Simulations of crystal aggregation and growth: Towards correct crystal area

AIChE Journal ◽  
2019 ◽  
Vol 65 (5) ◽  
pp. e16525
Author(s):  
Tijana Kovačević ◽  
Heiko Briesen
Keyword(s):  
Crystal Aggregation

scholarly journals Observations and modelling of microphysical variability, aggregation and sedimentation in tropical anvil cirrus outflow regions

2012 ◽  
Vol 12 (14) ◽  
pp. 6609-6628 ◽  
Author(s):  
M. W. Gallagher ◽  
P. J. Connolly ◽  
I. Crawford ◽  
A. Heymsfield ◽  
K. N. Bower ◽  
...  
Keyword(s):  
Electric Fields ◽  
Numerical Models ◽  
Average Particle Size ◽  
Average Particle ◽  
Ice Crystal ◽  
Crystal Aggregation ◽  
Ice Water Content ◽  
Differential Sedimentation ◽  
High Electric Fields ◽  
Ice Water

Abstract. Aircraft measurements of the microphysics of a tropical convective anvil (at temperatures ~−60 °C) forming above the Hector storm, over the Tiwi Islands, Northern Australia, have been conducted with a view to determining ice crystal aggregation efficiencies from in situ measurements. The observed microphysics have been compared to an explicit bin-microphysical model of the anvil region, which includes crystal growth by vapour diffusion and aggregation and the process of differential sedimentation. It has been found in flights made using straight and level runs perpendicular to the storm that the number of ice crystals initially decreased with distance from the storm as aggregation took place resulting in larger crystals, followed by their loss from the cloud layer due to sedimentation. The net result was that the mass (i.e. Ice Water Content) in the anvil Ci cloud decreased, but also that the average particle size (weighted by number) remained relatively constant along the length of the anvil outflow. Comparisons with the explicit microphysics model showed that the changes in the shapes of the ice crystal spectra as a function of distance from the storm could be explained by the model if the aggregation efficiency was set to values of Eagg~0.5 and higher. This result is supported by recent literature on aggregation efficiencies for complex ice particles and suggests that either the mechanism of particle interlocking is important to the aggregation process, or that other effects are occuring, such as enhancement of ice-aggregation by high electric fields that arise as a consequence of charge separation within the storm. It is noteworthy that this value of the ice crystal aggregation efficiency is much larger than values used in cloud resolving models at these temperatures, which typically use E~0.0016. These results are important to understanding how cold clouds evolve in time and for the treatment of the evolution of tropical Ci in numerical models.

The effect of concentration on the performance of two DDT cattle-dipping formulations

1963 ◽  
Vol 14 (1) ◽  
pp. 119 ◽  
Author(s):  
DK O'Neill
Keyword(s):  
Size And Shape ◽  
Early Stages ◽  
Haemaphysalis Bispinosa ◽  
Crystal Aggregation ◽  
Surface Active Agents ◽  
Surface Active ◽  
Biological Performance

Dipping trials with two supelcooled melt formulations of DDT, in which the DDT concentrations were raised progressively to four times the usual strength, showed that whilst more DDT was deposited both on the hair of calves and on bush ticks (Haemaphysalis bispinosa Neumann) as the DDT concentration was increased and the dip aged, the toxicity to ticks of both formulations increased only during the early stages of each trial. Clearly the size and shape of the DDT crystals which developed in both dips and the degree of crystal aggregation were important factors which influenced the deposition of DDT and its toxicity. Of the forms of DDT present, the toxicity is attributed mainly to microcrystals of colloidal dimensions. Additions of formulation would serve to maintain but not increase the concentration of these microcrystals. Differences in performance of the dips is ascribed to the composition of the soaps (i.e. surface active agents) in the formulations. The experiments emphasize the importance of the nature of the deposit, and indicate that increases in dip concentration will not necessarily give better biological performance.

