Science of Water : Concepts and Applications

48 The Science of Water: Concepts and Applications
p wh
3
62.4 lb/ft 18ft
2
1123
lb/ft or 1123 psf
Waterworks operators generally measure pressure in pounds per square inch rather than pounds per
square foot; to convert, divide by 144 in. 2 /ft 2 (12 in. × 12 in. = 144 in. 2 ):
1123psf
2
P 78
. lb/in. or psi (rounded)
2
144in. /ft
PROPERTIES OF WATER
Table 3.1 shows the relationship between temperature, specifi c weight, and density of water.
DENSITY AND SPECIFIC GRAVITY
When it is said that iron is heavier than aluminum, it means that iron has greater density than aluminum.
In practice, what is really being said is that a given volume of iron is heavier than the same
volume of aluminum.
√ Important Point: What is density? Density is the mass per unit volume of a substance.
Suppose you had a tub of lard and a large box of cold cereal, each having a mass of 600 g. The
density of the cereal would be much less than the density of the lard because the cereal occupies a
much larger volume than the lard occupies.
The density of an object can be calculated by using the formula:
mass
Density
volume
In water treatment operations, perhaps the most common measures of density are pounds per
cubic foot (lb/ft 3 ) and pounds per gallon (lb/gal).
TABLE 3.1
Water Properties (temperature, specifi c weight, and density)
Temperature
(°F)
Specifi c Weight
(lb/ft 3 )
Density
(slugs/ft 3 )
Temperature
(°F)
Specifi c Weight
(lb/ft 3 )
Density
(slugs/ft 3 )
32 62.4 1.94 130 61.5 1.91
40 62.4 1.94 140 61.4 1.91
50 62.4 1.94 150 61.2 1.90
60 62.4 1.94 160 61.0 1.90
70 62.3 1.94 170 60.8 1.89
80 62.2 1.93 180 60.6 1.88
90 62.1 1.93 190 60.4 1.88
100 62.0 1.93 200 60.1 1.87
110 61.9 1.92 210 59.8 1.86
120 61.7 1.92
(3.2)