Ice Bridges Research Articles

Role of Molecular Water Layer State on Freezing Front Propagation Rate and Mode Studied with Thermal Imaging.

In this work, we study the relationship between the molecular water layer (MWL) and frost freezing onset and propagation. The progression of frost has been reported to be governed by various localized icing phenomena, including interdroplet ice bridging, dry zones, and frost halos. Reports studying the state of water on surfaces have revealed the presence of a thin nanometer water layer on a range of surfaces. Regardless of further investigations that show environmental humidity, temperature, and surface energy to affect the thickness of the MWL on surfaces, the influence of the MWL on frost nucleation and propagation has not yet been previously addressed in the literature. To study the effect of the MWL on surface freezing events, a range of surface-functionalized glass substrates were prepared. In situ monitoring of freezing events with thermal imaging allowed studying the effect of surface chemistry and environmental relative humidity (RH) on the thickness and continuity of the MWL. We argue that the observed icing nucleation and propagation kinetics are directly related to the presence and continuity of the MWL, which can be manipulated by controlling the environmental humidity and surface chemistry.

Ice‐Bridging Frustration by Self‐Ejection of Single Droplets Results in Superior Anti‐Frosting Surfaces

AbstractSurfaces capable of delaying the frosting passively and facilitating its removal are highly desirable in fields where ice introduces inefficiencies and risks. Coalescence‐induced condensation droplets jumping (CICDJ), enabled on highly hydrophobic surfaces, is already exploited to slow down the frosting but it is insufficient to completely eliminate the propagation by ice‐bridging. The study shows here how the self‐ejection of single condensation droplets can fully frustrate all the ice bridges, resulting in a frost velocity lower than 0.5 µm s−1 and thus falling below the current limits of passive surfaces. Arrays of truncated microcones, covered by uniformly hydrophobic nanostructures, enable individual condensation droplets to grow and self‐propel toward the top of the microstructures and then to self‐eject once a precise volume is reached. The independency of self‐ejection on the neighbor droplets allows a fine control of the droplets size and distance distributions and thus the ice‐bridging frustration. The truncated microcones with the smallest heads area fraction maximize the percentage of self‐ejecting droplets and minimize the frost velocity. The ice bridges frustration also implies a small frost area coverage, highly desirable in aeronautics and thermal machines.

Efficient anti-frosting on discrete nanoclusters via spatiotemporal control of condensation frosting dynamics

Tailoring the condensation frosting dynamics, particularly by surface topological designs, holds great promise to mitigate the frost accretion yet has proven challenging due to the complex and dynamic nature of interactions between vapor/liquid and surfaces. Herein, we propose a design of nanowire cluster (NC) isolated by grooves to spatiotemporally regulate the multiphase changes. The key feature lies in the integration of in-plane wetting discreteness and out-of-plane vapor flux gradient on the NC surface. By precise controlling the topology, e.g., in the case of vertex angle ∼ 30° and solid–liquid fraction ∼ 31%, the NC surface can spatially localize condensates on the cluster edges in stable Cassie state under both normal or low pressures, and temporally facilitate the removal of droplets at the minimized size even under −12 °C. Whereas the remaining droplets presented reduced mean size and a large spacing, which hindered inter-droplet ice bridging and droplet freezing. Notably, the sum of anti-frosting and frosting durations reached ∼ 200 min, which was ∼ 3 and ∼ 4 folds of other surfaces, at a temperature of −8 °C and relative humidity of ∼ 50%.

A Review of Condensation Frosting—Mechanisms and Promising Solutions

Icing in the form of condensation frosting occurs ubiquitously in our daily life and numerous industrial applications. As the frost layer mostly comprises mixed microscopic dendrites and discrete air pockets, condensation frosting manifests a thick porous media and thus catastrophically compromises the heat transfer efficiency of HVAC systems. Despite being a popular research topic for centuries, a few unprecedented advances in the study of condensation frosting have been only achieved very recently, such as the revealing of new features in the incipient stages of frost formation, which used to be too fast or too small to capture, and new anti-/de-frosting techniques have been developed based on the revealed physics. This work provides a comprehensive, up-to-date review of condensation frosting, with an emphasis placed on progress in the very latest decade. Fundamentals of condensation frosting, including condensation nucleation, coalescence and growth of the condensed drops, icing nucleation, formation of frost halos, freezing propagation via ice bridging, and lastly densification and fully developed frost layers, are introduced chronologically as what occurs. A summary of recent engineering efforts to alleviate the negative impacts of condensation frosting, referred to as anti-/de-frosting techniques, is also presented. The results of these studies can greatly enlighten the existing understanding of condensation frosting and, meanwhile, benefit the development of new anti-/de- frosting methods for numerous application backgrounds.

