Page 240 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

HEAT TRANSFER, INSULATION, AND FREEZE PROTECTION

5.24 CHAPTER FIVE

TABLE 5.7 Relationship between Water Temperature and
Volume

Temperature Specific volume, mL/g
°C °F Water Ice
−10 14 1.002069
−5 23 1.000825
0 32 1.0001324 1.0908
3 37.4 1.0000078
4 39.2 1.0000000
5 41 1.0000081
10 50 1.0002720

Source: Data of J. F. Mohler, at 1-atm pressure.

TABLE 5.8 Relationship between Freezing Point and Pressure for Water

Freezing point Pressure
°C °F atm psi

0 32 1 0
–5 23 590 8,660
–10 14 1,090 16,000
–22 –7.6 2,047 30,000

THE FREEZING OF WATER IN ATMOSPHERIC
VESSELS

General
The most common method used to store water is in an on ground or elevated water stor-
age tank made of either wood or steel. If enough heat cannot be added by means of new
water flowing into the tank to keep the water from freezing, it must be added by some other
means. In addition to the tank itself, the riser from grade up to the bottom of an elevated
tank must be protected also. It is generally thought that adequate heating of any tank is
almost as important as proper structural design.

The Mechanics of Ice Formation
Water in an open tank or vessel loses heat on all of the sides exposed to the atmosphere. For
a tank on grade, the loss of heat into the surrounding soil is not as great due to the insulat-
ing factor of that soil. However, the greatest amount of heat is lost through the surface of
the water. As the water cools, an internal circulation takes place because the surface layer
of water cools faster than the deeper water. This causes the surface layer to become denser,
resulting in that water migrating to the bottom of the tank and displacing the warmer water
to the top. This circulation will continue to take place until the temperature of most of the
water reaches about 32°F. When this occurs, the water is at its maximum density. At this

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