Vertical Flow Model Research Articles

Community composting strategies for biowaste treatment: methodology, bulking agent and compost quality

The European Union’s commitment to increase recycling and recovery rates of municipal solid waste requires significant changes in current waste management. Local governments are developing various strategies for treating the organic fraction of municipal waste (biowaste) via composting. Community composting centres (CCC), green waste collection, treatment points and community gardens are some of these new approaches. Population density and spatial distribution, together with the existence of community green areas, determine the location of the various infrastructures for recycling local biowaste. The composting process consumes high amounts of bulking agent (BA) necessary to provide the structure that allows, amongst other uses, biowaste aeration and microbial surface colonisation. Shredded green waste from parks, gardens and households can be used as BA in community composting and home composting. In this study, a total of 46 compost samples obtained from CCC with two types of handling were analysed: 22 samples treated by vertical flow (VF) and 24 samples treated by horizontal flow (HF). The HF model allowed better use of the volume of modular composting units and the VF model required less effort and time for the CCC operator. Mature, stable and high-nutrient-content composts were obtained with both models. These composts met the legal requirements to be used as an organic amendment, and they can be delivered to the participants or used in community gardens in the municipality.

Hydrogeophysical Inversion of Time‐Lapse ERT Data to Determine Hillslope Subsurface Hydraulic Properties

AbstractTime‐lapse electrical resistivity tomography (ERT) data are increasingly used to inform the hydrologic dynamics of mountainous environments at the hillslope scale. Despite their popularity and recent advancements in hydrogeophysical inversion methods, few studies have shown how time‐lapse ERT data can be used to determine hydraulic parameters of subsurface water flow models. This study uses synthetic and field‐collected, hillslope‐scale, time‐lapse ERT data to determine subsurface hydraulic properties of a two‐layer, physics‐based, 2‐D vertical flow model with predefined layer and boundary locations. Uncoupled and coupled hydrogeophysical inversion methods are combined with a fine‐earth fraction optimization scheme to reduce the number of parameters needing calibration and interpret the influence of the hydraulic parameters on the hydrologic model predictions. Inversions of synthetic ERT data recover the prescribed fine‐earth fraction bulk density to within 0.1 g cm−3. Field‐collected ERT data from a mountain hillslope result in hydrologic model dynamics that are consistent with previous studies and measured water content data but struggle to capture measured groundwater levels. The uncoupled hydrogeophysical inversion method is more sensitive to changes in hydraulic parameter values of the lower hydrologic model layer than the coupled hydrogeophysical inversion method. Time series of minimum objective function value simulations indicate that periodically collected ERT data may recover hydraulic parameters to a similar level of uncertainty as daily ERT data. Using simple hydrologic model domains within hydrogeophysical inversions shows promise for providing reasonable hydrologic predictions while maintaining relatively simple calibration schemes and should be explored further in future studies.

Implementation of Blood Flow Transport under Electrokinetic Flow Through Porous Fat Depot Within the Vertical Flow Model

Implementation of Blood Flow Transport under Electrokinetic Flow Through Porous Fat Depot Within the Vertical Flow Model

The effect of vertical split-flow patient management on emergency department throughput and efficiency

BackgroundTo address emergency department overcrowding operational research seeks to identify efficient processes to optimize flow of patients through the emergency department. Vertical flow refers to the concept of utilizing and assigning patients virtual beds rather than to an actual physical space within the emergency department to care of low acuity patients. The aim of this study is to evaluate the impact of vertical flow upon emergency department efficiency and patient satisfaction. MethodsProspective pre/post-interventional cohort study of all intend-to-treat patients presenting to the emergency department during a two-year period before and after the implementation of a vertical flow model. ResultsIn total 222,713 patient visits were included in the analysis with 107,217 patients presenting within the pre-intervention and 115,496 in the post-intervention groups. The results of the regression analysis demonstrate an improvement in throughput across the entire ED patient population, decreasing door to departure time by 17 min (95% CI 15–18) despite an increase in patient volume. No statistically significant difference in patient satisfaction scores were found between the pre- and post-intervention. ConclusionsInitiation of a vertical split flow model was associated with improved ED efficiency.