An evaluation of GPR monitoring methods on varying river ice conditions: A case study in Alaska

Ice roads and bridges across rivers, estuaries, and lakes are common transportation routes during winter in regions of the circumpolar north. Ice thickness, hydraulic hazards, climate variability and associated warmer air temperatures have always raised safety concerns and uncertainty among those who travel floating ice road routes. One way to address safety concerns is to monitor ice conditions throughout the season. We tested ground penetrating radar (GPR) for its ability and accuracy in measuring floating ice thickness under three specific conditions: 1) presence of snow cover and overflow, 2) presence of snow cover, and 3) bare ice, all common to Interior Alaska rivers. In addition, frazil ice was evaluated for its ability to interfere with the GPR measurement of ice thickness. We collected manual ice measurements and GPR cross-sectional transects over 2 years on the Tanana River near Fairbanks, Alaska, and for 1 year on the Yukon River near Tanana, Alaska. Ground truth measurements were compared with ice thickness calculated from an average velocity model created using GPR data. The error was as low as 2.3–6.4% on the Yukon River (Condition 3) and 4.6–9.5% on the Tanana River (Conditions 1 and 2), with the highest errors caused by overflow conditions. We determined that certain environmental conditions such as snow cover and overflow change the validity of an average velocity model for ice thickness identification using GPR, while frazil ice accumulation does not have a detectable effect on the strength of radar reflection at the ice-water interface with the frequencies tested. Ground penetrating radar is a powerful tool for measuring river ice thickness, yet further research is needed to advance the ability of rural communities to monitor ice thickness using fewer time-intensive manual measurements to determine the safety of ice cover on transportation routes.

Determining the appropriate fin spacing for high performance and low footprint of direct contact ambient air-based vaporization systems

The continuous growth of frost over the tubes during the operation of ambient air vaporizers (AAV), which are used to re-gasify the liquefied permanent gases, eventually creates ice bridges. This phenomenon not only increases the thermal resistance but also restricts the natural convective airflow. In the present paper, the effect of fin spacing on the performance of the natural and forced draft AAV is analysed under different weather conditions. Appropriate fin spacing at different operating conditions is calculated by the three-dimensional model solved in ANSYS Fluent. A dynamic numerical model is developed to predict the frost properties in a forced draft vaporizer. A higher fin spacing not only increases the footprint but also impairs the rate of heat transfer in a forced draft AAV. At 298 K air temperature and 0.7 RH, the rate of heat transfer through a forced draft AAV can be enhanced by 8% with the appropriate fin spacing. The forced draft vaporizers are less sensitive to weather conditions compared to the natural draft vaporizers. For the identical fin specification, the number of tubes needed for vaporizing 240 Nm3hr−1 of LN2 is 16 for the forced draft, while it is 36 for a natural draft AAV. With reduced fin spacing, the footprint of the vaporizer block can be reduced by as much as 65% in a forced draft vaporizer for the identical vaporization capacity and ambient conditions.

Gradient droplet distribution promotes spontaneous formation of frost-free zone

The inhibition of condensation frosting at harsh environments is critical in various anti-icing applications. However, frosting on the entire surface is the final fate for most passive anti-icing strategies as a result of inevitable ice nucleation of subcooled droplets from the surface edges or defects and the following inter-droplet freezing wave propagation. Here, we report the frost-free zone formation on a macro-ridged surface. We design a macroscale ridge on the surface and show that this surface configuration changes the spatial distribution of water vapor diffusion flux during the condensation stage, resulting in a gradient arrangement of condensate droplets according to their size. This allows numerous failures of local inter-droplet ice bridging in the area with a critical droplet coverage rate, which triggers the interruption of the global freezing wave propagation and the evaporation of the rest droplets to form a frost-free zone around the ridge corner. These findings extend our understanding of frost formation on the surface and provide a rationale for the surface design with impressive durable anti-frosting performance.

