Journal of Mechanical Science and Technology 34 (1) 2020 DOI 10.1007/s12206-019-1044-0 457 Journal of Mechanical Science and Technology 34 (1) 2020 Original Article DOI 10.1007/s12206-019-1044-0 Keywords: · Computational fluid dynamics · Forced convection · Heat transfer · Oval tube · Pressure drop · Vortex generators Correspondence to: Md. Ashiqur Rahman ashiqurrahman@me.buet.ac.bd Citation: Haque, M. R., Rahman, M. A. (2020). Numerical investigation of convective heat transfer characteristics of circular and oval tube banks with vortex generators. Jour- nal of Mechanical Science and Technol- ogy 34 (1) (2020) 457-467. http://doi.org/10.1007/s12206-019-1044-0 Received February 9th, 2019 Revised July 1st, 2019 Accepted September 18th, 2019 † Recommended by Editor Yong Tae Kang Numerical investigation of convective heat transfer characteristics of circular and oval tube banks with vortex genera- tors Mohammad Rejaul Haque 1 and Md. Ashiqur Rahman 2 1 Mechanical and Production Engineering, Ahsanullah University of Science & Technology, Dhaka-1208, Bangladesh, 2 Department of Mechanical Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka-1000, Bangladesh Abstract The present work represents a 3-D numerical investigation of forced convection heat transfer over circular and oval tube banks with longitudinal vortex generators (LVGs) for flow through a fin-and-tube heat exchanger. The thermo-hydraulic performance parameters are studied numerically using computational fluid dynamics (CFD) tool. It is found that within the range of Reynolds number (500-850) studied, the degree of heat transfer enhancement is greatly influenced by the tube shape. Heat transfer increases by 13 % when the angle of attack is varied from 15º to 25º, with a corresponding pressure drop of 40 % and 62 % for the oval tubes and circular tubes, respectively. The effect of the aspect ratio of the oval tubes is observed to be very significant. Several other performance parameters of the oval and circular tube banks with vortex generators under the same operating conditions are compared with a focus on finding an optimal configuration. 1. Introduction Heat exchangers (HE) are used for numerous areas of application. Hence, it is always de- sired to increase the efficiency of heat exchange devices to save energy as well as cost. Find- ing design improvements of heat exchangers to enhance their performance has for long re- ceived the attention of researchers because of their tremendous technical importance [1]. It is widely accepted that the enhancement of heat transfer obtained from the introduction of vortex generators (VG) of different types and shapes and configurations (longitudinal, transverse, curved, inclined, etc.) in channel flow is principally due few common mechanisms, explained elaborately by Tiggelbeck et al. [2]. These mechanisms include the generation of a secondary flow consisting of interacting vortices, development of three-dimensional turbulent boundary layer, and thinning of the sub-laminar boundary layer at the wall. Longitudinal vortex generators (LVGs), capable of generating interacting vortices or swirl flow along the flow direction, have received considerable attention from the researchers from the last two decades and have been studied for the air- or gas-side heat transfer augmentation of different types of HE. Fiebig [3, 4] reported that LVGs can significantly increase the heat trans- fer coefficient in laminar channel flows and can realize more significant heat transfer enhance- ment than the transverse VGs. An increase of 55- 65 % in the heat transfer coefficient with an associated pressure drop increase of 20-45 % for inline tube arrangement was reported. The findings of an experimental study on the heat and momentum transfer in a turbulent channel flow with LVGs were reported by Lau et al. [5]. The effect of installing vortex generators on different types of HE (fin-and tube, louvered) un- der different operating conditions (dry, wet and frosting) was studied and reported by several researchers, both experimentally and numerically [6-16]. The effects of using different types and configurations of VGs in flow fields with oval tube or tube array have also been examined © The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature 2020