Ice Bridges Research Articles

Self-ejections of multiple isolated slushes on disorderly grooved superhydrophobic surfaces

In this Letter, we developed a sprayable superhydrophobic coating with micro-sized disorder indentations to survey the self-ejections of isolated slushes on it during the defrosting process. The microstructures, chemical composition, hydrophobic characteristics, and self-ejection phenomenon of melting slushes on grooved superhydrophobic surfaces are presented. The grooved superhydrophobic surface demonstrates that multiple self-ejections of isolated melting slush off the original locations with no ice bridges or great surface energy release. In addition, the self-ejection of multiple isolated slushes observed generates enough kinetic energy and removes the residual melting slushes in ways of sweeping off. It is also found that the irregular melting slush with a greater deformation energy and surface contact area demonstrates shorter jumping distances compared to that with a spherical shape and low surface contact area. The observed short-distance self-ejection results from the defects of micro-pores on the indentations, leading to great dissipation in vapor pressures and reduced impact from volume fluctuations. Both the volume fluctuation of slush and the evaporation of intermediate liquid generate the pressure gradient in the upward direction and contribute to the self-ejection behavior of isolated melting slush. The results demonstrate the necessity of fabricating grooved superhydrophobic surfaces without micro-pores and conceptual feasibility of employing volume fluctuation of slush for the self-ejection of isolated single melting slush in the case of slushes with no ice bridges, small surface energy, and low inner vapor pressures.

How ice bridges the gap.

When supercooled dew droplets form on a chilled surface, the subsequent freezing process is driven by a fascinating phenomenon of propagating inter-droplet ice bridges. Here, we explore the range of conditions under which an individual ice dendrite can successfully bridge the gap from a frozen droplet to its nearest liquid neighbor. Ranging the droplet sizes from 1 μm-10 mm, we find that the criterion for ice bridging is purely geometric and independent of temperature, ambient humidity, and surface wettability. We model the growth of individual ice bridges as well as the global speed of percolating fronts sweeping across large droplet populations. We also give a dynamical law for dry zone formation when ice fails to bridge the gap.

Influence of Channel Morphology on Ice Conveyance and Bridging: Experiments with a Numerical Model

AbstractThis paper presents findings from a numerical model used to conduct experiments regarding the influence of channel morphology on ice conveyance and bridging. The morphologies considered are...

Mammals and long‐distance over‐water colonization: The case for rafting dispersal; the case against phantom causeways

AbstractIn the absence of evidence suggesting former ice or land bridges, the colonization of remote landmasses by non‐aquatic, non‐flying vertebrates is thought to result from long‐distance over‐water rafting (LDOR). However, Mazza et al. (2019) challenge the notion that mammals can make such journeys citing their perceived physiological inadequacies. They claim that lengthy transits combined with lack of food and water plus the stresses imposed by temperature, humidity and salinity render such passages impossible. We, though, contend that this reasoning is wrong. The few cases where LDOR has been invoked for mammal colonization have all involved small‐bodied animals, several of which are able to drastically reduce their metabolic rates through torpor/hibernation when food and water are scarce. Furthermore, there may be sustenance. Crucially, LDOR obviates the need for miraculous short‐lived causeways and the attendant issue of unrecognized large‐scale bidirectional invasions being made by other organisms that had access to the conduits.

Experimental investigation of condensation and freezing phenomena on hydrophilic and hydrophobic graphene coating

Graphene possesses exceptional electrical, mechanical, thermal, optical and chemical properties with potential for a wide range of applications. While most of the above properties are relatively well studied in past decade, it’s wetting phenomena and surface interactions with water molecules and droplets are still not understood. Graphene has potential for improving performance and saving energy in applications such as, frost delaying, aviation/transportation, and condensate harvesting. In the present study, surface engineering has been applied via graphene coatings to reveal new insight into condensation and freezing dynamics. The tests have been conducted in presence of non-condensable gases (air) at different relative humidity (RH), since RH significantly changes the nucleation energy barrier as well as the nucleation site density. Two sets of graphene coatings on quartz and silicon oxide surface were used to study the condensation and freezing dynamics. Droplet growth was followed by initial nucleation, direct growth, coalescence, and then sweeping off the surface. Later, the effect of ice bridging length, individual ice bridge velocity, and droplet diameter on frosting dynamics were explored for hydrophilic graphene surfaces. A ∼1.6× freezing delay was observed for the hydrophilic graphene coating at a temperature of 271 K and 40% RH compared to a temperature of 271 K and 60% RH. The hydrophobic graphene coating slows the inter-droplet wave propagation and delays frost formation at 60% RH compared to hydrophilic graphene coating. A maximum of ∼3.65× freezing delay was observed for InkJet-printed graphene (IPG) surface compared to hydrophilic graphene surface at the same freezing temperature due to fewer ice bridging instances and jumping droplet phenomenon. Both hydrophobic and hydrophilic graphene surfaces delay freezing compared to a plain silicon surface under same operating conditions. Moreover, the present study has found that surface energy play a more significant role in condensate harvesting compared to relative humidity. This result promises the applicability of engineered graphene surface for significant energy savings in frost delaying, thermal management, and condensate harvesting applications.

