scholarly journals Tomography-based monitoring of isothermal snow metamorphism under advective conditions

2015 ◽  
Vol 9 (1) ◽  
pp. 1021-1045
Author(s):  
P. P. Ebner ◽  
M. Schneebeli ◽  
A. Steinfeld
Keyword(s):  
Structural Dynamics ◽  
Transport Process ◽  
Laboratory Experiments ◽  
Time Lapse ◽  
Digital Geometry ◽  
X Ray ◽  
Effective Transport ◽  
Snow Metamorphism ◽  
Kelvin Effect ◽  
Micro Tomography

Abstract. Time-lapse X-ray micro-tomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. Diffusion and advection across the snow pores were analysed in controlled laboratory experiments. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective transport properties. The results showed that isothermal advection with saturated air have no influence on the coarsening rate that is typical for isothermal snow metamorphism. Diffusion originating in the Kelvin effect between snow structures dominates and is the main transport process in isothermal snow packs.

scholarly journals Tomography-based monitoring of isothermal snow metamorphism under advective conditions

2015 ◽  
Vol 9 (4) ◽  
pp. 1363-1371 ◽  
Author(s):  
P. P. Ebner ◽  
M. Schneebeli ◽  
A. Steinfeld
Keyword(s):  
Structural Dynamics ◽  
Effective Permeability ◽  
Laboratory Experiments ◽  
Time Lapse ◽  
Limiting Factor ◽  
Digital Geometry ◽  
X Ray ◽  
Snow Metamorphism ◽  
Kelvin Effect ◽  
Snow Microstructure

Abstract. Time-lapse X-ray microtomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. The effect of diffusion and advection across the snow pores on the snow microstructure were analysed in controlled laboratory experiments and possible effects on natural snowpacks discussed. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective permeability. The results showed that isothermal advection with saturated air have no influence on the coarsening rate that is typical for isothermal snow metamorphism. Isothermal snow metamorphism is driven by sublimation deposition caused by the Kelvin effect and is the limiting factor independently of the transport regime in the pores.

scholarly journals Vapor flux and recrystallization during dry snow metamorphism under a steady temperature gradient as observed by time-lapse micro-tomography

2012 ◽  
Vol 6 (5) ◽  
pp. 1141-1155 ◽  
Author(s):  
B. R. Pinzer ◽  
M. Schneebeli ◽  
T. U. Kaempfer
Keyword(s):  
Temperature Gradient ◽  
Physical Properties ◽  
Time Lapse ◽  
Phase Changes ◽  
External Temperature ◽  
Vapor Flux ◽  
Snow Metamorphism ◽  
Diffusion Enhancement ◽  
Micro Tomography ◽  
Snow Microstructure

Abstract. Dry snow metamorphism under an external temperature gradient is the most common type of recrystallization of snow on the ground. The changes in snow microstructure modify the physical properties of snow, and therefore an understanding of this process is essential for many disciplines, from modeling the effects of snow on climate to assessing avalanche risk. We directly imaged the microstructural changes in snow during temperature gradient metamorphism (TGM) under a constant gradient of 50 K m−1, using in situ time-lapse X-ray micro-tomography. This novel and non-destructive technique directly reveals the amount of ice that sublimates and is deposited during metamorphism, in addition to the exact locations of these phase changes. We calculated the average time that an ice volume stayed in place before it sublimated and found a characteristic residence time of 2–3 days. This means that most of the ice changes its phase from solid to vapor and back many times in a seasonal snowpack where similar temperature conditions can be found. Consistent with such a short timescale, we observed a mass turnover of up to 60% of the total ice mass per day. The concept of hand-to-hand transport for the water vapor flux describes the observed changes very well. However, we did not find evidence for a macroscopic vapor diffusion enhancement. The picture of {temperature gradient metamorphism} produced by directly observing the changing microstructure sheds light on the micro-physical processes and could help to improve models that predict the physical properties of snow.

scholarly journals CellDyM: A room temperature operating cryogenic cell for the dynamic monitoring of snow metamorphism by time‐lapse X‐ray microtomography

