scholarly journals Exploring Compatibility of Sherwood-Gilland NAPL Dissolution Models with Micro-Scale Physics Using an Alternative Volume Averaging Approach

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1525
Author(s):  
Scott K. Hansen
Keyword(s):  
Ad Hoc ◽  
Volume Fraction ◽  
Volume Averaging ◽  
Micro Scale ◽  
Advection Dispersion ◽  
Source Models ◽  
Napl Dissolution ◽  
The Difference ◽  
Geometric Lemma ◽  
Local Average

The dynamics of NAPL dissolution into saturated porous media are typically modeled by the inclusion of a reaction term in the advection-dispersion-reaction equation (ADRE) with the reaction rate defined by a Sherwood-Gilland empirical model. This stipulates, among other things, that the dissolution rate is proportional to a power of the NAPL volume fraction, and also to the difference between the local average aqueous concentration of the NAPL species and its thermodynamic saturation concentration. Solute source models of these sorts are ad hoc and empirically calibrated but have come to see widespread use in contaminant hydrogeology. In parallel, a number of authors have employed the method of volume averaging to derive upscaled transport equations describing the same dissolution and transport phenomena. However, these solutions typically yield forms of equations that are seemingly incompatible with Sherwood-Gilland source models. In this paper, we revisit the compatibility of the two approaches using a radically simplified alternative volume averaging analysis. We begin from a classic micro-scale formulation of the NAPL dissolution problem but develop some new simplification approaches (including a physics-preserving transformation of the domain and a new geometric lemma) which allow us to avoid solving traditional closure boundary value problems. We arrive at a general, volume-averaged governing equation that does not reduce to the ADRE with a Sherwood-Gilland source but find that the two approaches do align under straightforward advection-dominated conditions.

Averaged equations for inviscid disperse two-phase flow

1994 ◽  
Vol 267 ◽  
pp. 185-219 ◽  
Author(s):  
D. Z. Zhang ◽  
A. Prosperetti
Keyword(s):  
Ad Hoc ◽  
Volume Fraction ◽  
Detailed Comparison ◽  
Momentum Equation ◽  
Average Pressure ◽  
Rigid Spheres ◽  
Two Phase ◽  
Averaged Equations ◽  
Mass Coefficient ◽  
The Difference

Averaged equations governing the motion of equal rigid spheres suspended in a potential flow are derived from the equation for the probability distribution. A distinctive feature of this work is the derivation of the disperse-phase momentum equation by averaging the particle equation of motion directly, rather than the microscopic equation for the particle material. This approach is more flexible than the usual one and leads to a simpler and more fundamental description of the particle phase. The model is closed in a systematic way (i.e. with no ad hoc assumptions) in the dilute limit and in the linear limit. One of the closure quantities is related to the difference between the gradient of the average pressure and the average pressure gradient, a well-known problem in the widely used two-fluid engineering models. The present result for this quantity leads to the introduction of a modified added mass coefficient (related to Wallis's ‘exertia’) that remains very nearly constant with changes in the volume fraction and densities of the phases. Statistics of this coefficient are provided and exhibit a rather strong variability of up to 20% among different numerical simulations. A detailed comparison of the present results with those of other investigators is given in § 10.As a further illustration of the flexibility of the techniques developed in the paper, in Appendix C they are applied to the calculation of the so-called ‘particle stress’ tensor. This derivation is considerably simpler than others available in the literature.

Study of pumping effect in flow-through electrolysers

1983 ◽  
Vol 48 (8) ◽  
pp. 2232-2248 ◽  
Author(s):  
Ivo Roušar ◽  
Michal Provazník ◽  
Pavel Stuhl
Keyword(s):  
Natural Convection ◽  
Balance Equation ◽  
Volume Fraction ◽  
Industrial Applications ◽  
Pumping Effect ◽  
Flow Through ◽  
The Mean ◽  
The Difference

In electrolysers with recirculation, where a gas is evolved, the pumping of electrolyte from a lower to a higher level can be effected by natural convection due to the difference between the densities of the inlet electrolyte and the gaseous emulsion at the outlet. An accurate balance equation for calculation of the rate of flow of the pumped liquid is derived. An equation for the calculation of the mean volume fraction of bubbles in the space between the electrodes is proposed and verified experimentally on a pilot electrolyser. Two examples of industrial applications are presented.

