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In this experimental and theoretical study, the impact of non-spherical and spherical ice particles onto a solid surface is investigated. The impact velocity of the particles was varied between 1 and 74 m s −1 . The size of the particles ranged from 30 μm to 3.5 mm. The impact target consisted of a tiltable aluminium surface. The impact angles were set to 30° and 90° (normal impact). The impact process was recorded by a high-speed video system. Based on observations, four different fragmentation modes, characterized by different levels of particle damage, were defined. Fragmentation models for the description of the deformation of the particle and the development of cracks within the particle on impact are formulated and validated by the experiments. In particular, the velocity up to which no particle fragmentation occurs, and the maximum velocity up to which minor fragmentation occurs (both significantly dependent on the particle initial size) are well captured by the fragmentation models.

In this study melting of irregular ice crystals was observed in an acoustic levitator. The evolution of the particle shape is captured using a high-speed video system. Several typical phenomena have been discovered: change of the particle shape, appearance of a capillary flow of the melted liquid on the particle surface leading to liquid collection at the particle midsection (where the interface curvature is smallest), and appearance of sharp cusps at the particle tips. No such phenomena can be observed during melting of spherical particles. An approximate theoretical model is developed which accounts for the main physical phenomena associated with melting of an irregular particle. The agreement between the theoretical predictions for the melting time, for the evolution of the particle shape, and the corresponding experimental data is rather good.

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