TM 5-852-4/AFM 88-19, Chap. 4
m
the gravel pad to the duct air is 1.0 Btu/ft2 hr. The total
= duct spacing, 2.66 ft
heat flow X to the duct air from the floor and gravel pad
= cross sectional area of duct, 1.58 ft2
Ad
ρ
is (3.3 + 1.0) = 4.3 Btu/ft' hr. The heat flow to the duct air
= density of air, 0.083 lb/ft3 (fig. 4-30)
must equal the heat removed by the duct air.
= specific heat of air at constant pressure, 0.24
Cp
Heat added = heat removed
Btu/lb F
= temperature rise in duct air, 12F.
TR
φ lm= 60V Ad ρ Cp TR
Substitution of appropriate values gives a required air
Thus, the average duct air velocity required to
velocity.
2
extract this quantity (4.3 Btu/ft hr) of heat is determined
by the equation as shown below.
∅
= total heat flow to duct air, 4.3. Btu/ft2 hr
I
= length of duct, 220 ft
U. S. Army Corps of Engineers
Figure 4-30. Properties of dry air at atmospheric pressure14.
4-43
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