One-dimensional Transport Model Research Articles

Modeling and simulation of liquid pool fires with in-depth radiation absorption and heat transfer

In this paper we present a computational fluid dynamics model for predicting the heat release rates of liquid pool fires. The model makes use of the one-dimensional heat transfer solver to provide the liquid surface boundary condition for the gas phase solver. The in-depth radiation transport is solved by a one-dimensional radiation transport model together with effective absorption coefficients determined from experimental data. The model accounts for the convective heat transfer in the liquid phase by modifying the thermal conductivity. The model is implemented as a boundary condition in the fire dynamics simulator (FDS). The model is validated by comparing experimental and predicted evaporation rates for water and a range of hydrocarbon fuels. The sensitivity of the results to the modelling assumptions and model input parameters is studied. The in-depth heat transfer appears to have a significant effect on the fire dynamics, except for the peak burning rates, which depend most importantly on the gas phase combustion.

One-Dimensional Pit Experiments and Modeling to Determine Critical Factors for Pit Stability and Repassivation

Experiments on stainless steel artificial pit electrodes in sodium chloride were used to inform a diffusion model developed based on the mass transport behavior within a one-dimensional corroding pit. Measurable estimates of the dissolution flux as well as the potential describing the conditions of interest were obtained from experiment as the one-dimensional pit stability product under a salt film (i·x)saltfilm and the repassivation potential Erp, respectively. These parameter estimates were acquired as a function of pit depth and were related to the concentration of the metal cation at the corroding surface at each depth via a one-dimensional mass transport model. These results allowed for the construction of a quantitative framework relating the various electrochemical parameters describing the transition from pit stability to repassivation. Such an analysis permitted the straightforward estimate of the critical surface concentration associated with this transition, which resulted in a single conservative lower bound of 50% of the saturation concentration for the minimum aggressive chemistry to sustain stable pitting and prevent repassivation. Along with published data, these results were utilized to advance the idea that the critical pit solution chemistry is independent of bulk chloride concentration up to 4 M, a range frequently encountered in atmospheric conditions.

Extension of apparent devolatilization kinetics from thermally thin to thermally thick particles in zero dimensions for woody biomass

This work aims to provide an accurate and simple model, predicting the time dependent devolatilization of woody biomass at conditions (Tgas < 2000 K) and particle sizes (<2 mm) relevant to suspension fired boilers. The zero dimensional model is developed from reference calculations with a one-dimensional heat transport model coupled with a drying and a devolatilization model. The model output has been used to generate pyrolysis kinetics corrected for non-isothermal effects, i.e. intraparticle heat transport limitations. Analysis of the modeling results indicate that heat transport corrections of even small particles are necessary. The current work divides a given particle size distribution into suitable size categories based on their internal heat transport properties. The devolatilization is described by size category specific rate constants based on a single first order reaction mechanism. This approach allows for significantly more accurate devolatilization predictions of any particle size distribution to be described by simple kinetic mechanisms and isothermal particle heat balances. Such an approach is easily implemented into most commercial CFD (computational fluid dynamics) codes without adding any additional strain to the computational requirements.

Evaluating the Critical Chemistry for Repassivation at the Corroding Surface Using Mass Transport Model-Based Artificial Pit Experiments

One-dimensional mass transport model calculations were utilized to design experiments with stainless steel artificial pit electrodes to determine the critical concentration of cations at the corroding surface representing the transition between stable pitting and repassivation. Rapid polarization scans following salt film precipitation and consequent open circuit dilution to different surface concentrations permitted the evaluation of kinetics at various degrees of saturation. These experiments showed a distinct change in kinetics as the surface concentration decreased, thus identifying the critical pit chemistry for the onset of repassivation. Chemical modeling of oxide precipitation from solution permitted the investigation of oxide nucleation across varying surface concentration as a function of pH as the cause of repassivation. This analysis enabled the estimation of the pH at which the first oxide would precipitate in the critical pit solution chemistry, which when combined with cation hydrolysis calculations, resulted in the evaluation of the critical pH at the transition between pit stability and repassivation. A mixed potential theory-based analysis of these results was utilized to provide mechanistic support to the quantitative framework describing critical factors for pitting stability and repassivation.

