Heat exchanger is a device which used to transfer heat between fluids. The fluids stay separate with help of a solid wall so that they do not get mixed into each other. They are being used in refrigeration, air conditions, space heating, chemical plants, natural-gas processing, petrochemical plants and sewage plants. Its classical example can be found in an internal combustion engine. Engine coolant which is a circulating fluid flows through radiator coils and the air pass past the coils which cools the coolant and heat the incoming air.
Their classification of heat exchanger is according to the flow arrangement and there are three types. A parallel-flow heat exchanger in which the two fluids enter the exchanger at the same type and run parallel to each other. The design of the counter current is very efficient. It transfer heat from heat medium per unit mass, it’s a fact that temperature change with every unit length and gets higher. Then there is a cross-flow heat exchanger in which liquid travel from all angles from one to another. Heat exchangers are designed to enhance the surface area of the wall between the two fluids and minimize the resistance between two fluids. It increases the surface area and can conduit flow of liquid or persuade turbulence.
The pouring temperature across the heat surface get change with position but an appropriate temperature can be defined. It is the log mean temperature difference. Sometimes NTU method gets used because LMTD is not present.
The simplest heat exchangers are double pipe heat exchanger which is commonly being used in industry. They are cheap both in designs well as to be maintained that is why they are so much popular in small companies. But they are low efficient and need more space that is why now industries have moved towards more better exchangers such as shell and tube and plate. Double pipe exchangers are being used to teach the students. If a simple design is need than the loss of heat would have to avoid.
Shell and tube exchanger have a sequence of tubes. Two different sets of these tubes have different functions one contains liquid to be heated and cooled and on other set liquid flow on the tube to heat and cool the liquid inside them. They are being used for high pressure applications in which the temperature is more than 30 bars which are equal to 260 °C. Shells and tubes are healthy because of their shapes.
There are many other heat exchangers such as adiabatic wheel heat exchanger, Pillow plate heat exchanger, Fluid heat exchangers, Phase-change heat exchangers, and many more.