Sublimation Rate Research Articles

Sublimation-driven morphogenesis of Zen stones on ice surfaces

In this article, the formation of Zen stones on frozen lakes and the shape of the resulting pedestal are elucidated. Zen stones are natural structures in which a stone, initially resting on an ice surface, ends up balanced atop a narrow ice pedestal. We provide a physical explanation for their formation, sometimes believed to be caused by the melting of the ice. Instead, we show that slow surface sublimation is indeed the physical mechanism responsible for the differential ablation. Far from the stone, the sublimation rate is governed by the diffuse sunlight, while in its vicinity, the shade it creates inhibits the sublimation process. We reproduced the phenomenon in laboratory-scale experiments conducted in a lyophilizer and studied the dynamics of the morphogenesis. In this apparatus, which imposes controlled constant sublimation rate, a variety of model stones consisting of metal disks was used, which allows us to rule out the possible influence of the thermal conduction in the morphogenesis process. Instead, we show that the stone only acts as an umbrella whose shade hinders the sublimation, hence protecting the ice underneath, which leads to the formation of the pedestal. Numerical simulations, in which the local ablation rate of the surface depends solely on the visible portion of the sky, allow us to study the influence of the shape of the stone on the formation of the ice foot. Finally, we show that the far-infrared black-body irradiance of the stone itself leads to the formation of a depression surrounding the pedestal.

Wireless sensor networks for pharmaceutical lyophilization: Quantification of local gas pressure and temperature in primary drying

Wireless sensor networks have become prolific in a wide range of industrial processes and offer several key advantages over their wired counterparts in terms of positioning flexibility, modularity, interconnectivity, and data routing. We demonstrate their utility in pharmaceutical lyophilization by developing a series of wireless devices to measure spatial variations in gas pressure and temperature during primary drying. The influence of shelf temperature, chamber pressure, excipient concentration, and dryer configuration are explored for various representative cycles using a laboratory-scale pharmaceutical lyophilizer. Pressure and temperature variations across the shelf for these cases are shown to vary up to 1.2 Pa and 10 °C, respectively. Experimental measurements are supported by computational fluid dynamics simulations to reveal the mechanisms driving the vapor flow. The measurements and simulation data are then combined to estimate the shelf-wise sublimation rate in the inverse sense to within a deviation of 3% based on comparison with gravimetric data. We then apply the sublimation rate profile to obtain the vial heat transfer coefficient and product mass transfer resistance for a 5% w/v mannitol formulation. Finally, these parameters are applied to a one-dimensional quasi-steady heat transfer model to predict the evolution of the product temperature over the course of primary drying. Thermocouple measurements of product temperature are compared directly to the simulated data and demonstrate accuracy comparable to existing published one-dimensional models.

Reexamination of self-assembly of nucleator and its influence on the crystallization of polypropylene

In this study, the self-assembly phenomenon of nucleator N, N′-dicyclohexylterephthalamide (DCHT) in isotactic polypropylene (iPP) has been investigated and reexamined from the viewpoint of sublimation and condensation. A correlation between the crystallization temperature (Tc) of iPP and the final heating temperature (Tf) was constructed, in which a “V” shape phenomenon and its dependence on DCHT concentration are presented. With the increase of DCHT concentration, both the onset and the bottom of the “V” shift to a higher Tf, which is ascribed to faster saturation of DCHT vapor or slower sublimation rate of DCHT at same Tf for the hybrids with high DCHT concentration. A phase diagram distinguishing various assembly structures of DCHT with different nucleation ability is proposed based on the DSC and optical results, in which four regions are included. Considering the strong hydrogen bonding between DCHT molecules, a schematic condensation mechanism for the particular needle-like, agglomerates and flower-like structures were presented. Rheology results also provide indirect evidence to the phase transformation or condensation process, where two step condensation is observed and the lower temperature step could be attributed to the formation of agglomerates structure due to the “cage effect” of iPP supercooling melt to DCHT vapor.

