Environmental Engineering Reference
In-Depth Information
TABLE A.2
U.S. Commercial Units
SI Unit Value
a
Quantity
Unit
Symbol
Length
inch
in.
2.54E(
−
2)
m
Length
foot
ft
3.048E(
−
1)
m
Length
mile (statute)
mile
5280 ft
=
1.609E(3) m
4.0469E(3) m
2
Area
acre
3.7854E(
−
3) m
3
Volume
gallon (U.S.)
gal
42 gal (US)
=
1.5899E(
−
1) m
3
Volume
barrel
bbl
Force
pound (force)
lbf
4.448 N
Mass
pound (mass)
lbm
4.5359E(
−
1) kg
Mass
ton (short)
2000 lbm
=
9.07185E(2) kg
Energy
British thermal unit
Btu
1.05506E(3) J
Energy
Quad (1E(15) Btu)
Q
1.05506E(18) J
Energy
therm
therm
1.05506E(8) J
Power
horsepower
hp
7.46 E(2)
W
Pressure
pound (force)/square inch
psi
6.895E(3) Pa
◦
F
(5
/
9)
K
Temperature
Fahrenheit
a
Boldface values are exact.
listed in the third section of Table A.1, labeled “Defined units.” Among these we note the nautical
mile, which is the distance along the earth's surface corresponding to a minute of latitude, and the
velocity of a knot, or one nautical mile per hour, the usual unit of wind speed. The unit for small
geographic areas is the hectare, and the laboratory scale measure of volume is the liter (L). Large
masses are usually measured in metric tons (ton). The chemist's unit of energy is the calorie, which
equals the amount of heat required to warm a gram of water by one degree centigrade.
Unlike all the other industrialized nations, the United States has not adopted the metric system
of measurement for domestic and commercial purposes, but continues with the system of units it
inherited from England. To facilitate conversion to SI units, the values of pertinent U.S. commercial
units are listed in Table A.2.
Many of these units are commonly used in the United States. For example, the gallon (gal) is the
unit volume for retail sales of vehicle fuel, whereas the barrel is the preferred unit of international
petroleum suppliers and refiners. The unit of force is the pound force (lbf ), while the unit of mass
is the pound mass (lbm). For large amounts of mass, the short ton is used, to be distinguished from
the metric ton. The energy unit is the British thermal unit (Btu), the amount of heat required to
warm a pound mass of water by one degree Fahrenheit. The unit of power is the horsepower (hp).
A common pressure unit is the pound force per square inch (psi).
The conversion of quantities from one system of units is straightforward. For example, to
convert
x
Btu/lbm to SI units of J/kg, multiply by the conversion factors from Table A.2,
x
Btu
lbm
1
.
05506E
(
3
)
J
lbm
x
Btu/lbm
=
=
2
.
326E
(
3
)
x
J/kg
Btu
4
.
5359E
(
−
1
)
kg
In explaining the technology of energy systems in this text we have need to invoke the principles
of physics, chemistry, and thermodynamics. The quantitative application of these sciences requires
the measurement of certain properties of atoms and molecules that are used in defining important
