Heat Exchangers: Design, Operation ... - 123SeminarsOnly

48 3 Code and standards
3.5.2 Shell-Side Arrangements
1. The one-pass shell (Fig. 3.1E) is the most commonly used arrangement. Condensers
from single component vapors often have the nozzles moved to the center
of the shell for vacuum and steam services. Solid longitudinal baffle is provided to
form a two-pass shell (Fig. 3.1F). It may be insulated to improve thermal efficiency.
(See further discussion on baffles).
2. A two-pass shell can improve thermal effectiveness at a cost lower than for two
shells in series.
3. For split flow (Fig. 3.1G), the longitudinal baffle may be solid or perforated. The
latter feature is used with condensing vapors.
4. double-split-flow design is shown in Fig. 3.1H. The longitudinal baffles may be
solid or perforated.
5. The divided flow design (Fig. 3.1J), mechanically is like the one-pass shell except
for the addition of a nozzle. Divided flow is used to meet low-pressure-drop
requirements. The kettle reboiler is shown in Fig. 3.1K. When nucleate boiling is
to be done on the shell-side, this common design provides adequate dome space for
separation of vapor and liquid above the tube bundle and surge capacity beyond
the weir near the shell cover.
3.6 Baffles and tube bundles
3.6.1 The tube bundle
Tube bundle is the most important part of a tubular heat exchanger. The tubes generally
constitute the most expensive component of the exchanger and are the one most likely to
corrode. Tube sheets, baffles, or support plates, tie rods, and usually spacers complete
the bundle.
3.6.2 Baffle
Baffles are used to direct the side and tube side flows so that the fluid velocity is increased
to obtain higher heat transfer rate and reduce fouling deposits. In horizontal units baffle
are used to provide support against sagging and vibration damage. There are different
types of baffles:
1. segemntal
2. disc and doughnut
3. orifice
4. rod type
5. nest type
6. longitudinal
7. impingment
1. Segmental Baffles Segmental or cross-flow baffles are standard. Single, double,
and triple segmental baffles are used. Baffle cuts are illustrated in Fig. 3.16a. The
double segmental baffle reduces crossflow velocity for a given baffle spacing. The
triple segmental baffle reduces both cross-flow and long-flow velocities and has been
identified as the window-cut baffle.
Dr. Ali A. Rabah, Dept of Chemeng, U of K, Email : rabahss@hotamil.com