LBT Reveals Large Dust Particles and a High Mass-loss Rate for K2-22 b

Abstract The disintegrating planet candidate K2-22 b shows periodic and stochastic transits best explained by an escaping debris cloud. However, the mechanism that creates the debris cloud is unknown. The grain size of the debris as well as its sublimation rate can be helpful in understanding the environment that disintegrates the planet. Here, we present simultaneous photometry with the g band at 0.48 μm and K S band at 2.1 μm using the Large Binocular Telescope. During an event with very low dust activity, we put a new upper limit on the size of the planet of 0.71 R ⊕ or 4500 km. We also detected a medium depth transit that can be used to constrain the dust particle sizes. We find that the median particle size must be larger than about 0.5–1.0 μm, depending on the composition of the debris. This leads to a high mass-loss rate of about 3 × 108 kg s−1, which is consistent with hydrodynamic escape models. If they are produced by some alternate mechanism such as explosive volcanism, it would require extraordinary geological activity. Combining our upper limits on the planet size with the high mass-loss rate, we find a lifetime of the planet of less than 370 Myr. This drops to just 21 Myr when adopting the 0.02 M ⊕ mass predicted from hydrodynamical models.

High temperature failure modes of In2O3 thin films and improved thermal stability using Al2O3/ZrO2 protective layers

The limiting temperature of an In2O3 thin film sensor is much lower than its melting point. Herein, the failure modes of In2O3 thin films at high temperatures, including sublimation and changes in composition, have been studied. The edge and surface layer sublimation rates increased dramatically at 1350 °C, indicating that it is the limiting temperature of no-protection In2O3 films. In addition, oxygen atoms will escape from In2O3 thin films at high temperatures, forming oxygen vacancies. As the main current carrier type in In2O3, the increasing number of oxygen vacancies affects the resistance of In2O3 thin film sensors. To solve these problems and promote the high temperature performance of In2O3 thin films, protection methods based on Al2O3 and ZrO2 layers have been investigated. The ZrO2 protective layer alleviated the serious considerable sublimation of In2O3 thin films at high temperatures, and the Al2O3 protective layer was beneficial for reduction the escape of oxygen atoms. Finally, different protection layers were evaluated by in-situ resistivity measurements of In2O3 thin films at high temperatures. The resistance of the In2O3 thin film resistor with a protective multilayer consisting of Al2O3 and ZrO2 remained stable at 1360 °C, verifying the protection method effectively increased the thermal stability of In2O3 thin films.

Exploring the Effect of Dehydration on Water Migrating Property and Protein Changes of Large Yellow Croaker (Pseudosciaena crocea) during Frozen Storage.

This study aimed to explore the effect of dehydration on the water migrating property and protein changes of large yellow croaker during frozen storage. A freeze-dryer was used to accelerate experiments, which was isolated from oxygen and excluded the effects of protein oxidation. After dehydration time (3, 9, 18, and 30 h) for both fast- and slow-freezing samples, the results showed that the ice sublimation of samples containing small ice crystals was faster than that of samples containing large ice crystals in the early stages of dehydration, but in the latest stage, there was an opposite trend. The results indicated that dehydration reduced the water freedom degrees and water–protein interaction. At the same time, dehydration had a significant effect on protein secondary and tertiary structures. The significant increase in surface hydrophobicity and particle size indicated that dehydration exacerbated myofibrillar protein aggregation. The ΔH1 values (from 1.275 to 0.834 J/g for slow-freezing group and from 1.129 to 0.855 J/g for fast-freezing group) decreased gradually as the dehydration time extended, indicating the decrease in protein thermal stability. Additionally, significant protein degradation occurred when the water content of the sample decreased to a certain level. This study showed that ice crystal size had an important effect on the rate of ice sublimation, and the occurrence of dehydration during frozen storage accelerated the water loss and the decrease in protein stability.

