In this chapter various relevant concepts and definitions are introduced, and will be used throughout the course.

**Thermodynamics** is the science of energy, including energy storage
and energy in transit. The **Conservation
of Energy Principle** states that energy
cannot be created or destroyed, but can only change its form.
The three forms of energy storage of greatest interest to us are
**Potential Energy** (PE), **Kinetic
Energy** (KE), and **Internal Energy** (U), which
we introduce below. The two forms of energy in transit that we
consider are **Work** (W) and **Heat** (Q), and the interactions between these various forms
of energy are defined in terms of the **First Law of Thermodynamics**,
which we introduce in **Chapter 3**.

In this course we use the International System
(SI) units exclusively, with occasional lapses. In the US this
is an ongoing battle causing much confusion in the global technical
environment (refer to **wikipedia**
on this subject). Even the National Council of Examiners for Engineering
and Surveying (**NCEES)**
seems to be confused at this point - the Fundamentals of Engineering
(FE) Reference Handbook and exam contain exclusively SI units
and then, when you reach maturity and are ready to take the Professional
Engineering (PE) exam, you find that the English system of units
(USCS) is acceptable, and in some cases used exclusively. This
confusion reached a new climax when in the Fall of 1999, NASA's
$125 million **Mars
Climate Orbiter** broke up in the Martian atmosphere, because
scientists in one of NASA's subcontractors failed to convert critical
data from the English sytem to the SI system of units.

We begin with **Newton's Second Law**, as
follows:

The **Weight** of a body is the force acting on that body due to
the acceleration due to gravity (g = 9.807 [m/s^{2}]),
in accordance with the Universal Theory of Gravitation developed
by Isaac Newton. Legend has it that Newton was inspired by an
apple falling on his head, as is shown in a delightful website
by Mike Guidry of the University of Tennessee on **Sir
Isaac Newton**, in which we see a cartoon showing the apple
falling on Newton's head.

Well, this legend is extremely relevant, since
the weight of a small apple is approximately one Newton. Furthermore,
the mass of a plastic bottle containing one liter of water is
approximately one kilogram.

**Quick Quiz** - can you estimate how many Newtons (or apples)
a liter of water weighs?

At this point we note that the major confusion
of the English system of units came about because of the decision
to define mass and force independently as 1 lb (pound), when in
fact they are related through Newton's Second Law. In order to
justify this one has to separately define a pound mass (lbm) and
a pound force (lbf), thus since the acceleraton due to gravity
g = 32.2 [ft/s^{2}] we have:

One attempt to solve this paradox has been the introduction of a new unit of mass, the "slug", thus:

1 slug = 32.2 lbm

however I challenge anyone to go to the grocery store and request a slug of potatos.

We now consider the work done (W), the energy in transit requiring both the applied force (F) and movement (x). If the force (F) is constant over the distance moved (x) then the work done is given by:

However, in general the force (F) is not constant over the distance x, thus we need to sum all the incremental work processes taking into consideration the variation of the force (F). This leads to the equivalent integral form for determining work done (W) as follows:

Over the years we have developed a basic Units Survival Kit (for the SI challenged) in order to help convert between the USCS (English) system and the SI (International) system of units, as well as to develop a feel for the magnitudes of the various units.

**Quick Quiz** -
we all know (from reading our speedometers) that 50 mph is equivalent
to 80 km/hr.

1. What is the accuracy of this conversion?

2. Use this information to show that 9 mph is equivalent to 4
m/s.

We find that with the above survival kit we can determine many unit conversions between SI & English units, typically as demonstrated in the following block:

As we progress and learn new concepts we will add to this Survival Kit.

We introduce the various forms of energy of
interest to us in terms of a solid body having a mass m [kg].
These include potential, kinetic and internal energy. Potential
energy (PE) is associated with the elevation of the body, and
can be evaluated in terms of the work done to lift the body from
one datum level to another under a constant acceleration due to
gravity g [m/s^{2}], as follows:

Kinetic energy (KE) of a body is associated with its velocity [m/s] and can be evaluated in terms of the work required to change the velocity of the body, as follows:

Internal energy (U) of a body is that associated with the molecular activity of the body as indicated by its temperature T [°C], and can be evaluated in terms of the heat required to change the temperature of the body having a specific heat capacity C [J/kg.°C], as follows:

In order to gain an intuitive appreciation
for the relative magnitudes of the different forms of energy we
consider the (tongue-in-cheek) example of an attempt to cook a
turkey by potential energy. The turkey is brought to the top of
a 100 m building (about 30 stories) and then dropped from the
ledge. The potential energy is thus converted into kinetic energy,
and finally on impact the kinetic energy is converted into internal
energy. The increase in internal energy is represented by an increase
in temperature, and hopefully, if this experiment is repeated
enough times the temperature increase will allow the turkey to
cook. This remarkable experiment was first reported by R.C.Gimmi
and Gloria J Browne - **"Cooking
with Potential Energy"**, published in the **Journal
of Irreproducible Results** (Vol 33, 1987, pp 21-22).