Accelerated freezing due to droplet pinning on a nanopillared surface

The freezing process is significantly influenced by environmental factors and surface morphologies. At atmospheric pressure, a surface below the dew and freezing point temperature for a given relative humidity nucleates water droplets heterogeneously on the surface and then freezes. This paper examines the effect of nanostructured surfaces on the nucleation, growth, and subsequent freezing processes. Microsphere Photolithography (MPL) is used to pattern arrays of silica nanopillars. This technique uses a self-assembled lattice of microspheres to focus UV radiation to an array of photonic jets in photoresist. Silica is deposited using e-beam evaporation and lift-off. The samples were placed on a freezing stage at an atmospheric temperature of 22±0.5°C and relative humidities of 40% or 60%. The nanopillar surfaces had a significant effect on droplet dynamics and freezing behavior with freezing accelerated by an order of magnitude compared to a plain hydrophilic surface at 60% RH where the ice bridges need to cover a larger void for the propagation of the freezing front within the growing droplets. By pinning droplets, coalescence is suppressed for the nanopillared surface, altering the size distribution of droplets and accelerating the freezing process. The main mechanism affecting freezing characteristics was the pinning behavior of the nanopillared surface.

Condensation Frosting Characteristics of SAM-Coated Nanostructured Superhydrophobic Surface

The present study aims to experimentally investigate the condensation frosting characteristics of the SAM-coated superhydrophobic surfaces under various environmental conditions. The extensive experiments were carried out under the well-controlled conditions with the surface temperature ranging from [Formula: see text]C to [Formula: see text]C, the relative humidity of 60%, and the air temperature of 24[Formula: see text]C. The dynamics of condensation frosting was analyzed from the captured images by using CMOS camera. From the results, it was found that even if the substrate remained at a subfreezing temperature, the spontaneous freezing of supercooled condensates did not occur because of the free energy barrier of ice embryo at the interface of the substrate-supercooled droplet. The onset of condensate freezing was also triggered by probabilistic ice nucleation. In particular, the delay of the onset time of freezing was found for the nanostructured superhydrophobic surface and substantially dependent on the coolant temperature. Moreover, it observed the presence of an inter-droplet ice bridging between a frozen droplet and neighboring supercooled droplets.

Delayed condensation and frost formation on superhydrophobic carbon soot coatings by controlling the presence of hydrophilic active sites

Condensation frosting is an undesired natural phenomenon that could be impeded efficiently using appropriate wettability and morphologically patterned surfaces. The icephobic properties of carbon soot and the fabrication scalability of its synthesis method are a good foundation for anti-frosting applications; however, the fundamentals of frost growth and spreading on sooted surfaces have not been examined yet. In this study, we investigate the anti-frosting performance of three groups of superhydrophobic soot coatings by means of 16 MHz quartz crystal microbalances (QCMs). The analysis of the real-time sensor signal of each soot coated QCM pattern shows that frost formation and its propagation velocity depend on the quantity of oxygen functionalities and structural defects in the material. In turn, the reduction of both parameters shifts the onset of frost growth to temperatures below −20 °C, whereas the interdroplet ice bridging is slowed by a factor of four. Moreover, high-resolution scanning electron micrographs of the samples imply delamination upon defrosting of the soot with spherical-like morphology via polar interactions driven mechanism. These results reveal an opportunity for control of frost incipiency on sooted surfaces by adjusting the synthesis conditions and depositing soot coatings with as low as possible content of hydrophilic active sites.

Ice bridges and ridges in the Maxwell-EB sea ice rheology

Abstract. This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB), is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a Mohr–Coulomb damage criterion that allows for pure (uniaxial and biaxial) tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.

Formation of sea ice bridges in narrow straits in response to wind and water stresses

AbstractIce bridges are rigid structures composed of sea ice that form seasonally in the many straits and channels of the Canadian Arctic Archipelago. Driven primarily by atmospheric stresses, these ice bridges are formed when sufficiently thick ice “jams” during the course of its flow between land masses, resulting in a region of stationary compacted ice that is separated from a region of flowing open water (a polynya) by a static arch. Using a continuum description of sea ice that is widely used in climate modeling, we present an asymptotic theory of the process of formation of such bridges in slender channels when the motion of the ice is driven by external wind and water stresses. We show that for an arbitrary channel shape, ice bridges can only form within a range of ice properties that is determined by the channel geometry and the external stress. We then compare the results of our theory with direct numerical simulations and observational evidence. Finally, we provide simple analytical expressions for the mean velocity of the ice flow as a function of the channel shape, the properties of the ice, and the wind and water stresses along the channel.