ESTUDANDO A SUBLIMAÇÃO DE DIÓXIDO DE CARBONO

Background: The utilization of dry ice in cooling and storage units requires adjusting the intensity of sublimation due to the requirements of prudently using CO2 to maintain preset thermal conditions. Aim: When designing a carbon dioxide cycle, it is essential to consider the influence of thermal gradients on the adsorption and desorption of carbon dioxide. Methods: tests were conducted to study the production and sublimation of carbon dioxide. The testes were aimed to define the temperature relation of the dry ice sublimation period, the density of pressed СО2, and the humidity of the environment and concentration. Results and Discussion: According to the obtained test data, there was a linear relationship between the sublimation intensity and the ambient air temperature in the specified conditions. The effect of moisture condensation on the sublimation rate appeared weaker than expected, for the amount of moisture on the surface of the specimens was insignificant. The heat exchange was intensified by the fall of hoarfrost and the related surface expansion. However, much moisture froze out without reaching the dry ice surface, and the formed layer of ice formed a heat insulation surface, and the sublimation under that layer was less intensive. The direct influence of sublimation came from the pressure at which a specific specimen was formed; however, 75 kN pressure was optimal. Conclusion: Despite higher weight losses during the storage, the difference in spent energy is more critical than 90 kN. The factor no less important was the carbon dioxide storage temperature. The maximal sublimation time of a 55 g cylinder formed at 75 kN and stored at – 80°С was 135 hours, much higher than at similar parameters but at -60°С. That said, the amount of energy spent on operating a low-temperature chamber was almost identical.

STUDYING THE SUBLIMATION OF CARBON DIOXIDE

Background: The utilization of dry ice in cooling and storage units requires adjusting the intensity of sublimation due to the requirements of prudently using CO2 to maintain preset thermal conditions. Aim: When designing a carbon dioxide cycle, it is essential to consider the influence of thermal gradients on the adsorption and desorption of carbon dioxide. Methods: tests were conducted to study the production and sublimation of carbon dioxide. The testes were aimed to define the temperature relation of the dry ice sublimation period, the density of pressed СО2, and the humidity of the environment and concentration. Results and Discussion: According to the obtained test data, there was a linear relationship between the sublimation intensity and the ambient air temperature in the specified conditions. The effect of moisture condensation on the sublimation rate appeared weaker than expected, for the amount of moisture on the surface of the specimens was insignificant. The heat exchange was intensified by the fall of hoarfrost and the related surface expansion. However, much moisture froze out without reaching the dry ice surface, and the formed layer of ice formed a heat insulation surface, and the sublimation under that layer was less intensive. The direct influence of sublimation came from the pressure at which a specific specimen was formed; however, 75 kN pressure was optimal. Conclusion: Despite higher weight losses during the storage, the difference in spent energy is more critical than 90 kN. The factor no less important was the carbon dioxide storage temperature. The maximal sublimation time of a 55 g cylinder formed at 75 kN and stored at – 80°С was 135 hours, much higher than at similar parameters but at -60°С. That said, the amount of energy spent on operating a low-temperature chamber was almost identical.

Sublimation of composite ice and its influence on performance of ice shells

The long-span ice composite shell structure is a new type of ice and snow structure developed in recent years. The engineering practice of ice composite shell shows that sublimation is one of the important reasons for its damage and even collapse. In this paper, we firstly supplemented the existing H-K equation and obtained the revised ice sublimation equation through indoor evaporative plate experiment considering the influence of admixtures and wind speed. Afterwards, combining the simulations of solar radiation and CFD, the numerical simulation of sublimation distribution on the surface of were realized by programming in Grasshopper platform. During sublimation, the thickness of the ice composite shell decreases by 0.38 mm every 10 days and the sublimation rate on the sunny side was 1.7 times that on the shady side. Finally, the static performance and stability of the sublimated ice composite spherical shell were analyzed. After 70 days of sublimation, the thickness of the ice composite shell structure becomes thinner and uneven, which leads its sensitivity to external load increases.

