International Nuclear Information System (INIS)
Erckmann, V.; Gasparino, U.; Giannone, L.
1992-01-01
ECRH power modulation experiments in toroidal devices offer the chance to analyze the electron heat transport more conclusively: the electron heat wave propagation can be observed by ECE (or SX) leading to radial profiles of electron temperature modulation amplitude and time delay (phase shift). Taking also the stationary power balance into account, the local electron heat transport can be modelled by a combination of diffusive and convective transport terms. This method is applied to ECRH discharges in the W7-AS stellarator (B=2.5T, R=2m, a≤18 cm) where the ECRH power deposition is highly localized. In W7-AS, the T e modulation profiles measured by a high resolution ECE system are the basis for the local transport analysis. As experimental errors limit the separation of diffusive and convective terms in the electron heat transport for central power deposition, also ECRH power modulation experiments with off-axis deposition and inward heat wave propagation were performed (with 70 GHz o-mode as well as with 140 GHz x-mode for increased absorption). Because collisional electron-ion coupling and radiative losses are only small, low density ECRH discharges are best candidates for estimating the electron heat flux from power balance. (author) 2 refs., 3 figs
Energy Technology Data Exchange (ETDEWEB)
Erckmann, V; Gasparino, U; Giannone, L. (Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)) (and others)
1992-01-01
ECRH power modulation experiments in toroidal devices offer the chance to analyze the electron heat transport more conclusively: the electron heat wave propagation can be observed by ECE (or SX) leading to radial profiles of electron temperature modulation amplitude and time delay (phase shift). Taking also the stationary power balance into account, the local electron heat transport can be modelled by a combination of diffusive and convective transport terms. This method is applied to ECRH discharges in the W7-AS stellarator (B=2.5T, R=2m, a[<=]18 cm) where the ECRH power deposition is highly localized. In W7-AS, the T[sub e] modulation profiles measured by a high resolution ECE system are the basis for the local transport analysis. As experimental errors limit the separation of diffusive and convective terms in the electron heat transport for central power deposition, also ECRH power modulation experiments with off-axis deposition and inward heat wave propagation were performed (with 70 GHz o-mode as well as with 140 GHz x-mode for increased absorption). Because collisional electron-ion coupling and radiative losses are only small, low density ECRH discharges are best candidates for estimating the electron heat flux from power balance. (author) 2 refs., 3 figs.
Modelling of Temperature Profiles and Transport Scaling in Auxiliary Heated Tokamaks
DEFF Research Database (Denmark)
Callen, J.D.; Christiansen, J.P.; Cordey, J.G.
1987-01-01
time , the heating effectiveness η, and the energy offset W(0). Considering both the temperature profile responses and the global transport scaling, the constant heat pinch or excess temperature gradient model is found to best characterize the present JET data. Finally, new methods are proposed......The temperature profiles produced by various heating profiles are calculated from local heat transport models. The models take the heat flux to be the sum of heat diffusion and a non-diffusive heat flow, consistent with local measurements of heat transport. Two models are developed analytically...... in detail: (i) a heat pinch or excess temperature gradient model with constant coefficients; and (ii) a non-linear heat diffusion coefficient (χ) model. Both models predict weak (lesssim20%) temperature profile responses to physically relevant changes in the heat deposition profile – primarily because...
Fractional diffusion models of nonlocal transport
International Nuclear Information System (INIS)
Castillo-Negrete, D. del
2006-01-01
A class of nonlocal models based on the use of fractional derivatives (FDs) is proposed to describe nondiffusive transport in magnetically confined plasmas. FDs are integro-differential operators that incorporate in a unified framework asymmetric non-Fickian transport, non-Markovian ('memory') effects, and nondiffusive scaling. To overcome the limitations of fractional models in unbounded domains, we use regularized FDs that allow the incorporation of finite-size domain effects, boundary conditions, and variable diffusivities. We present an α-weighted explicit/implicit numerical integration scheme based on the Grunwald-Letnikov representation of the regularized fractional diffusion operator in flux conserving form. In sharp contrast with the standard diffusive model, the strong nonlocality of fractional diffusion leads to a linear in time response for a decaying pulse at short times. In addition, an anomalous fractional pinch is observed, accompanied by the development of an uphill transport region where the 'effective' diffusivity becomes negative. The fractional flux is in general asymmetric and, for steady states, it has a negative (toward the core) component that enhances confinement and a positive component that increases toward the edge and leads to poor confinement. The model exhibits the characteristic anomalous scaling of the confinement time, τ, with the system's size, L, τ∼L α , of low-confinement mode plasma where 1<α<2 is the order of the FD operator. Numerical solutions of the model with an off-axis source show that the fractional inward transport gives rise to profile peaking reminiscent of what is observed in tokamak discharges with auxiliary off-axis heating. Also, cold-pulse perturbations to steady sates in the model exhibit fast, nondiffusive propagation phenomena that resemble perturbative experiments
Paleoclassical electron heat transport
International Nuclear Information System (INIS)
Callen, J.D.
2005-01-01
Radial electron heat transport in low collisionality, magnetically-confined toroidal plasmas is shown to result from paleoclassical Coulomb collision processes (parallel electron heat conduction and magnetic field diffusion). In such plasmas the electron temperature equilibrates along magnetic field lines a long length L, which is the minimum of the electron collision length and a maximum effective half length of helical field lines. Thus, the diffusing field lines induce a radial electron heat diffusivity M ≅ L/(πR 0q ) ∼ 10 >> 1 times the magnetic field diffusivity η/μ 0 ≅ ν e (c/ω p ) 2 . The paleoclassical electron heat flux model provides interpretations for many features of 'anomalous' electron heat transport: magnitude and radial profile of electron heat diffusivity (in tokamaks, STs, and RFPs), Alcator scaling in high density plasmas, transport barriers around low order rational surfaces and near a separatrix, and a natural heat pinch (or minimum temperature gradient) heat flux form. (author)
International Nuclear Information System (INIS)
Travis, J.R.
1985-01-01
It is now possible to analyze the time-dependent, fully three-dimensional behavior of hydrogen diffusion flames in nuclear reactor containments. This analysis involves coupling the full Navier-Stokes equations with multi-species transport to the global chemical kinetics of hydrogen combustion. A transport equation for the subgrid scale turbulent kinetic energy density is solved to produce the time and space dependent turbulent transport coefficients. The heat transfer coefficient governing the exchange of heat between fluid computational cells adjacent to wall cells is calculated by a modified Reynolds analogy formulation. The analysis of a MARK-III containment indicates very complex flow patterns that greatly influence fluid and wall temperatures and heat fluxes. 18 refs., 24 figs
Diffusive heat transport across magnetic islands and stochastic layers in tokamaks
International Nuclear Information System (INIS)
Hoelzl, Matthias
2010-01-01
Heat transport in tokamak plasmas with magnetic islands and ergodic field lines was simulated at realistic plasma parameters in realistic tokamak geometries. This requires the treatment of anisotropic heat diffusion, which is more efficient along magnetic field lines by up to ten orders of magnitude than perpendicular to them. Comparisons with analytical predictions and experimental measurements allow to determine the stability properties of neoclassical tearing modes as well as the experimental heat diffusion anisotropy.
Hybrid transport and diffusion modeling using electron thermal transport Monte Carlo SNB in DRACO
Chenhall, Jeffrey; Moses, Gregory
2017-10-01
The iSNB (implicit Schurtz Nicolai Busquet) multigroup diffusion electron thermal transport method is adapted into an Electron Thermal Transport Monte Carlo (ETTMC) transport method to better model angular and long mean free path non-local effects. Previously, the ETTMC model had been implemented in the 2D DRACO multiphysics code and found to produce consistent results with the iSNB method. Current work is focused on a hybridization of the computationally slower but higher fidelity ETTMC transport method with the computationally faster iSNB diffusion method in order to maximize computational efficiency. Furthermore, effects on the energy distribution of the heat flux divergence are studied. Work to date on the hybrid method will be presented. This work was supported by Sandia National Laboratories and the Univ. of Rochester Laboratory for Laser Energetics.
Heat transport modelling in EXTRAP T2R
Frassinetti, L.; Brunsell, P. R.; Cecconello, M.; Drake, J. R.
2009-02-01
A model to estimate the heat transport in the EXTRAP T2R reversed field pinch (RFP) is described. The model, based on experimental and theoretical results, divides the RFP electron heat diffusivity χe into three regions, one in the plasma core, where χe is assumed to be determined by the tearing modes, one located around the reversal radius, where χe is assumed not dependent on the magnetic fluctuations and one in the extreme edge, where high χe is assumed. The absolute values of the core and of the reversal χe are determined by simulating the electron temperature and the soft x-ray and by comparing the simulated signals with the experimental ones. The model is used to estimate the heat diffusivity and the energy confinement time during the flat top of standard plasmas, of deep F plasmas and of plasmas obtained with the intelligent shell.
Understanding of flux-limited behaviors of heat transport in nonlinear regime
Energy Technology Data Exchange (ETDEWEB)
Guo, Yangyu, E-mail: yangyuhguo@gmail.com [Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084 (China); Jou, David, E-mail: david.jou@uab.es [Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia (Spain); Wang, Moran, E-mail: mrwang@tsinghua.edu [Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084 (China)
2016-01-28
The classical Fourier's law of heat transport breaks down in highly nonequilibrium situations as in nanoscale heat transport, where nonlinear effects become important. The present work is aimed at exploring the flux-limited behaviors based on a categorization of existing nonlinear heat transport models in terms of their theoretical foundations. Different saturation heat fluxes are obtained, whereas the same qualitative variation trend of heat flux versus exerted temperature gradient is got in diverse nonlinear models. The phonon hydrodynamic model is proposed to act as a standard to evaluate other heat flux limiters because of its more rigorous physical foundation. A deeper knowledge is thus achieved about the phenomenological generalized heat transport models. The present work provides deeper understanding and accurate modeling of nonlocal and nonlinear heat transport beyond the diffusive limit. - Highlights: • Exploring flux-limited behaviors based on a categorization of existing nonlinear heat transport models. • Proposing phonon hydrodynamic model as a standard to evaluate heat flux limiters. • Providing accurate modeling of nonlocal and nonlinear heat transport beyond the diffusive limit.
International Nuclear Information System (INIS)
Irishkin, M.; Imbeaux, F.; Aniel, T.; Artaud, J.F.
2015-01-01
Highlights: • We developed a method for automated comparison of experimental data with models. • A unique platform implements Bayesian analysis and integrated modelling tools. • The method is tokamak-generic and is applied to Tore Supra and JET pulses. • Validation of a heat transport model is carried out. • We quantified the uncertainties due to Te profiles in current diffusion simulations. - Abstract: In the context of present and future long pulse tokamak experiments yielding a growing size of measured data per pulse, automating data consistency analysis and comparisons of measurements with models is a critical matter. To address these issues, the present work describes an expert system that carries out in an integrated and fully automated way (i) a reconstruction of plasma profiles from the measurements, using Bayesian analysis (ii) a prediction of the reconstructed quantities, according to some models and (iii) a comparison of the first two steps. The first application shown is devoted to the development of an automated comparison method between the experimental plasma profiles reconstructed using Bayesian methods and time dependent solutions of the transport equations. The method was applied to model validation of a simple heat transport model with three radial shape options. It has been tested on a database of 21 Tore Supra and 14 JET shots. The second application aims at quantifying uncertainties due to the electron temperature profile in current diffusion simulations. A systematic reconstruction of the Ne, Te, Ti profiles was first carried out for all time slices of the pulse. The Bayesian 95% highest probability intervals on the Te profile reconstruction were then used for (i) data consistency check of the flux consumption and (ii) defining a confidence interval for the current profile simulation. The method has been applied to one Tore Supra pulse and one JET pulse.
Fractional diffusion models of transport in magnetically confined plasmas
International Nuclear Information System (INIS)
Castillo-Negrete, D. del; Carreras, B. A.; Lynch, V. E.
2005-01-01
Experimental and theoretical evidence suggests that transport in magnetically confined fusion plasmas deviates from the standard diffusion paradigm. Some examples include the confinement time scaling in L-mode plasmas, rapid pulse propagation phenomena, and inward transport in off-axis fueling experiments. The limitations of the diffusion paradigm can be traced back to the restrictive assumptions in which it is based. In particular, Fick's law, one of the cornerstones of diffusive transport, assumes that the fluxes only depend on local quantities, i. e. the spatial gradient of the field (s). another key issue is the Markovian assumption that neglects memory effects. Also, at a microscopic level, standard diffusion assumes and underlying Gaussian, uncorrelated stochastic process (i. e. a Brownian random walk) with well defined characteristic spatio-temporal scales. Motivated by the need to develop models of non-diffusive transport, we discuss here a class of transport models base on the use of fractional derivative operators. The models incorporates in a unified way non-Fickian transport, non-Markovian processes or memory effects, and non-diffusive scaling. At a microscopic level, the models describe an underlying stochastic process without characteristic spatio-temporal scales that generalizes the Brownian random walk. As a concrete case study to motivate and test the model, we consider transport of tracers in three-dimensional, pressure-gradient-driven turbulence. We show that in this system transport is non-diffusive and cannot be described in the context of the standard diffusion parading. In particular, the probability density function (pdf) of the radial displacements of tracers is strongly non-Gaussian with algebraic decaying tails, and the moments of the tracer displacements exhibit super-diffusive scaling. there is quantitative agreement between the turbulence transport calculations and the proposed fractional diffusion model. In particular, the model
Directory of Open Access Journals (Sweden)
Martin Gregory T
2004-11-01
Full Text Available Abstract Background Investigation of bioheat transfer problems requires the evaluation of temporal and spatial distributions of temperature. This class of problems has been traditionally addressed using the Pennes bioheat equation. Transport of heat by conduction, and by temperature-dependent, spatially heterogeneous blood perfusion is modeled here using a transport lattice approach. Methods We represent heat transport processes by using a lattice that represents the Pennes bioheat equation in perfused tissues, and diffusion in nonperfused regions. The three layer skin model has a nonperfused viable epidermis, and deeper regions of dermis and subcutaneous tissue with perfusion that is constant or temperature-dependent. Two cases are considered: (1 surface contact heating and (2 spatially distributed heating. The model is relevant to the prediction of the transient and steady state temperature rise for different methods of power deposition within the skin. Accumulated thermal damage is estimated by using an Arrhenius type rate equation at locations where viable tissue temperature exceeds 42°C. Prediction of spatial temperature distributions is also illustrated with a two-dimensional model of skin created from a histological image. Results The transport lattice approach was validated by comparison with an analytical solution for a slab with homogeneous thermal properties and spatially distributed uniform sink held at constant temperatures at the ends. For typical transcutaneous blood gas sensing conditions the estimated damage is small, even with prolonged skin contact to a 45°C surface. Spatial heterogeneity in skin thermal properties leads to a non-uniform temperature distribution during a 10 GHz electromagnetic field exposure. A realistic two-dimensional model of the skin shows that tissue heterogeneity does not lead to a significant local temperature increase when heated by a hot wire tip. Conclusions The heat transport system model of the
Heat transport in the XXZ spin chain: from ballistic to diffusive regimes and dephasing enhancement
International Nuclear Information System (INIS)
Mendoza-Arenas, J J; Al-Assam, S; Clark, S R; Jaksch, D
2013-01-01
In this work we study the heat transport in an XXZ spin-1/2 Heisenberg chain with homogeneous magnetic field, incoherently driven out of equilibrium by reservoirs at the boundaries. We focus on the effect of bulk dephasing (energy-dissipative) processes in different parameter regimes of the system. The non-equilibrium steady state of the chain is obtained by simulating its evolution under the corresponding Lindblad master equation, using the time evolving block decimation method. In the absence of dephasing, the heat transport is ballistic for weak interactions, while being diffusive in the strongly interacting regime, as evidenced by the heat current scaling with the system size. When bulk dephasing takes place in the system, diffusive transport is induced in the weakly interacting regime, with the heat current monotonically decreasing with the dephasing rate. In contrast, in the strongly interacting regime, the heat current can be significantly enhanced by dephasing for systems of small size. (paper)
Fractional Heat Conduction Models and Thermal Diffusivity Determination
Directory of Open Access Journals (Sweden)
Monika Žecová
2015-01-01
Full Text Available The contribution deals with the fractional heat conduction models and their use for determining thermal diffusivity. A brief historical overview of the authors who have dealt with the heat conduction equation is described in the introduction of the paper. The one-dimensional heat conduction models with using integer- and fractional-order derivatives are listed. Analytical and numerical methods of solution of the heat conduction models with using integer- and fractional-order derivatives are described. Individual methods have been implemented in MATLAB and the examples of simulations are listed. The proposal and experimental verification of the methods for determining thermal diffusivity using half-order derivative of temperature by time are listed at the conclusion of the paper.
Preisach hysteresis model for non-linear 2D heat diffusion
International Nuclear Information System (INIS)
Jancskar, Ildiko; Ivanyi, Amalia
2006-01-01
This paper analyzes a non-linear heat diffusion process when the thermal diffusivity behaviour is a hysteretic function of the temperature. Modelling this temperature dependence, the discrete Preisach algorithm as general hysteresis model has been integrated into a non-linear multigrid solver. The hysteretic diffusion shows a heating-cooling asymmetry in character. The presented type of hysteresis speeds up the thermal processes in the modelled systems by a very interesting non-linear way
A consistent transported PDF model for treating differential molecular diffusion
Wang, Haifeng; Zhang, Pei
2016-11-01
Differential molecular diffusion is a fundamentally significant phenomenon in all multi-component turbulent reacting or non-reacting flows caused by the different rates of molecular diffusion of energy and species concentrations. In the transported probability density function (PDF) method, the differential molecular diffusion can be treated by using a mean drift model developed by McDermott and Pope. This model correctly accounts for the differential molecular diffusion in the scalar mean transport and yields a correct DNS limit of the scalar variance production. The model, however, misses the molecular diffusion term in the scalar variance transport equation, which yields an inconsistent prediction of the scalar variance in the transported PDF method. In this work, a new model is introduced to remedy this problem that can yield a consistent scalar variance prediction. The model formulation along with its numerical implementation is discussed, and the model validation is conducted in a turbulent mixing layer problem.
Progress Report for Diffusion Welding of the NGNP Process Application Heat Exchangers
Energy Technology Data Exchange (ETDEWEB)
R.E. Mizia; D.E. Clark; M.V. Glazoff; T.E. Lister; T.L. Trowbridge
2011-12-01
The U.S. Department of Energy selected the high temperature gas-cooled reactor as the basis for the Next Generation Nuclear Plant (NGNP). The NGNP will demonstrate the use of nuclear power for electricity, hydrogen production, and process heat applications. The NGNP Project is currently investigating the use of metallic, diffusion welded, compact heat exchangers to transfer heat from the primary (reactor side) heat transport system to the secondary heat transport system. An intermediate heat exchanger will transfer this heat to downstream applications such as hydrogen production, process heat, and electricity generation. The channeled plates that make up the heat transfer surfaces of the intermediate heat exchanger will have to be assembled into an array by diffusion welding. This report describes the preliminary results of a scoping study that evaluated the diffusion welding process parameters and the resultant mechanical properties of diffusion welded joints using Alloy 800H. The long-term goal of the program is to progress towards demonstration of small heat exchanger unit cells fabricated with diffusion welds. Demonstration through mechanical testing of the unit cells will support American Society of Mechanical Engineers rules and standards development, reduce technical risk, and provide proof of concept for heat exchanger fabrication methods needed to deploy heat exchangers in several potential NGNP configurations.1 Researchers also evaluated the usefulness of modern thermodynamic and diffusion computational tools (Thermo-Calc and Dictra) in optimizing the parameters for diffusion welding of Alloy 800H. The modeling efforts suggested a temperature of 1150 C for 1 hour with an applied pressure of 5 MPa using 15 {micro}m nickel foil as joint filler to reduce chromium oxidation on the welded surfaces. Good agreement between modeled and experimentally determined concentration gradients was achieved
Anomalous Transport of Cosmic Rays in a Nonlinear Diffusion Model
Energy Technology Data Exchange (ETDEWEB)
Litvinenko, Yuri E. [Department of Mathematics, University of Waikato, P. B. 3105, Hamilton 3240 (New Zealand); Fichtner, Horst; Walter, Dominik [Institut für Theoretische Physik IV, Ruhr-Universität Bochum, Universitätsstrasse 150, D-44780 Bochum (Germany)
2017-05-20
We investigate analytically and numerically the transport of cosmic rays following their escape from a shock or another localized acceleration site. Observed cosmic-ray distributions in the vicinity of heliospheric and astrophysical shocks imply that anomalous, superdiffusive transport plays a role in the evolution of the energetic particles. Several authors have quantitatively described the anomalous diffusion scalings, implied by the data, by solutions of a formal transport equation with fractional derivatives. Yet the physical basis of the fractional diffusion model remains uncertain. We explore an alternative model of the cosmic-ray transport: a nonlinear diffusion equation that follows from a self-consistent treatment of the resonantly interacting cosmic-ray particles and their self-generated turbulence. The nonlinear model naturally leads to superdiffusive scalings. In the presence of convection, the model yields a power-law dependence of the particle density on the distance upstream of the shock. Although the results do not refute the use of a fractional advection–diffusion equation, they indicate a viable alternative to explain the anomalous diffusion scalings of cosmic-ray particles.
Hofmeister, A.
2010-12-01
Many measurements and models of heat transport in lower mantle candidate phases contain systematic errors: (1) conventional methods of insulators involve thermal losses that are pressure (P) and temperature (T) dependent due to physical contact with metal thermocouples, (2) measurements frequently contain unwanted ballistic radiative transfer which hugely increases with T, (3) spectroscopic measurements of dense samples in diamond anvil cells involve strong refraction by which has not been accounted for in analyzing transmission data, (4) the role of grain boundary scattering in impeding heat and light transfer has largely been overlooked, and (5) essentially harmonic physical properties have been used to predict anharmonic behavior. Improving our understanding of the physics of heat transport requires accurate data, especially as a function of temperature, where anharmonicity is the key factor. My laboratory provides thermal diffusivity (D) at T from laser flash analysis, which lacks the above experimental errors. Measuring a plethora of chemical compositions in diverse dense structures (most recently, perovskites, B1, B2, and glasses) as a function of temperature provides a firm basis for understanding microscopic behavior. Given accurate measurements for all quantities: (1) D is inversely proportional to [T x alpha(T)] from ~0 K to melting, where alpha is thermal expansivity, and (2) the damped harmonic oscillator model matches measured D(T), using only two parameters (average infrared dielectric peak width and compressional velocity), both acquired at temperature. These discoveries pertain to the anharmonic aspects of heat transport. I have previously discussed the easily understood quasi-harmonic pressure dependence of D. Universal behavior makes application to the Earth straightforward: due to the stiffness and slow motions of the plates and interior, and present-day, slow planetary cooling rates, Earth can be approximated as being in quasi
International Nuclear Information System (INIS)
Mantica, P.; Gorini, G.; Hogeweij, G.M.D.; Kloe, J. de; Lopez Cardozo, N.J.; Schilham, A.M.R.
2001-01-01
An overview of experimental transport studies performed on the Rijnhuizen Tokamak Project (RTP) using transient transport techniques in both Ohmic and ECH dominated plasmas is presented. Modulated Electron Cyclotron Heating (ECH) and oblique pellet injection (OPI) have been used to induce electron temperature (T e ) perturbations at different radial locations. These were used to probe the electron transport barriers observed near low order rational magnetic surfaces in ECH dominated steady-state RTP plasmas. Layers of inward electron heat convection in off-axis ECH plasmas were detected with modulated ECH. This suggests that RTP electron transport barriers consist of heat pinch layers rather than layers of low thermal diffusivity. In a different set of experiments, OPI triggered a transient rise of the core T e due to an increase of the T e gradient in the 1< q<2 region. These transient transport barriers were probed with modulated ECH and found to be due to a transient drop of the electron heat diffusivity, except for off-axis ECH plasmas, where a transient inward pinch is also observed. Transient transport studies in RTP could not solve this puzzling interplay between heat diffusion and convection in determining an electron transport barrier. They nevertheless provided challenging experimental evidence both for theoretical modelling and for future experiments. (author)
Progress Report for Diffusion Welding of the NGNP Process Application Heat Exchangers
Energy Technology Data Exchange (ETDEWEB)
R.E. Mizia; D.E. Clark; M.V. Glazoff; T.E. Lister; T.L. Trowbridge
2011-04-01
The NGNP Project is currently investigating the use of metallic, diffusion welded, compact heat exchangers to transfer heat from the primary (reactor side) heat transport system to the secondary heat transport system. The intermediate heat exchanger will transfer this heat to downstream applications such as hydrogen production, process heat, and electricity generation. The channeled plates that make up the heat transfer surfaces of the intermediate heat exchanger will have to be assembled into an array by diffusion welding.
A simple Boltzmann transport equation for ballistic to diffusive transient heat transport
International Nuclear Information System (INIS)
Maassen, Jesse; Lundstrom, Mark
2015-01-01
Developing simplified, but accurate, theoretical approaches to treat heat transport on all length and time scales is needed to further enable scientific insight and technology innovation. Using a simplified form of the Boltzmann transport equation (BTE), originally developed for electron transport, we demonstrate how ballistic phonon effects and finite-velocity propagation are easily and naturally captured. We show how this approach compares well to the phonon BTE, and readily handles a full phonon dispersion and energy-dependent mean-free-path. This study of transient heat transport shows (i) how fundamental temperature jumps at the contacts depend simply on the ballistic thermal resistance, (ii) that phonon transport at early times approach the ballistic limit in samples of any length, and (iii) perceived reductions in heat conduction, when ballistic effects are present, originate from reductions in temperature gradient. Importantly, this framework can be recast exactly as the Cattaneo and hyperbolic heat equations, and we discuss how the key to capturing ballistic heat effects is to use the correct physical boundary conditions
Mihaila, Bogdan; Stan, Marius; Crapps, Justin; Yun, Di
2013-02-01
We study the coupled thermal transport, oxygen diffusion, and thermal expansion in a generic nuclear fuel rod consisting of a (U) fuel pellet separated by a helium gap from zircaloy cladding. Steady-state and time-dependent finite-element simulations with a variety of initial- and boundary-value conditions are used to study the effect of the Pu content, y, and deviation from stoichiometry, x, on the temperature and deformation profiles in this fuel element. We find that the equilibrium radial temperature and deformation profiles are most sensitive to x at small values of y. For larger values of y, the effects of oxygen and Pu content are equally important. Following a change in the heat-generation rate, the centerline temperature, the radial deformation of the fuel pellet, and the centerline deviation from stoichiometry track each other closely in (U,Pu)O, as the characteristic time scales of the heat transport and oxygen diffusion are similar. This result is different from the situation observed in the case of UO fuels.
Diffusion induced by cyclotron resonance heating
International Nuclear Information System (INIS)
Riyopoulos, S.; Tajima, T.; Hatori, T.; Pfirsch, D.
1985-09-01
The wave induced particle transport during the ion cyclotron resonance heating is studied in collisionless toroidal plasmas. It is shown that the previously neglected non-conservation of the toroidal angular momentum IP/sub phi/ caused by the toroidal wave component E/sub phi/ is necessary to allow particle diffusion and yields the leading diffusive contribution. While the induced ion transport for the rf power in contemporary experiments is of the order of the neoclassical value, that of fast alpha particles is quite large if resonance is present
Modeling of heat transfer in a horizontal heat-generating layer by an effective diffusivity approach
International Nuclear Information System (INIS)
Cheung, F.B.; Shiah, S.W.
1994-01-01
The concept of effective diffusivity is employed to model various processes of heat transfer in a volumetrically heated fluid layer subjected to different initial and boundary conditions. The approach, which involves the solution of only heat diffusion equations, is found to give rather accurate predictions of the transient response of an initially stagnant fluid layer to a step input of power as well as the developing and decaying nature of the flow following a step change in the internal Rayleigh number from one state of steady convection to another. The approach is also found to be applicable to various flow regions of a heat-generating fluid layer, and is not limited to the case in which the entire layer is in turbulent motion. The simplicity and accuracy of the method are clearly illustrated in the analysis. Validity of the effective diffusivity approach is demonstrated by comparing the predicted results with corresponding experimental data
Wang, Chenghai; Yang, Kai
2018-04-01
Land surface models (LSMs) have developed significantly over the past few decades, with the result that most LSMs can generally reproduce the characteristics of the land surface. However, LSMs fail to reproduce some details of soil water and heat transport during seasonal transition periods because they neglect the effects of interactions between water movement and heat transfer in the soil. Such effects are critical for a complete understanding of water-heat transport within a soil thermohydraulic regime. In this study, a fully coupled water-heat transport scheme (FCS) is incorporated into the Community Land Model (version 4.5) to replaces its original isothermal scheme, which is more complete in theory. Observational data from five sites are used to validate the performance of the FCS. The simulation results at both single-point and global scale show that the FCS improved the simulation of soil moisture and temperature. FCS better reproduced the characteristics of drier and colder surface layers in arid regions by considering the diffusion of soil water vapor, which is a nonnegligible process in soil, especially for soil surface layers, while its effects in cold regions are generally inverse. It also accounted for the sensible heat fluxes caused by liquid water flow, which can contribute to heat transfer in both surface and deep layers. The FCS affects the estimation of surface sensible heat (SH) and latent heat (LH) and provides the details of soil heat and water transportation, which benefits to understand the inner physical process of soil water-heat migration.
Fractional single-phase-lagging heat conduction model for describing anomalous diffusion
Directory of Open Access Journals (Sweden)
T.N. Mishra
2016-03-01
Full Text Available The fractional single-phase-lagging (FSPL heat conduction model is obtained by combining scalar time fractional conservation equation to the single-phase-lagging (SPL heat conduction model. Based on the FSPL heat conduction model, anomalous diffusion within a finite thin film is investigated. The effect of different parameters on solution has been observed and studied the asymptotic behavior of the FSPL model. The analytical solution is obtained using Laplace transform method. The whole analysis is presented in dimensionless form. Numerical examples of particular interest have been studied and discussed in details.
Diffusive-to-ballistic transition of the modulated heat transport in a rarefied air chamber
Directory of Open Access Journals (Sweden)
C. L. Gomez-Heredia
2017-01-01
Full Text Available Modulated heat transfer in air subject to pressures from 760 Torr to 10-4 Torr is experimentally studied by means of a thermal-wave resonant cavity placed in a vacuum chamber. This is done through the analysis of the amplitude and phase delay of the photothermal signal as a function of the cavity length and pressure through of the Knudsen’s number. The viscous, transitional, and free molecular regimes of heat transport are observed for pressures P>1.5 Torr, 25 mTorr
diffusive and ballistic heat transport.
Modelling radionuclide transport in the geosphere: a review of the models available
International Nuclear Information System (INIS)
Cacas, M.C.; Cordier, E.; Coudrain-Ribstein, A.; Fargue, D.; Goblet, P.; Jamet, Ph.; Ledoux, E.; Marsily, G. de; Vinsot, A.; Brun, Ch.; Cernes, A.; Jacquier, Ph.; Lewi, J.; Priem, Th.
1990-01-01
Over the last twelve years, several models have been developed to simulate the transport of radionuclides in the environment of a radioactive waste repository: - continuous equivalent porous media flow and transport models using the finite element method in 1, 2 or 3 dimensions and taking into account various coupled mechanisms; - discontinuous stochastic fracture network models in 3 dimensions representing flow, transport, matrix diffusion, heat flow and mechanical stress; - geochemical models representing interactions between transported elements and a solid matrix; - transport process models coupling non dominant phenomena such as thermo-diffusion or thermo-gravitation. This paper reviews the role that each of these models can play in safety analyses. 3 refs [fr
International Nuclear Information System (INIS)
Yokoyama, Masayuki
2014-01-01
A statistical approach is proposed to predict thermal diffusivity profiles as a transport “model” in fusion plasmas. It can provide regression expressions for the ion and electron heat diffusivities (χ i and χ e ), separately, to construct their radial profiles. An approach that this letter is proposing outstrips the conventional scaling laws for the global confinement time (τ E ) since it also deals with profiles (temperature, density, heating depositions etc.). This approach has become possible with the analysis database accumulated by the extensive application of the integrated transport analysis suite to experiment data. In this letter, TASK3D-a analysis database for high-ion-temperature (high-T i ) plasmas in the LHD (Large Helical Device) is used as an example to describe an approach. (author)
Generalized heat-transport equations: parabolic and hyperbolic models
Rogolino, Patrizia; Kovács, Robert; Ván, Peter; Cimmelli, Vito Antonio
2018-03-01
We derive two different generalized heat-transport equations: the most general one, of the first order in time and second order in space, encompasses some well-known heat equations and describes the hyperbolic regime in the absence of nonlocal effects. Another, less general, of the second order in time and fourth order in space, is able to describe hyperbolic heat conduction also in the presence of nonlocal effects. We investigate the thermodynamic compatibility of both models by applying some generalizations of the classical Liu and Coleman-Noll procedures. In both cases, constitutive equations for the entropy and for the entropy flux are obtained. For the second model, we consider a heat-transport equation which includes nonlocal terms and study the resulting set of balance laws, proving that the corresponding thermal perturbations propagate with finite speed.
A diffusive ink transport model for lipid dip-pen nanolithography
Urtizberea, A.; Hirtz, M.
2015-09-01
Despite diverse applications, phospholipid membrane stacks generated by dip-pen nanolithography (DPN) still lack a thorough and systematic characterization that elucidates the whole ink transport process from writing to surface spreading, with the aim of better controlling the resulting feature size and resolution. We report a quantitative analysis and modeling of the dependence of lipid DPN features (area, height and volume) on dwell time and relative humidity. The ink flow rate increases with humidity in agreement with meniscus size growth, determining the overall feature size. The observed time dependence indicates the existence of a balance between surface spreading and the ink flow rate that promotes differences in concentration at the meniscus/substrate interface. Feature shape is controlled by the substrate surface energy. The results are analyzed within a modified model for the ink transport of diffusive inks. At any humidity the dependence of the area spread on the dwell time shows two diffusion regimes: at short dwell times growth is controlled by meniscus diffusion while at long dwell times surface diffusion governs the process. The critical point for the switch of regime depends on the humidity.Despite diverse applications, phospholipid membrane stacks generated by dip-pen nanolithography (DPN) still lack a thorough and systematic characterization that elucidates the whole ink transport process from writing to surface spreading, with the aim of better controlling the resulting feature size and resolution. We report a quantitative analysis and modeling of the dependence of lipid DPN features (area, height and volume) on dwell time and relative humidity. The ink flow rate increases with humidity in agreement with meniscus size growth, determining the overall feature size. The observed time dependence indicates the existence of a balance between surface spreading and the ink flow rate that promotes differences in concentration at the meniscus
Magnetic flux and heat losses by diffusive, advective, and Nernst effects in MagLIF-like plasma
International Nuclear Information System (INIS)
Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.
2014-01-01
The MagLIF approach to inertial confinement fusion involves subsonic/isobaric compression and heating of a DT plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot plasma to the cold liner is dominated by the transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ω e τ e effective diffusion coefficients determining the losses of heat and magnetic flux are both shown to decrease with ω e τ e as does the Bohm diffusion coefficient, which is commonly associated with low collisionality and two-dimensional transport. This family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics
SEAWAT-based simulation of axisymmetric heat transport.
Vandenbohede, Alexander; Louwyck, Andy; Vlamynck, Nele
2014-01-01
Simulation of heat transport has its applications in geothermal exploitation of aquifers and the analysis of temperature dependent chemical reactions. Under homogeneous conditions and in the absence of a regional hydraulic gradient, groundwater flow and heat transport from or to a well exhibit radial symmetry, and governing equations are reduced by one dimension (1D) which increases computational efficiency importantly. Solute transport codes can simulate heat transport and input parameters may be modified such that the Cartesian geometry can handle radial flow. In this article, SEAWAT is evaluated as simulator for heat transport under radial flow conditions. The 1971, 1D analytical solution of Gelhar and Collins is used to compare axisymmetric transport with retardation (i.e., as a result of thermal equilibrium between fluid and solid) and a large diffusion (conduction). It is shown that an axisymmetric simulation compares well with a fully three dimensional (3D) simulation of an aquifer thermal energy storage systems. The influence of grid discretization, solver parameters, and advection solution is illustrated. Because of the high diffusion to simulate conduction, convergence criterion for heat transport must be set much smaller (10(-10) ) than for solute transport (10(-6) ). Grid discretization should be considered carefully, in particular the subdivision of the screen interval. On the other hand, different methods to calculate the pumping or injection rate distribution over different nodes of a multilayer well lead to small differences only. © 2013, National Ground Water Association.
Perturbative Heat Transport Experiments on TJ-II
International Nuclear Information System (INIS)
Eguilor, S.; Castejon, F.; Luna, E. de la; Cappa, A.; Likin, K.; Fernandez, A.; Tj-II, T.
2002-01-01
Heat wave experiments are performed on TJ-II stellarator plasmas to estimate both heat diffusivity and power deposition profiles. High frequency ECRH modulation experiments are used to obtain the power deposition profiles, which is observed to be wider and duller than estimated by tracing techniques. The causes of this difference are discussed in the paper. Fourier analysis techniques are used to estimate the heat diffusivity in low frequency ECRH modulation experiments. This include the power deposition profile as a new ingredient. ECHR switch on/off experiments are exploited to obtain power deposition and heat diffusivities profile. Those quantities are compared with the obtained by modulation experiments and transport analysis, showing a good agreement. (Author) 18 refs
Perturbative Heat Transport Experiments on TJ-II
Energy Technology Data Exchange (ETDEWEB)
Eguilor, S.; Castejon, F.; Luna, E. de la; Cappa, A.; Likin, K.; Fernandez, A.; Tj-II, T.
2002-07-01
Heat wave experiments are performed on TJ-II stellarator plasmas to estimate both heat diffusivity and power deposition profiles. High frequency ECRH modulation experiments are used to obtain the power deposition profiles, which is observed to be wider and duller than estimated by tracing techniques. The causes of this difference are discussed in the paper. Fourier analysis techniques are used to estimate the heat diffusivity in low frequency ECRH modulation experiments. This include the power deposition profile as a new ingredient. ECHR switch on/off experiments are exploited to obtain power deposition and heat diffusivities profile. Those quantities are compared with the obtained by modulation experiments and transport analysis, showing a good agreement. (Author) 18 refs.
Energy Technology Data Exchange (ETDEWEB)
Kwong, S. [National Nuclear Laboratory (United Kingdom); Jivkov, A.P. [Research Centre for Radwaste and Decommissioning and Modelling and Simulation Centre, University of Manchester (United Kingdom)
2012-07-01
Deep geologic disposal of high activity and long-lived radioactive waste is gaining increasing support in many countries, where suitable low permeability geological formation in combination with engineered barriers are used to provide long term waste contaminant and minimise the impacts to the environment and risk to the biosphere. This modelling study examines the solute transport in fractured media under low flow velocities that are relevant to a deep geological environment. In particular, reactive solute transport through fractured media is studied using a 2-D model, that considers advection and diffusion, to explore the coupled effects of kinetic and equilibrium chemical processes. The effects of water velocity in the fracture, matrix porosity and diffusion on solute transport are investigated and discussed. Some illustrative modelled results are presented to demonstrate the use of the model to examine the effects of media degradation on solute transport, under the influences of hydrogeological (diffusion dominant) and microbially mediated chemical processes. The challenges facing the prediction of long term degradation such as cracks evolution, interaction and coalescence are highlighted. The potential of a novel microstructure informed modelling approach to account for these effects is discussed, particularly with respect to investigating multiple phenomena impact on material performance. The GRM code is used to examine the effects of media degradation for a geological waste disposal package, under the combined hydrogeological (diffusion dominant) and chemical effects in low groundwater flow conditions that are typical of deep geological disposal systems. An illustrative reactive transport modelling application demonstrates the use of the code to examine the interplay of kinetic controlled biogeochemical reactive processes with advective and diffusive transport, under the influence of media degradation. The initial model results are encouraging which show the
Comparison of empirical transport models with transient transport experiments in LHD
International Nuclear Information System (INIS)
Yakovlev, Mikhail; Inagaki, Shigeru; Ida, Katsumi
2004-01-01
A study of the electron transport in helical plasma of Large Helical Device (LHD) has been performed using a perturbation to an equilibrium state. The periodic perturbation in plasma is induced by on-axis Electron Cyclotron Heating (ECH) modulated signal for different temperatures of plasma electron. The experimental data are compared with results from simulation within framework of the diffusive model with additional convective term. The convection heat flux is introduced to describe the heat propagation in LHD. It has been shown that the dynamic plasma heat diffusivity coefficient χ e estimated from the transient analysis becomes larger with increasing electron temperature in LHD plasma. (author)
DEFF Research Database (Denmark)
Shapiro, Alexander
2004-01-01
The theory of transport properties in multicomponent gas and liquid mixtures, which was previously developed for diffusion coefficients, is extended onto thermodiffusion coefficients and heat conductivities. The derivation of the expressions for transport properties is based on the general statis...... of the heat conductivity coefficient for ideal gas. (C) 2003 Elsevier B.V. All rights reserved.......The theory of transport properties in multicomponent gas and liquid mixtures, which was previously developed for diffusion coefficients, is extended onto thermodiffusion coefficients and heat conductivities. The derivation of the expressions for transport properties is based on the general...
Modeling bioluminescent photon transport in tissue based on Radiosity-diffusion model
Sun, Li; Wang, Pu; Tian, Jie; Zhang, Bo; Han, Dong; Yang, Xin
2010-03-01
Bioluminescence tomography (BLT) is one of the most important non-invasive optical molecular imaging modalities. The model for the bioluminescent photon propagation plays a significant role in the bioluminescence tomography study. Due to the high computational efficiency, diffusion approximation (DA) is generally applied in the bioluminescence tomography. But the diffusion equation is valid only in highly scattering and weakly absorbing regions and fails in non-scattering or low-scattering tissues, such as a cyst in the breast, the cerebrospinal fluid (CSF) layer of the brain and synovial fluid layer in the joints. A hybrid Radiosity-diffusion model is proposed for dealing with the non-scattering regions within diffusing domains in this paper. This hybrid method incorporates a priori information of the geometry of non-scattering regions, which can be acquired by magnetic resonance imaging (MRI) or x-ray computed tomography (CT). Then the model is implemented using a finite element method (FEM) to ensure the high computational efficiency. Finally, we demonstrate that the method is comparable with Mont Carlo (MC) method which is regarded as a 'gold standard' for photon transportation simulation.
Energy Technology Data Exchange (ETDEWEB)
Clemencon, A.; Guivarch, C
2003-07-01
In order to make nuclear fusion energetically profitable, it is crucial to heat and confine the plasma efficiently. Studying the behavior of the heat diffusion coefficient is a key issue in this matter. The use of modulated electron cyclotron heating as a diagnostic has suggested the existence of a transport barrier under certain plasma conditions. We have determined the solution to the heat transport equation, for several heat diffusion coefficient profiles. By comparing the analytical solutions with experimental data; we are able to study the heat diffusion coefficient profile. Thus, in certain experiments, we can confirm that the heat diffusion coefficient switches from low to high values at the radius where the electron cyclotron heat deposition is made. (authors)
Energy Technology Data Exchange (ETDEWEB)
Zou, X.L.; Giruzzi, A.G.; Bouquey, F.; Clary, J.; Darbos, C.; Lennholm, M.; Magne, R.; Segui, J.L. [CEA Cadarache, Dept. de Recherches sur la Fusion Controlee, 13 - Saint-Paul-lez-Durance (France); Clemencon, A. [MIT, Electrochemical Energy Laboratory, Cambridge, MA (United States); Guivarch, C. [Ecole Nationale des Ponts et Chaussees, 77 - Marne-la-Vallee (France)
2004-07-01
An exact analytical solution of the electron heat diffusion equation in a cylinder has been found with a step-like diffusion coefficient, plus a monomial increase in the radial direction and a constant damping term. This model is sufficiently general to describe heat diffusion in the presence of a critical gradient threshold or a transport barrier, superimposed to the usual trend of increasing heat diffusivity from the plasma core to the edge. This type of representation allows us to see some well-known properties of heat transport phenomena in a different light. For instance, it has been shown that the contributions of the Eigenmodes to the time dependent solution grow at speeds that depend on the Eigenmode order i.e. at the beginning of the heating phase all the Eigenmodes are equally involved, whereas at the end only the lower order ones are left. This implies, e.g., that high frequency modulation experiments provide a characterization of transport phenomena that is intrinsically different with respect to power balance analysis of a stationary phase. It is particularly useful to analyse power switch on/off events and whenever high frequency modulations are not technically feasible. Low-frequency (1-2 Hz) ECRH modulation experiments have been performed on Tore Supra. A large jump (a factor of 8) in the heat diffusivity has been clearly identified at the ECRH power deposition layer. The amplitude and phase of several harmonics of the Fourier transform of the modulated temperature, as well as the time evolution of the modulated temperature have been reproduced by the analytical solution. The jump is found to be much weaker at lower ECRH power (one gyrotron)
A diffusive ink transport model for lipid dip-pen nanolithography.
Urtizberea, A; Hirtz, M
2015-10-14
Despite diverse applications, phospholipid membrane stacks generated by dip-pen nanolithography (DPN) still lack a thorough and systematic characterization that elucidates the whole ink transport process from writing to surface spreading, with the aim of better controlling the resulting feature size and resolution. We report a quantitative analysis and modeling of the dependence of lipid DPN features (area, height and volume) on dwell time and relative humidity. The ink flow rate increases with humidity in agreement with meniscus size growth, determining the overall feature size. The observed time dependence indicates the existence of a balance between surface spreading and the ink flow rate that promotes differences in concentration at the meniscus/substrate interface. Feature shape is controlled by the substrate surface energy. The results are analyzed within a modified model for the ink transport of diffusive inks. At any humidity the dependence of the area spread on the dwell time shows two diffusion regimes: at short dwell times growth is controlled by meniscus diffusion while at long dwell times surface diffusion governs the process. The critical point for the switch of regime depends on the humidity.
Progress in understanding heat transport at JET
International Nuclear Information System (INIS)
Mantica, P.; Garbet, X.; Angioni, C.
2005-01-01
This paper reports recent progress in understanding heat transport mechanisms either in conventional or advanced tokamak scenarios in JET. A key experimental tool has been the use of perturbative transport techniques, both by ICH power modulation and by edge cold pulses. The availability of such results has allowed careful comparison with theoretical modelling using 1D empirical or physics based transport models, 3D fluid turbulence simulations or gyrokinetic stability analysis. In conventional L- and H-mode plasmas the issue of temperature profile stiffness has been addressed. JET results are consistent with the concept of a critical inverse temperature gradient length above which transport is enhanced by the onset of turbulence. A threshold value R/L Te ∼5 has been found for the onset of stiff electron transport, while the level of electron stiffness appears to vary strongly with plasma parameters, in particular with the ratio of electron and ion heating: electrons become stiffer when ions are strongly heated, resulting in larger R/L Ti values. This behaviour has also been found theoretically, although quantitatively weaker than in experiments. In plasmas characterized by Internal Transport Barriers (ITB), the properties of heat transport inside the ITB layer and the ITB formation mechanisms have been investigated. The plasma current profile is found to play a major role in ITB formation. The effect of negative magnetic shear on electron and ion stabilization is demonstrated both experimentally and theoretically using turbulence codes. The role of rational magnetic surfaces in ITB triggering is well assessed experimentally, but still lacks a convincing theoretical explanation. Attempts to trigger an ITB by externally induced magnetic reconnection using saddle coils have shown that MHD islands in general do not produce a sufficient variation of ExB flow shear to lead to ITB formation. First results of perturbative transport in ITBs show that the ITB is a narrow
An alternative treatment of heat flow for charge transport in semiconductor devices
International Nuclear Information System (INIS)
Grupen, Matt
2009-01-01
A unique thermodynamic model of Fermi gases suitable for semiconductor device simulation is presented. Like other models, such as drift diffusion and hydrodynamics, it employs moments of the Boltzmann transport equation derived using the Fermi-Dirac distribution function. However, unlike other approaches, it replaces the concept of an electron thermal conductivity with the heat capacity of an ideal Fermi gas to determine heat flow. The model is used to simulate a field-effect transistor and show that the external current-voltage characteristics are strong functions of the state space available to the heated Fermi distribution.
Non-standard model for electron heat transport for multidimensional hydrodynamic codes
Energy Technology Data Exchange (ETDEWEB)
Nicolai, Ph.; Busquet, M.; Schurtz, G. [CEA/DAM-Ile de France, 91 - Bruyeres Le Chatel (France)
2000-07-01
In simulations of laser-produced plasma, modeling of heat transport requires an artificial limitation of standard Spitzer-Haerm fluxes. To improve heat conduction processing, we have developed a multidimensional model which accounts for non-local features of heat transport and effects of self-generated magnetic fields. This consistent treatment of both mechanisms has been implemented in a two-dimensional radiation-hydrodynamic code. First results indicate good agreements between simulations and experimental data. (authors)
Non-standard model for electron heat transport for multidimensional hydrodynamic codes
International Nuclear Information System (INIS)
Nicolai, Ph.; Busquet, M.; Schurtz, G.
2000-01-01
In simulations of laser-produced plasma, modeling of heat transport requires an artificial limitation of standard Spitzer-Haerm fluxes. To improve heat conduction processing, we have developed a multidimensional model which accounts for non-local features of heat transport and effects of self-generated magnetic fields. This consistent treatment of both mechanisms has been implemented in a two-dimensional radiation-hydrodynamic code. First results indicate good agreements between simulations and experimental data. (authors)
ECRH and electron heat transport in tokamaks
International Nuclear Information System (INIS)
Zou, X.L.; Giruzzi, G.; Dumont, R.J.
2003-01-01
It has been observed during the ECRH experiments in tokamaks that the shape of the electron temperature profile in stationary regimes is not very sensitive to the ECRH power deposition i.e. the temperature profile remains peaked at the center even though the ECRH power deposition is off-axis. Various models have been invoked for the interpretation of this profile resilience phenomenon: the inward heat pinch, the critical temperature gradient, the Self-Organized Criticality, etc. Except the pinch effect, all of these models need a specific form of the diffusivity in the heat transport equation. In this work, our approach is to solve a simplified time-dependent heat transport equation analytically in cylindrical geometry. The features of this analytical solution are analyzed, in particular the relationship between the temperature profile resilience and the Eigenmode of the physical system with respect to the heat transport phenomenon. Finally, applications of this analytical solution for the determination of the transport coefficient and the polarization of the EC waves are presented. It has been shown that the solution of the simplified transport equation in a finite cylinder is a Fourier-Bessel series. This series represents in fact a decomposition of the heat source in Eigenmode, which are characterized by the Bessel functions of order 0. The physical interpretation of the Eigenmodes is the following: when the heat source is given by a Bessel function of order 0, the temperature profile has exactly the same form as the source at every time. At the beginning of the power injection, the effectiveness of the temperature response is the same for each Eigenmode, and the response in temperature, having the same form as the source, is local. Conversely, in the later phase of the evolution, the effectiveness of the temperature response for each Eigenmode is different: the higher the order, the lower the effectiveness. In this case the response in temperature appears as
On the diffusive nature of W7-AS transport
International Nuclear Information System (INIS)
Stroth, U.; Giannone, L.; Erckmann, V.; Geist, T.; Hartfuss, H.J.; Jaenicke, R.; Kuehner, G.; Ringler, H.; Sardei, F.
1993-01-01
Particle and energy transport in W7-AS have many aspects which are in qualitative agreement with diffusive transport mechanisms. Unlike in tokamaks, the density profiles are flat in the source-free region and for the electron temperature no profile resilience is observed. A strong dependence of transport on the temperature gradient could be ruled out since agreement between the transport coefficients from steady state and perturbative studies has been observed both, in absolute value and parameter dependences. Furthermore, W7-AS transport was found to be compatible with a gyro-Bohm-like and, hence, local transport model. Similar to tokamaks, however, there are problems in relating the local transport coefficients to local plasma parameters. Especially the degradation of confinement with heating power cannot easily be connected to a local quantity. This difficulty is the subject of this paper. (orig.)
1D momentum-conserving systems: the conundrum of anomalous versus normal heat transport
International Nuclear Information System (INIS)
Li, Yunyun; Li, Nianbei; Hänggi, Peter; Li, Baowen; Liu, Sha
2015-01-01
Transport and the spread of heat in Hamiltonian one dimensional momentum conserving nonlinear systems is commonly thought to proceed anomalously. Notable exceptions, however, do exist of which the coupled rotator model is a prominent case. Therefore, the quest arises to identify the origin of manifest anomalous energy and momentum transport in those low dimensional systems. We develop the theory for both, the statistical densities for momentum- and energy-spread and particularly its momentum-/heat-diffusion behavior, as well as its corresponding momentum/heat transport features. We demonstrate that the second temporal derivative of the mean squared deviation of the momentum spread is proportional to the equilibrium correlation of the total momentum flux. Subtracting the part which corresponds to a ballistic momentum spread relates (via this integrated, subleading momentum flux correlation) to an effective viscosity, or equivalently, to the underlying momentum diffusivity. We next put forward the intriguing hypothesis: normal spread of this so adjusted excess momentum density causes normal energy spread and alike normal heat transport (Fourier Law). Its corollary being that an anomalous, superdiffusive broadening of this adjusted excess momentum density in turn implies an anomalous energy spread and correspondingly anomalous, superdiffusive heat transport. This hypothesis is successfully corroborated within extensive molecular dynamics simulations over large extended time scales. Our numerical validation of the hypothesis involves four distinct archetype classes of nonlinear pair-interaction potentials: (i) a globally bounded pair interaction (the noted coupled rotator model), (ii) unbounded interactions acting at large distances (the coupled rotator model amended with harmonic pair interactions), (iii) the case of a hard point gas with unbounded square-well interactions and (iv) a pair interaction potential being unbounded at short distances while displaying an
1D momentum-conserving systems: the conundrum of anomalous versus normal heat transport
Li, Yunyun; Liu, Sha; Li, Nianbei; Hänggi, Peter; Li, Baowen
2015-04-01
Transport and the spread of heat in Hamiltonian one dimensional momentum conserving nonlinear systems is commonly thought to proceed anomalously. Notable exceptions, however, do exist of which the coupled rotator model is a prominent case. Therefore, the quest arises to identify the origin of manifest anomalous energy and momentum transport in those low dimensional systems. We develop the theory for both, the statistical densities for momentum- and energy-spread and particularly its momentum-/heat-diffusion behavior, as well as its corresponding momentum/heat transport features. We demonstrate that the second temporal derivative of the mean squared deviation of the momentum spread is proportional to the equilibrium correlation of the total momentum flux. Subtracting the part which corresponds to a ballistic momentum spread relates (via this integrated, subleading momentum flux correlation) to an effective viscosity, or equivalently, to the underlying momentum diffusivity. We next put forward the intriguing hypothesis: normal spread of this so adjusted excess momentum density causes normal energy spread and alike normal heat transport (Fourier Law). Its corollary being that an anomalous, superdiffusive broadening of this adjusted excess momentum density in turn implies an anomalous energy spread and correspondingly anomalous, superdiffusive heat transport. This hypothesis is successfully corroborated within extensive molecular dynamics simulations over large extended time scales. Our numerical validation of the hypothesis involves four distinct archetype classes of nonlinear pair-interaction potentials: (i) a globally bounded pair interaction (the noted coupled rotator model), (ii) unbounded interactions acting at large distances (the coupled rotator model amended with harmonic pair interactions), (iii) the case of a hard point gas with unbounded square-well interactions and (iv) a pair interaction potential being unbounded at short distances while displaying an
Carbon dioxide sequestration: Modeling the diffusive and convective transport under a CO2 cap
Allen, Rebecca
2012-01-01
A rise in carbon dioxide levels from industrial emissions is contributing to the greenhouse effect and global warming. CO2 sequestration in saline aquifers is a strategy to reduce atmospheric CO2 levels. Scientists and researchers rely on numerical simulators to predict CO2 storage by modeling the fluid transport behaviour. Studies have shown that after CO2 is injected into a saline aquifer, undissolved CO2 rises due to buoyant forces and will spread laterally away from the injection site under an area of low permeability. CO2 from this ‘capped\\' region diffuses into the fluid underlying it, and the resulting CO2-fluid mixture increases in density. This increase in density leads to gravity-driven convection. Accordingly, diffusive-convective transport is important to model since it predicts an enhanced storage capacity of the saline aquifer. This work incorporates the diffusive and convective transport processes into the transport modeling equation, and uses a self-generated code. Discretization of the domain is done with a cell-centered finite difference method. Cases are set up using similar parameters from published literature in order to compare results. Enhanced storage capacity is predicted in this work, similar to work done by others. A difference in the onset of convective transport between this work and published results is noticed and discussed in this paper. A sensitivity analysis is performed on the density model used in this work, and on the diffusivity value assumed. The analysis shows that the density model and diffusivity value is a key component on simulation results. Also, perturbations are added to porosity and permeability in order to see the effect of perturbations on the onset of convection, and results agree with similar findings by others. This work provides a basis for studying other cases, such as the impact of heterogeneity on the diffusion-convective transport. An extension of this work may involve the use of an equation of state to
On the diffusive nature of W7-AS transport
Energy Technology Data Exchange (ETDEWEB)
Stroth, U; Giannone, L.; Erckmann, V; Geist, T; Hartfuss, H J; Jaenicke, R; Kuehner, G; Ringler, H; Sardei, F [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)
1994-12-31
Particle and energy transport in W7-AS have many aspects which are in qualitative agreement with diffusive transport mechanisms. Unlike in tokamaks, the density profiles are flat in the source-free region and for the electron temperature no profile resilience is observed. A strong dependence of transport on the temperature gradient could be ruled out since agreement between the transport coefficients from steady state and perturbative studies has been observed both, in absolute value and parameter dependences. Furthermore, W7-AS transport was found to be compatible with a gyro-Bohm-like and, hence, local transport model. Similar to tokamaks, however, there are problems in relating the local transport coefficients to local plasma parameters. Especially the degradation of confinement with heating power cannot easily be connected to a local quantity. This difficulty is the subject of this paper. (author) 2 refs., 4 figs.
On the diffusive nature of W7-AS transport
International Nuclear Information System (INIS)
Stroth, U.; Giannone, L.; Erckmann, V.; Geist, T.; Hartfuss, H.J.; Jaenicke, R.; Kuehner, G.; Ringler, H.; Sardei, F.
1993-01-01
Particle and energy transport in W7-AS have many aspects which are in qualitative agreement with diffusive transport mechanisms. Unlike in tokamaks, the density profiles are flat in the source-free region and for the electron temperature no profile resilience is observed. A strong dependence of transport on the temperature gradient could be ruled out since agreement between the transport coefficients from steady state and perturbative studies has been observed both, in absolute value and parameter dependences. Furthermore, W7-AS transport was found to be compatible with a gyro-Bohm-like and, hence, local transport model. Similar to tokamaks, however, there are problems in relating the local transport coefficients to local plasma parameters. Especially the degradation of confinement with heating power cannot easily be connected to a local quantity. This difficulty is the subject of this paper. (author) 2 refs., 4 figs
Electron heat transport studies using transient phenomena in ASDEX Upgrade
International Nuclear Information System (INIS)
Jacchia, A.; Angioni, C.; Manini, A.; Ryter, F.; Apostoliceanu, M.; Conway, G.; Fahrbach, H.-U.; Kirov, K.K.; Leuterer, F.; Reich, M.; Sutttrop, W.; Cirant, S.; Mantica, P.; De Luca, F.; Weiland, J.
2005-01-01
Experiments in tokamaks suggest that a critical gradient length may cause the resilient behavior of T e profiles, in the absence of ITBs. This agrees in general with ITG/TEM turbulence physics. Experiments in ASDEX Upgrade using modulation techniques with ECH and/or cold pulses demonstrate the existence of a threshold in R/L Te when T e >T i and T e ≤T i . For T e >T i linear stability analyses indicate that electron heat transport is dominated by TEM modes. They agree in the value of the threshold (both T e and n e ) and for the electron heat transport increase above the threshold. The stabilization of TEM modes by collisions yielded by gyro-kinetic calculations, which suggests a transition from TEM to ITG dominated transport at high collisionality, is experimentally demonstrated by comparing heat pulse and steady-state diffusivities. For the T e ∼T i discharges above the threshold the resilience, normalized by T e 3/2 , is similar to that of the TEM dominated cases, despite very different conditions. The heat pinch predicted by fluid modeling of ITG/TEM turbulence is investigated by perturbative transport in off-axis ECH-heated discharges. (author)
Study on neutron diffusion and time dependence heat ina fluidized bed nuclear reactor
International Nuclear Information System (INIS)
Vilhena, M.T. de.
