Research on the thermal response characteristics of building nano bead reflective insulation materials based on multi-physics field coupling

In this study, to advance the deployment of nano‑microbead reflective insulation in green, low‑carbon buildings, we developed a three‑dimensional mesoscopic model with randomly distributed nano‑beads in COMSOL Multiphysics. Using a coupled radiation-conduction approach, we systematically compared the outer-inner surface temperature difference under radiative‑only, conductive‑only, and fully coupled conditions as a function of solar irradiance. The coupled scenario exhibited the smallest temperature-rise slope, which supports improved insulation performance under the investigated conditions. Sensitivity analysis showed that a bead diameter of 100 μm and an 88% porosity minimize the equivalent thermal conductivity while ensuring adequate mechanical strength. Under a diurnal cycle of solar loading and natural convection, dynamic experiments revealed thermal relaxation times of approximately 2 h (outer surface) and 5 h (inner surface), and quantified a 3.0 °C reduction in outer‑surface temperature per 1 W/(m²·K) increase in the convection coefficient. These behaviors reflect a pseudo‑linear thermal response arising from the linearization of radiative heat transfer and homogeneity assumptions. Finally, we propose optimization strategies incorporating dynamic radiation, enhanced convective dissipation, and temperature‑dependent material properties to guide the design of high‑performance nano‑bead reflective insulation for building envelopes and photovoltaic applications.