Modified iron-molybdate catalysts with various metal oxides by a mechanochemical method: enhanced formaldehyde yield in methanol partial oxidation

A mechanochemical method was employed to prepare modified iron molybdate catalysts with various metal salts as precursors. The physicochemical properties of the iron molybdate catalysts were characterized, and their performances in catalyzing the reaction from methanol to formaldehyde (HCHO) were evaluated. Iron molybdate catalysts doped with Co(NO3)2 · 6H2Oand Al(NO3)3 · 9H2O resulted in high HCHO yields. Compared with a commercial catalyst, the HCHO yields in the reaction with the modified catalyst at an optimal Co/Mo molar ratio reached 97.37%. According to chemical state analysis, the formation of CoO and the efficient decrease in the MoO3 sublimation rate could be important factors enhancing the HCHO yield in reactions catalyzed with iron molybdate doped with different Co/Mo mole ratios.

The Spatio-Temporal Variability of Frost Blisters in a Perennial Frozen Lake along the Antarctic Coast as Indicator of the Groundwater Supply

Remote sensing, and unmanned aerial vehicles (UAVs) in particular, can be a valid tool for assessing the dynamics of cryotic features as frost blisters and to monitor the surface changes and the sublimation rates on perennially frozen lakes that host important ecosystems. In this paper, through the use of these remote sensing techniques, we aim to understand the type of groundwater supply of an Antarctic perennial frozen lake that encompasses two frost blisters (M1 and M2) through the temporal analysis of the features’ elevation changes (frost blisters and lake ice level). The frozen lake is located at Boulder Clay (northern Victoria Land, Antarctica). We relied on several photogrammetric models, past satellite images and ground pictures to conduct differencing of digital elevation models, areal variations and pixel counting. In addition, in situ measurements of the ice sublimation or snow accumulation were carried out. The two frost blisters showed different elevation trends with M1 higher in the past (1996–2004) than recently (2014–2019), while M2 showed an opposite trend, similarly to the ice level. Indeed, the linear regression between M2 elevation changes and the ice level variation was statistically significant, as well as with the annual thawing degree days, while M1 did not show significant results. From these results we can infer that the groundwater supply of M1 can be related to a sublake open talik (hydraulic system) as confirmed also by pressurized brines found below M1, during a drilling in summer 2019. For M2 the groundwater flow is still not completely clear although the hydrostatic system seems the easiest explanation as well as for the uplift of the lake ice.

The lifecycle of hollows on Mercury: An evaluation of candidate volatile phases and a novel model of formation

On Mercury, high-reflectance, flat-floored depressions called hollows are observed nearly globally within low-reflectance material, one of Mercury’s major color units. Hollows are thought to be young, or even currently active, features that form via sublimation, or a “sublimation-like” process. The apparent abundance of sulfides within LRM combined with spectral detections of sulfides associated with hollows suggests that sulfides may be the phase responsible for hollow formation. Despite the association of sulfides with hollows, it is still not clear whether sulfides are the hollow-forming phase. To better understand which phase(s) might be responsible for hollow formation, we calculated sublimation rates for 57 candidate hollow-forming volatile phases from the surface of Mercury and as a function of depth beneath regolith lag deposits of various thicknesses. We found that stearic acid (C18H36O2), fullerenes (C60, C70), and elemental sulfur (S) have the appropriate thermophysical properties to explain hollow formation. Stearic acid and fullerenes are implausible hollow-forming phases because they are unlikely to have been delivered to or generated on Mercury in high enough volume to account for hollows. We suggest that S is most likely the phase responsible for hollow formation based on its abundance on Mercury and its thermophysical properties. We discuss the possibility that S is the phase responsible for hollow formation within the hollow-formation model framework proposed by Blewett et al. (2013). However, several potential limitations with that model lead us to suggest an alternative hollow-formation model: a subsurface heat source (most often impact-induced) generates thermal systems that drive sulfur-rich fumaroles in which S and other phases accumulate on and within the surface at night and sublimate during the day to create hollows. We call this hollow-formation model “Sublimation Cycling Around Fumarole Systems” (SCArFS). We suggest that thermal decomposition of sulfides within LRM is a main contributor to S and S-bearing gases within the proposed fumarole systems and that (re-)precipitation of sulfides may occur at the surface along hollow floors and rims.

