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66131_Ludwig_CH10F 5/30/2001 4:35 PM Page 157

Heat Transfer 157

fer mechanisms (outside jackets and/or half-pipes, internal
vertical pipes, and internal coils). Jacketed vessels (external)
are often used for chemical reaction temperature control and
for the heating or cooling mixture being agitated in vessels.
Internal vertical or horizontal coils in a vessel can also be used
for temperature control. Gruver and Pike 163 recommend that
the use of a single fluid in the jackets/coils is better than
requiring complicated controls to switch types of fluids.
See Figures 10-93A and 10-93B as limited examples of
reaction and other process vessels that require heat transfer
for proper processing. Markovitz 202 reports improved heat
transfer for the inside of jacketed vessels when the surface
has been electropolished, which gives a fine, bright surface.
Heat transfer in agitated vessels with internal coils con-
taining the heat transfer fluid (process on outside of coil) is
expressed by the outside coefficient on coils 183
2 0.62 1>3 0.14
160nDa 2 1c p 2 1 2
h c D j
0.87 (10-129)
k 1 2 1k2 1 w 2
and as shown in Figure 10-94.
For heat transfer fluids inside reactor jackets or other
process vessels with agitation to fluids in vessels (Figure 10-
93A), the heat transfer is expressed 183 as
Figure 10-93A. Typical vessel external jackets for heat transfer.
2
160nDa 2 2>3 1c p 2 1>3 1 2 0.14
h j D j
0.36 (10-130)
k 1 2 1k2 1 w 2
and in Figure 10-94. Also see references 282 and 283.

where
2
h c average film coefficient, clean, Btu/(hr) (ft ) (°F)
D i or D j I.D. of vessel, ft
Da diameter of agitator, ft
k thermal conductivity of fluid processed,
2
Btu/(hr) (ft ) (°F/ft)
n rev/min of agitator
L length and thickness, ft, of coil or jacket
c p specific heat, Btu/(lb) (°F)
viscosity cps 2.42, lb/(hr) (ft)
density, lb ft 3
r fouling resistance, or tube resistance,
2
(hr) (ft ) (°F)/Btu
Subscripts:
w wall
Figure 10-93B. Process vessel with internal coil and agitation to j jacket side
improve heat transfer. (Used by permission: Engineering Manual c clean
Dowtherm™ Heat Transfer Fluids, ©1971. The Dow Chemical Co.)
i inside
Example 10-16. Heating Oil Using High Temperature
3
Baker and Walter report tests performed on open jack-
Heat Transfer Fluid 183 (used by permission of The Dow
eted agitated vessels and published some of the limited
Chemical Co., reference [183]©1971)
results for this type of equipment. These data indicate the
effects of jetting the fluid at various velocities into the jacket. You want to heat 9,000 lb/hr of oil from 500°F (260°C) to
Chapter 5, “Mixing of Liquids,” in Volume 1, 3rd Edition, 600°F (315.56°C). The oil is heat-sensitive and cannot be
of this set provides more details and various vessel heat trans- heated to more than 630°F (322.22° C). Condensing