Introduction ................................................................................................................................................ 1
Fundamental Concepts .............................................................................................................................. 1
Work ...................................................................................................................................................... 4
Temperature .......................................................................................................................................... 5
Matter ......................................................................................................................................................... 6
States of Matter ..................................................................................................................................... 6
Structure of Matter ................................................................................................................................ 7
Atomic and Molecular Weights .............................................................................................................. 7
Physical Measurements ................................................................................................................. 9
Measuring Pressure .............................................................................................................................. 9
Temperature Measurement ................................................................................................................. 12
Density Measurement ......................................................................................................................... 12
Specific Gravity Measurement ............................................................................................................ 13
Heating Value Measurement ............................................................................................................... 13
On-Line Gas Chromatography ............................................................................................................ 14
Natural Gas Properties ..................................................................................................................... 14
Basic Chromatography ........................................................................................................................ 14
Composition ........................................................................................................................................ 15
Specific Gravity Values ....................................................................................................................... 15
Natural Gas Temperatures .................................................................................................................. 16
Combustion of Natural Gas ................................................................................................................. 16
Gas Measurement Units ..................................................................................................................... 17
Fundamental Gas Laws ........................................................................................................................... 17
The Ideal Gas Laws ............................................................................................................................ 17
Practical Application—Boyle’s Law ..................................................................................................... 20
Practical Application—Charles’ Law ................................................................................................... 21
Behavior of Gases at High Pressure ................................................................................................... 22
Natural Gas Compressibility Factors ................................................................................................... 22
Equivalence of Some Units ................................................................................................................. 24
LIST OF TABLES
Page
Table 2-1: Fundamental Concepts ........................................................................................................... 1
Table 2-2. Conversion to SI Units ............................................................................................................. 1
Table 2-3: Molecular Weights of Some Common Gases .......................................................................... 8
Table 2-4: Atomic Weights of Some Common Elementary Substances ................................................... 8
Table 2-5: Effect of Altitude on Pressure ................................................................................................ 11
Table 2-6: Typical Composition of Natural Gas ...................................................................................... 15
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GAS DISTRIBUTION SELF-STUDY COURSE
Table 2-7: Ignition Temperatures ............................................................................................................ 17
Table 2-8: Measurement Units ............................................................................................................... 17
Table 2-9: Ideal Gas Law Terms ............................................................................................................ 18
Table 2-10: Ideal Gas Law Terms S.I. .................................................................................................... 18
Table 2-11: Table of Equivalents ............................................................................................................ 24
LIST OF FIGURES
Page
Figure 2-1: Simple Devices for Measuring Gas Pressure ......................................................................... 9
Figure 2-2. Bourdon Gage ....................................................................................................................... 11
Figure 2-3: Deadweight Piston Gage ...................................................................................................... 12
Figure 2-4: Specific Gravity Balance ...................................................................................................... 13
Figure 2-5: Specific Gravity Values ........................................................................................................ 15
Figure 2-6: Pipeline Heater ..................................................................................................................... 16
Figure 2-7: Boyle’s Law (Constant Temperature Assumed) ................................................................... 21
Figure 2-8: Charles' Law (Constant Temperature Assumed) ................................................................. 21
Figure 2-9: Schematic Compressibility Factor Chart .............................................................................. 23
CHAPTER 2 BASIC SCIENCE CONCEPTS 2-1
CHAPTER 2: BASIC SCIENCE CONCEPTS
Introduction
This chapter reviews the basic principles of physics, chemistry, and mathematics that will facilitate
understanding of course material. Because this chapter material is based upon a working knowledge of
elementary algebra, a review of this subject may be necessary for a complete understanding of the later
chapters.
Fundamental Concepts
All physical quantities are based on three fundamentals concepts: distance, time, and mass. These
concepts are used to describe properties of materials and define their physical quantities. They are
expressed in units of various sizes.
The International System, or the S.I. system, is referred to as the metric system and is based on the
units of meter, second, and kilogram. The centimeter-gram-second, or cgs system, was widely used in
scientific and engineering practice in Europe. In the United States, the cgs system is used for scientific
work, but the foot-pound-second, or fps system, is commonly used in engineering. Complete conversion
tables are found in publications of the American Society of Testing Materials (ASTM) and the Metric Unit
(SI) Application Guide for the American Gas Association.
