Page 458 - Handbook of Energy Engineering Calculations

Use the relation for pseudomolecular weight when the thermal
conductivity of one of the fluids is known. This relation is M = 0.636 (c/k) 3
4
s , where the symbols are as given in the Nomenclature list in this procedure.
Substituting, we have:
Tubeside:
4
3
3
M = 0.636 × 0.998 × 0.999 /0.368 = 12.63
Shellside:

2. Make a first trial to determine the heat-transfer surface area
2
Assume an overall heat-transfer coefficient, U, of 300 Btu/h ft .°F (1.7 W/m 2
2
2
· h · °C). Then, A = (3,233,790)/(300)(1.8)(66.5) = 90.05 ft (8.4 m ).
From a table of heat-exchanger design standards, such as Table 10, choose
300.5-in-outside-diameter tubes, 27.5-ft long, with a net free-flow area of 6.3
2
2
in ; A = heat-transfer area = 108 ft ; d = 0.3125 in. Then:
s
The maximum number of tubes for turbulent flow can be approximated by
the term W /2d z :
i
i i
n max = 30/2 × 0.402 × 0.55 = 68

Because flow will be turbulent for the exchanger selected, the proper heat-
transfer equations from Table 11 are: Eq. (1), tubeside; Eq. (8), shellside; Eq.
(11), tube wall; and Eq. (13) fouling.

TABLE 11 Empirical Heat-Transfer and Pressure-Drop

Relationships for Rating Spiral-Tube Heat Exchangers