Macropore-matrix mass transfer: reactive solute transport as quantified with Fluorescence imaging

2020 ◽  
Author(s):  
Christoph Haas ◽  
Ruth Ellerbrock ◽  
Horst H. Gerke
Keyword(s):  
Mass Transfer ◽  
Soil Properties ◽  
Fluorescence Imaging ◽  
Mass Exchange ◽  
Soil Structure ◽  
Transport Processes ◽  
Hydraulic Transport ◽  
Soil Matrix ◽  
Adsorption Sites ◽  
Sorption Characteristics

<p>Preferential flow paths in soils play a major role for transport processes of heat, gas, water, and solutes and are important adsorption sites. For mass-exchange processes and water storage in soils, small-scaled soil properties, like the spatial distribution of adsorption sites and their accessibility, and the permeability are crucial. Interfaces between macropores (i.e., earthworm burrows, cracks, and root channels) and the soil matrix control the mass exchange. Water and solute transfer through the interface between bio-pores, aggregate or crack surfaces and the matrix was traced at the scale of small soil blocks (≤45 mm edge length) with Fluorescein (i.e., a reactive, fluorescent dye). The objectives were to visualize and quantify hydraulic transport, and sorption characteristics of earthworm-, root- and shrinkage-induced interfaces. Batch experiments were performed to calibrate the Na-Fluorescein tracer concentration versus fluorescence-intensity relationship and to derive parameters for two kinetic sorption models (i.e., Freundlich vs. Langmuir). Fluorescence imaging in the laboratory of small soil blocks was applied with a self-constructed spraying device, and with the help of the calibration, small-scaled dye-concentration maps were derived. Time- and interface-dependent positions of the wetting fronts in vertical direction were estimated with the help of the cumulative infiltration. Assuming equilibrated conditions between Na-Fluorescein in solution (calculated by multiplying the locale dye-concentration and the local water content) and Na-Fluorescein sorbed to soil, the total mass transfers as a function of macropore-type and spraying time were determined. The results of the mass transfer for water and reactive solutes were characteristic for the soil structure type and depending on the composition of the macropore-matrix interface. Differences were explained by alterations in soil structure and chemical composition of the coatings. Results suggest relations between mass exchange and observable soil properties. This can be helpful for improving the numerical simulation of macropore-matrix mass transfer and inverse simulations of small-scaled hydraulic, transport, and sorption characteristics of macropore walls.</p>

Soil macropore-matrix mass exchange tracer experiments that account for sorption at macropore walls

2020 ◽  
Author(s):  
Horst H. Gerke ◽  
Jaromir Dusek ◽  
Martin Leue ◽  
Steffen Beck-Broichsitter ◽  
Martina Sobotkova ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Mass Exchange ◽  
Preferential Flow ◽  
Unsaturated Flow ◽  
Transfer Coefficients ◽  
Flow Paths ◽  
Soil Matrix ◽  
Specific Effects ◽  
The Matrix ◽  
Reactive Solutes

<p>The transfer of water and solutes between soil matrix and macropores controls preferential flow. Mass transfer depends on soil structural geometry and on properties of biopore walls and crack coatings that can differ from those of the matrix with respect to texture, organic matter, bulk density, and porosity. Agrochemicals and other solutes can react during transport along macropores, which has yet not been well-considered. The objective of this study was to study the specific effects of sorption on the reduction of mass exchange due to the effects of sorption at the macropore-matrix interface. Field and lab percolation experiments under unsaturated flow conditions were carried out with intact soil columns to simulate movement of bromide as a conservative and Brilliant Blue, iodide, and Na-Fluorescein as a reactive tracer. Sorption properties were determined separately for the biopore walls and crack coatings. The results suggest that preferential transport of reactive solutes depends even more strongly on the geometry and properties at flow paths surface than conservative solutes. If these properties can be determined, mass transfer coefficients in two-domain models can be related to soil structure and management.</p>

Modeling Transport in Porous Media With Phase Change: Applications to Food Processing