Table 2-1: Fundamental Concepts
Base Quantity Name Symbol
Length meter m
Mass kilogram kg
Time second s
Electric current ampere A
Temperature kelvin K
Amount of substance mole mol
Table 2-2. Conversion to SI Units
Derived Quantity Name Expression in terms of SI units
area square meter m2
volume cubic meter m3
speed, velocity meter per second m/s
acceleration meter per second squared m/s2
mass density kilogram per cubic meter kg/m3
force newton (N) m·kg·s-2
pressure pascal m-1·kg·s-2
energy, work joule (J) N-m m2·kg·s-2
electric potential volt (V) m2·kg·s-3·A-1
Length is a measure of the straight line distance between 2 points in space and is a 1-dimensional
concept. Standard units of length have been established and distances are given as multiples of these
2-2 GAS DISTRIBUTION SELF-STUDY COURSE
standard units. In the fps system, the standard unit of length is the foot, and in the S.I. system, the
standard unit of length is the meter (39.37 inches).
Area is a measure of the amount of surface within a 2-dimensional shape. Area has units of length
squared, square feet or square meters. Meaning an area is one length multiplied by another regardless
of the units.
Volume is a measure of the amount of space occupied by a 3-dimensional object. Volume has units of
length cubed: cm3, m3, in3, etc.
Mass is the quantity of matter in an object. In the fps system, the standard unit of mass is the pound. In
the S.I. variation, the standard unit of mass is the kilogram (2.2046 pounds).
It is important to distinguish between mass and weight. Mass represents a fixed quantity of matter and
relates to inertia. Weight is the force acting on a body due to gravity and varies with location. Weight is
the product of mass and the local gravitational acceleration, which varies somewhat with location. W =
mg
Time may be defined as the interval between the occurrence of two specified events, or as the duration
of an event. For example, the mean (average) solar day is defined as the average interval between two
successive transits of the sun’s center over the same reference line (meridian) on the earth’s surface.
For convenience, this interval is divided into hours, minutes, and seconds. The second is the basic unit
of time in the fps, cgs, and S.I. systems.
From these basic concepts and their measurements, many other physical quantities may be derived.
Speed is distance traveled divided by the time it takes. Speed = distance / time
Velocity is speed in a particular direction. Velocity is actually the change in position divided by the
change in time. V = Δ L / ΔT
Speed or velocity has the dimension L/T (for example, feet per second, miles per hour, or meters per
second). Speed describes how fast something is moving and does not involve a direction. Velocity is
very similar to speed except that it involves a direction as well as the speed. For velocity to be constant,
the speed and direction would both have to be constant. The only way an object can have a constant
velocity would be if it is sitting still or if it is moving in a straight line at a constant speed.
Acceleration is the change in the velocity of an object over a period of time: A = L/T2 (for example, feet
per second per second or meters per second per second). Since acceleration involves a change in
velocity, an object might be accelerating even though its speed is constant. How is this possible? Well,
it goes back to the difference between speed and velocity. Remember that velocity involves both speed
and direction. So, a changing velocity does not have to necessarily involve a change in speed. It could
just involve a change in direction.
For example, consider a car moving at a constant speed of 55 Miles Per Hour (mph) while turning in a
circle. The car's velocity is not constant, even though the speed is constant. This is because the
direction of motion is constantly changing while the car is turning. Since the direction is changing, even
though the speed is not, the velocity is changing. Remember, the velocity involves both speed and
direction. As a result, the car is accelerating, even though it is neither speeding up nor slowing down.
The car is accelerating because its velocity is changing.
CHAPTER 2 BASIC SCIENCE CONCEPTS 2-3
Force is also a derived quantity, with dimensions of length (L), mass (M)*, and time (T). This is
represented by the equation: Force = mass × acceleration.
A force is any stimulus that tends to set a body in motion, or alter its existing motion. A force can cause
a stationary object to begin to move, or cause a moving object to stop. Thus, if a body is in motion, a
force is required to either alter the direction of the motion or make the body go faster (accelerate) or
slower (decelerate). In the United States, weight and force are measured in foot pounds (lbF) to
distinguish them from pounds - mass (lbm). The S.I. unit of force is the Newton (N), defined as the force
to accelerate a mass of one kilogram by one meter per second squared (N = kgm / s2.
