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Geomorphology and Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Giovanni Barrocu, Saeid Eslamian
A branching drainage pattern, tree-like in plan, named dendritic drainage pattern, is typical of terrains of uniform lithology, as massive crystalline rocks and clay, where rocks have no conspicuous grain and offer nearly uniform resistance to erosion. Parallel patterns are found on steep slopes with little vegetation cover. Rectangular patterns are often related to the grid-like joint systems found in massive igneous rocks. In radial drainage, streams radiate from the center of a volcano or area of dome uplift. Centripetal drainage is the opposite of the radial type, where drainage is towards a subsiding central basin, as in volcanic craters. Where sediments are uplifted in a dome-like fashion, exploitation of the curved wicker beds can produce striking annular drainage patterns. In tilted sequences of sedimentary rocks, trellis patterns develop. Beds of softer rocks like clays and shale are eroded more quickly than harder rocks. Trunk valleys are opened along the strike of the rocks. Tributaries enter almost at right angles due to the structural control over facies slopes. Such classifications use time as the primary criterion and are qualitative as they do not consider directly the main variables, which influence river channel form. Tortuosity is the ratio of the actual length of a stream channel measured between two points, and along its centerline to the shortest (straight line) distance between those points.
Simulation Techniques for the Characterization of Structural and Transport Properties of Catalyst Pellets
Published in E. Robert Becker, Carmo J. Pereira, Computer-Aided Design of Catalysts, 2020
Sebastian C. Reyes, Enrique Iglesia
Figure 11a described tortuosity factors in compressed and sintered structures as a function of porosity. Tortuosity factors reflect the extended diffusion path length that molecules must follow as they move through the porous solid. Tortuosity is in effect an intrinsic property of the material; it is independent of the diffusion mechanism. In testing this we select a random-loose structure (Φ = 0.418) and use the hybrid technique to calculate tortuosity factors in all diffusion regimes. This requires estimating effective diffusivities (De) by varying the ratio r̄p/λ and calculating tortuosities given by τ=Φ·D¯/De, where D¯ is given by the Bosanquet approximation [12].
Environmental Fate and Transport of Solvent-Stabilizer Compounds
Published in Thomas K.G. Mohr, William H. DiGuiseppi, Janet K. Anderson, James W. Hatton, Jeremy Bishop, Barrie Selcoe, William B. Kappleman, Environmental Investigation and Remediation, 2020
Thomas K.G. Mohr, James Hatton
where L is the length of a straight path through the porous media, Le is the length of a tortuous path around solid grains, De is the effective diffusion coefficient of the water-borne contaminant, and Dw is the calculated or measured diffusion coefficient of the contaminant in pure water (Bear, 1972; Hoffman et al., 1998). The last expression, ϕP, provides an empirical way to obtain tortuosity, where ϕ is porosity and P is an empirical factor selected for the geological medium under consideration (Millington and Quirk, 1961; Parker et al., 1996). Tortuosity, sometimes represented with the Greek letter χ, accounts for all factors that limit solute diffusion through the porous medium such as the tortuous nature of the diffusion path, dead-end pores, and steric hindrance (Young and Ball, 1998). Higher tortuosity factors indicate shorter flow paths. Well-sorted sands (i.e., those that have essentially uniform grain size) have higher tortuosity factors because smaller grains are not filling pore spaces. Tortuosity factors in well-sorted, fine-grained sands range from 0.6 to 0.8, whereas τ in well-sorted, coarse-grained sands averages 0.4; for poorly sorted sands, τ ranges from 0.2 to 0.8 (Fetter, 1993; Hoffman et al., 1998). Barone et al. (1992) obtained tortuosity factors for the subject Sarnia clay of 0.65 from the calculated and measured diffusivities of chloroform and toluene. A theoretical estimate of tortuosity in unconsolidated materials is 0.67 (Bear, 1972).
High-strength clogging resistant permeable pavement
Published in International Journal of Pavement Engineering, 2021
Alalea Kia, Hong S. Wong, Christopher R. Cheeseman
For similar porosities, the permeabilities of CRP were about an order of magnitude larger than that of PC samples. The permeability of the densest CRP (< 5% porosity) were as high as the permeability of the most porous PC tested (> 30% porosity). Therefore, CRP can be engineered with low porosity and very high strength (> 50 MPa), yet with equal flow performance to conventional PC. This striking behaviour can be explained by differences in the pore structure. The pores in conventional PC have a complex structure with variable cross-sections and random interconnectivity. The pores are highly tortuous and heterogeneous. Tortuosity is related to the inverse of connectivity, and usually defined as the ratio of actual flow path length to the straight distance between the ends of the flow path (Bear 1988). Pores in conventional PC produce large tortuosity (> 1), the exact value varies depending on flow path. Conversely, CRP has a homogenous pore structure of constant cross-section and tortuosity of 1. Therefore, flow occurs much faster through CRP compared to conventional PC, resulting in substantially higher permeability.
Evaluation of microstructural properties in sand–sulphur–bitumen (SSB) mixes
Published in Road Materials and Pavement Design, 2021
Bignya Ranjan Pathi, Subhashree Jena, Mahabir Panda
The tortuous path of fluid could be attributed by many factors like the interconnectivity of the pores, irregular shape and size of the pore space, and their complex spatial organisation (Ghanbarian, Hunt, Sahimi, Ewing, & Skinner, 2013a). Due to the absence of direct experimental method to investigate tortuosity, it is often considered as an adjustable parameter in fluid flow equations. Ghanbarian, Hunt, Ewing, and Sahimi (2013b) also observed on the conceptual uncertainty, whether tortuosity is an intrinsic property of the medium, of a process within the medium, or neither, being simply an ad hoc parameter used to improve the agreement between theory and experiment. Nevertheless, recent advancement of laboratory based on X-Ray micro computed tomography (X-Ray CT) and imaging techniques have made it possible to measure tortuosity in various ways. Tjaden et al. (2017) reported that there is a lack of standardisation across different calculation approaches. They also mentioned that the differences between value of tortuosity measured by imaging, simulation and experimental based calculation methods can amount to more than a factor of 2. However, it received little attention because of the actual difficulties in both getting reliable results and understanding data (Barrande, Bouchet, & Denoyel, 2007).
Prediction of effective moisture diffusivity in plant tissue food materials over extended moisture range
Published in Drying Technology, 2020
Younas Dadmohammadi, Ashim K. Datta
Natural porous media such as plant tissue constitutes chaotic pore size distribution and morphology, which induces tortuous and meandering paths for fluid flow.[30] Water molecules must traverse a path inside the plant tissue longer than the actual size of the sample. Tortuosity can be defined as the ratio of the actual distance traveled by the fluid between two points in a porous media to the straight line distance between those two points[41]: where is tortuosity. The quantities and are the true and apparent (straight-line) distances, respectively, between two points in porous media. Tortuosity is an intrinsic property that is solely dependent on the structure of the porous medium.