Additively-manufactured metallic porous lattice heat exchangers for air-side heat transfer enhancement

Abstract

In this study, two novel porous lattice air-cooled heat exchangers (Lattice 1 and Lattice 2) were fabricated by the selective laser melting (SLM) technique from an aluminum alloy (AlSi10Mg) powder. Repetitions of the Rhombi-Octet unit cells of different cell sizes were used to form the porous matrices. Experiments were carried out in a wind tunnel to evaluate the thermal-hydraulic performances of the heat exchangers. The thermal performance indicators such as the overall thermal conductance (UA), air-side thermal resistance (Ra), air-side heat transfer coefficient (ha) and volumetric heat flux density (q˙v) of the porous lattice heat exchangers were determined and comparisons were made against two conventional fin-tube heat exchangers (Fin-tube 1 and Fin-tube 2). In addition, the pressure drops across the heat exchangers were also measured. Based on our investigations, it was determined that Lattice 1 exhibited approximately 40%–45% higher UA and ha than Lattice 2. However, the pressure drop across Lattice 1 was also higher than Lattice 2. At the same mass flow rate of air (m˙a), it was found that the ha values of the porous lattice heat exchangers were more than 2 times those of the fin-tube heat exchangers. The significantly higher ha values of the porous lattice are mainly attributed to the presence of interconnected pores and the formation of eddies downstream of the ligaments that improved fluid mixing. For the same pumping power (W˙/H), the use of the porous lattice heat exchangers also resulted in consistently higher ha values than the fin-tube heat exchangers. These results demonstrated the potential of using SLM to fabricate a new generation of commercial-scale compact heat exchangers made of porous lattices. These new porous lattice structures have enhanced the thermal performances of the heat exchanger with no penalty in pumping power.