Micro-CT investigation of urea crystal structures for frost analysis

Frost formation poses a significant challenge to the design and efficiency of air-source evaporator units. To model frost formation, a detailed understanding of the evolving three-dimensional microstructures that influence thermal and mass transport properties is essential. However, direct measurement of frost microstructures remains challenging. This study demonstrates that Micro-CT, combined with finite-element modelling, is a viable method for evaluating transport properties in complex microstructures. Using urea mushy layers as a stable, non-melting analogue, we successfully validated the methodology by resolving microstructural influences on thermal conductivity and mass diffusivity.

Our results highlight the significant role of structural complexity in transport behaviour, with ‘simple’ and ‘complex’ formations influencing heat and mass transfer differently. Deviations of at least 26.6 % between measured properties and predictions from empirical bulk-property models confirm that conventional approaches fail to capture the effects of structural heterogeneity. While these findings do not directly translate to frost formation, the validated methodology offers a foundation for improving frost prediction models by incorporating high-resolution structural data, ultimately enhancing the accuracy of thermal system designs in frost-prone environments.