The Role Of Heat Exchangers
Heat exchangers are devices used to efficiently transfer heat from one fluid to another whether they are separated or mixed together. In some instances, a solid wall separates the fluids so they donít mix while in other designs, the fluids come in direct contact with each other. Besides space heating and air conditioning, they are also used in chemical plants, petrochemical plants, petroleum refineries, processing of natural gas, refrigeration and power plants. Home heating systems use heat exchangers to heat to water or air which is then circulated throughout the house.
Heat exchangers are categorized depending on their flow arrangement. These are parallel-flow, counter-flow and cross-flow. In a parallel-flow heat exchanger, two fluids go into an exchanger at the same point and flow in parallel to each other. A counter-flow arrangement has the fluids entering the exchanger from opposite ends. This is considered the most efficient design as it transfers the most heat. In a cross-flow heat exchanger, the fluids flow perpendicularly to one another via the exchanger.
Heat exchangers come in various types Ė shell and tube, plate, regenerative, adiabatic, fluid and dynamic scraped surface. The shell and tube type is ideal for high-pressure applications. It features a series of tube bundles through which one of the fluids flow. The other fluid flows over the tubes to be heated or cooled. The tubes involved here can either be the plain or longitudinally finned.
The plate heat exchanger consists of several, thin and slightly-separated plates. These plates have very huge surface areas and passages for fluid flow to allow heat transfer. The bigger heat exchangers used in HVAC applications are called plate-and-frame. They feature the gasketed type when used in open loops for easier cleaning and inspection during disassembly.
In the regenerative heat exchanger, on the other hand, the heat for warming the fluids to be used in the process is actually already a result of a previous process. The fluid is used on either side of the heat exchanger which can be the plate and frame type or the shell and tube type.
Another type of heat exchanger is the adiabatic wheel. This type utilizes a big wheel with fine threads that rotate through the hot and cold liquids. Intermediate fluid or solid store is used here to keep the heat which is later transferred to the other side of the heat exchanger for release.
The fluid heat exchanger is normally used for cooling gases and getting rid of impurities. It is mostly used in espresso machines notably in cooling super-heated water which is used in extracting espresso.
The last type is the dynamic scraped surface used in heating or cooling liquid products, in the processes of crystallization and evaporation.
Maintenance is highly important to any equipment in the same way as the heat exchangers. Regular maintenance is vital in maximizing the efficiency of heat exchangers, saving extra repair costs and to keep them working for a long time. Problems can easily be detected without even requesting for a professional inspection just by observing sudden temperature and pressure changes. Investing in monitoring devices like pressure and temperature gauges, filters and back-flush valves is also a good option.