Types of Heat Exchangers
Heat exchangers are used to transfer heat from one fluid to another. One fluid will be heated and the other is cooled. One way of classifying heat exchangers is with regard to the types of fluids involved. For example an air to air heat exchanger transfers heat between two air streams. Another type is an air to water heat exchanger, like a car radiator. The water (with antifreeze in it) is cooled and the air passing through the radiator is heated. In general heat exchangers can be liquid to liquid, liquid to gas or gas to gas. The gas is often air, but a heat exchanger may be used to heat or cool other gases also.
Another way of classifying heat exchangers is by their general configuration. Some examples are crossflow, double pipe, shell and tube, flat plate, spiral, and finned tube. The car radiator shown is a crossflow heat exchanger, because the liquid is flowing vertically inside tubes and the air is flowing horizontally through the spaces between the finned tubes. Also, by the way, it is a finned tube heat exchanger because of the use of finned tubes in its construction.
A furnace heat exchanger is a gas to air heat exchanger. The hot combustion gases from a burning fuel are used to heat household air. The diagram at the right shows a possible flow pattern for a furnace heat exchanger.
A double pipe heat exchangers is one type used as an industrial heat exchanger. This is simply a smaller pipe fixed within a larger pipe. One fluid flows through the inside pipe and the other flows through the annular space between the two pipes. Usually the pipes are doubled back and forth to make the unit more compact as shown in the diagram at the left.