Physical mechanisms for delaying condensation freezing on grooved and sintered wicking surfaces

Heat pipes are passive heat transfer devices crucial for systems on spacecraft; however, they can freeze when exposed to extreme cold temperatures. The research on freezing mechanisms on wicked surfaces, such as those found in heat pipes, is limited. Surface characteristics, including surface topography, have been found to impact freezing. This work investigates freezing mechanisms on wicks during condensation freezing. Experiments were conducted in an environmental chamber at 22 °C and 60% relative humidity on three types of surfaces (i.e., plain copper, sintered heat pipe wicks, and grooved heat pipe wicks). The plain copper surface tended to freeze via ice bridging—consistent with other literature—before the grooved and sintered wicks at an average freezing time of 4.6 min with an average droplet diameter of 141.9 ± 58.1 μm at freezing. The grooved surface also froze via ice bridging but required, on average, almost double the length of time the plain copper surface took to freeze, 8.3 min with an average droplet diameter of 60.5 ± 27.9 μm at freezing. Bridges could not form between grooves, so initial freezing for each groove was stochastic. The sintered wick's surface could not propagate solely by ice bridging due to its topography, but also employed stochastic freezing and cascade freezing, which prompted more varied freezing times and an average of 10.9 min with an average droplet diameter of 97.4 ± 32.9 μm at freezing. The topography of the wicked surfaces influenced the location of droplet nucleation and, therefore, the ability for the droplet-to-droplet interaction during the freezing process.

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding

Bonded Discrete Element Simulations of Sea Ice With Non‐Local Failure: Applications to Nares Strait

AbstractThe discrete element method (DEM) can provide detailed descriptions of sea ice dynamics that explicitly model floes and discontinuities in the ice, which can be challenging to represent accurately with current models. However, floe‐scale stresses that inform lead formation in sea ice are difficult to calculate in current DEM implementations. In this paper, we use the ParticLS software library to develop a DEM that models the sea ice as a collection of discrete rigid particles that are initially bonded together using a cohesive beam model that approximates the response of an Euler‐Bernoulli beam located between particle centroids. Ice fracture and lead formation are determined based on the value of a non‐local Cauchy stress state around each particle and a Mohr‐Coulomb fracture model. Therefore, large ice floes are modeled as continuous objects made up of many bonded particles that can interact with each other, deform, and fracture. We generate particle configurations by discretizing the ice in MODIS satellite imagery into polygonal floes that fill the observed ice shape and extent. The model is tested on ice advecting through an idealized channel and through Nares Strait. The results indicate that the bonded DEM model is capable of qualitatively capturing the dynamic sea ice patterns through constrictions such as ice bridges, arch kinematic features, and lead formation. In addition, we apply spatial and temporal scaling analyses to illustrate the model's ability to capture heterogeneity and intermittency in the simulated ice deformation.

On the Intermittent Formation of an Ice Bridge (Nunniq) across Roes Welcome Sound, Northwestern Hudson Bay, and Its Use to Local Inuit Hunters

Ice bridges are unique features that form when sea ice consolidates and remains immobilized within channels. They form in many locations throughout the Arctic and are typically noted for the polynyas that form on their lee side. However, ice bridges also provide a temporary platform that may be used by both humans and wildlife to cross otherwise impassable channels. For generations, Inuit in Coral Harbour, Nunavut, have used an ice bridge to cross Roes Welcome Sound and expand their hunting territory, though they report that the bridge only forms approximately every four years. Of interest both to Inuit and the scientific community is why the bridge forms so intermittently, by what mechanisms, and whether the frequency will change with ongoing warming and sea ice loss. Using satellite imagery, we determined that the bridge formed during 14 of the past 50 years (1971 – 2020). Generally, the bridge forms between January and March, during a cold period that coincides with neap tide, and after surface winds have rotated from the prevailing northerly (along-channel) winds to west-northwesterly (across-channel) winds. This rotation compresses the existing ice pack against Southampton Island, where it remains stationary because of the calm along-channel winds and low tidal range, and coalesces under cold air temperatures. Breakup occurs between mid-June and early July after the onset of melt. Overall, the bridge forms when a specific set of conditions occur simultaneously; however, a warming climate, specifically a reduction in very cold days, and shorter ice season may affect the frequency of bridge formation, thereby limiting Inuit travel.