Hierarchical simulation of aquifer heterogeneity: implications of different simulation settings on solute-transport modeling

The fine-scale heterogeneity of porous media affects the large-scale transport of solutes and contaminants in groundwater and it can be reproduced by means of several geostatistical simulation tools. However, including the available geological information in these tools is often cumbersome. A hierarchical simulation procedure based on a binary tree is proposed and tested on two real-world blocks of alluvial sediments, of a few cubic meters volume, that represent small-scale aquifer analogs. The procedure is implemented using the sequential indicator simulation, but it is so general that it can be adapted to various geostatistical simulation tools, improving their capability to incorporate geological information, i.e., the sedimentological and architectural characterization of heterogeneity. When compared with a standard sequential indicator approach on bi-dimensional simulations, in terms of proportions and connectivity indicators, the proposed procedure yields reliable results, closer to the reference observations. Different ensembles of three-dimensional simulations based on different hierarchical sequences are used to perform numerical experiments of conservative solute transport and to obtain ensembles of equivalent pore velocity and dispersion coefficient at the scale length of the blocks (meter). Their statistics are used to estimate the impact of the variability of the transport properties of the simulated blocks on contaminant transport modeled on bigger domains (hectometer). This is investigated with a one-dimensional transport modeling based on the Kolmogorov-Dmitriev theory of branching stochastic processes. Applying the proposed approach with diverse binary trees and different simulation settings provides a great flexibility, which is revealed by the differences in the breakthrough curves.

An analytical discrete-ordinates solution for an improved one-dimensional model of three-dimensional transport in ducts

An analytical discrete-ordinates solution is developed for the problem of particle transport in ducts, as described by a one-dimensional model constructed with two basis functions. Two types of particle incidence are considered: isotropic incidence and incidence described by the Dirac delta distribution. Accurate numerical results are tabulated for the reflection probabilities of semi-infinite ducts and the reflection and transmission probabilities of finite ducts. It is concluded that the developed solution is more efficient than commonly used numerical implementations of the discrete-ordinates method.

Interfacial friction based quasi-continuum hydrodynamical model for nanofluidic transport of water.

In this work, we formulate a one-dimensional isothermal hydrodynamic transport model for water, which is an extension to our recently proposed hydrodynamic model for Lennard-Jones type fluid [R. Bhadauria and N. R. Aluru, J. Chem. Phys. 139, 074109 (2013)]. Viscosity variations in confinement are incorporated by the local average density method. Dirichlet boundary conditions are provided in the form of slip velocity that depends upon the macroscopic interfacial friction coefficient. The value of this friction coefficient is computed using a novel generalized Langevin equation formulation that eliminates the use of equilibrium molecular dynamics simulation. Gravity driven flows of SPC/E water confined between graphene and silicon slit shaped nanochannels are considered as examples for low and high friction cases. The proposed model yields good quantitative agreement with the velocity profiles obtained from non-equilibrium molecular dynamics simulations.

Correlating spin transport and electrode magnetization in a graphene spin valve: Simultaneous magnetic microscopy and non-local measurements

Using simultaneous magnetic force microscopy and transport measurements of a graphene spin valve, we correlate the non-local spin signal with the magnetization of the device electrodes. The imaged magnetization states corroborate the influence of each electrode within a one-dimensional spin transport model and provide evidence linking domain wall pinning to additional features in the transport signal.

Fluoride and nitrate removal from brackish groundwaters by batch-mode capacitive deionization

Capacitive deionization (CDI) is an emerging water desalination technology in which pairs of porous electrodes are electrically charged to remove ionic species from water. In this work, the feasibility of fluoride and nitrate removal from brackish groundwaters by batch-mode CDI was investigated. Initially, the effects of flow rate, initial fluoride concentration, and initial coexisting NaCl concentration on fluoride removal were studied. The steady-state fluoride concentration declined as the initial fluoride concentration decreased while initial NaCl concentration remained constant. Due to the competitive electrosorption between fluoride and chloride for limited pore surface sites, a higher initial chloride concentration resulted in a higher equilibrium dissolved fluoride concentration. A simplified one-dimensional transport model for dual anions was developed and found to reliably describe the dynamic process of removal of both fluoride and chloride ions in CDI cells over a range of well-defined operating conditions. Based on the ability of the model to describe fluoride removal, it was extended to description of nitrate removal from brackish groundwaters and also found to perform well. Thus, the approach to description of ion removal, at least in batch studies, appears robust and should assist in optimization of design and operating conditions such that optimal removal of trace ionic species is achieved even when high background concentrations of salt are present.

