Heat exchangers transfer heat energy from one fluid or gas to another without mixing the two. Heat from hot engine water is pumped through a radiator while air is blown through the radiator tins. The heat energy from the hot engine water is transferred into the air, keeping the water at the right temperature and preventing the engine from overheating. Automotive radiators are one example of heat exchangers that are liquid-to-air heat exchangers. Other types of heat exchangers include boilers, furnaces, refrigerators, and air conditioning systems. 

There are three main types of heat exchangers, as defined by their construction or body types: plate, air-cooled, and shell and tube. Plate heat exchangers are often used on low-viscous applications with moderate demands on pressures and operating temperatures, typically below 150°C. Gasket material is chosen to withstand the operating temperature and properties of the processing fluid. There are several types of plate heat exchangers, including gasketed, brazed, welded and semi-weld or hybrid types.

Air-cooled heat exchangers and shell and tube devices are common types of heat exchangers. Air-cooled heat exchangers have an integral electric motor or fluid-powered fan for cooling or heat removal of media. Some air-cooled models do not include the fan, but have cutouts for aftermarket fans. Shell and tube heat exchangers are used in applications where there are significant high-temperature and pressure demands. Tubular heat exchangers are also used when fluids contain particles that block the channels of plate heat exchangers. There are several types of shell and tube heat exchangers including U-tube, straight, and spiral.

U-tube heat exchangers consist of straight tubes bent into a U-shape. The bundle is fitted with tube supports or flow baffles, depending upon the fluid. The tube assembly is placed in a shell to contain the fluid on the outside of the tube bundle. A head assembly is bolted to the shell to direct the fluid into the tube bundle. 

Straight-tube and spiral heat exchangers designs are also available. Straight-tube designs are able to handle heavy fouling fluids or applications where temperatures cross conditions exist. Because of the straight tubes, the head assemblies can be removed and the tubes can be cleaned mechanically. Depending upon the tube sheet configuration (fixed or floating), the ability to handle large temperature differences between the fluids may be limited. Spiral heat exchangers have a spiral body made from two metal strips that are wound around a center to form two spiral channels. Other types of heat exchangers are also available.