Possibilities of intensifying heat transfer through finned surfaces in heat exchangers for high temperature applications

摘要

High temperature heat transfer application actually represents the case of a heat exchanger operated within a process with high temperature. In every industrial domain, a different value of temperature may be considered "high". We are active in the field of chemical, petrochemical, waste-to-energy, power and process energy recovery heat transfer applications. Here, tube-fin exchangers are successfully used for gas or liquid and/or aggressive fluids with temperatures up to 350 and/or 400℃. They are also frequently used in combustion systems with air preheating applications. Tubular heat exchangers, especially those with U-tubes, helical and straight tubes are most frequently used for high-temperature applications with temperatures above 650℃. Extended surfaces are used as an intensification approach to decrease the area requirements on flue gas side. Selection of an extended surface depends on the type of fuel being burned. Generally speaking, enhanced surfaces are used for gaseous media with low heat transfer coefficient. Fins substantially enhance the heat transfer area and consequently heat duty of the equipment. This paper describes this "passive" technique to enhancement of heat transfer in more detail and presents novel types of longitudinally finned tubes intensifying heat transfer by increasing heat transfer area and heat transfer coefficient. This means that the fins not only increase heat transfer area but also make the fluid flowing around them change flow direction, i.e., they increase turbulence. This consequently increases film heat transfer coefficient on fin side.