Abstract Structural failure of concrete buildings on fire and complete destruction of the monolithic refractory lining during their drying stage are dangerous examples of the effect of explosive ...spalling on partially saturated porous media. Several observations in both cases indicated the presence of moisture accumulation ahead of the drying front, which are in tune with the most common theories on the explosive spalling of concrete. Previous studies have shown evidence of the existence of this phenomenon, however, they were biased by artifacts and experimental limitations (such as the beam hardening effect and changes in the microstructure of the material due to the presence of pressure and temperature sensors). In the current work, rapid neutron tomography was used to investigate the in‐operando drying behavior of a high‐alumina refractory castable, proposing a novel experimental layout aimed at a truly one‐dimensional drying front. This setup provided more realistic boundary conditions, such as the behavior of a larger wall heated from one of its sides, while also preventing some nonphysical artifacts (notably beam hardening). By eliminating these aspects, a direct proof that moisture accumulates ahead of the drying front was obtained. This work also lays the basis for further studies focusing on the response sensitivity analysis to boundary conditions and other parameters (e.g., heating rates and properties of the sample related to the moisture clog formation), as well as useful data for the validation and characterization stages of numerical models of partially saturated porous media.
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•Vapor penetration in cracked concrete probed with fast neutron radiography.•Full-field analysis revealed moisture clogging and discontinuous moisture fronts.•Moisture accumulation ...was found to precede sudden jumps in moisture profiles.•Pressure driven moisture speed is 4 times the speed of capillary absorption.
This paper presents, for the first time, full-field dynamic measurements of vapour injection and condensation within a fractured concrete, observed in-operando by means of rapid neutron radiography (acquisition rate of 30 Hz with 87 μm pixel size). Time-dependant moisture evolution is analysed in terms of equivalent water thickness measurements. We observe that movement of condensed moisture along and transversely to the crack plane is non-monotonic in both space and time, exhibiting occasional sub-second jumps.
Dissolution of porous media induces positive feedback between fluid transport and chemical reactions at mineral surfaces, leading to the formation of wormhole-like channels within the rock. Wormholes ...provide highly efficient flow and transport paths within rock, and as such, understanding their formation is critical for controlling contaminant migration or preventing CO2 leakage during geological carbon sequestration. Here, using time-resolved X-ray tomography, we capture the dynamics of wormhole propagation, inaccessible by standard experimental methods. We find a highly non-trivial relationship between wormhole advancement and variations in permeability of the rock, with extensive periods of steady advancement not reflected by significant change in permeability. This is in contrast to most existing conceptual models where wormholes advance in a linear fashion. We show that this is caused by the presence of highly cemented regions which act as barriers to flow, as confirmed by multi-scale analysis of the pore geometry based on tomographic, (ultra) small angle neutron scattering, and optical microscopy measurements. These results demonstrate that time-lapse captured wormhole dynamics can be used to probe the internal structure of the rock.
•4D tomography reveals non-linear growth of wormholes guided by heterogeneities.•wormhole advancement does not need to be correlated to changes in permeability.•timelapse dynamics of a wormhole can be used to probe internal structure of the rock.
AbstractDue to their great performance and ease of installation, refractory castables are common ground materials to enable high‐temperature processes. However, their fully operational condition is ...slowed down by the gradual drying stage required. Therefore, better understanding of the moisture transport is essential to improve their efficiency and reduce the likelihood of explosive spalling events due to vapor pressurization. Neutron tomography provides a relevant inner view of the moisture distribution across a sample and its evolution over time. In this work, the effect of the heating rate on moisture clog was investigated and compared with available laboratory and industrial observations. It was found out that higher heating rates resulted in a faster and longer lasting water accumulation ahead of the drying front, in agreement with other macroscopic studies and explaining the common reasoning behind using slower heating rates and safer industrial operations. This study highlights the potential of neutron imaging for the ongoing effort to maximize the efficiency of the refractory castables drying process by controlling the moisture accumulation without exclusively relying on slower heating rates.
A large and increasing number of scientific domains pushes for high neutron imaging resolution achieved in reasonable times. Here we present the principle, design and performance of a detector based ...on infinity corrected optics combined with a crystalline Gd
Ga
O
: Eu scintillator, which provides an isotropic sub-4 µm true resolution. The exposure times are only of a few minutes per image. This is made possible also by the uniquely intense cold neutron flux available at the imaging beamline NeXT-Grenoble. These comparatively rapid acquisitions are compatible with multiple high quality tomographic acquisitions, opening new venues for in-operando testing, as briefly exemplified here.
