Surface properties of the chilled-mirror reveal dew point sensing performance via condensation process analysis

The chilled-mirror method directly measures dew point temperature via the fundamental physical phenomenon of gas–liquid phase change and is essential for precise humidity calibration and metrological traceability in various industrial and scientific applications. Given the dual function of chilled-mirror as both an optical reflector and the dew-forming surface, its physicochemical properties significantly influence the condensation performance. This study characterizes the mirror surface through surface roughness, substrate material, and apparent contact angle. The condensation development from water clusters to micrometer-scale droplets is observed via the optical intensity response in experiments with controlled thermodynamic conditions. Comparative analysis of condensation performance on mirror surfaces fabricated with various metal substrates (Au, Ag, and Rh) reveals that the material contributes to the cluster adsorption on the mirror surface through the van der Waals dispersion forces, which governs the water-metal interaction. And the enhanced surface roughness (quantified by ten-point heights) provides more available sites and leads to higher rates of droplet nucleation. Characterized by the apparent water contact angle, droplet morphology dominates the heat transfer efficiency during droplet growth. Furthermore, the droplets coalescence exposes available nucleation sites, advancing the droplet re-nucleation and promoting efficient condensation. The development of condensation is determined by the cooperative effect of multiple factors on the heat and mass transition. This study provides important theoretical support and experimental reference for the fabrication of mirror and improvement of condensation performance in the chilled-mirror dew point sensing.