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Amit Halder ◽  
Ashish Dhall ◽  
Ashim K. Datta
Keyword(s):  
Mass Transfer ◽  
Porous Media ◽  
Food Processing ◽  
Transport Processes ◽  
Phase Changes ◽  
Solid Matrix ◽  
Deep Fat Frying ◽  
Modeling Framework ◽  
Food Manufacturing ◽  
Food Processes

Fundamental, physics-based modeling of complex food processes is still in the developmental stages. This lack of development can be attributed to complexities in both the material and transport processes. Society has a critical need for automating food processes (both in industry and at home) while improving quality and making food safe. Product, process, and equipment designs in food manufacturing require a more detailed understanding of food processes that is possible only through physics-based modeling. The objectives of this paper are (1) to develop a general multicomponent and multiphase modeling framework that can be used for different thermal food processes and can be implemented in commercially available software (for wider use) and (2) to apply the model to the simulation of deep-fat frying and hamburger cooking processes and validate the results. Treating food material as a porous medium, heat and mass transfer inside such material during its thermal processing is described using equations for mass and energy conservation that include binary diffusion, capillary and convective modes of transport, and physicochemical changes in the solid matrix that include phase changes such as melting of fat and water and evaporation/condensation of water. Evaporation/condensation is considered to be distributed throughout the domain and is described by a novel nonequilibrium formulation whose parameters have been discussed in detail. Two complex food processes, deep-fat frying and contact heating of a hamburger patty, representing a large group of common food thermal processes with similar physics have been implemented using the modeling framework. The predictions are validated with experimental results from the literature. As the food (a porous hygroscopic material) is heated from the surface, a zone of evaporation moves from the surface to the interior. Mass transfer due to the pressure gradient (from evaporation) is significant. As temperature rises, the properties of the solid matrix change and the phases of frozen water and fat become transportable, thus affecting the transport processes significantly. Because the modeling framework is general and formulated in a manner that makes it implementable in commercial software, it can be very useful in computer-aided food manufacturing. Beyond its immediate applicability in food processing, such a comprehensive model can be useful in medicine (for thermal therapies such as laser surgery), soil remediation, nuclear waste treatment, and other fields where heat and mass transfer takes place in porous media with significant evaporation and other phase changes.

scholarly journals Modern approaches to the intensification of heat and mass exchange in multi-temperature condensation filters

2021 ◽  
Vol 2039 (1) ◽  
pp. 012018
Author(s):  
M V Malevany ◽  
D A Konovalov
Keyword(s):  
Mass Transfer ◽  
Heat Exchange ◽  
Heat And Mass Transfer ◽  
Liquid Flow ◽  
Mass Exchange ◽  
Single Phase ◽  
Heat And Mass Exchange ◽  
Analytical Review

Abstract The article considers the problems and features of heat and mass exchange on developed surfaces in the conditions of both single-phase and vapour-liquid flow during its condensation. We give a brief analytical review of studies of hydrodynamics and heat exchange in such systems. We analyzed the efficiency of the working channel of the condensation filter and identified problematic points. We offer possible methods for intensifying heat and mass transfer on working surfaces.

scholarly journals MATHEMATICAL MODELING OF THERMOGRAVITATIONAL AND THERMOCA-PILLARY CONVECTION IN GAS-LIQUID PROCESSES

2021 ◽  
Vol 2021 (1) ◽  
pp. 58-66
Author(s):  
Evgeniy Podoplelov ◽  
Aleksey Bal'chugov ◽  
Anatoliy Dement'ev ◽  
Anatoliy Glotov
Keyword(s):  
Mathematical Modeling ◽  
Mass Transfer ◽  
Phase Boundary ◽  
Mass Exchange ◽  
Exchange Process ◽  
Transfer Coefficients ◽  
Mass Exchange Process ◽  
Convective Flows ◽  
Liquid Phases ◽  
Turbulent Pulsations

. The interaction of gas and liquid phases in some cases is accompanied by the spontaneous occur-rence of convective flows and turbulent pulsations at the phase boundary and in adjacent areas. Hy-drodynamic instability allows to accelerate the interfacial transfer of matter and leads to an increase in mass transfer coefficients. Research in this field is not only theoretical, but also practical, since sur-face convection can be artificially created in apparatus for intensifying the mass exchange process.

