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178 Applied Process Design for Chemical and Petrochemical Plants

vacuum service and physically are very large in diameter omitted due to the generous fouling factor
when compared to an 8-ft tube unit (see Figures 10-96D recommended.
and 10-105).
The method presented here requires that the majority of where
2
the heat load be latent, with a reasonably small percentage, G gb mass velocity of liquid, lb/hr (ft ). For outside hori-
say 10—20%, being sensible load. zontal tubes, use projected area (diameter length)
Gilmour 51—54 has presented a boiling film relation, which is of the tube, not the outside surface area. This
assumes that only half of the tube is effective for
the result of the correlation of data covering a good range of
bubble release. This does not apply to actual heat
organic materials and water from subatmospheric to above
transfer area.
atmospheric pressure. This range has been the problem in
V vapor rate, lb/hr
most other attempts at correlation. The correlation is T s saturation temperature of liquid, °R
reported to have been successfully used on hundreds of L density of liquid, lb/ft 3
vaporizers and reboilers by the author. Palen and Small 90 T w temperature of heating surface, °R
have examined data using Gilmour’s equations. It has the v density of vapor, lb/ft 3
advantage of avoiding trial-and-error approaches. surface tension of liquid, lb/ft
c specific heat of liquid, Btu/lb (°F)
viscosity of liquid, lb/(hr) (ft)
Gilmour Method 52, 53 Modified 2
P pressure at which fluid is boiling, lb/ft abs
D tube diameter, ft (side where boiling takes place)
This process is applicable to vertical tube side vaporiza-
D s shell I.D., ft
tion only and to vertical and horizontal shell-side vaporiza- h s boiling side film coefficient, Btu/hr (ft ) (°F)
2
tion. L o length of shell, or length of one tube pass, ft
A surface area of tube, ft 2
1. Calculate the heat duty. For outside horizontal tube, use outside tube surface
2. Estimate a unit based upon suggested values of U from area. For vertical tubes with inside boiling, use inside
Tables 10-15 and 10-18A and the known LMTD. Check surface area of tube, A i .
to be certain that t o does not exceed critical value
between shell side and tube wall or the tube side tem-
proportionality constant for type of tube material
peratures (however expressed). t b boiling temperature difference between boiling fluid
and wall surface, on boiling side, °F
x weight percent vapor in fluid stream, for nucleate
3. Calculate film coefficient, h s , by
boiling only

1c21G gb 2 c 0.6 L 0.425
h s a b a b 1 2 (10-165) b. For tube-side vaporization:
0.3 2
D¿G gb k a
a b V L 2
G gb a b, mass velocity of liquid, lb>hr 1ft 2
A v
2
h s boiling side coefficient, Btu/hr (ft ) (°F) 4. For boiling in shell side of horizontal unit, a check

type metal factor point is

0.001 for copper and steel tubes

0.00059 for stainless steel and chromium-nickel

0.0004 for polished surfaces 6.665 V/ v D s L o must not exceed 1.0 (10-166A)
surface condition factor
1.0 for perfectly clean conditions, no pitting or corro- This is concerned with the maximum vapor rate from a
sion horizontal shell.
1.7 for average tube conditions 5. Check this second factor for condensate flooding in
2.5 for worst tube conditions horizontal units with a condensable heating medium,
such as steam, in the tubes:
Note: This is not fouling correction. Read Figure 10- 3 W 2.56
106. ft condensate>1sec21tube2 9.43D o H c
13,6002 n¿
a. For shell-side vaporization: (10-166B)
V p L
G gb a b (10-166) n number of tubes per pass
1D¿L2 p v W condensate rate, lb/hr
density, lb/ft 3
54
Note that Gilmour suggests that the correction for the D o tube diameter, outside, ft
number of vertical tube rows given in reference 53 be H c height of segment of circle divided by diameter