Importance of Heat Exchangers
The purpose of a heat exchanger is to transfer heat from one fluid to another fluid. A heat exchanger functions as an essential component for many of the appliances people use every day. For example, automobiles contain a heat exchanger, which keeps the vehicle from overheating. Air conditioners are also examples of heat exchangers. The mechanical device comes in various sizes and shapes. Heat exchanger construction consists of plates, shells and tubes.
Tube and Shell
The tube and shell construction represents the most fundamental and common category of heat exchangers. This device has a set of tubes positioned in a shell or container. The tube has fluid, called the "tube side fluid." The fluid outside the container is known as the "shell side fluid." A tube sheet separates the tube side fluid from the shell side fluid. Manufacturers use welded technology, also called "rolled and press fitted," which makes the tubes leak-proof.
This heat exchanger mechanism has plates, instead of tubes, to separate cold and hot fluids. The two fluids transfer back and forth between the plates. Individual plates have large surface areas, which makes for more space for heat transfer. When compared to a tube and shell heat exchanger of the same size, plate-type heat exchangers have the capacity to transfer more heat because of the larger area.
Plate-type heat exchangers also have a higher heat transfer efficiency; this feature enables smaller plate-type heat exchangers to have the same heat transfer capability as larger shell and tube devices. However, the slow progress made in developing a dependable method of sealing the gaskets located between the plates limits its use for high-pressure applications. Therefore, plate-type heat exchangers work only for low-pressure systems, such as oil coolers used in engines. Improvements in the seal technology do allow for the replacement of older shell and tube exchangers for more efficient plate models.
High Temperature/Steam Systems
Large steam systems, and other units requiring extremely high temperatures, depend on heat exchangers to heat the fluid in different stages. This enhances the system's effectiveness and efficiency. Heat exchangers play a significant role in the steam sequence of power generation systems. They help convert steam back into water, which returns to the generator and helps keep operation costs low. In addition, heat exchangers increase the efficiency of the steam cycle.
Another type of heat exchanger, the car radiator, is also referred to as an "air to liquid" heat exchanger. The coolant attracts heat from the vehicle's engine block, and transfers the heat to the radiator. The hot coolant flows from the radiator into the tube side of the heat exchanger or radiator. The cool air that flows over the exterior of the tubes picks up the heat. This process lowers the coolant's temperature.
An air conditioning system actually has two heat exchangers: the evaporator and the condenser. In both components, the refrigerant flows into the heat exchanger and transfers the heat. It either gains or releases it to the cooling method---water or air. The condenser transforms hot, high-pressure refrigerant to a cooled liquid. The cooled refrigerant flows into the evaporator, where the heat flow reverses. The cooled refrigerant absorbs the hot air flowing on the outside of the tubes, which cools the air, but boils the refrigerant.