metals Article Experimental Investigation of Pressure Drop Performance of Smooth and Dimpled Single Plate-Fin Heat Exchangers Kanishk Rauthan * , Ferdinando Guzzomi, Ana Vafadar , Kevin Hayward and Aakash Hurry   Citation: Rauthan, K.; Guzzomi, F.; Vafadar, A.; Hayward, K.; Hurry, A. Experimental Investigation of Pressure Drop Performance of Smooth and Dimpled Single Plate-Fin Heat Exchangers. Metals 2021, 11, 1757. https://doi.org/10.3390/ met11111757 Academic Editor: Atila Ertas Received: 1 October 2021 Accepted: 28 October 2021 Published: 1 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). School of Engineering, Edith Cowan University, Joondalup, WA 6027, Australia; f.guzzomi@ecu.edu.au (F.G.); a.vafadarshamasbi@ecu.edu.au (A.V.); Kevin.Hayward@ecu.edu.au (K.H.); a.hurry@ecu.edu.au (A.H.) * Correspondence: k.rauthan@ecu.edu.au; Tel.: +61-8-6304-4690 Abstract: Passive heat exchangers (HXs) form an inseparable part of the manufacturing industry as they provide high-efficiency cooling at minimal overhead costs. Along with the aspects of high thermal cooling, it is essential to monitor pressure loss while using plate-fin HXs because pressure loss can introduce additional power costs to a system. In this paper, an experimental study was conducted to look at the effects of dimples on the pressure drop characteristics of single plate-fin heat exchangers. To enable this, different configurations of National Advisory Committee for Aeronautics (NACA) fins with smooth surfaces and 2 mm-diameter dimples, 4 mm-diameter dimples and 6 mm-diameter dimples were designed and 3D printed using fused deposition modelling (FDM) of ABS plastic. The depth to diameter ratio for these dimples was kept constant at 0.3 with varied diameters and depths. These were then tested using a subsonic wind tunnel comprised of inlet and outlet pressure taps as well as a hot wire velocimeter. Measurements were taken for pressure differences as well as average velocity. These were then used to calculate friction factor values and to compare the smooth fin to the dimpled fins in relation to their relative pressure drop performance. It was observed that for lower velocities the 4 mm dimples provided minimum pressure drop, with a difference of 58% when compared to smooth fins. At higher velocities, 6 mm dimples increased the pressure drop by approximately 34% when compared to smooth fins. It can also be concluded from the observed data in this study that shallower dimples produce lower pressure drops compared to deeper dimples when the depth to diameter ratio is kept constant. Accordingly, deeper dimples are more effective in providing drag reduction at lower velocities, whereas shallower dimples are more effective for drag reduction at higher velocities. Keywords: pressure drop; heat exchanger; additive manufacturing; surface textures; dimples; drag reduction 1. Introduction When discussing heat exchangers (HXs), a primary or direct contact surface is de- fined as a surface that separates two fluids at different temperatures. As noted by Thu- lukkanam [1] and Shah and Sekulic [2], additional surfaces can be attached to a primary surface to increase the heat transfer area and further improve the heat transfer characteris- tics of an HX. These secondary appendages are referred to as fins and aid with convective heat transfer. With recent advancements in brazing and welding technology, most currently manu- factured compact heat exchangers (CHX) and plate-fin heat exchangers (PFHX) involve the brazing, semi-welding and all-welding of plates to a core [3]. Diffusion-bonded HXs have also been applied in high-pressure industrial contexts [4]. Another important development in HX manufacturing is the introduction of additive manufacturing (AM), which allows for complex geometries and matrices to be fabricated [5]. As a result, HXs have become more compact and more efficient [4]. For instance, in a study conducted by Wong et al. [6], it was concluded that an AM-fabricated lattice-structured HX provided minimal resistance to airflow as compared to traditional plate-fin and pin-fin HXs. Metals 2021, 11, 1757. https://doi.org/10.3390/met11111757 https://www.mdpi.com/journal/metals