2015 ◽  
Vol 42 (10) ◽  
pp. 3911-3918 ◽  
Author(s):  
N. Calonne ◽  
F. Flin ◽  
B. Lesaffre ◽  
A. Dufour ◽  
J. Roulle ◽  
...  
Keyword(s):  
Room Temperature ◽  
Time Lapse ◽  
Dynamic Monitoring ◽  
X Ray ◽  
Snow Metamorphism ◽  
Temperature Operating

scholarly journals Tomography-based observation of sublimation and snow metamorphism under temperature gradient and advective flow

2015 ◽  
Vol 9 (5) ◽  
pp. 4845-4864
Author(s):  
P. P. Ebner ◽  
M. Schneebeli ◽  
A. Steinfeld
Keyword(s):  
Water Vapor ◽  
Temperature Gradient ◽  
Phase Change ◽  
Atmospheric Chemistry ◽  
Solid Phase ◽  
Time Lapse ◽  
Advective Flow ◽  
Snow Metamorphism ◽  
Micro Tomography ◽  
Ice Sublimation

Abstract. Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray micro-tomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. The sublimation of water vapor for saturated air flowing across the snow sample was experimentally determined via variations of the porous ice structure. The results showed that the exothermic gas-to-solid phase change is favorable vis-a-vis the endothermic solid-to-gas phase change, thus leading to more ice deposition than ice sublimation. Sublimation has a marked effect on the structural change of the ice matrix but diffusion of water vapor in the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong reposition process of water molecules on the ice grains is relevant for atmospheric chemistry.

scholarly journals Vapor flux and recrystallization during dry snow metamorphism under a steady temperature gradient as observed by time-lapse micro-tomography

2012 ◽  
Vol 6 (3) ◽  
pp. 1673-1714 ◽  
Author(s):  
B. R. Pinzer ◽  
M. Schneebeli ◽  
T. U. Kaempfer
Keyword(s):  
Temperature Gradient ◽  
Physical Properties ◽  
Time Lapse ◽  
Steady Temperature ◽  
Data Set ◽  
External Temperature ◽  
Vapor Flux ◽  
Snow Metamorphism ◽  
Micro Tomography

Abstract. Dry snow metamorphism under an external temperature gradient is the most common type of recrystallization of snow on the ground. The changes in snow microstructure modify the physical properties of snow, and therefore an understanding of this process is essential for many disciplines, from modeling the effects of snow on climate to assessing avalanche risk. We directly imaged the microstructural changes in snow during metamorphism under a steady temperature gradient (STGM) of 50 K m−1, using in situ time-lapse X-ray micro-tomography. This novel and non-destructive technique directly reveals the amount of ice that sublimates and is deposited during metamorphism, and in addition the exact locations of these phase changes. From the four-dimensional data set, we calculated the average time that an ice volume stayed in place before it sublimated, and found a characteristic residence time of 2–3 days. This means that most of the ice changes its phase from solid to vapor and back many times in a seasonal snow pack, where similar temperature conditions can be found. Consistent with such a short timescale, we observed a mass turnover of up to 60 % of the total ice mass per day. The concept of hand-to-hand transport for the water vapor flux describes the observed changes very well. However, we did not find evidence for a macroscopic vapor diffusion enhancement. The picture of STGM that is produced by directly observing the microstructure of snow in situ sheds light on the micro-physical processes and could help to improve models that predict the physical properties of snow.

scholarly journals Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample

2016 ◽  
Vol 10 (2) ◽  
pp. 791-797 ◽  
Author(s):  
Pirmin Philipp Ebner ◽  
Martin Schneebeli ◽  
Aldo Steinfeld
Keyword(s):  
Temperature Gradient ◽  
Structural Dynamics ◽  
Time Lapse ◽  
Water Molecules ◽  
Matrix Diffusion ◽  
Snow Sample ◽  
Advective Flow ◽  
X Ray ◽  
Chemical Content ◽  
Snow Samples

Abstract. Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray microtomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Cold saturated air at the inlet was blown into the snow samples and warmed up while flowing across the sample with a temperature gradient of around 50 K m−1. Changes of the porous ice structure were observed at mid-height of the snow sample. Sublimation occurred due to the slight undersaturation of the incoming air into the warmer ice matrix. Diffusion of water vapor opposite to the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong recrystallization of water molecules in snow may impact its isotopic or chemical content.

