Page 123 - Design and Operation of Heat Exchangers and their Networks

Steady-state characteristics of heat exchangers 111

Fig. 3.8 A counterflow spiral plate heat exchanger.

Bes (2001) summarized the advantages of the spiral heat exchangers as
the following: (1) less inclination to fouling because each fluid has only
one flow cross section, (2) compact size of apparatus in comparison with
shell-and-tube heat exchangers, (3) easy disassembling and mechanical
cleaning, (4) self-cleaning due to highly turbulent flow, (5) well separation
of the two fluids, (6) elimination of free vibrations due to rigid shells and
spacer studs, (7) small pressure loss, and (8) high overall heat transfer coef-
ficients and thermal effectiveness. Since both fluids flow in the confined
internal flows, the overall heat transfer coefficients are in general somewhat
higher than conventional assemblies. The gaps between the plates can be
adjusted to obtain the desired flow characteristic for each medium. The spi-
ral heat exchanger tends to flush away scales as it forms due to the high tur-
bulence induced by the swirling path. Usually, the cooling medium enters at
the periphery and is in the outer passage so there is an effective blanket of
cooler liquid surrounding the spiral assembly. Therefore, thermal insulation
might not be required. Because of these advantages, spiral heat exchangers
have found wide applications in chemical, pharmacy, food, refining, and dye
industries.