Effects of Entrainment on Incapability of High Intensity Beam Drilling

The effects of entrainment accompanying mass, momentum, and energy transport from the keyhole wall on keyhole collapse during high-power-density laser or electron beam drilling are theoretically and systematically investigated in this study. High intensity beam drilling is widely used in components, packaging and manufacturing technologies, micro-electromechanical-systems (MEMS), rapid prototyping manufacturing, and keyhole welding. This study proposes a quasi-steady, one-dimensional transport model to predict supersonic and subsonic flow behavior of the two-phase, vapor–liquid dispersion in a keyhole and applies the Young–Laplace equation to calculate the keyhole shape. The results show that the keyhole collapse, representing decreased or vanished radius, is susceptible to mass ejection at the base and entrainment from the side wall. Deposition of a mixture of gas and droplets in the keyhole stabilizes deformation of the keyhole. Enhanced energy and decreased axial component of momentum associated with entrainment are also apt to keyhole collapse. The predicted results agree with axial variations of transport variables of a compressible flow through a divergent and convergent nozzle, and their exact analytical solutions in the absence of friction, energy absorption, and entrainment. An understanding of the effects of ejected and entrained mass in the keyhole on drilling efficiency is therefore provided.

Application of a new cellular model for bedload transporting extreme events at steep slopes

A cellular model for bedload transport at steep channel gradients and alluvial fans has been developed to simulate lateral distribution of erosion and deposition on alluvial fans of mountain streams. The cellular model, named FluviSed, applies a quasi-steady-state routing of a flood hydrograph over a rectangular grid. Bedload transport is calculated and the morphological changes are updated after each time step. FluviSed is designed to complement existing one-dimensional bedload transport simulation tools by using their outcome as an input for the simulation of inundated areas. The model has been evaluated against TomSed, a one-dimensional bedload transport model. Further, a back-calculation of a laboratory bedload experiment and a real flood event from 2005 at Schnannerbach in Austria are provided to test the model's suitability for reproducing morphological changes caused by flood events at high channel gradients.

Explicit Estimates of Arrival Times for Dispersion in Rivers

AbstractExplicit formulas for the times of arrival of the leading and trailing edges of a contaminant cloud are developed from a one-dimensional advection-dispersion model of transport. These times—defined as the times at which the concentration is some fraction α of the peak concentration—can be determined easily with iterations using a spreadsheet or other software, but this approach becomes time-consuming if many calculations are needed. Also, solutions to the transient storage zone model and its relatives can be made more efficient by identifying the arrival times of the edges of a contaminant cloud. The expressions for the arrival times depend only the fraction α and the Peclet number P. For 0.01 1 and 1% for P>20, and the expression for the time of arrival of the trailing edge is within 10–20% for P=1 and less than 1% for P>6. Despite the criticisms of the advection-dispersion model for transport in real waterways, the...

Model analyses of the contribution of in-channel processes to sediment concentration hysteresis loops

Summary Sediment concentration ( SC )–water discharge ( Q ) relations in rivers are typically governed by multiple and relatively complex processes. Due to hysteresis effects, sediment discharges can differ for similar or equivalent water discharges, which causes scatter in empirical datasets and may decrease the predictive power of SC rating curves. Such hysteresis effects must therefore be understood and accounted for to make dependable predictions for river system management. The overall objectives of this study are to develop modelling approaches suitable for reproducing and predicting hysteresis effects at larger scales and to investigate the possible contribution of in-channel processes (erosion and deposition) to sediment concentration hysteresis loops. To investigate relevant field-scale conditions, we develop a one-dimensional dynamic sediment transport model of the downstream Tuul River (northern Mongolia), investigating in-channel processes along a 141 km stretch during a hydrological year. The results show that the present modelling approach can reproduce both anti-clockwise and clockwise hysteresis effects. Importantly, in-channel processes alone can cause considerable anti-clockwise hysteresis effects without being reinforced by catchment processes such as hillslope erosion. Such specific contributions from in-channel processes introduced data scatter into the sediment rating curves, decreasing their R 2 -values from unity to approximately 0.5 to 0.6. More generally, possible changes in the number or magnitude of high-flow events, caused by climatic or other anthropogenic factors, could influence total sediment deposition, which was primarily found to occur during relatively short high-flow events. Such potential changes also have important implications for the possible spreading of polluted sediments.