Process optimization and transfer of freeze-drying in nested vial systems

Scale-up and transfer of freeze-drying processes is a crucial challenge in biopharma industry. With the success of small batch processing lines utilizing rack vial holding systems, further detailed knowledge about freeze-drying cycles and their scale-up for vials in a rack is required. Therefore, product temperature (TP) profiles as well as Kv values of vials nested in a Polyetheretherketon (PEEK) rack were compared to those of vials placed in a commonly used stainless steel tray. Additionally, both setups were challenged with varying fill volume and partially versus fully loaded rack. Additionally, a process developed for rack was compared to a tray freeze-drying cycle.Freeze-drying in vials placed in the rack is markedly faster for center vials and more homogeneous compared to vials in bulk tray setting, as indicated by TP and Kv values. Due to the more homogeneous drying the rack is more flexible regarding variation of the fill volume. The key point for the transfer of a freeze-drying cycle from rack to tray is to consider the higher sublimation rates in the rack by adapting chamber pressure or shelf temperature for the tray. Furthermore, transfer from one rack per shelf in a laboratory freeze-dryer to pilot scale with four racks per shelf was successful. Thus, understanding of the process in rack and tray setup was enhanced to ensure efficient scale-up and transfer of freeze-drying processes.

Equipment Capability Measurement of Laboratory Freeze-Dryers: a Comparison of Two Methods

The objective of this investigation was to evaluate two methods for measuring the maximum sublimation rate that a freeze-dryer will support—the minimum controllable pressure method and the choke point method. Both methods gave equivalent results, but the minimum controllable pressure method is preferred, since it is easier, faster, and less subjective. The ratio of chamber pressure to condenser pressure corresponding to the onset of choked flow was considerably higher in this investigation (up to about 20:1) than in previously published reports. This ratio was not affected by the location of the pressure gauge on the condenser; that is, on the foreline of the vacuum pump versus on the body of the condenser itself. The total water loss due to sublimation as measured by tunable diode laser absorption spectroscopy was consistently within 5% of gravimetrically determined weight loss, regardless of whether the measurement took place during choked versus non-choked process conditions.

Experimental and numerical study of insulation packages containing dry ice pellets

Shippers of healthcare and food products, in most cases, have regulatory responsibility to ensure quality by maintaining product’s temperature during transportation. Dry ice is commonly used as cold source inside the insulated cold-storage packages which are often transported via air freights. But dry ice sublimation can lead to asphyxiation of crew members or passengers due to which, several regulatory bodies have recommended safe limits of dry ice aboard aircraft mainly based on rule-of-thumb. Prior to establishing the limits, understanding dry ice sublimation is of paramount importance. Therefore the current research, experimentally and numerically explores dry ice sublimation packed in commonly encountered containers made of polystyrene foam. A three dimensional quasi-steady model is developed to predict variation of dry ice mass inside the insulation packages. The model is validated against mass and temperature measurements performed on two types of insulation packages made of different material and geometry. The model is able to fairly predict the reduction in dry ice mass over time and the end-of-sublimation time. Both experimental and numerical results show that the sublimation rate of dry ice can be reduced by covering the inner walls of insulation package with a reflective layer like aluminized mylar foil. The good agreement between model and experimental data of dry ice mass variation makes it possible for the shippers to use the modeling approach in estimating sublimation rates of dry ice.

Effect of air parameters on ice sublimation in ice rink

This study aims at the sublimation rate of ice and analyzes the influence of supply air and ice parameters on ice surface smoothness. The sublimation rate can be expressed as the product of the sublimation coefficient and humidity ratio difference. COMSOL Multiphysics is adopted as a simulation tool to calculate the associated ice sublimation rate. In ice rinks, the sublimation coefficient is 0.1–0.2 mm/(h·kPa), and the sublimation rate is 0–0.07 mm/h. The results show that the main factor affecting the sublimation coefficient is air velocity over the ice surface. Therefore, the ice sublimation can be decreased by reducing air velocity and decreasing humidity ratio difference between the air and ice surface. The aforementioned findings were applied in an actual curling venue to reduce the sublimation of the ice surface, and the accumulated sublimation within 10 h was reduced from 0.24 mm to 0.016 mm, which effectively solved the problem of ice surface unevenness. This study working on the ice sublimation rate provides inspiration for maintaining the ice stability in ice rinks and improving the quality of venues.

