Tuning the effective thermal conductivity and thermal response of Triply Periodic Minimal Surface-based composites through anisotropic geometry rescaling

This study investigates how the thermal conductivity of geometrically symmetric composites can be tuned by means of anisotropic rescaling operations. The composites addressed here are formed by filling Triply Periodic Minimal Surfaces (TPMS) lattice structures—characterized by high surface area and minimal curvature— with Phase Change Materials (PCMs). When the geometry of the lattice is modified via rescaling along a specific direction, the effective thermal conductivity tensor of the composite becomes anisotropic, favoring heat transfer along specific axes. This feature offers the possibility to preferentially drive heat fluxes to obtain more responsive systems for thermal management as in the case of PCMs. Finite element simulations of heat conduction are performed to evaluate the influence of geometric rescaling and porosity on the diagonal components of the composite's effective thermal conductivity tensor. Lattices made of highly conductive AlSi7Mg alloys, filled with either inorganic (Sn) and organic (paraffin) PCMs, are analysed for their potential in thermal energy management applications. Results show that anisotropic geometry rescaling can significantly alter thermal conductivity, particularly at low rescaling levels. The degree of enhancement depends on the choice of materials and the level of porosity. Analytical relationships are derived linking thermal conductivity with the extent of rescaling and the porosity of the composite PCM (C-PCM). Further, to test the effectiveness of thermal conductivity enhancement, transient regime analyses on different rescaled structures filled by the organic PCM are performed considering either linear temperature ramp or constant heat flow. The simulation results show that increasing the rescaling level accelerates PCM melting and therefore promotes faster heat storage, causing at the same time increased temperature inhomogeneities within the PCM domain. The study provides a new quantitative mapping of anisotropy as a function of scaling level and porosity and identifies topology-dependent responses to geometric stretching. The results highlight the trade-off between melting acceleration and temperature uniformity induced by geometric rescaling. • Forcing anisotropy, geometric unidirectional rescaling alters the effective conductivity of metal lattice filled with phase change materials • Small unidirectional rescaling determines a large increase in thermal anisotropy, which is no further improved by additional rescaling • Higher benefits are achieved by combining materials with large thermal conductivity mismatch