Double Pipe Heat Exchanger Construction, Working, Advantages and Disadvantages

It is the simplest type of heat exchanger used in industry. It is used when the required heat transfer area is relatively small.

Construction, and Working

It consists of concentric pipes, connecting tees, return heads, and return bends. The packing glands support the inner pipe within the outer pipe. A double pipe heat exchanger arranged in two legs [ i.e. when two lengths of inner pipe are connected by return bend] as shown in fig. is known as a single hairpin heat exchanger. 

Tees are provided with nozzle or screwed connections for permitting the entry and exit of the annulus fluid which crosses from one leg to the other through the return head.

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The return bend connects two legs of inner pipes to each other. This exchanger can be very easily assembled in any pipe-fitting shop as it consists of standard parts and it provides an expensive heat transfer surface. In this exchanger, one of the fluids flows through the inside pipe and the other fluid flows through the annular space created between two concentric pipes either in a co-current or counter-current fashion. 

It is usually employed for decreasing the temperature of a hot fluid with the help of a cold fluid when flow rates are low. These are commonly used in refrigeration services.

These exchangers are usually assembled in effective lengths of 3.65, 4.57, and 6 meters. The distance in each leg over which the heat transfer occurs is termed as the effective length.

Disadvantage

• Small heat transfer surface in large floor space as compared to another type (e.g. shell and tube heat exchanger)

• Dismantling requires a longer time 

• Maximum leakage points

Part of this, double pipe heat exchanger is very attractive where the total heat transfer surface required is small 9.29 m2 to 14 m2 or less. It is simple in construction, cheap, and easy to clean.

Advantages

•  Sutible to high-pressure application

• Modular type construction 

• it can be welded easily

• low cost in made. 

Take these Notes is, Orginal Sources: Unit Operations-II, KA Gavhane