Tafoni weathering is an azonal process: Examples from Antarctica, Sardinia and Australia

Cavernous weathering (tafoni) is described from coarse-grained granitic bedrock in Northern Victoria Land (Antarctica), northern Sardinia (Italy) and southwestern Australia. It also occurs elsewhere in the world and on other coarse-grained lithologies. The cause of this unusual in-situ flaking and granular disintegration is problematic. Azonal conditions appear to be: (1) the presence of salt, (2) aridity and (3) high evaporation and sublimation rates. Zonal (site-specific) considerations are: (1) snow may transport salts far inland in Antarctica and (2) epilithic and endolithic lichen growth may assist biological weathering in Sardinia and Antarctica. In stable landscapes of great antiquity, such as southwestern Australia, tafoni-like forms appear to have developed over millions of years; they suggest that salts in solution move slowly and continuously towards the surface where they evaporate. Combinations of these conditions result in tafoni in these different environments.

Light emission and structural changes in a suspended multiwall carbon nanotube on application of electric current

Light emission from a suspended multiwall carbon nanotube (MWCNT) on application of electric current was studied by in-situ transmission electron microscopy combined with optical spectroscopy. Excessive Joule heating led to layer-by-layer sublimation of the outer and/or inner shells of the MWCNT. The temperature during sublimation was estimated to be more than 2100 K from the sublimation rate of the MWCNT. Light emission spectra observed while applying an electric current to the MWCNT were composed of blackbody radiation and characteristic peaks. The energies of the peaks in the spectra were close to energy gaps between van Hove singularities calculated from the diameters of the constituent shells of the MWCNT, suggesting that the peaks in the spectra can be attributed to interband transitions between van Hove singularities in the electronic density of states in the MWCNT.

Mapping of Ice Storage Processes on the Moon with Time-dependent Temperatures

Abstract Lunar cold traps are defined by extremely low time-integrated sublimation loss, so that water ice is expected to accumulate in them. Due to the strong dependence of the sublimation rate on temperature, they have heretofore been delineated by the peak rather than the time-averaged sublimation rate. Here, time-averaged sublimation rates are calculated for the south polar region of the Moon based on 11 yr of Diviner surface temperature measurements. Data for each spatial pixel are binned according to subsolar (diurnal) and ecliptic (seasonal) longitude. Frequency-domain filtering of temperature time series is applied to interpolate and smooth the data set. The cold trap area is 17,000 km2 from 80°S to the south pole, about 24% larger than defined by peak temperature. In addition, subsurface ice stability is mapped based on solutions of the heat equation with Diviner surface temperatures as the upper boundary condition. Even a thin layer of dust reduces the sublimation loss dramatically. A third potential mechanism for ice storage, vapor pumping by temperature cycles, is also mapped, based on a model for the time-variable population of adsorbed water molecules on the lunar surface. The area of significant pumping is estimated to be 96,000 km2 poleward of 80°S. In summary, a new processing technique has been developed that exploits information about the time variability of lunar surface temperatures measured by Diviner, and it results in new maps for the geographic distribution of potential water-ice deposits in the south polar region of the Moon.

Impact of packing density on primary drying rate

Abstract This work aimed to determine the effect of packing density on the sublimation rate in a laboratory freeze dryer. Total amount of sublimed water was determined by gravimetric method while a total of seven experiments were performed under the same conditions (pressure, temperature, and drying time), at different configuration of the vials. The experiments confirmed that the higher the packing density, the lower the drying rate, and vice versa, the lower the packing density, the higher the drying rate. The effect of vials packing density was confirmed by experiments using a plastic rack, while the vials were separated and thus the packing density was lower. In this case, the drying rate was more homogeneous, which contributes to the higher quality of the final product.