X-ray micro tomography in the scanning electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 106-107 ◽  
Author(s):  
W. Brünger
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Target Surface ◽  
The Body ◽  
X Rays ◽  
Cross Sectional ◽  
X Ray ◽  
Micro Tomography ◽  
Scanning Electron

Reconstructive tomography is a new technique in diagnostic radiology for imaging cross-sectional planes of the human body /1/. A collimated beam of X-rays is scanned through a thin slice of the body and the transmitted intensity is recorded by a detector giving a linear shadow graph or projection (see fig. 1). Many of these projections at different angles are used to reconstruct the body-layer, usually with the aid of a computer. The picture element size of present tomographic scanners is approximately 1.1 mm2.Micro tomography can be realized using the very fine X-ray source generated by the focused electron beam of a scanning electron microscope (see fig. 2). The translation of the X-ray source is done by a line scan of the electron beam on a polished target surface /2/. Projections at different angles are produced by rotating the object.During the registration of a single scan the electron beam is deflected in one direction only, while both deflections are operating in the display tube.

Real-Space X-Ray Pair Distribution Function Analysis and Molecular-Dynamics Modelling of Diflunisal Channel Hydrates

2020 ◽  
Author(s):  
Anuradha Pallipurath ◽  
Francesco Civati ◽  
Jonathan Skelton ◽  
Dean Keeble ◽  
Clare Crowley ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Distribution Function ◽  
Structural Dynamics ◽  
First Principles ◽  
Pair Distribution Function ◽  
Function Analysis ◽  
Real Space ◽  
X Ray ◽  
Dynamics Modelling ◽  
Dynamics Simulations

X-ray pair distribution function analysis is used with first-principles molecular dynamics simulations to study the co-operative H<sub>2</sub>O binding, structural dynamics and host-guest interactions in the channel hydrate of diflunisal.

scholarly journals Freeze–Thaw Resistance and Air-Void Analysis of Concrete with Recycled Glass–Pozzolan Using X-ray Micro-Tomography

Materials ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 154
Author(s):  
Marija Krstic ◽  
Julio F. Davalos ◽  
Emanuele Rossi ◽  
Stefan C. Figueiredo ◽  
Oguzhan Copuroglu
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
The United States ◽  
Adsorption Method ◽  
X Ray ◽  
Freeze Thaw ◽  
Void System ◽  
Spatial Parameters ◽  
Micro Tomography ◽  
Air Void

Recent studies have shown promising potential for using Glass Pozzolan (GP) as an alternative supplementary cementitious material (SCM) due to the scarcity of fly ash and slag in the United States. However, comprehensive studies on the freeze–thaw (FT) resistance and air void system of mixtures containing GP are lacking. Therefore, this study aimed to evaluate GP’s effect on FT resistance and characterize mixtures with different GP contents, both macro- and microscopically. In this study, six concrete mixes were considered: Three mixes with 20%, 30% and 40% GP as cement replacements and two other comparable mixes with 30% fly ash and 40% slag, as well as a mix with 100% Ordinary Portland cement (OPC) as a reference. Concrete samples were prepared, cured and tested according to the ASTM standards for accelerated FT resistance for 1000 cycles and corresponding dynamic modulus of elasticity (Ed). All the samples showed minimal deterioration and scaling and high F/T resistance with a durability factor of over 90%. The relationships among FT resistance parameters, air-pressured method measurements of fresh concretes and air void analysis parameters of hardened concretes were examined in this study. X-ray micro-tomography (micro-CT scan) was used to evaluate micro-cracks development after 1000 freeze–thaw cycles and to determine spatial parameters of air voids in the concretes. Pore structure properties obtained from mercury intrusion porosimetry (MIP) and N2 adsorption method showed refined pore structure for higher cement replacement with GP, indicating more gel formation (C-S-H) which was verified by thermogravimetric analysis (TGA).

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