© Faculty of Mechanical Engineering, Belgrade. All rights reserved FME Transactions (2023) 51, 14-22 14 Karrar Gh. Fadhala M.Sc student Mechanical Engineering Department University of Technology Iraq Ekhlas M. Fayyadh Professor Mechanical Engineering Department University of Technology Iraq Ali F. Mohammed Lecturer Mechanical Engineering Department University of Technology Iraq Experimental Investigation on the Thermal-Hydraulic Performance of Channel with Gradient Metal Foam Baffles Metal foam is a novel material recently utilized in baffles as an alternative to solid baffles for reducing flow resistance. However, the metal foam baffles are accompanied by low heat transfer efficiency. To overcome this issue, a new design of copper foam baffles has been suggested in this research, called baffles having a gradient pore density of the copper foam. The pore density either increases or decreases towards the wall. So, the experimental tests were carried out in a square channel and heated uniformly at the bottom wall of the test section. Its walls are mounted copper foam baffles at a fixed porosity of 95%. Baffles were alternately fixed upon the walls' bottom and top in staggered mode. The results were determined for various kinds of copper foam (10 and 20) pores per inch (PPI), and the gradient pore density was either with the order decreasing (DPPI) 10/20 PPI or increasing (IPPI) 20/10 PPI with a window cut ratio of 25% and a constant heat flux of 4.4 kW/m 2 . The Reynolds number was changed from 3.8x10 4 to 5.4x10 4 . The data for conventional copper solid baffles were used to compare the influence of foam metal type. The obtained results revealed an enhancement in thermohydraulic performance for baffles with a gradient pore density of the order decreasing DPPI (10/20 PPI) higher than all the models of copper foam baffles. Keywords: Gradientmetal foam, Heat exchanger, Heat transfer enhancement, Gradientmetal foam baffles 1. INTRODUCTION The employments of channels with baffles are one of the most prevalent passive heat transfer augmentation solutions in single-phase internal flows. This passive heat transfer enhancement technique has been used for various industrial applications, such as shell-and-tube heat exchangers, labyrinth seals for turbo-machines, internal cooling systems of gas turbine blades, thermal regenerators, and electronic cooling devices, Hwang [1]. Despite this wide range of applications, the existence of such baffles causes the flow to separate, re-attach, and therefore generate the zones of opposite flow and the high shearing rates that affect the thermal-hydraulic performance. However, some researchers investigated the effect of the appropriate geometric parameters of the baffles, such as baffle height (or window cut ratio), baffle spacing, and the relative arrangement of baffles that gives the best heat transfer performance for a given pumping power or flow rate. For example, Habib et al.[2]studied the effect of a window-cutting ratio of solid baffles on the flow and heat transfer characteristics at turbulent flow. The experiments were carried out in a rectangular channel with baffles arranged as staggered with heating at a constant wall heat flux along the top and the bottom using air as the working fluid. The tests were performed at a range of Reynolds numbers from 8x10 3 up to 1.6 x10 3 with different values of window cut ratio of 0.3, 0.5, and 0.7. The researchers showed that as the window cut ratio decreased and the Reynolds number increased, the local and average heat transfer and pressure loss increased. However, the increase in the pressure loss was found to be much higher than the increase in the heat transfer coefficient. Li and Kottke[3] investigated the impact of the distance between the baffles in the models of shell-and-tube heat exchangers on the heat transfer and pressure drop experimentally. The expe– riments were conducted at a range of Reynolds numbers with different values of the distance between the baffles. Results demonstrated that for a fixed value of the Reynolds number, the heat exchange coefficient and the pressure drop increased as the distance between the baffles increased. Analysis of the turbulent flow in a rectangular channel with baffled plates was studied numerically and experimentally by Demartini et al.[4]. It was found that the greatest fluctuations in the pressure and velocity fields occurred near the deflectors. Saim et al. [5] investigated numerically the fluid flow and the heat transfer performances of a rectangular channel equipped with solid plate baffles, which are arranged on the top and bottom channel walls in a periodically staggered method. It was found that the vortex shedding produced by the baffle on the upper wall can additi– Received: October 2022, Accepted: December 2022 Correspondence to:Karrar Gh. Fadhala, Mechanical Engineering Department, University of Technology, Baghdad, Iraq E-mail: karraralb1@gmail.com doi: 10.5937/fme2301014F