Modelling coating cohesion effect on soil mechanical stability and permeability of the biopore - matrix interface pore region

2021 ◽  
Author(s):  
Luis Alfredo Pires Barbosa ◽  
Horst H. Gerke
Keyword(s):  
Axial Compression ◽  
Mechanical Stability ◽  
Transport Processes ◽  
Spherical Particles ◽  
External Loading ◽  
Hydraulic Permeability ◽  
Matrix Interface ◽  
Pore Region ◽  
Soil Matrix ◽  
Soil Stiffness

<p>Biopore surface is often characterized by finer particles and increased concentration of polysaccharides from root and earthworm exudates, presenting physico-chemical properties different from those of the soil matrix. Such exudates controls not only the wettability or sorption properties but also the adhesive forces of the surrounding soil particles. Thus, increased mechanical stability may be expected on biopore-matrix interface affecting preferential flow and transport processes, as well.</p> <p>However, it is still unknown (i) to what extent the particle cohesion in the coated region is able to increase the resilience of the biopore to an external loading and (ii) how it affects the permeability of the biopore-matrix pore region.</p> <p>We created a discrete element model (DEM) model of a hollow cylindrical soil sample with a coated biopore in the center (i.e., 1 cm height, 1 cm outer and 0.6 cm inner diameter). The spherical particles in the model presented diameter of 0.13 mm for the coated material and 0.22 mm for the soil matrix. The cohesion among particles in the soil matrix was set to a constant value of 10.9 MPa while the cohesion among particles in the coated region varied between 10.9 and 50.9 MPa. The sample was subjected to axial compression and the force and cracks recorded. The permeability in the radial direction from the biopore to soil matrix was calculated using ImageJ and a 3D stokes solver (FDMMS).</p> <p>The increment in the coating cohesion increased the overall soil stiffness in terms of the Young’s modulus. Before axial compression, the calculated hydraulic permeability for the interface coating and matrix was 182 μm<sup>2</sup>. After compression, although the lower coating cohesion resulted in a larger number of cracks, permeability increased with coating cohesion. This suggests that with increasing soil stiffness, the cracks decrease in number but increase in length (i.e. improved connectivity).</p>

Obvious and less obvious processes of aggregate formation in soil

2021 ◽  
Author(s):  
Hans-Jörg Vogel ◽  
Mar­ia Balseiro-Romero ◽  
Philippe C. Baveye ◽  
Alexandra Kravchenko ◽  
Wilfred Otten ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Structure ◽  
Solid Phase ◽  
Pore Space ◽  
Imaging Techniques ◽  
Mineral Soil ◽  
Aggregate Formation ◽  
Conceptual Approach ◽  
Soil Matrix ◽  
Biophysical Processes

<p>Soil structure, lately referred to as the ''architecture'' is a key to explain and understand all soil functions. The development of sophisticated imaging techniques over the last decades has led to significant progress in the description of this architecture and in particular of the geometry of the hierarchically-branched pore space in which transport of water, gases, solutes and particles occurs and where myriads of organisms live. Moreover, there are sophisticated tools available today to also visualize the spatial structure of the solid phase including mineral grains and organic matter. Hence, we do have access to virtually all components of soil architecture.</p><p>Unfortunately, it has so far proven very challenging to study the dynamics of soil architecture over time, which is of critical importance for soil as habitat and the turnover of organic matter. Several largely conflicting theories have been proposed to account for this dynamics, especially the formation of aggregates. We review these theories, and we propose a conceptual approach to reconcile them based on a consistent interpretation of experimental observations and by integrating known physical and biogeochemical processes. A key conclusion is that rather than concentrating on aggregate formation in the sense of how particles and organic matter reorganize to form aggregates as distinct functional units we should focus on biophysical processes that produce a porous, heterogeneous organo-mineral soil matrix that breaks into fragments of different size and stability when exposed to mechanical stress.  The unified vision we propose for soil architecture and the mechanisms that determine its temporal evolution, should pave the way towards a better understanding of soil processes and functions.</p>

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