Patterns of care in Italian psychiatric services and psychosocial outcome of schizophrenic patients. A three-year prospective study

1989 ◽  
Vol 4 (1) ◽  
pp. 23-31 ◽  
Author(s):  
D. Kemali ◽  
M. Maj ◽  
B. Carpiniello ◽  
R.D. Giurazza ◽  
M. Impagnatiello ◽  
...  
Keyword(s):  
Psychosocial Adjustment ◽  
Ad Hoc ◽  
Social Withdrawal ◽  
Skills Training ◽  
Favourable Outcome ◽  
Stepwise Logistic Regression ◽  
Psychosocial Outcome ◽  
Stepwise Logistic Regression Analysis ◽  
Schizophrenic Patients ◽  
The Difference

Summary141 patients with an ICD-9 diagnosis of schizophrenic psychosis were followed up prospectively for 3 years in 7 Italian centres, representative of the different degrees of application of the psychiatric reform law (Law 180) passed in 1978. It was agreed that each centre would treat the patients according to its routine, and that all contacts with the patients and each intervention performed would be carefully recorded in an ad hoc schedule. The baseline evaluation of psychosocial adjustment was performed by the Disability Assessment Schedule (DAS), and this assessment was then repeated every 6 months during the follow-up period. At the end of this period, the rating on the DAS section 5 was taken as a global measure of patients’ psychosocial outcome. On a stepwise logistic regression analysis, 2 variables were found to be significantly predictive of psychosocial outcome, that is the use of social and/or vocational skills training (associated with a favourable outcome) and the number of days/year of full hospitalization (associated with a poor outcome). Trieste and Arezzo were the only centres in which a significant improvement of the score on some DAS subscales (namely, “occupational role, interest” and “social withdrawal”) was detected. In the whole patient sample, the difference between the final and the baseline score on these subscales correlated significantly with the number/year of outpatient contacts and of home visits. These findings confirm the favourable impact of the community-oriented care provided in some Italian centres on the Psychosocial outcome of schizophrenic patients.

scholarly journals Allometric Equations for Estimating Biomass and Carbon Stocks in Afforested Open Woodlands with Black Spruce and Jack Pine, in the Eastern Canadian Boreal Forest

Forests ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 59
Author(s):  
Olivier Fradette ◽  
Charles Marty ◽  
Pascal Tremblay ◽  
Daniel Lord ◽  
Jean-François Boucher
Keyword(s):  
Large Scale ◽  
Ad Hoc ◽  
Black Spruce ◽  
Tree Height ◽  
Jack Pine ◽  
Carbon Stocks ◽  
Allometric Equations ◽  
C Stocks ◽  
The Difference ◽  
Canadian Boreal Forest

Allometric equations use easily measurable biometric variables to determine the aboveground and belowground biomasses of trees. Equations produced for estimating the biomass within Canadian forests at a large scale have not yet been validated for eastern Canadian boreal open woodlands (OWs), where trees experience particular environmental conditions. In this study, we harvested 167 trees from seven boreal OWs in Quebec, Canada for biomass and allometric measurements. These data show that Canadian national equations accurately predict the whole aboveground biomass for both black spruce and jack pine trees, but underestimated branches biomass, possibly owing to a particular tree morphology in OWs relative to closed-canopy stands. We therefore developed ad hoc allometric equations based on three power models including diameter at breast height (DBH) alone or in combination with tree height (H) as allometric variables. Our results show that although the inclusion of H in the model yields better fits for most tree compartments in both species, the difference is minor and does not markedly affect biomass C stocks at the stand level. Using these newly developed equations, we found that carbon stocks in afforested OWs varied markedly among sites owing to differences in tree growth and species. Nine years after afforestation, jack pine plantations had accumulated about five times more carbon than black spruce plantations (0.14 vs. 0.80 t C·ha−1), highlighting the much larger potential of jack pine for OW afforestation projects in this environment.

scholarly journals An Integrated Credit-Based Incentive Protocol for Symbol-Level Network-Coded Cooperative Content Distribution among Vehicular Nodes

