Toward a theory of the evolution of drop morphology and splintering by freezing

2021 ◽  
Author(s):  
Alexander Staroselsky ◽  
Ranadip Acharya ◽  
Alexander Khain
Keyword(s):  
Drop Size ◽  
Phase Field Model ◽  
Surface Fluxes ◽  
Freezing Process ◽  
Drop Surface ◽  
Surface Nucleation ◽  
Planar Front ◽  
Bulk Nucleation ◽  
Ice Shell

AbstractThe drop freezing process is described by a phase-field model. Two cases are considered: when the freezing is triggered by central nucleation and when nucleation occurs on the drop surface. Depending on the environmental temperature and drop size, different morphological structures develop. Detailed dendritic growth was simulated at the first stage of drop freezing. Independent of the nucleation location, a decrease in temperature within the range from ~ −5 to −25°C led to an increase in the number of dendrites and a decrease in their width and the interdendritic space. At temperatures lower than about −25°C, a planar front developed following surface nucleation, while dendrites formed a granular-like structure with small interdendritic distances following bulk nucleation. An ice shell grew in at the same time (but slower) as dendrites following surface nucleation, while it started forming once the dendrites have reached the drop surface in the case of central nucleation. The formed ice morphology at the first freezing stage predefined the splintering probability. We assume that stresses needed to break the ice shell arose from freezing of the water in the interdendritic spaces. Under this assumption, the number of possible splinters/fragments was proportional to the number of dendrites, and the maximum rate of splintering/fragmentation occurred within a temperature range of about −10 °C to −20°C, in agreement with available laboratory and in situ measurements. At temperatures < −25°C, freezing did not lead to the formation of significant stresses, making splintering unlikely. The number of dendrites increased with drop size, causing a corresponding increase in the number of splinters. Examples of morphology that favors drop cracking are presented, and the duration of the freezing stages is evaluated. Sensitivity of the freezing process to the surface fluxes is discussed.

Influence of Pressure on the Crystallization in SiO2f/SiO2 Composites

2007 ◽  
Vol 336-338 ◽  
pp. 1236-1238
Author(s):  
Chang Ming Xu ◽  
Shi Wei Wang ◽  
Xiao Xian Huang ◽  
Jing Kun Guo
Keyword(s):  
Phase Composition ◽  
Crystalline Phase ◽  
Hot Pressing ◽  
Crystallization Behavior ◽  
Nucleation Mechanism ◽  
Composition Analysis ◽  
Pressing Pressure ◽  
Surface Nucleation ◽  
Bulk Nucleation ◽  
Phase Composition Analysis

The influence of pressure on the crystallization behavior in SiO2f/SiO2 composites hotpressed at 1350°C was studied. The crystalline phase composition analysis on SiO2f/SiO2 composites revealed that the formation of cristobalite was promoted when the hot-pressing pressure ≤ 12 MPa, however suppressed with higher pressure applied. It can be ascribed to the nucleation mechanism change from surface nucleation to bulk nucleation. Analysis on relative density as well as fracture microstructure of SiO2f/SiO2 composites confirmed the conclusion.

Differentiating Freezing Drizzle and Freezing Rain in HRRR Model Forecasts

2021 ◽  
Author(s):  
Sarah Tessendorf ◽  
Allyson Rugg ◽  
Alexei Korolev ◽  
Ivan Heckman ◽  
Courtney Weeks ◽  
...  
Keyword(s):  
Drop Size ◽  
Prediction Models ◽  
Water Drop ◽  
Weather Prediction ◽  
Supercooled Liquid ◽  
Drop Diameter ◽  
Aircraft Icing ◽  
Freezing Rain ◽  
Primary Focus

