Page 307 - Fluid mechanics, heat transfer, and mass transfer
P. 307
SHELL AND TUBE HEAT EXCHANGERS
288
Disk and doughnut baffle.
FIGURE 10.21
which direct the flow radially across the tube field
(Figure 10.21).
➢ The potential bundle-to-shell bypass stream is
eliminated.
➢ This baffle type is veryeffectivein pressure drop to
FIGURE 10.19 Different arrangements for segmental baffles.
heat transfer conversion.
& Orifice Baffles: In an orifice baffle, shell side fluid
flows through the clearance between tube outside
. What is the purpose of a segmental baffle? diameter and baffle hole diameter (Figure 10.22).
& Segmental baffles direct flow across tube bundle,
& Rod Baffles: Metal rods rather than sheet metal
perpendicular to tube axis. baffles are used to support tubes and flow in the shell
. Show the arrangements for different types of baffles in a is mainly parallel to tube axis (Figure 10.23).
heat exchanger. & Eliminate tube vibrations, which occur with plate
& Plate baffles may be single segmental, double seg- baffles when fluid velocities are high and used wher-
mental,ortriplesegmental,asshowninFigures10.19 ever very low pressure drop is required.
and 10.20. ➢ Flow in the shell is mainly parallel to the tube
& Segmental Baffles: axis. Flow across the rods leads to vortex forma-
➢ The single and double segmental baffles are most tion, giving heat transfer coefficients for turbu-
frequently used. They divert the flow most effec- lent flow about 1.5 times those predicted by the
tively across the tubes. Dittus–Boelter equation for the same Reynolds
➢ The triple segmental baffles are used for low- number, but are not as high as those for a seg-
pressure applications. mentally baffled exchanger with close baffle
spacing.
& Disk and Doughnut Baffles: These baffles are com-
➢ Lower DP and reduced vibration make the rod
posed of alternating outer rings and inner disks,
baffle exchanger preferable for many applications.
➢ Tubes are arranged with square pitch. Rods, with a
diameter equal to the clearance between tube rows,
are attached to ring supports and placed between
alternate tubes in both horizontal and vertical
directions.
Segmental baffles. Orifice baffle.
FIGURE 10.20 FIGURE 10.22