2018 ◽  
Vol 8 (11) ◽  
pp. 2035 ◽  
Author(s):  
Ing-Chau Chang ◽  
Chin-En Yen ◽  
Jacky Lo
Keyword(s):  
Ad Hoc ◽  
High Efficiency ◽  
Performance Metrics ◽  
Content Distribution ◽  
Long Latency ◽  
Distribution Process ◽  
Distribution Operations ◽  
The Difference ◽  
Different Content ◽  
Content Information

In traditional symbol-level network coding (SLNC)-based cooperative content distribution approaches, they ignore nodes in the vehicular ad hoc network (VANET) having various network-coded content pieces and distinct levels of interests and selfishness for different kinds of content data, which further prevents these vehicular nodes from forwarding their content information to other nodes. With these approaches, these nodes suffer from the low ratio and the long latency to receive all content information. In this paper, based on distinct levels of node interests and selfishness on different content information, we first categorize vehicular nodes into four classes, that is, the destination, intermediate, irrelevant and overhearing ones and then designate their associated credit-based incentive approaches. Second, we modify the flow of traditional SLNC-based cooperative content distribution operations and propose the content bitmap to realize the difference of network-coded content pieces among vehicular nodes. Further, we rigidly combine the proposed credit-based incentive approach with the modified SLNC-based cooperative content distribution operations in SocialCode to encourage all classes of vehicular nodes to rise their incentives for sharing content data in the cooperative content distribution process. Finally, we perform NS-2 simulations on a street map of downtown Taipei, Taiwan to exhibit the high efficiency of SocialCode over related credit-based incentive approaches by analyzing the following performance metrics, that is, average decoding percentage, file downloading delay and credits, with respect to different file sizes and total numbers of vehicular nodes. As the best knowledge we have, SocialCode is one of the first few researches that works on the integration between the credit-based incentive protocol and the SLNC-based cooperative content distribution.

Dynamics of Ferroelectric and Nematic Liquid Crystals Confined in Porous Matrices

1994 ◽  
Vol 366 ◽  
Author(s):  
Fouad M. Aliev
Keyword(s):  
Liquid Crystals ◽  
Heterogeneous Media ◽  
Volume Fraction ◽  
Low Frequency ◽  
Pore Wall ◽  
Polar Molecules ◽  
Average Pore ◽  
Surface Polarization ◽  
The Difference ◽  
Frequency Relaxation

ABSTRACTWe performed dielectric spectroscopy measurements to study dynamics of collective modes of ferroelectric (FLC) and molecular motion of nematic (NLC) liquid crystals with polar molecules confined in silica macroporous and microporous glasses with average pore sizes of 1000 Å (volume fraction of pores 40%) and 100 Å (27%) respectively. For FLC the Goldstone and the soft modes are found in macropores. The rotational viscosity associated with the soft mode is about 10 times higher in pores than in the bulk. These modes are not detected in micropores although low frequency relaxation is present. The last one probably is not connected with the nature of liquid crystal but is associated with surface polarization effects typical for two component heterogeneous media. The difference between the dynamics of orientational motion of the polar molecules of NLC in confined geometries and in the bulk is qualitatively determined by the total energy Fs of the interaction between molecules and the surface of the pore wall, which is found Fs ≈ 102erg/cm2.

Towards an Improved Parameter-Free Entrainment Model for Snow Avalanches

2021 ◽  
Author(s):  
Dieter Issler
Keyword(s):  
Snow Cover ◽  
Ad Hoc ◽  
Shear Stresses ◽  
Entrainment Rate ◽  
Snow Layer ◽  
Present Contribution ◽  
Weak Layer ◽  
Model Combining ◽  
The Difference ◽  
The 1960S