1988-01-01
The purpose of this work is to model the neutron diffusion and heat transfer for a Fluidized Bed Nuclear Reactor and its solution by Laplace Transform Technique with numerical inversion using Fourier Series. Also Gaussian quadrature and residues techniques were applied for numerical inversion. The neutron transport, diffusion, and point Kinetic equation for this nuclear reactor concept are developed. A matricial and Taylor Series methods are proposed for the solution of the point Kinetic equation which is a time scale problem of Stiff type
DEFF Research Database (Denmark)
Vanderborght, Jan; Smits, Kathleen; Mosthaf, Klaus
Evaporation from the soil surface represents a water flow and transport process in a porous medium that is coupled with free air flow and with heat fluxes in the system. We give an overview of different model concepts that are used to describe this process. These range from non-isothermal two......-phase flow two-component transport in the porous medium that is coupled with one-phase flow two-component transport in the free air to isothermal water flow in the porous with upper boundary conditions defined by a potential evaporation flux when available energy and transfer to the free air flow...... models were found. The effect of vapor flow in the porous medium on cumulative evaporation could be evaluated using the desorptivity, Sevap, which represents a weighted average of liquid and vapor diffusivity over the range of soil water contents between the soil surface water content and the initial...
Theory of ion heat transport in tokamaks
International Nuclear Information System (INIS)
Gott, Y.V.; Yurchenko, E.I.
1987-01-01
Experiments which have been carried out in several tokamaks to determine the ion thermal conductivity show that it is several times the value predicted by the neoclassical theory. A possible explanation for this discrepancy is proposed. When the finite width of a banana is taken into account, there are substantial increases in the heat fluxes which stem from the important contribution of superthermal ions to the transport. If the electron diffusive flux is zero, a systematic account of the ions with E>T leads to an ion heat flux with a finite banana width which is two to four times the neoclassical prediction. The effect of the anomalous nature of the electron flux on the ion heat transport is analyzed. An expression is derived for calculating the ion heat transport over the entire range of collision rates
Electron heat transport in shaped TCV L-mode plasmas
International Nuclear Information System (INIS)
Camenen, Y; Pochelon, A; Bottino, A; Coda, S; Ryter, F; Sauter, O; Behn, R; Goodman, T P; Henderson, M A; Karpushov, A; Porte, L; Zhuang, G
2005-01-01
Electron heat transport experiments are performed in L-mode discharges at various plasma triangularities, using radially localized electron cyclotron heating to vary independently both the electron temperature T e and the normalized electron temperature gradient R/L T e over a large range. Local gyro-fluid (GLF23) and global collisionless gyro-kinetic (LORB5) linear simulations show that, in the present experiments, trapped electron mode (TEM) is the most unstable mode. Experimentally, the electron heat diffusivity χ e is shown to decrease with increasing collisionality, and no dependence of χ e on R/L T e is observed at high R/L T e values. These two observations are consistent with the predictions of TEM simulations, which supports the fact that TEM plays a crucial role in electron heat transport. In addition, over the broad range of positive and negative triangularities investigated, the electron heat diffusivity is observed to decrease with decreasing plasma triangularity, leading to a strong increase of plasma confinement at negative triangularity
Coupled light transport-heat diffusion model for laser dosimetry with dynamic optical properties
International Nuclear Information System (INIS)
London, R.A.; Glinsky, M.E.; Zimmerman, G.B.; Eder, D.C.; Jacques, S.L.
1995-01-01
The effect of dynamic optical properties on the spatial distribution of light in laser therapy is studied via numerical simulations. A two-dimensional, time dependent computer program called LATIS is used. Laser light transport is simulated with a Monte Carlo technique including anisotropic scattering and absorption. Thermal heat transport is calculated with a finite difference algorithm. Material properties are specified on a 2-D mesh and can be arbitrary functions of space and time. Arrhenius rate equations are solved for tissue damage caused by elevated temperatures. Optical properties are functions of tissue damage, as determined by previous measurements. Results are presented for the time variation of the light distribution and damage within the tissue as the optical properties of the tissue are altered
A microscopic model of ballistic-diffusive crossover
International Nuclear Information System (INIS)
Bagchi, Debarshee; Mohanty, P K
2014-01-01
Several low-dimensional systems show a crossover from diffusive to ballistic heat transport when system size is decreased. Although there is some phenomenological understanding of this crossover phenomenon at the coarse-grained level, a microscopic picture that consistently describes both the ballistic and the diffusive transport regimes has been lacking. In this work we derive a scaling form for the thermal current in a class of one dimensional systems attached to heat baths at boundaries and rigorously show that the crossover occurs when the characteristic length scale of the system competes with the system size. (paper)
DEFF Research Database (Denmark)
Nielsen, A. A. F.; Binning, Philip John; Kjeldsen, Peter
2015-01-01
Biocovers — layers of mature compost — can oxidise a considerable amount of methane emitted from landfi Different factors can affect oxidation, particularly tempera- ture. For better understanding of the processes and for future biocover designs, two models (analytic and numerical) were developed......) was 0.95 for the analytic model and 0.91 for the numerical model. The models can be used for different design scenarios (e.g. varying methane infl thickness or start of operation), and can also help understand the processes that take place in the system, e.g. how oxygen penetration depends on ambient....... Both models used the heat equation for heat transfer, and the numerical model used advection-diffusion model with dual Monod kinetics for gas transport. The results were validated with data from a Danish landfi The models correlated well with the observed data: the coefficient of determination (R2...
A non-local model analysis of heat pulse propagation
International Nuclear Information System (INIS)
Iwasaki, T.; Itoh, S.I.; Yagi, M.; Stroth, U.
1998-01-01
The anomalous transport in high temperature plasma has been studied for a long time, from the beginning of the fusion research. Since the electron channel in stellarators and tokamaks is clearly anomalous, it is of fundamental importance to investigate the electron heat diffusivity coefficient, χ e and to understand the physical mechanism. Recently, the experimental data for the transient transport of the heat pulse propagation in fusion plasma has been accumulated. An observation was reported on W7-AS which the heat flux changes faster than the change of the temperature profile, responding to the switching on off of the central heating power. The observation on the transient response has simulated the transport modeling, e.g., the critical marginality which implies the existence of a finite threshold in ∇T for the excitation of the turbulence, or the model in which the thermal conductivity is assumed to depend on the heating power. Extensive study is made by use of these models, and the critical marginally model seems to be insufficient to explain various transient transport. The rapid change of the plasma state and its hysteresis nature were successfully modeled by a heating-power-dependent model. The foundation of this model, however, is left for future work. The development of the transport modeling remains to be an urgent problem. In this paper, we investigate the role of the non-locality of the plasma transport in the study of the heat pulse propagation. For this purpose, a model equation is proposed, in which the non-local effect is taken into account in the heat flux. The properties of this model are investigated by performing a transport simulation. The organization of this paper is as follows: In Sec. II, the model equation is proposed and the properties of the model are explained. Using the model equation, the switching on off experiment is simulated in Sec. III. Summary and discussion are given in Sec. IV. (author)
International Nuclear Information System (INIS)
Marinak, M.
1990-02-01
The problem of deducing χ e from measurements of the propagation of a monopole heatpulse is considered. An extended diffusive model, which takes into account perturbed sources and sinks is extended to the case of a monopole heat input. χ e is expressed as a function of two observables, the heat pulse velocity and the radial damping rate. Two simple expressions valid for two different ranges of the radius of the poloidal waist of the beam power profile are given. The expressions are valid in the heat pulse measurement region, extending radially 0.05a beyond the beam power waist to near 0.6a. The inferred χ e is a local value, not an average value of the radial χ e profile. 7 refs., 6 figs., 1 tab
THE LOS ALAMOS NATIONAL LABORATORY ATMOSPHERIC TRANSPORT AND DIFFUSION MODELS
Energy Technology Data Exchange (ETDEWEB)
M. WILLIAMS [and others
1999-08-01
The LANL atmospheric transport and diffusion models are composed of two state-of-the-art computer codes. The first is an atmospheric wind model called HOThlAC, Higher Order Turbulence Model for Atmospheric circulations. HOTMAC generates wind and turbulence fields by solving a set of atmospheric dynamic equations. The second is an atmospheric diffusion model called RAPTAD, Random Particle Transport And Diffusion. RAPTAD uses the wind and turbulence output from HOTMAC to compute particle trajectories and concentration at any location downwind from a source. Both of these models, originally developed as research codes on supercomputers, have been modified to run on microcomputers. Because the capability of microcomputers is advancing so rapidly, the expectation is that they will eventually become as good as today's supercomputers. Now both models are run on desktop or deskside computers, such as an IBM PC/AT with an Opus Pm 350-32 bit coprocessor board and a SUN workstation. Codes have also been modified so that high level graphics, NCAR Graphics, of the output from both models are displayed on the desktop computer monitors and plotted on a laser printer. Two programs, HOTPLT and RAPLOT, produce wind vector plots of the output from HOTMAC and particle trajectory plots of the output from RAPTAD, respectively. A third CONPLT provides concentration contour plots. Section II describes step-by-step operational procedures, specifically for a SUN-4 desk side computer, on how to run main programs HOTMAC and RAPTAD, and graphics programs to display the results. Governing equations, boundary conditions and initial values of HOTMAC and RAPTAD are discussed in Section III. Finite-difference representations of the governing equations, numerical solution procedures, and a grid system are given in Section IV.
Measurement of heat and momentum eddy diffusivities in recirculating LMFBR outlet plenum flows
International Nuclear Information System (INIS)
Manno, V.P.; Golay, M.W.
1978-06-01
An optical technique has been developed for the measurement of the eddy diffusivity of heat in a transparent flowing medium. The method uses a combination of two established measurement tools: a Mach-Zehnder interferometer for the monitoring of turbulently fluctuating temperature and a Laser Doppler Anemometer (LDA) for the measurement of turbulent velocity fluctuations. The technique is applied to the investigation of flow fields characteristic of the LMFBR outlet plenum. The study is accomplished using air as the working fluid in a small scale Plexiglas test section. Lows are introduced into both the 1 / 15 scale FFTF outlet plenum and the 3 / 80 scale CRBR geometry plenum at inlet Reynolds numbers of 22,000. Measurements of the eddy diffusivity of heat and the eddy diffusivity of momentum are performed at a total of 11 measurement stations. Significant differences of the turbulence parameters are found between the two geometries, and the higher chimney structure of the CRBR case is found to be the major cause of the distinction. Spectral intensity studies of the fluctuating electronic analog signals of velocity and temperature are also performed. Error analysis of the overall technique indicates an experimental error of 10% in the determination of the eddy diffusivity of heat and 6% in the evaluation of turbulent momentum viscosity. In general it is seen that the turbulence in the cases observed is not isotropic, and use of isotropic turbulent heat and momentum diffusivities in transport modelling would not be a valid procedure
Non-diffusive transport in 3-D pressure driven plasma turbulence
International Nuclear Information System (INIS)
Del-Castillo-Negrete, D.; Carreras, B.A.; Lynch, V.
2005-01-01
Numerical evidence of non-diffusive transport in 3-dimensional, resistive, pressure-gradient-driven plasma turbulence is presented. It is shown that the probability density function (pdf) of tracers is strongly non-Gaussian and exhibits algebraic decaying tails. To describe these results, a transport model using fractional derivative operators in proposed. The model incorporates in a unified way non-locality (i.e., non-Fickian transport), memory effects (i.e., non-Markovian transport), and non-diffusive scaling features known to be present in fusion plasmas. There is quantitative agreement between the model and the turbulent transport numerical calculations. In particular, the model reproduces the shape and space-time scaling of the pdf, and the super-diffusive scaling of the moments. (author)
Directory of Open Access Journals (Sweden)
Koca Ilknur
2017-01-01
Full Text Available Recently Hristov using the concept of a relaxation kernel with no singularity developed a new model of elastic heat diffusion equation based on the Caputo-Fabrizio fractional derivative as an extended version of Cattaneo model of heat diffusion equation. In the present article, we solve exactly the Cattaneo-Hristov model and extend it by the concept of a derivative with non-local and non-singular kernel by using the new Atangana-Baleanu derivative. The Cattaneo-Hristov model with the extended derivative is solved analytically with the Laplace transform, and numerically using the Crank-Nicholson scheme.
A practical nonlocal model for heat transport in magnetized laser plasmas
International Nuclear Information System (INIS)
Nicolaie, Ph.D.; Feugeas, J.-L.A.; Schurtz, G.P.
2006-01-01
A model of nonlocal transport for multidimensional radiation magnetohydrodynamics codes is presented. In laser produced plasmas, it is now believed that the heat transport can be strongly modified by the nonlocal nature of the electron conduction. Other mechanisms, such as self-generated magnetic fields, may also affect the heat transport. The model described in this work, based on simplified Fokker-Planck equations aims at extending the model of G. Schurtz, Ph. Nicolaie, and M. Busquet [Phys. Plasmas 7, 4238 (2000)] to magnetized plasmas. A complete system of nonlocal equations is derived from kinetic equations with self-consistent electric and magnetic fields. These equations are analyzed and simplified in order to be implemented into large laser fusion codes and coupled to other relevant physics. The model is applied to two laser configurations that demonstrate the main features of the model and point out the nonlocal Righi-Leduc effect in a multidimensional case
Modeling cytoskeletal traffic: an interplay between passive diffusion and active transport.
Neri, Izaak; Kern, Norbert; Parmeggiani, Andrea
2013-03-01
We introduce the totally asymmetric simple exclusion process with Langmuir kinetics on a network as a microscopic model for active motor protein transport on the cytoskeleton, immersed in the diffusive cytoplasm. We discuss how the interplay between active transport along a network and infinite diffusion in a bulk reservoir leads to a heterogeneous matter distribution on various scales: we find three regimes for steady state transport, corresponding to the scale of the network, of individual segments, or local to sites. At low exchange rates strong density heterogeneities develop between different segments in the network. In this regime one has to consider the topological complexity of the whole network to describe transport. In contrast, at moderate exchange rates the transport through the network decouples, and the physics is determined by single segments and the local topology. At last, for very high exchange rates the homogeneous Langmuir process dominates the stationary state. We introduce effective rate diagrams for the network to identify these different regimes. Based on this method we develop an intuitive but generic picture of how the stationary state of excluded volume processes on complex networks can be understood in terms of the single-segment phase diagram.
A practical nonlocal model for heat transport in magnetized laser plasmas
Nicolaï, Ph. D.; Feugeas, J.-L. A.; Schurtz, G. P.
2006-03-01
A model of nonlocal transport for multidimensional radiation magnetohydrodynamics codes is presented. In laser produced plasmas, it is now believed that the heat transport can be strongly modified by the nonlocal nature of the electron conduction. Other mechanisms, such as self-generated magnetic fields, may also affect the heat transport. The model described in this work, based on simplified Fokker-Planck equations aims at extending the model of G. Schurtz, Ph. Nicolaï, and M. Busquet [Phys. Plasmas 7, 4238 (2000)] to magnetized plasmas. A complete system of nonlocal equations is derived from kinetic equations with self-consistent electric and magnetic fields. These equations are analyzed and simplified in order to be implemented into large laser fusion codes and coupled to other relevant physics. The model is applied to two laser configurations that demonstrate the main features of the model and point out the nonlocal Righi-Leduc effect in a multidimensional case.
International Nuclear Information System (INIS)
Kwong, S.; Jivkov, A.P.
2013-01-01
Deep geologic disposal of high activity and long-lived radioactive waste is being actively considered and pursued in many countries, where low permeability geological formations are used to provide long term waste contaminant with minimum impact to the environment and risk to the biosphere. A multi-barrier approach that makes use of both engineered and natural barriers (i.e. geological formations) is often used to further enhance the containment performance of the repository. As the deep repository system subjects to a variety of thermo-hydro-chemo-mechanical (THCM) effects over its long 'operational' lifespan (e.g. 0.1 to 1.0 million years, the integrity of the barrier system will decrease over time (e.g. fracturing in rock or clay)). This is broadly referred as media degradation in the present study. This modelling study examines the effects of media degradation on diffusion dominant solute transport in fractured media that are typical of deep geological environment. In particular, reactive solute transport through fractured media is studied using a 2-D model, that considers advection and diffusion, to explore the coupled effects of kinetic and equilibrium chemical processes, while the effects of degradation is studied using a pore network model that considers the media diffusivity and network changes. Model results are presented to demonstrate the use of a 3D pore-network model, using a novel architecture, to calculate macroscopic properties of the medium such as diffusivity, subject to pore space changes as the media degrade. Results from a reactive transport model of a representative geological waste disposal package are also presented to demonstrate the effect of media property change on the solute migration behaviour, illustrating the complex interplay between kinetic biogeochemical processes and diffusion dominant transport. The initial modelling results demonstrate the feasibility of a coupled modelling approach (using pore-network model and reactive
TOUGH, Unsaturated Groundwater Transport and Heat Transport Simulation
International Nuclear Information System (INIS)
Pruess, K.A.; Cooper, C.; Osnes, J.D.
1992-01-01
1 - Description of program or function: A successor to the TOUGH program, TOUGH2 offers added capabilities and user features, including the flexibility to handle different fluid mixtures (water, water with tracer; water, CO 2 ; water, air; water, air with vapour pressure lowering, and water, hydrogen), facilities for processing of geometric data (computational grids), and an internal version control system to ensure referenceability of code applications. TOUGH (Transport of Unsaturated Groundwater and Heat) is a multi-dimensional numerical model for simulating the coupled transport of water, vapor, air, and heat in porous and fractured media. The program provides options for specifying injection or withdrawal of heat and fluids. Although primarily designed for studies of high-level nuclear waste isolation in partially saturated geological media, it should also be useful for a wider range of problems in heat and moisture transfer, and in the drying of porous materials. For example, geothermal reservoir simulation problems can be handled simply by setting the air mass function equal to zero on input. The TOUGH simulator was developed for problems involving strongly heat-driven flow. To describe these phenomena a multi-phase approach to fluid and heat flow is used, which fully accounts for the movement of gaseous and liquid phases, their transport of latent transitions between liquid and vapor. TOUGH takes account of fluid flow in both liquid and gaseous phases occurring under pressure, viscous, and gravity forces according to Darcy's law. Interference between the phases is represented by means of relative permeability functions. The code handles binary, but not Knudsen, diffusion in the gas phase and capillary and phase absorption effects for the liquid phase. Heat transport occurs by means of conduction with thermal conductivity dependent on water saturation, convection, and binary diffusion, which includes both sensible and latent heat. 2 - Method of solution: All
Local and Nonlocal Parallel Heat Transport in General Magnetic Fields
International Nuclear Information System (INIS)
Castillo-Negrete, D. del; Chacon, L.
2011-01-01
A novel approach for the study of parallel transport in magnetized plasmas is presented. The method avoids numerical pollution issues of grid-based formulations and applies to integrable and chaotic magnetic fields with local or nonlocal parallel closures. In weakly chaotic fields, the method gives the fractal structure of the devil's staircase radial temperature profile. In fully chaotic fields, the temperature exhibits self-similar spatiotemporal evolution with a stretched-exponential scaling function for local closures and an algebraically decaying one for nonlocal closures. It is shown that, for both closures, the effective radial heat transport is incompatible with the quasilinear diffusion model.
A continuum self organized critically model of turbulent heat transport in tokamaks
Energy Technology Data Exchange (ETDEWEB)
Tangri, V; Das, A; Kaw, P; Singh, R [Institute for Plasma Research, Gandhinagar (India)
2003-09-01
Based on the now well known and experimentally observed critical gradient length (R/L{sub Te} = RT/{nabla}T) in tokamaks, we present a continuum one dimensional model for explaining self organized heat transport in tokamaks. Key parameters of this model include a novel hysteresis parameter which ensures that the switch of heat transport coefficient {chi} upwards and downwards takes place at two different values of R/L{sub Te}. Extensive numerical simulations of this model reproduce many features of present day tokamaks such as submarginal temperature profiles, intermittent transport events, 1/f scaling of the frequency spectra, propagating fronts, etc. This model utilises a minimal set of phenomenological parameters, which may be determined from experiments and/or simulations. Analytical and physical understanding of the observed features has also been attempted. (author)
International Nuclear Information System (INIS)
Colombant, Denis; Manheimer, Wallace
2010-01-01
Flux limitation and preheat are important processes in electron transport occurring in laser produced plasmas. The proper calculation of both of these has been a subject receiving much attention over the entire lifetime of the laser fusion project. Where nonlocal transport (instead of simple single flux limit) has been modeled, it has always been with what we denote the equivalent diffusion solution, namely treating the transport as only a diffusion process. We introduce here a new approach called the nonlocal source solution and show it is numerically viable for laser produced plasmas. It turns out that the equivalent diffusion solution generally underestimates preheat. Furthermore, the advance of the temperature front, and especially the preheat, can be held up by artificial 'thermal barriers'. The nonlocal source method of solution, on the other hand more accurately describes preheat and can stably calculate the solution for the temperature even if the heat flux is up the gradient.
Heat and momentum transport of ion internal transport barrier plasmas on Large Helical Device
International Nuclear Information System (INIS)
Nagaoka, K.; Ida, K.; Yoshinuma, M.
2010-11-01
The peaked ion-temperature profile with steep gradient so called ion internal transport barrier (ion ITB) was formed in the neutral beam heated plasmas on the Large Helical Device (LHD) and the high-ion-temperature regime of helical plasmas has been significantly extended. The ion thermal diffusivity in the ion ITB plasma decreases down to the neoclassical transport level. The heavy ion beam probe (HIBP) observed the smooth potential profile with negative radial electric field (ion root) in the core region where the ion thermal diffusivity decreases significantly. The large toroidal rotation was also observed in the ion ITB core and the transport of toroidal momentum was analyzed qualitatively. The decrease of momentum diffusivity with ion temperature increase was observed in the ion ITB core. The toroidal rotation driven by ion temperature gradient so called intrinsic rotation is also identified. (author)
Heat transport in the quasi-single-helicity islands of EXTRAP T2R
Frassinetti, L.; Brunsell, P. R.; Drake, J.
2009-03-01
The heat transport inside the magnetic island generated in a quasi-single-helicity regime of a reversed-field pinch device is studied by using a numerical code that simulates the electron temperature and the soft x-ray emissivity. The heat diffusivity χe inside the island is determined by matching the simulated signals with the experimental ones. Inside the island, χe turns out to be from one to two orders of magnitude lower than the diffusivity in the surrounding plasma, where the magnetic field is stochastic. Furthermore, the heat transport properties inside the island are studied in correlation with the plasma current and with the amplitude of the magnetic fluctuations.
Stochastic models of intracellular transport
Bressloff, Paul C.
2013-01-09
The interior of a living cell is a crowded, heterogenuous, fluctuating environment. Hence, a major challenge in modeling intracellular transport is to analyze stochastic processes within complex environments. Broadly speaking, there are two basic mechanisms for intracellular transport: passive diffusion and motor-driven active transport. Diffusive transport can be formulated in terms of the motion of an overdamped Brownian particle. On the other hand, active transport requires chemical energy, usually in the form of adenosine triphosphate hydrolysis, and can be direction specific, allowing biomolecules to be transported long distances; this is particularly important in neurons due to their complex geometry. In this review a wide range of analytical methods and models of intracellular transport is presented. In the case of diffusive transport, narrow escape problems, diffusion to a small target, confined and single-file diffusion, homogenization theory, and fractional diffusion are considered. In the case of active transport, Brownian ratchets, random walk models, exclusion processes, random intermittent search processes, quasi-steady-state reduction methods, and mean-field approximations are considered. Applications include receptor trafficking, axonal transport, membrane diffusion, nuclear transport, protein-DNA interactions, virus trafficking, and the self-organization of subcellular structures. © 2013 American Physical Society.
Diffusive flux in a model of stochastically gated oxygen transport in insect respiration
Energy Technology Data Exchange (ETDEWEB)
Berezhkovskii, Alexander M. [Mathematical and Statistical Computing Laboratory, Division of Computational Bioscience, Center for Information Technology, National Institutes of Health, Bethesda, Maryland 20892 (United States); Shvartsman, Stanislav Y. [Department of Chemical and Biological Engineering and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey 08544 (United States)
2016-05-28
Oxygen delivery to insect tissues is controlled by transport through a branched tubular network that is connected to the atmosphere by valve-like gates, known as spiracles. In certain physiological regimes, the spiracles appear to be randomly switching between open and closed states. Quantitative analysis of this regime leads a reaction-diffusion problem with stochastically switching boundary condition. We derive an expression for the diffusive flux at long times in this problem. Our approach starts with the derivation of the passage probability for a single particle that diffuses between a stochastically gated boundary, which models the opening and closing spiracle, and the perfectly absorbing boundary, which models oxygen absorption by the tissue. This passage probability is then used to derive an expression giving the diffusive flux as a function of the geometric parameters of the tube and characteristic time scales of diffusion and gate dynamics.
Chakraverty, S; Sahoo, B K; Rao, T D; Karunakar, P; Sapra, B K
2018-02-01
Modelling radon transport in the earth crust is a useful tool to investigate the changes in the geo-physical processes prior to earthquake event. Radon transport is modeled generally through the deterministic advection-diffusion equation. However, in order to determine the magnitudes of parameters governing these processes from experimental measurements, it is necessary to investigate the role of uncertainties in these parameters. Present paper investigates this aspect by combining the concept of interval uncertainties in transport parameters such as soil diffusivity, advection velocity etc, occurring in the radon transport equation as applied to soil matrix. The predictions made with interval arithmetic have been compared and discussed with the results of classical deterministic model. The practical applicability of the model is demonstrated through a case study involving radon flux measurements at the soil surface with an accumulator deployed in steady-state mode. It is possible to detect the presence of very low levels of advection processes by applying uncertainty bounds on the variations in the observed concentration data in the accumulator. The results are further discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.
Study of the electron heat transport in Tore-Supra tokamak
International Nuclear Information System (INIS)
Harauchamps, E.
2004-01-01
This work presents analytical solutions to the electron heat transport equation involving a damping term and a convection term in a cylindrical geometry. These solutions, processed by Matlab, allow the determination of the evolution of the radial profile of electron temperature in tokamaks during heating. The modulated injection of waves around the electron cyclotron frequency is an efficient tool to study heat transport experimentally in tokamaks. The comparison of these analytical solutions with experimental results from Tore-Supra during 2 discharges (30550 and 31165) shows the presence of a sudden change for the diffusion and damping coefficients. The hypothesis of the presence of a pinch spread all along the plasma might explain the shape of the experimental temperature profiles. These analytical solutions could be used to determine the time evolution of plasma density as well or of any parameter whose evolution is governed by a diffusion-convection equation. (A.C.)
International Nuclear Information System (INIS)
Zamengo, Massimiliano; Funada, Tomohiro; Morikawa, Junko
2017-01-01
Highlights: • Thermal diffusivity of Erythritol was measured by temperature wave method. • Thermal diffusivity was measured in function of temperature and during phase change. • Database of temperature-dependent thermal properties is used for numerical analysis. • Heat transfer and heat storage were analyzed in a fin-type heat exchanger. • Use of temperature-dependent properties in calculations lead to longer melting time. - Abstract: Temperature dependency of thermal diffusivity of erythritol was measured by temperature wave analysis (TWA) method. This modulating technique allowed measuring thermal diffusivity continuously, even during the phase transition solid-liquid. Together with specific heat capacity and specific enthalpy measured by differential scanning calorimetry, the values of measured properties were utilized in a bi-dimensional numerical model for analysis of heat transfer and heat storage performance. The geometry of the model is representative of a cross section of a fin-type heat exchanger, in which erythritol is filling the interspaces between fins. Time-dependent temperature change and heat storage performance were analyzed by considering the variation of thermophysical properties as a function of temperature. The numerical method can be utilized for a fast parametric analysis of heat transfer and heat storage performance into heat storage systems of phase-change materials and composites.
Modelling of shear effects on thermal and particle transport in advanced Tokamak scenarios
International Nuclear Information System (INIS)
Moreau, D.; Voitsekhovitch, I.; Baker, D.R.
1999-01-01
Evolution of thermal and particle internal transport barriers (ITBs) is studied by modelling the time-dependent energy and particle balance in DIII-D plasmas with reversed magnetic shear configurations and in JET discharges with monotonic or slightly reversed q-profiles and large ExB rotation shear. Simulations are performed with semi-empirical models for anomalous diffusion and particle pinch. Stabilizing effects of magnetic and ExB rotation shears are included in anomalous particle and heat diffusivity. Shear effects on particle and thermal transport are compared. Improved particle and energy confinement with the formation of an internal transport barrier (ITB) has been produced in DIII-D plasmas during current ramp-up accompanied with neutral beam injection (NBI). These plasmas are characterized by strong reversed magnetic shear and large ExB rotation shear which provide the reduction of anomalous fluxes. The formation of ITB's in the optimized shear (OS) JET scenario starts with strong NBI heating in a target plasma with a flat or slightly reversed q-profile pre-formed during current ramp-up with ion cyclotron resonance heating (ICRH). Our paper presents the modelling of particle and thermal transport for these scenarios. (authors)
Double diffusivity model under stochastic forcing
Chattopadhyay, Amit K.; Aifantis, Elias C.
2017-05-01
The "double diffusivity" model was proposed in the late 1970s, and reworked in the early 1980s, as a continuum counterpart to existing discrete models of diffusion corresponding to high diffusivity paths, such as grain boundaries and dislocation lines. It was later rejuvenated in the 1990s to interpret experimental results on diffusion in polycrystalline and nanocrystalline specimens where grain boundaries and triple grain boundary junctions act as high diffusivity paths. Technically, the model pans out as a system of coupled Fick-type diffusion equations to represent "regular" and "high" diffusivity paths with "source terms" accounting for the mass exchange between the two paths. The model remit was extended by analogy to describe flow in porous media with double porosity, as well as to model heat conduction in media with two nonequilibrium local temperature baths, e.g., ion and electron baths. Uncoupling of the two partial differential equations leads to a higher-ordered diffusion equation, solutions of which could be obtained in terms of classical diffusion equation solutions. Similar equations could also be derived within an "internal length" gradient (ILG) mechanics formulation applied to diffusion problems, i.e., by introducing nonlocal effects, together with inertia and viscosity, in a mechanics based formulation of diffusion theory. While being remarkably successful in studies related to various aspects of transport in inhomogeneous media with deterministic microstructures and nanostructures, its implications in the presence of stochasticity have not yet been considered. This issue becomes particularly important in the case of diffusion in nanopolycrystals whose deterministic ILG-based theoretical calculations predict a relaxation time that is only about one-tenth of the actual experimentally verified time scale. This article provides the "missing link" in this estimation by adding a vital element in the ILG structure, that of stochasticity, that takes into
International Nuclear Information System (INIS)
Hidalgo Lopez, A.
2002-01-01
The aim of this research is to simulate the isotopic and heat release and transport through the geosphere, from a geological repository of high level nuclear waste. in order to achieve it, different physical processes, that have to do with the problem, are considered: groundwater flow, radioactive decay, nuclide dissolution in groundwater, heat generation, mass and heat transport. Some of these phenomena are related among the, which allows to build a coupled model,which is the starting point to generate a FORTRAN code. The flow and transport models are developed in two spatial dimensions and are integrated in space by means of a finite volume method. The time integration is fulfilled by a θ-method. Moreover, the advection-diffusion equation is solved by two finite volume techniques. In the first one a linear interpolation is used whereas in the second it is used a quadratic one. Also, a consistency an stability study of both methods is carried out in order to compare their stability zones and the errors appearing. Stability is analysed by applying the von Neumann method, which is based upon Fourier series. Although it is a classical technique when dealing with finite-difference schemes, it is here applied to two finite volume schemes. (Author)
Energy Technology Data Exchange (ETDEWEB)
Fujii, H.; Itoi, R.; Fujii, J. [Kyushu University, Fukuoka (Japan). Faculty of Engineering, Department of Earth Resources Engineering; Uchida, Y. [Geological Survey of Japan, Tsukuba (Japan)
2005-06-01
In order to predict the long-term performance of large-scale ground-coupled heat pump (GCHP) systems, it is necessary to take into consideration well-to-well interference, especially in the presence of groundwater flow. A mass and heat transport model was developed to simulate the behavior of this type of system in the Akita Plain, northern Japan. The model was used to investigate different operational schemes and to maximize the heat extraction rate from the GCHP system. (author)
On Diffusive Climatological Models.
Griffel, D. H.; Drazin, P. G.
1981-11-01
A simple, zonally and annually averaged, energy-balance climatological model with diffusive heat transport and nonlinear albedo feedback is solved numerically. Some parameters of the model are varied, one by one, to find the resultant effects on the steady solution representing the climate. In particular, the outward radiation flux, the insulation distribution and the albedo parameterization are varied. We have found an accurate yet simple analytic expression for the mean annual insolation as a function of latitude and the obliquity of the Earth's rotation axis; this has enabled us to consider the effects of the oscillation of the obliquity. We have used a continuous albedo function which fits the observed values; it considerably reduces the sensitivity of the model. Climatic cycles, calculated by solving the time-dependent equation when parameters change slowly and periodically, are compared qualitatively with paleoclimatic records.
International Nuclear Information System (INIS)
Sanchez, R.; Milligen, B.Ph. van; Carreras, B.A.
2005-01-01
It is argued that the modeling of plasma transport in tokamaks may benefit greatly from extending the usual local paradigm to accommodate scale-free transport mechanisms. This can be done by combining Levy distributions and a nonlinear threshold condition within the continuous time random walk concept. The advantages of this nonlocal, nonlinear extension are illustrated by constructing a simple particle density transport model that, as a result of these ideas, spontaneously exhibits much of nondiffusive phenomenology routinely observed in tokamaks. The fluid limit of the system shows that the kind of equations that are appropriate to capture these dynamics are based on fractional differential operators. In them, effective diffusivities and pinch velocities are found that are dynamically set by the system in response to the specific characteristics of the fueling source and external perturbations. This fact suggests some dramatic consequences for the extrapolation of these transport properties to larger size systems
Ubiquity of non-diffusive momentum transport in JET H-modes
Weisen, H.; Camenen, Y.; Salmi, A.; Versloot, T. W.; de Vries, P. C.; Maslov, M.; Tala, T.; Beurskens, M.; Giroud, C.; JET-EFDA Contributors,
2012-01-01
A broad survey of the experimental database of neutral beam heated baseline H-modes and hybrid scenarios in the JET tokamak has established the ubiquity of non-diffusive momentum transport mechanisms in rotating plasmas. As a result of their presence, the normalized angular frequency gradient R
Energy Technology Data Exchange (ETDEWEB)
Duerigen, Susan
2013-05-15
The superior advantage of a nodal method for reactor cores with hexagonal fuel assemblies discretized as cells consisting of equilateral triangles is its mesh refinement capability. In this thesis, a diffusion and a simplified P{sub 3} (or SP{sub 3}) neutron transport nodal method are developed based on trigonal geometry. Both models are implemented in the reactor dynamics code DYN3D. As yet, no other well-established nodal core analysis code comprises an SP{sub 3} transport theory model based on trigonal meshes. The development of two methods based on different neutron transport approximations but using identical underlying spatial trigonal discretization allows a profound comparative analysis of both methods with regard to their mathematical derivations, nodal expansion approaches, solution procedures, and their physical performance. The developed nodal approaches can be regarded as a hybrid NEM/AFEN form. They are based on the transverse-integration procedure, which renders them computationally efficient, and they use a combination of polynomial and exponential functions to represent the neutron flux moments of the SP{sub 3} and diffusion equations, which guarantees high accuracy. The SP{sub 3} equations are derived in within-group form thus being of diffusion type. On this basis, the conventional diffusion solver structure can be retained also for the solution of the SP{sub 3} transport problem. The verification analysis provides proof of the methodological reliability of both trigonal DYN3D models. By means of diverse hexagonal academic benchmark and realistic detailed-geometry full-transport-theory problems, the superiority of the SP{sub 3} transport over the diffusion model is demonstrated in cases with pronounced anisotropy effects, which is, e.g., highly relevant to the modeling of fuel assemblies comprising absorber material.
Sweeney, K. E.; Roering, J. J.; Rempel, A. W.
2012-12-01
Convex hilltops formed by diffusive sediment transport are a fundamental feature of soil-mantled landscapes worldwide. Additionally, the competition and interaction between hillslopes and valleys control basic topographic metrics, such as relief, drainage density, and breaks in slope-area scaling. Despite recent progress in erosive landscape experiments, no published work has explored the competition of hillslope diffusion and channel advection experimentally. Here, we present preliminary findings on the plausibility of needle ice driven frost creep as a mechanism for laboratory hillslope transport of wet sediment. In nature, needle ice is a diurnal form of ice segregation, whereby liquid water held in sediment pore space is driven upward toward a near-surface freezing front by a temperature-controlled liquid pressure gradient. As needles grow perpendicular to the surface, sediment is incorporated in the growing needle ice by temperature perturbations and associated downward shifts in the freezing front. Sediment then moves downslope due to melting or sublimation of the ice needles. We constructed a slope of saturated sediment in a freezer to constrain the temperature, grain size, and soil moisture limits on laboratory needle ice growth and sediment transport. Surficial sediment transport is measured during experimentation by tracking the movement of colored grains. Additionally, at the end of each run we measure depth-dependent sediment transport by taking slices of the experimental slope and observing the displacement of buried columns of colored grains. In agreement with past work, we find that with temperatures just below freezing, soil moisture above 35%, and silt-sized sediment, the moisture migration induced by freezing releases enough latent heat to maintain the location of the freezing front and encourage needle ice growth. Our experiments demonstrate that the amount of sediment incorporated during needle growth, i.e., the transport efficiency, can be
Diffusion in higher dimensional SYK model with complex fermions
Cai, Wenhe; Ge, Xian-Hui; Yang, Guo-Hong
2018-01-01
We construct a new higher dimensional SYK model with complex fermions on bipartite lattices. As an extension of the original zero-dimensional SYK model, we focus on the one-dimension case, and similar Hamiltonian can be obtained in higher dimensions. This model has a conserved U(1) fermion number Q and a conjugate chemical potential μ. We evaluate the thermal and charge diffusion constants via large q expansion at low temperature limit. The results show that the diffusivity depends on the ratio of free Majorana fermions to Majorana fermions with SYK interactions. The transport properties and the butterfly velocity are accordingly calculated at low temperature. The specific heat and the thermal conductivity are proportional to the temperature. The electrical resistivity also has a linear temperature dependence term.
Kolesnichenko, A. V.; Marov, M. Ya.
2018-01-01
The defining relations for the thermodynamic diffusion and heat fluxes in a multicomponent, partially ionized gas mixture in an external electromagnetic field have been obtained by the methods of the kinetic theory. Generalized Stefan-Maxwell relations and algebraic equations for anisotropic transport coefficients (the multicomponent diffusion, thermal diffusion, electric and thermoelectric conductivity coefficients as well as the thermal diffusion ratios) associated with diffusion-thermal processes have been derived. The defining second-order equations are derived by the Chapman-Enskog procedure using Sonine polynomial expansions. The modified Stefan-Maxwell relations are used for the description of ambipolar diffusion in the Earth's ionospheric plasma (in the F region) composed of electrons, ions of many species, and neutral particles in a strong electromagnetic field.
Allen, Rebecca
2011-01-01
done on the diffusive-convective transport that occurs under a cap of CO2-saturated fluid, which results after CO2 is injected into an aquifer and spreads laterally under an area of low permeability. The diffusive-convective modeling reveals an enhanced
Basic Studies of Non-Diffusive Transport in Plasmas
Energy Technology Data Exchange (ETDEWEB)
Morales, George J. [University of California, Los Angeles, CA (United States); Maggs, James E. [University of California, Los Angeles, CA (United States)
2014-10-25
The project expanded and developed mathematical descriptions, and corresponding numerical modeling, of non-diffusive transport to incorporate new perspectives derived from basic transport experiments performed in the LAPD device at UCLA, and at fusion devices throughout the world. By non-diffusive it is meant that the transport of fundamental macroscopic parameters of a system, such as temperature and density, does not follow the standard diffusive behavior predicted by a classical Fokker-Planck equation. The appearance of non-diffusive behavior is often related to underlying microscopic processes that cause the value of a system parameter, at one spatial position, to be linked to distant events, i.e., non-locality. In the LAPD experiments the underlying process was traced to large amplitude, coherent drift-waves that give rise to chaotic trajectories. Significant advances were made in this project. The results have lead to a new perspective about the fundamentals of edge transport in magnetically confined plasmas; the insight has important consequences for worldwide studies in fusion devices. Progress was also made in advancing the mathematical techniques used to describe fractional diffusion.
Thermal diffusivity from heat wave propagation in Wendelstein 7-AS
International Nuclear Information System (INIS)
Hartfuss, H.J.; Erckmann, V.; Giannone, L.; Maassberg, H.; Tutter, M.
1991-01-01
Electron thermal diffusivity studies can be carried out in two ways: static and dynamic. In the static analysis, the transport coefficients are determined from the stationary power balance, in the dynamic analysis from the propagation of a small perturbation of the stationary plasma state which can be caused by either a sawtooth generated heat pulse or modulation of the heating power. Electron thermal diffusivity χ e is deduced from the evolution of the perturbed electron temperature T e at different locations r i in the plasma. χ e values obtained from perturbation analysis are usually greater than those calculated from power balance. It has been pointed out that there is a principal difference between static and perturbative analysis. Whereas the static method yields the transport coefficient χ e = q e /n e ∇T e , the perturbative methods leads to an icnrease of the flux q e as a result of an increase in the temperature gradient ∇T e . The quantity determined is an incremental χ e as defined by χ e inc =δq e /n e δ(∇T e ). By varying the modulation of the heating power at different frequencies and amplitudes one can address the question whether or not this discrepancy is a function of the varied parameters. (orig.)
Diffusion bonding in compact heat exchangers
International Nuclear Information System (INIS)
Southall, David
2009-01-01
Heatric's diffusion bonding process is a solid-state joining technology that produces strong, compact, all-metal heat exchanger cores. Diffusion bonding allows for a large quantity of joints to be made in geometries that would normally be inaccessible for conventional welding techniques. Since Heatric's diffusion bonding process uses no interlayer or braze alloy, the resulting heat exchanger core has consistent chemistry throughout and, under carefully controlled conditions, a return to parent metal strength can be reached. This paper will provide an overview of the diffusion bonding process and its origins, and also its application to compact heat exchanger construction. The paper will then discuss recent work that has been done to compare mechanical properties of Heatric's diffusion bonded material with material that has been conventionally welded, as well as with material tested in the as-received condition. (author)
Recent developments of diffusion processes and their applications fluid, heat and mass
Öchsner, Andreas; Murch, Graeme
2015-01-01
This topical volume on ""Recent Developments of Diffusion Processes and their Applications: Fluid, Heat and Mass"" addresses diffusion in a wider sense with a special focus on technical applications. Diffusion phenomena play an important role in the development of modern engineering materials and related fields. Understanding these different transport phenomena at many levels, from atomistic to macro, has therefore long attracted the attention of many researchers in materials science and engineering and related disciplines. The present topical volume captures a representative cross-section of
Hol C Y; Chen, B C; Tsai, Y H; Ma, C; Wen, M Y
2015-11-01
This paper investigates the thermal transport in hollow microscale and nanoscale spheres subject to electrical heat source using nontraditional thermal transport model. Working as supercapacitor electrodes, carbon hollow micrometer- and nanometer-sized spheres needs excellent heat transfer characteristics to maintain high specific capacitance, long cycle life, and high power density. In the nanoscale regime, the prediction of heat transfer from the traditional heat conduction equation based on Fourier's law deviates from the measured data. Consequently, the electrical heat source-induced heat transfer characteristics in hollow micrometer- and nanometer-sized spheres are studied using nontraditional thermal transport model. The effects of parameters on heat transfer in the hollow micrometer- and nanometer-sized spheres are discussed in this study. The results reveal that the heat transferred into the spherical interior, temperature and heat flux in the hollow sphere decrease with the increasing Knudsen number when the radius of sphere is comparable to the mean free path of heat carriers.
Sánchez, R.; van Milligen, B. Ph.; Carreras, B. A.
2005-05-01
It is argued that the modeling of plasma transport in tokamaks may benefit greatly from extending the usual local paradigm to accommodate scale-free transport mechanisms. This can be done by combining Lévy distributions and a nonlinear threshold condition within the continuous time random walk concept. The advantages of this nonlocal, nonlinear extension are illustrated by constructing a simple particle density transport model that, as a result of these ideas, spontaneously exhibits much of nondiffusive phenomenology routinely observed in tokamaks. The fluid limit of the system shows that the kind of equations that are appropriate to capture these dynamics are based on fractional differential operators. In them, effective diffusivities and pinch velocities are found that are dynamically set by the system in response to the specific characteristics of the fueling source and external perturbations. This fact suggests some dramatic consequences for the extrapolation of these transport properties to larger size systems.
Ancey, Christophe; Bohorquez, Patricio; Heyman, Joris
2016-04-01
The advection-diffusion equation arises quite often in the context of sediment transport, e.g., for describing time and space variations in the particle activity (the solid volume of particles in motion per unit streambed area). Stochastic models can also be used to derive this equation, with the significant advantage that they provide information on the statistical properties of particle activity. Stochastic models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. We develop an approach based on birth-death Markov processes, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received little attention. We show that particle advection produces nonlocal effects, which are more or less significant depending on the cell size and particle velocity. Albeit nonlocal, these effects look like (local) diffusion and add to the intrinsic particle diffusion (dispersal due to velocity fluctuations), with the important consequence that local measurements depend on both the intrinsic properties of particle displacement and the dimensions of the measurement system.
Transport modelling for ergodic configurations
International Nuclear Information System (INIS)
Runov, A.; Kasilov, S.V.; McTaggart, N.; Schneider, R.; Bonnin, X.; Zagorski, R.; Reiter, D.
2004-01-01
The effect of ergodization, either by additional coils like in TEXTOR-dynamic ergodic divertor (DED) or by intrinsic plasma effects like in W7-X, defines the need for transport models that are able to describe the ergodic configuration properly. A prerequisite for this is the concept of local magnetic coordinates allowing a correct discretization with minimized numerical errors. For these coordinates the appropriate full metric tensor has to be known. To study the transport in complex edge geometries (in particular for W7-X) two possible methods are used. First, a finite-difference discretization of the transport equations on a custom-tailored grid in local magnetic coordinates is used. This grid is generated by field-line tracing to guarantee an exact discretization of the dominant parallel transport (thus also minimizing the numerical diffusion problem). The perpendicular fluxes are then interpolated in a plane (a toroidal cut), where the interpolation problem for a quasi-isotropic system has to be solved by a constrained Delaunay triangulation (keeping the structural information for magnetic surfaces if they exist) and discretization. All toroidal terms are discretized by finite differences. Second, a Monte Carlo transport model originally developed for the modelling of the DED configuration of TEXTOR is used. A generalization and extension of this model was necessary to be able to handle W7-X. The model solves the transport equations with Monte Carlo techniques making use of mappings of local magnetic coordinates. The application of this technique to W7-X in a limiter-like configuration is presented. The decreasing dominance of parallel transport with respect to radial transport for electron heat, ion heat and particle transport results in increasingly steep profiles for the respective quantities within the islands. (author)
Allen, Rebecca
2011-05-01
An increase in the earth’s surface temperature has been directly linked to the rise of carbon dioxide (CO2) levels In the atmosphere and an enhanced greenhouse effect. CO2 sequestration is one of the proposed mitigation Strategies in the effort to reduce atmospheric CO2 concentrations. Globally speaking, saline aquifers provide an adequate storage capacity for the world’s carbon emissions, and CO2 sequestration projects are currently underway in countries such as Norway, Germany, Japan, USA, and others. Numerical simulators serve as predictive tools for CO2 storage, yet must model fluid transport behavior while coupling different transport processes together accurately. With regards to CO2 sequestration, an extensive amount of research has been done on the diffusive-convective transport that occurs under a cap of CO2-saturated fluid, which results after CO2 is injected into an aquifer and spreads laterally under an area of low permeability. The diffusive-convective modeling reveals an enhanced storage capacity in saline aquifers, due to the density increase between pure fluid and CO2‐saturated fluid. This work presents the transport modeling equations that are used for diffusive- convective modeling. A cell-centered finite difference method is used, and simulations are run using MATLAB. Two cases are explored in order to compare the results from this work’s self-generated code with the results published in literature. Simulation results match relatively well, and the discrepancy for a delayed onset time of convective transport observed in this work is attributed to numerical artifacts. In fact, onset time in this work is directly attributed to the instability of the physical system: this instability arises from non-linear coupling of fluid flow, transport, and convection, but is triggered by numerical errors in these simulations. Results from this work enable the computation of a value for the numerical constant that appears in the onset time equation that
Analytical modelling of hydrogen transport in reactor containments
International Nuclear Information System (INIS)
Manno, V.P.
1983-09-01
A versatile computational model of hydrogen transport in nuclear plant containment buildings is developed. The background and significance of hydrogen-related nuclear safety issues are discussed. A computer program is constructed that embodies the analytical models. The thermofluid dynamic formulation spans a wide applicability range from rapid two-phase blowdown transients to slow incompressible hydrogen injection. Detailed ancillary models of molecular and turbulent diffusion, mixture transport properties, multi-phase multicomponent thermodynamics and heat sink modelling are addressed. The numerical solution of the continuum equations emphasizes both accuracy and efficiency in the employment of relatively coarse discretization and long time steps. Reducing undesirable numerical diffusion is addressed. Problem geometry options include lumped parameter zones, one dimensional meshs, two dimensional Cartesian or axisymmetric coordinate systems and three dimensional Cartesian or cylindrical regions. An efficient lumped nodal model is included for simulation of events in which spatial resolution is not significant. Several validation calculations are reported
International Nuclear Information System (INIS)
Put, M.; Henrion, P.
1992-01-01
For the modelling of the migration of radionuclides in the Boom clay formation, the analytical code MICOF has been updated with a 3-dimensional analytical solution for discrete sources. the MICOF program is used for the calculation of the release of α and β emitters from the HIGH LEVEL RADIOACTIVE WASTES (HLW). A coherent conceptual model is developed which describes all the major physico-chemical phenomena influencing the migration of radionuclides in the Boom clay. The concept of the diffusion accessible porosity is introduced and included in the MICOF code. Different types of migration experiments are described with their advantages and disadvantages. The thermal impact of the HLW disposal in the stratified Boom clay formation has been evaluated by a finite element simulation of the coupled heat and mass transport equation. The results of the simulations show that under certain conditions thermal convection cells may form, but the convective heat transfer in the clay formation is negligible. 6 refs., 19 figs., 2 tabs., 5 appendices
Multimodel analysis of anisotropic diffusive tracer-gas transport in a deep arid unsaturated zone
Green, Christopher T.; Walvoord, Michelle Ann; Andraski, Brian J.; Striegl, Robert G.; Stonestrom, David A.
2015-01-01
Gas transport in the unsaturated zone affects contaminant flux and remediation, interpretation of groundwater travel times from atmospheric tracers, and mass budgets of environmentally important gases. Although unsaturated zone transport of gases is commonly treated as dominated by diffusion, the characteristics of transport in deep layered sediments remain uncertain. In this study, we use a multimodel approach to analyze results of a gas-tracer (SF6) test to clarify characteristics of gas transport in deep unsaturated alluvium. Thirty-five separate models with distinct diffusivity structures were calibrated to the tracer-test data and were compared on the basis of Akaike Information Criteria estimates of posterior model probability. Models included analytical and numerical solutions. Analytical models provided estimates of bulk-scale apparent diffusivities at the scale of tens of meters. Numerical models provided information on local-scale diffusivities and feasible lithological features producing the observed tracer breakthrough curves. The combined approaches indicate significant anisotropy of bulk-scale diffusivity, likely associated with high-diffusivity layers. Both approaches indicated that diffusivities in some intervals were greater than expected from standard models relating porosity to diffusivity. High apparent diffusivities and anisotropic diffusivity structures were consistent with previous observations at the study site of rapid lateral transport and limited vertical spreading of gas-phase contaminants. Additional processes such as advective oscillations may be involved. These results indicate that gases in deep, layered unsaturated zone sediments can spread laterally more quickly, and produce higher peak concentrations, than predicted by homogeneous, isotropic diffusion models.
Improved age-diffusion model for low-energy electron transport in solids. I. Theory
International Nuclear Information System (INIS)
Devooght, J.; Dubus, A.; Dehaes, J.C.
1987-01-01
We have developed in this paper a semianalytical electron transport model designed for parametric studies of secondary-electron emission induced by low-energy electrons (keV range) and by fast light ions (100 keV range). The primary-particle transport is assumed to be known and to give rise to an internal electron source. The importance of the nearly isotropic elastic scattering in the secondary-electron energy range (50 eV) and the slowing-down process strongly reduce the influence of the anisotropy of the internal electron source, and the internal electron flux is nearly isotropic as is evidenced by the experimental results. The differential energy behavior of the inelastic scattering kernel is very complicated and the real kernel is replaced by a synthetic scattering kernel of which parameters are obtained by energy and angle moments conservation. Through a P 1 approximation and the use of the synthetic scattering kernel, the Boltzmann equation is approximated by a diffusion--slowing-down equation for the isotropic part of the internal electron flux. The energy-dependent partial reflection boundary condition reduces to a Neumann-Dirichlet boundary condition. An analytical expression for the Green's function of the diffusion--slowing-down equation with the surface boundary condition is obtained by means of approximations close to the age-diffusion theory and the model allows for transient conditions. Independently from the ''improved age-diffusion'' model, a correction formula is developed in order to take into account the backscattering of primary electrons for an incident-electron problem
Three dimensional heat transport modeling in Vossoroca reservoir
Arcie Polli, Bruna; Yoshioka Bernardo, Julio Werner; Hilgert, Stephan; Bleninger, Tobias
2017-04-01
Freshwater reservoirs are used for many purposes as hydropower generation, water supply and irrigation. In Brazil, according to the National Energy Balance of 2013, hydropower energy corresponds to 70.1% of the Brazilian demand. Superficial waters (which include rivers, lakes and reservoirs) are the most used source for drinking water supply - 56% of the municipalities use superficial waters as a source of water. The last two years have shown that the Brazilian water and electricity supply is highly vulnerable and that improved management is urgently needed. The construction of reservoirs affects physical, chemical and biological characteristics of the water body, e.g. stratification, temperature, residence time and turbulence reduction. Some water quality issues related to reservoirs are eutrophication, greenhouse gas emission to the atmosphere and dissolved oxygen depletion in the hypolimnion. The understanding of the physical processes in the water body is fundamental to reservoir management. Lakes and reservoirs may present a seasonal behavior and stratify due to hydrological and meteorological conditions, and especially its vertical distribution may be related to water quality. Stratification can control heat and dissolved substances transport. It has been also reported the importance of horizontal temperature gradients, e.g. inflows and its density and processes of mass transfer from shallow to deeper regions of the reservoir, that also may impact water quality. Three dimensional modeling of the heat transport in lakes and reservoirs is an important tool to the understanding and management of these systems. It is possible to estimate periods of large vertical temperature gradients, inhibiting vertical transport and horizontal gradients, which could be responsible for horizontal transport of heat and substances (e.g. differential cooling or inflows). Vossoroca reservoir was constructed in 1949 by the impoundment of São João River and is located near to
Diffusion as a Ruler: Modeling Kinesin Diffusion as a Length Sensor for Intraflagellar Transport.
Hendel, Nathan L; Thomson, Matthew; Marshall, Wallace F
2018-02-06
An important question in cell biology is whether cells are able to measure size, either whole cell size or organelle size. Perhaps cells have an internal chemical representation of size that can be used to precisely regulate growth, or perhaps size is just an accident that emerges due to constraint of nutrients. The eukaryotic flagellum is an ideal model for studying size sensing and control because its linear geometry makes it essentially one-dimensional, greatly simplifying mathematical modeling. The assembly of flagella is regulated by intraflagellar transport (IFT), in which kinesin motors carry cargo adaptors for flagellar proteins along the flagellum and then deposit them at the tip, lengthening the flagellum. The rate at which IFT motors are recruited to begin transport into the flagellum is anticorrelated with the flagellar length, implying some kind of communication between the base and the tip and possibly indicating that cells contain some mechanism for measuring flagellar length. Although it is possible to imagine many complex scenarios in which additional signaling molecules sense length and carry feedback signals to the cell body to control IFT, might the already-known components of the IFT system be sufficient to allow length dependence of IFT? Here we investigate a model in which the anterograde kinesin motors unbind after cargo delivery, diffuse back to the base, and are subsequently reused to power entry of new IFT trains into the flagellum. By mathematically modeling and simulating such a system, we are able to show that the diffusion time of the motors can in principle be sufficient to serve as a proxy for length measurement. We found that the diffusion model can not only achieve a stable steady-state length without the addition of any other signaling molecules or pathways, but also is able to produce the anticorrelation between length and IFT recruitment rate that has been observed in quantitative imaging studies. Copyright © 2017 Biophysical
Diffusion transport of nanoparticles at nanochannel boundaries
International Nuclear Information System (INIS)
Mahadevan, T. S.; Milosevic, M.; Kojic, M.; Hussain, F.; Kojic, N.; Serda, R.; Ferrari, M.; Ziemys, A.
2013-01-01
The manipulation of matter at the nanoscale has unleashed a great potential for engineering biomedical drug carriers, but the transport of nanoparticles (NPs) under nanoscale confinement is still poorly understood. Using colloidal physics to describe NP interactions, we have computationally studied the passive transport of NPs using experimentally relevant conditions from bulk into a nanochannel of 60–90 nm height. NP size, channel height, and the Debye length are comparable so that changes in nanoscale dimensions may induce substantial changes in NP transport kinetics. We show that subtle changes in nanochannel dimensions may alter the energy barrier by about six orders of magnitude resulting in different NP penetration depths and diffusion mechanisms: ballistic, first-order and quasi zero-order transport regimes. The analysis of NP diffusion by continuum methods reveals that apparent diffusivity is reduced by decreasing channel size. The continuum finite element (FE) numerical method reproduced the colloidal model results only when surface interactions were accounted for. These results give a new insight into NP passive transport at the boundaries of nanoconfined domains, and have implications on the design of nanoscale fluidics and NP systems for biomedical and engineering applications.
Heat pulse analysis in JET and relation to local energy transport models
International Nuclear Information System (INIS)
Haas, J.C.M. de; Lopes Cardozo, N.J.; Han, W.; Sack, C.; Taroni, A.
1989-01-01
The evolution of a perturbation T e of the electron temperature depends on the linearised expression of the heat flux q e and may be not simply related to the local value of the electron heat conductivity χ e . It is possible that local heat transport models predicting similar temperature profiles and global energy confinement properties, imply a different propagation of heat pulses. We investigate here this possibility for the case of two models developed at JET. We also present results obtained at JET on a set of discharges covering the range of currents from 2 to 5 MA. Only L-modes, limiter discharges are considered here. Experimental results on the scaling of χ HP , the value of χ e related to heat pulse propagation, are compared with those of χ HP derived from the models. (author) 7 refs., 2 figs., 2 tabs
From conservative to reactive transport under diffusion-controlled conditions
Babey, Tristan; de Dreuzy, Jean-Raynald; Ginn, Timothy R.
2016-05-01
We assess the possibility to use conservative transport information, such as that contained in transit time distributions, breakthrough curves and tracer tests, to predict nonlinear fluid-rock interactions in fracture/matrix or mobile/immobile conditions. Reference simulated data are given by conservative and reactive transport simulations in several diffusive porosity structures differing by their topological organization. Reactions includes nonlinear kinetically controlled dissolution and desorption. Effective Multi-Rate Mass Transfer models (MRMT) are calibrated solely on conservative transport information without pore topology information and provide concentration distributions on which effective reaction rates are estimated. Reference simulated reaction rates and effective reaction rates evaluated by MRMT are compared, as well as characteristic desorption and dissolution times. Although not exactly equal, these indicators remain very close whatever the porous structure, differing at most by 0.6% and 10% for desorption and dissolution. At early times, this close agreement arises from the fine characterization of the diffusive porosity close to the mobile zone that controls fast mobile-diffusive exchanges. At intermediate to late times, concentration gradients are strongly reduced by diffusion, and reactivity can be captured by a very limited number of rates. We conclude that effective models calibrated solely on conservative transport information like MRMT can accurately estimate monocomponent kinetically controlled nonlinear fluid-rock interactions. Their relevance might extend to more advanced biogeochemical reactions because of the good characterization of conservative concentration distributions, even by parsimonious models (e.g., MRMT with 3-5 rates). We propose a methodology to estimate reactive transport from conservative transport in mobile-immobile conditions.
Transport equivalent diffusion constants for reflector region in PWRs
International Nuclear Information System (INIS)
Tahara, Yoshihisa; Sekimoto, Hiroshi
2002-01-01
The diffusion-theory-based nodal method is widely used in PWR core designs for reason of its high computing speed in three-dimensional calculations. The baffle/reflector (B/R) constants used in nodal calculations are usually calculated based on a one-dimensional transport calculation. However, to achieve high accuracy of assembly power prediction, two-dimensional model is needed. For this reason, the method for calculating transport equivalent diffusion constants of reflector material was developed so that the neutron currents on the material boundaries could be calculated exactly in diffusion calculations. Two-dimensional B/R constants were calculated using the transport equivalent diffusion constants in the two-dimensional diffusion calculation whose geometry reflected the actual material configuration in the reflector region. The two-dimensional B/R constants enabled us to predict assembly power within an error of 1.5% at hot full power conditions. (author)
Analysis of pedestal plasma transport
International Nuclear Information System (INIS)
Callen, J.D.; Groebner, R.J.; Osborne, T.H.; Canik, J.M.; Owen, L.W.; Pankin, A.Y.; Rafiq, T.; Rognlien, T.D.; Stacey, W.M.
