Page 41 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10A 5/30/2001 4:08 PM Page 31
Heat Transfer
Figure 10-21A. Impingement baffles and fluid-flow patterns. (Used by shell-side fluid, so they normally will be of the same material
permission: Brown & Root, Inc.)
Figure 10-21B. Impingement fluid-flow pattern with annular inlet dis- should be used. Any baffle segment requires a minimum of
tributor. (Used by permission: Brown & Root, Inc.)
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Figure 10-21C. Impingement baffle located in inlet nozzle neck.
Longitudinal baffles must also be compatible with the
as tubes or baffles. This baffle never extends the full inside
length of the shell, because fluid must flow by its far end for
the return pass in reaching the exchanger outlet.
6. Tie Rods
Tie rods with concentric tube spacers are used to space
the baffles and tube supports along the tube bundle. The
baffles or supports must be held fixed in position because
any chattering or vibration with respect to the tubes may
wear and eventually destroy the tube at the baffle location.
The number of tie rods used depends upon the size and
construction of the exchanger bundle. The material of the
rods and spacers must be the same or equivalent to that of
the baffles or bundle tubes. Provision must be made in the
tubesheet layout for these rods, which is usually accom-
plished by omitting a tube (or more) at selected locations
on the outer periphery of the tube bundle. The rod is usu-
ally threaded into the back of only one of the tubesheets,
being free at the other end, terminating with the last baffle
or support by means of lock washers or similar fool-proof fas-
tening. See the upper portion of Figure 10-22 for tie rod
spacers.
Table 10-7 shows suggested tie rod count and diameter for
various sizes of heat exchangers, as recommended by
107
TEMA . Other combinations of tie rod number and diam-
eter with equivalent metal area are permissible; however, no
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fewer than four tie rods, and no diameter less than / 8 -in.,
three points of support.