Dynamics of Frost Propagation on Breath Figures.

We investigate the process of condensation frosting on flat surfaces using thermal imaging microscopy. This method is particularly well-suited to characterize the frosting of polydisperse assemblies of dew droplets, also called breath figures, that transform into ice droplets by the propagation of frost fronts. The front propagation speed is found to be a nonmonotonous function of the characteristic droplet size of the breath figure. In our experimental conditions, the propagation speed is maximum around 70 μm s-1 for a characteristic droplet radius of around 300 μm. We mainly show that the frost propagation speed is governed by the competition between two characteristic time scales. The first one is the freezing time of individual droplets, and the other one is the formation time of interdroplet ice bridges that grow from frozen to liquid droplets. In addition, the experiments reveal that the mean ice bridge speed is constant regardless of the characteristic radius of the liquid droplets in the breath figure. A theoretical mean-field analysis without any adjustable parameters recovers all of the features of the front propagation observed in experiments.

Water droplet bouncing on pre-frosted superhydrophobic carbon soot — A step forward in designing passive icephobic surfaces

The devastating repercussions of natural freezing rain phenomena on a variety of industrial facilities might be avoided if the surface-under-attack is designed to be superhydrophobic, thus, repelling the impacting supercooled droplets and remaining free of ice. Regrettably, in climate regions with negative temperatures and highly humid atmosphere, the supersaturated water vapor freezes within the micro- nanocavities of the non-wettable surface and droplet bouncing associated with superhydrophobicity could no longer be preserved. This article explores the possibility of fabricating superhydrophobic carbon soot coatings that would maintain droplet rebound even if their surface is covered with frost. By analyzing the droplet impact dynamics on two groups of frosted soot coatings, differing by morphology, roughness, surface chemistry and porosity, we show for the first time that the liquid meniscus impalement can be cancelled when the soot consists primarily of macropores and oxygen functional groups below 7 at. %. Such a surface configuration ensures minimum energy losses (qualitatively defined) right after the dynamic collision due to the sparsely inceptive ice bridges that normally enhance the heat transfer at the contact interface. The results reported herein could be a useful platform for developing universal icephobic surfaces applicable to harsh environments.

The Winter Heat Budget of Sea Ice in Kotzebue Sound: Residual Ocean Heat and the Seasonal Roles of River Outflow

AbstractThe winters of 2017/18 and 2018/19 saw unprecedented sea ice minima in the Bering and Chukchi Seas. Kotzebue Sound, located in the southeastern corner of the Chukchi Sea, remained largely ice‐free throughout the winter in a stark departure from both recorded history and Indigenous oral history. The only sea ice that persisted throughout the winter was landfast ice and most of this occupied a small corner of the Sound near the outflow of the Noatak and Kobuk Rivers. We present oceanographic and atmospheric time series from a heavily instrumented “ice‐tethered observatory” located on this landfast ice above the river outflow channel. This observing station was deployed as part of the Ikaaġvik Sikukun (Iñupiaq for “Ice Bridges”) project, in which hypotheses and subsequent observational programs were co‐produced in partnership with an Indigenous Elder Advisory Council in Kotzebue. The measurements allow us to quantify the heat budget of the ice above the outflow channel, and identify the ocean as the primary source of heat contributing to thinning of the ice, which began in early February and accelerated rapidly before the recovery of the station in April of 2019. In concert with the ice‐tethered observations, we use 2 years of oceanographic measurements from the mouth of Kotzebue Sound to characterize the influence of river outflow on the heat budget of the landfast ice, revealing a seasonal pattern in which the rivers promote ice formation and growth in the fall/winter, but help to drive melting of the ice in spring and early summer.

