By Ashutosh Kumar Dubey

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.

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

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.

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.

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.

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

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.

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