A heat exchanger is a device used to transfer heat from one fluid to another while preventing the two from intermingling. The three main types are shell and tube heat exchangers, air-cooled heat exchangers and plate heat exchangers. Generally, there is a metal wall partitioned between the two fluids that acts as a conductor. A hot solution flowing on one side of the barrier transfers its heat to a cooler solution flowing on the other side. Thermal energy only flows from the hotter to the cooler in an attempt to reach equilibrium. The surface area of a heat exchanger affects its speed and efficiency: the larger a heat exchanger’s surface area, the faster and more efficient the heat transfer.

Heat exchangers are typically constructed of steel, titanium, copper, bronze, stainless steel, aluminum or cast iron. One of the biggest problems heat exchanger manufacturers have to prevent is corrosion, which is common due to the constant flowing of liquid. Unfortunately, this is very difficult to avoid. To help prevent this, tubing must be resistant to general corrosion, pitting, stress-corrosion cracking (SCC), selective leaching and oxygen cell attack in service. Some heat exchanger designs use fins to provide greater thermal conductivity, which also helps.

Heat exchangers are quite common, although they are not always known by that name. For instance, a car’s radiator is a useful device for transferring heat from the engine to the air. Other examples of commercial uses for heat exchangers include spa and swimming pool heating, home radiators, hot water radiators, refrigerators and air conditioners. Whether in commercial or industrial use, heat exchangers are vital as energy and money saving devices since most mechanical, chemical and energy systems require heat transferal of some sort.

Custom heat exchangers perform a crucial role in the design, operation and maintenance of heating and air-conditioning systems, vehicle design, power plants, refrigeration, chemical and industrial engineering systems. They are also important in settings such as food processing, industrial engineer processes, pharmaceutical, pulp and paper and the steel industry. All power generation industries need them. Other industries that use heat exchangers include aerospace, chemical, marine, semiconductor, petrochemical, electronic, automotive, water treatment facilities and textiles. Heat exchangers are useful to almost everyone.

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Types

• Air-cooled heat exchangers have a central motor fan for heat removal.
  
• Brazed plate heat exchangers are made up of specially formed plates, vacuum brazed together.
  
• Gasketed plate heat exchangers are the most common. Elastomer gaskets are used in the plates, which contain the pressure and control the flow of each medium.
  
• Plate heat exchangers use corrugated plates that are mounted on a frame and fastened together. They are designed so that the flows of hot and cool liquids run counter to each other, and are used when temperature and pressure demands are moderate.


Plate Heat Exchanger. (image courtesy of Flatplate.com)

• Semi-welded or hybrid plate exchangers consist of pairs of plates that are laser welded together into cassettes. These allow one fluid to flow in a welded channel and the other to flow in a gasketed channel.
  
• Tube-and-shell heat exchangers consist of tubes that are run through a large circular tank, called the shell. Tube-and-shell (or tubular) heat exchangers are used in applications where the pressure and temperature demands are high, and when the fluid contains particles that block the channels of a plate heat exchanger.



Shell & Tube Heat Exchanger. (image courtesy of www.apiheattransfer.com)

• Welded plate heat exchangers are fully welded and require no gaskets. These are usually constructed of one material, generally stainless steel.