On the Physical Settings of Ice Bridge Formation in Nares Strait

AbstractThe ice bridge that forms seasonally across Nares Strait impedes the southward transport of sea ice from the Lincoln Sea to Baffin Bay and contributes to the maintenance of the North Water Polynya. Previous studies have quantified how the bridge affects ice export and highlighted a long term decline in the duration of the bridge; however, the specific mechanism by which the bridge forms has remained unstudied. In this study we first used a mix of satellite imagery to refine the timing of formation for the 16 bridges that formed between 2000 and 2021, and subsequently examine the atmospheric and oceanic forcing around these events. It was found that, on average, the ice bridges formed 3 days earlier than reported in previous studies. In general, the bridges formed during periods of cold air temperatures (less than −15°C), around neap tide, and during a cessation or even reversal in the prevailing north‐northeasterly winds. Specific quantitative criteria of the environmental conditions favorable for bridge formation are presented and discussed. It was shown, however, that the alignment of these conditions does not always lead to the formation of a bridge, indicating that other factors such as ice thickness and landfast ice stability may limit the formation. A comparison of ice freeboard in Kane Basin between winter 2020 (bridge) and 2019 (no bridge) revealed that the ice pack was thinner in 2019, which may have precluded the formation of the bridge. This is critical as the Arctic ice pack continues to thin.

Condensation Frosting on Micropillar Surfaces - Effect of Microscale Roughness on Ice Propagation.

Microscale surface structures have been widely explored as a promising tool for antifreezing or frost avoidance on heat transfer surfaces. Despite studies of many surface feature designs, the mechanisms associated with condensation freezing and ice propagation on microstructured surfaces have yet to be thoroughly elucidated, espectially when it comes to quantitative understanding. In this work, condensation freezing on circular micropillar surfaces is investigated, with varying pillar spacing and height (layout/microscale roughness) but a constant pillar diameter. The pillar layout is found to have significant effects on both liquid nucleation and neighboring droplet interactions, as reflected by the condensation droplet distribution prior to soilidification and eventually the freezing front propagation area velocity. In general, nucleation is preferred on the pillar top rather than the bottom of the pillared surface unless there is a large distance between the pillars. Interactions between neighboring droplets solely on pillar tops (or bottom surfaces) can induce heterogeneity in the droplet distribution and slow freezing front propagation. Based on the roles the pillars play in nucleation, droplet coalescence, and ice bridging, four different condensation states are identified and related to the layout of the pillars, and the freezing front area propagation velocity is found to be different in each state. The findings provide a quantitative basis for designing antifreezing surfaces, applicable to a wide range of thermal systems.

Promote anti- /de- frosting by suppressing directional ice bridging

Condensation frost is one of the most common types of icing encountered in nature and industrial applications, while its accretion induces multiple non-negligible negative impacts. Many passive anti-/de- frosting approaches by tailoring surface topology and chemistry have been reported recently. To date, however, reliable engineered surfaced that can be compatible with heat exchangers from both mechanical and economic perspectives are limited. In this paper, we present a hierarchically structured surface that can profoundly reduce the frost coverage, and meanwhile promote the rapid removal of frost melts. This surface consists of microgroove pattern and nanoblade structure, where the former provides preferential sites for the growth of condensed droplets, and the latter promises a robust water repellent nature. During frosting, the ice phase spreads only among droplets on groove edges while condensed droplets in valleys are completely evaporated off, yielding a typical pattern that ice stripes distribute discretely in the dry background. During defrosting, frost melts coalesce into large droplets that spontaneously depart the substrate surface. Our results open up a new avenue for surface engineering, particularly on the design of economic and scalable anti-/de- frosting surfaces.