The elucidation of lithium ion transport pathways through a solid electrolyte separator is a vital step toward development of reliable, functional all‐solid‐state batteries. Here, advantage has been ...taken of the significantly higher neutron attenuation coefficient of one of the most abundant stable isotopes of lithium, 6Li, with respect to that of naturally occurring lithium isotope mixture, to perform neutron imaging on a purpose built all‐solid‐state lithium–sulfur battery. Increasing the 6Li content in the anode while using natural lithium in the solid electrolyte separator and the cathode enhances the contrast such that it is possible to differentiate, during the initial discharge, between the mobile lithium ions diffusing through the cell from the anode and those that are initially located in the solid electrolyte. The sensitivity of neutrons to the different lithium isotopes means that operando neutron radiography allows demonstration of the lithium ion diffusion through the cell while in situ neutron tomography has permitted presentation, in three dimensions, of the distribution of the trapped lithium ions inside the cell in charged and discharged states.
This paper presents an in-situ observation, using neutron imaging, of delayed crack propagation in a high-strength martensitic steel specimen. Delayed cracking is believed to be caused by hydrogen ...embrittlement occurring due to the slow diffusion and accumulation of hydrogen ahead of a crack front, causing decreased ductility and eventual cracking under constant load. The experiment involved mechanical loading of a single-edge-notch bend specimen while submerged in an electrolyte solution (H2O + 3.5% NaCl) under cathodic polarization to facilitate hydrogen ingress. Intermittent crack propagation was observed for 12 h after the environment had been removed. The stress state at each crack configuration was extracted from a three-dimensional elastic–plastic finite element simulation, which was tailored to match the quantitative information acquired from the neutron radiographs of the fracture process. To gain insight into the evolution of hydrogen concentration with crack propagation, a modeling scheme for stress-assisted hydrogen diffusion was also employed.
•Three-dimensional local model of NH3 sorption on solid SrCl2 was developed.•Detailed data from neutron radiography was used for the model validation.•Neutron radiography is a superior alternative to ...conventional validation methods.
Thermochemical heat storage may become a key technology in balancing intermittent renewables by regulating production and demand peaks and in increasing the efficiency of energy systems by reusing waste heat. Nowadays, there is a limited number of commercial products based on this technology, and for larger market penetration an improvement of the technology must be achieved. To advance thermochemical heat storage systems, one has to pay particular attention to studying the processes occurring inside the reactors. For the investigation of the sorption processes with further optimization of the reactor design, a local numerical model of the reactor, carefully validated at the local and global scales, is of significant importance.
In the present study, we developed a three dimensional local model of a thermochemical reactor that utilizes ammonia sorption on solid SrCl2. This model simulates the effects of the chemical reaction, heat transfer, and mass transfer separately, and this is its main difference from already existing SrCl2-ammonia models. For the model validation, we used neutron radiography, an alternative to the conventional techniques, i.e., temperature and flowrate measurements. In contrast to these, neutron radiography allows following the state of the reactive bed not for a discrete number of points but via a 2D map. The results of the study demonstrate that the model developed herein is in a good agreement with the detailed neutron radiography data. Since neutron radiography was used as a validation tool for a numerical model for the first time, the procedure of the comparison between the results from our model and neutron radiography was carefully documented. An additional, successful, validation was provided through temperature and flowrate measurements.
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•Drying response error map for monophase compared to multiphase model is obtained.•The effect of desorption isoterm thermal evolution on drying response is quantified.•The effect of intrinsic ...permeability thermal evolution on drying kinetics is quantified.
The drying of cement-based materials affects directly their durability, which has a major financial/societal impact. Notably, the variation of saturation of the porous network as well as drying shrinkage are fundamental processes since they drive together cracking and the penetration rate of aggressive chemicals. Many macroscopic models describe the moisture transport within porous media. They can be broadly divided into two main categories: multiphase macro-models which take into account the presence of three fluid phases (liquid water, vapor and dry air), and simplified models considering less phases under the main assumption of constant gas pressure during the drying process. Moreover, the choice of different behavior laws, which describe different evolutions of desorption isotherms, relative permeability, permeability to liquid water in function of temperature, has a major impact on mass loss amount and kinetics. Quantification of these simplifications effects regarding the used model and the choice of behavior laws was done by comparing mass loss response surfaces in a relative humidity and temperature space for multiple configurations. The results show relative error maps at early, mid and late drying stages for every compared case.
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