
A 
A →A ' 
(Eq. 1.10)
where A' is the area at the “point” in the same limiting sense as used in
the definition of density.
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Pressure Units
►SI unit of pressure is the pascal:
1 pascal = 1 N/m2
►Multiples of the pascal are frequently used:
►1 kPa = 103 N/m2
►1 bar = 105 N/m2
►1 MPa = 106 N/m2
►English units for pressure are:
►pounds force per square foot, lbf / ft2
►pounds force per square inch, lbf / in2
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Absolute Pressure
►Absolute pressure: Pressure with respect to the zero pressure of a
complete vacuum.
►Absolute pressure must be used in thermodynamic relations.
►Pressure-measuring devices often indicate the difference between the
absolute pressure of a system and the absolute pressure of the
atmosphere outside the measuring device.
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Gage and Vacuum Pressure of pressure measuring devices
►When system pressure is greater than
atmospheric pressure, the term gage pressure is
used.
p(gage) = p(absolute) – patm(absolute)
(Eq. 1.14)
►When atmospheric pressure is greater than
system pressure, the term vacuum pressure is
used.
p(vacuum) = patm(absolute) – p(absolute)
(Eq. 1.15)
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Temperature (T)
►If two blocks (one warmer than the other) are brought into contact and
isolated from their surroundings, they would interact thermally with
changes in observable properties.
►When all changes in observable properties cease, the two blocks are in
thermal equilibrium.
►Temperature is a physical property that determines whether the two
objects are in thermal equilibrium.
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Thermometers
►Any object with at least one measurable property that changes as its
temperature changes can be used as a thermometer.
►Such a property is called a thermometric property.
►The substance that exhibits changes in the thermometric property is
known as a thermometric substance.
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Thermometers
►Example: Liquid-in-glass thermometer
►Consists of glass capillary tube connected to a bulb filled with liquid and
sealed at the other end. Space above liquid is occupied by vapor of liquid or
an inert gas.
►As temperature increases, liquid expands in volume and rises in the
capillary. The length (L) of the liquid in the capillary depends on the
temperature.
►The liquid is the thermometric substance.
►L is the thermometric property.
►Other types of thermometers:
►Thermocouples
►Thermistors
►Radiation thermometers and optical pyrometers
Temperature Scales
►Kelvin scale: An absolute thermodynamic temperature scale whose unit
of temperature is the kelvin (K); an SI base unit for temperature.
►Rankine scale: An absolute thermodynamic temperature scale with
absolute zero that coincides with the absolute zero of the Kelvin scale; an
English base unit for temperature.
T(oR) = 1.8T(K)
(Eq. 1.16)
►Celsius scale (oC):
T(oC) = T(K) – 273.15 (Eq. 1.17)
►Fahrenheit scale (oF):
T(oF) = T(oR) – 459.67 (Eq. 1.18)
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Design
➢ Engineering design is a decision-making process that draws principles from
engineering and fields
➢ Fundamental elements include establishment of objectives, synthesis,
analysis, construction, testing, and evaluation.
➢ Designs are typically subject to constraints including economics, safety,
and environmental impact.
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Problem-Solving Methodology
►Known: Read the problem, think about it, and identify what is
known.
►Find: State what is to be determined.
►Schematic and Given Data: Draw a sketch of system and label with
all relevant information/data.
►Engineering Model: List all simplifying assumptions and idealizations
made.
►Analysis: Reduce appropriate governing equations and relationships
to forms that will produce the desired results.
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