Experimental Studies of Ice Crystal Accretion on Axisymmetric Bodies at Aeroengine Conditions

2020 ◽  
Vol 36 (6) ◽  
pp. 836-850
Author(s):  
Alexander Bucknell ◽  
Matthew McGilvray ◽  
David R. H. Gillespie ◽  
Geoff Jones ◽  
Alasdair Reed ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Ice Crystal ◽  
Axisymmetric Bodies

Empirical Formulation for number of ice crystal fragments by sublimational breakup

2020 ◽  
Author(s):  
Akash Deshmukh ◽  
Vaughan Phillips
Keyword(s):  
Relative Humidity ◽  
Cloud Model ◽  
Experimental Studies ◽  
Ice Crystal ◽  
Initial Size ◽  
Sublimation Process ◽  
Numerical Formulation ◽  
High Concentrations ◽  
Ice Multiplication ◽  
Ice Production

<p>There is much uncertainty about high concentrations of ice observed in clouds and their origins. In the literature, there have been previous experimental studies reported about the sublimation process of an ice crystal causes emission of fragments by breakup.   Such sublimational breakup is a type of secondary ice production, which in natural clouds can cause ice multiplication. </p><p>To represent this process of sublimation breakup in any cloud model, the present study proposes a numerical formulation of the number of ice fragments generated by sublimation of pristine ice crystal. This is done by amalgamating laboratory observations from previous published studies. The number of ice fragments determined by relative humidity (RH) and initial size of the ice particle were measured in the published experiments, and by simulating them we are able to infer parameters of a sublimation breakup scheme.   At small initial sizes, the dependency on size prevails, whereas at larger sizes both dependencies are comparable. This formulation is compared with observations to see the behaviour of it.</p>

scholarly journals A Molecular Perspective on Water Vapour Accommodation into Ice and Its Dependence on Temperature

2020 ◽  
Author(s):  
Daniel Schlesinger ◽  
Samuel J. Lowe ◽  
Tinja Olenius ◽  
Xiangrui Kong ◽  
Jan B. C. Pettersson ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Order Parameter ◽  
Potential Temperature ◽  
Experimental Studies ◽  
Accommodation Coefficient ◽  
Recent Experimental Data ◽  
Ice Crystal ◽  
Cloud Particle ◽  
Data Set ◽  
Accommodation Process

<div> <div> <div> <p>Accommodation of vapour phase water molecules into ice crystal surfaces is a fundamental process controlling atmospheric ice crystal growth. Experimental studies investigating the accommodation process with various different techniques report widely spread values of the water accommodation coefficient on ice, αice, and the results on its potential temperature- dependence are inconclusive. We run molecular dynamics simulations of molecules condensing onto the basal plane of ice Ih using the TIP4P/Ice empirical force field and characterize the accommodated state from this molecular perspective, utilizing the interaction energy, the tetrahedrality order parameter and the distance below the instantaneous interface as criteria. Changes of the order parameter turn out to be a suitable measure to distinguish between surface and bulk states of a molecule condensing onto the disordered interface. In light of the findings from the molecular dynamics, we discuss and re- analyse a recent experimental data set on αice obtained with an environmental molecular beam (EMB) setup [Kong et al, Journal of Physical Chemistry A, 2014] using kinetic molecular flux modelling, aiming at a more comprehensive picture of the accommodation process from a molecular perspective. These results indicate that the experimental observations indeed cannot be explained by evaporation alone. At the same time our results raise the issue of rapidly growing relaxation times upon decreasing temperature, challenging future experimental efforts to cover relevant time scales. Finally, we discuss the relevance of the water accommodation coefficient on ice in the context of atmospheric cloud particle growth processes. </p> </div> </div> </div>

Nonrectilinear Light Propagation in Integrated Photoelasticity of Axisymmetric Bodies

1984 ◽  
Vol 8 (4) ◽  
pp. 195-200 ◽  
Author(s):  
Hillar K. Aben ◽  
Bogdan R. Krasnowski ◽  
Jerzy T. Pindera
Keyword(s):  
Light Propagation ◽  
Stress Gradient ◽  
High Stress ◽  
Experimental Studies ◽  
General Character ◽  
Deflection Of Light ◽  
Order Of Magnitude ◽  
Fringe Patterns ◽  
Axisymmetric Bodies ◽  
High Stress Gradient