2010-01-01
An H-mode edge pedestal plasma transport benchmarking exercise was undertaken for a single DIII-D pedestal. Transport modelling codes used include 1.5D interpretive (ONETWO, GTEDGE), 1.5D predictive (ASTRA) and 2D ones (SOLPS, UEDGE). The particular DIII-D discharge considered is 98889, which has a typical low density pedestal. Profiles for the edge plasma are obtained from Thomson and charge-exchange recombination data averaged over the last 20% of the average 33.53 ms repetition time between type I edge localized modes. The modelled density of recycled neutrals is largest in the divertor X-point region and causes the edge plasma source rate to vary by a factor ∼10 2 on the separatrix. Modelled poloidal variations in the densities and temperatures on flux surfaces are small on all flux surfaces up to within about 2.6 mm (ρ N > 0.99) of the mid-plane separatrix. For the assumed Fick's-diffusion-type laws, the radial heat and density fluxes vary poloidally by factors of 2-3 in the pedestal region; they are largest on the outboard mid-plane where flux surfaces are compressed and local radial gradients are largest. Convective heat flows are found to be small fractions of the electron (∼ 2 s -1 . Electron heat transport is found to be best characterized by electron-temperature-gradient-induced transport at the pedestal top and paleoclassical transport throughout the pedestal. The effective ion heat diffusivity in the pedestal has a different profile from the neoclassical prediction and may be smaller than it. The very small effective density diffusivity may be the result of an inward pinch flow nearly balancing a diffusive outward radial density flux. The inward ion pinch velocity and density diffusion coefficient are determined by a new interpretive analysis technique that uses information from the force balance (momentum conservation) equations; the paleoclassical transport model provides a plausible explanation of these new results. Finally, the measurements
3D modeling of groundwater heat transport in the shallow Westliches Leibnitzer Feld aquifer, Austria
Rock, Gerhard; Kupfersberger, Hans
2018-02-01
For the shallow Westliches Leibnitzer feld aquifer (45 km2) we applied the recently developed methodology by Kupfersberger et al. (2017a) to derive the thermal upper boundary for a 3D heat transport model from observed air temperatures. We distinguished between land uses of grass and agriculture, sealed surfaces, forest and water bodies. To represent the heat flux from heated buildings and the mixture between different land surfaces in urban areas we ran the 1D vertical heat conduction module SoilTemp which is coupled to the heat transport model (using FEFLOW) on a time step basis. Over a simulation period of 23 years the comparison between measured and observed groundwater temperatures yielded NSE values ranging from 0.41 to 0.92 including readings at different depths. The model results showed that the thermal input signals lead to distinctly different vertical groundwater temperature distributions. To overcome the influence of specific warm or cold years we introduced the computation of an annual averaged groundwater temperature profile. With respect to the use of groundwater cooling or heating facilities we evaluated the application of vertically averaged statistical groundwater temperature distributions compared to the use of temperature distributions at selected dates. We concluded that the heat transport model serves well as an aquifer scale management tool to optimize the use of the shallow subsurface for thermal purposes and to analyze the impacts of corresponding measures on groundwater temperatures.
Continuous versus discontinuous albedo representations in a simple diffusive climate model
Simmons, P. A.; Griffel, D. H.
1988-07-01
A one-dimensional annually and zonally averaged energy-balance model, with diffusive meridional heat transport and including icealbedo feedback, is considered. This type of model is found to be very sensitive to the form of albedo used. The solutions for a discontinuous step-function albedo are compared to those for a more realistic smoothly varying albedo. The smooth albedo gives a closer fit to present conditions, but the discontinuous form gives a better representation of climates in earlier epochs.
International Nuclear Information System (INIS)
Chatthong, B.; Onjun, T.; Imbeaux, F.; Sarazin, Y.; Strugarek, A.; Picha, R.; Poolyarat, N.
2011-06-01
Full text: Formation of transport barrier in fusion plasma is studied using a simple one-field bistable S-curve bifurcation model. This model is characterized by an S-line with two stable branches corresponding to the low (L) and high (H) confinement modes, connected by an unstable branch. Assumptions used in this model are such that the reduction in anomalous transport is caused by v E velocity shear effect and also this velocity shear is proportional to pressure gradient. In this study, analytical and numerical approaches are used to obtain necessary conditions for transport barrier formation, i.e. the ratio of anomalous over neoclassical coefficients and heat flux thresholds which must be exceeded. Several profiles of heat sources are considered in this work including constant, Gaussian, and hyperbolic tangent forms. Moreover, the effect of perturbation in heat flux is investigated with respect to transport barrier formation
Energy and variance budgets of a diffusive staircase with implications for heat flux scaling
Hieronymus, M.; Carpenter, J. R.
2016-02-01
Diffusive convection, the mode of double-diffusive convection that occur when both temperature and salinity increase with increasing depth, is commonplace throughout the high latitude oceans and diffusive staircases constitute an important heat transport process in the Arctic Ocean. Heat and buoyancy fluxes through these staircases are often estimated using flux laws deduced either from laboratory experiments, or from simplified energy or variance budgets. We have done direct numerical simulations of double-diffusive convection at a range of Rayleigh numbers and quantified the energy and variance budgets in detail. This allows us to compare the fluxes in our simulations to those derived using known flux laws and to quantify how well the simplified energy and variance budgets approximate the full budgets. The fluxes are found to agree well with earlier estimates at high Rayleigh numbers, but we find large deviations at low Rayleigh numbers. The close ties between the heat and buoyancy fluxes and the budgets of thermal variance and energy have been utilized to derive heat flux scaling laws in the field of thermal convection. The result is the so called GL-theory, which has been found to give accurate heat flux scaling laws in a very wide parameter range. Diffusive convection has many similarities to thermal convection and an extension of the GL-theory to diffusive convection is also presented and its predictions are compared to the results from our numerical simulations.
Ali, H.; Yilbas, B. S.
2016-09-01
Phonon cross-plane transport across silicon and diamond thin films pair is considered, and thermal boundary resistance across the films pair interface is examined incorporating the cut-off mismatch and diffusive mismatch models. In the cut-off mismatch model, phonon frequency mismatch for each acoustic branch is incorporated across the interface of the silicon and diamond films pair in line with the dispersion relations of both films. The frequency-dependent and transient solution of the Boltzmann transport equation is presented, and the equilibrium phonon intensity ratios at the silicon and diamond film edges are predicted across the interface for each phonon acoustic branch. Temperature disturbance across the edges of the films pair is incorporated to assess the phonon transport characteristics due to cut-off and diffusive mismatch models across the interface. The effect of heat source size, which is allocated at high-temperature (301 K) edge of the silicon film, on the phonon transport characteristics at the films pair interface is also investigated. It is found that cut-off mismatch model predicts higher values of the thermal boundary resistance across the films pair interface as compared to that of the diffusive mismatch model. The ratio of equilibrium phonon intensity due to the cut-off mismatch over the diffusive mismatch models remains >1 at the silicon edge, while it becomes <1 at the diamond edge for all acoustic branches.
Transport modeling of L- and H-mode discharges with LHCD on EAST
Li, M. H.; Ding, B. J.; Imbeaux, F.; Decker, J.; Zhang, X. J.; Kong, E. H.; Zhang, L.; Wei, W.; Shan, J. F.; Liu, F. K.; Wang, M.; Xu, H. D.; Yang, Y.; Peysson, Y.; Basiuk, V.; Artaud, J.-F.; Yuynh, P.; Wan, B. N.
2013-04-01
High-confinement (H-mode) discharges with lower hybrid current drive (LHCD) as the only heating source are obtained on EAST. In this paper, an empirical transport model of mixed Bohm/gyro-Bohm for electron and ion heat transport was first calibrated against a database of 3 L-mode shots on EAST. The electron and ion temperature profiles are well reproduced in the predictive modeling with the calibrated model coupled to the suite of codes CRONOS. CRONOS calculations with experimental profiles are also performed for electron power balance analysis. In addition, the time evolutions of LHCD are calculated by the C3PO/LUKE code involving current diffusion, and the results are compared with experimental observations.
Chen, Jiajia; Pitchai, Krishnamoorthy; Birla, Sohan; Negahban, Mehrdad; Jones, David; Subbiah, Jeyamkondan
2014-10-01
A 3-dimensional finite-element model coupling electromagnetics and heat and mass transfer was developed to understand the interactions between the microwaves and fresh mashed potato in a 500 mL tray. The model was validated by performing heating of mashed potato from 25 °C on a rotating turntable in a microwave oven, rated at 1200 W, for 3 min. The simulated spatial temperature profiles on the top and bottom layer of the mashed potato showed similar hot and cold spots when compared to the thermal images acquired by an infrared camera. Transient temperature profiles at 6 locations collected by fiber-optic sensors showed good agreement with predicted results, with the root mean square error ranging from 1.6 to 11.7 °C. The predicted total moisture loss matched well with the observed result. Several input parameters, such as the evaporation rate constant, the intrinsic permeability of water and gas, and the diffusion coefficient of water and gas, are not readily available for mashed potato, and they cannot be easily measured experimentally. Reported values for raw potato were used as baseline values. A sensitivity analysis of these input parameters on the temperature profiles and the total moisture loss was evaluated by changing the baseline values to their 10% and 1000%. The sensitivity analysis showed that the gas diffusion coefficient, intrinsic water permeability, and the evaporation rate constant greatly influenced the predicted temperature and total moisture loss, while the intrinsic gas permeability and the water diffusion coefficient had little influence. This model can be used by the food product developers to understand microwave heating of food products spatially and temporally. This tool will allow food product developers to design food package systems that would heat more uniformly in various microwave ovens. The sensitivity analysis of this study will help us determine the most significant parameters that need to be measured accurately for reliable
Numerical modelling of transient heat and moisture transport in protective clothing
International Nuclear Information System (INIS)
Łapka, P; Furmański, P; Wisniewski, T S
2016-01-01
The paper presents a complex model of heat and mass transfer in a multi-layer protective clothing exposed to a flash fire and interacting with the human skin. The clothing was made of porous fabric layers separated by air gaps. The fabrics contained bound water in the fibres and moist air in the pores. The moist air was also present in the gaps between fabric layers or internal fabric layer and the skin. Three skin sublayers were considered. The model accounted for coupled heat transfer by conduction, thermal radiation and associated with diffusion of water vapour in the clothing layers and air gaps. Heat exchange due to phase transition of the bound water were also included in the model. Complex thermal and mass transfer conditions at internal or external boundaries between fabric layers and air gaps as well as air gap and skin were assumed. Special attention was paid to modelling of thermal radiation which was coming from the fire, penetrated through protective clothing and absorbed by the skin. For the first time non-grey properties as well as optical phenomena at internal or external boundaries between fabric layers and air gaps as well as air gap and skin were accounted for. A series of numerical simulations were carried out and the risk of heat injures was estimated. (paper)
Study of heat transfer and particle transport in Tore Supra and HL-2A tokamaks
International Nuclear Information System (INIS)
Song, S.
2011-12-01
This thesis reports on experimental studies of heat and particles transport performed on 2 large tokamaks: Tore Supra (based at CEA/Cadarache, France) and HL-2A (based at the Southwestern Institute of Physics, Chengdu, China). The modulated source is the Electron Cyclotron Resonance Heating (ECRH) for the heat pinch and density pump-out studies, while the non-local transport experiments use the Supersonic Molecular Beam Injection (SMBI) as source of modulation. The emphasis is put on the inward heat pinch. In the off-axis ECRH modulation experiments on Tore Supra with low frequency (1 Hz), strong heat inward transport has been observed, in particular for low density. Two transport models have been applied in order to analyze the experimental behavior. The first one is the linear pinch model (LPM) and the second one is an empirical model based on micro-instabilities theory, named Critical Gradient Model (CGM). Good agreement has been found for all harmonics between the experimental data and the simulation using LPM. On the other hand, good agreement has not been achieved using CGM. The density pump-out with large particles and energy losses during ECRH is commonly observed in tokamaks. A new dynamic approach using the modulation technique has been used in HL-2A for analyzing the transient phase of the density pump-out. A correlation between the turbulence increase and the density pump-out has been found. The non-local transport phenomenon, characterized by a fast transient process compared to the normal diffusive response to the perturbation is observed. Both phenomena, i.e., pump-out and non-locality, show as simultaneous variation of density and temperature. This can be an inspiration for the usage of a transport matrix which considers the density and temperature evolution together. Simulations with a simple transport matrix, with non-diagonal terms coupling temperature and density qualitatively reproduce the non-local and pump-out effects qualitatively
A statistical approach to strange diffusion phenomena
International Nuclear Information System (INIS)
Milligen, B.Ph. van; Carreras, B.A.; Sanchez, R.
2005-01-01
The study of particle (and heat) transport in fusion plasmas has revealed the existence of what might be called 'unusual' transport phenomena. Such phenomena are: unexpected scaling of the confinement time with system size, power degradation (i.e. sub-linear scaling of energy content with power input), profile stiffness (also known as profile consistency), rapid transient transport phenomena such as cold and heat pulses (travelling much faster than the diffusive timescale would allow), non-local behaviour and central profile peaking during off-axis heating, associated with unexplained inward pinches. The standard modelling framework, essentially equal to Fick's Law plus extensions, has great difficulty in providing an all-encompassing and satisfactory explanation of all these phenomena. This difficulty has motivated us to reconsider the basics of the modelling of diffusive phenomena. Diffusion is based on the well-known random walk. The random walk is captured in all its generality in the Continuous Time Random Walk (CTRW) formalism. The CTRW formalism is directly related to the well-known Generalized Master Equation, which describes the behaviour of tracer particle diffusion on a very fundamental level, and from which the phenomenological Fick's Law can be derived under some specific assumptions. We show that these assumptions are not necessarily satisfied under fusion plasma conditions, in which case other equations (such as the Fokker-Planck diffusion law or the Master Equation itself) provide a better description of the phenomena. This fact may explain part of the observed 'strange' phenomena (namely, the inward pinch). To show how the remaining phenomena mentioned above may perhaps find an explanation in the proposed alternative modelling framework, we have designed a toy model that incorporates a critical gradient mechanism, switching between rapid (super-diffusive) and normal diffusive transport as a function of the local gradient. It is then demonstrated
Thermal diffusivity from heat wave propagation in Wendelstein 7-AS
Energy Technology Data Exchange (ETDEWEB)
Hartfuss, H J; Erckmann, V; Giannone, L.; Maassberg, H; Tutter, M [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)
1991-01-01
Electron thermal diffusivity studies can be carried out in two ways: static and dynamic. In the static analysis, the transport coefficients are determined from the stationary power balance, in the dynamic analysis from the propagation of a small perturbation of the stationary plasma state which can be caused by either a sawtooth generated heat pulse or modulation of the heating power. Electron thermal diffusivity [chi][sub e] is deduced from the evolution of the perturbed electron temperature T[sub e] at different locations r[sub i] in the plasma. [chi][sub e] values obtained from perturbation analysis are usually greater than those calculated from power balance. It has been pointed out that there is a principal difference between static and perturbative analysis. Whereas the static method yields the transport coefficient [chi][sub e]=q[sub e]/n[sub e][nabla]T[sub e], the perturbative method leads to an increase of the flux q[sub e] as a result of an increase in the temperature gradient [nabla]T[sub e]. The quantity determined is an incremental [chi][sub e] as defined by [chi][sub e][sup inc]=[partial derivative]q[sub e]/n[sub e][partial derivative]([nabla]T[sub e]). By varying the modulation of the heating power at different frequencies and amplitudes one can address the question whether or not this discrepancy is a function of the varied parameters. (author) 7 refs., 2 figs.
Diffusive-to-ballistic transition of the modulated heat transport in a rarefied air chamber
Gomez-Heredia, C. L.; Macias, J.; Ordonez-Miranda, J.; Ares, O.; Alvarado-Gil, J. J.
2017-01-01
Modulated heat transfer in air subject to pressures from 760 Torr to 10-4 Torr is experimentally studied by means of a thermal-wave resonant cavity placed in a vacuum chamber. This is done through the analysis of the amplitude and phase delay of the photothermal signal as a function of the cavity length and pressure through of the Knudsen's number. The viscous, transitional, and free molecular regimes of heat transport are observed for pressures P>1.5 Torr, 25 mTorrheat transport.
Integrated Temperature Sensors based on Heat Diffusion
Van Vroonhoven, C.P.L.
2015-01-01
This thesis describes the theory, design and implementation of a new class of integrated temperature sensors, based on heat diffusion. In such sensors, temperature is sensed by measuring the time it takes for heat to diffuse through silicon. An on-chip thermal delay can be determined by geometry and
Some factors affecting radiative heat transport in PWR cores
International Nuclear Information System (INIS)
Hall, A.N.
1989-04-01
This report discusses radiative heat transport in Pressurized Water Reactor cores, using simple models to illustrate basic features of the transport process. Heat transport by conduction and convection is ignored in order to focus attention on the restrictions on radiative heat transport imposed by the geometry of the heat emitting and absorbing structures. The importance of the spacing of the emitting and absorbing structures is emphasised. Steady state temperature distributions are found for models of cores which are uniformly heated by fission product decay. In all of the models, a steady state temperature distribution can only be obtained if the central core temperature is in excess of the melting point of UO 2 . It has recently been reported that the MIMAS computer code, which takes into account radiative heat transport, has been used to model the heat-up of the Three Mile Island-2 reactor core, and the computations indicate that the core could not have reached the melting point of UO 2 at any time or any place. We discuss this result in the light of the calculations presented in this paper. It appears that the predicted stabilisation of the core temperatures at ∼ 2200 0 C may be a consequence of the artificially large spacing between the radial rings employed in the MIMAS code, rather than a result of physical significance. (author)
International Nuclear Information System (INIS)
Fichot, Floriana; Duval, Fabiena; Garcia, Aureliena; Belloni, Julien; Quintard, Michel
2005-01-01
Full text of publication follows: In the framework of its research programme on severe nuclear reactor accidents, IRSN investigates the water flooding of an overheated porous bed, where complex two-phase flows are likely to exist. The goal is to describe the flow with a general model, covering rods and debris beds regions in the vessel. A better understanding of the flow at the pore level appears to be necessary in order to justify and improve closure laws of macroscopic models. Although the Direct Numerical Simulation (DNS) of two-phase flows is possible with several methods, applications are now limited to small computational domains, typically of the order of a few centimeters. Therefore, numerical solutions at the reactor scale can only be obtained by using averaged models. Volume averaging is the most traditional way of deriving such models. For nuclear safety codes, a control volume must include a few rods or a few debris particles, with a characteristic dimension of a few centimeters. The difficulty usually met with averaged models is the closure of several transport or source terms which appear in the averaged conservation equations (for example the interfacial drag or the heat transfers between phases) [2]. In the past, the closure of these terms was obtained, when possible, from one-dimensional experiments that allowed measurements of heat flux or pressure drops. For more complex flows, the experimental measurement of local parameters is often impossible and the effective properties cannot be determined easily. An alternative way is to perform 'numerical experiments' with numerical simulations of the local flow. As mentioned above, the domain of application of DNS corresponds to the size of control volumes necessary to derive averaged models. Therefore DNS appears as a powerful tool to investigate the local features of a two-phase flow in complex geometries. Diffuse interface methods provide a way to model flows with interfacial phenomena through an
Directory of Open Access Journals (Sweden)
Rong Ren
2017-04-01
Full Text Available Temperature is an integral part of soil quality in terms of moisture content; coupling between water and heat can render a soil fertile, and plays a role in water conservation. Although it is widely recognized that both water and heat transport are fundamental factors in the quantification of soil mass and energy balance, their computation is still limited in most models or practical applications in the root zone under non-isothermal conditions. This research was conducted to: (a implement a fully coupled mathematical model that contains the full coupled process of soil water and heat transport with plants focused on the influence of temperature gradient on soil water redistribution and on the influence of change in soil water movement on soil heat flux transport; (b verify the mathematical model with detailed field monitoring data; and (c analyze the accuracy of the model. Results show the high accuracy of the model in predicting the actual changes in soil water content and temperature as a function of time and soil depth. Moreover, the model can accurately reflect changes in soil moisture and heat transfer in different periods. With only a few empirical parameters, the proposed model will serve as guide in the field of surface irrigation.
International Nuclear Information System (INIS)
Viswanathan, H.S.
1995-01-01
The finite element code FEHMN is a three-dimensional finite element heat and mass transport simulator that can handle complex stratigraphy and nonlinear processes such as vadose zone flow, heat flow and solute transport. Scientists at LANL have been developed hydrologic flow and transport models of the Yucca Mountain site using FEHMN. Previous FEHMN simulations have used an equivalent K d model to model solute transport. In this thesis, FEHMN is modified making it possible to simulate the transport of a species with a rigorous chemical model. Including the rigorous chemical equations into FEHMN simulations should provide for more representative transport models for highly reactive chemical species. A fully kinetic formulation is chosen for the FEHMN reactive transport model. Several methods are available to computationally implement a fully kinetic formulation. Different numerical algorithms are investigated in order to optimize computational efficiency and memory requirements of the reactive transport model. The best algorithm of those investigated is then incorporated into FEHMN. The algorithm chosen requires for the user to place strongly coupled species into groups which are then solved for simultaneously using FEHMN. The complete reactive transport model is verified over a wide variety of problems and is shown to be working properly. The simulations demonstrate that gas flow and carbonate chemistry can significantly affect 14 C transport at Yucca Mountain. The simulations also provide that the new capabilities of FEHMN can be used to refine and buttress already existing Yucca Mountain radionuclide transport studies
Bioheat model evaluations of laser effects on tissues: role of water evaporation and diffusion
Nagulapally, Deepthi; Joshi, Ravi P.; Thomas, Robert J.
2011-03-01
A two-dimensional, time-dependent bioheat model is applied to evaluate changes in temperature and water content in tissues subjected to laser irradiation. Our approach takes account of liquid-to-vapor phase changes and a simple diffusive flow of water within the biotissue. An energy balance equation considers blood perfusion, metabolic heat generation, laser absorption, and water evaporation. The model also accounts for the water dependence of tissue properties (both thermal and optical), and variations in blood perfusion rates based on local tissue injury. Our calculations show that water diffusion would reduce the local temperature increases and hot spots in comparison to simple models that ignore the role of water in the overall thermal and mass transport. Also, the reduced suppression of perfusion rates due to tissue heating and damage with water diffusion affect the necrotic depth. Two-dimensional results for the dynamic temperature, water content, and damage distributions will be presented for skin simulations. It is argued that reduction in temperature gradients due to water diffusion would mitigate local refractive index variations, and hence influence the phenomenon of thermal lensing. Finally, simple quantitative evaluations of pressure increases within the tissue due to laser absorption are presented.
Heat Diffusion in Gases, Including Effects of Chemical Reaction
Hansen, C. Frederick
1960-01-01
The diffusion of heat through gases is treated where the coefficients of thermal conductivity and diffusivity are functions of temperature. The diffusivity is taken proportional to the integral of thermal conductivity, where the gas is ideal, and is considered constant over the temperature interval in which a chemical reaction occurs. The heat diffusion equation is then solved numerically for a semi-infinite gas medium with constant initial and boundary conditions. These solutions are in a dimensionless form applicable to gases in general, and they are used, along with measured shock velocity and heat flux through a shock reflecting surface, to evaluate the integral of thermal conductivity for air up to 5000 degrees Kelvin. This integral has the properties of a heat flux potential and replaces temperature as the dependent variable for problems of heat diffusion in media with variable coefficients. Examples are given in which the heat flux at the stagnation region of blunt hypersonic bodies is expressed in terms of this potential.
Modeling and simulation of spin-polarized transport at the kinetic and diffusive level
International Nuclear Information System (INIS)
Possanner, S.
2012-01-01
The aim of this thesis is to contribute to the understanding of spin-induced phenomena in electron motion. These phenomena arise when electrons move through a (partially) magnetic environment, in such a way that its magnetic moment (spin) may interact with the surroundings. The pure quantum nature of the spin requires transport models that deal with effects like quantum coherence, entanglement (correlation) and quantum dissipation. On the meso- and macroscopic level it is not yet clear under which circumstances these quantum effects may transpire. The purpose of this work is, on the one hand, to derive novel spin transport models from basic principles and, on the other hand, to develop numerical algorithms that allow for a solution of these new and other existing model equations. The thesis consists of four parts. The first part comprises an overview of fundamental spin-related concepts in electronic transport such as the giant-magneto-resistance (GMR) effect, the spin-transfer torque in metallic magnetic multilayers and the matrix-character of transport equations that take spin-coherent electron states into account. In particular, we consider the diffusive Zhang-Levy-Fert (ZLF) model, an exchange-torque model that consists of the Landau-Lifshitz equation and a heuristic matrix spin-diffusion equation. A finite difference scheme based on Strang operator splitting is developed that enables a numerical, self-consistent solution of this non-linear system within multilayer structures. Finally, the model is tested by comparison of numerical results to recent experimental data. In part two we propose a matrix-Boltzmann equation that allows for the description of spin-coherent electron transport on a kinetic level. The novelty here is a linear collision operator in which the transition rates from momentum k to momentum k' are modeled by a 2x2 Hermitian matrix; hence the mean-free paths of spin-up and spin-down electrons are represented by the eigenvalues of this
Quantum Transmission Conditions for Diffusive Transport in Graphene with Steep Potentials
Barletti, Luigi; Negulescu, Claudia
2018-05-01
We present a formal derivation of a drift-diffusion model for stationary electron transport in graphene, in presence of sharp potential profiles, such as barriers and steps. Assuming the electric potential to have steep variations within a strip of vanishing width on a macroscopic scale, such strip is viewed as a quantum interface that couples the classical regions at its left and right sides. In the two classical regions, where the potential is assumed to be smooth, electron and hole transport is described in terms of semiclassical kinetic equations. The diffusive limit of the kinetic model is derived by means of a Hilbert expansion and a boundary layer analysis, and consists of drift-diffusion equations in the classical regions, coupled by quantum diffusive transmission conditions through the interface. The boundary layer analysis leads to the discussion of a four-fold Milne (half-space, half-range) transport problem.
Parallel heat transport in integrable and chaotic magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Castillo-Negrete, D. del; Chacon, L. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States)
2012-05-15
The study of transport in magnetized plasmas is a problem of fundamental interest in controlled fusion, space plasmas, and astrophysics research. Three issues make this problem particularly challenging: (i) The extreme anisotropy between the parallel (i.e., along the magnetic field), {chi}{sub ||} , and the perpendicular, {chi}{sub Up-Tack }, conductivities ({chi}{sub ||} /{chi}{sub Up-Tack} may exceed 10{sup 10} in fusion plasmas); (ii) Nonlocal parallel transport in the limit of small collisionality; and (iii) Magnetic field lines chaos which in general complicates (and may preclude) the construction of magnetic field line coordinates. Motivated by these issues, we present a Lagrangian Green's function method to solve the local and non-local parallel transport equation applicable to integrable and chaotic magnetic fields in arbitrary geometry. The method avoids by construction the numerical pollution issues of grid-based algorithms. The potential of the approach is demonstrated with nontrivial applications to integrable (magnetic island), weakly chaotic (Devil's staircase), and fully chaotic magnetic field configurations. For the latter, numerical solutions of the parallel heat transport equation show that the effective radial transport, with local and non-local parallel closures, is non-diffusive, thus casting doubts on the applicability of quasilinear diffusion descriptions. General conditions for the existence of non-diffusive, multivalued flux-gradient relations in the temperature evolution are derived.
Energy Technology Data Exchange (ETDEWEB)
Telfeyan, Katherine Christina [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ware, Stuart Douglas [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Reimus, Paul William [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Birdsell, Kay Hanson [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-11-06
Diffusion cell and diffusion wafer experiments were conducted to compare methods for estimating matrix diffusion coefficients in rock core samples from Pahute Mesa at the Nevada Nuclear Security Site (NNSS). A diffusion wafer method, in which a solute diffuses out of a rock matrix that is pre-saturated with water containing the solute, is presented as a simpler alternative to the traditional through-diffusion (diffusion cell) method. Both methods yielded estimates of matrix diffusion coefficients that were within the range of values previously reported for NNSS volcanic rocks. The difference between the estimates of the two methods ranged from 14 to 30%, and there was no systematic high or low bias of one method relative to the other. From a transport modeling perspective, these differences are relatively minor when one considers that other variables (e.g., fracture apertures, fracture spacings) influence matrix diffusion to a greater degree and tend to have greater uncertainty than diffusion coefficients. For the same relative random errors in concentration measurements, the diffusion cell method yields diffusion coefficient estimates that have less uncertainty than the wafer method. However, the wafer method is easier and less costly to implement and yields estimates more quickly, thus allowing a greater number of samples to be analyzed for the same cost and time. Given the relatively good agreement between the methods, and the lack of any apparent bias between the methods, the diffusion wafer method appears to offer advantages over the diffusion cell method if better statistical representation of a given set of rock samples is desired.
Telfeyan, Katherine; Ware, S. Doug; Reimus, Paul W.; Birdsell, Kay H.
2018-02-01
Diffusion cell and diffusion wafer experiments were conducted to compare methods for estimating effective matrix diffusion coefficients in rock core samples from Pahute Mesa at the Nevada Nuclear Security Site (NNSS). A diffusion wafer method, in which a solute diffuses out of a rock matrix that is pre-saturated with water containing the solute, is presented as a simpler alternative to the traditional through-diffusion (diffusion cell) method. Both methods yielded estimates of effective matrix diffusion coefficients that were within the range of values previously reported for NNSS volcanic rocks. The difference between the estimates of the two methods ranged from 14 to 30%, and there was no systematic high or low bias of one method relative to the other. From a transport modeling perspective, these differences are relatively minor when one considers that other variables (e.g., fracture apertures, fracture spacings) influence matrix diffusion to a greater degree and tend to have greater uncertainty than effective matrix diffusion coefficients. For the same relative random errors in concentration measurements, the diffusion cell method yields effective matrix diffusion coefficient estimates that have less uncertainty than the wafer method. However, the wafer method is easier and less costly to implement and yields estimates more quickly, thus allowing a greater number of samples to be analyzed for the same cost and time. Given the relatively good agreement between the methods, and the lack of any apparent bias between the methods, the diffusion wafer method appears to offer advantages over the diffusion cell method if better statistical representation of a given set of rock samples is desired.
Zhukovsky, K.; Oskolkov, D.
2018-03-01
A system of hyperbolic-type inhomogeneous differential equations (DE) is considered for non-Fourier heat transfer in thin films. Exact harmonic solutions to Guyer-Krumhansl-type heat equation and to the system of inhomogeneous DE are obtained in Cauchy- and Dirichlet-type conditions. The contribution of the ballistic-type heat transport, of the Cattaneo heat waves and of the Fourier heat diffusion is discussed and compared with each other in various conditions. The application of the study to the ballistic heat transport in thin films is performed. Rapid evolution of the ballistic quasi-temperature component in low-dimensional systems is elucidated and compared with slow evolution of its diffusive counterpart. The effect of the ballistic quasi-temperature component on the evolution of the complete quasi-temperature is explored. In this context, the influence of the Knudsen number and of Cauchy- and Dirichlet-type conditions on the evolution of the temperature distribution is explored. The comparative analysis of the obtained solutions is performed.
Diffusive smoothing of surfzone bathymetry by gravity-driven sediment transport
Moulton, M. R.; Elgar, S.; Raubenheimer, B.
2012-12-01
Gravity-driven sediment transport often is assumed to have a small effect on the evolution of nearshore morphology. Here, it is shown that down-slope gravity-driven sediment transport is an important process acting to smooth steep bathymetric features in the surfzone. Gravity-driven transport can be modeled as a diffusive term in the sediment continuity equation governing temporal (t) changes in bed level (h): ∂h/∂t ≈ κ ▽2h, where κ is a sediment diffusion coefficient that is a function of the bed shear stress (τb) and sediment properties, such as the grain size and the angle of repose. Field observations of waves, currents, and the evolution of large excavated holes (initially 10-m wide and 2-m deep, with sides as steep as 35°) in an energetic surfzone are consistent with diffusive smoothing by gravity. Specifically, comparisons of κ estimated from the measured bed evolution with those estimated with numerical model results for several transport theories suggest that gravity-driven sediment transport dominates the bed evolution, with κ proportional to a power of τb. The models are initiated with observed bathymetry and forced with observed waves and currents. The diffusion coefficients from the measurements and from the model simulations were on average of order 10-5 m2/s, implying evolution time scales of days for features with length scales of 10 m. The dependence of κ on τb varies for different transport theories and for high and low shear stress regimes. The US Army Corps of Engineers Field Research Facility, Duck, NC provided excellent logistical support. Funded by a National Security Science and Engineering Faculty Fellowship, a National Defense Science and Engineering Graduate Fellowship, and the Office of Naval Research.
Interpretation of heat and density pulse measurements in JET in terms of coupled transport
International Nuclear Information System (INIS)
Haas, J.C.M. de; O'Rourke, J.; Sips, A.C.C.; Lopes Cardozo, N.J.
1990-01-01
The perturbations of electron density and temperature profiles in a tokamak following a sawtooth collapse are considered. An analytic model for the interpretation of such perturbations is presented. It is shown that the perturbation can be decomposed into two contributions, which are eigenmodes of the linearised coupled diffusion equations for particle and energy. The approximations made in the analytical treatment are checked using computer simulations. Measurements of heat and density pulses in Joint European Torus are used to illustrate the power of the new approach. It is shown that using the coupled equations, an improved description of the heat and density pulses is obtained. The analysis yields the four diffusion coefficients in the linearised transport matrix. The non-zero off-diagonal elements explain certain salient features of the measurements, notably a marked decrease of the local density which occurs during the maximum of the temperature pulse. (author)
MODELING OF THE GROUNDWATER TRANSPORT AROUND A DEEP BOREHOLE NUCLEAR WASTE REPOSITORY
Energy Technology Data Exchange (ETDEWEB)
N. Lubchenko; M. Rodríguez-Buño; E.A. Bates; R. Podgorney; E. Baglietto; J. Buongiorno; M.J. Driscoll
2015-04-01
The concept of disposal of high-level nuclear waste in deep boreholes drilled into crystalline bedrock is gaining renewed interest and consideration as a viable mined repository alternative. A large amount of work on conceptual borehole design and preliminary performance assessment has been performed by researchers at MIT, Sandia National Laboratories, SKB (Sweden), and others. Much of this work relied on analytical derivations or, in a few cases, on weakly coupled models of heat, water, and radionuclide transport in the rock. Detailed numerical models are necessary to account for the large heterogeneity of properties (e.g., permeability and salinity vs. depth, diffusion coefficients, etc.) that would be observed at potential borehole disposal sites. A derivation of the FALCON code (Fracturing And Liquid CONvection) was used for the thermal-hydrologic modeling. This code solves the transport equations in porous media in a fully coupled way. The application leverages the flexibility and strengths of the MOOSE framework, developed by Idaho National Laboratory. The current version simulates heat, fluid, and chemical species transport in a fully coupled way allowing the rigorous evaluation of candidate repository site performance. This paper mostly focuses on the modeling of a deep borehole repository under realistic conditions, including modeling of a finite array of boreholes surrounded by undisturbed rock. The decay heat generated by the canisters diffuses into the host rock. Water heating can potentially lead to convection on the scale of thousands of years after the emplacement of the fuel. This convection is tightly coupled to the transport of the dissolved salt, which can suppress convection and reduce the release of the radioactive materials to the aquifer. The purpose of this work has been to evaluate the importance of the borehole array spacing and find the conditions under which convective transport can be ruled out as a radionuclide transport mechanism
Evidence and concepts for nonlocal transport
International Nuclear Information System (INIS)
Callen, J.D.; Kissick, M.W.
1997-08-01
Up until a few years ago, most transient transport studies observed primarily diffusive plasma transport responses to fast, localized perturbations. Recently, a number of experiments have, in addition, observed nonlocal electron heat responses. Most remarkably, in cold pulse experiments the abrupt edge cooling via radiative processes can induce both a diffusive cooling response moving in from the edge, and simultaneously a rising electron temperature in the central core of tokamak plasmas--an opposite response even before the diffusive cooling from the edge reaches the center. These and other nonlocal electron heat transport conundrums from recent experiments are reviewed. Also, models and physical processes being advanced to explain these puzzling phenomena are discussed. The importance of resolving this transport enigma is emphasized
Predictability of solute transport in diffusion-controlled hydrogeologic regimes
International Nuclear Information System (INIS)
Gillham, R.W.; Cherry, J.A.
1983-01-01
Hydrogeologic regimes that are favourable for the subsurface management of low-level radioactive wastes must have transport properties that will limit the migration velocity of contaminants to some acceptably low value. Of equal importance, for the purpose of impact assessment and licensing, is the need to be able to predict, with a reasonable degree of certainty and over long time periods, what the migration velocity of the various contaminants of interest will be. This paper presents arguments to show that in addition to having favourable velocity characteristics, transport in saturated, diffusion-controlled hydrogeologic regimes is considerably more predictable than in the most common alternatives. The classical transport models for unsaturated, saturated-advection-controlled and saturated-diffusion-controlled environments are compared, with particular consideration being given to the difficulties associated with the characterization of the respective transport parameters. Results are presented which show that the diffusion of non-reactive solutes and solutes that react according to a constant partitioning ratio (K/sub d/) are highly predictable under laboratory conditions and that the diffusion coefficients for the reactive solutes can be determined with a reasonable degree of accuracy from independent measurements of bulk density, porosity, distribution coefficient and tortuosity. Field evidence is presented which shows that the distribution of environmental isotopes and chloride in thick clayey deposits is consistent with a diffusion-type transport process in these media. These results are particularly important in that they not only demonstrate the occurrence of diffusion-controlled hydrogeologic regimes, but they also demonstrate the predictability of the migration characteristics over very long time periods
Energy Technology Data Exchange (ETDEWEB)
Wang, Chi-Jen [Iowa State Univ., Ames, IA (United States)
2013-01-01
In this thesis, we analyze both the spatiotemporal behavior of: (A) non-linear “reaction” models utilizing (discrete) reaction-diffusion equations; and (B) spatial transport problems on surfaces and in nanopores utilizing the relevant (continuum) diffusion or Fokker-Planck equations. Thus, there are some common themes in these studies, as they all involve partial differential equations or their discrete analogues which incorporate a description of diffusion-type processes. However, there are also some qualitative differences, as shall be discussed below.
Numerical modelling of coupled fluid, heat, and solute transport in deformable fractured rock
International Nuclear Information System (INIS)
Chan, T.; Reid, J.A.K.
1987-01-01
This paper reports on a three-dimensional (3D) finite-element code, MOTIF (model of transport in fractured/porous media), developed to model the coupled processes of groundwater flow, heat transport, brine transport, and one-species radionuclide transport in geological media. Three types of elements are available: a 3D continuum element, a planar fracture element that can be oriented in any arbitrary direction in 3D space or pipe flow in 3D space, and a line element for simulating fracture flow in 2D space or pipe flow in 3D space. As a quality-assurance measure, the MOTIF code was verified by comparison of its results with analytical solutions and other published numerical solutions
Experimental constraints on transport
International Nuclear Information System (INIS)
Luce, T.C.; Petty, K.H.; Burrell, K.H.; Forest, C.B.; Gohil, P.; Groebner, R.J.; De Haas, J.C.M.; James, R.A.; Makowski, M.A.
1994-12-01
Characterization of the cross-field energy transport in magnetic confinement experiments in a manner applicable to the accurate assessment of future machine performance continues to be a challenging goal. Experimental results from the DIII-D tokamak in the areas of dimensionless scaling and non-diffusive transport represent progress toward this goal. Dimensionless scaling shows how beneficial the increase in machine size and magnetic field is for future devices. The experiments on DIII-D are the first to determine separately the electron and ion scaling with normalized gyroradius ρ * ; the electrons scale as expected from gyro-Bohm class theories, while the ions scale consistent with the Goldston empirical scaling. This result predicts an increase in transport relative to Bohm diffusion as ρ * decreases in future devices. The existence of distinct ρ * scalings for ions and electrons cautions against a physical interpretation of one-fluid or global analysis. The second class of experiments reported here are the first to demonstrate the existence of non-diffusive energy transport. Electron cyclotron heating was applied at the half radius; the electron temperature profile remains substantially peaked. Power balance analysis indicates that heat must flow in the direction of increasing temperature, which is inconsistent with purely diffusive transport. The dynamics of electron temperature perturbations indicate the presence in the heat flux of a term dependent on temperature rather than its gradient. These two observations strongly constrain the types of models which can be applied to cross-field heat transport
DEFF Research Database (Denmark)
Deepagoda Thuduwe Kankanamge Kelum, Chamindu; Smits, Kathleen; Ramirez, Jamie
2016-01-01
porous media transport properties, key transport parameters such as thermal conductivity and gas diffusivity are particularly important to describe temperature-induced heat transport and diffusion-controlled gas transport processes, respectively. Despite many experimental and numerical studies focusing...... transport models (thermal conductivity, saturated hydraulic conductivity, and gas diffusivity). An existing thermal conductivity model was improved to describe the distinct three-region behavior in observed thermal conductivity–water saturation relations. Applying widely used parametric models for saturated......Detailed characterization of partially saturated porous media is important for understanding and predicting vadose zone transport processes. While basic properties (e.g., particle- and pore-size distributions and soil-water retention) are, in general, essential prerequisites for characterizing most...
International Nuclear Information System (INIS)
Viswanathan, H.S.
1996-08-01
The finite element code FEHMN, developed by scientists at Los Alamos National Laboratory (LANL), is a three-dimensional finite element heat and mass transport simulator that can handle complex stratigraphy and nonlinear processes such as vadose zone flow, heat flow and solute transport. Scientists at LANL have been developing hydrologic flow and transport models of the Yucca Mountain site using FEHMN. Previous FEHMN simulations have used an equivalent Kd model to model solute transport. In this thesis, FEHMN is modified making it possible to simulate the transport of a species with a rigorous chemical model. Including the rigorous chemical equations into FEHMN simulations should provide for more representative transport models for highly reactive chemical species. A fully kinetic formulation is chosen for the FEHMN reactive transport model. Several methods are available to computationally implement a fully kinetic formulation. Different numerical algorithms are investigated in order to optimize computational efficiency and memory requirements of the reactive transport model. The best algorithm of those investigated is then incorporated into FEHMN. The algorithm chosen requires for the user to place strongly coupled species into groups which are then solved for simultaneously using FEHMN. The complete reactive transport model is verified over a wide variety of problems and is shown to be working properly. The new chemical capabilities of FEHMN are illustrated by using Los Alamos National Laboratory's site scale model of Yucca Mountain to model two-dimensional, vadose zone 14 C transport. The simulations demonstrate that gas flow and carbonate chemistry can significantly affect 14 C transport at Yucca Mountain. The simulations also prove that the new capabilities of FEHMN can be used to refine and buttress already existing Yucca Mountain radionuclide transport studies
Energy Technology Data Exchange (ETDEWEB)
Harauchamps, E
2004-07-01
This work presents analytical solutions to the electron heat transport equation involving a damping term and a convection term in a cylindrical geometry. These solutions, processed by Matlab, allow the determination of the evolution of the radial profile of electron temperature in tokamaks during heating. The modulated injection of waves around the electron cyclotron frequency is an efficient tool to study heat transport experimentally in tokamaks. The comparison of these analytical solutions with experimental results from Tore-Supra during 2 discharges (30550 and 31165) shows the presence of a sudden change for the diffusion and damping coefficients. The hypothesis of the presence of a pinch spread all along the plasma might explain the shape of the experimental temperature profiles. These analytical solutions could be used to determine the time evolution of plasma density as well or of any parameter whose evolution is governed by a diffusion-convection equation. (A.C.)
Interpretation of heat and density pulse propagation in tokamaks
International Nuclear Information System (INIS)
Sips, A.C.C.; Costley, A.E.; O'Rourke, J.O.
1991-01-01
This paper addresses two key issues in current research on sawtooth induced heat and density pulse measurements in Tokamaks and their interpretation. First, heat and density pulses in JET and TXT show different qualitative behaviour implying substantially different transport coefficients. Second, a new description of the heat pulse has been used to describe measurements cannot be simulated with the widely used diffusive model. In this paper, we show that consistency between all these measurements can be obtained assuming a diffusive propagation for the heat and density pulses and using linearised coupled transport equations. (author) 6 refs., 5 figs
Jaworski, Jacek; Redlarski, Grzegorz
2014-08-01
This paper presents a model of alveolar-capillary oxygen diffusion with dynamics of air transport through the respiratory tract. For this purpose electrical model representing the respiratory tract mechanics and differential equations representing oxygen membrane diffusion are combined. Relevant thermodynamic relations describing the mass of oxygen transported into the human body are proposed as the connection between these models, as well as the influence of ventilation-perfusion mismatch on the oxygen diffusion. The model is verified based on simulation results of varying exercise intensities and statistical calculations of the results obtained during various clinical trials. The benefit of the approach proposed is its application in simulation-based research aimed to generate quantitative data of normal and pathological conditions. Based on the model presented, taking into account many essential physiological processes and air transport dynamics, comprehensive and combined studies of the respiratory efficiency can be performed. The impact of physical exercise, precise changes in respiratory tract mechanics and alterations in breathing pattern can be analyzed together with the impact of various changes in alveolar-capillary oxygen diffusion. This may be useful in simulation of effects of many severe medical conditions and increased activity level. Copyright © 2014 Elsevier Ltd. All rights reserved.
Hofmeister, Anne M.; Dong, Jianjun; Branlund, Joy M.
2014-04-01
We show that laser-flash analysis measurements of the temperature (T) dependence of thermal diffusivity (D) for diverse non-metallic (e.g., silicates) single-crystals is consistently represented by D(T) = FT-G + HT above 298 K, with G ranging from 0.3 to 2, depending on structure, and H being ˜10-4 K-1 for 51 single-crystals, 3 polycrystals, and two glasses unaffected by disorder or reconstructive phase transitions. Materials exhibiting this behavior include complex silicates with variable amounts of cation disorder, perovskite structured materials, and graphite. The high-temperature term HT becomes important by ˜1300 K, above which temperature its contribution to D(T) exceeds that of the FT-G term. The combination of the FT-G and HT terms produces the nearly temperature independent high-temperature region of D previously interpreted as the minimal phonon mean free path being limited by the finite interatomic spacing. Based on the simplicity of the fit and large number of materials it represents, this finding has repercussions for high-temperature models of heat transport. One explanation is that the two terms describing D(T) are associated with two distinct microscopic mechanisms; here, we explore the possibility that the thermal diffusivity of an electrical insulator could include both a contribution of lattice phonons (the FT-G term) and a contribution of diffusive bulk phonon-polaritons (BPP) at infrared (IR) frequencies (the HT term). The proposed BPP diffusion exists over length scales smaller than the laboratory sample sizes, and transfers mixed light and vibrational energy at a speed significantly smaller than the speed of light. Our diffusive IR-BPP hypothesis is consistent with other experimental observations such as polarization behavior, dependence of D on the number of IR peaks, and H = 0 for Ge and Si, which lack IR fundamentals. A simple quasi-particle thermal diffusion model is presented to begin understanding the contribution from bulk phonon
Sui, Jize; Zhao, Peng; Cheng, Zhengdong; Zheng, Liancun; Zhang, Xinxin
2017-02-01
The rheological and heat-conduction constitutive models of micropolar fluids (MFs), which are important non-Newtonian fluids, have been, until now, characterized by simple linear expressions, and as a consequence, the non-Newtonian performance of such fluids could not be effectively captured. Here, we establish the novel nonlinear constitutive models of a micropolar fluid and apply them to boundary layer flow and heat transfer problems. The nonlinear power law function of angular velocity is represented in the new models by employing generalized "n-diffusion theory," which has successfully described the characteristics of non-Newtonian fluids, such as shear-thinning and shear-thickening fluids. These novel models may offer a new approach to the theoretical understanding of shear-thinning behavior and anomalous heat transfer caused by the collective micro-rotation effects in a MF with shear flow according to recent experiments. The nonlinear similarity equations with a power law form are derived and the approximate analytical solutions are obtained by the homotopy analysis method, which is in good agreement with the numerical solutions. The results indicate that non-Newtonian behaviors involving a MF depend substantially on the power exponent n and the modified material parameter K 0 introduced by us. Furthermore, the relations of the engineering interest parameters, including local boundary layer thickness, local skin friction, and Nusselt number are found to be fitted by a quadratic polynomial to n with high precision, which enables the extraction of the rapid predictions from a complex nonlinear boundary-layer transport system.
Maelfeyt, Bryan; Gopinathan, Ajay
Intracellular transport occurs in nearly all eukaryotic cells, where materials such as proteins, lipids, carbohydrates, and nucleic acids travel to target locations through phases of passive, diffusion-based transport and active, motor-driven transport along filaments that make up the cell's cytoskeleton.We develop a computational model of the process with explicit cytoskeletal filament networks. In the active transport phase, cargo moves in straight lines along these filaments that are spread throughout the cell. To model the passive transport phase of cargo in the cytoplasm, where anomalous sub-diffusion is thought to take place, we implement a continuous-time random walk. We use this approach to provide a stepping stone to a predictive model where we can determine transport properties over a cytoskeletal network provided by experimental images of real filaments. We illustrate our approach by modeling the transport of insulin out of the cell and determining the impact of network geometry, anomalous sub-diffusion and motor number on the first-passage time distributions for insulin granules reaching their target destinations on the membrane.
A simple model of the effect of ocean ventilation on ocean heat uptake
Nadiga, Balu; Urban, Nathan
2017-11-01
Transport of water from the surface mixed layer into the ocean interior is achieved, in large part, by the process of ventilation-a process associated with outcropping isopycnals. Starting from such a configuration of outcropping isopycnals, we derive a simple model of the effect of ventilation on ocean uptake of anomalous radiative forcing. This model can be seen as an improvement of the popular anomaly-diffusing class of energy balance models (AD-EBM) that are routinely employed to analyze and emulate the warming response of both observed and simulated Earth system. We demonstrate that neither multi-layer, nor continuous-diffusion AD-EBM variants can properly represent both surface-warming and the vertical distribution of ocean heat uptake. The new model overcomes this deficiency. The simplicity of the models notwithstanding, the analysis presented and the necessity of the modification is indicative of the role played by processes related to the down-welling branch of global ocean circulation in shaping the vertical distribution of ocean heat uptake.
Numerical modeling of coupled water flow and heat transport in soil and snow
Thijs J. Kelleners; Jeremy Koonce; Rose Shillito; Jelle Dijkema; Markus Berli; Michael H. Young; John M. Frank; William Massman
2016-01-01
A one-dimensional vertical numerical model for coupled water flow and heat transport in soil and snow was modified to include all three phases of water: vapor, liquid, and ice. The top boundary condition in the model is driven by incoming precipitation and the surface energy balance. The model was applied to three different terrestrial systems: A warm desert bare...
International Nuclear Information System (INIS)
Kovac, D.; Otto, G.; Hobler, G.
2005-01-01
In this paper we present a model of amorphous pocket formation that is based on binary collision simulations to generate the distribution of deposited energy, and on numerical solution of the heat transport equation to describe the quenching process. The heat transport equation is modified to consider the heat of melting when the melting temperature is crossed at any point in space. It is discretized with finite differences on grid points that coincide with the crystallographic lattice sites, which allows easy determination of molten atoms. Atoms are considered molten if the average of their energy and the energy of their neighbors meets the melting criterion. The results obtained with this model are in good overall agreement with published experimental data on P, As, Te and Tl implantations in Si and with data on the polyatomic effect at cryogenic temperature
A variable-order fractal derivative model for anomalous diffusion
Directory of Open Access Journals (Sweden)
Liu Xiaoting
2017-01-01
Full Text Available This paper pays attention to develop a variable-order fractal derivative model for anomalous diffusion. Previous investigations have indicated that the medium structure, fractal dimension or porosity may change with time or space during solute transport processes, results in time or spatial dependent anomalous diffusion phenomena. Hereby, this study makes an attempt to introduce a variable-order fractal derivative diffusion model, in which the index of fractal derivative depends on temporal moment or spatial position, to characterize the above mentioned anomalous diffusion (or transport processes. Compared with other models, the main advantages in description and the physical explanation of new model are explored by numerical simulation. Further discussions on the dissimilitude such as computational efficiency, diffusion behavior and heavy tail phenomena of the new model and variable-order fractional derivative model are also offered.
Heat transport modeling of the dot spectroscopy platform on NIF
Farmer, W. A.; Jones, O. S.; Barrios, M. A.; Strozzi, D. J.; Koning, J. M.; Kerbel, G. D.; Hinkel, D. E.; Moody, J. D.; Suter, L. J.; Liedahl, D. A.; Lemos, N.; Eder, D. C.; Kauffman, R. L.; Landen, O. L.; Moore, A. S.; Schneider, M. B.
2018-04-01
Electron heat transport within an inertial-fusion hohlraum plasma is difficult to model due to the complex interaction of kinetic plasma effects, magnetic fields, laser-plasma interactions, and microturbulence. Here, simulations using the radiation-hydrodynamic code, HYDRA, are compared to hohlraum plasma experiments which contain a Manganese-Cobalt tracer dot (Barrios et al 2016 Phys. Plasmas 23 056307). The dot is placed either on the capsule or on a film midway between the capsule and the laser-entrance hole. From spectroscopic measurements, electron temperature and position of the dot are inferred. Simulations are performed with ad hoc flux limiters of f = 0.15 and f = 0.03 (with electron heat flux, q, limited to fnT 3/2/m 1/2), and two more physical means of flux limitation: the magnetohydrodynamics and nonlocal packages. The nonlocal model agrees best with the temperature of the dot-on-film and dot-on-capsule. The hohlraum produced x-ray flux is over-predicted by roughly ˜11% for the f = 0.03 model and the remaining models by ˜16%. The simulated trajectories of the dot-on-capsule are slightly ahead of the experimental trajectory for all but the f = 0.03 model. The simulated dot-on-film position disagrees with the experimental measurement for all transport models. In the MHD simulation of the dot-on-film, the dot is strongly perturbative, though the simulation predicts a peak dot-on-film temperature 2-3 keV higher than the measurement. This suggests a deficiency in the MHD modeling possibly due to the neglect of the Righi-Leduc term or interpenetrating flows of multiple ion species which would reduce the strength of the self-generated fields.
Modelling and simulation of diffusive processes methods and applications
Basu, SK
2014-01-01
This book addresses the key issues in the modeling and simulation of diffusive processes from a wide spectrum of different applications across a broad range of disciplines. Features: discusses diffusion and molecular transport in living cells and suspended sediment in open channels; examines the modeling of peristaltic transport of nanofluids, and isotachophoretic separation of ionic samples in microfluidics; reviews thermal characterization of non-homogeneous media and scale-dependent porous dispersion resulting from velocity fluctuations; describes the modeling of nitrogen fate and transport
Directory of Open Access Journals (Sweden)
Zheng Miao
2014-04-01
Full Text Available The transport phenomena in a passive direct methanol fuel cell (DMFC were numerically simulated by the proposed two-dimensional two-phase nonisothermal mass transport model. The anisotropic transport characteristic and deformation of the gas diffusion layer (GDL were considered in this model. The natural convection boundary conditions were adopted for the transport of methanol, oxygen, and heat at the GDL outer surface. The effect of methanol concentration in the reservoir on cell performance was examined. The distribution of multiphysical fields in the membrane electrode assembly (MEA, especially in the catalyst layers (CLs, was obtained and analyzed. The results indicated that transport resistance for the methanol mainly existed in the MEA while that for oxygen and heat was primarily due to natural convection at the GDL outer surface. Because of the relatively high methanol concentration, the local reaction rate in CLs was mainly determined by the overpotential. Methanol concentration between 3 M and 4 M was recommended for passive liquid feed DMFC in order to achieve a balance between the cell performance and the methanol crossover.
Classical transport in field reversed mirrors: reactor implications
International Nuclear Information System (INIS)
Auerbach, S.P.; Condit, W.C.
1980-01-01
Assuming that the field-reversed mirror (or the closely related spheromak) turns out to be stable, the next crucial issue is transport of particles and heat. Of particular concern is the field null on axis (the X-point), which at first glance seems to allow particles to flow out unhindered. We have evaluated the classical diffusion coefficients for particles and heat in field-reversed mirrors, with particular reference to a class of Hill's vortex models. Two fairly surprising results emerge from this study. First, the diffusion-driven flow of particles and heat is finite at the X-points. This may be traced to the geometrical constraint that the current (and hence the ion-electron drag force, which causes cross-field transport) must vanish on axis. This conclusion holds for any transport model. Second, the classical diffusion coefficient D(psi), which governs both particle and heat flux, is finite on the separatrix. Indeed, in a wide class of Hill's vortex equilibria (spherical, oblate, or prolate) D(psi) is essentially independent of psi (except for the usual factor of n
Low frequency turbulence, particle and heat transport in the Wisconsin levitated octupole
International Nuclear Information System (INIS)
Garner, H.R.
1982-01-01
Low frequency turbulence in the drift frequency range and its relation to the observed particle transport in the Wisconsin Levitated Octupole has been studied with a microwave scattering apparatus. The experimental parameters were T/sub e/ approx. T/sub i/ 13 cm -3 , 200 G < B/sub p-average/ < 1.25 kG. The effect of shear on the transport was studied by the addition of a small toroidal field. By matching experimentally measured density profiles to those given by numerical solutions of the transport equations, diffusion coefficients were obtained. Time dependent density fluctuation spectra were measured with an 8 mm microwave scattering diagnostic to correlate the drift wave portion of the spectrum with the observed diffusion. The density fluctuation spectrum of low frequency (1 kHz < ω < 6 MHz) turbulence was measured for several values of perpendicular wavenumber, k/sub perpendicular to/. Electron heat transport was studied by fitting experimentally measured electron temperature profiles to those predicted by numerical solutions of electron energy transport equation
Model of diffusers / permeators for hydrogen processing
International Nuclear Information System (INIS)
Jacobs, W. D.; Hang, T.
2008-01-01
Palladium-silver (Pd-Ag) diffusers are mainstays of hydrogen processing. Diffusers separate hydrogen from inert species such as nitrogen, argon or helium. The tubing becomes permeable to hydrogen when heated to more than 250 C and a differential pressure is created across the membrane. The hydrogen diffuses better at higher temperatures. Experimental or experiential results have been the basis for determining or predicting a diffuser's performance. However, the process can be mathematically modeled, and comparison to experimental or other operating data can be utilized to improve the fit of the model. A reliable model-based diffuser system design is the goal which will have impacts on tritium and hydrogen processing. A computer model has been developed to solve the differential equations for diffusion given the operating boundary conditions. The model was compared to operating data for a low pressure diffuser system. The modeling approach and the results are presented in this paper. (authors)
Quantum-corrected drift-diffusion models for transport in semiconductor devices
International Nuclear Information System (INIS)
De Falco, Carlo; Gatti, Emilio; Lacaita, Andrea L.; Sacco, Riccardo
2005-01-01
In this paper, we propose a unified framework for Quantum-corrected drift-diffusion (QCDD) models in nanoscale semiconductor device simulation. QCDD models are presented as a suitable generalization of the classical drift-diffusion (DD) system, each particular model being identified by the constitutive relation for the quantum-correction to the electric potential. We examine two special, and relevant, examples of QCDD models; the first one is the modified DD model named Schroedinger-Poisson-drift-diffusion, and the second one is the quantum-drift-diffusion (QDD) model. For the decoupled solution of the two models, we introduce a functional iteration technique that extends the classical Gummel algorithm widely used in the iterative solution of the DD system. We discuss the finite element discretization of the various differential subsystems, with special emphasis on their stability properties, and illustrate the performance of the proposed algorithms and models on the numerical simulation of nanoscale devices in two spatial dimensions
International Nuclear Information System (INIS)
Wang, Fuqiang; Tan, Jianyu; Wang, Zhiqiang
2014-01-01
Highlights: • Using local thermal non-equilibrium model to solve heat transfer of porous media. • CH 4 /H 2 O mixture is adopted as feeding gas of porous media receiver. • Radiative transfer equation between porous strut is solved by Rosseland approximation. • Transport and thermophysical models not included in Fluent are programmed by UDFs. • Variations of model on thermal performance of porous media receiver are studied. - Abstract: The local thermal non-equilibrium model is adopted to solve the steady state heat and mass transfer problems of porous media solar receiver. The fluid entrance surface is subjected to concentrated solar radiation, and CH 4 /H 2 O mixture is adopted as feeding gas. The radiative heat transfer equation between porous strut is solved by Rosseland approximation. The impacts of variation in transport and thermophysical characteristics model of gas mixture on thermal performance of porous media receiver are investigated. The transport and thermophysical characteristics models which are not included in software Fluent are programmed by user defined functions (UDFs). The numerical results indicate that models of momentum source term for porous media receiver have significant impact on pressure drop and static pressure distribution, and the radiative heat transfer cannot be omitted during the thermal performance analysis of porous media receiver
Kinetic modeling of divertor heat load fluxes in the Alcator C-Mod and DIII-D tokamaks
Energy Technology Data Exchange (ETDEWEB)
Pankin, A. Y. [Tech-X Corporation, Boulder, Colorado 80303 (United States); Rafiq, T.; Kritz, A. H. [Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015 (United States); Park, G. Y. [National Fusion Research Institute, Daejeon, 305-333 (Korea, Republic of); Chang, C. S.; Ku, S. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States); Brunner, D.; Hughes, J. W.; LaBombard, B.; Terry, J. L. [MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States); Groebner, R. J. [General Atomics, San Diego, California 92121 (United States)
2015-09-15
The guiding-center kinetic neoclassical transport code, XGC0 [Chang et al., Phys. Plasmas 11, 2649 (2004)], is used to compute the heat fluxes and the heat-load width in the outer divertor plates of Alcator C-Mod and DIII-D tokamaks. The dependence of the width of heat-load fluxes on neoclassical effects, neutral collisions, and anomalous transport is investigated using the XGC0 code. The XGC0 code includes realistic X-point geometry, a neutral source model, the effects of collisions, and a diffusion model for anomalous transport. It is observed that the width of the XGC0 neoclassical heat-load is approximately inversely proportional to the total plasma current I{sub p.} The scaling of the width of the divertor heat-load with plasma current is examined for an Alcator C-Mod discharge and four DIII-D discharges. The scaling of the divertor heat-load width with plasma current is found to be weaker in the Alcator C-Mod discharge compared to scaling found in the DIII-D discharges. The effect of neutral collisions on the 1/I{sub p} scaling of heat-load width is shown not to be significant. Although inclusion of poloidally uniform anomalous transport results in a deviation from the 1/I{sub p} scaling, the inclusion of the anomalous transport that is driven by ballooning-type instabilities results in recovering the neoclassical 1/I{sub p} scaling. The Bohm or gyro-Bohm scalings of anomalous transport do not strongly affect the dependence of the heat-load width on plasma current. The inclusion of anomalous transport, in general, results in widening the width of neoclassical divertor heat-load and enhances the neoclassical heat-load fluxes on the divertor plates. Understanding heat transport in the tokamak scrape-off layer plasmas is important for strengthening the basis for predicting divertor conditions in ITER.