What a disappointment! At 0.33°C per fall it will require repeating the experiment 600 times just to reach the cooking temperature of 200°C.

For purposes of analysis we consider two types of Thermodynamic Systems:

**Closed System**- usually referred to as a**System**or a**Control Mass**. This type of system is separated from its surroundings by a physical boundary. Energy in transit in the form of Work or Heat can flow across the system boundary, however there can be no mass flow across the boundary. One typical example of a system is a piston / cylinder device in which the system is defined as the fixed mass of fluid contained within the cylinder.

**Open System**- usually referred to as a**Control Volume**. In this case, in addition to work or heat, we have mass flow of the working fluid across the system boundaries through inlet and outlet ports. In this course we will be exclusively concerned with steady flow control volumes, in that the net mass of working fluid within the system boundaries remains constant (ie mass flow in [kg/s] = mass flow out [kg/s]). The following sections refer mainly to systems - we will consider control volumes in more detail starting with**Chapter 4a**.

The closed system shown above can be defined
by its various **Properties**, such as its pressure (P), temperature (T), volume
(V) and mass (m). We will introduce and define the various properties
of thermodynamic interest as needed in context. Furthermore the
properties can be either **Extensive** or **Intensive** (or **Specific**). An extensive property is one whose value depends
on the mass of the system, as opposed to an intensive property
(such as pressure or temperature) which is independent of the
system mass. A specific property is an intensive property which
has been obtained by dividing the extensive property by the mass
of the system. Two examples follow - notice that specific properties
will always have kilograms (kg) in the units denominater.

One often used exception to the above definitions is the concept of Specific Weight, defined as the weight per unit volume. We will not be using this concept throughout this text.

The **State** of a system is defined by the values of the various
intensive properties of the system. The **State Postulate** states that
if two independent intensive property values are defined, then
all the other intensive property values (and thus the state of
the system) are also defined. This can significantly simplify
the graphical representation of a system, since only two-dimensional
plots are required. Note that pressure and temperature are not
necessarily independent properties, thus a boiling liquid will
change its state from liquid to vapor at a constant temperature
and pressure.

We assume that throughout the system **Equilibrium**
conditions prevail, thus there are no temperature or pressure
gradients or transient effects. At any instant the entire system
is under chemical and phase equilibrium.

A **Process** is a change of state of a system from an initial to
a final state due to an energy interaction (work or heat) with
its surroundings. For example in the following diagram the system
has undergone a compression process in the piston-cylinder device.

The **Process
Path** defines the type of process undergone.
Typical process paths are:

**Isothermal**(constant temperature process)**Isochoric**or**Isometric**(constant volume process)**Isobaric**(constant pressure process)**Adiabatic**(no heat flow to or from the system during the process)

We assume that all processes are **Quasi-Static**
in that equilibrium is attained after each incremental step of
the process.

A system undergoes a **Cycle** when it goes through
a sequence of processes that leads the system back to its original
state.

The basic unit of pressure is the Pascal [Pa],
however practical units are kiloPascal [kPa], bar [100 kPa] or
atm (atmosphere) [101.32 kPa]. The **Gage** (or **Vacuum**)
pressure is related to the **Absolute** pressure as shown in the diagram below:

The basic method of measuring pressure is by
means of a **Manometer**, as shown below:

The atmospheric pressure is measured by means
of a **Mercury Barometer** as follows:

**Solved
Problem 1.1 - Using a Barometer to determine
the Height of a Building**** **This solved problem allows us to determine the height
of a building in terms of the difference in atmospheric pressure
between the top and bottom of the building. Note that according
to legend, when this problem was put to Nobel Prize Winner Niels
Bohr (while still a student), he came up with an interesting response,
as shown on the following Australian website of the **Virtual
Teacher**.

Temperature is a measure of molecular activity, and a temperature difference between two bodies in contact (for example the immediate surroundings and the system) is the driving force leading to heat transfer between them.

Both the **Fahrenheit** and the **Celsius** scales are in common usage in the US, hence it is
important to be able to convert between them. Furthermore we will
find that in some cases we require the **Absolute** (**Rankine**
and **Kelvin**) temperature scales (for example when using the Ideal
Gas Equation of State), thus we find it convenient to plot all
four scales as follows:

Notice from the plot that -40°C equals -40°F, leading to convenient formulas for converting between the two scales as follows:

**Quick Quiz** -
The temperature in Chicago in winter can be as low as 14°F.
What is the temperature in °C, K, and °R. [-10°C, 263 K, 474°R] Note that by convention 263 K is read "263 Kelvin,"
and not "263 degrees Kelvin".

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Engineering Thermodynamics by Israel Urieli is licensed under a
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