Thermal Conductivity and Convection Heat Transfer Coefficient of Aluminum Cellular Structures Filled with Water and Air

The present study investigates the thermal conductivity (λ) and convective heat transfer coefficient (h) of AA 6082 aluminum cellular structures immersed in water and air using a thermal conductivity probe (TCP) manufactured by the authors. The probe is a cylindrical needle 0.6 mm in diameter (D) and 60 mm in length (L), obtaining an L/D ratio = 100 ratio, which satisfies the infinite line-source assumption and enables discrimination between pure-fluid and composite (fluid + solid) thermal behavior. Cellular samples are manufactured with the Lost-PLA process and tested at temperatures of 5, 20, and 40 °C, feeding the TCP with different currents, under controlled heating conditions. The results show that the presence of the aluminum cellular structure enhances heat transfer compared with that of pure fluids. In air, the effective thermal conductivity is higher by approximately 37–45% than that in pure air, reaching about 0.038 W m−1 K−1 at higher temperatures. In water, λ increases from approximately 0.8 to 1.2 W m−1 K−1 over the investigated temperature range, corresponding to an enhancement of about 45–80% compared with that of pure water. Similarly, the convective heat transfer coefficient is higher by about 22–32% in air (h ≈ 38–41 W m−2 K−1) and 19–54% in water (up to ~440 W m−2 K−1), depending on temperature. These results indicate that the high thermal conductivity of the aluminum skeleton mainly improves conduction (“thermal bridging”), while convection may be locally affected within the pores. This study confirms the capability of the TCP method to discriminate between fluid and composite heat transfer contributions and highlights the potential of additively manufactured aluminum cellular structures for lightweight thermal management applications.