• additive manufacturing
• cellular solids
• convection
• heat transfer
• pcm

Cellular solids are materials consisting of interconnected networks of plates or struts that form the cell boundaries. These cells may be either open or closed and can exhibit either stochastic structures, such as metal foams, or non-stochastic ordered configurations, such as honeycombs. Cellular solids have uses across multiple fields, including biomedical engineering, aerospace, transportation, heat exchange, and numerous other areas. This Thesis specifically addresses the applications of cellular solids in thermal applications, focusing on two principal aspects: single-phase convective heat transfer and fluid flow, and solid-liquid phase change within open-cell cellular solids.
In single-phase applications, open-cell cellular solids are generally used in heat exchangers, where the cellular structure (typically metallic) markedly improves the heat transfer. The enhanced thermal performance is primarily attributed to the increased heat transfer surface area and improved fluid mixing provided by the cellular configuration. Cellular solids are used in multifunctional contexts, simultaneously serving structural and thermal management roles. Among various cellular architectures, strut-based lattice structures have proven particularly promising when shifting from purely thermal applications toward multi-objective designs, as they can act both as heat exchangers and mechanical load-bearing components. In this context, one of the goals of this Thesis is to experimentally characterize the convective heat transfer and pressure drop in strut-based lattice structures. This characterization has led to the formulation of scaling laws that are useful for predicting the performance of body-centered cubic (bcc) and face-centered cubic with z-strut (f2ccz) lattice structures within heat exchangers.
Regarding the use of cellular solids with materials undergoing a phase change, this thesis specifically focuses on the solid-liquid transition. These materials, known as phase-change materials (PCMs), are characterized by a high latent heat of fusion and phase transitions within a narrow temperature range. They are particularly interesting because of their applications in thermal energy storage, passive cooling, and temperature regulation. However, their inherently low thermal conductivity limits their thermal responsiveness. One effective strategy for enhancing the thermal performance of PCMs is to couple them with highly conductive cellular solids. Unfortunately, the transient nature of phase change phenomena renders the application of classical methods inappropriate for designing thermal storage and heat exchangers. To date, the strategies and methodologies used to characterize and predict the melting dynamics of the PCMs is a subject of discussion. During PCM melting inside an enclosure heated from the side, various melting regimes typically arise, including conductive, convective, and shrinking solids. The first is the conductive regime, where the melting front is vertical and conduction dominates heat transfer. Then there is the convective regime, in which the melting front takes a typical inflected form owing to the action of gravity. Finally, in the last regime, the shrinking solid begins when the melting front reaches the wall opposite the heated one. Similar regimes may occur in the melting of PCM within cellular solids, such as open-cell metal foams, in which the metallic structure simultaneously enhances conductive heat transfer and restricts convective fluid motion. Another objective of this Thesis is to experimentally identify the transition point, from conduction-dominated to convection-dominated melting regimes within cellular structures, specifically in metal foams and strut-based lattice. Therefore, a map was constructed to predict the onset of natural convection during the melting process of organic PCMs within aluminum foams and bcc lattice structures, considering both metallic and resin-based materials.
Lastly, the shrinking-solid regime of an organic PCM within a vertical tube-in-tube heat exchanger featuring a high aspect ratio was investigated. The analysis specifically addressed the influence of the initial and boundary conditions on the melting dynamics. The results highlighted a clear relationship between the liquid fraction and height of the melting front, which was consistently observed regardless of variations in the initial or boundary conditions.
The Thesis is structured into three main parts: Part I provides a literature review on cellular solids in thermal applications, particularly focusing on single-phase heat transfer, fluid flow, and solid-liquid phase change; Part II details experimental investigations of single-phase convective heat transfer and fluid flow in strut-based lattice structures; Part III explores natural convection phenomena during PCM melting within aluminum foams and strut-based lattice structures.