Industrial Heat Exchangers: Design, Construction Types, Service and Maintenance Needs
July 21, 2014
The Design and Construction of the Heat Exchanger
The design and construction type that a heat exchanger employs is extremely important because it largely determines what setting the heat exchanger will be used in, what types of fluids it is suitable for, its capacity and efficiency, the physical size it takes up, and even how costly, complicated, and frequent the maintenance will be. The following is a brief list and description of several of the major and notable design and construction styles of heat exchangers:
Double Pipe Heat Exchanger - The double pipe heat exchanger is the simplest and most basic type of industrial heat exchanger. This style is inexpensive to design and build and the units are also inexpensive to maintain. These qualities make double pipe heat exchangers very popular with smaller companies, or companies with limited resources. Due to their very simple, basic design they are also often used for beginning stage teaching and illustrative purposes within the heat exchanger industry. However, they require a high amount of space relative to their scale of operation and they aren't very efficient.
Shell and Tube Heat Exchanger - The shell and tube heat exchanger design features a shell casing containing a series of tubes. The tubes will contain the fluid to be heated or cooled while the second fluid will flow over those tubes thereby absorbing or providing the heat. This style of heat exchanger is commonly used for high pressure applications because the shell shape and design is very robust. The tube design itself is very important with this type of heat exchanger and factors such as tube diameter, tube thickness, tube length, tube pitch, tube corrugation, and tube layout should all be taken into consideration to maximize strength and efficiency based on the application the heat exchanger will have.
Plate Heat Exchanger - Plate heat exchangers are composed of a series of thin, slightly separated plates. They feature a very large surface area and fluid flow passages to facilitate the heat transfer. This type of heat exchanger can be made very space efficient and thanks to advances in gasket and brazing technology this design is becoming increasingly practical. There are a variety of different types of plate heat exchangers in use which depending on the type of plates used and the configuration that the plates employ.
Plate and Shell Heat Exchanger - Plate and shell heat exchangers combine features of both the shell and tube heat exchanger and the plate heat exchanger. They feature a shell casing with a fully-welded, circular plate pack at their core. Nozzles carry the fluid flow in and out of the plate pack. This type of heat exchanger design is ideal for high heat transfer and can operate at high pressure and temperature levels. It also features a relatively compact, space efficient size.
Adiabatic Wheel Heat Exchanger - Adiabatic wheel heat exchangers feature a large wheel that has fine threads. The wheel rotates through the hot and cold fluids, thereby accomplishing the heat exchange.
Plate Fin Heat Exchanger - The plate fin heat exchanger uses fins to increase its effectiveness. The fins are sandwiched within passages of plates and utilize cross-flow and countercurrent-flow. The fins themselves may be straight fins, offset fins, or wavy fins. This type of heat exchanger is usually lightweight and operates at a lower temperature. It is particularly effective for gas treatment. However, it is usually somewhat more difficult to clean than other unit types and its passageways may be prone to clogging.
Pillow Plate Heat Exchanger - The pillow plate heat exchanger design features two sheets of metal welded together. A thin sheet of metal is spot-welded onto the surface of a thicker sheet of metal. After welding is complete the enclosed space is pressurized with enough force to make the thin sheet of metal bulge outward, creating the heat exchanger’s characteristic “pillow” appearance. The expanded internal space can then be used for the heat exchanger liquids to flow through.
Waste Heat Recovery Units - Waste heat recovery units are ideal for use in refineries and plants because they work by capturing “waste heat” and then transferring it to a working medium that needs to be heated. Often the waste heat is in the form of hot gas exhaust such as might exit a gas turbine or diesel engine. The working medium is often water, oil, or another fluid that needs the heat to accomplish its process. Waste heat recovery units are often known by their acronym, WHRUs.
Dynamic Scraped Surface Heat Exchanger - Dynamic scraped surface heat exchangers are heat exchangers whose surfaces are continuously scraped as they operate. This helps prevent fouling and allows for longer run times. This makes them ideal for high-viscosity products, crystallization processes, or other applications that would otherwise lead to high rates of fouling.
Phase-change Heat Exchangers (Boilers) - Phase-change heat exchangers are heat exchangers which are designed to make the substance being heated or cooled change from one phase to another. For instance a gas might condense into a liquid or a liquid might boil into a gas. Heat exchangers that function to turn liquid water into steam are so common that they are generally considered their own class of equipment: boilers.
Heat Exchanger Maintenance and Servicing
In order to continue to be efficient, useful, and safe, heat exchangers require regular maintenance and servicing. This can include needing replacement parts from time to time as well.