A heat exchanger is a mechanism that transfers heat to a solid object and a fluid or among two or more fluids. These fluids are separated by a wall so that they do not get mixed, on the other hand, they might also be in direct contact. Heat exchangers play a vital role in the working of many systems and processes. For instance, the heat exchanger is used in the boiler of the hot water, the freezer. In the former cases heat is transferred to the boiler and in the latter, the heat is transferred away so the freezer remains cool.
In industries, they are used in different processes. For example, in the power industry, water has to be heated into steam to run the turbines. The steam is superheated so as to avoid any moisture as it may damage the turbines and can cost millions to the company. So it is essential to keep the heat exchangers in top condition.
There are many types of heat exchangers. The double pipe heat exchangers are very simple in mechanism and are used in industries. They are cheaper in maintenance and design. On the contrary, they have low efficiency and occupy a huge space. Because of this reason modern industries use more efficient heat exchangers called the shell and tube or plate.
The heat exchanger has several tubes. These are available in a wide variety of materials including duplex stainless steels, austenitic stainless steels, nickel alloys, zirconium and titanium that are suitable for all types of heat exchangers like condensers, seawater coolers, heaters, evaporators, and re-heaters.
The heat exchanger tubes are finned, plain, internal or external. Normal heat exchanger units make use of plain tubes while the finned tubes provide a high heat transfer surface. Another kind of tube is the duplex tube which is fitted within a tube by drawing the tube which is out into the inner tube.
The diameter of the tubes varies from 6mm up to 40mm. The thickness depends on the construction materials and its diameters. The tube length varies from 0.5 to 6m. They lay either on a square or an equilateral triangular pitch.
If the heat exchanger tube breaks, it can be fixed by expanding the ends of the tube in the tube sheet holes by expanding and rotating tool.
Applications and Uses
The heat exchanger tubes are used for the different purposes such as heating or re-heating, cooling of gases, fluids or air in many industries like the chemical, hydrocarbon processing, oil refining, and aerospace.
It is also used in Power generation i.e. Nuclear, Solar and Thermal Power Plants, Oil and Gas, Refinery and Petrochemical, Process Industries, Chemical and Fertilizer, Atomic energy, Defence and Aerospace, Pulp and Paper Industries etc.
The heat exchanger tubes are available in two types – a) Straight b) U- bent
a) Straight tubes:
The two ends of the tube are fixed to the tube sheets. One fluid goes to the tube and the other to the shell. They have excellent high fouling qualities. They are used where there is frequent high-temperature cross. The straight tubes heat exchanger can be cleaned easily.
b) U- bent tubes:
U – bent tubes consists of a U – shaped tube fixed to a tube sheet and is supported by tube baffles. These are of superior quality. U – bent tubes can be customised as per the client’s needs. These tubes are cut with specific leg lengths, its ends are deburred and the bores are cleaned properly with a dry air.
While manufacturing heat exchanger tubes there are several factors to be considered:
- Dimensional tolerances for diameter
- Wall thickness
- Mechanical properties
- Corrosion resistance
- Surface finish
The heat exchanger tubes must undergo inspection. This is very important as their surface is the most dominant area of transfer of heat or any corrosion which can have drastic effects on its efficiency.
Remote field electromagnetic technique is one of the best techniques to inspect the tubes. It is an advanced method of testing compared to the basic inspection techniques such as visual inspection, magnetic particle, and dye penetrant testing used by other companies.
If the heat exchanger tubes are properly cleaned and maintained it ensures you a long life of the unit and thus helps in low consumption of energy.
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