Possibilities of intensifying heat transfer through finned surfaces in heat exchangers for high temperature applications Petr Stehlík, Zden  ek Jegla, Bohuslav Kilkovský * Brno University of Technology, Institute of Process and Environmental Engineering e VUT ÚPEI, Technick a 2, 616 69 Brno, Czech Republic article info Article history: Received 17 January 2014 Received in revised form 12 May 2014 Accepted 15 May 2014 Available online xxx Keywords: High temperature application Heat exchanger Heat transfer Enhanced surface Intensification Finned tubes abstract 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  C. 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  C. 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 conse- quently increases film heat transfer coefficient on fin side. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction First, it is necessary to design the overall system with respect to the process in question [1] and only then one can consider heat exchanger networks (HEN) and heat exchangers as pieces of equipment. A novel design approach for HEN retrofits based on heat transfer enhancement is shown in Ref. [2]. The experience from industrial practice in terms of providing technical solutions increasing performance of heat exchangers through process enhancement technologies is presented in Ref. [3]. Heat exchangers perform satisfactorily only if they are correctly designed, installed, and operated. Selection of a suitable heat exchanger type, especially in case of high-temperature applica- tions, is therefore of paramount importance. 1.1. Definition of “high temperature application” High temperature application actually means that the equip- ment is operated within a process with high temperature streams. The problem, however, is how to define “high temperature”. In every industrial domain, a different value may be considered “high”, that is, a very different value will be denoted as such e.g. in cryogenics and in incineration. Even with respect to the human body, high temperature is understood in various ways. For example, normal human body temperature is approx. 37  C and temperature around 38  C is already a fever, while temperature above 40  C is considered extreme, so-called hyperpyrexia. Burns may already occur upon touching a surface hotter than 45  C (depending on the actual temperature and length of the touch). In food industry, temperatures above 80  C are usually considered high. In elec- tronics, high temperature is typically above 85  C [4]. In any case, this paper is focused on the field of chemical, petrochemical, waste-to-energy, power, and process energy recovery heat transfer applications. In petrochemical industry, high * Corresponding author. E-mail addresses: stehlik@fme.vutbr.cz (P. Stehlík), kilkovsky@fme.vutbr.cz (B. Kilkovský). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng http://dx.doi.org/10.1016/j.applthermaleng.2014.05.052 1359-4311/© 2014 Elsevier Ltd. All rights reserved. Applied Thermal Engineering xxx (2014) 1e5 Please cite this article in press as: P. Stehlík, et al., Possibilities of intensifying heat transfer through finned surfaces in heat exchangers for high temperature applications, Applied Thermal Engineering (2014), http://dx.doi.org/10.1016/j.applthermaleng.2014.05.052