Introduction of a Horizontal and Vertical Split Flow Model of Emergency Department Patients as a Response to Overcrowding

IntroductionED overcrowding is an issue that is affecting every emergency department and every hospital. The inability to maintain patient flow into and out of the emergency department paralyzes the ability to provide effective and timely patient care. Many solutions have been proposed on how to mitigate the effects of ED overcrowding. Solutions involve either hospital-wide initiatives or ED-based solutions. In this article, the authors seek to describe and provide metrics for a patient flow methodology that targets ESI 3 patients in a vertical flow model. MethodsIn the Stanford Emergency Department, a vertical flow model was created from existing ED space by removing fold-down horizontal stretchers and replacing them with multiple chairs that allowed for assessment and medical management in an upright sitting position. The model was launched and sustained through frequent interdisciplinary huddles, detailed inclusion and exclusion criteria, scripted text on how to promote the flow model to patients, and close analytics of metrics. Metrics for success included patient length of stay (LOS) for those triaged to the vertical flow area compared with ESI 3 patients triaged to the traditional emergency department as a comparison group. The secondary outcome is the total number of patients seen in the vertical flow area. This was a 6-month—September 2014, to February 2015—retrospective pre- and postintervention study that examined LOS as a marker for effective launch and implementation of a vertical patient workflow model. ResultsThe patients triaged to the vertical flow area in the study period tended to be younger than in the control period (43 years versus 52 years, P = 0.00). There was a significant decrease in our primary end point: the total LOS for ESI 3 patients triaged to the vertical flow area (270 minutes versus 384 minutes, P = 0.00). ConclusionImplementation of a vertical patient flow strategy can decrease LOS for the vertical ESI 3 patients based upon the inclusion and exclusion criteria. Furthermore, this is accomplished with minimal financial investment within the physical constraints of an existing emergency department.Image 1

A two-fluid model for vertical flow applied to CO2 injection wells

Flow of CO2 in wells is associated with substantial variations in thermophysical properties downhole, due to the coupled transient processes involved: complex flow patterns, density changes, phase transitions, and heat transfer to and from surroundings. Large temperature variations can lead to thermal stresses and subsequent loss of well integrity, and it is therefore crucial to employ models that can predict this accurately. In this work, we present a model for vertical well flow that includes both two-phase flow and heat conduction. The flow is described by a two-fluid model, where mass transfer between the phases is modelled by relaxation source terms that drive the phases towards thermodynamic equilibrium. We suggest a new formulation of the mass transfer process that satisfies the second law of thermodynamics, and that is also continuous in the single-phase limit. This provides a more robust transition from two-phase to single-phase flow than the previous formulation. The model predicts which flow regimes are present downhole, and calculates friction and heat transfer depending on this. Moreover, the flow model is coupled with a heat conduction model for the layers that comprise the well, including tubing, packer fluid, casing, cement or drilling mud, and rock formation. This enables prediction of the temperature in the well fluid and in each layer of the well. The model is applied to sudden shut-in and blowout cases of a CO2 injection well, where we employ the highly accurate Span–Wagner reference equation-of-state to describe the thermodynamics of CO2. We predict pressure, temperature and flow regimes during these cases and discuss implications for well integrity.

An Integrated Horizontal- and Vertical-Flow Simulation With Application to Wax Precipitation

Summary There is a lack of comprehensive simulation tools that (a) accommodate the complexities of advanced completions together with near-wellbore behavior and that (b) have reliable wax-precipitation models for production planning. In this work, these issues are tackled by combining three specific models. First, a steady-state, three-phase, nonisothermal flow model in advanced horizontal completions was implemented to run fluid-specific simulations, thereby calculating field-specific flow conditions. This is useful in situations when fluid-specific temperature calculations are important, such as wax crystallization. Second, a nonisothermal, vertical flow model was developed by combining Hagedorn and Brown's multiphase-flow correlation with Ramey's multiphase-temperature model by solving them in sequence (iteratively). The advanced horizontal-well model and vertical flow model were coupled iteratively at the bottom hole where the two models meet. Third, two different analytical wax-crystallization models were incorporated in the aforementioned coupled flow simulator to calculate the location of wax precipitation along the vertical section of the well. These three simulation models, individually and in combination, were tested and found to be in par with theory, expectations, and published results. In addition, a significant difference was noted between Ramey's analytical temperature profile (which is a widely used approximation) and the complete Ramey's model integrated with the simulator developed in this work.

