Environmental Engineering Reference
In-Depth Information
■
Example 11.5
Problem:
Find the circumference of a circle that has a diameter of 25 ft (π = 3.14).
Solution:
C
= π ×
D
= 3.14 × 25 ft = 78.5 ft
■
Example 11.6
Problem:
A circular chemical holding tank has a diameter of 18 meters (m). What is
the circumference of this tank?
Solution:
C
= π ×
D
= 3.14 × 18 m = 56.52 m
■
Example 11.7
Problem:
An influent pipe inlet opening has a diameter of 6 ft. What is the circum-
ference of the inlet opening?
Solution:
C
= π ×
D
= 3.14 × 6 ft = 18.84 ft
AREA
For area measurements in water/wastewater operations, three basic shapes are par-
ticularly important—namely, circles, rectangles, and triangles. Area is the amount of
surface an object contains or the amount of material it takes to cover the surface. The
area on top of a chemical tank is called the
surface area.
The area of the end of a ven-
tilation duct is called the
cross-sectional area
(the area at right angles to the length of
ducting). Area is usually express in square units, such as square inches (in.
2
) or square
feet (ft
2
). Land may also be expressed in terms of square miles (sections) or acres
(43,560 ft
2
) or, in the metric system, as hectares (2.47 acres, 10,000 m
2
, or 107,600 ft
2
).
a
rea
of
a
r
eCtangle
A rectangle is a two-dimensional box. The area of a rectangle is found by multiply-
ing the length (
L
) times the width (
W
) (see Figure 11.5).
Area =
L
×
W
(11.3)
L
W
FIGURE 11.5
Area of a rectangle.
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