Page 152 - Introduction to Marine Engineering

138 Auxiliaries

Heat exchangers

Heat exchangers on board ship are mainly coolers where a hot liquid is
cooled by sea water. There are some instances where liquid heating is
required, such as heavy fuel oil heaters and sea water heaters for tank
cleaning. Although being heat exchangers, the main condenser for a
steam ship and the evaporator/distiller are dealt with separately (see
Chapter 5).
The heat exchange process is accomplished by having the two liquids
pass on either side of a conducting surface. The heat from the hot liquid
passes to the cold liquid and the conducting surface, i.e. the tube wall, is
at a temperature between the two. It is usual for marine heat exchangers
to have the two liquids flowing in opposite directions, i.e. counter or
contra flow. This arrangement provides a fairly constant temperature
difference between the two liquids and therefore the maximum heat
transfer for the available surface area.

Coolers
Coolers at sea fall into two groups, shell and tube and the plate type. Both
are considered below.

Shell and tube
In the shell and tube design a tube bundle or stack is fitted into a shell
(Figure 7.4). The end plates are sealed at either end of the shell and
Safety expansion ring
and double joint

Radial flow circular
baffles
Visible joint
Corrosion resistors

Removable covers, for
cleaning and inspection

Removable straight
tube
Figure 7.4 Shell and tube heat exchanger