Porosity formation during atmospheric ice accretion: measurements using micro-computed tomography

Abstract

Atmospheric ice accretion results from the exposure of technical equipment or facilities to cold and humid environments. Supercooled droplets in a cloud can impact an airplane's surface and quickly form an ice layer. The presence of air pockets in such a layer is well known and explains the white appearance of some of the accretions. However, estimation of its porosity values and studies on the pore formation mechanics remain limited. In this study, we performed tests in an icing wind tunnel and scans with micro-computed tomography to address these issues. Here, we show that the accretion has closed porosity below 1%, which is mostly produced by the interaction between a spray-like impact on the water surface. The insights we provide here are important to improve ice accretion modelling techniques and establish a different approach to address the interaction between the cloud and the surfaces exposed to atmospheric icing.

Internal and interfacial microstructure characterization of ice droplets on surfaces by X-ray computed tomography

“…Pore formation and porosity inside frozen droplets is rarely discussed in research focusing on icing, there are, however, two studies which have investigated porosity inside ice using XCT 18 [33,46]. In these studies, the majority of pores have a similar equivalent diameter compared to the results obtained in this study.…”

“…In comparison with the very few studies in this domain, the present research focuses on the ice and surface simultaneously (instead of only focusing on the bulk ice [28,[32][33][34][35][36]). Furthermore, employing a higher resolution (voxel size of 3.6 µm) unravelling additional details.…”

“…7.067 µm) uses an ice wind tunnel to simulate atmospheric ice accretion. This led to a mean pore diameter of 40 µm; however, the air trapped between impacting droplets formed rime ice with the largest pores reaching diameters up to 250 µm [33]. Additionally, both studies used higher temperatures, -15°C and -4.5°C, respectively.…”

“…Accordingly, they have studied the geometry of ice indirectly through the cast. In another study, Velandia et al [33] 5 employed XCT for imaging small ice samples cut from ice accreted on the model of an engine nacelle inlet. Here, they have directly imaged the internal structure of the accreted ice.…”

Introduction to the Annals of Glaciology ‘Ice in a Sustainable Society’ issue

“…For those still in doubt, all those topics are indeed relevant for glaciologists and their studies have been published in the Journal of Glaciology and the Annals of Glaciology (e.g. Nishio and others, 1982; Gayet and Bain, 1983; Krass, 1984; Delisle, 1993; Hvidberg, 2003; Velandia and others, 2021).…”