Time‐dependence of the spatial pattern of accumulation rate in East Antarctica deduced from isochronic radar layers using a 3‐D numerical ice flow model

In East Antarctica surface mass balance data can only be obtained from the sparsely distributed ice cores when considering time periods greater than a few decades. Observations of internal layers measured by airborne ice penetrating radar, in principle, permit extrapolation of mass balance information from these ice cores. We use radar survey lines gathered in the 1970s, and a three‐dimensional numerical model, to investigate the feasibility of such extrapolation, seeking to match the calculations of englacial layer geometry with observations. First, we justify the use of a three‐dimensional model by showing that simple vertical flow models cannot explain all the observations and that horizontal advection is a significant glacial process. Then we examine processes that affect calculations of layer geometry, finding that spatial accumulation‐rate patterns are extremely important while geothermal heat flux and flow mode (sliding or internal deformation) are of substantially less importance. Where the layer is from the Last Glacial Maximum (17.5 ka), we find a very good match between the spatial pattern of accumulation rates inferred from this layer and the modern spatial pattern of accumulation rates. When considering deeper layers from beyond the current interglacial, we find that a different spatial accumulation‐rate pattern must have existed, in addition to the known change in accumulation rate from ice cores. The glacial spatial accumulation‐rate pattern would have had proportionally greater accumulation at the South Pole than now, compared with the Vostok and Dome C ice cores.

Coupled Aquifer‐Borehole Simulation

A model coupling fluid hydraulics in a borehole with fluid flow in an aquifer is developed in this paper. Conservation of momentum is used to create a one-dimensional steady-state model of vertical flow in an open borehole combined with radially symmetric flow in an aquifer and with inflow to the well through the wellbore screen. Both laminar and turbulent wellbore conditions are treated. The influence of inflow through the wellbore screen on vertical flow in the wellbore is included, using a relation developed by Siwoń (1987). The influence of inflow reduces the predicted vertical variation in head up to 15% compared to a calculation of head losses due to fluid acceleration and the conventional Colebrook-White formulation of friction losses in a circular pipe. The wellbore flow model is embedded into the MODFLOW-2000 ground water flow code. The nonlinear conservation of momentum equations are iteratively linearized to calculate the conductance terms for vertical flow in the wellbore. The resulting simulations agree favorably with previously published results when the model is adjusted to meet the assumptions of the previous coupled models.

Interfacial Area Transport in Horizontal Bubbly Flow with 90-deg Elbow

The present study develops an interfacial area transport equation applicable to an air-water horizontal bubbly flow with a flow restriction. The experiments are performed in a round glass pipe of 50.3-mm inner diameter, along which a 90-deg elbow is installed at L/D = 206.6 from the two-phase mixture inlet. In total, 15 different flow conditions in the bubbly flow regime are studied. The detailed local two-phase flow parameters are acquired by a double-sensor conductivity probe at four different axial locations. The effect of the elbow is evident in the distribution of local parameters as well as in the development of interfacial structures. The elbow clearly promotes bubble interactions resulting in significant changes in both the void fraction and interfacial area concentration. In the present study, the elbow is found to promote the coalescence mechanism while reducing the disintegration mechanism. These geometric effects are also reflected in the axial development of one-dimensional two-phase flow parameters. In the present analysis, the interfacial area transport equation is developed in one-dimensional form via area-averaging based on the existing model for vertical flow. In the averaging process, characteristic nonuniform distributions of the two-phase flow parameters in horizontal two-phase flow are treated mathematically by covariance calculations. Furthermore, the change in pressure due to the minor loss of the elbow is taken into consideration by using a newly developed correlation analogous to Lockhart and Martinelli’s. In total, 60 area-averaged data points are employed to benchmark the present model. The present model predicts the data well with an average percent difference of approximately ±10%.