AbstractSupercooled large drop (SLD) icing poses a unique hazard for aircraft and has resulted in new regulations regarding aircraft certification to fly in regions of known or forecast SLD icing conditions. The new regulations define two SLD icing categories based upon the maximum supercooled liquid water drop diameter (Dmax): freezing drizzle (100–500 μm) and freezing rain (> 500 μm). Recent upgrades to U.S. operational numerical weather prediction models lay a foundation to provide more relevant aircraft icing guidance including the potential to predict explicit drop size. The primary focus of this paper is to evaluate a proposed method for estimating the maximum drop size from model forecast data to differentiate freezing drizzle from freezing rain conditions. Using in-situ cloud microphysical measurements collected in icing conditions during two field campaigns between January and March 2017, this study shows that the High-Resolution Rapid Refresh model is capable of distinguishing SLD icing categories of freezing drizzle and freezing rain using a Dmax extracted from the rain category of the microphysics output. It is shown that the extracted Dmax from the model correctly predicted the observed SLD icing category as much as 99% of the time when the HRRR accurately forecast SLD conditions; however, performance varied by the method to define Dmax and by the field campaign dataset used for verification.

“Sintering” Models and In-Situ Experiments: Data Assimilation for Microstructure Prediction in SLS Additive Manufacturing of Nylon Components

MRS Advances ◽  
2020 ◽  
Vol 5 (29-30) ◽  
pp. 1593-1601
Author(s):  
W. Steven Rosenthal ◽  
Francesca C. Grogan ◽  
Yulan Li ◽  
Erin I. Barker ◽  
Josef F. Christ ◽  
...  
Keyword(s):  
Adaptive Sampling ◽  
Selective Laser Sintering ◽  
Phase Field Model ◽  
Estimation Algorithm ◽  
Model Parameters ◽  
Multiple Data ◽  
In Situ Experiments ◽  
Parameter Estimation Algorithm ◽  
Microstructure Prediction

ABSTRACTSelective laser sintering methods are workhorses for additively manufacturing polymer-based components. The ease of rapid prototyping also means it is easy to produce illicit components. It is necessary to have a data-calibrated in-situ physical model of the build process in order to predict expected and defective microstructure characteristics that inform component provenance. Toward this end, sintering models are calibrated and characteristics such as component defects are explored. This is accomplished by assimilating multiple data streams, imaging analysis, and computational model predictions in an adaptive Bayesian parameter estimation algorithm. From these data sources, along with a phase-field model, bulk porosity distributions are inferred. Model parameters are constrained to physically-relevant search directions by sensitivity analysis, and then matched to predictions using adaptive sampling. Using this feedback loop, data-constrained estimates of sintering model parameters along with uncertainty bounds are obtained.

scholarly journals Comment on evidence for surface-initiated homogenous nucleation

2003 ◽  
Vol 3 (4) ◽  
pp. 3361-3372 ◽  
Author(s):  
J. E. Kay ◽  
V. Tsemekhman ◽  
B. Larson ◽  
M. Baker ◽  
B. Swanson
Keyword(s):  
Laboratory Experiments ◽  
Drop Size ◽  
Supercooled Water ◽  
Ice Nucleation ◽  
Surface Nucleation ◽  
Embryo Formation ◽  
Homogenous Nucleation ◽  
Atmospheric Data ◽  
Water Drops

Abstract. We investigate theoretical, laboratory, and atmospheric evidence for a recently proposed hypothesis: homogenous ice nucleation occurs at the surface, not in the volume, of supercooled water drops. Using existing thermodynamic arguments, laboratory experiments, and atmospheric data, we conclude that ice embryo formation at the surface cannot be confirmed or disregarded. Ice nucleation rates measured as a function of drop size in an air ambient could help distinguish between volume and surface nucleation rates.

scholarly journals Sensitivity of land surface and Cumulus schemes for Thunderstorm prediction

2016 ◽  
Vol XLI-B8 ◽  
pp. 271-275
Author(s):  
Dinesh Kumar ◽  
U. C. Mohanty ◽  
Krishan Kumar
Keyword(s):  
Land Surface ◽  
Process Model ◽  
Atmospheric Condition ◽  
Surface Fluxes ◽  
Lower Atmosphere ◽  
Freezing Process ◽  
Precipitation Process ◽  
Convective System ◽  
Cumulus Schemes ◽  
Physical Parameterizations

