Things Found in Heat Exchangers
- Heat exchangers usually have a thermally conductive element, a tube or plate that transfers heat energy from one material to another. Tubes in the heat exchanger create a surface for heat to pass through from one liquid to another. The tubes are sometimes seamless, but are other times welded. Manufacturers mostly make them from copper or steel alloys, though some are made from aluminum, nickel or titanium for various reasons. Some tubes are bare, while others have extended surfaces on the outside. The tubes pass through holes in tube sheets, round plates designed to take tubes with grooves or holes.
- Various parts fasten to the shell, including spacer rods and gaskets. Shells are containers for the fluid. The liquid enters and exits the shell through nozzles. Shells usually have circular cross-sections. Some exchangers need small diameter shells, which engineers can make by cutting pipe to a specific diameter and length. Manufacturers usually use low carbon steel to make large shells, since they're more economical. However, when vulnerable to high temperature or corrosion, engineers sometimes use other metal alloys.
- Inlet nozzles have impingement plates to prevent a sudden impact from high velocity water into the tubes, which can cause erosion and vibrations. Impingement plates are objects found inside the shell that absorb the water. Tube-side channels control the flow of liquid in the exchanger. These parts need more corrosion resistance, since the liquids they're exposed to usually have corrosive properties.
- Baffles support the tubes and keep them in the right position. They also guide the flow back and forth, increasing the heat transfer velocity. Baffles have spacing that equalizes the free flow areas through the window and across the tube bank. Some baffles are in segments. Double-segmental baffles maintain the benefits of segmental baffles and keep pressure from exiting the flowing gases.