Modeling the effects of throughfall reduction on soil water content in a Brazilian Oxisol under a moist tropical forest

Access to water reserves in deep soil during drought periods determines whether or not the tropical moist forests of Amazonia will be buffered from the deleterious effects of water deficits. Changing climatic conditions are predicted to increase periods of drought in Amazonian forests and may lead to increased tree mortality, changes in forest composition, or greater susceptibility to fire. A throughfall reduction experiment has been established in the Tapajós National Forest of east‐central Amazonia (Brazil) to test the potential effects of severe water stress during prolonged droughts. Using time domain reflectometry observations of water contents from this experiment, we have developed a dynamic, one‐dimensional, vertical flow model to enhance our understanding of hydrologic processes within these tall‐stature forests on well‐drained, upland, deep Oxisols and to simulate changes in the distribution of soil water. Simulations using 960 days of data accurately captured mild soil water depletion near the surface after the first treatment year and decreasing soil moisture at depth during the second treatment year. The model is sensitive to the water retention and unsaturated flow equation parameters, specifically the van Genuchten parameters θs, θr, and n, but less sensitive to Ks and α. The low root‐mean‐square error between observed and predicted volumetric soil water content suggests that this vertical flow model captures the most important hydrologic processes in the upper landscape position of this study site. The model indicates that present rates of evapotranspiration within the exclusion plot have been sustained at the expense of soil water storage.

要求分析と設計プロセス分析に基づく接合設計支援システムの構築

This paper deals with Design Supporting System that aims to support activities of welding design and joint design comprehensively. The following concepts are introduced into our system in order to deal with both the welding design and joint design explicitly:(1) Design information on both joint and welding is clearly and explicitly defined as product data.(2) The phase of joint design is different from the phase of welding design, and these two phases start from the division of the full structure into parts and end in determining values of detailed to execute welding operations.(3) Joint and welding is decomposed into some data, and appropriate design procedures depend on the decomposed data.(4) Determining optimal joint data is converted into selecting the optimal plan from a lot of feasible design plans. That is to say, a lot of feasible plans in every design stages are created semi-automatically and evaluations of each plan are calculated automatically by our system. As a result, optimal design plans are selected and the design stage moves to the next.(5) The design processes that are explicitly described are utilized in our system.In order to implement our system, two design process models of both welding and joint are discussed in this report: one model is Vertical Flow Model and the other is Horizontal Flow Model. The Vertical Flow Model indicates the design process among design stages, on the other hand, the Horizontal Flow Model indicates the value determination activities in each design stage.Some examples of both welding design and joint design by using our system are shown in this paper.

Evaluation of DRAINMOD for predicting water table heights in irrigated fields at the Jordan Valley

A detailed field experiment was carried out in the Jordan Valley, south of Lake Kinneret, Israel for evaluation of the water management model DRAINMOD. This field was chosen to represent the local agro-climate conditions of that zone. Banana crop was grown and was irrigated daily with about 3200 mm/year and 0.5 leaching fraction. Subsurface drainage system with 2.5 m drain depth and 160 m drain spacing existed in the field. The water table depth was measured with about 100 piezometers, in which most of them were observed weekly, and four were continuosly recording piezometers. Five identical drainage plots were selected, out of 10 existing, as replicates for the evaluation of DRAINMOD. Deviations in a range of 0.3–1.7 m between observed water table depth and that simulated by DRAINMOD were found in four out of the five replicates. A reasonable agreement was found only in one drainage plot out of the five tested. These findings contradict the world wide convention that DRAINMOD simulation is in a good agreement with observed field data. An additional study was therefore conducted to explore the reasons for these large deviations. Three reasons were suggested: (i) a strong side effect by the Jordan River, which flows some 350 m west to the test field; a very steep 4.6% gradient was found toward the Jordan River; (ii) presence of sandy permeable layers below the depth of the drains which magnifies the boundary condition effect of the Jordan River; (iii) a very significant component of deep and lateral seepage (more than 50% of the yearly irrigation plus rainfall). A combination of these three reasons was suggested as an explanation to the apparent large disagreement. It was therefore recommended not to use DRAINMOD or similar vertical flow models for simulation of water table depths in irrigated fields with subsurface drain pipe systems in the Jordan Valley.