<p>On physical grounds, the rate of bed entrainment in gravity mass flows should be determined by the properties of the bed material and the dynamical variables of the flow. Due to the complexity of the process, most entrainment formulas proposed in the literature contain some ad-hoc parameter not tied to measurable snow properties. Among the very few models without free parameters are the Eglit–Grigorian–Yakimov (EGY) model of frontal entrainment from the 1960s and two formulas for basal entrainment, one from the 1970s due to Grigorian and Ostroumov (GO) and one (IJ) implemented in NGI’s flow code MoT-Voellmy. A common feature of these three approaches is their treating erosion as a shock and exploiting jump conditions for mass and momentum across the erosion front. The erosion or entrainment rate is determined by the difference between the avalanche-generated stress at the erosion front and the strength of the snow cover. The models differ with regard to how the shock is oriented and which momentum components are considered. The present contribution shows that each of the three models has some shortcomings: The EGY model is ambiguous if the avalanche pressure is too small to entrain the entire snow layer, the IJ model neglects normal stresses, and the GO model disregards shear stresses and acceleration of the eroded mass. As they stand, neither the GO nor the IJ model capture situations―observed experimentally by means of profiling radar―in which the snow cover is not eroded progressively but suddenly fails on a buried weak layer as the avalanche flows over it. We suggest a way to resolve the ambiguity in the EGY model and sketch a more comprehensive model combining all three approaches to capture gradual entrainment from the snow-cover surface together with erosion along a buried weak layer.</p>

scholarly journals Reading the bed morphology of a mountain stream: a geomorphometric study on high-resolution topographic data

2010 ◽  
Vol 14 (2) ◽  
pp. 393-405 ◽  
Author(s):  
S. Trevisani ◽  
M. Cavalli ◽  
L. Marchi
Keyword(s):  
High Resolution ◽  
Ad Hoc ◽  
Flow Direction ◽  
Spatial Scales ◽  
Mountain Stream ◽  
Topographic Data ◽  
The Difference ◽  
Morphological Differences ◽  
High Level ◽  
Local Anomalies

Abstract. High-resolution topographic data expand the potential of quantitative analysis of the earth surface, improving the interpretation of geomorphic processes. In particular, the morphologies of the channel beds of mountain streams, which are characterised by strong spatial variability, can be analysed much more effectively with this type of data. In this study, we analysed the aerial LiDAR topographic data of a headwater stream, the Rio Cordon (watershed area: 5 km2), located in the Dolomites (north-eastern Italy). The morphology of the channel bed of Rio Cordon is characterised by alternating step pools, cascades, and rapids with steps. We analysed the streambed morphology by means of ad hoc developed morphometric indices, capable of highlighting morphological features at a high level of spatial resolution. To perform the analysis and the data interpolation, we carried out a channel-oriented coordinate transformation. In the new coordinate system, the calculation of morphometric indices in directions along and transverse to the flow direction is straightforward. Three geomorphometric indices were developed and applied as follows: a slope index computed on the whole width of the channel bed, directional variograms computed along the flow direction and perpendicular to it, and local anomalies, calculated as the difference between directional variograms at different spatial scales. Directional variograms in the flow direction and local anomalies have proven to be effective at recognising morphologic units, such as steps, pools and clusters of large boulders. At the spatial scale of channel reaches, these indices have demonstrated a satisfactory capability to outline patterns associated with boulder cascades and rapids with steps, whereas they did not clearly differentiate between morphologies with less marked morphological differences, such as step pools and cascades.

scholarly journals Hydrodynamic analysis of a liquid-solid fluidized bed via cfd-dem simulations, stability analysis, and tomography

2021 ◽  
Author(s):  
Hussein Zbib
Keyword(s):  
Stability Analysis ◽  
Fluidized Bed ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Percentage Error ◽  
Particle Interactions ◽  
Particle Volume ◽  
Computational Fluid Dynamics Cfd ◽  
The Difference ◽  
Dem Model

A coupled computational fluid dynamics (CFD) and discrete element method (DEM) model was developed to analyze the fluid-particle and particle-particle interactions in a 3D liquid-solid fluidized bed (LSFB). The CFD-DEM model was validated using the Electrical Resistance Tomography (ERT) experimental method. ERT was employed to measure the bed-averaged particle volume fraction (BPVF) of 0.002 m glass beads fluidized with water for various particle numbers and flow rates. It was found that simulations employing the combination of the Gidaspow drag model with pressure gradient and virtual mass forces provided the least percentage error between experiments and simulations. It was also found that contact parameters must be calibrated to account for the particles being wet. The difference between simulations and experiments was 4.74%. The CFD-DEM model was also employed alongside stability analysis to investigate the hydrodynamic behavior within the LSFB and the intermediate flow regime for all cases studied.

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