Application of diffusion theory to neutral atom transport in fusion plasmas
International Nuclear Information System (INIS)
Hasan, M.Z.; Conn, R.W.; Pomraning, G.C.
1987-01-01
It is found that the energy dependent diffusion theory provides excellent accuracy in the modelling of transport of neutral atoms in fusion plasmas. Two reasons in particular explain the good accuracy. First, while the plasma is optically thick for low energy neutrals, it is optically thin for high energy neutrals and the diffusion theory with Marshak boundary conditions gives accurate results for an optically thin medium, even for small values of c, the ratio of the scattering cross-section to the total cross-section. Second, the effective value of c at low energy is very close to 1 because of the downscattering via collisions of high energy neutrals. The first reason is proven computationally and theoretically by solving the transport equation in a power series in c and solving the diffusion equation with 'general' Marshak boundary conditions. The second reason is established numerically by comparing the results from a one-dimensional, general geometry, multigroup diffusion theory code, written for this purpose, with the results obtained using the transport code ANISN. Earlier studies comparing one-speed diffusion and transport theory indicated that the diffusion theory would be inaccurate. A detailed analysis shows that this conclusion is limited to a very specific case. Surprisingly, for a very wide range of conditions and when energy dependence is included, the diffusion theory is highly accurate. (author)
International Nuclear Information System (INIS)
Soeldner, F.X.; Pereverzev, G.V.; Bartiromo, R.; Fahrbach, H.U.; Leuterer, F.; Murmann, H.D.; Staebler, A.; Steuer, K.H.
1993-01-01
Transport code calculations were made for experiments with the combined operation of lower hybrid current drive and heating and of neutral beam injection heating on ASDEX. Peaking or flattening of the electron temperature profile are mainly explained by modifications of the MHD induced electron heat transport. They originate from current profile changes due to lower hybrid and neutral beam current drive and to contributions from the bootstrap current. Ion heat transport cannot be described by one single model for all heating scenarios. The ion heat conductivity is reduced during lower hybrid heated phases with respect to Ohmic and neutral beam heating. (author). 13 refs, 5 figs
Diffusion coefficient for anomalous transport
International Nuclear Information System (INIS)
1986-01-01
A report on the progress towards the goal of estimating the diffusion coefficient for anomalous transport is given. The gyrokinetic theory is used to identify different time and length scale inherent to the characteristics of plasmas which exhibit anomalous transport
Modeling VOC transport in simulated waste drums
International Nuclear Information System (INIS)
Liekhus, K.J.; Gresham, G.L.; Peterson, E.S.; Rae, C.; Hotz, N.J.; Connolly, M.J.
1993-06-01
A volatile organic compound (VOC) transport model has been developed to describe unsteady-state VOC permeation and diffusion within a waste drum. Model equations account for three primary mechanisms for VOC transport from a void volume within the drum. These mechanisms are VOC permeation across a polymer boundary, VOC diffusion across an opening in a volume boundary, and VOC solubilization in a polymer boundary. A series of lab-scale experiments was performed in which the VOC concentration was measured in simulated waste drums under different conditions. A lab-scale simulated waste drum consisted of a sized-down 55-gal metal drum containing a modified rigid polyethylene drum liner. Four polyethylene bags were sealed inside a large polyethylene bag, supported by a wire cage, and placed inside the drum liner. The small bags were filled with VOC-air gas mixture and the VOC concentration was measured throughout the drum over a period of time. Test variables included the type of VOC-air gas mixtures introduced into the small bags, the small bag closure type, and the presence or absence of a variable external heat source. Model results were calculated for those trials where the VOC permeability had been measured. Permeabilities for five VOCs [methylene chloride, 1,1,2-trichloro-1,2,2-trifluoroethane (Freon-113), 1,1,1-trichloroethane, carbon tetrachloride, and trichloroethylene] were measured across a polyethylene bag. Comparison of model and experimental results of VOC concentration as a function of time indicate that model accurately accounts for significant VOC transport mechanisms in a lab-scale waste drum
Murthy, P.V.S.N.
2011-12-26
Thermo-diffusion effect on free convection heat and mass transfer from a vertical surface embedded in a liquid saturated thermally stratified non - Darcy porous medium has been analyzed using a local non-similar procedure. The wall temperature and concentration are constant and the medium is linearly stratified in the vertical direction with respect to the thermal conditions. The fluid flow, temperature and concentration fields are affected by the complex interactions among the diffusion ratio Le, buoyancy ratio N, thermo-diffusion parameter Sr and stratification parameter ?. Non-linear interactions of all these parameters on the convective transport has been analyzed and variation of heat and mass transfer coefficients with thermo-diffusion parameter in the thermally stratified non-Darcy porous media is presented through computer generated plots.
Murthy, P.V.S.N.; El-Amin, Mohamed
2011-01-01
Thermo-diffusion effect on free convection heat and mass transfer from a vertical surface embedded in a liquid saturated thermally stratified non - Darcy porous medium has been analyzed using a local non-similar procedure. The wall temperature and concentration are constant and the medium is linearly stratified in the vertical direction with respect to the thermal conditions. The fluid flow, temperature and concentration fields are affected by the complex interactions among the diffusion ratio Le, buoyancy ratio N, thermo-diffusion parameter Sr and stratification parameter ?. Non-linear interactions of all these parameters on the convective transport has been analyzed and variation of heat and mass transfer coefficients with thermo-diffusion parameter in the thermally stratified non-Darcy porous media is presented through computer generated plots.
Diffusion in condensed matter methods, materials, models
Kärger, Jörg
2005-01-01
Diffusion as the process of particle transport due to stochastic movement is a phenomenon of crucial relevance for a large variety of processes and materials. This comprehensive, handbook- style survey of diffusion in condensed matter gives detailed insight into diffusion as the process of particle transport due to stochastic movement. Leading experts in the field describe in 23 chapters the different aspects of diffusion, covering microscopic and macroscopic experimental techniques and exemplary results for various classes of solids, liquids and interfaces as well as several theoretical concepts and models. Students and scientists in physics, chemistry, materials science, and biology will benefit from this detailed compilation.
Heat in the Barents Sea: transport, storage, and surface fluxes
Directory of Open Access Journals (Sweden)
L. H. Smedsrud
2010-02-01
Full Text Available A column model is set up for the Barents Sea to explore sensitivity of surface fluxes and heat storage from varying ocean heat transport. Mean monthly ocean transport and atmospheric forcing are synthesised and force the simulations. Results show that by using updated ocean transports of heat and freshwater the vertical mean hydrographic seasonal cycle can be reproduced fairly well.
Our results indicate that the ~70 TW of heat transported to the Barents Sea by ocean currents is lost in the southern Barents Sea as latent, sensible, and long wave radiation, each contributing 23–39 TW to the total heat loss. Solar radiation adds 26 TW in the south, as there is no significant ice production.
The northern Barents Sea receives little ocean heat transport. This leads to a mixed layer at the freezing point during winter and significant ice production. There is little net surface heat loss annually in the north. The balance is achieved by a heat loss through long wave radiation all year, removing most of the summer solar heating.
During the last decade the Barents Sea has experienced an atmospheric warming and an increased ocean heat transport. The Barents Sea responds to such large changes by adjusting temperature and heat loss. Decreasing the ocean heat transport below 50 TW starts a transition towards Arctic conditions. The heat loss in the Barents Sea depend on the effective area for cooling, and an increased heat transport leads to a spreading of warm water further north.
International Nuclear Information System (INIS)
Tamura, Junji; Kido, Hiroko; Hato, Shinji; Homma, Toshimitsu
2009-03-01
Straight-line or segmented plume models as atmospheric diffusion models are commonly used in probabilistic accident consequence assessment (PCA) codes due to cost and time savings. The PCA code, OSCAAR developed by Japan Atomic Energy Research Institute (Present; Japan Atomic Energy Agency) uses the variable puff trajectory model to calculate atmospheric transport and dispersion of released radionuclides. In order to investigate uncertainties involved with the structure of the atmospheric dispersion/deposition model in OSCAAR, we have introduced the more sophisticated computer codes that included regional meteorological models RAMS and atmospheric transport model HYPACT, which were developed by Colorado State University, and comparative analyses between OSCAAR and RAMS/HYPACT have been performed. In this study, model verification of OSCAAR and RAMS/HYPACT was conducted using data of long term atmospheric diffusion experiments, which were carried out in Tokai-mura, Ibaraki-ken. The predictions by models and the results of the atmospheric diffusion experiments indicated relatively good agreements. And it was shown that model performance of OSCAAR was the same degree as it of RAMS/HYPACT. (author)
Transperitoneal transport of creatinine. A comparison of kinetic models
DEFF Research Database (Denmark)
Fugleberg, S; Graff, J; Joffe, P
1994-01-01
Six kinetic models of transperitoneal creatinine transport were formulated and validated on the basis of experimental results obtained from 23 non-diabetic patients undergoing peritoneal dialysis. The models were designed to elucidate the presence or absence of diffusive, non-lymphatic convective...... including all three forms of transport is superior to other models. We conclude that the best model of transperitoneal creatinine transport includes diffusion, non-lymphatic convective transport and lymphatic convective transport....
Transport of neutral solute across articular cartilage: the role of zonal diffusivities.
Arbabi, V; Pouran, B; Weinans, H; Zadpoor, A A
2015-07-01
Transport of solutes through diffusion is an important metabolic mechanism for the avascular cartilage tissue. Three types of interconnected physical phenomena, namely mechanical, electrical, and chemical, are all involved in the physics of transport in cartilage. In this study, we use a carefully designed experimental-computational setup to separate the effects of mechanical and chemical factors from those of electrical charges. Axial diffusion of a neutral solute Iodixanol into cartilage was monitored using calibrated microcomputed tomography micro-CT images for up to 48 hr. A biphasic-solute computational model was fitted to the experimental data to determine the diffusion coefficients of cartilage. Cartilage was modeled either using one single diffusion coefficient (single-zone model) or using three diffusion coefficients corresponding to superficial, middle, and deep cartilage zones (multizone model). It was observed that the single-zone model cannot capture the entire concentration-time curve and under-predicts the near-equilibrium concentration values, whereas the multizone model could very well match the experimental data. The diffusion coefficient of the superficial zone was found to be at least one order of magnitude larger than that of the middle zone. Since neutral solutes were used, glycosaminoglycan (GAG) content cannot be the primary reason behind such large differences between the diffusion coefficients of the different cartilage zones. It is therefore concluded that other features of the different cartilage zones such as water content and the organization (orientation) of collagen fibers may be enough to cause large differences in diffusion coefficients through the cartilage thickness.
Mongiovì, Maria Stella; Jou, David; Sciacca, Michele
2018-01-01
This review paper puts together some results concerning non equilibrium thermodynamics and heat transport properties of superfluid He II. A one-fluid extended model of superfluid helium, which considers heat flux as an additional independent variable, is presented, its microscopic bases are analyzed, and compared with the well known two-fluid model. In laminar situations, the fundamental fields are density, velocity, absolute temperature, and heat flux. Such a theory is able to describe the thermomechanical phenomena, the propagation of two sounds in liquid helium, and of fourth sound in superleak. It also leads in a natural way to a two-fluid model on purely macroscopical grounds and allows a small amount of entropy associated with the superfluid component. Other important features of liquid He II arise in rotating situations and in superfluid turbulence, both characterized by the presence of quantized vortices (thin vortex lines whose circulation is restricted by a quantum condition). Such vortices have a deep influence on the transport properties of superfluid helium, as they increase very much its thermal resistance. Thus, heat flux influences the vortices which, in turn, modify the heat flux. The dynamics of vortex lines is the central topic in turbulent superfluid helium. The model is generalized to take into account the vortices in different cases of physical interest: rotating superfluids, counterflow superfluid turbulence, combined counterflow and rotation, and mass flow in addition to heat flow. To do this, the averaged vortex line density per unit volume L, is introduced and its dynamical equations are considered. Linear and non-linear evolution equations for L are written for homogeneous and inhomogeneous, isotropic and anisotropic situations. Several physical experiments are analyzed and the influence of vortices on the effective thermal conductivity of turbulent superfluid helium is found. Transitions from laminar to turbulent flows, from diffusive to
Model Comparison for Electron Thermal Transport
Moses, Gregory; Chenhall, Jeffrey; Cao, Duc; Delettrez, Jacques
2015-11-01
Four electron thermal transport models are compared for their ability to accurately and efficiently model non-local behavior in ICF simulations. Goncharov's transport model has accurately predicted shock timing in implosion simulations but is computationally slow and limited to 1D. The iSNB (implicit Schurtz Nicolai Busquet electron thermal transport method of Cao et al. uses multigroup diffusion to speed up the calculation. Chenhall has expanded upon the iSNB diffusion model to a higher order simplified P3 approximation and a Monte Carlo transport model, to bridge the gap between the iSNB and Goncharov models while maintaining computational efficiency. Comparisons of the above models for several test problems will be presented. This work was supported by Sandia National Laboratory - Albuquerque and the University of Rochester Laboratory for Laser Energetics.
A two-parameter nondiffusive heat conduction model for data analysis in pump-probe experiments
Ma, Yanbao
2014-12-01
Nondiffusive heat transfer has attracted intensive research interests in last 50 years because of its importance in fundamental physics and engineering applications. It has unique features that cannot be described by the Fourier law. However, current studies of nondiffusive heat transfer still focus on studying the effective thermal conductivity within the framework of the Fourier law due to a lack of a well-accepted replacement. Here, we show that nondiffusive heat conduction can be characterized by two inherent material properties: a diffusive thermal conductivity and a ballistic transport length. We also present a two-parameter heat conduction model and demonstrate its validity in different pump-probe experiments. This model not only offers new insights of nondiffusive heat conduction but also opens up new avenues for the studies of nondiffusive heat transfer outside the framework of the Fourier law.
Application of diffusion theory to neutral atom transport in fusion plasmas
International Nuclear Information System (INIS)
Hasan, M.Z.; Conn, R.W.; Pomraning, G.C.
1986-05-01
It is found that energy dependent diffusion theory provides excellent accuracy in the modelling of transport of neutral atoms in fusion plasmas. Two reasons in particular explain the good accuracy. First, while the plasma is optically thick for low energy neutrals, it is optically thin for high energy neutrals and diffusion theory with Marshak boundary conditions gives accurate results for an optically thin medium even for small values of 'c', the ratio of the scattering to the total cross section. Second, the effective value of 'c' at low energy becomes very close to one due to the down-scattering via collisions of high energy neutrals. The first reason is proven both computationally and theoretically by solving the transport equation in a power series in 'c' and the diffusion equation with 'general' Marshak boundary conditions. The second reason is established numerically by comparing the results from a one-dimensional, general geometry, multigroup diffusion theory code, written for this purpose, with the results obtained using the transport code ANISN
International Nuclear Information System (INIS)
Cartier, J.
2006-04-01
This thesis focuses on mathematical analysis, numerical resolution and modelling of the transport equations. First of all, we deal with numerical approximation of the solution of the transport equations by using a mixed-hybrid scheme. We derive and study a mixed formulation of the transport equation, then we analyse the related variational problem and present the discretization and the main properties of the scheme. We particularly pay attention to the behavior of the scheme and we show its efficiency in the diffusion limit (when the mean free path is small in comparison with the characteristic length of the physical domain). We present academical benchmarks in order to compare our scheme with other methods in many physical configurations and validate our method on analytical test cases. Unstructured and very distorted meshes are used to validate our scheme. The second part of this thesis deals with two transport problems. The first one is devoted to the study of diffusion due to boundary conditions in a transport problem between two plane plates. The second one consists in modelling and simulating radiative transfer phenomenon in case of the industrial context of inertial confinement fusion. (author)
Miniature Heat Transport System for Spacecraft Thermal Control
Ochterbeck, Jay M.; Ku, Jentung (Technical Monitor)
2002-01-01
Loop heat pipes (LHP) are efficient devices for heat transfer and use the basic principle of a closed evaporation-condensation cycle. The advantage of using a loop heat pipe over other conventional methods is that large quantities of heat can be transported through a small cross-sectional area over a considerable distance with no additional power input to the system. By using LHPs, it seems possible to meet the growing demand for high-power cooling devices. Although they are somewhat similar to conventional heat pipes, LHPs have a whole set of unique properties, such as low pressure drops and flexible lines between condenser and evaporator, that make them rather promising. LHPs are capable of providing a means of transporting heat over long distances with no input power other than the heat being transported because of the specially designed evaporator and the separation of liquid and vapor lines. For LHP design and fabrication, preliminary analysis on the basis of dimensionless criteria is necessary because of certain complicated phenomena that take place in the heat pipe. Modeling the performance of the LHP and miniaturizing its size are tasks and objectives of current research. In the course of h s work, the LHP and its components, including the evaporator (the most critical and complex part of the LHP), were modeled with the corresponding dimensionless groups also being investigated. Next, analysis of heat and mass transfer processes in the LHP, selection of the most weighted criteria from known dimensionless groups (thermal-fluid sciences), heat transfer rate limits, (heat pipe theory), and experimental ratios which are unique to a given heat pipe class are discussed. In the third part of the report, two-phase flow heat and mass transfer performances inside the LHP condenser are analyzed and calculated for Earth-normal gravity and microgravity conditions. On the basis of recent models and experimental databanks, an analysis for condensing two-phase flow regimes
Modeling unsteady-state VOC transport in simulated waste drums
International Nuclear Information System (INIS)
Liekhus, K.J.; Gresham, G.L.; Peterson, E.S.; Rae, C.; Hotz, N.J.; Connolly, M.J.
1994-01-01
This report is a revision of an EG ampersand G Idaho informal report originally titled Modeling VOC Transport in Simulated Waste Drums. A volatile organic compound (VOC) transport model has been developed to describe unsteady-state VOC permeation and diffusion within a waste drum. Model equations account for three primary mechanisms for VOC transport from a void volume within the drum. These mechanisms are VOC permeation across a polymer boundary, VOC diffusion across an opening in a volume boundary, and VOC solubilization in a polymer boundary. A series of lab-scale experiments was performed in which the VOC concentration was measured in simulated waste drums under different conditions. A lab-scale simulated waste drum consisted of a sized-down 55-gal metal drum containing a modified rigid polyethylene drum liner. Four polyethylene bags were sealed inside a large polyethylene bag, supported by a wire cage, and placed inside the drum liner. The small bags were filled with VOC-air gas mixture and the VOC concentration was measured throughout the drum over a period of time. Test variables included the type of VOC-air gas mixtures introduced into the small bags, the small bag closure type, and the presence or absence of a variable external heat source. Model results were calculated for those trials where the permeability had been measured
Coupled heat transfer in high temperature transporting system with semitransparent/opaque material
International Nuclear Information System (INIS)
Du Shenghua; Xia Xinjin
2010-01-01
The heat transfer model of the aerodynamic heating coupled with radiative cooling was developed. The thermal protect system includes the higher heat flux region with high temperature semitransparent material, the heat transporting channel and the lower heat flux region with metal. The control volume method was combined with the Monte Carlo method to calculate the coupled heat transfer of the transporting system, and the thermal equilibrium equation for the transporting channel was solved simultaneously. The effect of the aeroheating flux radio, the area ratio of radiative surfaces, the convective heat transfer coefficient of the heat transporting channel on the radiative surface temperature and the fluid temperature in the heat transporting channel were analyzed. The effect of radiation and conduction in the semitransparent material was discussed. The result shows that to increase the convective heat transfer coefficient in heat flux channel can enhance the heat transporting ability of the system, but the main parameter to effect on the temperature of the heat transporting system is the area ratio of radiative surfaces. (authors)
The brush model - a new approach to numerical modeling of matrix diffusion in fractured clay stone
International Nuclear Information System (INIS)
Lege, T.; Shao, H.
1998-01-01
A special approach for numerical modeling of contaminant transport in fractured clay stone is presented. The rock matrix and the fractures are simulated with individual formulations for FE grids and transport, coupled into a single model. The capacity of the rock matrix to take up contaminants is taken into consideration with a discrete simulation of matrix diffusion. Thus, the natural process of retardation due to matrix diffusion can be better simulated than by a standard introduction of an empirical parameter into the transport equation. Transport in groundwater in fractured clay stone can be simulated using a model called a 'brush model'. The 'brush handle' is discretized by 2-D finite elements. Advective-dispersive transport in groundwater in the fractures is assumed. The contaminant diffuses into 1D finite elements perpendicular to the fractures, i.e., the 'bristles of the brush'. The conclusion is drawn that matrix diffusion is an important property of fractured clay stone for contaminant retardation. (author)
Three-dimensional model of heat transport during In Situ Vitrification with melting and cool down
International Nuclear Information System (INIS)
Hawkes, G.L.
1993-01-01
A potential technology for permanent remediation of buried wastes is the In Situ Vitrification (ISV) process. This process uses electrical resistance heating to melt waste and contaminated soil in place to produce a durable, glasslike material that encapsulates and immobilizes buried wastes. The magnitude of the resulting electrical resistance heating is sufficient to cause soil melting. As the molten region grows, surface heat losses cause the soil near the surface to re solidify. This paper presents numerical results obtained by considering heat transport and melting when solving the conservation of mass and energy equations using finite element methods. A local heat source is calculated by solving the electric field equation and calculating a Joule Heat source term. The model considered is a three-dimensional model of the electrodes and surrounding soil. Also included in the model is subsidence; where the surface of the melted soil subsides due to the change in density when the soil melts. A power vs. time profile is implemented for typical ISV experiments. The model agrees well with experimental data for melt volume and melt shape
International Nuclear Information System (INIS)
Peters, M.
1996-01-01
In the first experiment the plasma current in the RTP tokamak is varied. Here the underlying idea was to check whether at a low plasma current, transport in the tokamak resembles transport in stellarators more than at higher currents. Secondly, experiments have been done to study the relation of the diffusivity χ to the temperature and its gradient in both W7-AS and RTP. In this case the underlying idea was to find the explanation for the phenomenon observed in both tokamaks and stellarators that the quality of the confinement degrades when more heating is applied. A possible explanation is that the diffusivity increases with the temperature or its gradient. Whereas in standard tokamak and stellarator experiments the temperature and its gradient are strongly correlated, a special capability of the plasma heating system of W7-AS and RTP can force them to decouple. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Peters, M
1996-01-16
In the first experiment the plasma current in the RTP tokamak is varied. Here the underlying idea was to check whether at a low plasma current, transport in the tokamak resembles transport in stellarators more than at higher currents. Secondly, experiments have been done to study the relation of the diffusivity {chi} to the temperature and its gradient in both W7-AS and RTP. In this case the underlying idea was to find the explanation for the phenomenon observed in both tokamaks and stellarators that the quality of the confinement degrades when more heating is applied. A possible explanation is that the diffusivity increases with the temperature or its gradient. Whereas in standard tokamak and stellarator experiments the temperature and its gradient are strongly correlated, a special capability of the plasma heating system of W7-AS and RTP can force them to decouple. (orig.).
Development of CANDU 6 Primary Heat Transport System Modeling Program
International Nuclear Information System (INIS)
Seo, Hyung-beom; Kim, Sung-min; Park, Joong-woo; Kim, Kwang-su; Ko, Dae-hack; Han, Bong-seob
2007-01-01
NUCIRC is a steady-state thermal-hydraulic code used for design and performance analyses of CANDU Heat Transport System. The code is used to build PHT model in Wolsong NPP and to calculate channel flow distribution. Wolsong NPP has to calculate channel flow distribution and quality of coolant at the ROH header after every outage by OPP (Operating Policy and Principal). PHT modeling work is time consuming which need a lot of operation experience and specialty. It is very difficult to build PHT model as plant operator in two weeks which is obligate for plant operation after every outage. That is why Wolsong NPP develop NUMODEL (NUcirc MODELing) with many-years experience and a know-how of using NUCIRC code. NUMODEL is computer program which is used to create PHT model based on utilizing NUCIRC code
Pal, van der M.; Graaf, van der E.R.; Meijer, de R.J.; Wit, de M.H.; Hendriks, N.A.
2000-01-01
This study describes an approach for measuring and modelling diffusive and advective transport of radon through building materials. The goal of these measurements and model calculations is to improve our understanding concerning the factors influencing the transport of radon through building
Carbon dioxide sequestration: Modeling the diffusive and convective transport under a CO2 cap
Allen, Rebecca; Sun, Shuyu
2012-01-01
of low permeability. CO2 from this ‘capped' region diffuses into the fluid underlying it, and the resulting CO2-fluid mixture increases in density. This increase in density leads to gravity-driven convection. Accordingly, diffusive-convective transport
Non-Fourier Vernotte-Cattaneo numerical model for heat conduction in a BWR fuel rod
Energy Technology Data Exchange (ETDEWEB)
Espinosa-Martinez, E.G.; Vazquez-Rodriguez, A.; Varela-Ham, J.R.; Espinosa-Paredes, G., E-mail: gepe@xanum.uam.mx [Universidad Autonoma Metropolitana, Area de Ingenieria en Recursos Energeticos, Iztapalapa (Mexico)
2014-07-01
A fuel rod mathematical model based on transient heat conduction as constitutive Non-Fourier law for Light Water Reactors (LWRs) transient analysis is presented. The structure of the fuel pellet is affected due to high temperatures and irradiation, which eventually produce fracture or cracks. In principle the fractures are saturated of gas. Then, the Fourier law of the heat conduction is not strictly applicable to describe these phenomena, where the physical properties such as thermal conductivity, heat capacity and density correspond to a heterogeneous material due to gas, and therefore the thermal diffusion process due to molecular transport in the fuel pellet is affected. From the point of view of nuclear reactor safety analysis, the heat transfer from the fuel to the coolant is crucial and superheating of the wall can cause the cladding failure. In the classical theory of diffusion, the Fourier law of heat conduction is used to describe the relation between the heat flux vector and the temperature gradient assuming that the heat propagation speeds are infinite. The Non-Fourier approach presented in this work eliminates the assumption of an infinite thermal wave speed, therefore time-dependent heat sources were considered in the fuel rod heat transfer model. The numerical experiments in a BWR, show that the Non-Fourier approach is crucial in the pressurization transients such as turbine trip and reactor isolation. (author)
Non-Fourier Vernotte-Cattaneo numerical model for heat conduction in a BWR fuel rod
International Nuclear Information System (INIS)
Espinosa-Martinez, E.G.; Vazquez-Rodriguez, A.; Varela-Ham, J.R.; Espinosa-Paredes, G.
2014-01-01
A fuel rod mathematical model based on transient heat conduction as constitutive Non-Fourier law for Light Water Reactors (LWRs) transient analysis is presented. The structure of the fuel pellet is affected due to high temperatures and irradiation, which eventually produce fracture or cracks. In principle the fractures are saturated of gas. Then, the Fourier law of the heat conduction is not strictly applicable to describe these phenomena, where the physical properties such as thermal conductivity, heat capacity and density correspond to a heterogeneous material due to gas, and therefore the thermal diffusion process due to molecular transport in the fuel pellet is affected. From the point of view of nuclear reactor safety analysis, the heat transfer from the fuel to the coolant is crucial and superheating of the wall can cause the cladding failure. In the classical theory of diffusion, the Fourier law of heat conduction is used to describe the relation between the heat flux vector and the temperature gradient assuming that the heat propagation speeds are infinite. The Non-Fourier approach presented in this work eliminates the assumption of an infinite thermal wave speed, therefore time-dependent heat sources were considered in the fuel rod heat transfer model. The numerical experiments in a BWR, show that the Non-Fourier approach is crucial in the pressurization transients such as turbine trip and reactor isolation. (author)
Materials for nuclear diffusion-bonded compact heat exchangers
International Nuclear Information System (INIS)
Li, Xiuqing; Smith, Tim; Kininmont, David; Dewson, Stephen John
2009-01-01
This paper discusses the characteristics of materials used in the manufacture of diffusion bonded compact heat exchangers. Heatric have successfully developed a wide range of alloys tailored to meet process and customer requirements. This paper will focus on two materials of interest to the nuclear industry: dual certified SS316/316L stainless steel and nickel-based alloy Inconel 617. Dual certified SS316/316L is the alloy used most widely in the manufacture of Heatric's compact heat exchangers. Its excellent mechanical and corrosion resistance properties make it a good choice for use with many heat transfer media, including water, carbon dioxide, liquid sodium, and helium. As part of Heatric's continuing product development programme, work has been done to investigate strengthening mechanisms of the alloy; this paper will focus in particular on the effects of nitrogen addition. Another area of Heatric's programme is Alloy 617. This alloy has recently been developed for diffusion bonded compact heat exchanger for high temperature nuclear applications, such as the intermediate heat exchanger (IHX) for the very high temperature nuclear reactors for production of electricity, hydrogen and process heat. This paper will focus on the effects of diffusion bonding process and cooling rate on the properties of alloy 617. This paper also compares the properties and discusses the applications of these two alloys to compact heat exchangers for various nuclear processes. (author)
Fourno, A.; Grenier, C.; Benabderrahmane, H.
2003-04-01
Modeling flow and transport in natural fractured media is a difficult issue due among others to the complexity of the system, the particularities of the geometrical features, the strong parameter value contrasts between the fracture zones (flow zones) and the matrix zones (no flow zones). This lead to the development of dedicated tools like for instance discrete fracture network models (DFN). We follow here another line applicable for classical continuous modeling codes. The fracture network is not meshed here but presence of fractures is taken into account by means of continuous heterogeneous fields (permeability, porosity, head, velocity, concentration ...). This line, followed by different authors, is referred as smeared fracture approach and presents the following advantages: the approach is very versatile because no dedicated spatial discretization effort is required (we use a basic regular mesh, simulations can be done on a rough mesh saving computer time). This makes this kind of approach very promising for taking heterogeneity of properties as well as uncertainties into account within a Monte Carlo framework for instance. Furthermore, the geometry of the matrix blocks where transfers proceed by diffusion is fully taken into account contrary to classical simplified 1D approach for instance. Nevertheless continuous heterogeneous field representation of a fractured medium requires a homogenization process at the scale of the mesh considered. Literature proves that this step of homogenization for transport is still a challenging task. Consequently, the level precision of the results has to be estimated. We precedently proposed a new approach dedicated to Mixed and Hybrid Finite Element approach. This numerical scheme is very interesting for such highly heterogeneous media and in particular guaranties exact conservation of mass flow for each mesh leading to good transport results. We developed a smeared fractures approach to model flow and transport limited to
Application of a numerical transport correction in diffusion calculations
International Nuclear Information System (INIS)
Tomatis, Daniele; Dall'Osso, Aldo
2011-01-01
Full core calculations by ordinary transport methods can demand considerable computational time, hardly acceptable in the industrial work frame. However, the trend of next generation nuclear cores goes toward more heterogeneous systems, where transport phenomena of neutrons become very important. On the other hand, using diffusion solvers is more practical allowing faster calculations, but a specific formulation of the diffusion coefficient is requested to reproduce the scalar flux with reliable physical accuracy. In this paper, the Ronen method is used to evaluate numerically the diffusion coefficient in the slab reactor. The new diffusion solution is driven toward the solution of the integral neutron transport equation by non linear iterations. Better estimates of currents are computed and diffusion coefficients are corrected at node interfaces, still assuming Fick's law. This method enables obtaining closer results to the transport solution by a common solver in multigroup diffusion. (author)
Anomalous transport regimes in a stochastic advection-diffusion model
International Nuclear Information System (INIS)
Dranikov, I.L.; Kondratenko, P.S.; Matveev, L.V.
2004-01-01
A general solution to the stochastic advection-diffusion problem is obtained for a fractal medium with long-range correlated spatial fluctuations. A particular transport regime is determined by two basic parameters: the exponent 2h of power-law decay of the two-point velocity correlation function and the mean advection velocity u. The values of these parameters corresponding to anomalous diffusion are determined, and anomalous behavior of the tracer distribution is analyzed for various combinations of u and h. The tracer concentration is shown to decrease exponentially at large distances, whereas power-law decay is predicted by fractional differential equations. Equations that describe the essential characteristics of the solution are written in terms of coupled space-time fractional differential operators. The analysis relies on a diagrammatic technique and makes use of scale-invariant properties of the medium
Modelling mass and heat transfer in nano-based cancer hyperthermia.
Nabil, M; Decuzzi, P; Zunino, P
2015-10-01
We derive a sophisticated mathematical model for coupled heat and mass transport in the tumour microenvironment and we apply it to study nanoparticle delivery and hyperthermic treatment of cancer. The model has the unique ability of combining the following features: (i) realistic vasculature; (ii) coupled capillary and interstitial flow; (iii) coupled capillary and interstitial mass transfer applied to nanoparticles; and (iv) coupled capillary and interstitial heat transfer, which are the fundamental mechanisms governing nano-based hyperthermic treatment. This is an improvement with respect to previous modelling approaches, where the effect of blood perfusion on heat transfer is modelled in a spatially averaged form. We analyse the time evolution and the spatial distribution of particles and temperature in a tumour mass treated with superparamagnetic nanoparticles excited by an alternating magnetic field. By means of numerical experiments, we synthesize scaling laws that illustrate how nano-based hyperthermia depends on tumour size and vascularity. In particular, we identify two distinct mechanisms that regulate the distribution of particle and temperature, which are characterized by perfusion and diffusion, respectively.
Moment approach to neoclassical flows, currents and transport in auxiliary heated tokamaks
International Nuclear Information System (INIS)
Kim, Yil Bong.
1988-02-01
The moment approach is utilized to derive the full complement of neoclassical transport processes in auxiliary heated tokamaks. The effects of auxiliary heating [neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH)] considered arise from the collisional interaction between the background plasma species and the fast-ion-tail species. From a known fast ion distribution function we evaluate the parallel (to the magnetic field) momentum and heat flow inputs to the background plasma. Then, through the momentum and heat flow balance equations, we can determine the induced parallel flows (and current) and radial transpot fluxes in ''equilibrium'' (on the time scale much longer than the collisional relaxation time, i.e., t >> 1ν/sub ii/). In addition to the fast-ion-induced current, the total neoclassical current includes the boostap current, which is driven by the pressure and temperature gradients, the Pfirsch-Schlueter current which is required for charge neutrality, and the neoclassical (including trapped particle effects) Spitzer current due to the parallel electric field. The radial transport fluxes also include off-diagonal compnents in the transport matrix which correspond to the Ware (neoclassical) pinch due to the inductive applied electric field an the fast-ion-induced radial fluxes, in addition to the usual pressure- and temperature-gradient-driven fluxes (particle diffusion and heat conduction). Once the tranport coefficient are completely determined, the radial fluxes and the heat fluxes can be substituted into the density and energy evolution equations to provide a complete description of ''equilibrium'' (δδt << ν/sub ii/) neoclassical transport processes in a plasma. 47 refs., 14 figs
Plasma transport in mixed magnetic topologies
International Nuclear Information System (INIS)
Hegna, C.C.; Callen, J.D.
1992-12-01
A simple model is introduced to illustrate some features concerning anomalous transport associated with magnetic turbulence. For magnetic topologies that are described as bands of stochasticity separated by regions with good flux surfaces, the transport coefficients deviate significantly from those describing completely stochastic magnetic fields. It is possible to have the electron heat diffusivity exceed a runaway electron diffusion coefficient, despite the existence of widespread magnetic stochasticity. Comparing the ratios of transport coefficients is not an accurate way to determine whether anomalous plasma transport is controlled by electrostatic or electromagnetic fluctuations
Unconditionally stable diffusion-acceleration of the transport equation
International Nuclear Information System (INIS)
Larsen, E.W.
1982-01-01
The standard iterative procedure for solving fixed-source discrete-ordinates problems converges very slowly for problems in optically large regions with scattering ratios c near unity. The diffusion-synthetic acceleration method has been proposed to make use of the fact that for this class of problems the diffusion equation is often an accurate approximation to the transport equation. However, stability difficulties have historically hampered the implementation of this method for general transport differencing schemes. In this article we discuss a recently developed procedure for obtaining unconditionally stable diffusion-synthetic acceleration methods for various transport differencing schemes. We motivate the analysis by first discussing the exact transport equation; then we illustrate the procedure by deriving a new stable acceleration method for the linear discontinuous transport differencing scheme. We also provide some numerical results
Unconditionally stable diffusion-acceleration of the transport equation
International Nuclear Information System (INIS)
Larson, E.W.
1982-01-01
The standard iterative procedure for solving fixed-source discrete-ordinates problems converges very slowly for problems in optically thick regions with scattering ratios c near unity. The diffusion-synthetic acceleration method has been proposed to make use of the fact that for this class of problems, the diffusion equation is often an accurate approximation to the transport equation. However, stability difficulties have historically hampered the implementation of this method for general transport differencing schemes. In this article we discuss a recently developed procedure for obtaining unconditionally stable diffusion-synthetic acceleration methods for various transport differencing schemes. We motivate the analysis by first discussing the exact transport equation; then we illustrate the procedure by deriving a new stable acceleration method for the linear discontinuous transport differencing scheme. We also provide some numerical results
Power dependence of ion thermal diffusivity at the internal transport barrier in JT-60U
Energy Technology Data Exchange (ETDEWEB)
Sakamoto, Yoshiteru; Suzuki, Takahiro; Ide, Shunsuke [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment] [and others
2002-09-01
The formation properties of an internal transport barrier (ITB) were investigated in a weak positive magnetic shear plasma by changing the neutral beam heating power. The ion thermal diffusivity in the core region shows L-mode state, weak ITB, and strong ITB, depending upon the heating power. Two features of ITB formation were experimentally confirmed. Weak ITB was formed in spite of the absence of an apparent transition in an ion temperature profile. On the other hand, strong ITB appeared after an apparent transition from the weak ITB. In addition, the ion thermal diffusivity at the ITB is correlated to the radial electric field shear. In the case of the weak ITB, ion thermal diffusivity decreased gradually with increases in the radial electric field shear. There exists a threshold in the radial electric field shear, which allows for a change in state from that of weak to strong ITBs. (author)
Relationship between particle and heat transport in JT-60U plasmas with internal transport barrier
International Nuclear Information System (INIS)
Takenaga, H.
2002-01-01
Relationship between particle and heat transport in an internal transport barrier (ITB) has been systematically investigated for the first time in reversed shear (RS) and high-β p ELMy H-mode (weak positive shear) plasmas of JT-60U for understanding of compatibility of improved energy confinement and effective particle control such as exhaust of helium ash and reduction in impurity contamination. In the RS plasma, no helium and carbon accumulation inside the ITB is observed even with highly improved energy confinement. In the high-β p plasma, both helium and carbon density profiles are flat. As the ion temperature profile changes from parabolic- to box-type, the helium diffusivity decreases by a factor of about 2 as well as the ion thermal diffusivity in the RS plasma. The measured soft X-ray profile is more peaked than that calculated by assuming the same n AR profile as the n e profile in the Ar injected RS plasma with the box-type profile, suggesting accumulation of Ar inside the ITB. Particle transport is improved with no change of ion temperature in the RS plasma, when density fluctuation is drastically reduced by a pellet injection. (author)
Random walk, diffusion and mixing in simulations of scalar transport in fluid flows
International Nuclear Information System (INIS)
Klimenko, A Y
2008-01-01
Physical similarity and mathematical equivalence of continuous diffusion and particle random walk form one of the cornerstones of modern physics and the theory of stochastic processes. In many applied models used in simulation of turbulent transport and turbulent combustion, mixing between particles is used to reflect the influence of the continuous diffusion terms in the transport equations. We show that the continuous scalar transport and diffusion can be accurately specified by means of mixing between randomly walking Lagrangian particles with scalar properties and assess errors associated with this scheme. This gives an alternative formulation for the stochastic process which is selected to represent the continuous diffusion. This paper focuses on statistical errors and deals with relatively simple cases, where one-particle distributions are sufficient for a complete description of the problem.
Monte Carlo simulation of neutron transport phenomena
International Nuclear Information System (INIS)
Srinivasan, P.
2009-01-01
Neutron transport is one of the central problems in nuclear reactor related studies and other applied sciences. Some of the major applications of neutron transport include nuclear reactor design and safety, criticality safety of fissile material handling, neutron detector design and development, nuclear medicine, assessment of radiation damage to materials, nuclear well logging, forensic analysis etc. Most reactor and dosimetry studies assume that neutrons diffuse from regions of high to low density just like gaseous molecules diffuse to regions of low concentration or heat flow from high to low temperature regions. However while treatment of gaseous or heat diffusion is quite accurately modeled, treatment of neutron transport as simple diffusion is quite limited. In simple diffusion, the neutron trajectories are irregular, random and zigzag - where as in neutron transport low reaction cross sections (1 barn- 10 -24 cm 2 ) lead to long mean free paths which again depend on the nature and irregularities of the medium. Hence a more accurate representation of the neutron transport evolved based on the Boltzmann equation of kinetic gas theory. In fact the neutron transport equation is a linearized version of the Boltzmann gas equation based on neutron conservation with seven independent variables. The transport equation is difficult to solve except in simple cases amenable to numerical methods. The diffusion (equation) approximation follows from removing the angular dependence of the neutron flux
Diffusive transport of radon in a homogeneous column of dry sand
van der Spoel, W.H.; van der Graaf, E.R.; de Meijer, R.J.
To validate a model for radon transport in soil, measurements of diffusive radon transport under well-defined and controlled conditions have been made in a homogeneous column of dry sand with an air-filled volume on top. This volume simulates a crawl space. The measurements concern time-dependent
Energy Technology Data Exchange (ETDEWEB)
Hidalgo Lopez, A [Universidad Politecnica de Madrid (Spain)
2002-07-01
The aim of this research is to simulate the isotopic and heat release and transport through the geosphere, from a geological repository of high level nuclear waste. in order to achieve it, different physical processes, that have to do with the problem, are considered: groundwater flow, radioactive decay, nuclide dissolution in groundwater, heat generation, mass and heat transport. Some of these phenomena are related among the, which allows to build a coupled model,which is the starting point to generate a FORTRAN code. The flow and transport models are developed in two spatial dimensions and are integrated in space by means of a finite volume method. The time integration is fulfilled by a {theta}-method. Moreover, the advection-diffusion equation is solved by two finite volume techniques. In the first one a linear interpolation is used whereas in the second it is used a quadratic one. Also, a consistency an stability study of both methods is carried out in order to compare their stability zones and the errors appearing. Stability is analysed by applying the von Neumann method, which is based upon Fourier series. Although it is a classical technique when dealing with finite-difference schemes, it is here applied to two finite volume schemes. (Author)
International Nuclear Information System (INIS)
Helander, P.; Hazeltine, R.D.; Catto, P.J.
1996-01-01
The orderings in the kinetic equations commonly used to study the plasma core of a tokamak do not allow a balance between parallel ion streaming and radial diffusion, and are, therefore, inappropriate in the plasma edge. Different orderings are required in the edge region where radial transport across the steep gradients associated with the scrape-off layer is large enough to balance the rapid parallel flow caused by conditions close to collecting surfaces (such as the Bohm sheath condition). In the present work, we derive and solve novel kinetic equations, allowing for such a balance, and construct distinctive transport laws for impure, collisional, edge plasmas in which the perpendicular transport is (i) due to Coulomb collisions of ions with heavy impurities, or (ii) governed by anomalous diffusion driven by electrostatic turbulence. In both the collisional and anomalous radial transport cases, we find that one single diffusion coefficient determines the radial transport of particles, momentum and heat. The parallel transport laws and parallel thermal force in the scrape-off layer assume an unconventional form, in which the relative ion-impurity flow is driven by a combination of the conventional parallel gradients, and new (i) collisional or (ii) anomalous terms involving products of radial derivatives of the temperature and density with the radial shear of the parallel velocity. Thus, in the presence of anomalous radial diffusion, the parallel ion transport cannot be entirely classical, as usually assumed in numerical edge computations. The underlying physical reason is the appearance of a novel type of parallel thermal force resulting from the combined action of anomalous diffusion and radial temperature and velocity gradients. In highly sheared flows the new terms can modify impurity penetration into the core plasma
A reduced model for ion temperature gradient turbulent transport in helical plasmas
International Nuclear Information System (INIS)
Nunami, M.; Watanabe, T.-H.; Sugama, H.
2013-07-01
A novel reduced model for ion temperature gradient (ITG) turbulent transport in helical plasmas is presented. The model enables one to predict nonlinear gyrokinetic simulation results from linear gyrokinetic analyses. It is shown from nonlinear gyrokinetic simulations of the ITG turbulence in helical plasmas that the transport coefficient can be expressed as a function of the turbulent fluctuation level and the averaged zonal flow amplitude. Then, the reduced model for the turbulent ion heat diffusivity is derived by representing the nonlinear turbulent fluctuations and zonal flow amplitude in terms of the linear growth rate of the ITG instability and the linear response of the zonal flow potentials. It is confirmed that the reduced transport model results are in good agreement with those from nonlinear gyrokinetic simulations for high ion temperature plasmas in the Large Helical Device. (author)
FEFLOW finite element modeling of flow, mass and heat transport in porous and fractured media
Diersch, Hans-Jörg G
2013-01-01
Placing advanced theoretical and numerical methods in the hands of modeling practitioners and scientists, this book explores the FEFLOW system for solving flow, mass and heat transport processes in porous and fractured media. Offers applications and exercises.
Impact of plasma triangularity and collisionality on electron heat transport in TCV L-mode plasmas
International Nuclear Information System (INIS)
Camenen, Y.; Pochelon, A.; Behn, R.; Bottino, A.; Bortolon, A.; Coda, S.; Karpushov, A.; Sauter, O.; Zhuang, G.
2007-01-01
The impact of plasma shaping on electron heat transport is investigated in TCV L-mode plasmas. The study is motivated by the observation of an increase in the energy confinement time with decreasing plasma triangularity which may not be explained by a change in the temperature gradient induced by changes in the geometry of the flux surfaces. The plasma triangularity is varied over a wide range, from positive to negative values, and various plasmas conditions are explored by changing the total electron cyclotron (EC) heating power and the plasma density. The mid-radius electron heat diffusivity is shown to significantly decrease with decreasing triangularity and, for similar plasma conditions, only half of the EC power is required at a triangularity of -0.4 compared with +0.4 to obtain the same temperature profile. Besides, the observed dependence of the electron heat diffusivity on the electron temperature, electron density and effective charge can be grouped in a unique dependence on the plasma effective collisionality. In summary, the electron heat transport level exhibits a continuous decrease with decreasing triangularity and increasing collisionality. Local gyro-fluid and global gyro-kinetic simulations predict that trapped electron modes are the most unstable modes in these EC heated plasmas with an effective collisionality ranging from 0.2 to 1. The modes stability dependence on the plasma triangularity is investigated
Relationship between particle and heat transport in JT-60U plasmas with internal transport barrier
International Nuclear Information System (INIS)
Takenaga, Hidenobu; Higashijima, S.; Oyama, N.
2003-01-01
The relationship between particle and heat transport in an internal transport barrier (ITB) has been systematically investigated in reversed shear (RS) and high β p ELMy H-mode plasmas in JT-60U. No helium and carbon accumulation inside the ITB is observed even with ion heat transport reduced to a neoclassical level. On the other hand, the heavy impurity argon is accumulated inside the ITB. The argon density profile estimated from the soft x-ray profile is more peaked, by a factor of 2-4 in the RS plasma and of 1.6 in the high β p mode plasma, than the electron density profile. The helium diffusivity (D He ) and the ion thermal diffusivity (χ i ) are at an anomalous level in the high β p mode plasma, where D He and χ i are higher by a factor of 5-10 than the neoclassical value. In the RS plasma, D He is reduced from the anomalous to the neoclassical level, together with χ i . The carbon and argon density profiles calculated using the transport coefficients reduced to the neoclassical level only in the ITB are more peaked than the measured profiles, even when χ i is reduced to the neoclassical level. Argon exhaust from the inside of the ITB is demonstrated by applying ECH in the high β p mode plasma, where both electron and argon density profiles become flatter. The reduction of the neoclassical inward velocity for argon due to the reduction of density gradient is consistent with the experimental observation. In the RS plasma, the density gradient is not decreased by ECH and argon is not exhausted. These results suggest the importance of density control to suppress heavy impurity accumulation. (author)
Relationship between particle and heat transport in JT-60U plasmas with internal transport barrier
International Nuclear Information System (INIS)
Takenaga, H.; Higashijima, S.; Oyama, N.
2003-01-01
The relationship between particle and heat transport in an internal transport barrier (ITB) has been systematically investigated in reversed shear (RS) and high β p ELMy H-mode plasmas in JT-60U. No helium and carbon accumulation inside the ITB is observed even with ion heat transport reduced to a neoclassical level. On the other hand, the heavy impurity argon is accumulated inside the ITB. The argon density profile estimated from the soft x-ray profile is more peaked, by a factor of 2-4 in the RS plasma and of 1.6 in the high β p mode plasma, than the electron density profile. The helium diffusivity (D He ) and the ion thermal diffusivity (χ i ) are at an anomalous level in the high β p mode plasma, where D He and χ i are higher by a factor of 5-10 than the neoclassical value. In the RS plasma, D He is reduced from the anomalous to the neoclassical level, together with χ i . The carbon and argon density profiles calculated using the transport coefficients reduced to the neoclassical level only in the ITB are more peaked than the measured profiles, even when χ i is reduced to the neoclassical level. Argon exhaust from the inside of the ITB is demonstrated by applying ECH in the high β p mode plasma, where both electron and argon density profiles become flatter. The reduction of the neoclassical inward velocity for argon due to the reduction of density gradient is consistent with the experimental observation. In the RS plasma, the density gradient is not decreased by ECH and argon is not exhausted. These results suggest the importance of density gradient control to suppress heavy impurity accumulation. (author)
Plasma transport simulation modelling for helical confinement systems
International Nuclear Information System (INIS)
Yamazaki, K.; Amano, T.
1992-01-01
New empirical and theoretical transport models for helical confinement systems are developed on the basis of the neoclassical transport theory, including the effect of the radial electric field and of multi-helicity magnetic components as well as the drift wave turbulence transport for electrostatic and electromagnetic modes or the anomalous semi-empirical transport. These electron thermal diffusivities are compared with experimental data from the Compact Helical System which indicate that the central transport coefficient of a plasma with electron cyclotron heating agrees with neoclassical axisymmetric value and the transport outside the half-radius is anomalous. On the other hand, the transport of plasmas with neutral beam injection heating is anomalous in the whole plasma region. This anomaly is not explained by the electrostatic drift wave turbulence models in these discharges with flat density profiles. For a detailed prediction of the plasma parameters in the Large Helical Device (LHD), 3-D equilibrium/1-D transport simulations including empirical or drift wave turbulence models are performed which suggest that the global confinement time of the LHD is determined mainly by the electron anomalous transport in the plasma edge region rather than by the helical ripple transport in the core region. Even if the ripple loss can be eliminated, the increase in global confinement is 10%. However, the rise in the central ion temperature is more than 20%. If the anomalous loss can be reduced to half of the value used in the present scaling, as is the case in the H-mode of tokamak discharges, the neoclassical ripple loss through the ion channel becomes important even in the plasma core. The 5% radial inward shift of the plasma column with respect to the major radius improves the plasma confinement and increases the fusion product by more than 50% by reducing the neoclassical asymmetric ion transport loss and increasing the plasma radius (10%). (author). 32 refs, 7 figs
Zhang, Yong; Green, Christopher T.; Tick, Geoffrey R.
2015-01-01
This study evaluates the role of the Peclet number as affected by molecular diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numerical experiments show that 1) the Peclet number affects both the duration of the power-law segment of tracer breakthrough curves (BTCs) and the transition rate from anomalous to Fickian transport by determining the solute residence time for a given low-permeability layer, 2) mechanical dispersion has a limited contribution to the anomalous characteristics of late-time transport as compared to molecular diffusion due to an almost negligible velocity in floodplain deposits, and 3) the initial source dimensions only enhance the power-law tail of the BTCs at short travel distances. A tempered stable stochastic (TSS) model is then applied to analyze the modeled transport. Applications show that the time-nonlocal parameters in the TSS model relate to the Peclet number, Pe. In particular, the truncation parameter in the TSS model increases nonlinearly with a decrease in Pe due to the decrease of the mean residence time, and the capacity coefficient increases with an increase in molecular diffusion which is probably due to the increase in the number of immobile particles. The above numerical experiments and stochastic analysis therefore reveal that the Peclet number as affected by molecular diffusion controls transient anomalous transport in alluvial aquifer–aquitard complexes.
International Nuclear Information System (INIS)
Groebner, R.J.
1986-04-01
The study of ion transport in neutral beam-heated discharges in tokamaks is necessary to determine if neoclassical theory can reliably be used to predict the performance of future machines. Previous studies of ion tranport have generally been difficult due to the lack of information regarding the ion temperature profile. The standard procedure used to study ion transport has been to model the T/sub i/ profile with the assumption that the ion thermal diffusivity profile chi/sub i/(r) was equal to a multiplier times chi/sub i//sup neo/(r), the ion thermal diffusivity calculated from neoclassical theory. The multiplier was varied until the calculated T/sub i/ profile agreed with the available ion temperature data, usually T/sub i/(0) or the measured neutron rate. Values of the multiplier in the range of 1 to 10 have generally been obtained with few estimates of the uncertainties in these values. Furthermore, there have been few, if any, attempts to calculate chi/sub i/ by modeling the ion temperature profiles in other ways. As a result, the issue as to whether or not the ion transport in tokamaks is in agreement with neoclassical theory has not been definitively answered
Coupled Transport Phenomena in the Opalinus Clay: Implications for Radionuclide Transport
International Nuclear Information System (INIS)
Soler, J.M.
1999-09-01
Coupled phenomena (thermal and chemical osmosis, hyperfiltration, coupled diffusion, thermal diffusion, thermal filtration, Dufour effect) may play an important role in fluid, solute and heat transport in clay-rich formations, such as the Opalinus Clay (OPA), which are being considered as potential hosts for radioactive waste repositories. In this study, the potential effects of coupled phenomena on radionuclide transport in the vicinity of a repository for vitrified high-level radioactive waste (HLW) and spent nuclear fuel (SF) hosted by the Opalinus Clay, at times equal to or greater than the expected lifetime of the waste canisters (about 1000 years), have been addressed. Firstly, estimates of the solute fluxes associated with chemical osmosis, hyperfiltration, thermal diffusion and thermal osmosis have been calculated. Available experimental data concerning coupled transport phenomena in compacted clays, and the hydrogeological and geochemical conditions to which the Opalinus Clay is subject, have been used for these estimates. These estimates suggest that thermal osmosis is the only coupled transport mechanism that could have a strong impact on solute and fluid transport in the vicinity of the repository. Secondly, estimates of the heat fluxes associated with thermal filtration and the Dufour effect in the vicinity of the repository have been calculated. The calculated heat fluxes are absolutely negligible compared to the heat flux caused by thermal conduction. As a further step to obtain additional insight into the effects of coupled phenomena on solute transport, the solute fluxes associated with advection, chemical diffusion, thermal and chemical osmosis, hyperfiltration and thermal diffusion have been incorporated into a simple one-dimensional transport equation. The analytical solution of this equation, with appropriate parameters, shows again that thermal osmosis is the only coupled transport mechanism that could have a strong effect on repository
Coupled Transport Phenomena in the Opalinus Clay: Implications for Radionuclide Transport
Energy Technology Data Exchange (ETDEWEB)
Soler, J.M.
1999-09-01
Coupled phenomena (thermal and chemical osmosis, hyperfiltration, coupled diffusion, thermal diffusion, thermal filtration, Dufour effect) may play an important role in fluid, solute and heat transport in clay-rich formations, such as the Opalinus Clay (OPA), which are being considered as potential hosts for radioactive waste repositories. In this study, the potential effects of coupled phenomena on radionuclide transport in the vicinity of a repository for vitrified high-level radioactive waste (HLW) and spent nuclear fuel (SF) hosted by the Opalinus Clay, at times equal to or greater than the expected lifetime of the waste canisters (about 1000 years), have been addressed. Firstly, estimates of the solute fluxes associated with chemical osmosis, hyperfiltration, thermal diffusion and thermal osmosis have been calculated. Available experimental data concerning coupled transport phenomena in compacted clays, and the hydrogeological and geochemical conditions to which the Opalinus Clay is subject, have been used for these estimates. These estimates suggest that thermal osmosis is the only coupled transport mechanism that could have a strong impact on solute and fluid transport in the vicinity of the repository. Secondly, estimates of the heat fluxes associated with thermal filtration and the Dufour effect in the vicinity of the repository have been calculated. The calculated heat fluxes are absolutely negligible compared to the heat flux caused by thermal conduction. As a further step to obtain additional insight into the effects of coupled phenomena on solute transport, the solute fluxes associated with advection, chemical diffusion, thermal and chemical osmosis, hyperfiltration and thermal diffusion have been incorporated into a simple one-dimensional transport equation. The analytical solution of this equation, with appropriate parameters, shows again that thermal osmosis is the only coupled transport mechanism that could have a strong effect on repository
MODELING AND ANALYSIS OF FISSION PRODUCT TRANSPORT IN THE AGR-3/4 EXPERIMENT
Energy Technology Data Exchange (ETDEWEB)
Humrickhouse, Paul W.; Collin, Blaise P.; Hawkes, Grant L.; Harp, Jason M.; Demkowicz, Paul A.; Petti, David A.
2016-11-01
In this work we describe the ongoing modeling and analysis efforts in support of the AGR-3/4 experiment. AGR-3/4 is intended to provide data to assess fission product retention and transport (e.g., diffusion coefficients) in fuel matrix and graphite materials. We describe a set of pre-test predictions that incorporate the results of detailed thermal and fission product release models into a coupled 1D radial diffusion model of the experiment, using diffusion coefficients reported in the literature for Ag, Cs, and Sr. We make some comparisons of the predicted Cs profiles to preliminary measured data for Cs and find these to be reasonable, in most cases within an order of magnitude. Our ultimate objective is to refine the diffusion coefficients using AGR-3/4 data, so we identify an analytical method for doing so and demonstrate its efficacy via a series of numerical experiments using the model predictions. Finally, we discuss development of a post-irradiation examination plan informed by the modeling effort and simulate some of the heating tests that are tentatively planned.
Energy Technology Data Exchange (ETDEWEB)
Cartier, J
2006-04-15
This thesis focuses on mathematical analysis, numerical resolution and modelling of the transport equations. First of all, we deal with numerical approximation of the solution of the transport equations by using a mixed-hybrid scheme. We derive and study a mixed formulation of the transport equation, then we analyse the related variational problem and present the discretization and the main properties of the scheme. We particularly pay attention to the behavior of the scheme and we show its efficiency in the diffusion limit (when the mean free path is small in comparison with the characteristic length of the physical domain). We present academical benchmarks in order to compare our scheme with other methods in many physical configurations and validate our method on analytical test cases. Unstructured and very distorted meshes are used to validate our scheme. The second part of this thesis deals with two transport problems. The first one is devoted to the study of diffusion due to boundary conditions in a transport problem between two plane plates. The second one consists in modelling and simulating radiative transfer phenomenon in case of the industrial context of inertial confinement fusion. (author)
Up-gradient transport in a probabilistic transport model
DEFF Research Database (Denmark)
Gavnholt, J.; Juul Rasmussen, J.; Garcia, O.E.
