International Journal of Thermal Sciences 151 (2020) 106256 Available online 21 January 2020 1290-0729/© 2020 Elsevier Masson SAS. All rights reserved. Experimental investigation of effect of different tube row-numbers, fn pitches and operating conditions on thermal and hydraulic performances of louvered and wavy fnned heat exchangers Abdulkerim Okbaz a, * , Ali Pınarbas ¸ı b , Ali Bahadır Olcay c a Dogus University, Faculty of Engineering, Department of Mechanical Engineering, Acibadem, Kadıkoy, 34722, Istanbul, Turkey b Yildiz Technical University, Faculty of Mechanical Engineering, Besiktas, Istanbul, 34349, Turkey c Yeditepe University, Faculty of Engineering, Department of Mechanical Engineering, Kayisdagi Cad., 34755, Istanbul, Turkey A R T I C L E INFO Keywords: Louvered fns Wavy fns Effect of tube row Fin types Heat exchanger Heat transfer Heat transfer enhancement Pressure drop ABSTRACT Heat exchangers are used in air conditioners, heat pumps, marine, land and air vehicles, refrigeration systems, thermal and nuclear power plants, etc. Increasing heat transfer capacity of a heat exchanger means that the volume of the heat exchanger and the material used will be reduced. Besides, effects of some geometric pa- rameters on heat transfer and pressure drop are more complex depending on the fn structure in fn and tube heat exchangers. In this study, three of the most dominant parameters affecting the thermal-hydraulic performance of a fnned and tube heat exchanger were experimentally investigated. These are fn-type (louvered and wavy fns), fn pitch and number of tube-rows. The intermittent geometric structures of louvered fns break growing of the boundary layer and reduce its thickness yielding heat transfer enhancement. On the other hand, wavy fns cause an increase in the heat transfer area due to its large fow length and create instabilities in the fow due to fow separations increasing the heat transfer coeffcient. In the present study, specifcally fve louvered fnned and three wavy fnned and round tube heat exchanger prototypes were manufactured. Heat transfer and pressure drop experiments of these heat exchangers were performed at a wind tunnel in a conditioned room. Heat transfer and pressure drop characteristics were presented as heat transfer coeffcient h o , Stanton number St, Nusselt number Nu, dimensionless pressure drop coeffcient C p , Colburn-j factor, Fanning friction factor f, j louver /j wavy , f louver /f wavy , j/f 1/3 ratios and JF factor. The results were examined from the point of heat transfer and pressure drop mechanisms of louvered and wavy fns for the different number of tube-rows, fn pitches and air inlet velocities. It is found that Colburn-j factors and Fanning friction f factors of the LFRTHXs are higher than those of the WFRTHXs for all the studied cases. Colburn-j factors of the LFRTHXs are higher by 16.4–6.9%, 28.5–18.3% and 25–11.7% than those of the WFRTHXs for the cases of two tube-rows, three tube-rows and four tube-rows, respectively. On the other hand, pressure drops of the LFRTHXs are signifcantly higher than those of WFRTHXs. However, the thermal-hydraulic performances of the LFRTHXs are still higher than that of WFRTHXs. The thermal-hydraulic performance criteria j/f 1/3 ratios of the LFRTHXs are higher by 9.6–4.1%, 22.1–16% and 16.8–7.4% than those of the WFRTHXs for the cases of two tube-rows, three tube-rows and four tube-rows, respectively. 1. Introduction Heat exchangers with fn-and-tube are widely used in industrial and daily applications such as air-conditioning, ventilating, heating, refrig- eration systems, automobiles and chemical industries. Any enhance- ment in the heat exchangers’ thermal and hydraulic performance will lead to energy and material savings. In the case of heat exchangers with fns, the thermal resistance of airside is generally the dominant param- eter (it accounts for 80% or more of the total thermal resistance [1]) which determines the thermal performance. Louvered fns application to enhance the heat exchangers’ thermal and hydraulic performances is a cost-effective method. The non-continuous surfaces of louvers stop the growing of the boundary layer and cause an enhancement in the heat transfer coeffcient consequently. Besides, the periodic motion of air through the neighboring fns by following the direction of louvers * Corresponding author. E-mail address: aokbaz@dogus.edu.tr (A. Okbaz). Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: http://www.elsevier.com/locate/ijts https://doi.org/10.1016/j.ijthermalsci.2019.106256 Received 11 June 2019; Received in revised form 10 December 2019; Accepted 31 December 2019