Heat exchangers are devices that transfer heat between two fluids to control the temperature of one fluid. There are various types of heat exchangers that differ based on their flow arrangement, surface compactness, construction technique, and whether they use direct or indirect contact between fluids. Common examples include shell and tube heat exchangers, which contain multiple tubes in a shell, and plate heat exchangers, which use metal plates to transfer heat. Coaxial heat exchangers consist of an inner corrugated tube within an outer tube to efficiently transfer heat between fluids flowing separately within the tubes.

1. By Ashutosh Kumar Dubey

2. A heat exchanger is a system designed to transfer heat between two
fluids to control the temperature of one of the fluids. They are
widely used in space heating , condensers and evaporators used in
air conditioning units and refrigerators, Boilers and condensers in
thermal power plants are examples of large industrial heat
exchangers. There are heat exchangers in our automobiles in the
form of radiators and oil coolers. Heat exchangers are also
abundant in chemical and process industries, and sewage
treatment.

3. Heat exchanger is divided on the basis of
1.Flow arrangement
a) Single pass (parallel flow, counter-flow, cross –flow)
b) Multi-pass (parallel flow, counter-flow, split-flow, divided flow)
2.Surface compactness
Non-compact (surface area density < 700 m2/m3)
Compact (surface area density > 700 m2/m3)
3.Contacting technique
a) Indirect contact
b) Direct contact
4.Construction
a) Tubular (double-pipe, shell and tube, spiral tube)
b) Plate (plate and frame (gasket and welded plate),spiral plate)
c) Extended surface (plate-fin, tube-fin)
d) Regenerative

4. The double-pipe heat exchanger is one of the simplest types of heat
exchangers. It is called a double-pipe exchanger because one fluid flows inside
a pipe and the other fluid flows between that pipe and another pipe that
surrounds the first. This is a concentric tube construction. Flow in a double-pipe
heat exchanger can be co-current or counter-current and Cross flow just
doesn't work for a double pipe heat exchanger.

5. Shell-and-tube heat exchangers contain a large number of tubes (sometimes
several hundred) packed in a shell with their axes parallel to that of the shell.
Baffles are commonly placed in the shell to force the shell-side fluid to flow
across the shell to enhance heat transfer and to enhance heat transfer and to
maintain from spacing between the tubes. It used in systems because of its
higher operating temperatures and pressures.

6. A plate heat exchanger is a type of heat exchanger that uses metal plates to
transfer heat between two fluid. the heat exchanger contains a fully welded
circular plate pack made by pressing and cutting round plates and welding
them together. Larger commercial versions use gasket between the plates,
smaller version tend to be brazed. Plate and shell technology offers high heat
transfer, high pressure, high operating temperature, compact size, low fouling
and close approach temperature.

7. Three flow arrangement are possible in heat exchange
1.parallel flow
When working fluid pass from one tube and refrigerant pass from other tube
and their direction of flow is in same direction then heat exchanger act as a
heat exchanger with parallel flow.
2.Counter flow
When working fluid pass from one tube and refrigerant pass from other tube
and their but direction of flow is in different direction then heat exchanger act
as a heat exchanger with counter flow.
3.Cross flow
In compact heat exchangers, the two fluids usually move perpendicular to each
other and such flow configuration is called each other, and such flow
configuration is called cross-flow.
There are two types of cross flow heat exchangers
(a) Unmixed and (b) Mixed flow

8. Coaxial heat exchanger consists of one inner corrugated tube and one outer
tube. Hot and cold fluid separately flow in inner tube and between tubes for
heat transferring. The corrugated inner tube generates more area and increases
the heat transfer between water and refrigerant. The coaxial heat exchanger
can be applied on marine ship refrigerate equipment, food or medical
processing, chemical processing, water-source heat pump, geothermal
heat pump, water heater, air chiller, refrigerate equipment, HVAC(as a
condenser or evaporator), water chiller.

9. Factor due to which co-axial heat exchanger is
preferred over other heat exchanger
1.High heat transfer efficiency
2.Easy Installation
3.Multi-spiral structure of inner tube imparts outstanding anti-freezing
capability to coaxial heat exchanger.
3.No choke problem
4.More durable and save space
5.Wide application