Weight is a particular kind of force. The weight of a mass is the force that the earth pulls on the mass (W
= mg). At locations on the earth’s surface where the force exerted on a one-pound mass by the action of
gravity is one pound of force, the acceleration is 32.1740 feet per second2 (9.80665 meters per second).
Here, gc is also equal to 32.174 numerically, but its units are (lbm/lbF) X ft/s2.
The value of acceleration due to gravity varies slightly from point to point on the earth’s surface. When a
body is weighed, the force measured is that necessary to restrain the body from accelerating under the
force of gravity toward the center of the Earth. Thus, the body weight of a body will vary slightly
according to its geographical location. In contrast to this, mass refers to a quantity of matter and does
not change with a different location.
Pressure is also a derived quantity, with dimensions of length (L), mass (M) and time (T). Pressure is
defined as force per unit area.
Example:
Determine the weight of a one-pound mass under the standard condition of gravity acceleration.
Substitution of the value 32.174 for gc gives:
F = (1 lbm/gc) 32.174 = (1 lbm/32.174) 32.174 = 1 lbF.
In S.I. units using 1 kg,
F = (1 kg/gc) 9.80665 = (1 kg/9.80665) (9.80665) = 1 kgf = 9.80665 N
In other words, one pound-mass will weigh exactly one pound-force under the standard gravity
condition. Note: gc is often rounded to 32.17 or even 32.2, depending on the accuracy desired.
Example:
Determine the weight of this same body if it is located at a point where the acceleration due to
gravity is 32.093 ft/s2.
F = (m/gc) g = (1 lbm/32.17) 32.093 = 0.9974 lbF
Thus, the same body would weigh slightly less where the acceleration due to gravity is less.
If one took this same mass to the moon, where the gravitational effect is very much less than on earth,
the weight would be correspondingly less.
Example:
Calculate the force necessary to uniformly accelerate a 10-lb (4.5359 kg) ball from rest to a velocity
of 30 ft/s (9.1441 m/s) in 5 seconds. This force is shown to be 1.86 lbF (8.2954 N) as follows.
* The S.I. symbol for its unit of length, the meter (sometimes spelled metre), is also abbreviated as m.
2-4 GAS DISTRIBUTION SELF-STUDY COURSE
Initial velocity = 0 ft/s; (s = second) (0 m/s)
Velocity at the end of 5 s = 30 ft/s (9.1441 m/s)
Uniform acceleration = (30 – 0)/5 = 6 ft/s2 (1.8288 m/s2)
Force = (10/32.17)6 = 1.86 lbF (8.2954 N)
Work
When the action of a force on a body causes it to move in the direction of the force, work is done. Work
is measured as the product of the force and distance through which it moves in the direction of the force.
W = Fd
w = work done on a body
F = Force exerted on the body
d = Distance the body moves in the direction of the force
Bodies in motion have kinetic energy; this can be used to do work or produce heat. The amount of this
energy is given by the equation
KE = mv2/2
KE = Kinetic energy of a body
v = Velocity of a body
m = Mass of the body. As indicated m can be calculated from weight. Thus, lbm = lbF x gc/g.
The unit of KE is the ft-poundal, if m is expressed in lbm and v is in ft/s. The engineering unit is the ftpound.
Poundals can be converted to lbF by dividing by gc. The S.I. unit is the Joule.
Example:
Calculate the kinetic energy of a 2500 pound (lbF) (1134 kg) automobile traveling at a velocity of 60
mph (96.6 km/h). First the velocity unit, miles per hour, is converted to feet per second to obtain
consistent units. Use the fact that 1 mass-pound weighs about 1 force-pound.
ft/s = (mph)/ft/mile)(h/s). Here, 60 X 5280 X (1/3600) = 88
ft/s = (26.8m/s)
KE = ½ (2500)(882) = 9,680,000 ft-poundals
Or KE = 9,680,000/32.174 = 300,864 ft-lbF (407,917 J or 407.9 kJ)
Although similar to the kinetic energy of a moving mass, the kinetic energy of the moving parts of a
machine is sometimes referred to as mechanical energy.
