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Common Questions About Heating, Ventilation and Cooling
What is a heat exchanger?
A heat exchanger is a device that is used to transfer heat from one fluid to another. The fluids may be separated by a solid wall or may be in direct contact with each other. For better efficiency, most of the heat exchangers are designed to maximize the surface area of the wall between the fluids and minimize the fluid flow resistance.
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Heat exchangers are widely used in air conditioners, refrigerators, space heaters, and electric generators. They are also used in chemical processing. A radiator of a car is the most common example of a heat exchanger. In a radiator, a hot engine cooling fluid transfers heat to air flowing through the radiator.
According to the flow arrangement, heat exchangers are classified into three types: Parallel flow, counter flow and cross flow heat exchangers. In parallel-flow heat exchangers, two fluids enter at the same end and move in parallel to each other as they flow to the other end. In a counter-flow heat exchanger, fluids enter from opposite ends. Counter-flow heat exchangers transfer the maximum amount of heat and hence are considered the most efficient heat exchangers. In a cross-flow heat exchanger, fluids move perpendicular to one another.
Heat exchangers come in four different designs: shell and tube, plate, regenerative, and intermediate fluid or solid. The shell and tube heat exchanger is made up of multiple finned tubes through which one of the fluids runs. The other fluid runs over the finned tubes to be heated or cooled.
A plate heat exchanger is composed of multiple, thin plates of large surface areas. There are fluid flow passages for heat transfer and the fluids are separated by plates. A stacked plate arrangement is more effective in a given space than the shell and tube heat exchanger.
Third type of heat exchangers is the regenerative heat exchanger which takes advantage of the heat from a specific process in order to warm the fluid used in the same process. Same type of fluid is used either side of the heat exchanger. These heat exchangers can have the shell and tube design or the plate design.
Fourth type of heat exchanger is known as the intermediate fluid or solid heat exchanger. This type of heat exchanger uses the fluids or solids within it to hold heat, which is then moved to the other side of the heat exchanger to be released. This method is generally used to cool gases and removing impurities at the same time.