Suspended single-walled carbon-nanotube field-effect transistor for gas sensing application

We investigate the pressure dependence of transfer characteristics of suspended single-walled carbon-nanotube field-effect transistors. We find that the gate bias around the charge neutral point with low drain current is appropriate for gas sensing application, while the high gate bias condition with high drain current that induces Joule heating in the suspended region for the desorption of the adsorbed molecules is preferable for the vacuum gauge application based on the heat exchange surrounding gas molecules, where the temperature at the suspended channel is investigated based on the simple one-dimensional heat transport model. We also revealed that the pressure dependence of the channel conductance at the gate bias around the charge neutral point can be explained by the Langmuir isotherm.

Transport of carboxyl-functionalized carbon black nanoparticles in saturated porous media: Column experiments and model analyses

The aim of this study was to investigate the transport behavior of carboxyl-functionalized carbon black nanoparticles (CBNPs) in porous media including quartz sand, iron oxide-coated sand (IOCS), and aluminum oxide-coated sand (AOCS). Two sets of column experiments were performed under saturated flow conditions for potassium chloride (KCl), a conservative tracer, and CBNPs. Breakthrough curves were analyzed to obtain mass recovery and one-dimensional transport model parameters. The first set of experiments was conducted to examine the effects of metal (Fe, Al) oxides and flow rate (0.25 and 0.5mLmin−1) on the transport of CBNPs suspended in deionized water. The results showed that the mass recovery of CBNPs in quartz sand (flow rate=0.5mLmin−1) was 83.1%, whereas no breakthrough of CBNPs (mass recovery=0%) was observed in IOCS and AOCS at the same flow rate, indicating that metal (Fe, Al) oxides can play a significant role in the attachment of CBNPs to porous media. In addition, the mass recovery of CBNPs in quartz sand decreased to 76.1% as the flow rate decreased to 0.25mLmin−1. Interaction energy profiles for CBNP–porous media were calculated using DLVO theory for sphere–plate geometry, demonstrating that the interaction energy for CBNP–quartz sand was repulsive, whereas the interaction energies for CBNP–IOCS and CBNP–AOCS were attractive with no energy barriers. The second set of experiments was conducted in quartz sand to observe the effect of ionic strength (NaCl=0.1 and 1.0mM; CaCl2=0.01 and 0.1mM) and pH (pH=4.5 and 5.4) on the transport of CBNPs suspended in electrolyte. The results showed that the mass recoveries of CBNPs in NaCl=0.1 and 1.0mM were 65.3 and 6.4%, respectively. The mass recoveries of CBNPs in CaCl2=0.01 and 0.1mM were 81.6 and 6.3%, respectively. These results demonstrated that CBNP attachment to quartz sand can be enhanced by increasing the electrolyte concentration. Interaction energy profiles demonstrated that the interaction energy profile for CBNP–quartz sand was compressed and that the energy barrier decreased as the electrolyte concentration increased. Furthermore, the mass recovery of CBNPs in the presence of divalent ions (CaCl2=0.1mM) was far lower than that in the presence of monovalent ions (NaCl=0.1mM), demonstrating a much stronger effect of Ca2+ than Na+ on CBNP transport. Mass recovery of CBNPs at pH4.5 was 55.6%, which was lower than that (83.1%) at pH5.4, indicating that CBNP attachment to quartz sand can be enhanced by decreasing the pH. The sticking efficiencies (α) calculated from the mass recovery by colloid filtration theory were in the range from 2.1×10−2 to 4.5×10−1, which were far greater than the values (2.56×10−6–3.33×10−2) of theoretical sticking efficiencies (αtheory) calculated from the DLVO energy by the Maxwell model.