2005-01-01
The transport of particles or heat against the driving gradient is studied by employing a probabilistic transport model with a characteristic particle step length that depends on the local concentration or heat gradient. When this gradient is larger than a prescribed critical value, the standard....... These results supplement recent works by van Milligen [Phys. Plasmas 11, 3787 (2004)], which applied Levy distributed step sizes in the case of supercritical gradients to obtain the up-gradient transport. (c) 2005 American Institute of Physics....
Diffusion related isotopic fractionation effects with one-dimensional advective–dispersive transport
Energy Technology Data Exchange (ETDEWEB)
Xu, Bruce S. [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada); Lollar, Barbara Sherwood [Earth Sciences Department, University of Toronto, 22 Russell Street, Toronto, ON M5S 3B1 (Canada); Passeport, Elodie [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada); Chemical Engineering and Applied Chemistry Department, University of Toronto, 200 College Street, Toronto, ON M5S 3E5 (Canada); Sleep, Brent E., E-mail: sleep@ecf.utoronto.ca [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada)
2016-04-15
larger than 10, DRIF effects will likely not be observable for common groundwater contaminants. Importantly, under most field conditions, D{sub mech}/D{sub eff} ≥ 10 is usually satisfied in the longitudinal direction, suggesting that DRIF is not likely to be observable in most groundwater systems in which contaminant transport is predominantly one-dimensional. Given the importance in the MDL it is recommended that MDL should always be explicitly reported in both modeling and field studies. - Highlights: • Diffusion-related isotope fractionation (DRIF) in subsurface contaminant transport • Investigation of effect of ratio of mechanical dispersion to diffusion • No observable DRIF for mechanical dispersion to diffusion ratio above 10 • Ratio of source concentration to detection limit important • Plume lengths over which DRIF is detectable are limited.
Diffusion related isotopic fractionation effects with one-dimensional advective–dispersive transport
International Nuclear Information System (INIS)
Xu, Bruce S.; Lollar, Barbara Sherwood; Passeport, Elodie; Sleep, Brent E.
2016-01-01
effects will likely not be observable for common groundwater contaminants. Importantly, under most field conditions, D_m_e_c_h/D_e_f_f ≥ 10 is usually satisfied in the longitudinal direction, suggesting that DRIF is not likely to be observable in most groundwater systems in which contaminant transport is predominantly one-dimensional. Given the importance in the MDL it is recommended that MDL should always be explicitly reported in both modeling and field studies. - Highlights: • Diffusion-related isotope fractionation (DRIF) in subsurface contaminant transport • Investigation of effect of ratio of mechanical dispersion to diffusion • No observable DRIF for mechanical dispersion to diffusion ratio above 10 • Ratio of source concentration to detection limit important • Plume lengths over which DRIF is detectable are limited.
Ma, Hao; Tian, Zhiting
2018-01-10
Tapered bottlebrush polymers have novel nanoscale polymer architecture. Using nonequilibrium molecular dynamics simulations, we showed that these polymers have the unique ability to generate thermal rectification in a single polymer molecule and offer an exceptional platform for unveiling different heat conduction regimes. In sharp contrast to all other reported asymmetric nanostructures, we observed that the heat current from the wide end to the narrow end (the forward direction) in tapered bottlebrush polymers is smaller than that in the opposite direction (the backward direction). We found that a more disordered to less disordered structural transition within tapered bottlebrush polymers is essential for generating nonlinearity in heat conduction for thermal rectification. Moreover, the thermal rectification ratio increased with device length, reaching as high as ∼70% with a device length of 28.5 nm. This large thermal rectification with strong length dependence uncovered an unprecedented phenomenon-diffusive thermal transport in the forward direction and ballistic thermal transport in the backward direction. This is the first observation of radically different transport mechanisms when heat flow direction changes in the same system. The fundamentally new knowledge gained from this study can guide exciting research into nanoscale organic thermal diodes.
Theory of anomalous transport in toroidal helical plasmas
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.; Fukuyama, A.
1992-03-01
Theoretical model of the anomalous transport in Torsatron/Heliotron plasmas is developed, based on the current-diffusive interchange instability which is destabilized due to the averaged magnetic hill near edge. Analytic formula of transport coefficient is derived. This model explains the high edge transport, the power degradation and energy confinement scaling law and the enhanced heat-pulse thermal conduction. (author)
Multi-phase reactive transport theory
International Nuclear Information System (INIS)
Lichtner, P.C.
1995-07-01
Physicochemical processes in the near-field region of a high-level waste repository may involve a diverse set of phenomena including flow of liquid and gas, gaseous diffusion, and chemical reaction of the host rock with aqueous solutions at elevated temperatures. This report develops some of the formalism for describing simultaneous multicomponent solute and heat transport in a two-phase system for partially saturated porous media. Diffusion of gaseous species is described using the Dusty Gas Model which provides for simultaneous Knudsen and Fickian diffusion in addition to Darcy flow. A new form of the Dusty Gas Model equations is derived for binary diffusion which separates the total diffusive flux into segregative and nonsegregative components. Migration of a wetting front is analyzed using the quasi-stationary state approximation to the Richards' equation. Heat-pipe phenomena are investigated for both gravity- and capillary-driven reflux of liquid water. An expression for the burnout permeability is derived for a gravity-driven heat-pipe. Finally an estimate is given for the change in porosity and permeability due to mineral dissolution which could occur in the region of condensate formation in a heat-pipe
Interaction and diffusion transport of americium in soils
Energy Technology Data Exchange (ETDEWEB)
Ramirez-Guinart, Oriol; Rigol, Anna; Vidal, Miquel [Analytical Chemistry department, Faculty of Chemistry, University of Barcelona, Marti i Franques 1-11, 08028, Barcelona (Spain)
2014-07-01
The final disposal of High Level Radioactive Wastes (HLRW) is based on its long-term storage in underground facilities located in geological stable sites with a multi-barrier system, the so called Deep Geological Repositories (DGR), that will keep HLRW confined for >10.000 years. After this period of time, leachates rich in long-live radioisotopes might escape from DGR and start to transport towards the biosphere. There is still a lack of information concerning the interaction and transport in soils of some radionuclides present in HLRW, especially for radionuclides that present a high sorption, such as americium (Am). Having reliable information about the mobility of radionuclides in soils is crucial in order to develop risk assessment models and to take proper decisions in case of soil contamination. The aim of the present work was, by means of laboratory scale experiments, to study the interaction and, for first time, to evaluate the diffusion transport of {sup 241}Am in soils. The {sup 241}Am interaction in soils was assessed by applying sorption batch assays to 20 soil samples with contrasted edaphic properties which allowed us to quantify the solid-liquid distribution coefficient (K{sub d}) and desorption percentage. K{sub d} (Am) values ranged from 10{sup 3} to 10{sup 5} L kg{sup -1} and desorption percentages were always less than 2% which denoted a high capacity of the soil to incorporate the Am and a low reversibility of the sorption process. The influence of soil properties in {sup 241}Am interaction was studied by means of multiple linear and multivariate regressions. Although a single correlation between K{sub d} (Am) values and a soil property was not found, the main properties affecting {sup 241}Am interaction in soils were soil pH, carbonate and organic matter contents in the soil. Finally, additional batch assays at different controlled pH were done to study Am sorption as a function of the contact solution pH. A variation of the Am sorption
Hydrodynamic theory of convective transport across a dynamically stabilized diffuse boundary layer
International Nuclear Information System (INIS)
Gerhauser, H.
1983-09-01
The diffuse boundary layer between miscible liquids is subject to Rayleigh-Taylor instabilities if the heavy fluid is supported by the light one. The resulting rapid interchange of the liquids can be suppressed by enforcing vertical oscillations on the whole system. This dynamic stabilization is incomplete and produces some peculiar novel transport phenomena such as decay off the density profile into several steps, periodic peeling of density sheets of the boundary layer and the appearance of steady vortex flow. The theory presented in this paper identifies the basic mechanism as formation of convective cells leading to enhanced diffusion, and explains previous experimental results with water and ZnJ 2 -solutions. A nonlinear treatment of the stationary convective flow problem gives the saturation amplitude of the ground mode and provides an upper bound for the maximum convective transport. The hydrodynamic model can be used for visualizing similar transport processes in the plasma of toroidal confinement devices such as sawtooth oscillations in soft disruptions of tokamak discharges and anomalous diffusion by excitation of convective cells. The latter process is investigated here in some detail, leading to the result that the maximum possible transport is of the order of Bohm diffusion. (orig.)
Flow, transport and diffusion in random geometries II: applications
Asinari, Pietro
2015-01-07
Multilevel Monte Carlo (MLMC) is an efficient and flexible solution for the propagation of uncertainties in complex models, where an explicit parametrization of the input randomness is not available or too expensive. We present several applications of our MLMC algorithm for flow, transport and diffusion in random heterogeneous materials. The absolute permeability and effective diffusivity (or formation factor) of micro-scale porous media samples are computed and the uncertainty related to the sampling procedures is studied. The algorithm is then extended to the transport problems and multiphase flows for the estimation of dispersion and relative permeability curves. The impact of water drops on random stuctured surfaces, with microfluidics applications to self-cleaning materials, is also studied and simulated. Finally the estimation of new drag correlation laws for poly-dispersed dilute and dense suspensions is presented.
Flow, transport and diffusion in random geometries II: applications
Asinari, Pietro; Ceglia, Diego; Icardi, Matteo; Prudhomme, Serge; Tempone, Raul
2015-01-01
Multilevel Monte Carlo (MLMC) is an efficient and flexible solution for the propagation of uncertainties in complex models, where an explicit parametrization of the input randomness is not available or too expensive. We present several applications of our MLMC algorithm for flow, transport and diffusion in random heterogeneous materials. The absolute permeability and effective diffusivity (or formation factor) of micro-scale porous media samples are computed and the uncertainty related to the sampling procedures is studied. The algorithm is then extended to the transport problems and multiphase flows for the estimation of dispersion and relative permeability curves. The impact of water drops on random stuctured surfaces, with microfluidics applications to self-cleaning materials, is also studied and simulated. Finally the estimation of new drag correlation laws for poly-dispersed dilute and dense suspensions is presented.
Advanced transport modeling of toroidal plasmas with transport barriers
International Nuclear Information System (INIS)
Fukuyama, A.; Murakami, S.; Honda, M.; Izumi, Y.; Yagi, M.; Nakajima, N.; Nakamura, Y.; Ozeki, T.
2005-01-01
Transport modeling of toroidal plasmas is one of the most important issue to predict time evolution of burning plasmas and to develop control schemes in reactor plasmas. In order to describe the plasma rotation and rapid transition self-consistently, we have developed an advanced scheme of transport modeling based on dynamical transport equation and applied it to the analysis of transport barrier formation. First we propose a new transport model and examine its behavior by the use of conventional diffusive transport equation. This model includes the electrostatic toroidal ITG mode and the electromagnetic ballooning mode and successfully describes the formation of internal transport barriers. Then the dynamical transport equation is introduced to describe the plasma rotation and the radial electric field self-consistently. The formation of edge transport barriers is systematically studied and compared with experimental observations. The possibility of kinetic transport modeling in velocity space is also examined. Finally the modular structure of integrated modeling code for tokamaks and helical systems is discussed. (author)
The Role of Ocean and Atmospheric Heat Transport in the Arctic Amplification
Vargas Martes, R. M.; Kwon, Y. O.; Furey, H. H.
2017-12-01
Observational data and climate model projections have suggested that the Arctic region is warming around twice faster than the rest of the globe, which has been referred as the Arctic Amplification (AA). While the local feedbacks, e.g. sea ice-albedo feedback, are often suggested as the primary driver of AA by previous studies, the role of meridional heat transport by ocean and atmosphere is less clear. This study uses the Community Earth System Model version 1 Large Ensemble simulation (CESM1-LE) to seek deeper understanding of the role meridional oceanic and atmospheric heat transports play in AA. The simulation consists of 40 ensemble members with the same physics and external forcing using a single fully coupled climate model. Each ensemble member spans two time periods; the historical period from 1920 to 2005 using the Coupled Model Intercomparison Project Phase 5 (CMIP5) historical forcing and the future period from 2006 to 2100 using the CMIP5 Representative Concentration Pathways 8.5 (RCP8.5) scenario. Each of the ensemble members are initialized with slightly different air temperatures. As the CESM1-LE uses a single model unlike the CMIP5 multi-model ensemble, the internal variability and the externally forced components can be separated more clearly. The projections are calculated by comparing the period 2081-2100 relative to the time period 2001-2020. The CESM1-LE projects an AA of 2.5-2.8 times faster than the global average, which is within the range of those from the CMIP5 multi-model ensemble. However, the spread of AA from the CESM1-LE, which is attributed to the internal variability, is 2-3 times smaller than that of the CMIP5 ensemble, which may also include the inter-model differences. CESM1LE projects a decrease in the atmospheric heat transport into the Arctic and an increase in the oceanic heat transport. The atmospheric heat transport is further decomposed into moisture transport and dry static energy transport. Also, the oceanic heat
Rock-matrix diffusion in transport of salinity. Implementation in CONNECTFLOW
International Nuclear Information System (INIS)
Hoch, A.R.; Jackson, C.P.
2004-07-01
calculations were carried out for a Base Case without rock-matrix diffusion, but with the porosity taken to be all of the accessible porosity in the rock matrix, and for nine variants with different values of the rock-matrix diffusion parameters. In the calculations, piecewise linear interpolation was used for the residual pressure and the salinity, and piecewise constant interpolation was used for the groundwater density. Nodal quadrature helps to avoid so-called 'mass-matrix' ripples in the salinity resulting from the finite-element discretisation of the time derivative terms in the flow and transport equations. These changes make the numerical equations less non-linear and therefore easier to solve. In the sequential iteration scheme, at each time step: (i) the average density in each element is calculated from a suitable equation; (ii) the residual pressure at the end of the time step is calculated (using the calculated average density) from a discretised version of the steady-state flow equations; (iii) the salinity at the end of the time step is calculated from a discretised version of the salinity transport equation using the calculated average density and calculated flow. There are different variants of this scheme, in which a single cycle of the above calculations is carried out for each time step, or a fixed number of cycles is carried out, or the cycles are repeated until convergence is obtained for the non-linear equations at each time step. It was found that, for the realistic example, repeating the cycles until convergence was obtained required a small time step, leading to prohibitively long calculations. However, if the time-stepping scheme that involved only a single cycle for each time step was used, it was found to be possible to use much larger time steps, similar to those used in calculations for the model without rock-matrix diffusion. This scheme was therefore adopted for the calculations.With these changes, it proved to be possible to carry out
Energy Technology Data Exchange (ETDEWEB)
Xu, Z., E-mail: zhanjie.xu@kit.ed [Forschungszentrum Karlsruhe, P.O. Box 3640, 76021 Karlsruhe (Germany); Travis, J.R. [Ingenieurbuero DuBois-Pitzer-Travis, 63071 Offenbach (Germany); Breitung, W.; Jordan, T. [Forschungszentrum Karlsruhe, P.O. Box 3640, 76021 Karlsruhe (Germany)
2010-12-15
Potentially explosive dust aerosol mobilization in the vacuum vessel is an important safety issue of the ITER facility, especially in scenarios of loss of vacuum accidents. Therefore dust mobilization modeling is ongoing in Research Center Karlsuhe. At first the aerosol particle model in the GASFLOW computer code is introduced briefly. To verify the particle model, a series of particle diffusion problems are simulated in one-, two- and three-dimensions. In each problem a particle source is initially exposed to an advective gas flow. Then a dust cloud is formed in the down stream. To obtain the theoretical solution about the particle concentration in the dust cloud, the governing diffusion partial differential equations with an additional advection term are solved by using Green's function method. Different spatial and temporal characters about the particle sources are also considered, e.g., instantaneous or continuous sources, line, or volume sources and so forth. The GASFLOW simulation results about the particle concentrations and the corresponding Green's function solutions are compared case by case. Very good agreements are found between the theoretical solutions and the GASGLOW simulations, when the drag force between the micron-sized particles and the conveying gas flow meets the Stokes' law about resistance. This situation is corresponding to a very small Reynolds number based on the particle diameter, with a negligible inertia effect of the particles. This verification work shows that the particle model of the GASFLOW code can reproduce numerically particle transport and diffusion in a good way.
International Nuclear Information System (INIS)
Zhang, Dingkang; Rahnema, Farzad; Ougouag, Abderrfi M.
2011-01-01
A response-based local transport method has been developed in 2-D (r, θ) geometry for coupling to any coarse-mesh (nodal) diffusion method/code. Monte Carlo method is first used to generate a (pre-computed) the response function library for each unique coarse mesh in the transport domain (e.g., the outer reflector region of the Pebble Bed Reactor). The scalar flux and net current at the diffusion/transport interface provided by the diffusion method are used as an incoming surface source to the transport domain. A deterministic iterative sweeping method together with the response function library is utilized to compute the local transport solution within all transport coarse meshes. After the partial angular currents crossing the coarse mesh surfaces are converged, albedo coefficients are computed as boundary conditions for the diffusion methods. The iteration on the albedo boundary condition (for the diffusion method via transport) and the incoming angular flux boundary condition (for the transport via diffusion) is continued until convergence is achieved. The method was tested for in a simplified 2-D (r, θ) pebble bed reactor problem consisting of an inner reflector, an annular fuel region and a controlled outer reflector. The comparisons have shown that the results of the response-function-based transport method agree very well with a direct MCNP whole core solution. The agreement in coarse mesh averaged flux was found to be excellent: relative difference of about 0.18% and a maximum difference of about 0.55%. Note that the MCNP uncertainty was less than 0.1%. (author)
Characterization and modeling of thermal diffusion and aggregation in nanofluids.
Energy Technology Data Exchange (ETDEWEB)
Gharagozloo, Patricia E.; Goodson, Kenneth E. (Stanford University, Stanford, CA)
2010-05-01
Fluids with higher thermal conductivities are sought for fluidic cooling systems in applications including microprocessors and high-power lasers. By adding high thermal conductivity nanoscale metal and metal oxide particles to a fluid the thermal conductivity of the fluid is enhanced. While particle aggregates play a central role in recent models for the thermal conductivity of nanofluids, the effect of particle diffusion in a temperature field on the aggregation and transport has yet to be studied in depth. The present work separates the effects of particle aggregation and diffusion using parallel plate experiments, infrared microscopy, light scattering, Monte Carlo simulations, and rate equations for particle and heat transport in a well dispersed nanofluid. Experimental data show non-uniform temporal increases in thermal conductivity above effective medium theory and can be well described through simulation of the combination of particle aggregation and diffusion. The simulation shows large concentration distributions due to thermal diffusion causing variations in aggregation, thermal conductivity and viscosity. Static light scattering shows aggregates form more quickly at higher concentrations and temperatures, which explains the increased enhancement with temperature reported by other research groups. The permanent aggregates in the nanofluid are found to have a fractal dimension of 2.4 and the aggregate formations that grow over time are found to have a fractal dimension of 1.8, which is consistent with diffusion limited aggregation. Calculations show as aggregates grow the viscosity increases at a faster rate than thermal conductivity making the highly aggregated nanofluids unfavorable, especially at the low fractal dimension of 1.8. An optimum nanoparticle diameter for these particular fluid properties is calculated to be 130 nm to optimize the fluid stability by reducing settling, thermal diffusion and aggregation.
Liquid water transport mechanism in the gas diffusion layer
Energy Technology Data Exchange (ETDEWEB)
Zhou, P.; Wu, C.W. [State Key Laboratory of Structure Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty of Vehicle Engineering and Mechanics, Dalian University of Technology, Dalian 116024 (China)
2010-03-01
We developed an equivalent capillary model of a microscale fiber-fence structure to study the microscale evolution and transport of liquid in a porous media and to reveal the basic principles of water transport in gas diffusion layer (GDL). Analytical solutions using the model show that a positive hydraulic pressure is needed to drive the liquid water to penetrate through the porous GDL even consisting of the hydrophilic fibers. Several possible contributions for the water configuration, such as capillary pressure, gravity, vapor condensation, wettability and microstructures of the GDL, are discussed using the lattice Boltzmann method (LBM). It is found that the distribution manners of the fibers and the spatial mixed-wettability in the GDL also play an important role in the transport of liquid water. (author)
Analytical solutions of a fractional diffusion-advection equation for solar cosmic-ray transport
International Nuclear Information System (INIS)
Litvinenko, Yuri E.; Effenberger, Frederic
2014-01-01
Motivated by recent applications of superdiffusive transport models to shock-accelerated particle distributions in the heliosphere, we analytically solve a one-dimensional fractional diffusion-advection equation for the particle density. We derive an exact Fourier transform solution, simplify it in a weak diffusion approximation, and compare the new solution with previously available analytical results and with a semi-numerical solution based on a Fourier series expansion. We apply the results to the problem of describing the transport of energetic particles, accelerated at a traveling heliospheric shock. Our analysis shows that significant errors may result from assuming an infinite initial distance between the shock and the observer. We argue that the shock travel time should be a parameter of a realistic superdiffusive transport model.
Benchmarks with diffusion theory and transport theory
International Nuclear Information System (INIS)
Cunha Menezes Filho, A. da; Souza, A.L. de.
1984-01-01
The multiplication factor and some spectral indices for five critical assemblies (ZPR-6-7, ZPR-3-11, GODIVA, BIG-TEN and FLATTOP) are calculated by Diffusion and Transport Theory, with group constants generated by MC 2 (for diffusion calculations) and by NJOY (for transport calculations). The discrepancies encountered in the ZPR-6-7 spectra, can be tracked to the large differences in the elastic cross section for Iron, calculated by MC 2 and NJOY. (Author) [pt
Energy Technology Data Exchange (ETDEWEB)
Marinoni, A [Politecnico di Milano, dipartimento di Ingegneria Nucleare, Milano (Italy); Mantica, P [Istituto di Fisica del Plasma, Euratom-ENEA-CNR Association, Milan (Italy); Eester, D Van [LPP-ERM/KMS, Association EURATOM-Belgian State, TEC, B-1000 Brussels (Belgium); Imbeaux, F [Association EURATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, 13108 Saint Paul lez Durance (France); Mantsinen, M [Helsinki University of Technology, Association Euratom-Tekes, PO Box 2200 (Finland); Hawkes, N [Euratom-UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon (United Kingdom); Joffrin, E [Association EURATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, 13108 Saint Paul lez Durance (France); Kiptily, V [Euratom-UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon (United Kingdom); Pinches, S D [Max Plank Institut fur Plasmaphysik, Euratom Association, Garching (Germany); Salmi, A [Helsinki University of Technology, Association Euratom-Tekes, PO Box 2200 (Finland); Sharapov, S [Euratom-UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon (United Kingdom); Voitsekhovitch, I [Euratom-UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon (United Kingdom); Vries, P de [FOM Institut voor Plasmafysica, Association Euratom-FOM, Nieuwegein, The (Netherlands); Zastrow, K D [Euratom-UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon (United Kingdom)
2006-10-15
Understanding the physics of internal transport barriers (ITBs) is a crucial issue in developing ITER relevant advanced tokamak scenarios. To gain new information on ITBs, RF power modulation experiments, mainly devoted to the study of electron heat transport through ITBs, have been performed on the JET tokamak. The main physics results have been reported in [1]. The present paper describes in detail the data analysis and numerical modelling work carried out for the interpretation of the experiments. ITBs located in the negative shear region behave as localized insulating layers able to stop the heat wave propagation, thus implying that the ITB is a region of low diffusivity characterized by a loss of stiffness. Various sources of spurious effects affecting the interpretation of the results are analysed and discussed. First principle based models have so far failed to predict the temperature profile in the first place, which prevented their application to modulation results, while empirical transport models have been set up and reproduce the major part of the data.
Reactive transport modelling of a heating and radiation experiment in the Boom clay (Belgium)
International Nuclear Information System (INIS)
Montenegro, L.; Samper, J.; Delgado, J.
2003-01-01
Most countries around the world consider Deep Geological Repositories (DGR) as the most safe option for the final disposal of high level radioactive waste (HLW). DGR is based on adopting a system of multiple barriers between the HLW and the biosphere. Underground laboratories provide information about the behaviour of these barriers at real conditions. Here we present a reactive transport model for the CERBERUS experiment performed at the HADES underground laboratory at Mol (Belgium) in order to characterize the thermal (T), hydrodynamic (H) and geochemical (G) behaviour of the Boon clay. This experiment is unique because it addresses the combined effect of heat and radiation produced by the storage of HLW in a DGR. Reactive transport models which are solved with CORE, are used to perform quantitative predictions of Boom clay thermo-hydro-geochemical (THG) behaviour. Numerical results indicate that heat and radiation cause a slight oxidation near of the radioactive source, pyrite dissolution, a pH decrease and slight changes in the pore water chemical composition of the Boom clay. (Author) 33 refs
International Nuclear Information System (INIS)
Despois, J.
1977-01-01
Recalling the close connections existing between heat transport and storage, some general considerations on the problem of heat distribution and transport are presented 'in order to set out the problem' of storage in concrete form. This problem is considered in its overall plane, then studied under the angle of the different technical choices it involves. The two alternatives currently in consideration are described i.e.: storage in a mined cavity and underground storage as captive sheet [fr
Hermans, Thomas; Daoudi, Moubarak; Vandenbohede, Alexander; Robert, Tanguy; Caterina, David; Nguyen, Frédéric
2012-01-01
Groundwater resources are increasingly used around the world as geothermal systems. Understanding physical processes and quantification of parameters determining heat transport in porous media is therefore important. Geophysical methods may be useful in order to yield additional information with greater coverage than conventional wells. We report a heat transport study during a shallow heat injection and storage field test. Heated water (about 50°C) was injected for 6 days at the rate of 80 l...
Thermal model of spent fuel transport cask
International Nuclear Information System (INIS)
Ahmed, E.E.M.; Rahman, F.A.; Sultan, G.F.; Khalil, E.E.
1996-01-01
The investigation provides a theoretical model to represent the thermal behaviour of the spent fuel elements when transported in a dry shipping cask under normal transport conditions. The heat transfer process in the spent fuel elements and within the cask are modeled which include the radiant heat transfer within the cask and the heat transfer by thermal conduction within the spent fuel element. The model considers the net radiant method for radiant heat transfer process from the inner most heated element to the surrounding spent elements. The heat conduction through fuel interior, fuel-clad interface and on clad surface are also presented. (author) 6 figs., 9 refs
Interface methods for hybrid Monte Carlo-diffusion radiation-transport simulations
International Nuclear Information System (INIS)
Densmore, Jeffery D.
2006-01-01
Discrete diffusion Monte Carlo (DDMC) is a technique for increasing the efficiency of Monte Carlo simulations in diffusive media. An important aspect of DDMC is the treatment of interfaces between diffusive regions, where DDMC is used, and transport regions, where standard Monte Carlo is employed. Three previously developed methods exist for treating transport-diffusion interfaces: the Marshak interface method, based on the Marshak boundary condition, the asymptotic interface method, based on the asymptotic diffusion-limit boundary condition, and the Nth-collided source technique, a scheme that allows Monte Carlo particles to undergo several collisions in a diffusive region before DDMC is used. Numerical calculations have shown that each of these interface methods gives reasonable results as part of larger radiation-transport simulations. In this paper, we use both analytic and numerical examples to compare the ability of these three interface techniques to treat simpler, transport-diffusion interface problems outside of a more complex radiation-transport calculation. We find that the asymptotic interface method is accurate regardless of the angular distribution of Monte Carlo particles incident on the interface surface. In contrast, the Marshak boundary condition only produces correct solutions if the incident particles are isotropic. We also show that the Nth-collided source technique has the capacity to yield accurate results if spatial cells are optically small and Monte Carlo particles are allowed to undergo many collisions within a diffusive region before DDMC is employed. These requirements make the Nth-collided source technique impractical for realistic radiation-transport calculations
Energy Technology Data Exchange (ETDEWEB)
Cartier, J
2006-04-15
This thesis focuses on mathematical analysis, numerical resolution and modelling of the transport equations. First of all, we deal with numerical approximation of the solution of the transport equations by using a mixed-hybrid scheme. We derive and study a mixed formulation of the transport equation, then we analyse the related variational problem and present the discretization and the main properties of the scheme. We particularly pay attention to the behavior of the scheme and we show its efficiency in the diffusion limit (when the mean free path is small in comparison with the characteristic length of the physical domain). We present academical benchmarks in order to compare our scheme with other methods in many physical configurations and validate our method on analytical test cases. Unstructured and very distorted meshes are used to validate our scheme. The second part of this thesis deals with two transport problems. The first one is devoted to the study of diffusion due to boundary conditions in a transport problem between two plane plates. The second one consists in modelling and simulating radiative transfer phenomenon in case of the industrial context of inertial confinement fusion. (author)
Collective diffusion and quantum chaos in holography
Wu, Shao-Feng; Wang, Bin; Ge, Xian-Hui; Tian, Yu
2018-05-01
We define a particular combination of charge and heat currents that is decoupled with the heat current. This "heat-decoupled" (HD) current can be transported by diffusion at long distances, when some thermoelectric conductivities and susceptibilities satisfy a simple condition. Using the diffusion condition together with the Kelvin formula, we show that the HD diffusivity can be same as the charge diffusivity and also the heat diffusivity. We illustrate that such mechanism is implemented in a strongly coupled field theory, which is dual to a Lifshitz gravity with the dynamical critical index z =2 . In particular, it is exhibited that both charge and heat diffusivities build the relationship to the quantum chaos. Moreover, we study the HD diffusivity without imposing the diffusion condition. In some homogeneous holographic lattices, it is found that the diffusivity/chaos relation holds independently of any parameters, including the strength of momentum relaxation, chemical potential, or temperature. We also show a counter example of the relation and discuss its limited universality.
Startup analysis for a high temperature gas loaded heat pipe
Sockol, P. M.
1973-01-01
A model for the rapid startup of a high-temperature gas-loaded heat pipe is presented. A two-dimensional diffusion analysis is used to determine the rate of energy transport by the vapor between the hot and cold zones of the pipe. The vapor transport rate is then incorporated in a simple thermal model of the startup of a radiation-cooled heat pipe. Numerical results for an argon-lithium system show that radial diffusion to the cold wall can produce large vapor flow rates during a rapid startup. The results also show that startup is not initiated until the vapor pressure p sub v in the hot zone reaches a precise value proportional to the initial gas pressure p sub i. Through proper choice of p sub i, startup can be delayed until p sub v is large enough to support a heat-transfer rate sufficient to overcome a thermal load on the heat pipe.
Transport phenomena in sharply contrasting media with a diffusion barrier
International Nuclear Information System (INIS)
Dvoretskaya, O A; Kondratenko, P S
2011-01-01
Using the advection–diffusion equation, we analytically study contaminant transport in a sharply contrasting medium with a diffusion barrier due to localization of a contaminant source in a low-permeability medium. Anomalous diffusion behavior and a crossover between different transport regimes are observed. The diffusion barrier results in exponential attenuation of the source power, retardation of the contaminant plume growth and modification of the concentration distribution at large distances. (paper)
Energy Technology Data Exchange (ETDEWEB)
Daurelle, J V; Cadene, V; Occelli, R [Universite de Provence, 13 - Marseille (France)
1997-12-31
In the numerical modeling of thermal industrial problems, radiant heat transfers remain difficult to take into account and require important computer memory and long computing time. These difficulties are enhanced when radiant heat transfers are coupled with finite-elements diffusive heat transfers because finite-elements architecture is complex and requires a lot of memory. In the case of radiant heat transfers along mobile boundaries, the methods must be optimized. The model described in this paper concerns the radiant heat transfers between diffuse grey surfaces. These transfers are coupled with conduction transfers in the limits of the diffusive opaque domain. 2-D and 3-D geometries are analyzed and two configurations of mobile boundaries are considered. In the first configuration, the boundary follows the deformation of the mesh, while in the second, the boundary moves along the fixed mesh. Matter displacement is taken into account in the term of transport of the energy equation, and an appropriate variation of the thermophysical properties of the transition elements between the opaque and transparent media is used. After a description of the introduction of radiative limit conditions in a finite-elements thermal model, the original methods used to optimize calculation time are explained. Two examples of application illustrate the approach used. The first concerns the modeling of radiant heat transfers between fuel rods during a reactor cooling accident, and the second concerns the study of heat transfers inside the air-gap of an electric motor. The method of identification of the mobile surface on the fixed mesh is described. (J.S.) 12 refs.
Energy Technology Data Exchange (ETDEWEB)
Daurelle, J.V.; Cadene, V.; Occelli, R. [Universite de Provence, 13 - Marseille (France)
1996-12-31
In the numerical modeling of thermal industrial problems, radiant heat transfers remain difficult to take into account and require important computer memory and long computing time. These difficulties are enhanced when radiant heat transfers are coupled with finite-elements diffusive heat transfers because finite-elements architecture is complex and requires a lot of memory. In the case of radiant heat transfers along mobile boundaries, the methods must be optimized. The model described in this paper concerns the radiant heat transfers between diffuse grey surfaces. These transfers are coupled with conduction transfers in the limits of the diffusive opaque domain. 2-D and 3-D geometries are analyzed and two configurations of mobile boundaries are considered. In the first configuration, the boundary follows the deformation of the mesh, while in the second, the boundary moves along the fixed mesh. Matter displacement is taken into account in the term of transport of the energy equation, and an appropriate variation of the thermophysical properties of the transition elements between the opaque and transparent media is used. After a description of the introduction of radiative limit conditions in a finite-elements thermal model, the original methods used to optimize calculation time are explained. Two examples of application illustrate the approach used. The first concerns the modeling of radiant heat transfers between fuel rods during a reactor cooling accident, and the second concerns the study of heat transfers inside the air-gap of an electric motor. The method of identification of the mobile surface on the fixed mesh is described. (J.S.) 12 refs.
Integrated heat transport simulation of high ion temperature plasma of LHD
International Nuclear Information System (INIS)
Murakami, S.; Yamaguchi, H.; Sakai, A.
2014-10-01
A first dynamical simulation of high ion temperature plasma with carbon pellet injection of LHD is performed by the integrated simulation GNET-TD + TASK3D. NBI heating deposition of time evolving plasma is evaluated by the 5D drift kinetic equation solver, GNET-TD and the heat transport of multi-ion species plasma (e, H, He, C) is studied by the integrated transport simulation code, TASK3D. Achievement of high ion temperature plasma is attributed to the 1) increase of heating power per ion due to the temporal increase of effective charge, 2) reduction of effective neoclassical transport with impurities, 3) reduction of turbulence transport. The reduction of turbulence transport is most significant contribution to achieve the high ion temperature and the reduction of the turbulent transport from the L-mode plasma (normal hydrogen plasma) is evaluated to be a factor about five by using integrated heat transport simulation code. Applying the Z effective dependent turbulent reduction model we obtain a similar time behavior of ion temperature after the C pellet injection with the experimental results. (author)
International Nuclear Information System (INIS)
Mizia, R.E.; Clark, D.E.; Glazoff, M.V.; Lister, Tedd E.; Trowbridge, T.L.
2011-01-01
A research effort was made to evaluate the usefulness of modern thermodynamic and diffusion computational tools, Thermo-Calc(copyright) and Dictra(copyright), in optimizing the parameters for diffusion welding of Alloy 800H. This would achieve a substantial reduction in the overall number of experiments required to achieve optimal welding and post-weld heat treatment conditions. This problem is important because diffusion welded components of Alloy 800H are being evaluated for use in assembling compact, micro-channel heat exchangers that are being proposed in the design of a high temperature gas-cooled reactor by the US Department of Energy. The modeling was done in close contact with experimental work. The latter included using the Gleeble 3500 System(reg sign) for welding simulation, mechanical property measurement, and light optical and Scanning Electron Microscopy. The modeling efforts suggested a temperature of 1150 C for 1 hour with an applied pressure of 5 MPa using a 15 μm Ni foil as a joint filler to reduce chromium oxidation on the welded surfaces. Good agreement between modeled and experimentally determined concentration gradients was achieved, and model refinements to account for the complexity of actual alloy materials are suggested.
Adoption of renewable heating systems: An empirical test of the diffusion of innovation theory
International Nuclear Information System (INIS)
Franceschinis, Cristiano; Thiene, Mara; Scarpa, Riccardo; Rose, John; Moretto, Michele; Cavalli, Raffaele
2017-01-01
The implementation of heating technologies based on renewable resources is an important part of Italy's energy policy. Yet, despite efforts to promote the uptake of such technologies, their diffusion is still limited while heating systems based on fossil fuels are still predominant. Theory suggests that beliefs and attitudes of individual consumers play a crucial role in the diffusion of innovative products. However, empirical studies corroborating such observations are still thin on the ground. We use a Choice Experiment and a Latent Class-Random Parameter model to analyze preferences of households in the Veneto region (North-East Italy) for key features of ambient heating systems. We evaluate the coherence of the underlying preference structure using as criteria psychological constructs from the Theory of Diffusion of Innovation by Rogers. Our results broadly support this theory by providing evidence of segmentation of the population consistent with the individuals' propensity to adopt innovations. We found that preferences for heating systems and respondents' willingness to pay for their key features vary across segments. These results enabled us to generate maps that show how willingness to pay estimates vary across the region and can guide local policy design aimed at stimulating adoption of sustainable solutions. - Highlights: • We relate preferences for wood pellet heating systems to Diffusion of Innovation theory. • We found a segmentation of the population according to individual innovativeness. • Preferences for wood pellet heating systems vary across population segments. • Public intervention seems necessary to foster adoption among late adopters.
Asymmetric diffusion model for oblique-incidence reflectometry
Institute of Scientific and Technical Information of China (English)
Yaqin Chen; Liji Cao; Liqun Sun
2011-01-01
A diffusion theory model induced by a line source distribution is presented for oblique-incidence reflectom-etry. By fitting to this asymmetric diffusion model, the absorption and reduced scattering coefficients μa and μ's of the turbid medium can both be determined with accuracy of 10% from the absolute profile of the diffuse reflectance in the incident plane at the negative position -1.5 transport mean free path (mfp') away from the incident point; particularly, μ's can be estimated from the data at positive positions within 0-1.0 mfp' with 10% accuracy. The method is verified by Monte Carlo simulations and experimentally tested on a phantom.%A diffusion theory model induced by a line source distribution is presented for oblique-incidence reflectometry.By fitting to this asymmetric diffusion model,the absorption and reduced scattering coefficients μa and μ's of the turbid medium can both be determined with accuracy of 10％ from the absolute profile of the diffuse reflectance in the incident plane at the negative position -1.5 transport mean free path (mfp')away from the incident point;particularly,μ's can be estimated from the data at positive positions within 0-1.0 mfp' with 10％ accuracy.The method is verified by Monte Carlo simulations and experimentally tested on a phantom.Knowledge about the optical properties,including the absorption coefficient (μa) and the reduced scattering coefficient (μ's =μs(1-g)),where μs is the scattering coefficient and g is the anisotropy factor of scattering,of biological tissues plays an important role for optical therapeutic and diagnostic techniques in medicine.
Characterization of supersonic radiation diffusion waves
International Nuclear Information System (INIS)
Moore, Alastair S.; Guymer, Thomas M.; Morton, John; Williams, Benjamin; Kline, John L.; Bazin, Nicholas; Bentley, Christopher; Allan, Shelly; Brent, Katie; Comley, Andrew J.; Flippo, Kirk; Cowan, Joseph; Taccetti, J. Martin; Mussack-Tamashiro, Katie; Schmidt, Derek W.; Hamilton, Christopher E.; Obrey, Kimberly; Lanier, Nicholas E.; Workman, Jonathan B.; Stevenson, R. Mark
2015-01-01
Supersonic and diffusive radiation flow is an important test problem for the radiative transfer models used in radiation-hydrodynamics computer codes owing to solutions being accessible via analytic and numeric methods. We present experimental results with which we compare these solutions by studying supersonic and diffusive flow in the laboratory. We present results of higher-accuracy experiments than previously possible studying radiation flow through up to 7 high-temperature mean free paths of low-density, chlorine-doped polystyrene foam and silicon dioxide aerogel contained by an Au tube. Measurements of the heat front position and absolute measurements of the x-ray emission arrival at the end of the tube are used to test numerical and analytical models. We find excellent absolute agreement with simulations provided that the opacity and the equation of state are adjusted within expected uncertainties; analytical models provide a good phenomenological match to measurements but are not in quantitative agreement due to their limited scope. - Highlights: • The supersonic, diffusion of x-rays through sub-solid density materials is studied. • The data are more diffusive and of higher velocity than any prior work. • Scaled 1D analytic diffusion models reproduce the heat front evolution. • Refined radiation transport approximations are tested in numerical simulations. • Simulations match the data if material properties are adjusted within uncertainties
Directory of Open Access Journals (Sweden)
María I. Vázquez
2015-12-01
Full Text Available Synthesis of a nanoporous alumina membrane (NPAM by the two-step anodization method and its morphological and chemical surface characterization by analyzing Scanning Electron Microscopy (SEM micrographs and X-Ray Photoelectron Spectroscopy (XPS spectra is reported. Influence of electrical and diffusive effects on the NaCl transport across the membrane nanopores is determined from salt diffusion measurements performed with a wide range of NaCl concentrations, which allows the estimation of characteristic electrochemical membrane parameters such as the NaCl diffusion coefficient and the concentration of fixed charges in the membrane, by using an appropriated model and the membrane geometrical parameters (porosity and pore length. These results indicate a reduction of ~70% in the value of the NaCl diffusion coefficient through the membrane pores with respect to solution. The transport number of ions in the membrane pores (Na+ and Cl−, respectively were determined from concentration potential measurements, and the effect of concentration-polarization at the membrane surfaces was also considered by comparing concentration potential values obtained with stirred solutions (550 rpm and without stirring. From both kinds of results, a value higher than 0.05 M NaCl for the feed solution seems to be necessary to neglect the contribution of electrical interactions in the diffusive transport.
Diffusion theory model for optimization calculations of cold neutron sources
International Nuclear Information System (INIS)
Azmy, Y.Y.
1987-01-01
Cold neutron sources are becoming increasingly important and common experimental facilities made available at many research reactors around the world due to the high utility of cold neutrons in scattering experiments. The authors describe a simple two-group diffusion model of an infinite slab LD 2 cold source. The simplicity of the model permits to obtain an analytical solution from which one can deduce the reason for the optimum thickness based solely on diffusion-type phenomena. Also, a second more sophisticated model is described and the results compared to a deterministic transport calculation. The good (particularly qualitative) agreement between the results suggests that diffusion theory methods can be used in parametric and optimization studies to avoid the generally more expensive transport calculations
Wu, M; Li, J; Ludwig, A; Kharicha, A
2014-09-01
Part 1 of this two-part investigation presented a multiphase solidification model incorporating the finite diffusion kinetics and ternary phase diagram with the macroscopic transport phenomena (Wu et al., 2013). In Part 2, the importance of proper treatment of the finite diffusion kinetics in the calculation of macrosegregation is addressed. Calculations for a two-dimensional (2D) square casting (50 × 50 mm 2 ) of Fe-0.45 wt.%C-1.06 wt.%Mn considering thermo-solutal convection and crystal sedimentation are performed. The modeling result indicates that the infinite liquid mixing kinetics as assumed by classical models (e.g., the Gulliver-Scheil or lever rule), which cannot properly consider the solute enrichment of the interdendritic or inter-granular melt at the early stage of solidification, might lead to an erroneous estimation of the macrosegregation. To confirm this statement, further theoretical and experimental evaluations are desired. The pattern and intensity of the flow and crystal sedimentation are dependent on the crystal morphologies (columnar or equiaxed); hence, the potential error of the calculated macrosegregation caused by the assumed growth kinetics depends on the crystal morphology. Finally, an illustrative simulation of an engineering 2.45-ton steel ingot is performed, and the results are compared with experimental results. This example demonstrates the model applicability for engineering castings regarding both the calculation efficiency and functionality.
VS2DRTI: Simulating Heat and Reactive Solute Transport in Variably Saturated Porous Media.
Healy, Richard W; Haile, Sosina S; Parkhurst, David L; Charlton, Scott R
2018-01-29
Variably saturated groundwater flow, heat transport, and solute transport are important processes in environmental phenomena, such as the natural evolution of water chemistry of aquifers and streams, the storage of radioactive waste in a geologic repository, the contamination of water resources from acid-rock drainage, and the geologic sequestration of carbon dioxide. Up to now, our ability to simulate these processes simultaneously with fully coupled reactive transport models has been limited to complex and often difficult-to-use models. To address the need for a simple and easy-to-use model, the VS2DRTI software package has been developed for simulating water flow, heat transport, and reactive solute transport through variably saturated porous media. The underlying numerical model, VS2DRT, was created by coupling the flow and transport capabilities of the VS2DT and VS2DH models with the equilibrium and kinetic reaction capabilities of PhreeqcRM. Flow capabilities include two-dimensional, constant-density, variably saturated flow; transport capabilities include both heat and multicomponent solute transport; and the reaction capabilities are a complete implementation of geochemical reactions of PHREEQC. The graphical user interface includes a preprocessor for building simulations and a postprocessor for visual display of simulation results. To demonstrate the simulation of multiple processes, the model is applied to a hypothetical example of injection of heated waste water to an aquifer with temperature-dependent cation exchange. VS2DRTI is freely available public domain software. © 2018, National Ground Water Association.
Non-local model analysis of heat pulse propagation
International Nuclear Information System (INIS)
Iwasaki, Takuya; Itoh, Sanae-I.; Yagi, Masatoshi
1998-01-01
A new theoretical model equation which includes the non-local effect in the heat flux is proposed to study the transient transport phenomena. A non-local heat flux, which is expressed in terms of the integral equation, is superimposed on the conventional form of the heat flux. This model is applied to describe the experimental results from the power switching [Stroth U, et al 1996 Plasma Phys. Control. Fusion 38 1087] and the power modulation experiments [Giannone L, et al 1992 Nucl. Fusion 32 1985] in the W7-AS stellarator. A small fraction of non-local component in the heat flux is found to be very effective in modifying the response against an external modulation. The transient feature of the transport property, which are observed in the response of heat pulse propagation, are qualitatively reproduced by the transport simulations based on this model. A possibility is discussed to determine the correlation length of the non-local effect experimentally by use of the results of transport simulations. (author)
Energy Technology Data Exchange (ETDEWEB)
Bencs, László, E-mail: bencs.laszlo@wigner.mta.hu [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Laczai, Nikoletta [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Ajtony, Zsolt [Institute of Food Science, University of West Hungary, H-9200 Mosonmagyaróvár, Lucsony utca 15–17 (Hungary)
2015-07-01
A combination of former convective–diffusive vapor-transport models is described to extend the calculation scheme for sensitivity (characteristic mass — m{sub 0}) in graphite furnace atomic absorption spectrometry (GFAAS). This approach encompasses the influence of forced convection of the internal furnace gas (mini-flow) combined with concentration diffusion of the analyte atoms on the residence time in a spatially isothermal furnace, i.e., the standard design of the transversely heated graphite atomizer (THGA). A couple of relationships for the diffusional and convectional residence times were studied and compared, including in factors accounting for the effects of the sample/platform dimension and the dosing hole. These model approaches were subsequently applied for the particular cases of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn analytes. For the verification of the accuracy of the calculations, the experimental m{sub 0} values were determined with the application of a standard THGA furnace, operating either under stopped, or mini-flow (50 cm{sup 3} min{sup −1}) of the internal sheath gas during atomization. The theoretical and experimental ratios of m{sub 0}(mini-flow)-to-m{sub 0}(stop-flow) were closely similar for each study analyte. Likewise, the calculated m{sub 0} data gave a fairly good agreement with the corresponding experimental m{sub 0} values for stopped and mini-flow conditions, i.e., it ranged between 0.62 and 1.8 with an average of 1.05 ± 0.27. This indicates the usability of the current model calculations for checking the operation of a given GFAAS instrument and the applied methodology. - Highlights: • A calculation scheme for convective–diffusive vapor loss in GFAAS is described. • Residence time (τ) formulas were compared for sensitivity (m{sub 0}) in a THGA furnace. • Effects of the sample/platform dimension and dosing hole on τ were assessed. • Theoretical m{sub 0} of 18 analytes were
Generalized diffusion theory for calculating the neutron transport scalar flux
International Nuclear Information System (INIS)
Alcouffe, R.E.
1975-01-01
A generalization of the neutron diffusion equation is introduced, the solution of which is an accurate approximation to the transport scalar flux. In this generalization the auxiliary transport calculations of the system of interest are utilized to compute an accurate, pointwise diffusion coefficient. A procedure is specified to generate and improve this auxiliary information in a systematic way, leading to improvement in the calculated diffusion scalar flux. This improvement is shown to be contingent upon satisfying the condition of positive calculated-diffusion coefficients, and an algorithm that ensures this positivity is presented. The generalized diffusion theory is also shown to be compatible with conventional diffusion theory in the sense that the same methods and codes can be used to calculate a solution for both. The accuracy of the method compared to reference S/sub N/ transport calculations is demonstrated for a wide variety of examples. (U.S.)
Diffusive limits for linear transport equations
International Nuclear Information System (INIS)
Pomraning, G.C.
1992-01-01
The authors show that the Hibert and Chapman-Enskog asymptotic treatments that reduce the nonlinear Boltzmann equation to the Euler and Navier-Stokes fluid equations have analogs in linear transport theory. In this linear setting, these fluid limits are described by diffusion equations, involving familiar and less familiar diffusion coefficients. Because of the linearity extant, one can carry out explicitly the initial and boundary layer analyses required to obtain asymptotically consistent initial and boundary conditions for the diffusion equations. In particular, the effects of boundary curvature and boundary condition variation along the surface can be included in the boundary layer analysis. A brief review of heuristic (nonasymptotic) diffusion description derivations is also included in our discussion
Diffuse-interface model for rapid phase transformations in nonequilibrium systems.
Galenko, Peter; Jou, David
2005-04-01
A thermodynamic approach to rapid phase transformations within a diffuse interface in a binary system is developed. Assuming an extended set of independent thermodynamic variables formed by the union of the classic set of slow variables and the space of fast variables, we introduce finiteness of the heat and solute diffusive propagation at the finite speed of the interface advancing. To describe transformations within the diffuse interface, we use the phase-field model which allows us to follow steep but smooth changes of phase within the width of the diffuse interface. Governing equations of the phase-field model are derived for the hyperbolic model, a model with memory, and a model of nonlinear evolution of transformation within the diffuse interface. The consistency of the model is proved by the verification of the validity of the condition of positive entropy production and by outcomes of the fluctuation-dissipation theorem. A comparison with existing sharp-interface and diffuse-interface versions of the model is given.
Modelling of water and chloride transport in concrete during yearly wetting/drying cycles
Van Der Zanden, A.J.J.; Taher, A.; Arends, T.
2015-01-01
The simultaneous transport of water and chloride in concrete has been modelled. The water transport is described with a concentration dependent diffusion coefficient. The chloride transport is modelled with a convective part, caused by the water transport, and a diffusive part, caused by the
International Nuclear Information System (INIS)
Seddeek, M.A.; Abdelmeguid, M.S.
2006-01-01
The effect of radiation and thermal diffusivity on heat transfer over a stretching surface with variable heat flux has been studied. The thermal diffusivity is assumed to vary as a linear function of temperature. The governing partial differential equations have been transformed to ordinary differential equations. The exact analytical solution for the velocity and the numerical solution for the temperature field are given. Numerical solutions are obtained for different values of variable thermal diffusivity, radiation, temperature parameter and Prandtl number
International Nuclear Information System (INIS)
Maya Sopha, Bertha; Kloeckner, Christian A.; Hertwich, Edgar G.
2011-01-01
Change in home heating to more efficient and renewable systems is important for a sound climate policy. The present paper aims to identify potential interventions for the uptake of wood-pellet heating in Norway using an agent-based model (ABM). The theoretically based, empirically founded, agent-based simulation demonstrates that financial support, i.e., a stable wood-pellet price, and technical development, i.e., functional reliability improvement, have to be established all at the same time for a successful wood-pellet market to start. Furthermore, a soft intervention through persuading households to use environmentally beneficial heating system is not a promising driver for wood-pellet diffusion. Limitations and suggestions for future work are also discussed. - Research highlights: → The theoretically based, empirically founded, agent-based simulation is applied to investigate potential policy options toward diffusion of wood-pellet heating in Norway. → Relative advantages are necessary for wood-pellet heating to be adopted, consistent with Diffusion of Innovation theory (). → Simultaneous development is also required for further uptake of wood-pellet heating, supporting the existing empirical hypothesis by . → Persuading households to use environmentally friendly heating system is not a promising driver, in line with empirical finding of , who investigated psychological factors underlying the adoption of wood-pellet heating.
Energy Technology Data Exchange (ETDEWEB)
Maya Sopha, Bertha, E-mail: bertha.sopha@ntnu.n [Industrial Ecology Programme and Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway); Kloeckner, Christian A. [Department of Psychology, Section for Risk Psychology, Environment and Safety (RIPENSA), Norwegian University of Science and Technology, NO-7491 Trondheim (Norway); Hertwich, Edgar G. [Industrial Ecology Programme and Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway)
2011-05-15
Change in home heating to more efficient and renewable systems is important for a sound climate policy. The present paper aims to identify potential interventions for the uptake of wood-pellet heating in Norway using an agent-based model (ABM). The theoretically based, empirically founded, agent-based simulation demonstrates that financial support, i.e., a stable wood-pellet price, and technical development, i.e., functional reliability improvement, have to be established all at the same time for a successful wood-pellet market to start. Furthermore, a soft intervention through persuading households to use environmentally beneficial heating system is not a promising driver for wood-pellet diffusion. Limitations and suggestions for future work are also discussed. - Research highlights: {yields} The theoretically based, empirically founded, agent-based simulation is applied to investigate potential policy options toward diffusion of wood-pellet heating in Norway. {yields} Relative advantages are necessary for wood-pellet heating to be adopted, consistent with Diffusion of Innovation theory (). {yields} Simultaneous development is also required for further uptake of wood-pellet heating, supporting the existing empirical hypothesis by . {yields} Persuading households to use environmentally friendly heating system is not a promising driver, in line with empirical finding of , who investigated psychological factors underlying the adoption of wood-pellet heating.
MODEL OF THE TOKAMAK EDGE DENSITY PEDESTAL INCLUDING DIFFUSIVE NEUTRALS
International Nuclear Information System (INIS)
BURRELL, K.H.
2003-01-01
OAK-B135 Several previous analytic models of the tokamak edge density pedestal have been based on diffusive transport of plasma plus free-streaming of neutrals. This latter neutral model includes only the effect of ionization and neglects charge exchange. The present work models the edge density pedestal using diffusive transport for both the plasma and the neutrals. In contrast to the free-streaming model, a diffusion model for the neutrals includes the effect of both charge exchange and ionization and is valid when charge exchange is the dominant interaction. Surprisingly, the functional forms for the electron and neutral density profiles from the present calculation are identical to the results of the previous analytic models. There are some differences in the detailed definition of various parameters in the solution. For experimentally relevant cases where ionization and charge exchange rate are comparable, both models predict approximately the same width for the edge density pedestal
Theoretical modeling of transport barriers in helical plasmas
International Nuclear Information System (INIS)
Toda, S.; Itoh, K.; Ohyabu, N.
2008-10-01
A unified transport modelling to explain electron Internal Transport Barriers (e-ITB) in helical plasmas and Internal Diffusion Barriers (IDB) observed in Large Helical Device (LHD) is proposed. The e-ITB can be predicted with the effect of zonal flows to obtain the e-ITB in the low collisional regime when the radial variation of the particle anomalous diffusivity is included. Transport analysis in this article can newly show that the particle fuelling induces the IDB formation when this unified transport modelling is used in the high collisional regime. The density limit for the IDB in helical plasmas is also examined including the effect of the radiation loss. (author)
Advective-diffusive transport of D2O in unsaturated media under evaporation condition
International Nuclear Information System (INIS)
Koarashi, Jun; Atarashi-Andoh, Mariko; Amano, Hikaru; Yamazawa, Hiromi; Iida, Takao
2003-01-01
Advective-diffusive transport of HTO in unsaturated media was investigated empirically using deuterated water (D 2 O) and columns filled with glass beads. The tortuosity factor was evaluated by numerical model calculations corresponding to first experiment for diffusion under no-evaporation condition. Temporal variations in depth profiles of D 2 O concentrations in the columns were observed by second experiment, which considers the transferring and spreading of D 2 O by pore-water flow caused by evaporation. Measurements and model calculations indicated that diffusion was about two times more efficient than dispersion for D 2 O spreading process under this evaporation condition. (author)
Water transport in gas diffusion media for PEM fuel cells. Experimental and numerical investigation
Energy Technology Data Exchange (ETDEWEB)
Roth, Joerg
2010-08-20
The water flux in partially saturated hydrophobic carbon fibre paper for polymer electrolyte membrane fuel cell applications is investigated and compared with the frequently used constitutive two-phase flow model based on Darcy's law. Further, the first steps towards a math-based material design for gas diffusion media are explored in this thesis. Two self-developed ex-situ experiments to investigate the liquid water transport are introduced. The first is a newly developed buoyancy-based measurement of the pressuresaturation relationship on thin porous material with an accuracy of 0.5 kPa for the pressure and {+-} 5% for the saturation. The second experiment measures the pressure drop in dependence of flow rates down to magnitudes of {mu}L/s across the partially saturated thin porous material. This flow rate is relevant for the fuel cell application. The liquid water transport through Toray 060 carbon fibre paper, impregnated with 7% and 10% PTFE is investigated at wet and dry boundary conditions. The experiments are also accompanied by analytical and numerical free surface modelling with the consideration of the material morphology and liquid-solid interaction. The imbibing and draining cases of an arrangement of six fibres at varying solid-liquid interaction and boundary conditions are studied with 'Surface Evolver'. In order to evaluate the findings of ex-situ and modelling work for applicability to water transport in fuel cell operation, the technique of nuclear magnetic resonance (NMR) imaging is assessed. The focus is on the visualisation of 2D and 3D water distribution in the operating fuel cell. The compatibility of the NMR experiment with fuel cell operation in relation to material selection, operating temperature, and current density is addressed. NMR imaging is employed for different current densities, stoichiometries, and fuel cell arrangements. The fuel cell arrangements differ by the cathode diffusion medium. Plain, hydrophobic, and
Heat diffusion and magnetic field generation
International Nuclear Information System (INIS)
Holstein, P.A.
1983-10-01
In the report of CECAM workshop in 1982 some results of heat diffusion, when the spontaneous B-field is calculated, have been given. Separately, a similar code (magneto-calo-dynamic or MCD code) has been built and it was interesting to compare them. Comparisom has been made during the workshop of October 1983
Global vertical mass transport by clouds - A two-dimensional model study
International Nuclear Information System (INIS)
Olofsson, Mats
1988-05-01
A two-dimensional global dispersion model, where vertical transport in the troposphere carried out by convective as well as by frontal cloud systems is explicitly treated, is developed from an existing diffusion model. A parameterization scheme for the cloud transport, based on global cloud statistics, is presented. The model has been tested by using Kr-85, Rn-222 and SO 2 as tracers. Comparisons have been made with observed distributions of these tracers, but also with model results without the cloud transport, using eddy diffusion as the primary means of vertical transport. The model results indicate that for trace species with a turnover time of days to weeks, the introduction of cloud-transport gives much more realistic simulations of their vertical distribution. Layers of increased mixing ratio with height, which can be found in real atmosphere, are reproduced in our cloud-transport model profiles, but can never be simulated with a pure eddy diffusion model. The horizontal transport in the model, by advection and eddy diffusion, gives a realistic distribution between the hemispheres of the more long-lived tracers (Kr-85). A combination of vertical transport by convective and frontal cloud systems is shown to improve the model simulations, compared to limiting it to convective transport only. The importance of including cumulus clouds in the convective transport scheme, in addition to the efficient transport by cumulonimbus clouds, is discussed. The model results are shown to be more sensitive to the vertical detrainment distribution profile than to the absolute magnitude of the vertical mass transport. The scavenging processes for SO 2 are parameterized without the introduction of detailed chemistry. An enhanced removal, due to the increased contact with droplets in the in-cloud lifting process, is introduced in the model. (author)
Single-phase pump model for analysis of LMFBR heat transport systems
International Nuclear Information System (INIS)
Madni, I.K.; Cazzoli, E.