The cloud processes play an important role in all forms of precipitation. Its proper representation is one of the challenging tasks in mesoscale numerical simulation. Studies have revealed that mesoscale feature require proper initialization which may likely to improve the convective system rainfall forecasts. Understanding the precipitation process, model initial condition accuracy and resolved/sub grid-scale precipitation processes representation, are the important areas which needed to improve in order to represent the mesoscale features properly. Various attempts have been done in order to improve the model performance through grid resolution, physical parameterizations, etc. But it is the physical parameterizations which provide a convective atmosphere for the development and intensification of convective events. Further, physical parameterizations consist of cumulus convection, surface fluxes of heat, moisture, momentum, and vertical mixing in the planetary boundary layer (PBL). How PBL and Cumulus schemes capture the evolution of thunderstorm have been analysed by taking thunderstorm cases occurred over Kolkata, India in the year 2011. PBL and cumulus schemes were customized for WSM-6 microphysics because WSM series has been widely used in operational forecast. Results have shown that KF (PBL scheme) and WSM-6 (Cumulus Scheme) have reproduced the evolution of surface variable such as CAPE, temperature and rainfall very much like observation. Further, KF and WSM-6 scheme also provided the increased moisture availability in the lower atmosphere which was taken to higher level by strong vertical velocities providing a platform to initiate a thunderstorm much better. Overestimation of rain in WSM-6 occurs primarily because of occurrence of melting and freezing process within a deeper layer in WSM-6 scheme. These Schemes have reproduced the spatial pattern and peak rainfall coverage closer to TRMM observation. It is the the combination of WSM-6, and KF schemes which have preformed reasonably well to reproduce the right atmospheric condition for a thunderstorm leading to improved spatial and temporal rainfall over the study domain. Thus the parameterization schemes of WMS-6 and KF have shown significant improvement by capturing the location, intensity and surface meteorological parameters closer to observed details.

scholarly journals Atmospheric CO<sub>2</sub> modeling at the regional scale: an intercomparison of 5 meso-scale atmospheric models

2007 ◽  
Vol 4 (3) ◽  
pp. 1923-1952 ◽  
Author(s):  
C. Sarrat ◽  
J. Noilhan ◽  
A. J. Dolman ◽  
C. Gerbig ◽  
R. Ahmadov ◽  
...  
Keyword(s):  
Regional Scale ◽  
Potential Temperature ◽  
Surface Fluxes ◽  
Systematic Evaluation ◽  
Atmospheric Models ◽  
Experimental Protocol ◽  
Intercomparison Exercise ◽  
Meteorological Models ◽  
Meso Scale

Abstract. Atmospheric CO2 modeling in interaction with the surface fluxes, at the regional scale is developed within the frame of the European project CarboEurope-IP and its Regional Experiment component. In this context, five meso-scale meteorological models participate in an intercomparison exercise. Using a common experimental protocol that imposes a large number of rules, two days of the CarboEurope Regional Experiment Strategy (CERES) campaign are simulated. A systematic evaluation of the models is done in confrontation with the observations, using statistical tools and direct comparisons. Thus, temperature and relative humidity at 2 m, wind direction, surface energy and CO2 fluxes, vertical profiles of potential temperature as well as in-situ CO2 concentrations comparisons between observations and simulations are examined. This intercomparison exercise shows also the models ability to represent the meteorology and carbon cycling at the synoptic and regional scale in the boundary layer, but also points out some of the major shortcomings of the models.

scholarly journals Comment on evidence for surface-initiated homogeneous nucleation

2003 ◽  
Vol 3 (5) ◽  
pp. 1439-1443 ◽  
Author(s):  
J. E. Kay ◽  
V. Tsemekhman ◽  
B. Larson ◽  
M. Baker ◽  
B. Swanson
Keyword(s):  
Homogeneous Nucleation ◽  
Laboratory Experiments ◽  
Drop Size ◽  
Supercooled Water ◽  
Ice Nucleation ◽  
Surface Nucleation ◽  
Embryo Formation ◽  
Atmospheric Data ◽  
Water Drops

