Page 216 - Chemical Process Equipment - Selection and Design

186 HEAT TRANSFER AND HEAT EXCHANGERS

TABLE 8.6. Typical Ranges of Individual Film and Fouling Coefficients [h Btu/(hr)(sqft)("F)]
Fluid and Process Conditions P (atrn) (Anmax ("F) IO4 h io4 4
Sensible
Water liquid 7.6-1 1.4 6-14
Ammonia liquid 7.1-9.5 0-6
Light organics liquid 28-38 6-11
Medium organics liquid 38-76 9-23
Heavy organics liquid heating 23-76 11-57
Heavy organics liquid cooling 142-378 11-57
Very heavy organics liquid heating 189-568 23-170
Very heavy organics liquid cooling 378-946 23-170
Gas 1-2 450-700 0-6
Gas 10 140-230 0-6
Gas 100 57-113 0-6
Condensing transfer
Steam ammonia all condensable 0.1 4.7-7.1 0-6
Steam ammonia 1% noncondensable 0.1 9.5-1 4.2 0-6
Steam ammonia 4% noncondensable 0.1 19-28 0-6
Steam ammonia all condensable 1 3.8-5.7 0-6
Steam ammonia all condensable 10 2.3-3.8 0-6
Light organics pure 0.1 28-38 0-6
Light organics 4% noncondensable 0.1 57-76 0-6
Light organics pure 10 8-19 0-6
Medium organics narrow range 1 14-38 6-30
Heavy organics narrow range 1 28-95 11-28
Light condensable mixes narrow range 1 23-57 0-1 1
Medium condensable mixes narrow range 1 38-95 6-23
Heavy condensable mixes medium range 1 95-1 90 11-45
Vaporizing transfer
Water <5 45 5.7-19 6-12
Water <IO0 36 3.8-1 4 6-12
Ammonia 130 36 11-19 6-12
Light organics pure 20 36 14-57 6-12
Light organics narrow range 20 27 19-76 6-17
Medium organics pure 20 36 16-57 6-17
Medium organics narrow range 20 27 23-95 6-17
Heavy organics pure 20 36 23-95 11-28
Heaw organics narrow range 20 27 38- 142 11-45
Very heavy organics narrow range 20 27 57-189 11 -57
Light organics have viscosity <I cP, typically similar to octane and lighter hydrocarbons.
Medium organics have viscosities in the range 1-5cP, like kerosene, hot gas oil, light crudes, etc.
Heavy organics have viscosities in the range 5-100 cP, cold gas oil, lube oils, heavy and reduced crudes, etc.
Very heavy organics have viscosities above 100 cP, asphalts, molten polymers, greases, etc.
Gases are all noncondensables except hydrogen and helium which have higher coefficients.
Conversion factor: 1 Btu/(hr)(sqft)("F) = 5.6745 W/m2 K.
(After HEDH, 1983, 3.1.4-4).

In a tower with height Z=3Oft and with both G and L at most usual situations, of which heat losses to ambient air are the
5000 lb/(hr)(cuft), for example, this formula gives h,a = 215. most common process. Simplified equations are shown for air.
In liquid-liquid contacting towers, data cited by Fair (1972) Transfer of heat by radiation is appreciable even at modest
range from 100-12,000 Btu/(hr)(cuft)("F) and heights of transfer temperatures; such data are presented in combination with
units in the range of 5 ft or so. In pipeline contactors, transfer rates convective coefficients in item 16 of this table.
of 6000-60,000 Btu/(hr)(cuft)("F) have been found, in some cases
as high as 200,000. FORCED CONVECTION
In some kinds of equipment, data only on mass transfer rates
may be known. From these, on the basis of the Chilton-Colburn Since the rate of heat transfer is enhanced by rapid movement of
analogy, corresponding values of heat transfer rates can be fluid past the surface, heat transfer processes are conducted under
estimated. such conditions whenever possible. A selection from the many
available correlations of forced convective heat transfer involving
NATURAL CONVECTION single phase fluids, including flow inside and outside bare and
extended surfaces, is presented in Table 8.10. Heat transfer
Coefficients of heat transfer by natural convection from bodies of resulting in phase change, as in condensation and vaporization, also
various shapes, chiefly plates and cylinders, are correlated in terms is covered in this table. Some special problems that arise in
of Grashof, Prandtl, and Nusselt numbers. Table 8.9 covers the interpreting phase change behavior will be mentioned following.