Crystal aggregation into periodically grating-banded assemblies in phthalic acid modulated by molten poly(ethylene oxide)

CrystEngComm ◽  
2020 ◽  
Vol 22 (3) ◽  
pp. 467-477 ◽  
Author(s):  
Tzu-Yu Chen ◽  
Eamor M. Woo ◽  
Selvaraj Nagarajan
Keyword(s):  
Ethylene Oxide ◽  
Small Molecule ◽  
Phthalic Acid ◽  
Ordered Structures ◽  
Crystal Aggregation ◽  
Banded Spherulites ◽  
Small Molecule Compound ◽  
Poly Ethylene Oxide ◽  
Poly Ethylene

A small-molecule compound, phthalic acid (PA), crystallized in the presence of poly(ethylene oxide) (PEO) with various compositions was utilized as a model to investigate the morphology and crystal assembly of periodically ordered structures in banded spherulites.

scholarly journals The Adhesion of Ice Spheres in Electric Fields

1967 ◽  
Vol 6 (46) ◽  
pp. 505-514 ◽  
Author(s):  
J. Latham ◽  
C. P. R. Saunders
Keyword(s):  
Relative Humidity ◽  
Electric Field ◽  
External Electric Field ◽  
Electric Fields ◽  
Environmental Temperature ◽  
Ice Crystal ◽  
Electrostatic Forces ◽  
Rate Of Growth ◽  
Crystal Aggregation

AbstractThe forceFrequired to separate two ice spheres was measured as a function of environmental temperatureT, relative humidityHand the strengthEof the external electric field in which the spheres were situated. It was found that over the entire attainable range ofTandH,Fincreased rapidly with increasingE. The increased adhesion was not accompanied by an increase in the rate of growth of the ice bridge between the two spheres and is explicable in terms of Davis’s (1964) calculations of the purely electrostatic forces between two spheres situated in an electric field. The experiments indicate that the rate of growth of snowflakes in a cloud by means of ice crystal aggregation will be markedly enhanced if the cloud is highly electrified.

Regulation by macromolecules of calcium oxalate crystal aggregation in stone formers

2005 ◽  
Vol 33 (3) ◽  
pp. 206-212 ◽  
Author(s):  
J. A. Wesson ◽  
V. Ganne ◽  
A. M. Beshensky ◽  
J. G. Kleinman
Keyword(s):  
Calcium Oxalate ◽  
Calcium Oxalate Crystal ◽  
Crystal Aggregation ◽  
Stone Formers

scholarly journals Observations and modelling of microphysical variability, aggregation and sedimentation in tropical storm cirrus outflow regions

2011 ◽  
Vol 11 (8) ◽  
pp. 23761-23800
Author(s):  
M. W. Gallagher ◽  
P. J. Connolly ◽  
A. Heymsfield ◽  
K. N. Bower ◽  
T. W. Choularton ◽  
...  
Keyword(s):  
Collection Efficiency ◽  
Aerosol Particles ◽  
Tropical Storm ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Aircraft Measurements ◽  
Ice Crystal ◽  
Crystal Aggregation ◽  
Small Crystals ◽  
Bulk Model

Abstract. Aircraft measurements of the microphysics of a tropical convective anvil (at temperatures ~−60 °C) forming above the HECTOR storm have been performed. The observed microphysics has been compared to a bulk and explicit microphysical model of the anvil region including crystal aggregation and sedimentation. It has been found that in flights made using straight and level runs perpendicular to the storm that the number of ice crystals initially decreased with distance from the storm as aggregation took place resulting in larger crystals followed by their loss due to sedimentation. At still greater distances from the storm the number of very small crystals increased. This is attributed to the formation of new ice crystals on aerosol particles as the ice super saturation rose following the depletion of the larger ice particles following aggregation and sedimentation. Comparison with the explicit microphysics model showed that the changes in the shapes of the ice crystal spectra as a function of distance from the storm could be explained by the explicit microphysical model if the aggregation efficiency was set to E~0.02. It is noteworthy that this aggregation efficiency is much larger than values normally used in cloud resolving models at these temperatures (typically E~0.0016). Furthermore if the bulk model is used then optimum agreement was reached with a collection efficiency for aggregation of E~0.05. These results are important for the treatment of the evolution and lifetime of tropical cirrus clouds.

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