Landfast sea ice material properties derived from ice bridge simulations using the Maxwell elasto-brittle rheology

Abstract. The Maxwell elasto-brittle (MEB) rheology is implemented in the Eulerian finite-difference (FD) modeling framework commonly used in classical viscous-plastic (VP) models. The role of the damage parameterization, the cornerstone of the MEB rheology, in the formation and collapse of ice arches and ice bridges in a narrow channel is investigated. Ice bridge simulations are compared with observations to derive constraints on the mechanical properties of landfast sea ice. Results show that the overall dynamical behavior documented in previous MEB models is reproduced in the FD implementation, such as the localization of the damage in space and time and the propagation of ice fractures in space at very short timescales. In the simulations, an ice arch is easily formed downstream of the channel, sustaining an ice bridge upstream. The ice bridge collapses under a critical surface forcing that depends on the material cohesion. Typical ice arch conditions observed in the Arctic are best simulated using a material cohesion in the range of 5–10 kN m−2. Upstream of the channel, fracture lines along which convergence (ridging) takes place are oriented at an angle that depends on the angle of internal friction. Their orientation, however, deviates from the Mohr–Coulomb theory. The damage parameterization is found to cause instabilities at large compressive stresses, which prevents the production of longer-term simulations required for the formation of stable ice arches upstream of the channel between these lines of fracture. Based on these results, we propose that the stress correction scheme used in the damage parameterization be modified to remove numerical instabilities.

Hazardous Ice Phenomena In Rivers Of The Russian Arctic Zone Under Current Climate Conditions And The Safety Of Water Use

The ice regime of the Russian Arctic rivers and its hazardous manifestations under current climate conditions are characterized. The ice phenomena in rivers in the region determine the conditions of navigation, water supply, hydropower station (HPS) operation, and the construction of temporary ice bridges and roads. Data of more than 100 hydrological gages over period from 1936 to 2016 were used to compile various cartographic materials and to analyze the spatial variations of the dates of ice phenomena, the duration of ice-free and ice cover periods, and the maximal ice thickness. Special attention is paid to the characteristics of level regime in periods with ice phenomena. Data on the frequency of floodplain inundation during spring ice run, the hazard of ice jams, and the seasonal features of the passage of maximal annual water level are generalized.The observed changes in ice regime characteristics and ice hazard are analyzed. The years of the start of statistically significant shift of the periods of ice phenomena, caused by both climate changes and anthropogenic impact, are identified. The increase in the duration of the ice-free period was found to be not greater than 3–4 days for East Siberian rivers, 5–6 days for the Middle and West Siberian rivers, and up to 10–12 days for the rivers in the European part. A decrease in the maximal ice thickness is most pronounced in the rivers of the Northern European Russia, where it is 10–15 cm. The frequency of floodplain inundation during spring ice run remains constant.

Frost Halo Dynamics on Superhydrophobic Surfaces

Abstract Understanding the frosting mechanisms on solid surfaces is crucial to a broad range of industrial sectors such as aerospace, power transmission, and refrigeration. During the last few decades, extensive studies have been conducted on fundamental frosting phenomena, including ice nucleation, growth, bridging, and frost propagation, with few studies focusing on frost halo formation which has been shown to affect frosting dynamics on hydrophilic substrates. The role of frost halo dynamics formation on superhydrophobic surface remains unclear due to limited characterization in the past. Here, in order to study frost propagation dynamics, particularly freezing-induced vapor diffusion and frost halo formation, condensation frosting on highly-reflective nanostructured superhydrophobic surfaces (θ ≈170º) was visualized using high-speed top-view optical microscopy. Condensation frosting was initiated by cooling the surface to -20 ± 0.5°C in atmospheric conditions (relative humidity ≈50% and air temperature ≈25°C). We show that the wave front reaches neighboring supercooled droplets along the path of frost propagation, resulting in supercooled droplet freezing within ~100 ms and numerous microscale (~1 µm) condensing droplets forming around the primary freezing droplet. The microscale droplets form a condensate halo stretching two times the freezing droplet radius. The condensate halo was formed by the rapid evaporation of the supercooled recalescent freezing droplet due to the fast (~100 ms) release of latent heat, resulting in the heating of the freezing droplet and thus outwards diffusion of vapor. Further diffusion of vapor led to the subsequent evaporation of the halo condensate droplets within ~4 s. Interestingly, accompanied by the freezing of the primary droplet and condensate halo formation, the neighboring satellite droplets in the halo zone were observed to oscillate directionally and dramatically, indicative of the presence of a strong flow field disturbance due to rapid vapor diffusion. The visualizations presented here not only help to quantify the physics of condensate halo formation during frost wave propagation on superhydrophobic surfaces, but also provide insights into the role of freezing-induced vapor diffusion during frost dynamics.