The Experts below are selected from a list of 84 Experts worldwide ranked by ideXlab platform
Cevdet Demirtas - One of the best experts on this subject based on the ideXlab platform.
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experimental and theoretical analysis of drying carrots
Desalination, 2009Co-Authors: Ahmet Kaya, Orhan Aydin, Cevdet DemirtasAbstract:Abstract The drying characteristics of carrots are investigated experimentally and theoretically for different drying conditions. Carrot slices with three different thicknesses are used. Initially, sorption isotherms of the dried carrot slices are determined for different temperatures and equilibrium relative himidity (e.r.h.). Experiments are conducted for drying air temperatures of 35, 45 and 55°C, mean velocities of 0.2, 0.4 and 0.6 m/s and, relative humidity values of 40, 55 and 70%. In the covered ranges, the values of the effective moisture diffusivity, Deff, are obtained from the Fick's diffusion Model varying from 1.257 × 10−9 to 2.200 × 10−9. The effects of the governing drying parameters on the total drying time are determined. A mathematical Model based on the Fickian Model was established to describe the mass transfer in a carrot slice. Comparison of experimental and calculated results shows good agreement.
Peter K Kitanidis - One of the best experts on this subject based on the ideXlab platform.
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teaching and communicating dispersion in hydrogeology with emphasis on the applicability of the Fickian Model
Advances in Water Resources, 2017Co-Authors: Peter K KitanidisAbstract:Abstract The process of dispersion in porous media is the effect of combined variability in fluid velocity and concentration at scales smaller than the ones resolved that contributes to spreading and mixing. It is usually introduced in textbooks and taught in classes through the Fick-Scheidegger parameterization, which is introduced as a scientific law of universal validity. This parameterization is based on observations in bench-scale laboratory experiments using homogeneous media. Fickian means that dispersive flux is proportional to the gradient of the resolved concentration while the Scheidegger parameterization is a particular way to compute the dispersion coefficients. The unresolved scales are thus associated with the pore-grain geometry that is ignored when the composite pore-grain medium is replaced by a homogeneous continuum. However, the challenge faced in practice is how to account for dispersion in numerical Models that discretize the domain into blocks, often cubic meters in size, that contain multiple geologic facies. Although the Fick-Scheidegger parameterization is by far the one most commonly used, its validity has been questioned. This work presents a method of teaching dispersion that emphasizes the physical basis of dispersion and highlights the conditions under which a Fickian dispersion Model is justified. In particular, we show that Fickian dispersion has a solid physical basis provided that an equilibrium condition is met. The issue of the Scheidegger parameterization is more complex but it is shown that the approximation that the dispersion coefficients should scale linearly with the mean velocity is often reasonable, at least as a practical approximation, but may not necessarily be always appropriate. Generally in Hydrogeology, the Scheidegger feature of constant dispersivity is considered as a physical law and inseparable from the Fickian Model, but both perceptions are wrong. We also explain why Fickian dispersion fails under certain conditions, such as dispersion inside and directly upstream of a contaminant source. Other issues discussed are the relevance of column tests and confusion regarding the meaning of terms dispersion and Fickian.
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a mathematical and computational study of the dispersivity tensor in anisotropic porous media
Advances in Water Resources, 2013Co-Authors: Yuan Liu, Peter K KitanidisAbstract:Abstract Dispersive transport in porous media is usually described through a Fickian Model, in which the flux is the product of a dispersion tensor times the concentration gradient. This Model is based on certain implicit assumptions, including slowly varying conditions. About fifty years ago, it was first suggested that the parameterization of the second-order dispersion tensor for anisotropic porous media involves a fourth-order dispersivity tensor. However, the properties of the dispersivity tensor have not been adequately studied. This work contributes to achieving a better grasp of dispersion in anisotropic porous media through a number of ways. First, with clearly stated assumptions and from first principles, we use the method of moments to derive a mathematical formula for the fourth-order dispersivity tensor, and show that it is a function of pore geometry, fluid velocity, and pore diffusion. Second, by using pore-scale flow and transport simulations through orderly and randomly packed 2-D and 3-D porous media, we evaluate the effects of the three factors on dispersivity. Different relationships with the Peclet number are observed for the longitudinal and transverse dispersivities and for orderly and randomly packed media. Third, we discuss the limitations of 2-D periodic media with simple structures in computing transverse dispersivity, which is more accurately predicted in the 3-D periodic media and 2-D randomly packed media. Fourth, we exhibit through numerical simulations that the method of moments can, computational limitations notwithstanding, be extended to stationary porous media.
Tejraj M Aminabhavi - One of the best experts on this subject based on the ideXlab platform.
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diffusion and sorption of organic liquids through polymer membranes 5 neoprene styrene butadiene rubber ethylene propylene diene terpolymer and natural rubber versus hydrocarbons c8 c16
Macromolecules, 1991Co-Authors: Shivaputrappa B Harogoppad, Tejraj M AminabhaviAbstract:Diffusion and sorption of four long-chain hydrocarbons, namely, 2,2,4-trimethylpentane, dodecane, tetradecane, and hexadecane, through four commercial polymer membranes has been studied in the temperature interval of 25-60°C by conventional weight gain experiments. The diffusion results have been analyzed in terms of the simple Fickian Model. The slightly anomalous transport behavior of the polymer-solvent systems has been attributed to a slow leaching out of the indigenous elastomer compounds and/or additives during solvent immersion
Ahmet Kaya - One of the best experts on this subject based on the ideXlab platform.
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experimental and theoretical analysis of drying carrots
Desalination, 2009Co-Authors: Ahmet Kaya, Orhan Aydin, Cevdet DemirtasAbstract:Abstract The drying characteristics of carrots are investigated experimentally and theoretically for different drying conditions. Carrot slices with three different thicknesses are used. Initially, sorption isotherms of the dried carrot slices are determined for different temperatures and equilibrium relative himidity (e.r.h.). Experiments are conducted for drying air temperatures of 35, 45 and 55°C, mean velocities of 0.2, 0.4 and 0.6 m/s and, relative humidity values of 40, 55 and 70%. In the covered ranges, the values of the effective moisture diffusivity, Deff, are obtained from the Fick's diffusion Model varying from 1.257 × 10−9 to 2.200 × 10−9. The effects of the governing drying parameters on the total drying time are determined. A mathematical Model based on the Fickian Model was established to describe the mass transfer in a carrot slice. Comparison of experimental and calculated results shows good agreement.
John S Roberts - One of the best experts on this subject based on the ideXlab platform.
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measuring moisture diffusivity of potato and carrot core and cortex during convective hot air and isothermal drying
Journal of Food Engineering, 2006Co-Authors: Jaruk Srikiatden, John S RobertsAbstract:Moisture transfer during drying of hygroscopic non-porous materials (potato, carrot core and carrot cortex) was investigated. Drying curves and temperature profiles were obtained from cylindrical samples (0.7 and 1.4 diameter) under convective hot air drying (40, 50, 60, and 70 °C and 1.5 and 3 m/s air velocity). The effective moisture diffusivity of these materials were in the range of reported values. Temperature dependence of the effective moisture diffusivity was found to follow the Arrhenius relationship. However, the prediction of moisture loss failed to follow experimental drying curves. Temperature profiles during convective hot air drying showed temperature gradients, which explains the discrepancy between experimental data and Model predictions. Therefore, an isothermal drying apparatus that combines microwave energy and convective hot air was used to quantify the drying kinetics. Using effective moisture diffusivity experimentally determined under isothermal conditions, Fickian Model was found to accurately predict moisture loss during isothermal drying.