Abstract. We investigate theoretical, laboratory, and atmospheric evidence for a recently proposed hypothesis: homogeneous ice nucleation initiates at the surface, not in the volume, of supercooled water drops. Using existing thermodynamic arguments, laboratory experiments, and atmospheric data, we conclude that ice embryo formation at the surface cannot be confirmed or disregarded. Ice nucleation rates measured as a function of drop size in an air ambient could help distinguish between volume and surface nucleation rates.

scholarly journals Assessing Surface Heat Flux Products with In Situ Observations over the Australian Sector of the Southern Ocean

2019 ◽  
Vol 36 (9) ◽  
pp. 1849-1861
Author(s):  
Vidhi Bharti ◽  
Eric Schulz ◽  
Christopher W. Fairall ◽  
Byron W. Blomquist ◽  
Yi Huang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Southern Ocean ◽  
Sensible Heat Flux ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Atmospheric Composition ◽  
Systematic Bias ◽  
Positive Bias

Given the large uncertainties in surface heat fluxes over the Southern Ocean, an assessment of fluxes obtained by European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) product, the Australian Integrated Marine Observing System (IMOS) routine observations, and the Objectively Analyzed Air–Sea Heat Fluxes (OAFlux) project hybrid dataset is performed. The surface fluxes are calculated using the COARE 3.5 bulk algorithm with in situ data obtained from the NOAA Physical Sciences Division flux system during the Clouds, Aerosols, Precipitation, Radiation, and Atmospheric Composition over the Southern Ocean (CAPRICORN) experiment on board the R/V Investigator during a voyage (March–April 2016) in the Australian sector of the Southern Ocean (43°–53°S). ERA-Interim and OAFlux data are further compared with the Southern Ocean Flux Station (SOFS) air–sea flux moored surface float deployed for a year (March 2015–April 2016) at ~46.7°S, 142°E. The results indicate that ERA-Interim (3 hourly at 0.25°) and OAFlux (daily at 1°) estimate sensible heat flux H s accurately to within ±5 W m−2 and latent heat flux H l to within ±10 W m−2. ERA-Interim gives a positive bias in H s at low latitudes (<47°S) and in H l at high latitudes (>47°S), and OAFlux displays consistently positive bias in H l at all latitudes. No systematic bias with respect to wind or rain conditions was observed. Although some differences in the bulk flux algorithms are noted, these biases can be largely attributed to the uncertainties in the observations used to derive the flux products.

ZrO2-nucleated calcium aluminate glass-ceramics with mid-infrared transparency

2006 ◽  
Vol 21 (2) ◽  
pp. 465-472 ◽  
Author(s):  
Jiin-Jyh Shyu ◽  
Hung-Chuan Mai
Keyword(s):  
Surface Layer ◽  
Calcium Aluminate ◽  
Glass Ceramics ◽  
Nucleating Agent ◽  
Mid Infrared ◽  
Glass Addition ◽  
Parent Glass ◽  
Surface Nucleation ◽  
Bulk Nucleation ◽  
Aluminate Glass

A silica-free MgO–CaO–BaO–Al2O3–ZrO2 glass was converted into glass-ceramic by adding zirconia as a nucleating agent. The crystallization and properties of the glass-ceramics were investigated. It was found that ZrO2 is an efficient nucleating agent for the present calcium aluminate glass. Addition of an appropriate amount of ZrO2 changed the crystallization behavior from surface nucleation to internal nucleation. The primary crystalline phase was Ca3Al2O6, which exhibited bulk nucleation. When the crystallizing time was increased, BaAl2O4 formed as a surface layer that grew from the surface into the interior of the sample. The hardness was increased when the parent glass was converted into glass-ceramics. The glass-ceramics without BaAl2O4 surface layer have visible-to-infrared transparency comparable with the parent glass. The transparency was substantially reduced after the development of the surface layer.

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