--From table 12-4, m = 0.95 inch/(EF)(d)

(3) Ice thickness on water bodies can be esti-

mated from the previous depth of freezing equations

or from equations 12-3 with the m values in table

x = (0.95)(3000)

12-4 (see example 12-9a). Snow cover has a

= 52 inches

significant insulting effect and can significantly

= 4.33 feet.

reduce the maximum ice thickness (see example 12-

9b). The ice formation can be greater than calculted

--The Stefan equation (equation 12-4) can also be

if the weight of snow or the lowering of the water

used:

level causes cracks in the ice and water overflows

onto the surface. This water is drawn into the snow

and the mixture refreezes and bonds to the original

ice.

where

k = thermal conductivity of material above

the freezing isotherm, ice in this case, so

from table 12-2:

ice = 1.28 BTU/ft hr EF

k

L = volumetric latent heat of material

undergoing phase change, in this case

water, so:

Latent heat of water at 32EF =

144 BTU/lb

Eight typical examples are given below to illustrate

Density of water at 32EF = 62.4 lb/ft3

the utilization of the calculation procedures des-

L = (144 BTU/lb)(62.4 lb/ft3) =

cribed above.

8985.6 BTU/ft3

Ig = (3000EF d)(24 hr/day) = 72,000 EF hr

on a water reservoir with no snow cover when the

annual air freezing index (Ig) is 3000 EF d. Use

equation 12-3:

x = m(Ig)

= 4.5 ft.

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