Visual experimental study on the aging mechanism of slush nitrogen and particle evolution law using multiscale imaging technology

To investigate the mechanisms and phenomena of slush hydrogen aging, a visual testing platform was developed. Aging experiments were conducted with evolutionary particle imaging, the objective of which was to obtain the characteristics of the particle size distribution and time-dependent evolution curves of the distribution. The aging vessel employs a double-nested Dewar configuration, where slush nitrogen is stored in the vertically suspended inner vessel. The particle evolution was captured by high-speed cameras coupled with microscopic imaging, and the subsequent analysis of the data was conducted by machine learning-based image processing techniques. Evacuation rate significantly influences the structure of the nitrogen-consolidated layer, thereby dictating aging morphology and ultimately determining successful production of high-quality slush nitrogen. Five distinct evolutionary stages were identified: flocculent phase, transparent fragments phase, irregular porous dendrites phase, acicular dendrites phase, and near-spherical dense particles phase. Analysis of two trials revealed particle equivalent diameters primarily distributed in 0.12–0.2 mm (log-normal distribution) and 0.06–0.15 mm (quasi-Gaussian distribution) ranges. These findings provide critical insights into slush nitrogen aging mechanisms, offering guidance for aging simulations and practical strategies for industrial-scale production of high-performance cryogenic slurries. • Double-nested dewar was used in cryogenic slush aging observation experiments. • Microphotography for clear acquisition of slush nitrogen particle evolution images. • Discuss the importance of the aging process for high quality slush nitrogen. • Aging experiment results are consistent with Ostwald Ripening law. • Aging particle size distribution evolves from gamma to normal-like distribution.