Frost spreading on microscale wettability/morphology patterned surfaces

Frost on a solid surface spreads essentially via building up ice bridges between condensed droplets. Modulation of condensate droplet distributions is thus an effective approach to control frost spreading. Here, we investigate the effects of both surface wettability and morphological patterns on the frost spreading velocity for various substrate surface temperatures. Our experimental results showed that the morphological patterned surfaces drastically retard frost spreading while the effect of the wettability patterned surfaces is not significant. The frost spreading velocity increases with decreasing substrate temperature on the smooth surfaces and the wettability patterned surfaces. The morphology patterned surface effectively resists frost spreading over a wide range of subcooled temperatures. A simple model is proposed to elaborate the effects of wettability, morphology, and temperature on the frost spreading velocity and the model is found to be in reasonable agreement with our experiments. Additionally, microphotography reveals ice bridging regimes in different cases. Our findings facilitate understanding of the frost spreading dynamics which can lead to the novel designs of frost-free surfaces.

Wind-Driven Formation of Ice Bridges in Straits.

Ice bridges are static structures composed of tightly packed sea ice that can form during the course of its flow through a narrow strait. Despite their important role in local ecology and climate, the formation and breakup of ice bridges is not well understood and has proved difficult to predict. Using long-wave approximations and a continuum description of sea ice dynamics, we develop a one-dimensional theory for the wind-driven formation of ice bridges in narrow straits, which is verified against direct numerical simulations. We show that for a given wind stress and minimum and maximum channel widths, a steady-state ice bridge can only form beyond a critical value of the thickness and the compactness of the ice field. The theory also makes quantitative predictions for ice fluxes, which are particularly useful to estimate the ice export associated with the breakup of ice bridges. We note that similar ideas are applicable to dense granular flows in confined geometries.

How Ice Bridges Form

How Ice Bridges Form

Investigation on shed icicle characteristics and induced surface discharges along a suspension insulator string during ice accretion

This investigation focuses on the dynamic process of ice accretion and induced surface discharges along a suspension insulator string in relation with the icicle characteristics in icing conditions. Using a high-speed camera to record the insulator performance, the growth parameters of icicles at different shed edges were calculated and the characteristics of surface discharges were analysed with regards to the lapse time of ice accretion. It was found that the electric field strength can be quickly enhanced to the threshold value of air breakdown strength at the initial stage of ice accumulation, resulting in weak and unstable discharges at the air gaps between the icicles and the insulator shed surface. As the icicle kept elongating toward ice bridging, the discharges became stronger and more stable. The obtained results will be helpful to improve the operating safety of suspension insulators of power networks subjected to icing.

On Localized Vapor Pressure Gradients Governing Condensation and Frost Phenomena.

Interdroplet vapor pressure gradients are the driving mechanism for several phase-change phenomena such as condensation dry zones, interdroplet ice bridging, dry zones around ice, and frost halos. Despite the fundamental nature of the underlying pressure gradients, the majority of studies on these emerging phenomena have been primarily empirical. Using classical nucleation theory and Becker-Döring embryo formation kinetics, here we calculate the pressure field for all possible modes of condensation and desublimation in order to gain fundamental insight into how pressure gradients govern the behavior of dry zones, condensation frosting, and frost halos. Our findings reveal that in a variety of phase-change systems the thermodynamically favorable mode of nucleation can switch between condensation and desublimation depending upon the temperature and wettability of the surface. The calculated pressure field is used to model the length of a dry zone around liquid or ice droplets over a broad parameter space. The long-standing question of whether the vapor pressure at the interface of growing frost is saturated or supersaturated is resolved by considering the kinetics of interdroplet ice bridging. Finally, on the basis of theoretical calculations, we propose that there exists a new mode of frost halo that is yet to be experimentally observed; a bimodal phase map is developed, demonstrating its dependence on the temperature and wettability of the underlying substrate. We hope that the model and predictions contained herein will assist future efforts to exploit localized vapor pressure gradients for the design of spatially controlled or antifrosting phase-change systems.