A coupled modelling effort to study the fate of contaminated sediments downstream of the Coles Hill deposit, Virginia, USA

Abstract. This paper presents the preliminary results of a coupled modelling effort to study the fate of tailings (radioactive waste-by product) downstream of the Coles Hill uranium deposit located in Virginia, USA. The implementation of the overall modelling process includes a one-dimensional hydraulic model to qualitatively characterize the sediment transport process under severe flooding conditions downstream of the potential mining site, a two-dimensional ANSYS Fluent model to simulate the release of tailings from a containment cell located partially above the local ground surface into the nearby streams, and a one-dimensional finite-volume sediment transport model to examine the propagation of a tailings sediment pulse in the river network located downstream. The findings of this investigation aim to assist in estimating the potential impacts that tailings would have if they were transported into rivers and reservoirs located downstream of the Coles Hill deposit that serve as municipal drinking water supplies.

Modeling the transport behavior of 16 emerging organic contaminants during soil aquifer treatment

In this study, four one-dimensional flow and transport models based on the data of a field scale experiment in Greece were constructed to investigate the transport behavior of sixteen organic trace pollutants during soil aquifer treatment. At the site, tap water and treated wastewater were intermittently infiltrated into a porous aquifer via a small pilot pond. Electrical conductivity data was used to calibrate the non-reactive transport models. Transport and attenuation of the organic trace pollutants were simulated assuming 1st order degradation and linear adsorption. Sorption was found to be largely insignificant at this site for the compounds under investigation. In contrast, flow path averaged first order degradation rate constants were mostly higher compared to the literature and lay between 0.036d−1 for clofibric acid and 0.9d−1 for ibuprofen, presumably owing to the high temperatures and a well adapted microbial community originating from the wastewater treatment process. The study highlights the necessity to obtain intrinsic attenuation parameters at each site, as findings cannot easily be transferred from one site to another.

Evaluation of Parameter and Model Uncertainty in Simple Applications of a 1D Sediment Transport Model

AbstractThis paper separately evaluates two methods from Bayesian Statistics to estimate parameter and model uncertainty in simulations from a one-dimensional (1D) sediment transport model. The first method, multivariate shuffled complex evolution metropolis-uncertainty analysis (MSU), is an algorithm that identifies the most likely parameter values and estimates parameter uncertainty for models with multiple outputs. The second method, Bayesian model averaging (BMA), determines a combined prediction based on three sediment transport equations that are calibrated with MSU and evaluates the uncertainty associated with the selection of the transport equation. These tools are applied to simulations of three flume experiments. For these cases, MSU does not converge substantially faster than a previously used and simpler parameter uncertainty method, but its ability to consider correlation between parameters improves its estimate of the uncertainty. Also, the BMA results suggest that a combination of transport...

Role of Time Relaxation in a One-Dimensional Diffusion-Advection Model of Water and Salt Transport

The transport of salt, necessarily coupled with the transport of water, through porous building materials may heavily limit their durability due to possible deterioration and structural damage. Usually, the binding of salt to the pore walls is assumed to occur instantly, as soon as the salt is transported by water to a given position. We consider the advection-diffusion model of the transport and generalize it to include possible delays in the binding. Applying the Boltzmann-Matano method, we calculate the diffusion coefficient of the salt in dependence on the salt concentration and show that it increases with the rate of binding. We apply our results to an example of the chloride transport in a lime plaster.

Analysis of the mixing processes in the subtropical Advancetown Lake, Australia

Summary This paper presents an extensive investigation of the mixing processes occurring in the subtropical monomictic Advancetown Lake, which is the main water body supplying the Gold Coast City in Australia. Meteorological, chemical and physical data were collected from weather stations, laboratory analysis of grab samples and an in-situ Vertical Profiling System (VPS), for the period 2008–2012. This comprehensive, high frequency dataset was utilised to develop a one-dimensional model of the vertical transport and mixing processes occurring along the water column. Multivariate analysis revealed that air temperature and rain forecasts enabled a reliable prediction of the strength of the lake stratification. Vertical diffusion is the main process driving vertical mixing, particularly during winter circulation. However, a high reservoir volume and warm winters can limit the degree of winter mixing, causing only partial circulation to occur, as was the case in 2013. This research study provides a comprehensive approach for understanding and predicting mixing processes for similar lakes, whenever high-frequency data are available from VPS or other autonomous water monitoring systems.