1978-05-01
A single-phase pump model for transient and steady-state analysis of LMFBR heat transport systems is presented. Fundamental equations of the model are angular momentum balance to determine transient impeller speed and mass balance (including thermal expansion effects) to determine the level of sodium in the pump tank. Pump characteristics are modeled by homologous head and torque relations. All regions of pump operation are represented with reverse rotation allowed. The model also includes option for enthalpy rise calculations and pony motor operation. During steady state, the pump operating speed is determined by matching required head with total load in the circuit. Calculated transient results are presented for pump coastdown and double-ended pipe break accidents. The report examines the influence of frictional torque and specific speed on predicted response for the pump coastdown to natural circulation transient. The results for a double-ended pipe break accident indicate the necessity of including all regions of operation for pump characteristics
How to approximate the heat equation with Neumann boundary conditions by nonlocal diffusion problems
Cortazar, C.; Elgueta, M.; Rossi, J. D.; Wolanski, N.
2006-01-01
We present a model for nonlocal diffusion with Neumann boundary conditions in a bounded smooth domain prescribing the flux through the boundary. We study the limit of this family of nonlocal diffusion operators when a rescaling parameter related to the kernel of the nonlocal operator goes to zero. We prove that the solutions of this family of problems converge to a solution of the heat equation with Neumann boundary conditions.
THE ISOTROPIC DIFFUSION SOURCE APPROXIMATION FOR SUPERNOVA NEUTRINO TRANSPORT
International Nuclear Information System (INIS)
Liebendoerfer, M.; Whitehouse, S. C.; Fischer, T.
2009-01-01
Astrophysical observations originate from matter that interacts with radiation or transported particles. We develop a pragmatic approximation in order to enable multidimensional simulations with basic spectral radiative transfer when the available computational resources are not sufficient to solve the complete Boltzmann transport equation. The distribution function of the transported particles is decomposed into a trapped particle component and a streaming particle component. Their separate evolution equations are coupled by a source term that converts trapped particles into streaming particles. We determine this source term by requiring the correct diffusion limit for the evolution of the trapped particle component. For a smooth transition to the free streaming regime, this 'diffusion source' is limited by the matter emissivity. The resulting streaming particle emission rates are integrated over space to obtain the streaming particle flux. Finally, a geometric estimate of the flux factor is used to convert the particle flux to the streaming particle density, which enters the evaluation of streaming particle-matter interactions. The efficiency of the scheme results from the freedom to use different approximations for each particle component. In supernovae, for example, reactions with trapped particles on fast timescales establish equilibria that reduce the number of primitive variables required to evolve the trapped particle component. On the other hand, a stationary-state approximation considerably facilitates the treatment of the streaming particle component. Different approximations may apply in applications to stellar atmospheres, star formation, or cosmological radiative transfer. We compare the isotropic diffusion source approximation with Boltzmann neutrino transport of electron flavor neutrinos in spherically symmetric supernova models and find good agreement. An extension of the scheme to the multidimensional case is also discussed.
DEFF Research Database (Denmark)
Chambon, Julie Claire Claudia; Damgaard, Ida; Jeannottat, Simon
. Degradation and transport processes of chlorinated ethenes are not well understood in such geological settings, therefore risk assessment and remediation at these sites are particularly challenging. In this work, a combined approach of chemical and isotope analysis on core samples, and reactive transport...... the source zone (between 6 and 12 mbs). Concentrations and stable isotope ratios of the mother compounds and their daughter products, as well as redox parameters, fatty acids and microbial data, were analyzed with discrete sub-sampling along the cores. More samples (each 5 mm) were collected around...... of dechlorination and degradation pathways (biotic reductive dechlorination or abiotic β-elimination with iron minerals) in three core profiles. The model includes diffusion in the matrix, sequential reductive dechlorination, abiotic degradation, isotope fractionation due to degradation and due to diffusion...
Reaction-diffusion pulses: a combustion model
International Nuclear Information System (INIS)
Campos, Daniel; Llebot, Josep Enric; Fort, Joaquim
2004-01-01
We focus on a reaction-diffusion approach proposed recently for experiments on combustion processes, where the heat released by combustion follows first-order reaction kinetics. This case allows us to perform an exhaustive analytical study. Specifically, we obtain the exact expressions for the speed of the thermal pulses, their maximum temperature and the condition of self-sustenance. Finally, we propose two generalizations of the model, namely, the case of several reactants burning together, and that of time-delayed heat conduction. We find an excellent agreement between our analytical results and simulations
Reaction-diffusion pulses: a combustion model
Energy Technology Data Exchange (ETDEWEB)
Campos, Daniel [Grup de FIsica EstadIstica, Dept. de FIsica, Universitat Autonoma de Barcelona, E-08193 Bellaterrra (Spain); Llebot, Josep Enric [Grup de FIsica EstadIstica, Dept. de FIsica, Universitat Autonoma de Barcelona, E-08193 Bellaterrra (Spain); Fort, Joaquim [Dept. de FIsica, Univ. de Girona, Campus de Montilivi, 17071 Girona, Catalonia (Spain)
2004-07-02
We focus on a reaction-diffusion approach proposed recently for experiments on combustion processes, where the heat released by combustion follows first-order reaction kinetics. This case allows us to perform an exhaustive analytical study. Specifically, we obtain the exact expressions for the speed of the thermal pulses, their maximum temperature and the condition of self-sustenance. Finally, we propose two generalizations of the model, namely, the case of several reactants burning together, and that of time-delayed heat conduction. We find an excellent agreement between our analytical results and simulations.
Diffuse Ceiling Ventilation and the Influence of Room Height and Heat Load Distribution
DEFF Research Database (Denmark)
Nielsen, Peter Vilhelm; Vilsbøll, Rasmus W; Liu, Li
2015-01-01
Diffuse ceiling (inlet) ventilation is an air distribution system that supplies air from the entire ceiling surface, giving a low supply velocity. The flow pattern in the room is controlled by the heat sources. The system generates high mixing flow and the air velocities in the room are expected...... to be not much influenced by the flow rate to the room but dependent on the heat load. Previous studies have shown that diffuse ceiling ventilation has an ability to remove large heat loads without compromising the indoor climate. However, recent experiments indicate that the maximum accepted heat load decreases...... with a large room height and it decreases in connection with certain heat load distributions. Room geometries and heat load distributions that are optimal for diffuse ceiling ventilation are discussed. A simplified design procedure is introduced....
Changing storm track diffusivity and the upper limit to poleward latent heat transport
Caballero, R.
2010-12-01
Poleward atmospheric energy transport plays a key role in the climate system by helping set the mean equator-pole temperature gradient. The mechanisms controlling the response of poleward heat flux to climate change are still poorly understood. Recent work shows that midlatitude poleward latent heat flux in atmospheric GCMs generally increases as the climate warms but reaches an upper limit at sufficiently high temperature and decreases with further warming. The reasons for this non-monotonic behavior have remained unclear. Simple arguments suggests that the latent heat flux Fl should scale as Fl ˜ vref qs, where vref is a typical meridional velocity in the baroclinic zone and qs is saturation humidity. While vref decreases with temperature, qs increases much more rapidly, so this scaling implies monotonically increasing moisture flux. We study this problem using a series of simulations employing NCAR’s CAM3 GCM coupled to a slab-ocean aquaplanet and spanning a wide range of atmospheric CO2 concentrations. We find that a modified scaling, Fl ˜ vref2 qs, describes the changes in moisture flux much more accurately. Using Lagrangian trajectory analysis, we explain the success of this scaling in terms of changes in the mixing length, which contracts proportionally to vref.
Heat transfer enhancement in nanofluids. A numerical approach
International Nuclear Information System (INIS)
Fariñas Alvariño, P; Sáiz Jabardo, J M; Arce, A; Llamas Galdo, M I
2012-01-01
The aim of the reported investigation is to asses the effect of brownian and thermophoretic diffusion in nanofluids convective heat transfer. In order to capture these effects, a new equation for particles distribution had to be consider. Momentum and energy equations have been reformulated in order to include brownian and thermophretic diffusion. These modes of diffusion have been suggested extensively in the literature but their effect on momentum and energy transport has not yet been numerically analyzed. In order to obtain a solution for the modified set of governing equations, a new CFD solver had to be devised. The new solver has been applied to a case study involving hydrodynamic and thermally developing laminar flow regime in a pipe. Pure base fluid solutions have been used to asses the accuracy of the model. Numerical nanofluid solutions compare reasonably well with both experimental results obtained elsewhere and the Churchill and Ozoe correlation. The observed heat transfer enhancement by the nanofluid has been attributed to its transport properties rather than to another transport mechanism.
Effects on atmospheric diffusion of meterological processes in coastal zones
International Nuclear Information System (INIS)
Raynor, G.S.
1977-01-01
Meteorological processes in coastal zones differ from those inland because of the surface discontinuity between land and water. The difference in heating between the two surfaces gives rise to sea or lake breeze circulations which can transport pollutants in nongradient directions and recirculate them over source areas. The step change in surface characteristics at the land-water interface also causes formation of internal boundary layers having different transport velocities and diffusion rates than unmodified air upwind or above the boundary. These features require a more extensive measurement program and more versatile diffusion models than at inland sites
Plasma transport simulation modeling for helical confinement systems
International Nuclear Information System (INIS)
Yamazaki, K.; Amano, T.
1991-08-01
New empirical and theoretical transport models for helical confinement systems are developed based on the neoclassical transport theory including the effect of radial electric field and multi-helicity magnetic components, and the drift wave turbulence transport for electrostatic and electromagnetic modes, or the anomalous semi-empirical transport. These electron thermal diffusivities are compared with CHS (Compact Helical System) experimental data, which indicates that the central transport coefficient of the ECH plasma agrees with the neoclassical axi-symmetric value and the transport outside the half radius is anomalous. On the other hand, the transport of NBI-heated plasmas is anomalous in the whole plasma region. This anomaly is not explained by the electrostatic drift wave turbulence models in these flat-density-profile discharges. For the detailed prediction of plasma parameters in LHD (Large Helical Device), 3-D(dimensional) equilibrium/1-D transport simulations including empirical or drift wave turbulence models are carried out, which suggests that the global confinement time of LHD is determined mainly by the electron anomalous transport near the plasma edge region rather than the helical ripple transport in the core region. Even if the ripple loss can be eliminated, the increase of the global confinement is 10%. However, the rise in the central ion temperature is more than 20%. If the anomalous loss can be reduced to the half level of the present scaling, like so-called 'H-mode' of the tokamak discharge, the neoclassical ripple loss through the ion channel becomes important even in the plasma core. The 5% radial inward shift of the plasma column with respect to the major radius is effective for improving plasma confinement and raising more than 50% of the fusion product by reducing this neoclassical asymmetric ion transport loss and increasing 10% in the plasma radius. (author)
Ancey, C.; Bohorquez, P.; Heyman, J.
2015-12-01
The advection-diffusion equation is one of the most widespread equations in physics. It arises quite often in the context of sediment transport, e.g., for describing time and space variations in the particle activity (the solid volume of particles in motion per unit streambed area). Phenomenological laws are usually sufficient to derive this equation and interpret its terms. Stochastic models can also be used to derive it, with the significant advantage that they provide information on the statistical properties of particle activity. These models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. Among these stochastic models, the most common approach consists of random walk models. For instance, they have been used to model the random displacement of tracers in rivers. Here we explore an alternative approach, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. Birth-death Markov processes are well suited to this objective. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received no attention. We therefore look into the possibility of deriving the advection-diffusion equation (with a source term) within the framework of birth-death Markov processes. We show that in the continuum limit (when the cell size becomes vanishingly small), we can derive an advection-diffusion equation for particle activity. Yet while this derivation is formally valid in the continuum limit, it runs into difficulty in practical applications involving cells or meshes of finite length. Indeed, within our stochastic framework, particle advection produces nonlocal effects, which are more or less significant depending on the cell size and particle velocity. Albeit nonlocal, these effects look like (local) diffusion and add to the intrinsic particle diffusion (dispersal due
Directory of Open Access Journals (Sweden)
Meng Zhi-Jun
2016-01-01
Full Text Available This paper addresses a new application of the local fractional variational iteration algorithm III to solve the local fractional diffusion equation defined on Cantor sets associated with non-differentiable heat transfer.
International Nuclear Information System (INIS)
Epperlein, E.M.
1992-01-01
Preliminary 1-D studies of nonlocal heat transport in spherical plasmas based on the Fokker-Planck code SPARK indicate significant levels of electron preheat and radial heat flux across a spherical heat sink surface kept at fixed temperature. However, the diffusive approximation to the Fokker-Planck equation is shown to be particularly sensitive to the nature of the inner surface boundary condition chosen. A suggested remedy is the inclusion of a target capsule in future simulations studies with SPARK
Estimating thermal diffusivity and specific heat from needle probe thermal conductivity data
Waite, W.F.; Gilbert, L.Y.; Winters, W.J.; Mason, D.H.
2006-01-01
Thermal diffusivity and specific heat can be estimated from thermal conductivity measurements made using a standard needle probe and a suitably high data acquisition rate. Thermal properties are calculated from the measured temperature change in a sample subjected to heating by a needle probe. Accurate thermal conductivity measurements are obtained from a linear fit to many tens or hundreds of temperature change data points. In contrast, thermal diffusivity calculations require a nonlinear fit to the measured temperature change occurring in the first few tenths of a second of the measurement, resulting in a lower accuracy than that obtained for thermal conductivity. Specific heat is calculated from the ratio of thermal conductivity to diffusivity, and thus can have an uncertainty no better than that of the diffusivity estimate. Our thermal conductivity measurements of ice Ih and of tetrahydrofuran (THF) hydrate, made using a 1.6 mm outer diameter needle probe and a data acquisition rate of 18.2 pointss, agree with published results. Our thermal diffusivity and specific heat results reproduce published results within 25% for ice Ih and 3% for THF hydrate. ?? 2006 American Institute of Physics.
International Nuclear Information System (INIS)
Wu Rui; Zhu Xun; Liao Qiang; Wang Hong; Ding Yudong; Li Jun; Ye Dingding
2010-01-01
In proton exchange membrane fuel cell (PEMFC) models, oxygen effective diffusivity is the most important parameter to characterize the oxygen transport in the gas diffusion layer (GDL). However, its determination is a challenge due to its complex dependency on GDL structure. In the present study, a three-dimensional network consisting of spherical pores and cylindrical throats is developed and used to investigate the effects of GDL structural parameters on oxygen effective diffusivity under the condition with/without water invasion process. Oxygen transport in the throat is described by Fick's law and water invasion process in the network is simulated using the invasion percolation with trapping algorithm. The simulation results reveal that oxygen effective diffusivity is slightly affected by network size but increases with decreasing the network heterogeneity and with increasing the pore connectivity. Impacts of network anisotropy on oxygen transport are also investigated in this paper. The anisotropic network is constructed by constricting the throats in the through-plane direction with a constriction factor. It is found that water invasion has a more severe negative influence on oxygen transport in an anisotropic network. Finally, two new correlations are introduced to determine the oxygen effective diffusivity for the Toray carbon paper GDLs.
Neutron transport equation - indications on homogenization and neutron diffusion
International Nuclear Information System (INIS)
Argaud, J.P.
1992-06-01
In PWR nuclear reactor, the practical study of the neutrons in the core uses diffusion equation to describe the problem. On the other hand, the most correct method to describe these neutrons is to use the Boltzmann equation, or neutron transport equation. In this paper, we give some theoretical indications to obtain a diffusion equation from the general transport equation, with some simplifying hypothesis. The work is organised as follows: (a) the most general formulations of the transport equation are presented: integro-differential equation and integral equation; (b) the theoretical approximation of this Boltzmann equation by a diffusion equation is introduced, by the way of asymptotic developments; (c) practical homogenization methods of transport equation is then presented. In particular, the relationships with some general and useful methods in neutronic are shown, and some homogenization methods in energy and space are indicated. A lot of other points of view or complements are detailed in the text or the remarks
Reactive transport modeling of the ABM experiment with Comsol Multiphysics
International Nuclear Information System (INIS)
Pekala, Marek; Idiart, Andres; Arcos, David
2012-01-01
Document available in extended abstract form only. The Swedish Organisation for Radioactive Waste Disposal (SKB) is considering disposal of the High Level Waste in a deep underground repository in a crystalline rock. According to the disposal concept, bentonite clay will be used in the near-field of the waste packages as buffer material. From solute transport point of view, the bentonite buffer is expected to provide a favourable environment, where radionuclide migration would be limited to slow diffusion and further retarded by sorption. In the KBS-3 repository design, the MX-80 bentonite is the reference buffer material. However, SKB has also been investigating alternative buffer materials. To this end, the field experiment Alternative Buffer Materials (ABM) was started at the Aespoe URL in 2006. Three packages of eleven different compacted bentonite blocks in different configurations have been tested over varying time scales. The packages with outer diameter of 0.28 m were deposited into 3 meter deep boreholes. After installation, packages were saturated and heated differently to target values. This contribution concerns the evolution of Package 1, which was initiated in December 2006 and ran for about 2.5 years. Post-mortem examination after retrieval showed that the initially contrasting chloride concentrations and cation-exchanger compositions between different bentonite blocks became significantly homogenised. It is thought that this behaviour could be explained as a first approximation by diffusion of major ions between the bentonite blocks coupled with cation-exchange. In this work, a modelling study to verify this hypothesis has been undertaken. In addition, the feasibility of implementing a reactive transport model into the Finite Element code COMSOL Multiphysics has been tested. The model considers a two-dimensional axisymmetric geometry of the depositional borehole, and includes coupled diffusion and cation-exchange of Na, K, Ca and Mg (as a chloride
Actinide transport in Topopah Spring Tuff: Pore size, particle size, and diffusion
International Nuclear Information System (INIS)
Buchholtz ten Brink, M.; Phinney, D.L.; Smith, D.K.
1991-04-01
Diffusive transport rates for aqueous species in a porous medium are a function of sorption, molecular diffusion, and sample tortuosity. With heterogeneous natural samples, an understanding of the effect of multiple transport paths and sorption mechanisms is particularly important since a small amount of radioisotope traveling via a faster-than-anticipated transport path may invalidate the predictions of transport codes which assume average behavior. Static-diffusion experiments using aqueous 238 U tracer in tuff indicated that U transport was faster in regions of greater porosity and that apparent diffusion coefficients depended on the scale (m or μm) over which concentration gradients were measured in Topopah Spring Tuff. If a significant fraction of actinides in high-level waste are released to the environment in forms that do not sorb to the matrix, they may be similarly transported along fast paths in porous regions of the tuff. To test this, aqueous diffusion rates in tuff were measured for 238 U and 239 Pu leached from doped glass. Measured transport rates and patterns were consistent in both systems with a dual-porosity transported moeld. In addition, filtration or channelling of actinides associated with colloidal particles may significantly affect the radionuclide transport rate in Topopah Spring tuff. 9 refs., 7 figs
Nonlinear thermal convection in a layer of nanofluid under G-jitter and internal heating effects
Directory of Open Access Journals (Sweden)
Bhadauria B. S.
2014-01-01
Full Text Available This paper deals with a mathematical model of controlling heat transfer in nanofluids. The time-periodic vertical vibrations of the system are considered to effect an external control of heat transport along with internal heating effects. A weakly non-linear stability analysis is based on the five-mode Lorenz model using which the Nusselt number is obtained as a function of the thermal Rayleigh number, nano-particle concentration based Rayleigh number, Prandtl number, Lewis number, modified diffusivity ratio, amplitude and frequency of modulation. It is shown that modulation can be effectively used to control convection and thereby heat transport. Further, it is found that the effect of internal Rayleigh number is to enhance the heat and nano-particles transport.
EFFECT OF SANDSTONE ANISOTROPY ON ITS HEAT AND MOISTURE TRANSPORT PROPERTIES
Directory of Open Access Journals (Sweden)
Jan Fořt
2015-09-01
Full Text Available Each type of natural stone has its own geological history, formation conditions, different chemical and mineralogical composition, which influence its possible anisotropy. Knowledge in the natural stones anisotropy represents crucial information for the process of stone quarrying, its correct usage and arrangement in building applications. Because of anisotropy, many natural stones exhibit different heat and moisture transport properties in various directions. The main goal of this study is to analyse several anisotropy indices and their effect on heat transport and capillary absorption. For the experimental determination of the anisotropy effect, five types of sandstone coming from different operating quarries in the Czech Republic are chosen. These materials are often used for restoration of culture heritage monuments as well as for other building applications where they are used as facing slabs, facade panels, decoration stones, paving, etc. For basic characterization of studied materials, determination of their bulk density, matrix density and total open porosity is done. Chemical composition of particular sandstones is analysed by X-Ray Fluorescence. Anisotropy is examined by the non-destructive measurement of velocity of ultrasonic wave propagation. On the basis of ultrasound testing data, the relative anisotropy, total anisotropy and anisotropy coefficient are calculated. Then, the measurement of thermal conductivity and thermal diffusivity in various directions of samples orientation is carried out. The obtained results reveal significant differences between the parameters characterizing the heat transport in various directions, whereas these values are in accordance with the indices of anisotropy. Capillary water transport is described by water absorption coefficient measured using a sorption experiment, which is performed for distilled water and 1M NaCl water solution. The measured data confirm the effect of anisotropy which is
Canning by the diffusion caused by a heated die
International Nuclear Information System (INIS)
Gauthron, M.
1959-01-01
In this process, the uranium fuel is clad with a zirconium can by passing the element through a die. The operation takes place at a temperature varying between 500 and 1000 deg. C. The heating is obtained by passing low voltage electric current through the can. This process differs from the co-extrusion process in that the uranium is not deformed. The uranium is therefore machined to the final dimensions before canning, it can also be hollow. Two types of processes can be adopted for the extrusion: a) Process in which the binding of the can to the uranium is obtained without diffusion (here the can is at high temperature - subsequently cooled - and the uranium is at a low temperature); b) Process in which uranium-zirconium diffusion is initiated. No matter which process is adopted the element is subsequently heat treated in an over at 800 deg. C in order to obtain the final diffusion. The quality of this diffusion is dependent on the initial state of the surfaces and on the degree of vacuum maintained during the operation. (author) [fr
Probabilistic transport models for fusion
International Nuclear Information System (INIS)
Milligen, B.Ph. van; Carreras, B.A.; Lynch, V.E.; Sanchez, R.
2005-01-01
A generalization of diffusive (Fickian) transport is considered, in which particle motion is described by probability distributions. We design a simple model that includes a critical mechanism to switch between two transport channels, and show that it exhibits various interesting characteristics, suggesting that the ideas of probabilistic transport might provide a framework for the description of a range of unusual transport phenomena observed in fusion plasmas. The model produces power degradation and profile consistency, as well as a scaling of the confinement time with system size reminiscent of the gyro-Bohm/Bohm scalings observed in fusion plasmas, and rapid propagation of disturbances. In the present work we show how this model may also produce on-axis peaking of the profiles with off-axis fuelling. It is important to note that the fluid limit of a simple model like this, characterized by two transport channels, does not correspond to the usual (Fickian) transport models commonly used for modelling transport in fusion plasmas, and behaves in a fundamentally different way. (author)
Numerical simulation of the transport phenomena due to sudden heating in porous media
Energy Technology Data Exchange (ETDEWEB)
Lei, S.Y.; Zheng, G.Y.; Wang, B.X.; Yang, R.G.; Xia, C.M.
1997-07-01
Such process as wet porous media suddenly heated by hot fluids frequently occurs in nature and in industrial applications. The three-variable simulation model was developed to predict violent transport phenomena due to sudden heating in porous media. Two sets of independent variables were applied to different regions in porous media in the simulation. For the wet zone, temperature, wet saturation and air pressure were used as the independent variables. For the dry zone, the independent variables were temperature, vapor pressure and air pressure. The model simulated two complicated transport processes in wet unsaturated porous media which is suddenly heated by melting metal or boiling water. The effect of the gas pressure is also investigated on the overall transport phenomena.
Stochastic models of intracellular transport
Bressloff, Paul C.; Newby, Jay M.
2013-01-01
mechanisms for intracellular transport: passive diffusion and motor-driven active transport. Diffusive transport can be formulated in terms of the motion of an overdamped Brownian particle. On the other hand, active transport requires chemical energy, usually
A simulation of heat transfer during billet transport
Energy Technology Data Exchange (ETDEWEB)
Jaklic, A.; Glogovac, B. [Institute of Metals and Technology, Ljubljana (Slovenia); Kolenko, T. [University of Ljubljana (Slovenia). Faculty of Natural Science and Technology; Zupancic, B. [University of Ljubljana (Slovenia). Faculty of Electrical Engineering; Zak, B. T. [Terming d.o.o., Ljubljana (Slovenia)
2002-07-01
This paper presents a simulation model for billet cooling during the billet's transport from the reheating furnace to the rolling mill. During the transport, the billet is exposed to radiation, convection and conduction. Due to the rectangular shape of the billet, the three-dimensional finite-difference model could be applied to calculate the heat conduction inside the billet. The billets are reheated in a gas-fired walking-beam furnace and are exposed to scaling. The model takes into account the effect of the thin oxide scale. We proved that the scale significantly affects the temperature distribution in the billet and should not be neglected. The model was verified by using a thermal camera. (author)
Periodic heat wave determination of thermal diffusivity of clays ...
African Journals Online (AJOL)
The responses of Ankaful, Tetegu (# 1 & 2) and Mamfe clays to periodic heat waves were analyzed to deter-mine the thermal diffusivity values. The temperature amplitude attenuated with depth of penetration, while the phase shift increased. The thermal diffusivity values ranged from 3.0 - 9.5 x 10P-7P mP2P/s by amplitude ...
Diffusion and transport coefficients in synthetic opals
International Nuclear Information System (INIS)
Sofo, J. O.; Mahan, G. D.
2000-01-01
Opals are structures composed of close-packed spheres in the size range of nano to micrometers. They are sintered to create small necks at the points of contact. We have solved the diffusion problem in such structures. The relation between the diffusion coefficient and the thermal and electrical conductivity is used to estimate the transport coefficients of opal structures as a function of the neck size and the mean free path of the carriers. The theory presented is also applicable to the diffusion problem in other periodic structures. (c) 2000 The American Physical Society
Bridger, D. W.; Allen, D. M.
2014-01-01
A modeling study was carried out to evaluate the influence of aquifer heterogeneity, as represented by geologic layering, on heat transport and storage in an aquifer thermal energy storage (ATES) system in Agassiz, British Columbia, Canada. Two 3D heat transport models were developed and calibrated using the flow and heat transport code FEFLOW including: a "non-layered" model domain with homogeneous hydraulic and thermal properties; and, a "layered" model domain with variable hydraulic and thermal properties assigned to discrete geological units to represent aquifer heterogeneity. The base model (non-layered) shows limited sensitivity for the ranges of all thermal and hydraulic properties expected at the site; the model is most sensitive to vertical anisotropy and hydraulic gradient. Simulated and observed temperatures within the wells reflect a combination of screen placement and layering, with inconsistencies largely explained by the lateral continuity of high permeability layers represented in the model. Simulation of heat injection, storage and recovery show preferential transport along high permeability layers, resulting in longitudinal plume distortion, and overall higher short-term storage efficiencies.
Heat transport in low-dimensional materials: A review and perspective
Directory of Open Access Journals (Sweden)
Zhiping Xu
2016-05-01
Full Text Available Heat transport is a key energetic process in materials and devices. The reduced sample size, low dimension of the problem and the rich spectrum of material imperfections introduce fruitful phenomena at nanoscale. In this review, we summarize recent progresses in the understanding of heat transport process in low-dimensional materials, with focus on the roles of defects, disorder, interfaces, and the quantum-mechanical effect. New physics uncovered from computational simulations, experimental studies, and predictable models will be reviewed, followed by a perspective on open challenges.
Diffusion and transport phenomena in a collisional magnetoplasma ...
Indian Academy of Sciences (India)
Boltzmann-transport equation is analytically solved for two-component magnetoplasma using Chapman-Enskog analysis to include collisional diffusion transport having anisotropies in both streaming velocity and temperature components. The modified collisional integrals are analytically solved with flux integrals and ...
Energy Technology Data Exchange (ETDEWEB)
Lasuik, J.; Shalchi, A., E-mail: andreasm4@yahoo.com [Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2 (Canada)
2017-09-20
Recently, a new theory for the transport of energetic particles across a mean magnetic field was presented. Compared to other nonlinear theories the new approach has the advantage that it provides a full time-dependent description of the transport. Furthermore, a diffusion approximation is no longer part of that theory. The purpose of this paper is to combine this new approach with a time-dependent model for parallel transport and different turbulence configurations in order to explore the parameter regimes for which we get ballistic transport, compound subdiffusion, and normal Markovian diffusion.
International Nuclear Information System (INIS)
Goto, T.; Tsushima, H.; Sakurai, N.; Jo, T.
2006-01-01
MONJU is a prototype fast breeder reactor (FBR). Modification work commenced in March 2005. Since June 2004, MONJU has changed to one-loop operation of the primary heat transport system (PHTS) with all of the secondary heat transport systems (SHTS) drained of sodium. The purposes of this change are to shorten the modification period and to reduce the cost incurred for circuit trace heating electrical consumption. Before changing condition, the following issues were investigated to show that this mode of operation was possible. The heat loss from the reactor vessel and the single primary loop must exceed the decay heat by an acceptable margin but the capacity of pre-heaters to keep the sodium within the primary vessel at about 200 deg. C must be maintained. With regard to the heat loss and the decay heat, the estimated heat loss in the primary system was in the range of 90-170 kW in one-loop operation, and the calculated decay heat was 21.2 kW. Although the heat input of the primary pump was considered, it was clear that circuit heat loss greatly exceeded the decay heat. As for pre-heaters, effective capacity was less than the heat loss. Therefore, the temperature of the reactor vessel room was raised to reduce the heat loss. One-loop operation of the PHTS was able to be executed by means of these measures. The cost of electrical consumption in the power plant has been reduced by one-loop operation of the PHTS and the modification period was shortened. (authors)
International Nuclear Information System (INIS)
Dubus, A.; Devooght, J.; Dehaes, J.C.
1987-01-01
The ''improved age-diffusion'' model for secondary-electron transport is applied to aluminum. Electron cross sections for inelastic collisions with the free-electron gas using the Lindhard dielectric function and for elastic collisions with the randomly distributed ionic cores are used in the calculations. The most important characteristics of backward secondary-electron emission induced by low-energy electrons on polycrystalline Al targets are calculated and compared to experimental results and to Monte Carlo calculations. The model appears to predict the electronic yield, the energy spectra, and the spatial dependence of secondary emission with reasonable accuracy
Two simple models of classical heat pumps.
Marathe, Rahul; Jayannavar, A M; Dhar, Abhishek
2007-03-01
Motivated by recent studies of models of particle and heat quantum pumps, we study similar simple classical models and examine the possibility of heat pumping. Unlike many of the usual ratchet models of molecular engines, the models we study do not have particle transport. We consider a two-spin system and a coupled oscillator system which exchange heat with multiple heat reservoirs and which are acted upon by periodic forces. The simplicity of our models allows accurate numerical and exact solutions and unambiguous interpretation of results. We demonstrate that while both our models seem to be built on similar principles, one is able to function as a heat pump (or engine) while the other is not.
International Nuclear Information System (INIS)
Kasahara, Seiji; Kamiji, Yu; Terada, Atsuhiko; Yan Xing; Inagaki, Yoshiyuki; Murata, Tetsuya; Mori, Michitsugu
2015-01-01
A district heating and snow melting system utilizing waste heat from Gas Turbine High temperature Gas Reactor of 300 MW_e (GTHTR300), a heat-electricity cogeneration design of high temperature gas-cooled reactor, was analyzed. Application areas are set in Sapporo and Ishikari, the heavy snowfall cities in Northern Japan. The heat transport analyses are carried out by modeling the components in the system; pipelines of the secondary water loops between GTHTR300s and heat demand district and heat exchangers to transport the heat from the secondary water loops to the tertiary loops in the district. Double pipe for the secondary loops are advantageous for less heat loss and smaller excavation area. On the other hand, these pipes has disadvantage of more electricity consumption for pumping. Most of the heat demand in the month of maximum requirement can be supplied by 2 GTHTR300s and delivered by 9 secondary loops and around 5000 heat exchangers. Closer location of GTHTR300 site to the heat demand district is largely advantageous economically. Less decrease of the distance from 40 km to 20 km made the heat loss half and cost of the heat transfer system 22% smaller. (author)
Particle and heat transport in Tokamaks
International Nuclear Information System (INIS)
Chatelier, M.
1984-01-01
A limitation to performances of tokamaks is heat transport through magnetic surfaces. Principles of ''classical'' or ''neoclassical'' transport -i.e. transport due to particle and heat fluxes due to Coulomb scattering of charged particle in a magnetic field- are exposed. It is shown that beside this classical effect, ''anomalous'' transport occurs; it is associated to the existence of fluctuating electric or magnetic fields which can appear in the plasma as a result of charge and current perturbations. Tearing modes and drift wave instabilities are taken as typical examples. Experimental features are presented which show that ions behave approximately in a classical way whereas electrons are strongly anomalous [fr
DEFF Research Database (Denmark)
Larsen, E.H.; Møbjerg, N.; Sørensen, Jens Nørkær
2006-01-01
transport similar to rat proximal tubule. Na+ recirculation is required for truly isotonic transport. The tonicity of the absorbate and the recirculation flux depend critically on ion permeabilities of interspace basement membrane. Conclusion: Our model based on solute-solvent coupling in lateral space......Aim: By mathematical modelling, we analyse conditions for near-isotonic and isotonic transport by mammalian kidney proximal tubule. Methods: The model comprises compliant lateral intercellular space (lis) and cells, and infinitely large luminal and peritubular compartments with diffusible species......: Na+, K+, Cl and an intracellular non-diffusible anion. Unknown model variables are solute concentrations, electrical potentials, volumes and hydrostatic pressures in cell and lis, and transepithelial potential. We used data mainly from rat proximal tubule to model epithelial cells and interspace...
Oxygen transport in waterlogged soils, Part II. Diffusion coefficients
International Nuclear Information System (INIS)
Obando Moncayo, F.H.
2004-01-01
Several equations are available for Oxygen Transport in Waterlogged Soils and have been used for soils and plants. All of them are some form of first Fick's law as given by dQ = - DA(dc/dx)/dt. This equation illustrates some important aspects of aeration in waterlogged soils; first, D is a property of the medium and the gas, and is affected by temperature T. Likewise, the amount of diffusing substance dQ in dt is a direct function of the cross sectional area A and inversely proportional to the distance x. In fact, increasing the water content of air-dry soil, drastically decreases A and creates a further resistance for the flow of oxygen through water films around root plants, soil micro organisms and soil aggregates. The solid phase is also limiting the cross-section of surface of the free gaseous diffusion and the length and tortuosity of diffusion path in soil. In most of cases, soil gas porosity and tortuosity of soil voids are expressed in the equations of diffusion as a broad 'diffusion coefficient' (apparent coefficient diffusion). The process of soil respiration is complicated, involves many parameters, and is difficult to realistically quantify. With regard to the oxygen supply, it is convenient to distinguish macro and micro models, and hence, the flux of oxygen is assumed to have two steps. The first step is related to oxygen diffusion from the atmosphere and the air-filled porosity. The second step is related to the oxygen diffusion through water-films in and around plant roots, soil micro organisms and aggregates. Because of these models we obtain coefficients of macro or micro diffusion, rates of macro or micro diffusion, etc. In the macro diffusion process oxygen is transferred in the soil profile, mainly from the soil surface to a certain depth of the root zone, while micro diffusion deals with the flux over very short distances. Both processes, macro and micro diffusion are highly influenced by soil water content. Of course, if water is added to
Modelling anisotropic water transport in polymer composite
Indian Academy of Sciences (India)
This work reports anisotropic water transport in a polymer composite consisting of an epoxy matrix reinforced with aligned triangular bars made of vinyl ester. By gravimetric experiments, water diffusion in resin and polymer composites were characterized. Parameters for Fickian diffusion and polymer relaxation models were ...
A turbulent transport network model in MULTIFLUX coupled with TOUGH2
International Nuclear Information System (INIS)
Danko, G.; Bahrami, D.; Birkholzer, J.T.
2011-01-01
A new numerical method is described for the fully iterated, conjugate solution of two discrete submodels, involving (a) a transport network model for heat, moisture, and airflows in a high-permeability, air-filled cavity; and (b) a variably saturated fractured porous medium. The transport network submodel is an integrated-parameter, computational fluid dynamics solver, describing the thermal-hydrologic transport processes in the flow channel system of the cavity with laminar or turbulent flow and convective heat and mass transport, using MULTIFLUX. The porous medium submodel, using TOUGH2, is a solver for the heat and mass transport in the fractured rock mass. The new model solution extends the application fields of TOUGH2 by integrating it with turbulent flow and transport in a discrete flow network system. We present demonstrational results for a nuclear waste repository application at Yucca Mountain with the most realistic model assumptions and input parameters including the geometrical layout of the nuclear spent fuel and waste with variable heat load for the individual containers. The MULTIFLUX and TOUGH2 model elements are fully iterated, applying a programmed reprocessing of the Numerical Transport Code Functionalization model-element in an automated Outside Balance Iteration loop. The natural, convective airflow field and the heat and mass transport in a representative emplacement drift during postclosure are explicitly solved in the new model. The results demonstrate that the direction and magnitude of the air circulation patterns and all transport modes are strongly affected by the heat and moisture transport processes in the surrounding rock, justifying the need for a coupled, fully iterated model solution such as the one presented in the paper.
Hierarchic modeling of heat exchanger thermal hydraulics
International Nuclear Information System (INIS)
Horvat, A.; Koncar, B.
2002-01-01
Volume Averaging Technique (VAT) is employed in order to model the heat exchanger cross-flow as a porous media flow. As the averaging of the transport equations lead to a closure problem, separate relations are introduced to model interphase momentum and heat transfer between fluid flow and the solid structure. The hierarchic modeling is used to calculate the local drag coefficient C d as a function of Reynolds number Re h . For that purpose a separate model of REV is built and DNS of flow through REV is performed. The local values of heat transfer coefficient h are obtained from available literature. The geometry of the simulation domain and boundary conditions follow the geometry of the experimental test section used at U.C.L.A. The calculated temperature fields reveal that the geometry with denser pin-fins arrangement (HX1) heats fluid flow faster. The temperature field in the HX2 exhibits the formation of thermal boundary layer between pin-fins, which has a significant role in overall thermal performance of the heat exchanger. Although presented discrepancies of the whole-section drag coefficient C d are large, we believe that hierarchic modeling is an appropriate strategy for calculation of complex transport phenomena in heat exchanger geometries.(author)
International Nuclear Information System (INIS)
Sohn, Chae Hoon
2007-01-01
Extinction characteristics of hydrogen-air diffusion flames are investigated numerically by adopting counterflow flame configuration. At various pressures, effect of radiative heat loss on flame extinction is examined. Only gas-phase radiation is considered here. Radiative heat loss depends on flame thickness, temperature, H 2 O concentration, and pressure. From flame structures at various pressures, flame thickness decreases with pressure, but its gradient decreases at high pressure. Flame temperature and mole fraction of H 2 O increase slightly with pressure. Accordingly, as pressure increases, radiative heat loss becomes dominant. When radiative heat loss is considered, radiation-induced extinction is observed at low strain rate in addition to transport-induced extinction. As pressure increases, flammable region shifts to the high-temperature region and then, shrunk to the point on the coordinate plane of flame temperature and strain rate
Transport modelling including radial electric field and plasma rotation
International Nuclear Information System (INIS)
Fukuyama, A.; Fuji, Y.; Itoh, S.-I.
1994-01-01
Using a simple turbulent transport model with a constant diffusion coefficient and a fixed temperature profile, the density profile in a steady state and the transient behaviour during the co and counter neutral beam injection are studied. More consistent analysis has been initiated with a turbulent transport model based on the current diffusive high-n ballooning mode. The enhancement of the radial electric field due to ion orbit losses and the reduction of the transport due to the poloidal rotation shear are demonstrated. The preliminary calculation indicates a sensitive temperature dependence of the density profile. (author)
Benchmarking of a Markov multizone model of contaminant transport.
Jones, Rachael M; Nicas, Mark
2014-10-01
A Markov chain model previously applied to the simulation of advection and diffusion process of gaseous contaminants is extended to three-dimensional transport of particulates in indoor environments. The model framework and assumptions are described. The performance of the Markov model is benchmarked against simple conventional models of contaminant transport. The Markov model is able to replicate elutriation predictions of particle deposition with distance from a point source, and the stirred settling of respirable particles. Comparisons with turbulent eddy diffusion models indicate that the Markov model exhibits numerical diffusion in the first seconds after release, but over time accurately predicts mean lateral dispersion. The Markov model exhibits some instability with grid length aspect when turbulence is incorporated by way of the turbulent diffusion coefficient, and advection is present. However, the magnitude of prediction error may be tolerable for some applications and can be avoided by incorporating turbulence by way of fluctuating velocity (e.g. turbulence intensity). © The Author 2014. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.
Modeling microscale heat transfer using Calore.
Energy Technology Data Exchange (ETDEWEB)
Gallis, Michail A.; Rader, Daniel John; Wong, Chung-Nin Channy; Bainbridge, Bruce L.; Torczynski, John Robert; Piekos, Edward Stanley
2005-09-01
Modeling microscale heat transfer with the computational-heat-transfer code Calore is discussed. Microscale heat transfer problems differ from their macroscopic counterparts in that conductive heat transfer in both solid and gaseous materials may have important noncontinuum effects. In a solid material, three noncontinuum effects are considered: ballistic transport of phonons across a thin film, scattering of phonons from surface roughness at a gas-solid interface, and scattering of phonons from grain boundaries within the solid material. These processes are modeled for polycrystalline silicon, and the thermal-conductivity values predicted by these models are compared to experimental data. In a gaseous material, two noncontinuum effects are considered: ballistic transport of gas molecules across a thin gap and accommodation of gas molecules to solid conditions when reflecting from a solid surface. These processes are modeled for arbitrary gases by allowing the gas and solid temperatures across a gas-solid interface to differ: a finite heat transfer coefficient (contact conductance) is imposed at the gas-solid interface so that the temperature difference is proportional to the normal heat flux. In this approach, the behavior of gas in the bulk is not changed from behavior observed under macroscopic conditions. These models are implemented in Calore as user subroutines. The user subroutines reside within Sandia's Source Forge server, where they undergo version control and regression testing and are available to analysts needing these capabilities. A Calore simulation is presented that exercises these models for a heated microbeam separated from an ambient-temperature substrate by a thin gas-filled gap. Failure to use the noncontinuum heat transfer models for the solid and the gas causes the maximum temperature of the microbeam to be significantly underpredicted.
Manipulation of heat-diffusion channel in laser thermal lithography.
Wei, Jingsong; Wang, Yang; Wu, Yiqun
2014-12-29
Laser thermal lithography is a good alternative method for forming small pattern feature size by taking advantage of the structural-change threshold effect of thermal lithography materials. In this work, the heat-diffusion channels of laser thermal lithography are first analyzed, and then we propose to manipulate the heat-diffusion channels by inserting thermal conduction layers in between channels. Heat-flow direction can be changed from the in-plane to the out-of-plane of the thermal lithography layer, which causes the size of the structural-change threshold region to become much smaller than the focused laser spot itself; thus, nanoscale marks can be obtained. Samples designated as "glass substrate/thermal conduction layer/thermal lithography layer (100 nm)/thermal conduction layer" are designed and prepared. Chalcogenide phase-change materials are used as thermal lithography layer, and Si is used as thermal conduction layer to manipulate heat-diffusion channels. Laser thermal lithography experiments are conducted on a home-made high-speed rotation direct laser writing setup with 488 nm laser wavelength and 0.90 numerical aperture of converging lens. The writing marks with 50-60 nm size are successfully obtained. The mark size is only about 1/13 of the focused laser spot, which is far smaller than that of the light diffraction limit spot of the direct laser writing setup. This work is useful for nanoscale fabrication and lithography by exploiting the far-field focusing light system.
Temperature mapping, thermal diffusivity and subsoil heat flux at ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
vide an understanding of the gain or loss of heat by the soil from the atmosphere. Many studies made earlier have been related to sim- ilar issues such as prediction of soil tempera- tures; heat storage variations; thermal diffusivity of the soil, etc. (Kelkar et al 1980; Chowdhury et al 1991; Lamba and Khambete 1991; Retnaku ...
Discrete Diffusion Monte Carlo for Electron Thermal Transport
Chenhall, Jeffrey; Cao, Duc; Wollaeger, Ryan; Moses, Gregory
2014-10-01
The iSNB (implicit Schurtz Nicolai Busquet electron thermal transport method of Cao et al. is adapted to a Discrete Diffusion Monte Carlo (DDMC) solution method for eventual inclusion in a hybrid IMC-DDMC (Implicit Monte Carlo) method. The hybrid method will combine the efficiency of a diffusion method in short mean free path regions with the accuracy of a transport method in long mean free path regions. The Monte Carlo nature of the approach allows the algorithm to be massively parallelized. Work to date on the iSNB-DDMC method will be presented. This work was supported by Sandia National Laboratory - Albuquerque.
Modeling Diffusion and Buoyancy-Driven Convection with Application to Geological CO2 Storage
Allen, Rebecca
2015-04-01
ABSTRACT Modeling Diffusion and Buoyancy-Driven Convection with Application to Geological CO2 Storage Rebecca Allen Geological CO2 storage is an engineering feat that has been undertaken around the world for more than two decades, thus accurate modeling of flow and transport behavior is of practical importance. Diffusive and convective transport are relevant processes for buoyancy-driven convection of CO2 into underlying fluid, a scenario that has received the attention of numerous modeling studies. While most studies focus on Darcy-scale modeling of this scenario, relatively little work exists at the pore-scale. In this work, properties evaluated at the pore-scale are used to investigate the transport behavior modeled at the Darcy-scale. We compute permeability and two different forms of tortuosity, namely hydraulic and diffusive. By generating various pore ge- ometries, we find hydraulic and diffusive tortuosity can be quantitatively different in the same pore geometry by up to a factor of ten. As such, we emphasize that these tortuosities should not be used interchangeably. We find pore geometries that are characterized by anisotropic permeability can also exhibit anisotropic diffusive tortuosity. This finding has important implications for buoyancy-driven convection modeling; when representing the geological formation with an anisotropic permeabil- ity, it is more realistic to also account for an anisotropic diffusivity. By implementing a non-dimensional model that includes both a vertically and horizontally orientated 5 Rayleigh number, we interpret our findings according to the combined effect of the anisotropy from permeability and diffusive tortuosity. In particular, we observe the Rayleigh ratio may either dampen or enhance the diffusing front, and our simulation data is used to express the time of convective onset as a function of the Rayleigh ratio. Also, we implement a lattice Boltzmann model for thermal convective flows, which we treat as an analog for
Helium, Iron and Electron Particle Transport and Energy Transport Studies on the TFTR Tokamak
Synakowski, E. J.; Efthimion, P. C.; Rewoldt, G.; Stratton, B. C.; Tang, W. M.; Grek, B.; Hill, K. W.; Hulse, R. A.; Johnson, D .W.; Mansfield, D. K.; McCune, D.; Mikkelsen, D. R.; Park, H. K.; Ramsey, A. T.; Redi, M. H.; Scott, S. D.; Taylor, G.; Timberlake, J.; Zarnstorff, M. C. (Princeton Univ., NJ (United States). Plasma Physics Lab.); Kissick, M. W. (Wisconsin Univ., Madison, WI (United States))
1993-03-01
Results from helium, iron, and electron transport on TFTR in L-mode and Supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the Supershot The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the Supershot, differences are found in the L-Mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of three larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor.
Helium, iron and electron particle transport and energy transport studies on the TFTR tokamak
International Nuclear Information System (INIS)
Synakowski, E.J.; Efthimion, P.C.; Rewoldt, G.; Stratton, B.C.; Tang, W.M.; Grek, B.; Hill, K.W.; Hulse, R.A.; Johnson, D.W.; Mansfield, D.K.; McCune, D.; Mikkelsen, D.R.; Park, H.K.; Ramsey, A.T.; Redi, M.H.; Scott, S.D.; Taylor, G.; Timberlake, J.; Zarnstorff, M.C.
1993-03-01
Results from helium, iron, and electron transport on TFTR in L-mode and Supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the Supershot The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the Supershot, differences are found in the L-Mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of three larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor
Convective and diffusive effects on particle transport in asymmetric periodic capillaries.
Directory of Open Access Journals (Sweden)
Nazmul Islam
Full Text Available We present here results of a theoretical investigation of particle transport in longitudinally asymmetric but axially symmetric capillaries, allowing for the influence of both diffusion and convection. In this study we have focused attention primarily on characterizing the influence of tube geometry and applied hydraulic pressure on the magnitude, direction and rate of transport of particles in axi-symmetric, saw-tooth shaped tubes. Three initial value problems are considered. The first involves the evolution of a fixed number of particles initially confined to a central wave-section. The second involves the evolution of the same initial state but including an ongoing production of particles in the central wave-section. The third involves the evolution of particles a fully laden tube. Based on a physical model of convective-diffusive transport, assuming an underlying oscillatory fluid velocity field that is unaffected by the presence of the particles, we find that transport rates and even net transport directions depend critically on the design specifics, such as tube geometry, flow rate, initial particle configuration and whether or not particles are continuously introduced. The second transient scenario is qualitatively independent of the details of how particles are generated. In the third scenario there is no net transport. As the study is fundamental in nature, our findings could engender greater understanding of practical systems.
Resuspension of toxic aerosol using MATHEW--ADPIC wind field--transport and diffusion codes
International Nuclear Information System (INIS)
Porch, W.M.
1979-01-01
Computer codes have been written which estimate toxic aerosol resuspension based on computed deposition from a primary source, wind, and surface characteristics. The primary deposition pattern and the transport, diffusion, and redeposition of the resuspended toxic aerosol are calculated using a mass-consistent wind field model including topography (MATHEW) and a particle-in-cell diffusion and transport model (ADPIC) which were developed at LLL. The source term for resuspended toxic aerosol is determined by multiplying the total aerosol flux as a function of wind speed by the area of highest concentration and the fraction of suspended material estimated to be toxic. Preliminary calculations based on a test problem at the Nevada Test Site determined an hourly averaged maximum resuspension factor of 10 -4 for a 15 m/sec wind which is within an admittedly large range of resuspension factor measurements using experimental data
Heat transport and surface heat transfer with helium in rotating channels
International Nuclear Information System (INIS)
Schnapper, C.
1978-06-01
Heat transport and surface heat transfer with helium in rotating radially arranged channels were experimentally studied with regard to cooling of large turbogenerators with superconducting windings. Measurements with thermosiphon and thermosiphon loops of different channel diameters were performed, and results are presented. The thermodynamic state of the helium in a rotating thermosiphon and the mass flow rate in a thermosiphon loop is characterized by formulas. Heat transport by directed convection in thermosiphon loops is found to be more efficient 12 cm internal convection in thermosiphons. Steady state is reached sooner in thermosiphon loops than in thermosiphons, when heat load suddenly changes. In a very large centrifugal field single-phase heat transfer with natural and forced convection is described by similar formulas which are also applicable 10 thermosiphons in gravitation field or to heat transfer to non-rotating helium. (orig.) [de
Modelling of ion thermal transport in ergodic region of collisionless toroidal plasma
International Nuclear Information System (INIS)
Kanno, Ryutaro; Nunami, Masanori; Satake, Shinsuke; Ohyabu, Nobuyoshi; Takamaru, Hisanori; Okamoto, Masao
2009-09-01
In recent tokamak experiments it has been found that so-called diffusion theory based on the 'diffusion of magnetic field lines' overestimates the radial energy transport in the ergodic region of the collisionless plasma affected by resonant magnetic perturbations (RMPs), though the RMPs induce chaotic behavior of the magnetic field lines. The result implies that the modelling of the transport should be reconsidered for low collisionality cases. A computer simulation study of transport in the ergodic region is required for understanding fundamental properties of collisionless ergodized-plasmas, estimating the transport coefficients, and reconstructing the modelling of the transport. In this paper, we report the simulation study of thermal transport in the ergodic region under the assumption of neglecting effects of an electric field, impurities and neutrals. Because of the simulations neglecting interactions with different particle-species and saving the computational time, we treat ions (protons) in our numerical-study of the transport. We find that the thermal diffusivity in the ergodic region is extremely small compared to the one predicted by the theory of field-line diffusion and that the diffusivity depends on both the collision frequency and the strength of RMPs even for the collisionless ergodized-plasma. (author)
International Nuclear Information System (INIS)
Icleanu, D.L.; Prisecaru, I.
2015-01-01
This paper aims at modeling the cooling of the primary heat transport system using shutdown cooling system (SDCS), for a CANDU 6 NPP in all operating modes, normal and abnormal (particularly in case of LOCA accident), using the Flowmaster calculation code. The modelling of heavy water flow through the shutdown cooling system and primary heat transport system was performed to determine the distribution of flows, pressure in various areas of the hydraulic circuit and the pressure loss corresponding to the components but also for the heat calculation of the heat exchangers related to the system. The results of the thermo-hydraulic analysis show that in all cases analyzed, normal operation and for LOCA accident regime, the performance requirements are confirmed by analysis
Experimental Electron Heat Diffusion in TJ-II ECRH Plasmas
Energy Technology Data Exchange (ETDEWEB)
Vargas, V.I.; Lopez-Bruna, D.; Herranz, J.; Castejon, F.
2006-07-01
Interpretative transport has been used to revisit the global scalings of TJ-II ECRH plasmas from a local perspective. Density, rotational transform and ERCH power scans were analysed based upon Thomson Scattering data (electron density and temperature) in steady state discharges. A simple formula to obtain the thermal conductivity, assuming pure diffusion and negligible convective heat fluxes was used in a set of 161 discharges. All the analysis was performed with the ASTRA transport shell. The density scan indicates that inside n=0,4 there is no significant change of e with density in the range studied (0.4
Experimental Electron Heat Diffusion in TJ-II ECRH Plasmas
International Nuclear Information System (INIS)
Vargas, V.I.; Lopez-Bruna, D.; Herranz, J.; Castejon, F.
2006-01-01
Interpretative transport has been used to revisit the global scalings of TJ-II ECRH plasmas from a local perspective. Density, rotational transform and ERCH power scans were analysed based upon Thomson Scattering data (electron density and temperature) in steady state discharges. A simple formula to obtain the thermal conductivity, assuming pure diffusion and negligible convective heat fluxes was used in a set of 161 discharges. All the analysis was performed with the ASTRA transport shell. The density scan indicates that inside n=0,4 there is no significant change of e with density in the range studied (0.4 (1019m-3) 1.0), while in 0,5 <0,8 approximately, e decreases with density. In the rotational transform scan it is found that the values of e when a low order rational of the rotational transform is present locally seem to be smaller for the corresponding range, although it is apparent a general beneficial effect of the corresponding change in magnetic structure. Finally, in the ECRH power scan, e is found to have an overall increment in 0,2< n0,6 when QECH increases from 200 to 400 kW, although it is less significant in the density gradient region (n 0,7). (Author) 22 refs
Directory of Open Access Journals (Sweden)
Dietmar Gerteisen
2013-09-01
Full Text Available In order to model the liquid water transport in the porous materials used in polymer electrolyte membrane (PEM fuel cells, the pore network models are often applied. The presented model is a novel approach to further develop these models towards a percolation model that is based on the fiber structure rather than the pore structure. The developed algorithm determines the stable liquid water paths in the gas diffusion layer (GDL structure and the transitions from the paths to the subsequent paths. The obtained water path network represents the basis for the calculation of the percolation process with low calculation efforts. A good agreement with experimental capillary pressure-saturation curves and synchrotron liquid water visualization data from other literature sources is found. The oxygen diffusivity for the GDL with liquid water saturation at breakthrough reveals that the porosity is not a crucial factor for the limiting current density. An algorithm for condensation is included into the model, which shows that condensing water is redirecting the water path in the GDL, leading to an improved oxygen diffusion by a decreased breakthrough pressure and changed saturation distribution at breakthrough.
Advanced diffusion processes and phenomena
Öchsner, Andreas; Belova, Irina
2014-01-01
This topical volume on Advanced Diffusion Processes and Phenomena addresses diffusion in a wider sense of not only mass diffusion but also heat diffusion in fluids and solids. Both diffusion phenomena play an important role in the characterization of engineering materials and corresponding structures. Understanding these different transport phenomena at many levels, from atomistic to macro, has therefore long attracted the attention of many researchers in materials science and engineering and related disciplines. The present topical volume captures a representative cross-section of some of the
Research on heat and mass transfer model for passive containment cooling system
International Nuclear Information System (INIS)
Jiang Xiaowei; Yu Hongxing; Sun Yufa; Huang Daishun
2013-01-01
Different with the traditional dry style containment design without external cooling, the PCCS design increased the temperature difference between the wall and the containment atmosphere significantly, and also the absolute temperature of the containment surfaces will be lower, affecting properties relevant in the condensation process. A research on the heat and mass transfer model has been done in this paper, especially the improvement on the condensation and evaporation model in the presence of noncondensable gases. Firstly, the Peterson's diffusion layer model was proved to equivalent to the stagnant film model adopted by CONTAIN code using the Clausius-Clapeyron equation, then a factor which can be used to stagnant film model was derived from the comparison between the Y.Liao's generalized diffusion layer model and the Peterson's diffusion layer model. Finally, the model in CONTAIN code used to compute the condensation and evaporation mass flux was modified using the factor, and the Wisconsin condensation tests and Westinghouse film evaporation on heated plate tests were simulated which had proved the improved model can predict more closer value of the heat and mass transfer coefficient to experimental value than original model. (authors)
Roubíček, Tomáš; Tomassetti, Giuseppe
2018-06-01
A theory of elastic magnets is formulated under possible diffusion and heat flow governed by Fick's and Fourier's laws in the deformed (Eulerian) configuration, respectively. The concepts of nonlocal nonsimple materials and viscous Cahn-Hilliard equations are used. The formulation of the problem uses Lagrangian (reference) configuration while the transport processes are pulled back. Except the static problem, the demagnetizing energy is ignored and only local non-self-penetration is considered. The analysis as far as existence of weak solutions of the (thermo) dynamical problem is performed by a careful regularization and approximation by a Galerkin method, suggesting also a numerical strategy. Either ignoring or combining particular aspects, the model has numerous applications as ferro-to-paramagnetic transformation in elastic ferromagnets, diffusion of solvents in polymers possibly accompanied by magnetic effects (magnetic gels), or metal-hydride phase transformation in some intermetallics under diffusion of hydrogen accompanied possibly by magnetic effects (and in particular ferro-to-antiferromagnetic phase transformation), all in the full thermodynamical context under large strains.
Non-kinematic Flux-transport Dynamos Including the Effects of Diffusivity Quenching
Energy Technology Data Exchange (ETDEWEB)
Ichimura, Chiaki; Yokoyama, Takaaki [Department of Earth and Planetary Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
2017-04-10
Turbulent magnetic diffusivity is quenched when strong magnetic fields suppress turbulent motion in a phenomenon known as diffusivity quenching. Diffusivity quenching can provide a mechanism for amplifying magnetic field and influencing global velocity fields through Lorentz force feedback. To investigate this effect, we conducted mean field flux-transport dynamo simulations that included the effects of diffusivity quenching in a non-kinematic regime. We found that toroidal magnetic field strength is amplified by up to approximately 1.5 times in the convection zone as a result of diffusivity quenching. This amplification is much weaker than that in kinematic cases as a result of Lorentz force feedback on the system’s differential rotation. While amplified toroidal fields lead to the suppression of equatorward meridional flow locally near the base of the convection zone, large-scale equatorward transport of magnetic flux via meridional flow, which is the essential process of the flux-transport dynamo, is sustainable in our calculations.
Electron Currents and Heating in the Ion Diffusion Region of Asymmetric Reconnection
Graham, D. B.; Khotyaintsev, Yu. V.; Norgren, C.; Vaivads, A.; Andre, M.; Lindqvist, P. A.; Marklund, G. T.; Ergun, R. E.; Paterson, W. R.; Gershman, D. J.;
2016-01-01
In this letter the structure of the ion diffusion region of magnetic reconnection at Earths magnetopause is investigated using the Magnetospheric Multiscale (MMS) spacecraft. The ion diffusion region is characterized by a strong DC electric field, approximately equal to the Hall electric field, intense currents, and electron heating parallel to the background magnetic field. Current structures well below ion spatial scales are resolved, and the electron motion associated with lower hybrid drift waves is shown to contribute significantly to the total current density. The electron heating is shown to be consistent with large-scale parallel electric fields trapping and accelerating electrons, rather than wave-particle interactions. These results show that sub-ion scale processes occur in the ion diffusion region and are important for understanding electron heating and acceleration.