Nonlinear characteristics of leakage current for flashover monitoring of ice-covered suspension insulators

This paper investigates nonlinear characteristics of leakage current (LC) for analyzing and monitoring AC flashover performance of ice-covered suspension insulators. The experiments were carried out in a cold climate room of CIGELE Laboratories according to the methods recommended by IEEE Std. 1783/2009. The maximum withstand voltage (V MW = 81 kV rms ) and minimum flashover voltage (V MF = 84 kV rms ) were obtained to reflect electrical performance of suspension insulators under a most dangerous ice type. The ice accretion process, the length, width and number of icicles associated with the appearance of partial discharges were observed and discussed to present the final formation of a relatively uniform ice layer and vertical icicles along the insulator string. This ice-covered insulator string was characterized by air gaps on the grounded-side shed space and complete ice bridging of the other shed spaces, which have significant influence on the development of arcing discharges leading to flashover. Nonlinear characteristics of LC were analyzed by using a recurrent plot (RP) technique, which graphically gives nonlinear variations of LC on RP maps as well as nonlinear indicators for quantitative prediction of the flashover. The obtained results reveal that dynamic behavior (initiation, propagation, extinguishment and re-ignition) of arcing discharges on ice-covered suspension insulators can be visually reflected by the texture transition of RP maps of LC, which correlate with different stages during the flashover process. The quantitative indicators including a recurrence rate (RR) value lower than 0.24 and a deterministic (DET) value lower than 0.965 are proposed as the predictive values to indicate the highest probability of flashover occurrence. The results obtained will be helpful to predict most hazards of ice-covered outdoor insulators; this is one of monitoring methods based on LC characteristic analysis.

Controlling condensation and frost growth with chemical micropatterns.

In-plane frost growth on chilled hydrophobic surfaces is an inter-droplet phenomenon, where frozen droplets harvest water from neighboring supercooled liquid droplets to grow ice bridges that propagate across the surface in a chain reaction. To date, no surface has been able to passively prevent the in-plane growth of ice bridges across the population of supercooled condensate. Here, we demonstrate that when the separation between adjacent nucleation sites for supercooled condensate is properly controlled with chemical micropatterns prior to freezing, inter-droplet ice bridging can be slowed and even halted entirely. Since the edge-to-edge separation between adjacent supercooled droplets decreases with growth time, deliberately triggering an early freezing event to minimize the size of nascent condensation was also necessary. These findings reveal that inter-droplet frost growth can be passively suppressed by designing surfaces to spatially control nucleation sites and by temporally controlling the onset of freezing events.

Isolation of peripheral populations of Canada lynx (Lynx canadensis)

Landscape barriers to gene flow, such as rivers, can affect animal populations by limiting the potential for rescue of these isolated populations. We tested the riverine barrier hypothesis, predicting that the St. Lawrence River in eastern Canada would cause genetic divergence of Canada lynx (Lynx canadensis Kerr, 1792) populations by restricting dispersal and gene flow. We sampled 558 lynx from eastern Canada and genotyped these at 14 microsatellite loci. We found three genetic clusters, defined by the St. Lawrence River and the Strait of Belle Isle, a waterway separating Newfoundland from mainland Canada. However, these waterways were not absolute barriers, as we found 24 individuals that appeared to have crossed them. Peripheral populations of lynx are threatened in parts of Canada and the USA, and it is thought that these populations are maintained by immigration from the core. Our findings suggest that in eastern North America, rescue might be less likely because the St. Lawrence River restricts dispersal. We found that ice cover was often sufficient to allow lynx to walk across the ice in winter. If lynx used ice bridges in winter, then climate warming could cause a reduction in the extent and longevity of river and sea ice, further isolating these peripheral lynx populations.

Physical-geographical aspects of formation of artificial firn-ice massives

Построены карты суточной производительности намораживания искусственного фирна методом зимнего дождевания для каждого месяца с отрицательной температурой воздуха ниже −5 °С на территории России. Оценена потенциально возможная производительность намораживания ледяного материала методами зимнего дождевания и тонкослойным наливом в современных климатических условиях. Рассмотрена роль климатических изменений в снижении производительности намораживания в разных регионах России. Анализ климатических условий в 1961–2000 и 2001–2010 гг. показал, что на территории России производительность намораживания искусственного фирна снизилась с 5–10% в Сибири до 20–40% в центральных и южных районах Европейской территории России.

Dimensioning of booster sheds for icing protection of post station insulators

The main objective of this paper is to introduce an analytical and numerical method to calculate the diameter and position of booster sheds (BSs) on post station insulators under heavy icing conditions. Numerical simulations using the finite element method (FEM), implemented by the commercial software Comsol Multiphysics, were performed to calculate the influence of BSs on voltage drops along two units of a standard post insulator under heavy icing conditions. The shape of ice accretion and icicles used in the present study were based on laboratory tests carried out at CIGELE. The presented simulations and analytical calculations seem to be efficient options to quantify the effects of the electric field and ice bridging on the dimensioning of the BSs along the post insulator. Based on the obtained results, the electric field strength would be the main factor involved for BSs close to the HV electrode whereas ice-bridging (icicle length) would be the main one for those close to the ground electrode.