A heat exchanger is a device used to transfer heat between one or more fluids. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact.[1] They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air.

1. TEMA Designations for Shell-and-Tube Heat Exchangers
Stationary Head Types Shell Types Rear Head Types
A
channel and removable cover
E
one pass shell
L
fixed tubesheet
like 'A' stationary head
B
bonnet (integral cover)
F
two pass shell
with longitudinal baffle
M
fixed tubesheet
like 'B' stationary head

2. C
channel integral with
tubesheet and removable cover
G
split flow
N
fixed tubesheet
like 'C' stationary head
N
channel integral
with tubesheet and removable cover
H
double split flow
P
outside packed floating head
D
special high pressure closure
J
divided flow
S
floating head
with backing device (split_ring)
K
kettle type reboiler
T
pull through floating head
X
cross flow
U
u tube bundle

3. W
packed floating tube sheet
with lantern ring