GRIZZLY Model of Multi-Reactive Species Diffusion, Moisture/Heat Transfer and Alkali-Silica Reaction for Simulating Concrete Aging and Degradation
Energy Technology Data Exchange (ETDEWEB)
Huang, Hai [Idaho National Lab. (INL), Idaho Falls, ID (United States); Spencer, Benjamin W. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Cai, Guowei [Vanderbilt Univ., Nashville, TN (United States)
2015-09-01
Concrete is widely used in the construction of nuclear facilities because of its structural strength and its ability to shield radiation. The use of concrete in nuclear power plants for containment and shielding of radiation and radioactive materials has made its performance crucial for the safe operation of the facility. As such, when life extension is considered for nuclear power plants, it is critical to have accurate and reliable predictive tools to address concerns related to various aging processes of concrete structures and the capacity of structures subjected to age-related degradation. The goal of this report is to document the progress of the development and implementation of a fully coupled thermo-hydro-mechanical-chemical model in GRIZZLY code with the ultimate goal to reliably simulate and predict long-term performance and response of aged NPP concrete structures subjected to a number of aging mechanisms including external chemical attacks and volume-changing chemical reactions within concrete structures induced by alkali-silica reactions and long-term exposure to irradiation. Based on a number of survey reports of concrete aging mechanisms relevant to nuclear power plants and recommendations from researchers in concrete community, we’ve implemented three modules during FY15 in GRIZZLY code, (1) multi-species reactive diffusion model within cement materials; (2) coupled moisture and heat transfer model in concrete; and (3) anisotropic, stress-dependent, alkali-silica reaction induced swelling model. The multi-species reactive diffusion model was implemented with the objective to model aging of concrete structures subjected to aggressive external chemical attacks (e.g., chloride attack, sulfate attack, etc.). It considers multiple processes relevant to external chemical attacks such as diffusion of ions in aqueous phase within pore spaces, equilibrium chemical speciation reactions and kinetic mineral dissolution/precipitation. The moisture/heat
Hydrogen bonds and heat diffusion in α-helices: a computational study.
Miño, German; Barriga, Raul; Gutierrez, Gonzalo
2014-08-28
Recent evidence has shown a correlation between the heat diffusion pathways and the known allosteric communication pathways in proteins. Allosteric communication in proteins is a central, yet unsolved, problem in biochemistry, and the study and characterization of the structural determinants that mediate energy transfer among different parts of proteins is of major importance. In this work, we characterized the role of hydrogen bonds in diffusivity of thermal energy for two sets of α-helices with different abilities to form hydrogen bonds. These hydrogen bonds can be a constitutive part of the α-helices or can arise from the lateral chains. In our in vacuo simulations, it was observed that α-helices with a higher possibility of forming hydrogen bonds also had higher rates of thermalization. Our simulations also revealed that heat readily flowed through atoms involved in hydrogen bonds. As a general conclusion, according to our simulations, hydrogen bonds fulfilled an important role in heat diffusion in structural patters of proteins.
Heat transport in McMurdo Sound first-year fast ice
Trodahl, H. J.; McGuinness, M. J.; Langhorne, P. J.; Collins, K.; Pantoja, A. E.; Smith, I. J.; Haskell, T. G.
2000-05-01
We have monitored the temperature field within first-year sea ice in McMurdo Sound over two winter seasons, with sufficient resolution to determine the thermal conductivity from the thermal waves propagating down through the ice. Data reduction has been accomplished by direct reference to energy conservation, relating the rate of change of the internal energy density to the divergence of the heat current density. Use of this procedure, rather than the wave attenuation predicted by the thermal diffusion equation, avoids difficulties arising from a strongly temperature dependent thermal diffusivity. The thermal conductivity is an input parameter for ice growth and climate models, and the values commonly used in the models are predicted to depend on temperature, salinity, and the volume fraction of air. The present measurements were performed at depths in the ice where the air volume is small and the salinity is nearly constant, and they permit the determination of the absolute magnitude of the thermal conductivity and its temperature dependence. The weak temperature dependence is similar to that predicted by the models in the literature, but the magnitude is smaller by ˜10% than the predicted value most commonly used in climate and sea ice models. In the first season we find an additional scatter in the results at driving temperature gradients larger than ˜10-15 °C/m. We suggest that the scatter arises from a nonlinear contribution to the heat current, possibly associated with the onset of convective motion in brine inclusions. Episodic convective events are also observed. We have further determined the growth rate of the ice and compared it with the rate explained by the heat flux from the ice-water interface. The data show a sudden rise of growth rate, without a rise in heat flux through the ice, which coincides in time and depth with the appearance of platelet ice. Finally, we discuss the observation of radiative solar heating at depth in the ice and
Transport properties site descriptive model. Guidelines for evaluation and modelling
International Nuclear Information System (INIS)
Berglund, Sten; Selroos, Jan-Olof
2004-04-01
transport properties, and hence the guidelines in this report, involve two main categories of parameters: Parameters that characterise the retention properties of geologic materials. These parameters quantify the diffusion and sorption properties of intact and altered rock, fracture coatings and fracture-filling materials, and are described within the framework of the 3D geometric models devised by Geology. Parameters that characterise solute transport along flow paths (flow-related transport parameters). These parameters include the 'F-parameter' and 'water travel time', tw, and parameters that account for spatial variability in diffusion and sorption. The flow-related parameters are obtained by means of particle tracking simulations in groundwater flow models
Photothermal heating in metal-embedded microtools for material transport
DEFF Research Database (Denmark)
Villangca, Mark Jayson; Palima, Darwin; Banas, Andrew Rafael
2016-01-01
Material transport is an important mechanism in microfluidics and drug delivery. The methods and solutions found in literature involve passively diffusing structures, microneedles and chemically fueled structures. In this work, we make use of optically actuated microtools with embedded metal layer...... as heating element for controlled loading and release. The new microtools take advantage of the photothermal-induced convection current to load and unload cargo. We also discuss some challenges encountered in realizing a self-contained polymerized microtool. Microfluidic mixing, fluid flow control...... and convection currents have been demonstrated both experimentally and numerically for static metal thin films or passively floating nanoparticles. Here we show an integration of aforementioned functionalities in an opticallyfabricated and actuated microtool. As proof of concept, we demonstrate loading...
Energy Technology Data Exchange (ETDEWEB)
Maher, A.R.; Al-Baghdadi, S. [International Technological Univ., London (United Kingdom). Dept. of Mechanical Engineering; Haroun, A.K.; Al-Janabi, S. [Babylon Univ., Babylon (Iraq). Dept. of Mechanical Engineering
2007-07-01
Fuel cell technology is expected to play an important role in meeting the growing demand for distributed generation because it can convert the chemical energy of a clean fuel directly into electrical energy. An operating fuel cell has varying local conditions of temperature, humidity, and power generation across the active area of the fuel cell in 3D. This paper presented a model that was developed to improve the basic understanding of the transport phenomena and thermal stresses in PEM fuel cells, and to investigate the behaviour of polymer membrane under hygro and thermal stresses during the cell operation. This comprehensive 3D, multiphase, non-isothermal model accounts for the major transport phenomena in a PEM fuel cell, notably convective and diffusive heat and mass transfer; electrode kinetics; transport and phase change mechanism of water; and potential fields. The model accounts for the liquid water flux inside the gas diffusion layers by viscous and capillary forces and can therefore predict the amount of liquid water inside the gas diffusion layers. This study also investigated the key parameters affecting fuel cell performance including geometry, materials and operating conditions. The model considers the many interacting, complex electrochemical, transport phenomena, thermal stresses and deformation that cannot be studied experimentally. It was concluded that the model can provide a computer-aided tool for the design and optimization of future fuel cells with much higher power density and lower cost. 21 refs., 2 tabs., 14 figs.
Wen, Jessica; Koo, Soh Myoung; Lape, Nancy
2018-02-01
While predictive models of transdermal transport have the potential to reduce human and animal testing, microscopic stratum corneum (SC) model output is highly dependent on idealized SC geometry, transport pathway (transcellular vs. intercellular), and penetrant transport parameters (e.g., compound diffusivity in lipids). Most microscopic models are limited to a simple rectangular brick-and-mortar SC geometry and do not account for variability across delivery sites, hydration levels, and populations. In addition, these models rely on transport parameters obtained from pure theory, parameter fitting to match in vivo experiments, and time-intensive diffusion experiments for each compound. In this work, we develop a microscopic finite element model that allows us to probe model sensitivity to variations in geometry, transport pathway, and hydration level. Given the dearth of experimentally-validated transport data and the wide range in theoretically-predicted transport parameters, we examine the model's response to a variety of transport parameters reported in the literature. Results show that model predictions are strongly dependent on all aforementioned variations, resulting in order-of-magnitude differences in lag times and permeabilities for distinct structure, hydration, and parameter combinations. This work demonstrates that universally predictive models cannot fully succeed without employing experimentally verified transport parameters and individualized SC structures. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.
International Nuclear Information System (INIS)
Unal, C.; Bohl, W.R.; Pasamehmetoglu, K.O.
1999-01-01
Complex ladder-like structures recently have been considered as the target design for accelerator applications. The decay heat, during a postulated beyond design-basis loss-of-coolant accident in the target where all normal and emergency cooling fails, is removed mainly by radiation heat transfer. Modeling of the radiation transport in complex ladder-like structures has several challenges and limitations when the standard net-radiation model is used. This paper proposes a simplified lumped, or 'hot-rung' model, that considers the worst elements and utilizes the standard net-radiation method. The net-radiation model would under-predict structure temperatures if surfaces were subject to non-uniform radiosity. The proposed model was assessed to suggest corrections to account for the non-uniform radiosity. The non-uniform radiosity effect causes the proposed hot-rung model to under-predict the center-rung temperatures by ∼4-74 C when all parametrics, including temperatures up to 1500 C, were considered. These temperatures are small. The proposed model predicted that an important effect of decreasing the emissivity was smoothing of non-isothermal effects. The radiosity effects are more pronounced when there are strong temperature gradients. Uniform rung temperatures tend to decrease the radiosity effects. We concluded that a relatively simple model that is conservative with respect to radiosity effects could be developed. (orig.)
Poloidal profiles and transport during turbulent heating
International Nuclear Information System (INIS)
Mascheroni, P.L.
1977-01-01
The current penetration stage of a turbulently heated tokamak is modeled. The basic formulae are written in slab geometry since the dominant anomalous transport has a characteristic frequency much larger than the bounce frequency. Thus, the basic framework is provided by the Maxwell and fluid equations, with classical and anomalous transport. Quasi-neutrality is used. It is shown that the anomalous collision frequency dominates the anomalous viscosity and thermal conductivity, and that the convective wave transport can be neglected. For these numerical estimates, the leading term in the quasi-linear series is used. During the current penetration stage the distribution function for the particles will depart from a single Maxwellian type. Hence, the first objective was to numerically compare calculated poloidal magnetic field profiles with measured, published poloidal profiles. The poloidal magnetic field has been calculated using a code which handles the anomalous collision frequency self-consistently. The agreement is good, and it is concluded that the current penetration stage can be satisfactorily described by this model
Thickness Optimisation of Textiles Subjected to Heat and Mass Transport during Ironing
Directory of Open Access Journals (Sweden)
Korycki Ryszard
2016-09-01
Full Text Available Let us next analyse the coupled problem during ironing of textiles, that is, the heat is transported with mass whereas the mass transport with heat is negligible. It is necessary to define both physical and mathematical models. Introducing two-phase system of mass sorption by fibres, the transport equations are introduced and accompanied by the set of boundary and initial conditions. Optimisation of material thickness during ironing is gradient oriented. The first-order sensitivity of an arbitrary objective functional is analysed and included in optimisation procedure. Numerical example is the thickness optimisation of different textile materials in ironing device.
A Note on Diffusive Mass Transport.
Haynes, Henry W., Jr.
1986-01-01
Current chemical engineering textbooks teach that the driving force for diffusive mass transport in ideal solutions is the gradient in mole fraction. This is only true for ideal solution liquids. Therefore, it is shown that the appropriate driving force for use with ideal gases is the gradient in partial pressure. (JN)
MATHEMATICAL MODELLING OF OPERATION HEAT NETWORKS IN VIEW OF HEAT LOSS
Directory of Open Access Journals (Sweden)
ZBARAZ L. I.
2016-08-01
Full Text Available Goal. In recent years, due to a significant rise in price of energy, the reduction of direct costs for heating becomes a priority. In the utilities especially important to optimization of energy heating system equipment. During transport of thermal energy in the distribution networks thermal losses occur along the length of the hydraulic pipes and the coolant pumping losses. These loss-dependence of the particular distribution network. Changing temperature and the hydraulic regime at the source necessary to achieve the minimum cost of transport for today acting tariffs for energy. Scientific novelty. The studies received law changes head to the source at the qualitative and quantitative methods of regulation. Results. A mathematical model of an extensive network of decentralized heat source heating, which are analyzed using different methods of regulating and found the best.
Circum-Antarctic Shoreward Heat Transport Derived From an Eddy- and Tide-Resolving Simulation
Stewart, Andrew L.; Klocker, Andreas; Menemenlis, Dimitris
2018-01-01
Almost all heat reaching the bases of Antarctica's ice shelves originates from warm Circumpolar Deep Water in the open Southern Ocean. This study quantifies the roles of mean and transient flows in transporting heat across almost the entire Antarctic continental slope and shelf using an ocean/sea ice model run at eddy- and tide-resolving (1/48°) horizontal resolution. Heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day, respectively. It is shown that eddies transfer heat across the continental slope (ocean depths greater than 1,500 m), but tides produce a stronger shoreward heat flux across the shelf break (ocean depths between 500 m and 1,000 m). However, the tidal heat fluxes are approximately compensated by mean flows, leaving the eddy heat flux to balance the net shoreward heat transport. The eddy-driven cross-slope overturning circulation is too weak to account for the eddy heat flux. This suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around Antarctica, though likely modulated by tides and surface forcing.
Tait, Peter W
2011-07-01
Increasing heat may impede peoples' ability to be active outdoors thus limiting active transport options. Co-benefits from mitigation of and adaptation to global warming should not be assumed but need to be actively designed into strategies.
Oproglidis, T. A.; Karatsori, T. A.; Barraud, S.; Ghibaudo, G.; Dimitriadis, C. A.
2018-04-01
In this work, we extend our analytical compact model for nanoscale junctionless triple-gate (JL TG) MOSFETs, capturing carrier transport from drift-diffusion to quasi-ballistic regime. This is based on a simple formulation of the low-field mobility extracted from experimental data using the Y-function method, taking into account the ballistic carrier motion and an increased carrier scattering in process-induced defects near the source/drain regions. The case of a Schottky junction in non-ideal ohmic contact at the drain side was also taken into account by modifying the threshold voltage and ideality factor of the JL transistor. The model is validated with experimental data for n-channel JL TG MOSFETs with channel length varying from 95 down to 25 nm. It can be easily implemented as a compact model for use in Spice circuit simulators.
Turbulent transport in the atmospheric surface layer
Energy Technology Data Exchange (ETDEWEB)
Tagesson, Torbern [Dept. of Physical Geography and Ecosystem Science, Lund Univ., Lund (Sweden)
2012-04-15
In the modelling of transport and accumulation of the radioactive isotope carbon-14 (C-14) in the case of a potential release from a future repository of radioactive waste, it is important to describe the transport of the isotope in the atmosphere. This report aims to describe the turbulent transport within the lower part of the atmosphere; the inertial surface layer and the roughness sublayer. Transport in the inertial surface layer is dependent on several factors, whereof some can be neglected under certain circumstances. Under steady state conditions, fully developed turbulent conditions, in flat and horizontal homogeneous areas, it is possible to apply an eddy diffusivity approach for estimating vertical transport of C. The eddy diffusivity model assumes that there is proportionality between the vertical gradient and the transport of C. The eddy diffusivity is depending on the atmospheric turbulence, which is affected by the interaction between mean wind and friction of the ground surface and of the sensible heat flux in the atmosphere. In this report, it is described how eddy diffusivity of the inertial surface layer can be estimated from 3-d wind measurements and measurements of sensible heat fluxes. It is also described how to estimate the eddy diffusivity in the inertial surface layer from profile measurements of temperature and wind speed. Close to the canopy, wind and C profiles are influenced by effects of the surface roughness; this section of the atmosphere is called the roughness sublayer. Its height is up to {approx}3 times the height of the plant canopy. When the mean wind interacts with the canopy, turbulence is not only produced by shear stress and buoyancy, it is additionally created by wakes, which are formed behind the plants. Turbulence is higher than it would be over a flat surface, and the turbulent transport is hereby more efficient. Above the plant canopy, but still within the roughness sublayer, a function that compensates for the effect
Turbulent transport in the atmospheric surface layer
International Nuclear Information System (INIS)
Tagesson, Torbern
2012-04-01
In the modelling of transport and accumulation of the radioactive isotope carbon-14 (C-14) in the case of a potential release from a future repository of radioactive waste, it is important to describe the transport of the isotope in the atmosphere. This report aims to describe the turbulent transport within the lower part of the atmosphere; the inertial surface layer and the roughness sublayer. Transport in the inertial surface layer is dependent on several factors, whereof some can be neglected under certain circumstances. Under steady state conditions, fully developed turbulent conditions, in flat and horizontal homogeneous areas, it is possible to apply an eddy diffusivity approach for estimating vertical transport of C. The eddy diffusivity model assumes that there is proportionality between the vertical gradient and the transport of C. The eddy diffusivity is depending on the atmospheric turbulence, which is affected by the interaction between mean wind and friction of the ground surface and of the sensible heat flux in the atmosphere. In this report, it is described how eddy diffusivity of the inertial surface layer can be estimated from 3-d wind measurements and measurements of sensible heat fluxes. It is also described how to estimate the eddy diffusivity in the inertial surface layer from profile measurements of temperature and wind speed. Close to the canopy, wind and C profiles are influenced by effects of the surface roughness; this section of the atmosphere is called the roughness sublayer. Its height is up to ∼3 times the height of the plant canopy. When the mean wind interacts with the canopy, turbulence is not only produced by shear stress and buoyancy, it is additionally created by wakes, which are formed behind the plants. Turbulence is higher than it would be over a flat surface, and the turbulent transport is hereby more efficient. Above the plant canopy, but still within the roughness sublayer, a function that compensates for the effect of
Energy Technology Data Exchange (ETDEWEB)
Sachs, W. [Institut fuer Erdoel- und Erdgasforschung, Clausthal-Zellerfeld (Germany)
1998-12-31
Optimisation of gas production necessitates accurate knowledge of gas transport mechanisms. In view of the extreme temperatures, pressures, and permeability conditions of underground gas deposits, linear transfer of existing knowledge will be inappropriate. The author therefore uses a simple capillary bundle model with exemplary pressures, temperatures and permeabilities in order to assess the contribution of transport by diffusion. The diffusion coefficients, which are required for this and so far could not be measured under pressure, were determined by a new experimental method whose results will permit a better interpretation of the concentration dependence of the diffusion coefficient. The velocity of methane inflow and outflow in the water-filled pore space may provide knowledge on problems of gas storage in the pore space. (orig.) [Deutsch] Fuer den Foerderprozess und insbesondere seine Optimierung ist eine genaue Kenntnis der Transportmechanismen wesentlich. Unter den drastischen Bedingungen fuer Temperatur, Druck und Permeabilitaet tiefliegender Gas-Lagerstaetten mag die Uebertragung der bisherigen Vorstellungen ueber den Transport in der Lagerstaette zu einer unvollstaendigen Beschreibung fuehren. Unter Anwendung eines einfachen Kapillarbuendelmodells wird mit Beispielen fuer Druck, Temperatur und Permeabilitaet der moegliche Beitrag des Transports durch Diffusion abgeschaetzt. Zur Bestimmung der hierfuer notwendigen und bisher unter Druckbeaufschlagung nicht gemessenen Diffusionskoeffizienten wurde eine neue experimentelle Methode angewandt, deren Ergebnisse eine weiterfuehrende Interpretation der Konzentrationsabhaengigkeit des Diffusionskoeffizienten ermoeglichen. Auch fuer Fragestellungen der Speicherung von Gas im Porenraum kann die Geschwindigkeit der Ein- und Ausloesung von Methan im wasserhaltigen Porenraum von Interesse sein. (orig.)
CHMTRNS, Non-Equilibrium Chemical Transport Code
International Nuclear Information System (INIS)
Noorishad, J.; Carnahan, C.L.; Benson, L.V.
1998-01-01
1 - Description of program or function: CHMTRNS simulates solute transport for steady one-dimensional fluid flow by convection and diffusion or dispersion in a saturated porous medium based on the assumption of local chemical equilibrium. The chemical interactions included in the model are aqueous-phase complexation, solid-phase ion exchange of bare ions and complexes using the surface complexation model, and precipitation or dissolution of solids. The program can simulate the kinetic dissolution or precipitation for calcite and silica as well as irreversible dissolution of glass. Thermodynamic parameters are temperature dependent and are coupled to a companion heat transport simulator; thus, the effects of transient temperature conditions can be considered. Options for oxidation-reduction (redox) and C-13 fractionation as well as non-isothermal conditions are included. 2 - Method of solution: The governing equations for both reactive chemical and heat transport are discretized in time and space. For heat transport, the Crank-Nicolson approximation is used in conjunction with a LU decomposition and backward substitution solution procedure. To deal with the strong nonlinearity of the chemical transport equations, a generalized Newton-Raphson method is used
Random variability in mesoscale wind observations and implications for diffusion models
Energy Technology Data Exchange (ETDEWEB)
Hanna, S.R. [Sigma Research Corp., Concord, MA (United States)
1994-12-31
The investigation reported in this paper grew out of a preliminary analysis of methods by which regional air quality models such as the Regional Oxidant Model account for horizontal transport and diffusion. It was discovered that there is a variety of often inconsistent methods used to parameterize horizontal diffusion at meso- and regional scales, and the time seemed ripe to review and compare and contrast these schemes. This paper provides a brief overview of the major issues that were uncovered and lists a few specific examples of the technical approaches that are used. Subsequent sections cover the basic physics of horizontal diffusion, the characteristics of observed wind fields, and methods of parameterizing horizontal diffusion in air quality models.
Possible role of oceanic heat transport in early Eocene climate
Sloan, L. C.; Walker, J. C.; Moore, T. C. Jr
1995-01-01
Increased oceanic heat transport has often been cited as a means of maintaining warm high-latitude surface temperatures in many intervals of the geologic past, including the early Eocene. Although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically, determining how additional oceanic heat transport would take place has yet to be accomplished. That the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked. Using early Eocene climate as an example, we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early Eocene conditions. Our interpolation of early Eocene paleotemperature data indicate that an approximately 30% increase in poleward heat transport would be required to maintain Eocene high-latitude temperatures. This increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early Eocene rates. Either oceanic processes were very different from those of the present to produce the early Eocene climate conditions or oceanic heat transport was not the primary cause of that climate. We believe that atmospheric processes, with contributions from other factors, such as clouds, were the most likely primary cause of early Eocene climate.
Macroscopic modeling for heat and water vapor transfer in dry snow by homogenization.
Calonne, Neige; Geindreau, Christian; Flin, Frédéric
2014-11-26
Dry snow metamorphism, involved in several topics related to cryospheric sciences, is mainly linked to heat and water vapor transfers through snow including sublimation and deposition at the ice-pore interface. In this paper, the macroscopic equivalent modeling of heat and water vapor transfers through a snow layer was derived from the physics at the pore scale using the homogenization of multiple scale expansions. The microscopic phenomena under consideration are heat conduction, vapor diffusion, sublimation, and deposition. The obtained macroscopic equivalent model is described by two coupled transient diffusion equations including a source term arising from phase change at the pore scale. By dimensional analysis, it was shown that the influence of such source terms on the overall transfers can generally not be neglected, except typically under small temperature gradients. The precision and the robustness of the proposed macroscopic modeling were illustrated through 2D numerical simulations. Finally, the effective vapor diffusion tensor arising in the macroscopic modeling was computed on 3D images of snow. The self-consistent formula offers a good estimate of the effective diffusion coefficient with respect to the snow density, within an average relative error of 10%. Our results confirm recent work that the effective vapor diffusion is not enhanced in snow.
International Nuclear Information System (INIS)
Li Rong; Yang Fuquan; Sloan, James J; Scholtz, M Trevor
2011-01-01
We have combined the US EPA MM5/MCIP/SMOKE/CMAQ modeling system with a dynamic soil model, the pesticide emission model (PEM), to create a multimedia chemical transport model capable of describing the important physical and chemical processes involving pesticides in the soil, in the atmosphere, and on the surface of vegetation. These processes include: agricultural practices (e.g. soil tilling and pesticide application mode); advection and diffusion of pesticides, moisture, and heat in the soil; partitioning of pesticides between soil organic carbon and interstitial water and air; emissions from the soil to the atmosphere; gas-particle partitioning and transport in the atmosphere; and atmospheric chemistry and dry and wet deposition of pesticides to terrestrial and water surfaces. The modeling system was tested by simulating toxaphene in a domain that covers most of North America for the period from 1 January 2000 to 31 December 2000. The results show obvious transport of the pesticide from the heavily contaminated soils in the southern United States and Mexico to water bodies including the Atlantic Ocean, the Gulf of Mexico and the Great Lakes, leading to significant dry and wet deposition into these ecosystems. The spatial distributions of dry and wet depositions differ because of their different physical mechanisms; the former follows the distribution of air concentrations whereas the latter is more biased to the North East due to the effect of precipitation.
Energy Technology Data Exchange (ETDEWEB)
Li Rong; Yang Fuquan; Sloan, James J [Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1 (Canada); Scholtz, M Trevor, E-mail: sloanj@connect.uwaterloo.ca [ORTECH Environmental, 2395 Speakman Drive, Mississauga, ON L5K 1B3 (Canada)
2011-07-15
We have combined the US EPA MM5/MCIP/SMOKE/CMAQ modeling system with a dynamic soil model, the pesticide emission model (PEM), to create a multimedia chemical transport model capable of describing the important physical and chemical processes involving pesticides in the soil, in the atmosphere, and on the surface of vegetation. These processes include: agricultural practices (e.g. soil tilling and pesticide application mode); advection and diffusion of pesticides, moisture, and heat in the soil; partitioning of pesticides between soil organic carbon and interstitial water and air; emissions from the soil to the atmosphere; gas-particle partitioning and transport in the atmosphere; and atmospheric chemistry and dry and wet deposition of pesticides to terrestrial and water surfaces. The modeling system was tested by simulating toxaphene in a domain that covers most of North America for the period from 1 January 2000 to 31 December 2000. The results show obvious transport of the pesticide from the heavily contaminated soils in the southern United States and Mexico to water bodies including the Atlantic Ocean, the Gulf of Mexico and the Great Lakes, leading to significant dry and wet deposition into these ecosystems. The spatial distributions of dry and wet depositions differ because of their different physical mechanisms; the former follows the distribution of air concentrations whereas the latter is more biased to the North East due to the effect of precipitation.
Li, Rong; Scholtz, M. Trevor; Yang, Fuquan; Sloan, James J.
2011-07-01
We have combined the US EPA MM5/MCIP/SMOKE/CMAQ modeling system with a dynamic soil model, the pesticide emission model (PEM), to create a multimedia chemical transport model capable of describing the important physical and chemical processes involving pesticides in the soil, in the atmosphere, and on the surface of vegetation. These processes include: agricultural practices (e.g. soil tilling and pesticide application mode); advection and diffusion of pesticides, moisture, and heat in the soil; partitioning of pesticides between soil organic carbon and interstitial water and air; emissions from the soil to the atmosphere; gas-particle partitioning and transport in the atmosphere; and atmospheric chemistry and dry and wet deposition of pesticides to terrestrial and water surfaces. The modeling system was tested by simulating toxaphene in a domain that covers most of North America for the period from 1 January 2000 to 31 December 2000. The results show obvious transport of the pesticide from the heavily contaminated soils in the southern United States and Mexico to water bodies including the Atlantic Ocean, the Gulf of Mexico and the Great Lakes, leading to significant dry and wet deposition into these ecosystems. The spatial distributions of dry and wet depositions differ because of their different physical mechanisms; the former follows the distribution of air concentrations whereas the latter is more biased to the North East due to the effect of precipitation.
International Nuclear Information System (INIS)
Premuda, F.
1983-01-01
Two lines in improved neutron diffusion theory extending the efficiency of finite-difference diffusion codes to the field of optically small systems, are here reviewed. The firs involves the nodal solution for tensorial diffusion equation in slab geometry and tensorial formulation in parallelepiped and cylindrical gemometry; the dependence of critical eigenvalue from small slab thicknesses is also analitically investigated and finally a regularized tensorial diffusion equation is derived for slab. The other line refer to diffusion models formally unchanged with respect to the classical one, but where new size-dependent RTGB definitions for diffusion parameters are adopted, requiring that they allow to reproduce, in diffusion approach, the terms of neutron transport global balance; the trascendental equation for the buckling, arising in slab, sphere and parallelepiped geometry from the above requirement, are reported and the sizedependence of the new diffusion coefficient and extrapolated end point is investigated
Directory of Open Access Journals (Sweden)
Sang Soon Hwang
2008-03-01
Full Text Available Modeling and simulation for heat and mass transport in micro channel are beingused extensively in researches and industrial applications to gain better understanding of thefundamental processes and to optimize fuel cell designs before building a prototype forengineering application. In this study, we used a single-phase, fully three dimensionalsimulation model for PEMFC that can deal with both anode and cathode flow field forexamining the micro flow channel with electrochemical reaction. The results show thathydrogen and oxygen were solely supplied to the membrane by diffusion mechanism ratherthan convection transport, and the higher pressure drop at cathode side is thought to becaused by higher flow rate of oxygen at cathode. And it is found that the amount of water incathode channel was determined by water formation due to electrochemical reaction pluselectro-osmotic mass flux directing toward the cathode side. And it is very important tomodel the back diffusion and electro-osmotic mass flux accurately since the two flux wasclosely correlated each other and greatly influenced for determination of ionic conductivityof the membrane which directly affects the performance of fuel cell.
Lee, Pil Hyong; Han, Sang Seok; Hwang, Sang Soon
2008-03-03
Modeling and simulation for heat and mass transport in micro channel are beingused extensively in researches and industrial applications to gain better understanding of thefundamental processes and to optimize fuel cell designs before building a prototype forengineering application. In this study, we used a single-phase, fully three dimensionalsimulation model for PEMFC that can deal with both anode and cathode flow field forexamining the micro flow channel with electrochemical reaction. The results show thathydrogen and oxygen were solely supplied to the membrane by diffusion mechanism ratherthan convection transport, and the higher pressure drop at cathode side is thought to becaused by higher flow rate of oxygen at cathode. And it is found that the amount of water incathode channel was determined by water formation due to electrochemical reaction pluselectro-osmotic mass flux directing toward the cathode side. And it is very important tomodel the back diffusion and electro-osmotic mass flux accurately since the two flux wasclosely correlated each other and greatly influenced for determination of ionic conductivityof the membrane which directly affects the performance of fuel cell.
Endothelial Thermotolerance Impairs Nanoparticle Transport in Tumors.
Bagley, Alexander F; Scherz-Shouval, Ruth; Galie, Peter A; Zhang, Angela Q; Wyckoff, Jeffrey; Whitesell, Luke; Chen, Christopher S; Lindquist, Susan; Bhatia, Sangeeta N
2015-08-15
The delivery of diagnostic and therapeutic agents to solid tumors is limited by physical transport barriers within tumors, and such restrictions directly contribute to decreased therapeutic efficacy and the emergence of drug resistance. Nanomaterials designed to perturb the local tumor environment with precise spatiotemporal control have demonstrated potential to enhance drug delivery in preclinical models. Here, we investigated the ability of one class of heat-generating nanomaterials called plasmonic nanoantennae to enhance tumor transport in a xenograft model of ovarian cancer. We observed a temperature-dependent increase in the transport of diagnostic nanoparticles into tumors. However, a transient, reversible reduction in this enhanced transport was seen upon reexposure to heating, consistent with the development of vascular thermotolerance. Harnessing these observations, we designed an improved treatment protocol combining plasmonic nanoantennae with diffusion-limited chemotherapies. Using a microfluidic endothelial model and genetic tools to inhibit the heat-shock response, we found that the ability of thermal preconditioning to limit heat-induced cytoskeletal disruption is an important component of vascular thermotolerance. This work, therefore, highlights the clinical relevance of cellular adaptations to nanomaterials and identifies molecular pathways whose modulation could improve the exposure of tumors to therapeutic agents. ©2015 American Association for Cancer Research.
Directory of Open Access Journals (Sweden)
M. Farooq
Full Text Available This research article investigates the squeezing flow of Newtonian fluid with variable viscosity over a stretchable sheet inserted in Darcy porous medium. Cattaneo-Christov double diffusion models are implemented to scrutinize the characteristics of heat and mass transfer via variable thermal conductivity and variable mass diffusivity. These models are the modification of conventional laws of Fourier’s and Fick’s via thermal and solutal relaxation times respectively. The homotopy analysis Method (HAM is being utilized to provide the solution of highly nonlinear system of coupled partial differential equations after converted into dimensionless governing equations. The behavior of flow parameters on velocity, concentration, and temperature distributions are sketched and analyzed physically. The result indicates that both concentration and temperature distributions decay for higher solutal and thermal relaxation parameters respectively. Keywords: Squeezing flow, Porous medium, Variable viscosity, Cattaneo-Christov heat and mass flux models, Variable thermal conductivity, Variable mass diffusivity
Physical aspects of thermotherapy: A study of heat transport with a view to treatment optimisation
Olsrud, Johan Karl Otto
1998-12-01
Local treatment with the aim to destruct tissue by heating (thermotherapy) may in some cases be an alternative or complement to surgical methods, and has gained increased interest during the last decade. The major advantage of these, often minimally-invasive methods, is that the disease can be controlled with reduced treatment trauma and complications. The extent of thermal damage is a complex function of the physical properties of tissue, which influence the temperature distribution, and of the biological response to heat. In this thesis, methods of obtaining a well-controlled treatment have been studied from a physical point of view, with emphasis on interstitial laser-induced heating of tumours in the liver and intracavitary heating as a treatment for menorrhagia. Hepatic inflow occlusion, in combination with temperature-feedback control of the output power of the laser, resulted in well defined damaged volumes during interstitial laser thermotherapy in normal porcine liver. In addition, phantom experiments showed that the use of multiple diffusing laser fibres allows heating of clinically relevant tissue volumes in a single session. Methods for numerical simulation of heat transport were used to calculate the temperature distribution and the results agreed well with experiments. It was also found from numerical simulation that the influence of light transport on the damaged volume may be negligible in interstitial laser thermotherapy in human liver. Finite element analysis, disregarding light transport, was therefore proposed as a suitable method for 3D treatment planning. Finite element simulation was also used to model intracavitary heating of the uterus, with the purpose of providing an increased understanding of the influence of various treatment parameters on blood flow and on the depth of tissue damage. The thermal conductivity of human uterine tissue, which was used in these simulations, was measured. Furthermore, magnetic resonance imaging (MRI) was
Validation of transport models using additive flux minimization technique
Energy Technology Data Exchange (ETDEWEB)
Pankin, A. Y.; Kruger, S. E. [Tech-X Corporation, 5621 Arapahoe Ave., Boulder, Colorado 80303 (United States); Groebner, R. J. [General Atomics, San Diego, California 92121 (United States); Hakim, A. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451 (United States); Kritz, A. H.; Rafiq, T. [Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015 (United States)
2013-10-15
A new additive flux minimization technique is proposed for carrying out the verification and validation (V and V) of anomalous transport models. In this approach, the plasma profiles are computed in time dependent predictive simulations in which an additional effective diffusivity is varied. The goal is to obtain an optimal match between the computed and experimental profile. This new technique has several advantages over traditional V and V methods for transport models in tokamaks and takes advantage of uncertainty quantification methods developed by the applied math community. As a demonstration of its efficiency, the technique is applied to the hypothesis that the paleoclassical density transport dominates in the plasma edge region in DIII-D tokamak discharges. A simplified version of the paleoclassical model that utilizes the Spitzer resistivity for the parallel neoclassical resistivity and neglects the trapped particle effects is tested in this paper. It is shown that a contribution to density transport, in addition to the paleoclassical density transport, is needed in order to describe the experimental profiles. It is found that more additional diffusivity is needed at the top of the H-mode pedestal, and almost no additional diffusivity is needed at the pedestal bottom. The implementation of this V and V technique uses the FACETS::Core transport solver and the DAKOTA toolkit for design optimization and uncertainty quantification. The FACETS::Core solver is used for advancing the plasma density profiles. The DAKOTA toolkit is used for the optimization of plasma profiles and the computation of the additional diffusivity that is required for the predicted density profile to match the experimental profile.
Validation of transport models using additive flux minimization technique
International Nuclear Information System (INIS)
Pankin, A. Y.; Kruger, S. E.; Groebner, R. J.; Hakim, A.; Kritz, A. H.; Rafiq, T.
2013-01-01
A new additive flux minimization technique is proposed for carrying out the verification and validation (V and V) of anomalous transport models. In this approach, the plasma profiles are computed in time dependent predictive simulations in which an additional effective diffusivity is varied. The goal is to obtain an optimal match between the computed and experimental profile. This new technique has several advantages over traditional V and V methods for transport models in tokamaks and takes advantage of uncertainty quantification methods developed by the applied math community. As a demonstration of its efficiency, the technique is applied to the hypothesis that the paleoclassical density transport dominates in the plasma edge region in DIII-D tokamak discharges. A simplified version of the paleoclassical model that utilizes the Spitzer resistivity for the parallel neoclassical resistivity and neglects the trapped particle effects is tested in this paper. It is shown that a contribution to density transport, in addition to the paleoclassical density transport, is needed in order to describe the experimental profiles. It is found that more additional diffusivity is needed at the top of the H-mode pedestal, and almost no additional diffusivity is needed at the pedestal bottom. The implementation of this V and V technique uses the FACETS::Core transport solver and the DAKOTA toolkit for design optimization and uncertainty quantification. The FACETS::Core solver is used for advancing the plasma density profiles. The DAKOTA toolkit is used for the optimization of plasma profiles and the computation of the additional diffusivity that is required for the predicted density profile to match the experimental profile
Crowding and hopping in a protein’s diffusive transport on DNA
International Nuclear Information System (INIS)
Koslover, Elena F; Spakowitz, Andrew J; Díaz de la Rosa, Mario
2017-01-01
Diffusion is a ubiquitous phenomenon that impacts virtually all processes that involve random fluctuations, and as such, the foundational work of Smoluchowski has proven to be instrumental in addressing innumerable problems. Here, we focus on a critical biological problem that relies on diffusive transport and is analyzed using a probabilistic treatment originally developed by Smoluchowski. The search of a DNA binding protein for its specific target site is believed to rely on non-specific binding to DNA with transient hops along the chain. In this work, we address the impact of protein crowding along the DNA on the transport of a DNA-binding protein. The crowders dramatically alter the dynamics of the protein while bound to the DNA, resulting in single-file transport that is subdiffusive in nature. However, transient unbinding and hopping results in a long-time behavior (shown to be superdiffusive) that is qualitatively unaffected by the crowding on the DNA. Thus, hopping along the chain mitigates the role that protein crowding has in restricting the translocation dynamics along the chain. The superdiffusion coefficient is influenced by the quantitative values of the effective binding rate, which is influenced by protein crowding. We show that vacancy fraction and superdiffusion coefficient exhibits a non-monotonic relationship under many circumstances. We leverage analytical theory and dynamic Monte Carlo simulations to address this problem. With several additional contributions, the core of our modeling work adopts a reaction-diffusion framework that is based on Smoluchowski’s original work. (paper)
Convective-diffusive transport of fission products in the gap of a failed fuel element
International Nuclear Information System (INIS)
Lian, Z.W.; Carlucci, L.N.; Arimescu, V.I.
1995-03-01
A model is presented to describe the transport behaviour of gaseous fission products along the axial fuel-to-sheathe gap of a failed fuel element to the coolant system. The model is applicable to an element having failed under normal operating conditions or loss-of coolant-accident conditions. Because of the large differences in operating parameters, the transport characteristics of gaseous fission products in a failed element under these two operating conditions are significantly different. However, in both cases the transport process can be described by convection-diffusion caused by the continuous release of fission products from the fuel to the gap. Under normal operating conditions, the bulk-flow velocity is found to be negligible, due to the low release rate of fission products from fuel. The process can be well approximated by the diffusion of fission products in a stagnant gas-steam mixture. The effect of convection on the fission product transport, however, becomes significant under loss-of-coolant-accident conditions, where the release rates of fission products from fuel can be several orders of magnitude higher that that under normal operating conditions. The convection of the mixture in the gap not only contributes an additional flux to the gas-mixture transport, but also increases the gradient of fission products concentration across the opening, and therefore increases the diffusion flux to the coolant. As a result of the bulk flow, the transport of fission products along the gap is accelerated and the hold-up of short-lived isotopes in the gap is significantly reduced. Steam ingress through the opening into the gap is obstructed by the bulk flow, resulting in low steam concentrations in the gap under loss-of-coolant-accident conditions. (author). 6 refs., 8 figs
Heat Transfer Modeling for Rigid High-Temperature Fibrous Insulation
Daryabeigi, Kamran; Cunnington, George R.; Knutson, Jeffrey R.
2012-01-01
Combined radiation and conduction heat transfer through a high-temperature, high-porosity, rigid multiple-fiber fibrous insulation was modeled using a thermal model previously used to model heat transfer in flexible single-fiber fibrous insulation. The rigid insulation studied was alumina enhanced thermal barrier (AETB) at densities between 130 and 260 kilograms per cubic meter. The model consists of using the diffusion approximation for radiation heat transfer, a semi-empirical solid conduction model, and a standard gas conduction model. The relevant parameters needed for the heat transfer model were estimated from steady-state thermal measurements in nitrogen gas at various temperatures and environmental pressures. The heat transfer modeling methodology was evaluated by comparison with standard thermal conductivity measurements, and steady-state thermal measurements in helium and carbon dioxide gases. The heat transfer model is applicable over the temperature range of 300 to 1360 K, pressure range of 0.133 to 101.3 x 10(exp 3) Pa, and over the insulation density range of 130 to 260 kilograms per cubic meter in various gaseous environments.
Conceptual model for transport processes in the Culebra Dolomite Member, Rustler Formation
International Nuclear Information System (INIS)
Holt, R.M.
1997-08-01
The Culebra Dolomite Member of the Rustler Formation represents a possible pathway for contaminants from the Waste Isolation Pilot Plant underground repository to the accessible environment. The geologic character of the Culebra is consistent with a double-porosity, multiple-rate model for transport in which the medium is conceptualized as consisting of advective porosity, where solutes are carried by the groundwater flow, and fracture-bounded zones of diffusive porosity, where solutes move through slow advection or diffusion. As the advective travel length or travel time increases, the nature of transport within a double-porosity medium changes. This behavior is important for chemical sorption, because the specific surface area per unit mass of the diffusive porosity is much greater than in the advective porosity. Culebra transport experiments conducted at two different length scales show behavior consistent with a multiple-rate, double-porosity conceptual model for Culebra transport. Tracer tests conducted on intact core samples from the Culebra show no evidence of significant diffusion, suggesting that at the core scale the Culebra can be modeled as a single-porosity medium where only the advective porosity participates in transport. Field tracer tests conducted in the Culebra show strong double-porosity behavior that is best explained using a multiple-rate model
Role of ocean heat transport in climates of tidally locked exoplanets around M dwarf stars.
Hu, Yongyun; Yang, Jun
2014-01-14
The distinctive feature of tidally locked exoplanets is the very uneven heating by stellar radiation between the dayside and nightside. Previous work has focused on the role of atmospheric heat transport in preventing atmospheric collapse on the nightside for terrestrial exoplanets in the habitable zone around M dwarfs. In the present paper, we carry out simulations with a fully coupled atmosphere-ocean general circulation model to investigate the role of ocean heat transport in climate states of tidally locked habitable exoplanets around M dwarfs. Our simulation results demonstrate that ocean heat transport substantially extends the area of open water along the equator, showing a lobster-like spatial pattern of open water, instead of an "eyeball." For sufficiently high-level greenhouse gases or strong stellar radiation, ocean heat transport can even lead to complete deglaciation of the nightside. Our simulations also suggest that ocean heat transport likely narrows the width of M dwarfs' habitable zone. This study provides a demonstration of the importance of exooceanography in determining climate states and habitability of exoplanets.
Quantum Non-Markovian Langevin Equations and Transport Coefficients
International Nuclear Information System (INIS)
Sargsyan, V.V.; Antonenko, N.V.; Kanokov, Z.; Adamian, G.G.
2005-01-01
Quantum diffusion equations featuring explicitly time-dependent transport coefficients are derived from generalized non-Markovian Langevin equations. Generalized fluctuation-dissipation relations and analytic expressions for calculating the friction and diffusion coefficients in nuclear processes are obtained. The asymptotic behavior of the transport coefficients and correlation functions for a damped harmonic oscillator that is linearly coupled in momentum to a heat bath is studied. The coupling to a heat bath in momentum is responsible for the appearance of the diffusion coefficient in coordinate. The problem of regression of correlations in quantum dissipative systems is analyzed
Jocelyn, Alan; Kar, Aravinda; Fanourakis, Alexander; Flower, Terence; Ackerman, Mike; Keevil, Allen; Way, Jerome
2010-06-01
Many from within manufacturing industry consider superplastic forming (SPF) to be ‘high tech’, but it is often criticized as too complicated, expensive, slow and, in general, an unstable process when compared to other methods of manipulating sheet materials. Perhaps, the fundamental cause of this negative perception of SPF, and also of diffusion bonding (DB), is the fact that the current process of SPF/DB relies on indirect sources of heating to produce the conditions necessary for the material to be formed. Thus, heat is usually derived from the electrically heated platens of hydraulic presses, to a lesser extent from within furnaces and, sometimes, from heaters imbedded in ceramic moulds. Recent evaluations of these isothermal methods suggest they are slow, thermally inefficient and inappropriate for the process. In contrast, direct heating of only the material to be formed by modern, electrically efficient, lasers could transform SPF/DB into the first choice of designers in aerospace, automotive, marine, medical, architecture and leisure industries. Furthermore, ‘variable temperature’ direct heating which, in theory, is possible with a laser beam(s) may provide a means to control material thickness distribution, a goal of enormous importance as fuel efficient, lightweight structures for transportation systems are universally sought. This paper compares, and contrasts, the two systems and suggests how a change to laser heating might be achieved.
Heat Transfer in Directional Water Transport Fabrics
Directory of Open Access Journals (Sweden)
Chao Zeng
2016-10-01
Full Text Available Directional water transport fabrics can proactively transfer moisture from the body. They show great potential in making sportswear and summer clothing. While moisture transfer has been previously reported, heat transfer in directional water transport fabrics has been little reported in research literature. In this study, a directional water transport fabric was prepared using an electrospraying technique and its heat transfer properties under dry and wet states were evaluated, and compared with untreated control fabric and the one pre-treated with NaOH. All the fabric samples showed similar heat transfer features in the dry state, and the equilibrium temperature in the dry state was higher than for the wet state. Wetting considerably enhanced the thermal conductivity of the fabrics. Our studies indicate that directional water transport treatment assists in moving water toward one side of the fabric, but has little effect on thermal transfer performance. This study may be useful for development of “smart” textiles for various applications.
Predicting the weathering of fuel and oil spills: A diffusion-limited evaporation model.
Kotzakoulakis, Konstantinos; George, Simon C
2018-01-01
The majority of the evaporation models currently available in the literature for the prediction of oil spill weathering do not take into account diffusion-limited mass transport and the formation of a concentration gradient in the oil phase. The altered surface concentration of the spill caused by diffusion-limited transport leads to a slower evaporation rate compared to the predictions of diffusion-agnostic evaporation models. The model presented in this study incorporates a diffusive layer in the oil phase and predicts the diffusion-limited evaporation rate. The information required is the composition of the fluid from gas chromatography or alternatively the distillation data. If the density or a single viscosity measurement is available the accuracy of the predictions is higher. Environmental conditions such as water temperature, air pressure and wind velocity are taken into account. The model was tested with synthetic mixtures, petroleum fuels and crude oils with initial viscosities ranging from 2 to 13,000 cSt. The tested temperatures varied from 0 °C to 23.4 °C and wind velocities from 0.3 to 3.8 m/s. The average absolute deviation (AAD) of the diffusion-limited model ranged between 1.62% and 24.87%. In comparison, the AAD of a diffusion-agnostic model ranged between 2.34% and 136.62% against the same tested fluids. Copyright © 2017 Elsevier Ltd. All rights reserved.
Decay to Equilibrium for Energy-Reaction-Diffusion Systems
Haskovec, Jan
2018-02-06
We derive thermodynamically consistent models of reaction-diffusion equations coupled to a heat equation. While the total energy is conserved, the total entropy serves as a driving functional such that the full coupled system is a gradient flow. The novelty of the approach is the Onsager structure, which is the dual form of a gradient system, and the formulation in terms of the densities and the internal energy. In these variables it is possible to assume that the entropy density is strictly concave such that there is a unique maximizer (thermodynamical equilibrium) given linear constraints on the total energy and suitable density constraints. We consider two particular systems of this type, namely, a diffusion-reaction bipolar energy transport system, and a drift-diffusion-reaction energy transport system with confining potential. We prove corresponding entropy-entropy production inequalities with explicitly calculable constants and establish the convergence to thermodynamical equilibrium, first in entropy and later in L norm using Cziszár–Kullback–Pinsker type inequalities.
Decay to Equilibrium for Energy-Reaction-Diffusion Systems
Haskovec, Jan; Hittmeir, Sabine; Markowich, Peter A.; Mielke, Alexander
2018-01-01
We derive thermodynamically consistent models of reaction-diffusion equations coupled to a heat equation. While the total energy is conserved, the total entropy serves as a driving functional such that the full coupled system is a gradient flow. The novelty of the approach is the Onsager structure, which is the dual form of a gradient system, and the formulation in terms of the densities and the internal energy. In these variables it is possible to assume that the entropy density is strictly concave such that there is a unique maximizer (thermodynamical equilibrium) given linear constraints on the total energy and suitable density constraints. We consider two particular systems of this type, namely, a diffusion-reaction bipolar energy transport system, and a drift-diffusion-reaction energy transport system with confining potential. We prove corresponding entropy-entropy production inequalities with explicitly calculable constants and establish the convergence to thermodynamical equilibrium, first in entropy and later in L norm using Cziszár–Kullback–Pinsker type inequalities.
A mobile-mobile transport model for simulating reactive transport in connected heterogeneous fields
Lu, Chunhui; Wang, Zhiyuan; Zhao, Yue; Rathore, Saubhagya Singh; Huo, Jinge; Tang, Yuening; Liu, Ming; Gong, Rulan; Cirpka, Olaf A.; Luo, Jian
2018-05-01
Mobile-immobile transport models can be effective in reproducing heavily tailed breakthrough curves of concentration. However, such models may not adequately describe transport along multiple flow paths with intermediate velocity contrasts in connected fields. We propose using the mobile-mobile model for simulating subsurface flow and associated mixing-controlled reactive transport in connected fields. This model includes two local concentrations, one in the fast- and the other in the slow-flow domain, which predict both the concentration mean and variance. The normalized total concentration variance within the flux is found to be a non-monotonic function of the discharge ratio with a maximum concentration variance at intermediate values of the discharge ratio. We test the mobile-mobile model for mixing-controlled reactive transport with an instantaneous, irreversible bimolecular reaction in structured and connected random heterogeneous domains, and compare the performance of the mobile-mobile to the mobile-immobile model. The results indicate that the mobile-mobile model generally predicts the concentration breakthrough curves (BTCs) of the reactive compound better. Particularly, for cases of an elliptical inclusion with intermediate hydraulic-conductivity contrasts, where the travel-time distribution shows bimodal behavior, the prediction of both the BTCs and maximum product concentration is significantly improved. Our results exemplify that the conceptual model of two mobile domains with diffusive mass transfer in between is in general good for predicting mixing-controlled reactive transport, and particularly so in cases where the transfer in the low-conductivity zones is by slow advection rather than diffusion.
Energy Technology Data Exchange (ETDEWEB)
Fujii, Hikari; Itoi, Ryuichi [Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395 (Japan); Inatomi, Tadasuke [YBM Co. Ltd., Kishiyama 589-10 Kitahata, Karatsu 847-1211 (Japan); Uchida, Youhei [Geological Survey of Japan, AIST Tsukuba Central 7, Tsukuba 305-8567 (Japan)
2007-10-15
The thermophysical properties of subsurface materials (soils, sediments and rocks) and groundwater flow strongly affect the heat exchange rates of ground heat exchangers (GHEs). These rates can be maximized and the installation costs of the ground-coupled heat pump (GCHP) systems reduced by developing suitability maps based on local geological and hydrological information. Such maps were generated for the Chikushi Plain (western Japan) using field-survey data and a numerical modeling study. First, a field-wide groundwater model was developed for the area and the results matched against measured groundwater levels and vertical temperature profiles. Single GHE models were then constructed to simulate the heat exchange performance at different locations in the plain. Finally, suitability maps for GCHP systems were prepared using the results from the single GHE models. Variations in the heat exchange rates of over 40% revealed by the map were ascribed to differences in the GHE locations, confirming how important it is to use appropriate thermophysical data when designing GCHP systems. (author)
S sub(N) transport and diffusion acceleration
International Nuclear Information System (INIS)
Gho, C.J.
1986-01-01
After brief description of the characteristics and history of S sub(N) transport method and the present development of transport codes, the technique of diffusion acceleration and the characteristics of its implementation in BISTRO computer code are exposed. It is showed that the method to discretize algorithms leads to strongly results using some simple calculations which alloy to compare the performance of BISTRO computer code to distinguished versions of DOT computer code. (M.C.K.) [pt
Diffusion approximation for modeling of 3-D radiation distributions
International Nuclear Information System (INIS)
Zardecki, A.; Gerstl, S.A.W.; De Kinder, R.E. Jr.
1985-01-01
A three-dimensional transport code DIF3D, based on the diffusion approximation, is used to model the spatial distribution of radiation energy arising from volumetric isotropic sources. Future work will be concerned with the determination of irradiances and modeling of realistic scenarios, relevant to the battlefield conditions. 8 refs., 4 figs
Transient heat transport studies in JET conventional and advanced tokamak plasmas
International Nuclear Information System (INIS)
Mantica, P.; Coffey, I.; Dux, R.
2003-01-01
Transient transport studies are a valuable complement to steady-state analysis for the understanding of transport mechanisms and the validation of physics-based transport models. This paper presents results from transient heat transport experiments in JET and their modelling. Edge cold pulses and modulation of ICRH (in mode conversion scheme) have been used to provide detectable electron and ion temperature perturbations. The experiments have been performed in conventional L-mode plasmas or in Advanced Tokamak regimes, in the presence of an Internal Transport Barrier (ITB). In conventional plasmas, the issues of stiffness and non-locality have been addressed. Cold pulse propagation in ITB plasmas has provided useful insight into the physics of ITB formation. The use of edge perturbations for ITB triggering has been explored. Modelling of the experimental results has been performed using both empirical models and physics-based models. Results of cold pulse experiments in ITBs have also been compared with turbulence simulations. (author)
Ion heat transport studies in JET
DEFF Research Database (Denmark)
Mantica, P; Angioni, C; Baiocchi, B
2011-01-01
Detailed experimental studies of ion heat transport have been carried out in JET exploiting the upgrade of active charge exchange spectroscopy and the availability of multi-frequency ion cyclotron resonance heating with 3He minority. The determination of ion temperature gradient (ITG) threshold a...
Modelling of transport phenomena
International Nuclear Information System (INIS)
Itoh, Kimitaka; Itoh, Sanae; Fukuyama, Atsushi.
1993-09-01
In this review article, we discuss key features of the transport phenomena and theoretical modelling to understand them. Experimental observations have revealed the nature of anomalous transport, i.e., the enhancement of the transport coefficients by the gradients of the plasma profiles, the pinch phenomena, the radial profile of the anomalous transport coefficients, the variation of the transport among the Bohm diffusion, Pseudo-classical confinement, L-mode and variety of improved confinement modes, and the sudden jumps such as L-H transition. Starting from the formalism of the transport matrix, the modelling based on the low frequency instabilities are reviewed. Theoretical results in the range of drift wave frequency are examined. Problems in theories based on the quasilinear and mixing-length estimates lead to the renewal of the turbulence theory, and the physics picture of the self-sustained turbulence is discussed. The theory of transport using the fluid equation of plasma is developed, showing that the new approach is very promising in explaining abovementioned characteristics of anomalous transport in both L-mode and improved confinement plasmas. The interference of the fluxes is the key to construct the physics basis of the bifurcation theory for the L-H transition. The present status of theories on the mechanisms of improved confinement is discussed. Modelling on the nonlocal nature of transport is briefly discussed. Finally, the impact of the anomalous transport on disruptive phenomena is also described. (author) 95 refs
Accurate numerical simulation of reaction-diffusion processes for heavy oil recovery
Energy Technology Data Exchange (ETDEWEB)
Govind, P.A.; Srinivasan, S. [Society of Petroleum Engineers, Richardson, TX (United States)]|[Texas Univ., Austin, TX (United States)
2008-10-15
This study evaluated a reaction-diffusion simulation tool designed to analyze the displacement of carbon dioxide (CO{sub 2}) in a simultaneous injection of carbon dioxide and elemental sodium in a heavy oil reservoir. Sodium was used due to the exothermic reaction of sodium with in situ that occurs when heat is used to reduce oil viscosity. The process also results in the formation of sodium hydroxide that reduces interfacial tension at the bitumen interface. A commercial simulation tool was used to model the sodium transport mechanism to the reaction interface through diffusion as well as the reaction zone's subsequent displacement. The aim of the study was to verify if the in situ reaction was able to generate sufficient heat to reduce oil viscosity and improve the displacement of the heavy oil. The study also assessed the accuracy of the reaction front simulation tool, in which an alternate method was used to model the propagation front as a moving heat source. The sensitivity of the simulation results were then evaluated in relation to the diffusion coefficient in order to understand the scaling characteristics of the reaction-diffusion zone. A pore-scale simulation was then up-scaled to grid blocks. Results of the study showed that when sodium suspended in liquid CO{sub 2} is injected into reservoirs, it diffuses through the carrier phase and interacts with water. A random walk diffusion algorithm with reactive dissipation was implemented to more accurately characterize reaction and diffusion processes. It was concluded that the algorithm modelled physical dispersion while neglecting the effect of numerical dispersion. 10 refs., 3 tabs., 24 figs.
Modelling the Molecular Transportation of Subcutaneously Injected Salubrinal
Directory of Open Access Journals (Sweden)
Andy Chen
2011-01-01
Full Text Available For the subcutaneous administration of a chemical agent (salubrinal, we constructed a mathematical model of molecule transportation and subsequently evaluated the kinetics of diffusion, convection, and molecular turnover. Salubrinal is a potential therapeutic agent that can reduce cellular damage and death. The understanding of its temporal profiles in local tissue as well as in a whole body is important to develop a proper strategy for its administration. Here, the diffusion and convection kinetics was formulated using partial and ordinary differential equations in one- and three-dimensional (semi-spherical coordinates. Several key parameters including an injection velocity, a diffusion coefficient, thickness of subcutaneous tissue, and a permeability factor at the tissue-blood boundary were estimated from experimental data in rats. With reference to analytical solutions in a simplified model without convection, numerical solutions revealed that the diffusion coefficient and thickness of subcutaneous tissue determined the timing of the peak concentration in the plasma, and its magnitude was dictated by the permeability factor. Furthermore, the initial velocity, induced by needle injection, elevated an immediate transport of salubrinal at t < 1h. The described analysis with a combination of partial and ordinary differential equations contributes to the prediction of local and systemic effects and the understanding of the transportation mechanism of salubrinal and other agents.
Turbulent transport regimes and the SOL heat flux width
Myra, J. R.; D'Ippolito, D. A.; Russell, D. A.
2014-10-01
Understanding the responsible mechanisms and resulting scaling of the scrape-off layer (SOL) heat flux width is important for predicting viable operating regimes in future tokamaks, and for seeking possible mitigation schemes. Simulation and theory results using reduced edge/SOL turbulence models have produced SOL widths and scalings in reasonable accord with experiments in many cases. In this work, we attempt to qualitatively and conceptually understand various regimes of edge/SOL turbulence and the role of turbulent transport in establishing the SOL heat flux width. Relevant considerations include the type and spectral characteristics of underlying instabilities, the location of the gradient drive relative to the SOL, the nonlinear saturation mechanism, and the parallel heat transport regime. Recent SOLT turbulence code results are employed to understand the roles of these considerations and to develop analytical scalings. We find a heat flux width scaling with major radius R that is generally positive, consistent with older results reviewed in. The possible relationship of turbulence mechanisms to the heuristic drift mechanism is considered, together with implications for future experiments. Work supported by US DOE grant DE-FG02-97ER54392.
Studies of heat transport to forced-flow He II
International Nuclear Information System (INIS)
Dresner, L.; Kashani, A.; Van Sciver, S.W.