The general character as well as the order of magnitude of deflection of light in axisymmetric photoelastic specimens has been investigated. Experimental studies of deflection of light in case of a particular axisymmetric state of stress with high stress gradient has been carried out. It has been shown that the integral fringe patterns depend strongly on the parameters of the recording system. Fringes of a different origin have been observed together with the integral fringe pattern.

scholarly journals Experimental Studies of Ice Crystal Accretion on an Axisymmetric Body at Engine-Realistic Conditions

2018 ◽  
Author(s):  
Alexander J. Bucknell ◽  
Matthew McGilvray ◽  
David Gillespie ◽  
Geoff Jones ◽  
Alasdair Reed ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Axisymmetric Body ◽  
Ice Crystal

scholarly journals Contact freezing: a review of experimental studies

2013 ◽  
Vol 13 (19) ◽  
pp. 9745-9769 ◽  
Author(s):  
L. A. Ladino Moreno ◽  
O. Stetzer ◽  
U. Lohmann
Keyword(s):  
Qualitative Difference ◽  
Experimental Studies ◽  
Experimental Information ◽  
Cloud Formation ◽  
Ice Crystal ◽  
Ice Cloud ◽  
Quantitative Calculation ◽  
Ice Nuclei ◽  
Immersion Freezing ◽  
Reported Data

Abstract. This manuscript compiles both theoretical and experimental information on contact freezing with the aim to better understand this potentially important but still not well quantified heterogeneous freezing mode. There is no complete theory that describes contact freezing and how the energy barrier has to be overcome to nucleate an ice crystal by contact freezing. Experiments on contact freezing conducted using the cold plate technique indicate that it can initiate ice formation at warmer temperatures than immersion freezing. Additionally, a qualitative difference in the freezing temperatures between contact and immersion freezing has been found using different instrumentation and different ice nuclei. There is a lack of data on collision rates in most of the reported data, which inhibits a quantitative calculation of the freezing efficiencies. Thus, new or modified instrumentation to study contact nucleation in the laboratory and in the field are needed to identify the conditions at which contact nucleation could occur in the atmosphere. Important questions concerning contact freezing and its potential role for ice cloud formation and climate are also summarized.

scholarly journals A Molecular Perspective on Water Vapour Accommodation into Ice and Its Dependence on Temperature

2020 ◽  
Author(s):  
Daniel Schlesinger ◽  
Samuel J. Lowe ◽  
Tinja Olenius ◽  
Xiangrui Kong ◽  
Jan B. C. Pettersson ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Order Parameter ◽  
Potential Temperature ◽  
Experimental Studies ◽  
Accommodation Coefficient ◽  
Recent Experimental Data ◽  
Ice Crystal ◽  
Cloud Particle ◽  
Data Set ◽  
Accommodation Process

<div> <div> <div> <p>Accommodation of vapour phase water molecules into ice crystal surfaces is a fundamental process controlling atmospheric ice crystal growth. Experimental studies investigating the accommodation process with various different techniques report widely spread values of the water accommodation coefficient on ice, αice, and the results on its potential temperature- dependence are inconclusive. We run molecular dynamics simulations of molecules condensing onto the basal plane of ice Ih using the TIP4P/Ice empirical force field and characterize the accommodated state from this molecular perspective, utilizing the interaction energy, the tetrahedrality order parameter and the distance below the instantaneous interface as criteria. Changes of the order parameter turn out to be a suitable measure to distinguish between surface and bulk states of a molecule condensing onto the disordered interface. In light of the findings from the molecular dynamics, we discuss and re- analyse a recent experimental data set on αice obtained with an environmental molecular beam (EMB) setup [Kong et al, Journal of Physical Chemistry A, 2014] using kinetic molecular flux modelling, aiming at a more comprehensive picture of the accommodation process from a molecular perspective. These results indicate that the experimental observations indeed cannot be explained by evaporation alone. At the same time our results raise the issue of rapidly growing relaxation times upon decreasing temperature, challenging future experimental efforts to cover relevant time scales. Finally, we discuss the relevance of the water accommodation coefficient on ice in the context of atmospheric cloud particle growth processes. </p> </div> </div> </div>

High-pressure freezing of cells in suspension for low-voltage scanning electron microscopy (LVSEM)

