Experimental investigation on heat transfer and pressure drops across a bcc lattice structure

The Periodic Open Cell Structures (POCS) are a category of structures fascinating in the field of heat exchange. POCS exhibit an ordered geometry defined by a periodic arrangement of elementary cells and are typically produced using Additive Manufacturing (AM) techniques. They can be constructed with complex geometries and utilize different categories of materials such as polymers, ceramics, and metals. Due to this high design freedom, the thermophysical properties of these matrices can be highly adaptable to the specific needs of various applications. This study focuses on characterizing pressure losses and thermal exchange properties of a lattice truss structure with a body-centered cubic (bcc) topology printed using AM techniques in AlSi10Mg. Fig. 1 depicts the studied sample, a 50 mm side cube of 1000 unit cells. Each elementary cell has a side length of 5 mm, and the strut diameter is 0.747 mm. The sample has a porosity of 0.9. The bcc topology is isotropic in every principal direction; therefore, fluid efflux through the lattice was studied in a single direction. The objective is to assess pressure losses and thermal exchange associated with the airflow through the structure. The main components of the experimental setup include a flow channel, the test section, and Long Wave InfraRed camera (Fig. 2). The flow channel is used for measuring flow rate (according to EN ISO 5167-2) and pressure losses through the tested sample. The test section consists of a housing for the sample and four heaters. The heaters are applied to the walls of the POCS parallel to the fluid direction and are independently powered to ensure uniform heat flux on the sample walls. Lastly, the I.R. camera allows for visualizing the temperature distribution on the sample's outlet side. Various tests were conducted under steady-state conditions with imposed heat flux. Pressure drops and temperature values were measured in different heat flux conditions at the sample walls, varying the airflow rate. The overall power supplied to the sample (for each flow rate) was varied with the following steps: 0 W, 8 W, 16 W, 32 W, and 64 W. Fig.3 presents some of the results. The Reynolds-Nusselt diagram shows a generally increasing trend in convective heat transfer coefficient with increasing air velocity, for each overall thermal power value supplied to the flow. The Reynolds-Hagen graph characterizes pressure drop through the sample versus Reynold number, exhibiting an increasing trend analogous to Nusselt vs. Reynolds. The relationship between pressure drops and thermal exchange properties can be visualized in the Hagen-Nusselt plane. Finally, the diagram reporting Nusselt/Hagen ratio vs. Reynolds shows a well-defined general trend and a consistent clustering of experimental points. The analysis indicates that the Nusselt number increases more slowly than the Hagen number as the Reynolds number increases. This result suggests that pressure losses increase more than the convective heat transfer coefficient as airflow velocity rises