1985-01-01
Analytical and experimental studies of heat transport to forced-flow He II are reported. The work is pertinent to the transfer of He II in space. An analytical model has been developed that establishes a condition for two-phase flow to occur in the transfer line. This condition sets an allowable limit to the heat leak into the transfer line. Experimental measurements of pressure drop and flow meter performances indicate that turbulent He II can be analyzed in terms of classical pressure drop correlations
Energy Technology Data Exchange (ETDEWEB)
Fisher, A. C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Bailey, D. S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kaiser, T. B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Eder, D. C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Gunney, B. T. N. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Masters, N. D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Koniges, A. E. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Anderson, R. W. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2015-02-01
Here, we present a novel method for the solution of the diffusion equation on a composite AMR mesh. This approach is suitable for including diffusion based physics modules to hydrocodes that support ALE and AMR capabilities. To illustrate, we proffer our implementations of diffusion based radiation transport and heat conduction in a hydrocode called ALE-AMR. Numerical experiments conducted with the diffusion solver and associated physics packages yield 2nd order convergence in the L_{2} norm.
International Nuclear Information System (INIS)
Gavryushenko, D.A.; Sisojev, V.M.; Cherevko, K.V.; Vlasenko, T.S.
2017-01-01
The work is devoted to the up to date problem that is the description of the radioactive particle diffusion processes. One of the aims of the present study is to estimate the effects caused by the irradiation of the liquid systems on the ongoing transport processes. That can allow predicting the behavior of the liquid systems in the presence of the radioactive sources. The main objective of the present work is studying the radioactive particles diffusion phenomena with the possible facilitated diffusion processes being considered. The phenomena are studied based on the fundamental relations of the nonequilibrium statistical thermodynamics. The diffusive flows are evaluated with the special attention given to the accounting of the entropy effects due to the appearance of the new radioactive particles in the system. The developed approach is used to estimate the diffusive flow of the radioactive particles for the case of the plane-parallel pore with the semi-transparent walls. The choice of a model can be justified as it might be used to describe the production of the radioactive contaminated water when the radionuclide face the diffusion process after being washed from the radioactive wastes and the rests of the nuclear fuel. Within the suggested model it is shown that the diffusion coefficient depends on the structural properties of the liquid systems that might be changed under the influence of the irradiation. The obtained equations for calculating the diffusive flows show the definite stabilizing effect in respect to the concentration difference in between the boundaries of the plane-parallel pore. It leads to the decreased changes of the diffusive flow when the concentrations of the radioactive particles at the boundaries are changed in comparison with those observed for the constant diffusion coefficient. The observed behavior for the ideal solution model is explained by the entropy effects. The qualitative analysis of the possible influence of the changes in
Modelling of Innovation Diffusion
Directory of Open Access Journals (Sweden)
Arkadiusz Kijek
2010-01-01
Full Text Available Since the publication of the Bass model in 1969, research on the modelling of the diffusion of innovation resulted in a vast body of scientific literature consisting of articles, books, and studies of real-world applications of this model. The main objective of the diffusion model is to describe a pattern of spread of innovation among potential adopters in terms of a mathematical function of time. This paper assesses the state-of-the-art in mathematical models of innovation diffusion and procedures for estimating their parameters. Moreover, theoretical issues related to the models presented are supplemented with empirical research. The purpose of the research is to explore the extent to which the diffusion of broadband Internet users in 29 OECD countries can be adequately described by three diffusion models, i.e. the Bass model, logistic model and dynamic model. The results of this research are ambiguous and do not indicate which model best describes the diffusion pattern of broadband Internet users but in terms of the results presented, in most cases the dynamic model is inappropriate for describing the diffusion pattern. Issues related to the further development of innovation diffusion models are discussed and some recommendations are given. (original abstract
Nonlocal transport in the presence of transport barriers
Del-Castillo-Negrete, D.
2013-10-01
There is experimental, numerical, and theoretical evidence that transport in plasmas can, under certain circumstances, depart from the standard local, diffusive description. Examples include fast pulse propagation phenomena in perturbative experiments, non-diffusive scaling in L-mode plasmas, and non-Gaussian statistics of fluctuations. From the theoretical perspective, non-diffusive transport descriptions follow from the relaxation of the restrictive assumptions (locality, scale separation, and Gaussian/Markovian statistics) at the foundation of diffusive models. We discuss an alternative class of models able to capture some of the observed non-diffusive transport phenomenology. The models are based on a class of nonlocal, integro-differential operators that provide a unifying framework to describe non- Fickian scale-free transport, and non-Markovian (memory) effects. We study the interplay between nonlocality and internal transport barriers (ITBs) in perturbative transport including cold edge pulses and power modulation. Of particular interest in the nonlocal ``tunnelling'' of perturbations through ITBs. Also, flux-gradient diagrams are discussed as diagnostics to detect nonlocal transport processes in numerical simulations and experiments. Work supported by the US Department of Energy.
Energy Technology Data Exchange (ETDEWEB)
Weber, Adam
2010-03-05
A macroscopic-modeling methodology to account for the chemical and structural properties of fuel-cell diffusion media is developed. A previous model is updated to include for the first time the use of experimentally measured capillary pressure -- saturation relationships through the introduction of a Gaussian contact-angle distribution into the property equations. The updated model is used to simulate various limiting-case scenarios of water and gas transport in fuel-cell diffusion media. Analysis of these results demonstrate that interfacial conditions are more important than bulk transport in these layers, where the associated mass-transfer resistance is the result of higher capillary pressures at the boundaries and the steepness of the capillary pressure -- saturation relationship. The model is also used to examine the impact of a microporous layer, showing that it dominates the response of the overall diffusion medium. In addition, its primary mass-transfer-related effect is suggested to be limiting the water-injection sites into the more porous gas-diffusion layer.
Transport Studies and Modeling in PEM Fuel Cells
Energy Technology Data Exchange (ETDEWEB)
Mittelsteadt, Cortney K. [Giner, Inc., Auburndale, MA (United States); Xu, Hui [Giner, Inc., Auburndale, MA (United States); Brawn, Shelly [Giner, Inc., Auburndale, MA (United States)
2014-07-30
This project’s aim was to develop fuel cell components (i.e. membranes, gas-diffusion media (GDM), bipolar plates and flow fields) that possess specific properties (i.e. water transport and conductivity). A computational fluid dynamics model was developed to elucidate the effect of certain parameters on these specific properties. Ultimately, the model will be used to determine sensitivity of fuel cell performance to component properties to determine limiting components and to guide research. We have successfully reached our objectives and achieved most of the milestones of this project. We have designed and synthesized a variety of hydrocarbon block polymer membranes with lower equivalent weight, structure, chemistry, phase separation and process conditions. These membranes provide a broad selection with optimized water transport properties. We have also designed and constructed a variety of devices that are capable of accurately measuring the water transport properties (water uptake, water diffusivity and electro-osmatic drag) of these membranes. These transport properties are correlated to the membranes’ structures derived from X-ray and microscopy techniques to determine the structure-property relationship. We successfully integrated hydrocarbon membrane MEAs with a current distribution board (CBD) to study the impact of hydrocarbon membrane on water transport in fuel cells. We have designed and fabricated various GDM with varying substrate, diffusivity and micro-porous layers (MPL) and characterized their pore structure, tortuosity and hydrophobicity. We have derived a universal chart (MacMullin number as function of wet proofing and porosity) that can be used to characterize various GDM. The abovementioned GDMs have been evaluated in operating fuel cells; their performance is correlated to various pore structure, tortuosity and hydrophobicity of the GDM. Unfortunately, determining a universal relationship between the MacMullin number and these properties
An Overview of Liquid Fluoride Salt Heat Transport Systems
Energy Technology Data Exchange (ETDEWEB)
Holcomb, David Eugene [ORNL; Cetiner, Sacit M [ORNL
2010-09-01
Heat transport is central to all thermal-based forms of electricity generation. The ever increasing demand for higher thermal efficiency necessitates power generation cycles transitioning to progressively higher temperatures. Similarly, the desire to provide direct thermal coupling between heat sources and higher temperature chemical processes provides the underlying incentive to move toward higher temperature heat transfer loops. As the system temperature rises, the available materials and technology choices become progressively more limited. Superficially, fluoride salts at {approx}700 C resemble water at room temperature being optically transparent and having similar heat capacity, roughly three times the viscosity, and about twice the density. Fluoride salts are a leading candidate heat-transport material at high temperatures. Fluoride salts have been extensively used in specialized industrial processes for decades, yet they have not entered widespread deployment for general heat transport purposes. This report does not provide an exhaustive screening of potential heat transfer media and other high temperature liquids such as alkali metal carbonate eutectics or chloride salts may have economic or technological advantages. A particular advantage of fluoride salts is that the technology for their use is relatively mature as they were extensively studied during the 1940s-1970s as part of the U.S. Atomic Energy Commission's program to develop molten salt reactors (MSRs). However, the instrumentation, components, and practices for use of fluoride salts are not yet developed sufficiently for commercial implementation. This report provides an overview of the current understanding of the technologies involved in liquid salt heat transport (LSHT) along with providing references to the more detailed primary information resources. Much of the information presented here derives from the earlier MSR program. However, technology has evolved over the intervening years
International Nuclear Information System (INIS)
Mishra, S.; Chakraborty, S.; DebRoy, T.
2005-01-01
A transport phenomena-based mathematical model is developed to understand liquation cracking in weldments during fusion welding. Equations of conservation of mass, momentum, heat, and solute transport are numerically solved considering nonequilibrium solidification and filler metal addition to determine the solid and liquid phase fractions in the solidifying region and the solute distribution in the weld pool. An effective partition coefficient that considers the local interface velocity and the undercooling is used to simulate solidification during welding. The calculations show that convection plays a dominant role in the solute transport inside the weld pool. The predicted weld-metal solute content agreed well with the independent experimental observations. The liquation cracking susceptibility in Al-Cu alloy weldments could be reliably predicted by the model based on the computed solidifying weld-metal composition and solid fraction considering nonequilibrium solidification
International Nuclear Information System (INIS)
Runchal, A.K.; Sagar, B.; Baca, R.G.; Kline, N.W.
1985-09-01
Postclosure performance assessment of the proposed high-level nuclear waste repository in flood basalts at Hanford requires that the processes of fluid flow, heat transfer, and mass transport be numerically modeled at appropriate space and time scales. A suite of computer models has been developed to meet this objective. The theory of one of these models, named PORFLO, is described in this report. Also presented are a discussion of the numerical techniques in the PORFLO computer code and a few computational test cases. Three two-dimensional equations, one each for fluid flow, heat transfer, and mass transport, are numerically solved in PORFLO. The governing equations are derived from the principle of conservation of mass, momentum, and energy in a stationary control volume that is assumed to contain a heterogeneous, anisotropic porous medium. Broad discrete features can be accommodated by specifying zones with distinct properties, or these can be included by defining an equivalent porous medium. The governing equations are parabolic differential equations that are coupled through time-varying parameters. Computational tests of the model are done by comparisons of simulation results with analytic solutions, with results from other independently developed numerical models, and with available laboratory and/or field data. In this report, in addition to the theory of the model, results from three test cases are discussed. A users' manual for the computer code resulting from this model has been prepared and is available as a separate document. 37 refs., 20 figs., 15 tabs
Ungar, Lyle H.; Bennett, Mark J.; Brown, Robert A.
1985-01-01
The shape and stability of two-dimensional finite-amplitude cellular interfaces arising during directional solidification are compared for several solidification models that account differently for latent heat released at the interface, unequal thermal conductivities of melt and solid, and solute diffusivity in the solid. Finite-element analysis and computer-implemented perturbation methods are used to analyze the families of steadily growing cellular forms that evolve from the planar state. In all models a secondary bifurcation between different families of finite-amplitude cells exists that halves the spatial wavelength of the stable interface. The quantitative location of this transition is very dependent on the details of the model. Large amounts of solute diffusion in the solid retard the growth of large-amplitude cells.
Zhang, Chuang; Guo, Zhaoli; Chen, Songze
2017-12-01
An implicit kinetic scheme is proposed to solve the stationary phonon Boltzmann transport equation (BTE) for multiscale heat transfer problem. Compared to the conventional discrete ordinate method, the present method employs a macroscopic equation to accelerate the convergence in the diffusive regime. The macroscopic equation can be taken as a moment equation for phonon BTE. The heat flux in the macroscopic equation is evaluated from the nonequilibrium distribution function in the BTE, while the equilibrium state in BTE is determined by the macroscopic equation. These two processes exchange information from different scales, such that the method is applicable to the problems with a wide range of Knudsen numbers. Implicit discretization is implemented to solve both the macroscopic equation and the BTE. In addition, a memory reduction technique, which is originally developed for the stationary kinetic equation, is also extended to phonon BTE. Numerical comparisons show that the present scheme can predict reasonable results both in ballistic and diffusive regimes with high efficiency, while the memory requirement is on the same order as solving the Fourier law of heat conduction. The excellent agreement with benchmark and the rapid converging history prove that the proposed macro-micro coupling is a feasible solution to multiscale heat transfer problems.
A desk study of surface diffusion and mass transport in clay
International Nuclear Information System (INIS)
Cook, A.J.
1988-09-01
The concept of a geological barrier to radionuclide migration from theoretical radioactive waste repositories has drawn attention to the physico-chemical properties of clays, which are traditionally regarded as retarding media. This report addresses the different mechanisms of transport of radionuclides through clay and in particular focuses on the surface diffusion movement of sorbed cations. The relative contributory importance of the different transport mechanisms is governed by the pore size distributions and interconnections within the clay fabric. Surface diffusion data in the literature have been from experiments using compacted montmorillonite and biotite gneiss. A possible programme of laboratory work is outlined, based on diffusion experiments, which describes the way of measuring the effect of surface diffusion more accurately in clays, mudstones and shales. (author)
Modelling thermal radiation and soot formation in buoyant diffusion flames
International Nuclear Information System (INIS)
Demarco Bull, R.A.
2012-01-01
The radiative heat transfer plays an important role in fire problems since it is the dominant mode of heat transfer between flames and surroundings. It controls the pyrolysis, and therefore the heat release rate, and the growth rate of the fire. In the present work a numerical study of buoyant diffusion flames is carried out, with the main objective of modelling the thermal radiative transfer and the soot formation/destruction processes. In a first step, different radiative property models were tested in benchmark configurations. It was found that the FSCK coupled with the Modest and Riazzi mixing scheme was the best compromise in terms of accuracy and computational requirements, and was a good candidate to be implemented in CFD codes dealing with fire problems. In a second step, a semi-empirical soot model, considering acetylene and benzene as precursor species for soot nucleation, was validated in laminar co flow diffusion flames over a wide range of hydrocarbons (C1-C3) and conditions. In addition, the optically-thin approximation was found to produce large discrepancies in the upper part of these small laminar flames. Reliable predictions of soot volume fractions require the use of an advanced radiation model. Then the FSCK and the semi-empirical soot model were applied to simulate laboratory-scale and intermediate-scale pool fires of methane and propane. Predicted flame structures as well as the radiant heat flux transferred to the surroundings were found to be in good agreement with the available experimental data. Finally, the interaction between radiation and turbulence was quantified. (author)
Dynamic model of ion and water transport in ionic polymer-metal composites
Directory of Open Access Journals (Sweden)
Zicai Zhu
2011-12-01
Full Text Available In the process of electro-mechanical transduction of ionic polymer-metal composites (IPMCs, the transport of ion and water molecule plays an important role. In this paper, the theoretical transport models of IPMCs are critically reviewed, with particular emphasis on the recent developments in the latest decade. The models can be divided into three classes, thermodynamics of irreversible process model, frictional model and Nernst-Planck (NP equation model. To some extent the three models can be transformed into each other, but their differences are also obvious arising from the various mechanisms that considered in different models. The transport of ion and water molecule in IPMCs is compared with that in membrane electrode assembly and electrodialysis membrane to identify and clarify the fundamental transport mechanisms in IPMCs. And an improved transport model is proposed and simplified for numerical analysis. The model considers the convection effect rather than the diffusion as the major transport mechanism, and both the self-diffusion and the electroosmosis drag are accounted for in the water flux equation.
Energy Technology Data Exchange (ETDEWEB)
Fisher, Kaitlynn; Barron, S. C.; Knepper, R.; Weihs, T. P., E-mail: weihs@jhu.edu [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218-2689 (United States); Bonds, M. A.; Browning, N. D. [Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616 (United States); Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Livi, K. J. T. [High-Resolution Analytical Electron Microbeam Facility, Integrated Imaging Center, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Campbell, G. H. [Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
2013-12-28
We describe the energy and sequence of phase transformations in multilayered Al/Zr foils with atomic ratios of 3 Al:1 Zr during low temperature (<350 °C) heat treatments in a differential scanning calorimeter. The initial phase formed is an Al-rich amorphous phase that appears to grow by Zr diffusion through the amorphous phase. The subsequent nucleation and growth of tetragonal Al{sub 3}Zr along the Al/amorphous layer interface is mediated by Al diffusion through the crystalline intermetallic phase. Diffusion coefficients associated with these processes are higher than expected from reports of diffusivities measured at higher temperatures. The inferred heat of formation of the tetragonal Al{sub 3}Zr phase is 1240 ± 40 J/g (53 ± 2 kJ/mol atom). No anomalous variation in the energy or sequence of phase transformations is found with bilayer thickness for samples with bilayer thickness in the range of 17 nm to 90 nm despite anomalies in the bilayer dependence of self-propagating reaction velocities in the same foils.
Thermal transport in low dimensions from statistical physics to nanoscale heat transfer
2016-01-01
Understanding non-equilibrium properties of classical and quantum many-particle systems is one of the goals of contemporary statistical mechanics. Besides its own interest for the theoretical foundations of irreversible thermodynamics(e.g. of the Fourier's law of heat conduction), this topic is also relevant to develop innovative ideas for nanoscale thermal management with possible future applications to nanotechnologies and effective energetic resources. The first part of the volume (Chapters 1-6) describes the basic models, the phenomenology and the various theoretical approaches to understand heat transport in low-dimensional lattices (1D e 2D). The methods described will include equilibrium and nonequilibrium molecular dynamics simulations, hydrodynamic and kinetic approaches and the solution of stochastic models. The second part (Chapters 7-10) deals with applications to nano and microscale heat transfer, as for instance phononic transport in carbon-based nanomaterials, including the prominent case of na...
Analytical solution to the hybrid diffusion-transport equation
International Nuclear Information System (INIS)
Nanneh, M.M.; Williams, M.M.R.
1986-01-01
A special integral equation was derived in previous work using a hybrid diffusion-transport theory method for calculating the flux distribution in slab lattices. In this paper an analytical solution of this equation has been carried out on a finite reactor lattice. The analytical results of disadvantage factors are shown to be accurate in comparison with the numerical results and accurate transport theory calculations. (author)
Modelling anisotropic water transport in polymer composite ...
Indian Academy of Sciences (India)
Parameters for Fickian diffusion and polymer relaxation models were determined by .... Water transport process of resin and polymer composite specimens at ..... simulation. ... Kwon Y W and Bang H 1997 Finite element method using matlab.
Reaction-diffusion systems in intracellular molecular transport and control.
Soh, Siowling; Byrska, Marta; Kandere-Grzybowska, Kristiana; Grzybowski, Bartosz A
2010-06-07
Chemical reactions make cells work only if the participating chemicals are delivered to desired locations in a timely and precise fashion. Most research to date has focused on active-transport mechanisms, although passive diffusion is often equally rapid and energetically less costly. Capitalizing on these advantages, cells have developed sophisticated reaction-diffusion (RD) systems that control a wide range of cellular functions-from chemotaxis and cell division, through signaling cascades and oscillations, to cell motility. These apparently diverse systems share many common features and are "wired" according to "generic" motifs such as nonlinear kinetics, autocatalysis, and feedback loops. Understanding the operation of these complex (bio)chemical systems requires the analysis of pertinent transport-kinetic equations or, at least on a qualitative level, of the characteristic times of the constituent subprocesses. Therefore, in reviewing the manifestations of cellular RD, we also describe basic theory of reaction-diffusion phenomena.
Turbulent transport of energetic ions
International Nuclear Information System (INIS)
Dannert, Tilman; Hauff, Thilo; Jenko, Frank; Guenter, Sibylle
2006-01-01
Approaching ITER operation, the issue of anomalous transport of fast particles becomes more and more important. This is partly because the ITER heating and current drive system relies heavily on neutral beam injection. Moreover burning plasmas are heated by fast fusion α particles.Fusion α particles are characterised by a fixed energy and an isotropic velocity distribution. Therefore they have gyroradii one magnitude larger than the thermal ions. The dependency of the particle diffusion of α test particles on the Kubo number K = VExBτc/λc (VExB mean E x B velocity, τc, λc correlation time and length of the turbulent potential) is presented. For different turbulent regimes, different dependency of the diffusion on the gyroradius is found. For large Kubo numbers, the transport is found to remain constant for gyroradii up to the correlation length of the potential, whereas it is drastically reduced in the small Kubo number regime.In the second part, a model for beam ions injected along the equilibrium magnetic field is described. The beam ions are treated gyrokinetically in a self-consistent way with the equilibrium distribution function taken as a shifted Maxwellian. The implications of such a model for the Vlasov equation, the field equations, and the calculation of moments and fluxes are discussed. Linear and nonlinear results, obtained with the gyrokinetic flux tube code GENE show the existence of a new instability driven by fast beam ions. The instability has a maximum growth rate at perpendicular wave numbers of kyρs ∼ 0.15 and depends mainly on the beam velocity and the density gradient of the beam ions. This instability leads to a replacement of bulk ion particle transport by fast ion particle transport, connected to a strongly enhanced heat flux. In the presence of this instability, the turbulent particle and heat transport is dominated by fast ions
'Thermal ghosts': apparent decay of fixed surfaces caused by heat diffusion
International Nuclear Information System (INIS)
Livadiotis, George
2007-01-01
The behaviour concerning classical heat diffusion on fixed thermal surfaces, studied by observations, still holds surprises. As soon as convective and radiative processes are negligible within the medium, this is considered to be free from energy sources and sinks. Then, the heat diffusion equation is conveniently solved using standard Fourier methods. Some considerations about the contrast effect suggest that the surface boundary would rather be observed to follow specific area decay dynamics than remaining fixed and static. Here it is shown that the apparent boundary lies on a specific isothermal spatiotemporal curve, which depends on the observing device. This is characterized by a slight, though determinative, difference between its radiance and that of the ambient background. Thereafter, the heat diffusion yields apparent boundary shrinkage with the passing of time. This phenomenon is particularly notable for two reasons: its lifetime and final decay rate depend only on the medium thermal properties, while being independent of the apparent boundary spatiotemporal curve. Thus, the former provides a suitable method for measuring the medium thermal properties via the observational data. The latter strongly reveal a kind of universality of some characteristic properties of the phenomenon, common to all observers
Climate in the Absence of Ocean Heat Transport
Rose, B. E. J.
2015-12-01
The energy transported by the oceans to mid- and high latitudes is small compared to the atmosphere, yet exerts an outsized influence on the climate. A key reason is the strong interaction between ocean heat transport (OHT) and sea ice extent. I quantify this by comparing a realistic control climate simulation with a slab ocean simulation in which OHT is disabled. Using the state-of-the-art CESM with a realistic present-day continental configuration, I show that the absence of OHT leads to a 23 K global cooling and massive expansion of sea ice to near 30º latitude in both hemisphere. The ice expansion is asymmetric, with greatest extent in the South Pacific and South Indian ocean basins. I discuss implications of this enormous and asymmetric climate change for atmospheric circulation, heat transport, and tropical precipitation. Parameter sensitivity studies show that the simulated climate is far more sensitive to small changes in ice surface albedo in the absence of OHT, with some perturbations sufficient to cause a runaway Snowball Earth glaciation. I conclude that the oceans are responsible for an enormous global warming by mitigating an otherwise very potent sea ice albedo feedback, but that the magnitude of this effect is still rather uncertain. I will also present some ideas on adapting the simple energy balance model to account for the enhanced sensitivity of sea ice to heating from the ocean.
Reiss, P.
2018-05-01
Chemical analysis of lunar soil samples often involves thermal processing to extract their volatile constituents, such as loosely adsorbed water. For the characterization of volatiles and their bonding mechanisms it is important to determine their desorption temperature. However, due to the low thermal diffusivity of lunar regolith, it might be difficult to reach a uniform heat distribution in a sample that is larger than only a few particles. Furthermore, the mass transport through such a sample is restricted, which might lead to a significant delay between actual desorption and measurable outgassing of volatiles from the sample. The entire volatiles extraction process depends on the dynamically changing heat and mass transfer within the sample, and is influenced by physical parameters such as porosity, tortuosity, gas density, temperature and pressure. To correctly interpret measurements of the extracted volatiles, it is important to understand the interaction between heat transfer, sorption, and gas transfer through the sample. The present paper discusses the molecular kinetics and mechanisms that are involved in the thermal extraction process and presents a combined parametrical computation model to simulate this process. The influence of water content on the gas diffusivity and thermal diffusivity is discussed and the issue of possible resorption of desorbed molecules within the sample is addressed. Based on the multi-physical computation model, a case study for the ProSPA instrument for in situ analysis of lunar volatiles is presented, which predicts relevant dynamic process parameters, such as gas pressure and process duration.
Possible effects of drift wave turbulence on magnetic structure and plasma transport in tokamaks
International Nuclear Information System (INIS)
Callen, J.D.
1977-07-01
A new mechanism is proposed by which low level, drift wave type fluctuations, such as those observed in the ATC and TFR experiments, can cause anomalous radial electron heat transport in tokamaks. The model is based on the fact that since transport processes parallel to the magnetic field are many orders of magnitude more rapid than perpendicular ones, very small helically resonant magnetic perturbations that cause field lines to move radially allow the parallel transport process to contribute to radial electron heat transport. It is hypothesized that the small magnetic perturbations accompanying drift waves at any nonzero plasma β are large enough to produce significant effects in present tokamak experiments. The helical magnetic component of drift waves produces magnetic island structures whose spatial widths can easily exceed the ion gyroradius. In a drift wave oscillation period, electrons circumnavigate a magnetic island, whereas the slower moving ions see only a tilt of the magnetic field lines. Thus, electrons try to diffuse radially more rapidly than ions; however, a radialpotential builds up on a very short time scale to confine the electrons electrostatically and thereby keep the particle diffusion ambipolar. Nonetheless, this parallel electron diffusion process does cause net radial electron heat conduction through an ensemble of closely packed island structures. The heat conduction coefficient is estimated. Other effects that these magnetic flutters may have on plasma transport and runaway electron processes are also discussed
Jungclaus, Johann; Moreno-Chamarro, Eduardo; Lohmann, Katja
2016-04-01
While it is clear that the Atlantic Meridional Overturning Circulation (AMOC) is responsible for meridional heat transfer from the South Atlantic and the tropics to the North Atlantic, the majority of the heat transport in the northern North Atlantic and the Nordic seas is carried by the gyre system. However, the detailed mechanisms determining the interaction between and the temporal modulation of the components of the northward heat transport system are not clear. Long-term climate records and model simulations can help to identify important processes and to provide background for the changes that are presently observed. Multi-centennial proxy records from the subpolar North Atlantic and the Nordic Seas indicate, for example, an out-of-phase behavior of sea surface temperature and gyre circulation between the two regions with consequences for regional climate. Paleoceanographic evidence from Fram Strait shows a pronounced modulation of heat transfer to the Arctic by the Atlantic Water layer during the last 2000 years and reconstructions from the Subpolar North Atlantic suggest a role of ocean circulation in the transition between the Medieval Climate Anomaly and the Little Ice Age. Here we explore a small ensemble of last millennium simulations, carried out with the Max Planck Institute Earth System Model, and analyze mechanisms connecting the AMOC and gyre circulation and their relation to external forcing. Our results support the important role of the Subpolar Gyre strength and the related meridional mass and temperature fluxes. We find that the modulation of the northward heat transport into the Nordic Seas and the Arctic has pronounced impact on sea-ice distribution, ocean-atmosphere interaction, and the surface climate in Scandinavia and Western Europe.
Dense-gas dispersion advection-diffusion model
International Nuclear Information System (INIS)
Ermak, D.L.
1992-07-01
A dense-gas version of the ADPIC particle-in-cell, advection- diffusion model was developed to simulate the atmospheric dispersion of denser-than-air releases. In developing the model, it was assumed that the dense-gas effects could be described in terms of the vertically-averaged thermodynamic properties and the local height of the cloud. The dense-gas effects were treated as a perturbation to the ambient thermodynamic properties (density and temperature), ground level heat flux, turbulence level (diffusivity), and windfield (gravity flow) within the local region of the dense-gas cloud. These perturbations were calculated from conservation of energy and conservation of momentum principles along with the ideal gas law equation of state for a mixture of gases. ADPIC, which is generally run in conjunction with a mass-conserving wind flow model to provide the advection field, contains all the dense-gas modifications within it. This feature provides the versatility of coupling the new dense-gas ADPIC with alternative wind flow models. The new dense-gas ADPIC has been used to simulate the atmospheric dispersion of ground-level, colder-than-ambient, denser-than-air releases and has compared favorably with the results of field-scale experiments
Empirical particle transport model for tokamaks
International Nuclear Information System (INIS)
Petravic, M.; Kuo-Petravic, G.
1986-08-01
A simple empirical particle transport model has been constructed with the purpose of gaining insight into the L- to H-mode transition in tokamaks. The aim was to construct the simplest possible model which would reproduce the measured density profiles in the L-regime, and also produce a qualitatively correct transition to the H-regime without having to assume a completely different transport mode for the bulk of the plasma. Rather than using completely ad hoc constructions for the particle diffusion coefficient, we assume D = 1/5 chi/sub total/, where chi/sub total/ ≅ chi/sub e/ is the thermal diffusivity, and then use the κ/sub e/ = n/sub e/chi/sub e/ values derived from experiments. The observed temperature profiles are then automatically reproduced, but nontrivially, the correct density profiles are also obtained, for realistic fueling rates and profiles. Our conclusion is that it is sufficient to reduce the transport coefficients within a few centimeters of the surface to produce the H-mode behavior. An additional simple assumption, concerning the particle mean-free path, leads to a convective transport term which reverses sign a few centimeters inside the surface, as required by the H-mode density profiles
Penetration of Cosmic Rays into Dense Molecular Clouds: Role of Diffuse Envelopes
Ivlev, A. V.; Dogiel, V. A.; Chernyshov, D. O.; Caselli, P.; Ko, C.-M.; Cheng, K. S.
2018-03-01
A flux of cosmic rays (CRs) propagating through a diffuse ionized gas can excite MHD waves, thus generating magnetic disturbances. We propose a generic model of CR penetration into molecular clouds through their diffuse envelopes, and identify the leading physical processes controlling their transport on the way from a highly ionized interstellar medium to the dense interior of the cloud. The model allows us to describe a transition between a free streaming of CRs and their diffusive propagation, determined by the scattering on the self-generated disturbances. A self-consistent set of equations, governing the diffusive transport regime in an envelope and the MHD turbulence generated by the modulated CR flux, is characterized by two dimensionless numbers. We demonstrate a remarkable mutual complementarity of different mechanisms leading to the onset of the diffusive regime, which results in a universal energy spectrum of the modulated CRs. In conclusion, we briefly discuss implications of our results for several fundamental astrophysical problems, such as the spatial distribution of CRs in the Galaxy as well as the ionization, heating, and chemistry in dense molecular clouds. This paper is dedicated to the memory of Prof. Vadim Tsytovich.
Modelling of activity transport in PHWR
International Nuclear Information System (INIS)
Veena, S.N.; Rangarajan, S.; Narasimhan, S.V.; Horvath, G.L.
2000-01-01
The modelling of mass and activity transport in PHWR is of importance in predicting the build up of radiation field in and around the Primary Heat Transport system which will consequently help in planning the Dilute Chemical Decontamination and man rem budgeting. Modeling also helps in understanding the different parameters controlling the transport behaviour. Some of the important parameters include coolant chemistry like pH, physical parameters like temperature, the nature of the corrosion film and hence the effect of passivation techniques. VVER code for activity transport uses six nodes for the primary system and is essentially devised for stainless steel system. In the present work though based on this model, major modifications have been incorporated to suit the PHWR conditions. In the code, the PHT system of PHWR is suitably divided into 14 nodes, 5 in-core and 9 out of core nodes based on material and heat transfer properties. This paper describes the mechanisms involved in the various processes like generation of corrosion products, their release as well as their transport into the primary coolant, the activation of inactive corrosion product nuclides and the build up of radiation field due to 60 Co around the PHT system. (author)
Transport and diffusion climatology of the US Atlantic and Gulf coasts
International Nuclear Information System (INIS)
Raynor, G.S.; Hayes, J.V.
1980-01-01
This study is part of a larger study of coastal meteorology and diffusion and was planned to assist in site selection of energy facilities by describing the transport and diffusion climatology of the United States east and Gulf coasts in as much detail as can be extracted from readily available meteorological data. The area covered in this study is the United States east and Gulf coasts from Maine to Texas. The region studied is all within the coastal plain and is generally characterized by flat beaches and very gentle slopes inland except in New England, where the coast is more rugged and the terrain hilly close to the sea. Meteorological variables of primary concern in this study are those which govern or influence transport and diffusion of airborne gases and particles. The most important are wind direction and speed and some measure of diffusive capacity such as turbulence, gustiness or lapse rate. Eight stations were chosen to give four pairs for comparison between a coastal station and another somewhat farther inland. The pairs are Boston and Bedford, Massachusetts; Belmar and Lakehurst, New Jersey; Cape Kennedy and Orlando, Florida; and Galveston and Houston, Texas. The same years of data were obtained for both stations in each pair. Results of selected examples are presented. The frequency of calms and of winds in the three sectors relative to the coastline is reported for the 25 coastal stations from Portland, Maine (PWM) to Brownsville, Texas (BRO). Differences between day and night in wind direction distribution are shown for six selected stations. The frequency of the five diffusion rating classes at the same coastal stations during onshore winds is also shown. Differences in dffusion conditions between day and night at six selected stations are given. The results obtained were arranged for easy use with diffusion models in which the primary meteorological inputs are wind speed and measures of lateral and vertical diffusion
Modeling diffuse phosphorus emissions to assist in best management practice designing
Kovacs, Adam; Zessner, Matthias; Honti, Mark; Clement, Adrienne
2010-05-01
A diffuse emission modeling tool has been developed, which is appropriate to support decision-making in watershed management. The PhosFate (Phosphorus Fate) tool allows planning best management practices (BMPs) in catchments and simulating their possible impacts on the phosphorus (P) loads. PhosFate is a simple fate model to calculate diffuse P emissions and their transport within a catchment. The model is a semi-empirical, catchment scale, distributed parameter and long-term (annual) average model. It has two main parts: (a) the emission and (b) the transport model. The main input data of the model are digital maps (elevation, soil types and landuse categories), statistical data (crop yields, animal numbers, fertilizer amounts and precipitation distribution) and point information (precipitation, meteorology, soil humus content, point source emissions and reservoir data). The emission model calculates the diffuse P emissions at their source. It computes the basic elements of the hydrology as well as the soil loss. The model determines the accumulated P surplus of the topsoil and distinguishes the dissolved and the particulate P forms. Emissions are calculated according to the different pathways (surface runoff, erosion and leaching). The main outputs are the spatial distribution (cell values) of the runoff components, the soil loss and the P emissions within the catchment. The transport model joins the independent cells based on the flow tree and it follows the further fate of emitted P from each cell to the catchment outlets. Surface runoff and P fluxes are accumulated along the tree and the field and in-stream retention of the particulate forms are computed. In case of base flow and subsurface P loads only the channel transport is taken into account due to the less known hydrogeological conditions. During the channel transport, point sources and reservoirs are also considered. Main results of the transport algorithm are the discharge, dissolved and sediment
International Nuclear Information System (INIS)
Chang, C.S.; Hammett, G.W.; Goldston, R.J.
1990-01-01
Neoclassical transport of energetic minority tail ions, which are generated by high powered electromagnetic waves of the Ion Cyclotron Range of Frequencies (ICRF) at the fundamental harmonic resonance, is studied analytically in tokamak geometry. The effect of Coulomb collisions on the tail ion transport is investigated in the present work. The total tail ion transport will be the sum of the present collision-driven transport and the wave-driven transport, which is due to the ICRF-wave scattering of the tail particles as reported in the literature. The transport coefficients have been calculated kinetically, and it is found that the large tail ion viscosity, driven by the localized ICRF-heating and Coulomb slowing-down collisions, induces purely convective particle transport of the tail species, while the energy transport is both convective and diffusive. The rate of radial particle transport is shown to be usually small, but the rate of radial energy transport is larger and may not be negligible compared to the Coulomb slowing-down rate. 18 refs., 2 figs
Radiosity diffusion model in 3D
Riley, Jason D.; Arridge, Simon R.; Chrysanthou, Yiorgos; Dehghani, Hamid; Hillman, Elizabeth M. C.; Schweiger, Martin
2001-11-01
We present the Radiosity-Diffusion model in three dimensions(3D), as an extension to previous work in 2D. It is a method for handling non-scattering spaces in optically participating media. We present the extension of the model to 3D including an extension to the model to cope with increased complexity of the 3D domain. We show that in 3D more careful consideration must be given to the issues of meshing and visibility to model the transport of light within reasonable computational bounds. We demonstrate the model to be comparable to Monte-Carlo simulations for selected geometries, and show preliminary results of comparisons to measured time-resolved data acquired on resin phantoms.
Diffusion of innovative domestic heating systems and multi-storey wood-framed buildings in Sweden
Energy Technology Data Exchange (ETDEWEB)
Mahapatra, Krushna
2007-10-15
The diffusion of innovations that promote sustainable use of forest resources and energy efficiency is important for reducing greenhouse gas emission and dependency on oil. In this thesis the 'systems of innovation' (SI) approach is used to analyse the diffusion of multi-storey wood-framed buildings and wood pellet heating systems in Sweden. The diffusion of an innovative heating system (IHS) is influenced by the diffusion of other types of IHSs, making it complex to analyse the diffusion of all these systems simultaneously using the SI approach. Hence, an 'adopter-centric' approach was used, as homeowners make the decision to adopt an IHS, which affects the rate of adoption of that system. The SI analyses showed that several sources of path dependency, resulting from the establishment and growth of the concrete-based construction system over the past 100 years, hinder the expansion of a wood-based multi-storey construction system. However, development of the wood construction system was possible due to government policies and funding, the wood industry's interest in expanding the market for value-added wood products, and the involvement of the wood research community. The growth of the pellet market was supported by national energy policy, the abundance of raw material and broad dissemination of district heating systems. However, a lack of co-ordination between the pellet and equipment suppliers in the early phase of market development, high annual operating cost, lack of information, dissatisfaction among early adopters and technology lock-in contributed to its relatively slow growth. The adopter-centric approach included household questionnaire surveys: one covering the whole of Sweden in 2004 involving 1500 randomly selected homeowners with any type of heating system, and another in the city of Oestersund in 2005 of 700 homeowners who had resistance heaters. The same homeowners in Oestersund were re-surveyed in 2006 to analyse the
Oxygen diffusion in soils: Understanding the factors and processes needed for modeling
Directory of Open Access Journals (Sweden)
José Neira
2015-08-01
Full Text Available Oxygen is an important element for plant growth. Reducing its concentration in the soil affects plant physiological processes such as nutrient and water uptake as well as respiration, the redox potential of soil elements and the activity of microorganisms. The main mechanism of oxygen transport in the soil is by diffusion, a dynamic process greatly influenced by soil physical properties such as texture and structure, conditioning, pore size distribution, tortuosity and connectivity. Organic matter is a modifying agent of the soil's chemical and physical properties, affecting its structure and the porous matrix, which are determinants of oxygen transport. This study reviews the theory of soil gas diffusion and the effect of soil organic matter on the soil's physical properties and transport of gases. It also reviews gas diffusion models, particularly those including the effect of soil organic matter.
Edge modelling of ICFR heated plasmas on PLT
International Nuclear Information System (INIS)
Lehrman, I.S.
1990-01-01
Theoretical models are presented to explain the edge plasma-antenna interaction that occurs during ICRF heating. The periodic structure of the Faraday shield is found to result in strong ponderomotive force in the vicinity of the antenna. A fluid model, which incorporates the ponderomotive force, predicts an increase in particle transport to the Faraday shield. Kinetic modelling shows that the strong antenna near-fields act to increase the energy of deuterons that strike the shield, thereby increasing the sputtering of shield material. In addition, kinetic modelling shows that E parallel induced between adjacent shield elements acts to heat edge electron that transit close to the antenna. The predictions of the models are shown to be consistent with measurements of enhanced transport on PLT. (author). 27 refs, 17 figs
TEMPEST simulations of the plasma transport in a single-null tokamak geometry
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Rognlien, T.D.; Bodi, K.; Krasheninnikov, S.
2010-01-01
We present edge kinetic ion transport simulations of tokamak plasmas in magnetic divertor geometry using the fully nonlinear (full-f) continuum code TEMPEST. Besides neoclassical transport, a term for divergence of anomalous kinetic radial flux is added to mock up the effect of turbulent transport. To study the relative roles of neoclassical and anomalous transport, TEMPEST simulations were carried out for plasma transport and flow dynamics in a single-null tokamak geometry, including the pedestal region that extends across the separatrix into the scrape-off layer and private flux region. A series of TEMPEST simulations were conducted to investigate the transition of midplane pedestal heat flux and flow from the neoclassical to the turbulent limit and the transition of divertor heat flux and flow from the kinetic to the fluid regime via an anomalous transport scan and a density scan. The TEMPEST simulation results demonstrate that turbulent transport (as modelled by large diffusion) plays a similar role to collisional decorrelation of particle orbits and that the large turbulent transport (large diffusion) leads to an apparent Maxwellianization of the particle distribution. We also show the transition of parallel heat flux and flow at the entrance to the divertor plates from the fluid to the kinetic regime. For an absorbing divertor plate boundary condition, a non-half-Maxwellian is found due to the balance between upstream radial anomalous transport and energetic ion endloss.
Asymptotic solutions of numerical transport problems in optically thick, diffusive regimes
International Nuclear Information System (INIS)
Larsen, E.W.; Morel, J.E.; Miller, W.F. Jr.
1987-01-01
We present an asymptotic analysis of spatial differencing schemes for the discrete-ordinates equations, for diffusive media with spatial cells that are not optically thin. Our theoretical tool is an asymptotic expansion that has previously been used to describe the transform from analytic transport to analytic diffusion theory for such media. To introduce this expansion and its physical rationale, we first describe it for the analytic discrete-ordinates equations. Then, we apply the expansion to the spatially discretized discrete-ordinates equations, with the spatial mesh scaled in either of two physically relevant ways such that the optical thickness of the spatial cells is not small. If the result of either expansion is a legitimate diffusion description for either the cell-averaged or cell-edge fluxes, then we say that the approximate flux has the appropriate diffusion limit; otherwise, we say it does not. We consider several transport differencing schemes that are applicable in neutron transport and thermal radiation applications. We also include numerical results which demonstrate the validity of our theory and show that differencing schemes that do have a particular diffusion limit are substantially more accurate, in the regime described by the limit, than those that do not. copyright 1987 Academic Press, Inc
A non-Linear transport model for determining shale rock characteristics
Ali, Iftikhar; Malik, Nadeem
2016-04-01
Unconventional hydrocarbon reservoirs consist of tight porous rocks which are characterised by nano-scale size porous networks with ultra-low permeability [1,2]. Transport of gas through them is not well understood at the present time, and realistic transport models are needed in order to determine rock properties and for estimating future gas pressure distribution in the reservoirs. Here, we consider a recently developed non-linear gas transport equation [3], ∂p-+ U ∂p- = D ∂2p-, t > 0, (1) ∂t ∂x ∂x2 complimented with suitable initial and boundary conditions, in order to determine shale rock properties such as the permeability K, the porosity φ and the tortuosity, τ. In our new model, the apparent convection velocity, U = U(p,px), and the apparent diffusivity D = D(p), are both highly non-linear functions of the pressure. The model incorporate various flow regimes (slip, surface diffusion, transition, continuum) based upon the Knudsen number Kn, and also includes Forchchiemers turbulence correction terms. In application, the model parameters and associated compressibility factors are fully pressure dependent, giving the model more realism than previous models. See [4]. Rock properties are determined by solving an inverse problem, with model parameters adjustment to minimise the error between the model simulation and available data. It is has been found that the proposed model performs better than previous models. Results and details of the model will be presented at the conference. Corresponding author: namalik@kfupm.edu.sa and nadeem_malik@cantab.net References [1] Cui, X., Bustin, A.M. and Bustin, R., "Measurements of gas permeability and diffusivity of tight reservoir rocks: different approaches and their applications", Geofluids 9, 208-223 (2009). [2] Chiba R., Fomin S., Chugunov V., Niibori Y. and Hashida T., "Numerical Simulation of Non Fickian Diffusion and Advection in a Fractured Porous Aquifer", AIP Conference Proceedings 898, 75 (2007
International Nuclear Information System (INIS)
Zhou, W.; Arthur, R.; Xu, T.; Pruess, K.
2005-01-01
precipitation/dissolution and solute transport. Preliminary results show that during the early heating phase, reactions strongly depend on the magnitude of the temperature gradient across the buffer. As the temperature gradient diminishes, reactions are increasingly dominated by groundwater solutes diffusing into the bentonite pore water from the host rock. Bentonite effective diffusion coefficient plays an important role to long-term solute transport. [1] Arthur, R., W. Zhou, and B. Stromberg, (2003), 'THC modeling of the non-isothermal phase of near-field evolution' in Proceedings of the 10. International High-Level Radioactive Waste Management Conference, March 30-April 2, 2003, Las Vegas, Nevada, USA. [2] Hoekmark, H. and B. Faelth, (2003), Thermal dimensioning of the deep repository, SKB TR-03- 09, Swedish Nuclear Fuel and Waste Management Co., Stockholm, Sweden. [3] Bruno, J. D. Arcos, and L. Duro, (1999), Processes and features affecting the near field hydro-chemistry, SKB TR-99-29, Swedish Nuclear Fuel and Waste Management Co., Stockholm, Sweden. [4] Xu, T., E. Sonnenthal, N. Spycher, and K. Pruess, (2003), TOUGHREACT User's Guide: A Simulation Program for Non-isothermal Multiphase Reactive Geochemical Transport in Variably Saturated Geologic Media, LBNL-55460, Lawrence Berkeley National Laboratory, Berkeley, California, USA. (authors)
Source effects on impurity and heat transport in a tokamak
International Nuclear Information System (INIS)
Bennett, R.B.
1980-12-01
A recently developed generalization of neoclassical theory is extended here to study heat flux contributions to impurity transport, as well as the heat fluxes themselves. The theory accounts for the first four source moments, with external drags, which has been studied previously with either fewer moments or restricted to a collisional plasma. Conditions are established for which a momentum source may be used to modify the particle and heat transport. In the course of this work, the particle and heat transport is evaluated for a two species plasma with arbitrary plasma geometry, beta, and collisionality
Landauer-Datta-Lundstrom Generalized Transport Model for Nano electronics
International Nuclear Information System (INIS)
Kruglyak, Y.
2014-01-01
The Landauer-Datta-Lundstrom electron transport model is briefly summarized. If a band structure is given, the number of conduction modes can be evaluated and if a model for a mean-free-path for backscattering can be established, then the near-equilibrium thermoelectric transport coefficients can be calculated using the final expressions listed below for 1D, 2D, and 3D resistors in ballistic, quasi ballistic, and diffusive linear response regimes when there are differences in both voltage and temperature across the device. The final expressions of thermoelectric transport coefficients through the Fermi-Dirac integrals are collected for 1D, 2D, and 3D semiconductors with parabolic band structure and for 2D graphene linear dispersion in ballistic and diffusive regimes with the power law scattering.
ENERGETIC PARTICLE TRANSPORT ACROSS THE MEAN MAGNETIC FIELD: BEFORE DIFFUSION
International Nuclear Information System (INIS)
Laitinen, T.; Dalla, S.
2017-01-01
Current particle transport models describe the propagation of charged particles across the mean field direction in turbulent plasmas as diffusion. However, recent studies suggest that at short timescales, such as soon after solar energetic particle (SEP) injection, particles remain on turbulently meandering field lines, which results in nondiffusive initial propagation across the mean magnetic field. In this work, we use a new technique to investigate how the particles are displaced from their original field lines, and we quantify the parameters of the transition from field-aligned particle propagation along meandering field lines to particle diffusion across the mean magnetic field. We show that the initial decoupling of the particles from the field lines is slow, and particles remain within a Larmor radius from their initial meandering field lines for tens to hundreds of Larmor periods, for 0.1–10 MeV protons in turbulence conditions typical of the solar wind at 1 au. Subsequently, particles decouple from their initial field lines and after hundreds to thousands of Larmor periods reach time-asymptotic diffusive behavior consistent with particle diffusion across the mean field caused by the meandering of the field lines. We show that the typical duration of the prediffusive phase, hours to tens of hours for 10 MeV protons in 1 au solar wind turbulence conditions, is significant for SEP propagation to 1 au and must be taken into account when modeling SEP propagation in the interplanetary space.
ENERGETIC PARTICLE TRANSPORT ACROSS THE MEAN MAGNETIC FIELD: BEFORE DIFFUSION
Energy Technology Data Exchange (ETDEWEB)
Laitinen, T.; Dalla, S., E-mail: tlmlaitinen@uclan.ac.uk [Jeremiah Horrocks Institute, University of Central Lancashire, Preston (United Kingdom)
2017-01-10
Current particle transport models describe the propagation of charged particles across the mean field direction in turbulent plasmas as diffusion. However, recent studies suggest that at short timescales, such as soon after solar energetic particle (SEP) injection, particles remain on turbulently meandering field lines, which results in nondiffusive initial propagation across the mean magnetic field. In this work, we use a new technique to investigate how the particles are displaced from their original field lines, and we quantify the parameters of the transition from field-aligned particle propagation along meandering field lines to particle diffusion across the mean magnetic field. We show that the initial decoupling of the particles from the field lines is slow, and particles remain within a Larmor radius from their initial meandering field lines for tens to hundreds of Larmor periods, for 0.1–10 MeV protons in turbulence conditions typical of the solar wind at 1 au. Subsequently, particles decouple from their initial field lines and after hundreds to thousands of Larmor periods reach time-asymptotic diffusive behavior consistent with particle diffusion across the mean field caused by the meandering of the field lines. We show that the typical duration of the prediffusive phase, hours to tens of hours for 10 MeV protons in 1 au solar wind turbulence conditions, is significant for SEP propagation to 1 au and must be taken into account when modeling SEP propagation in the interplanetary space.
Jiang, Yueyang; Zhuang, Qianlai; O'Donnell, Jonathan A.
2012-01-01
Thawing and freezing processes are key components in permafrost dynamics, and these processes play an important role in regulating the hydrological and carbon cycles in the northern high latitudes. In the present study, we apply a well-developed soil thermal model that fully couples heat and water transport, to simulate the thawing and freezing processes at daily time steps across multiple sites that vary with vegetation cover, disturbance history, and climate. The model performance was evaluated by comparing modeled and measured soil temperatures at different depths. We use the model to explore the influence of climate, fire disturbance, and topography (north- and south-facing slopes) on soil thermal dynamics. Modeled soil temperatures agree well with measured values for both boreal forest and tundra ecosystems at the site level. Combustion of organic-soil horizons during wildfire alters the surface energy balance and increases the downward heat flux through the soil profile, resulting in the warming and thawing of near-surface permafrost. A projection of 21st century permafrost dynamics indicates that as the climate warms, active layer thickness will likely increase to more than 3 meters in the boreal forest site and deeper than one meter in the tundra site. Results from this coupled heat-water modeling approach represent faster thaw rates than previously simulated in other studies. We conclude that the discussed soil thermal model is able to well simulate the permafrost dynamics and could be used as a tool to analyze the influence of climate change and wildfire disturbance on permafrost thawing.
Atomistic models of Cu diffusion in CuInSe2 under variations in composition
Sommer, David E.; Dunham, Scott T.
2018-03-01
We construct an analytic model for the composition dependence of the vacancy-mediated Cu diffusion coefficient in undoped CuInSe2 using parameters from density functional theory. The applicability of this model is supported numerically with kinetic lattice Monte Carlo and Onsager transport tensors. We discuss how this model relates to experimental measurements of Cu diffusion, arguing that our results can account for significant contributions to the bulk diffusion of Cu tracers in non-stoichiometric CuInSe2.
Fluctuation of heat current in Josephson junctions
Directory of Open Access Journals (Sweden)
P. Virtanen
2015-02-01
Full Text Available We discuss the statistics of heat current between two superconductors at different temperatures connected by a generic weak link. As the electronic heat in superconductors is carried by Bogoliubov quasiparticles, the heat transport fluctuations follow the Levitov–Lesovik relation. We identify the energy-dependent quasiparticle transmission probabilities and discuss the resulting probability density and fluctuation relations of the heat current. We consider multichannel junctions, and find that heat transport in diffusive junctions is unique in that its statistics is independent of the phase difference between the superconductors.
On parameterization of heat conduction in coupled soil water and heat flow modelling
Czech Academy of Sciences Publication Activity Database
Votrubová, J.; Dohnal, M.; Vogel, T.; Tesař, Miroslav
2012-01-01
Roč. 7, č. 4 (2012), s. 125-137 ISSN 1801-5395 R&D Projects: GA ČR GA205/08/1174 Institutional research plan: CEZ:AV0Z20600510 Keywords : advective heat flux * dual-permeability model * soil heat transport * soil thermal conductivity * surface energy balance Subject RIV: DA - Hydrology ; Limnology Impact factor: 0.333, year: 2012
Laminar oxy-fuel diffusion flame supported by an oxygen-permeable-ion-transport membrane
Hong, Jongsup
2013-03-01
A numerical model with detailed gas-phase chemistry and transport was used to predict homogeneous fuel conversion processes and to capture the important features (e.g., the location, temperature, thickness and structure of a flame) of laminar oxy-fuel diffusion flames stabilized on the sweep side of an oxygen permeable ion transport membrane (ITM). We assume that the membrane surface is not catalytic to hydrocarbon or syngas oxidation. It has been demonstrated that an ITM can be used for hydrocarbon conversion with enhanced reaction selectivity such as oxy-fuel combustion for carbon capture technologies and syngas production. Within an ITM unit, the oxidizer flow rate, i.e., the oxygen permeation flux, is not a pre-determined quantity, since it depends on the oxygen partial pressures on the feed and sweep sides and the membrane temperature. Instead, it is influenced by the oxidation reactions that are also dependent on the oxygen permeation rate, the initial conditions of the sweep gas, i.e., the fuel concentration, flow rate and temperature, and the diluent. In oxy-fuel combustion applications, the sweep side is fuel-diluted with CO2, and the entire unit is preheated to achieve a high oxygen permeation flux. This study focuses on the flame structure under these conditions and specifically on the chemical effect of CO2 dilution. Results show that, when the fuel diluent is CO2, a diffusion flame with a lower temperature and a larger thickness is established in the vicinity of the membrane, in comparison with the case in which N2 is used as a diluent. Enhanced OH-driven reactions and suppressed H radical chemistry result in the formation of products with larger CO and H2O and smaller H2 concentrations. Moreover, radical concentrations are reduced due to the high CO2 fraction in the sweep gas. CO2 dilution reduces CH3 formation and slows down the formation of soot precursors, C2H2 and C2H4. The flame location impacts the species diffusion and heat transfer from the
International Nuclear Information System (INIS)
Taherkhani, Farid; Akbarzadeh, Hamed; Feyzi, Mostafa; Rafiee, Hamid Reza
2015-01-01
Molecular dynamics simulation has been implemented for doping effect on melting temperature, heat capacity, self-diffusion coefficient of gold–copper bimetallic nanostructure with 55 total gold and copper atom numbers and its bulk alloy. Trend of melting temperature for gold–copper bimetallic nanocluster is not same as melting temperature copper–gold bulk alloy. Molecular dynamics simulation of our result regarding bulk melting temperature is consistence with available experimental data. Molecular dynamics simulation shows that melting temperature of gold–copper bimetallic nanocluster increases with copper atom fraction. Semi-empirical potential model and quantum Sutton–Chen potential models do not change melting temperature trend with copper doping of gold–copper bimetallic nanocluster. Self-diffusion coefficient of copper atom is greater than gold atom in gold–copper bimetallic nanocluster. Semi-empirical potential within the tight-binding second moment approximation as new application potential model for melting temperature of gold–copper bulk structure shows better result in comparison with EAM, Sutton–Chen potential, and quantum Sutton–Chen potential models
Energy Technology Data Exchange (ETDEWEB)
Taherkhani, Farid, E-mail: faridtaherkhani@gmail.com, E-mail: f.taherkhani@razi.ac.ir [Razi University, Department of Physical Chemistry (Iran, Islamic Republic of); Akbarzadeh, Hamed [Hakim Sabzevari University, Department of Chemistry (Iran, Islamic Republic of); Feyzi, Mostafa; Rafiee, Hamid Reza [Razi University, Department of Physical Chemistry (Iran, Islamic Republic of)
2015-01-15
Molecular dynamics simulation has been implemented for doping effect on melting temperature, heat capacity, self-diffusion coefficient of gold–copper bimetallic nanostructure with 55 total gold and copper atom numbers and its bulk alloy. Trend of melting temperature for gold–copper bimetallic nanocluster is not same as melting temperature copper–gold bulk alloy. Molecular dynamics simulation of our result regarding bulk melting temperature is consistence with available experimental data. Molecular dynamics simulation shows that melting temperature of gold–copper bimetallic nanocluster increases with copper atom fraction. Semi-empirical potential model and quantum Sutton–Chen potential models do not change melting temperature trend with copper doping of gold–copper bimetallic nanocluster. Self-diffusion coefficient of copper atom is greater than gold atom in gold–copper bimetallic nanocluster. Semi-empirical potential within the tight-binding second moment approximation as new application potential model for melting temperature of gold–copper bulk structure shows better result in comparison with EAM, Sutton–Chen potential, and quantum Sutton–Chen potential models.
Ionic diffusion in quartz studied by transport measurements, SIMS and atomistic simulations
International Nuclear Information System (INIS)
Sartbaeva, Asel; Wells, Stephen A; Redfern, Simon A T; Hinton, Richard W; Reed, Stephen J B
2005-01-01
Ionic diffusion in the quartz-β-eucryptite system is studied by DC transport measurements, SIMS and atomistic simulations. Transport data show a large transient increase in ionic current at the α-β phase transition of quartz (the Hedvall effect). The SIMS data indicate two diffusion processes, one involving rapid Li + motion and the other involving penetration of Al and Li atoms into quartz at the phase transition. Atomistic simulations explain why the fine microstructure of twin domain walls in quartz near the transition does not hinder Li + diffusion
International Nuclear Information System (INIS)
Igna Junior, A.D.
1984-01-01
The relevant parameters of two steady-state models of a plasma column, in fusion regime, were analyzed for an ideal Tokamak. The neo-classical transport theory was considered in the banana regime and in the Pfirsch-Schlueter regime. The first model proposes a correction in the numerical coefficients of the transport equations. In the other one, a poloidal current from Pfirsch-Schlueter classical diffusion is considered aiming to satisfy the pressure balance. (M.C.K.) [pt
Analytical Solutions of Ionic Diffusion and Heat Conduction in Multilayered Porous Media
Directory of Open Access Journals (Sweden)
Yu Bai
2015-01-01
Full Text Available Ionic diffusion and heat conduction in a multiple layered porous medium have many important engineering applications. One of the examples is the chloride ions from deicers penetrating into concrete structures such as bridge decks. Different overlays can be placed on top of concrete surface to slowdown the chloride penetration. In this paper, the chloride ion diffusion equations were established for concrete structures with multiple layers of protective system. By using Laplace transformation, an analytical solution was developed first for chloride concentration profiles in two-layered system and then extended to multiple layered systems with nonconstant boundary conditions, including the constant boundary and linear boundary conditions. Because ionic diffusion in saturated media and heat conduction are governed by the same form of partial differential equations with different materials parameters, the analytical solution was further extended to handle heat conduction in a multiple layered system under nonconstant boundary conditions. The numerical results were compared with available test data. The basic trends of the analytical solution and the test data agreed quite well.
Auxiliary plasma heating and fueling models for use in particle simulation codes
International Nuclear Information System (INIS)
Procassini, R.J.; Cohen, B.I.
1989-01-01
Computational models of a radiofrequency (RF) heating system and neutral-beam injector are presented. These physics packages, when incorporated into a particle simulation code allow one to simulate the auxiliary heating and fueling of fusion plasmas. The RF-heating package is based upon a quasilinear diffusion equation which describes the slow evolution of the heated particle distribution. The neutral-beam injector package models the charge exchange and impact ionization processes which transfer energy and particles from the beam to the background plasma. Particle simulations of an RF-heated and a neutral-beam-heated simple-mirror plasma are presented. 8 refs., 5 figs
Lattice Boltzmann heat transfer model for permeable voxels
Pereira, Gerald G.; Wu, Bisheng; Ahmed, Shakil
2017-12-01
We develop a gray-scale lattice Boltzmann (LB) model to study fluid flow combined with heat transfer for flow through porous media where voxels may be partially solid (or void). Heat transfer in rocks may lead