1991 ◽  
Vol 49 ◽  
pp. 64-65
Author(s):  
Marek Malecki ◽  
James Pawley ◽  
Hans Ris
Keyword(s):  
Electron Microscopy ◽  
High Pressure ◽  
Low Voltage ◽  
Culture Media ◽  
Cell Structure ◽  
Freeze Substitution ◽  
Ice Crystal ◽  
High Pressure Freezing ◽  
Cell Culture Media ◽  
Voltage Scanning

The ultrastructure of cells suspended in physiological fluids or cell culture media can only be studied if the living processes are stopped while the cells remain in suspension. Attachment of living cells to carrier surfaces to facilitate further processing for electron microscopy produces a rapid reorganization of cell structure eradicating most traces of the structures present when the cells were in suspension. The structure of cells in suspension can be immobilized by either chemical fixation or, much faster, by rapid freezing (cryo-immobilization). The fixation speed is particularly important in studies of cell surface reorganization over time. High pressure freezing provides conditions where specimens up to 500μm thick can be frozen in milliseconds without ice crystal damage. This volume is sufficient for cells to remain in suspension until frozen. However, special procedures are needed to assure that the unattached cells are not lost during subsequent processing for LVSEM or HVEM using freeze-substitution or freeze drying. We recently developed such a procedure.

Cryosectioning plant roots prepared by high-pressure freezing

1987 ◽  
Vol 45 ◽  
pp. 662-663
Author(s):  
R.E. Crang ◽  
M. Mueller ◽  
K. Zierold
Keyword(s):  
High Pressure ◽  
Cell Walls ◽  
Plant Tissues ◽  
Ice Crystal ◽  
High Pressure Freezing ◽  
Vitreous State ◽  
Radial Depth ◽  
Irregular Topography ◽  
Considerable Depth ◽  
Conventional Freezing

Obtaining frozen-hydrated sections of plant tissues for electron microscopy and microanalysis has been considered difficult, if not impossible, due primarily to the considerable depth of effective freezing in the tissues which would be required. The greatest depth of vitreous freezing is generally considered to be only 15-20 μm in animal specimens. Plant cells are often much larger in diameter and, if several cells are required to be intact, ice crystal damage can be expected to be so severe as to prevent successful cryoultramicrotomy. The very nature of cell walls, intercellular air spaces, irregular topography, and large vacuoles often make it impractical to use immersion, metal-mirror, or jet freezing techniques for botanical material.However, it has been proposed that high-pressure freezing (HPF) may offer an alternative to the more conventional freezing techniques, inasmuch as non-cryoprotected specimens may be frozen in a vitreous, or near-vitreous state, to a radial depth of at least 0.5 mm.

High-pressure freezing and freeze substitution of plant tissue

1992 ◽  
Vol 50 (1) ◽  
pp. 748-749
Author(s):  
William P. Sharp ◽  
Robert W. Roberson
Keyword(s):  
High Pressure ◽  
Cell Structure ◽  
Leaf Tissue ◽  
Freeze Substitution ◽  
Crystal Formation ◽  
Ice Crystal ◽  
High Pressure Freezing ◽  
Cell Components ◽  
Cold Metal ◽  
Brome Grass

The aim of ultrastructural investigation is to analyze cell architecture and relate a functional role(s) to cell components. It is known that aqueous chemical fixation requires seconds to minutes to penetrate and stabilize cell structure which may result in structural artifacts. The use of ultralow temperatures to fix and prepare specimens, however, leads to a much improved preservation of the cell’s living state. A critical limitation of conventional cryofixation methods (i.e., propane-jet freezing, cold-metal slamming, plunge-freezing) is that only a 10 to 40 μm thick surface layer of cells can be frozen without distorting ice crystal formation. This problem can be allayed by freezing samples under about 2100 bar of hydrostatic pressure which suppresses the formation of ice nuclei and their rate of growth. Thus, 0.6 mm thick samples with a total volume of 1 mm3 can be frozen without ice crystal damage. The purpose of this study is to describe the cellular details and identify potential artifacts in root tissue of barley (Hordeum vulgari L.) and leaf tissue of brome grass (Bromus mollis L.) fixed and prepared by high-pressure freezing (HPF) and freeze substitution (FS) techniques.

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