In addition to mechanical forms of energy, there are other types, including potential energy, chemical
energy, electrical energy and heat. Many engineering problems involve the conversion of energy from
one form to another. For example, the chemical energy in a gaseous fuel can be used in an internal
combustion engine to drive a compressor that pumps gas through a transmission or distribution system.
In this case, the chemical energy is converted to heat by combustion in the engine. A portion of this
heat is converted to mechanical energy, which is transmitted through the compressor to the gas. Thus,
CHAPTER 2 BASIC SCIENCE CONCEPTS 2-5
the sequence chemical energy heat kinetic energy energy in the flowing gas briefly describes this
conversion process.
Temperature
Temperature is a measure of the quantity of heat in an object. Temperature is expressed more exactly
in degrees Fahrenheit (ºF) or degrees Celsius (ºC). On the Fahrenheit scale, the freezing point of water
is 32ºF, and the boiling point is 212ºF. The interval between the freezing and boiling points at normal
atmospheric pressure is uniformly divided into 180 degrees. On the Celsius scale, formerly called
centigrade, the corresponding interval is divided into 100 parts, with 0ºC as the freezing point and 100ºC
as the boiling point of water at atmospheric pressure conditions.
These two scales, Fahrenheit and Centigrade, are relative scales; that is, their zero points were
arbitrarily fixed by their inventors. Quite often it is necessary to use absolute temperatures instead of
relative temperatures. Absolute temperature scales have their zero point at the lowest possible
temperature which man believes can exist. As you may know, this lowest temperature is related both to
the ideal gas laws and to the laws of thermodynamics.
The absolute scale that is based on degree units the size of those in the Centigrade scale, is called the
Kelvin scale, after its inventor, Lord Kelvin; the absolute scale that corresponds to the Fahrenheit degree
scale is called the Rankine scale.
To convert temperature readings from one of these scales to the other, the following formulas are used.
ºF = 9/5ºC +32
Alternatively, ºC = 5/9(ºF- 32)
The formulas recognize not only the difference in size of the degrees used in the two scales, but the
arbitrary natures of the scales.
Example:
Convert a temperature of 25ºC to ºF, and a temperature of 60ºF to ºC.
Using the equations above:
ºF = (9/5)25 + 32 = 77
ºC = (5/9)(60-32) = (5/9)(28) = 15.6ºC
Absolute temperature scales are used in many engineering calculations. To determine absolute
temperatures on the Fahrenheit scale, 459.67 is added to the Fahrenheit temperature; on the Celsius
scale, 273.15 is added. Absolute zero is taken as the lowest temperature possible. On the Fahrenheit
scale, this point is 459.67º below 0ºF; on the Celsius scale, it is 273.15º below 0ºC. Therefore, 32ºF in
terms of absolute temperature is 459.67 + 32 = 481,56ºR; and 0ºC in terms of absolute temperatures is
273.15 + 0 = 273.15ºK. The Kelvin temperature is used in the S.I. units.
The concept of temperature makes it possible to express quantities of heat as a form of energy. Energy
transferred because of temperature difference is termed heat, and the driving force in heat transfer is
the temperature difference between the bodies involved.
Normally we express heat, work, or energy in the units of Btu’s (British thermal units) or calories. The
energy per unit mass then will be Btu per pound or calories per gram. The calorie is roughly defined as
the amount of energy required to raise the temperature of 1 gram of water 1 degree C at a pressure of 1
2-6 GAS DISTRIBUTION SELF-STUDY COURSE
atmosphere. (Similarly, a Btu is the amount of energy required to raise 1 pound of water 1 degree F.)
One larger unit of heat energy widely used in the gas distribution industry is the therm, which is 100,000
Btu.
Heat (typically symbolized as ―Q‖ in equations), as it applies to laws governing energy changes, is
commonly defined as that part of the total energy flow across a system boundary that is caused by
temperature difference between the system and its surroundings. Heat may be changed by conduction,
convection, or radiation.
Heat transferred by direct contact is called conduction.
Convection transfers heat through a fluid such as water or air by heating the fluid in contact