Analytical solutions for reactive transport under an infiltration–redistribution cycle

Transport of reactive solute in unsaturated soils under an infiltration–redistribution cycle is investigated. The study is based on the model of vertical flow and transport in the unsaturated zone proposed by Indelman et al. [J. Contam. Hydrol. 32 (1998) 77], and generalizes it by accounting for linear nonequilibrium kinetics. An exact analytical solution is derived for an irreversible desorption reaction. The transport of solute obeying linear kinetics is modeled by assuming equilibrium during the redistribution stage. The model which accounts for nonequilibrium during the infiltration and assumes equilibrium at the redistribution stage is termed partial equilibrium infiltration–redistribution model (PEIRM). It allows to derive approximate closed form solutions for transport in one-dimensional homogeneous soils. These solutions are further applied to computing the field-scale concentration by adopting the Dagan and Bresler [Soil Sci. Soc. Am. J. 43 (1979) 461] column model. The effect of soil heterogeneity on the solute spread is investigated by modeling the hydraulic saturated conductivity as a random function of horizontal coordinates. The quality of the PEIRM is illustrated by calculating the critical values of the Damköhler number which provide the achievable accuracy in estimating the solute mass in the mobile phase. The distinguishing feature of transport during the infiltration–redistribution cycle as compared to that of infiltration only is the finite depth of solute penetration. For irreversible desorption, the maximum solute penetration W/ θ r is determined by the amount of applied water W and the residual water content θ r. For sorption–desorption kinetics, the maximum depth of penetration z r e,∞ also depends on the ratio between the rate of application and the column-saturated conductivity. It is shown that z r e,∞ is bounded between the depths W/( θ r+ K d) and W/ θ r corresponding to the maximum solute penetration for equilibrium transport and for irreversible desorption, respectively. This feature of solute penetration explains the unusual phenomena of plume contraction after an initial period of spreading [Lessoff, S.C., Indelman, P., Dagan, G., 2002. Solute transport in infiltration–redistribution cycles in heterogeneous soils. In Raats, P.A.C., Smiles, D.,Warrick, A.W. (Eds), Environmental Mechanics: Water, Mass and Energy Transport in the Biosphere. American Geophysical Union, pp. 133–144]. Unlike transport under equilibrium conditions, when the solute is completely concentrated at the front, the solute under nonequilibrium conditions is spread out behind the front. Heterogeneity leads to additional spreading of the plume.

Tidal fluctuations in a leaky confined aquifer: localised effects of an overlying phreatic aquifer

Damping of tidal head fluctuations in a leaky confined coastal aquifer is enhanced by leakage into an overlying phreatic aquifer. We show that the phreatic aquifer is, however, resistant to the leakage flow and in particular, a deep phreatic aquifer can reduce the leakage effects significantly. An analytical solution, based on a vertical flow model for the phreatic aquifer, is derived for quantifying the role of this upper free water body in tidal propagation in the lower semi-confined aquifer.

Vertical mixing above a steady circular source of buoyancy

Experiments using water and brine were performed to simulate the mixing pattern above a slow steady circular release of light fuel gas into a region of otherwise quiescent, heavier air. The experiments reveal the existence of a horizontal inward moving boundary- or mixing-layer flow above the release surface. Over the central region of the release area the mixing layer turns upward and feeds a vertical buoyant plume. Measured mixing layer thicknesses and solute salt concentrations were compared with predictions based on a concentration boundary-layer type model combined with a model for vertical flow into the plume.

A three-dimensional multiphase flow model for assessing NAPL contamination in porous and fractured media, 2. Porous medium simulation examples

This paper discusses the verification and application of the three-dimensional (3-D) multiphase flow model presented by Huyakorn et al. (Part 1 in this issue) for assessing contamination due to subsurface releases of non-aqueous-phase liquids (NAPL's). Attention is focussed on situations involving one-, two- and three-dimensional flow through porous media. The model formulations and numerical schemes are tested for highly nonlinear field conditions. The utility and accuracy of various simplifications to certain simulation scenarios are assessed. Five simulation examples are included for demonstrative purposes. The first example verifies the model for vertical flow and compares the performance of the fully three-phase and the passive-air-phase formulations. Air-phase boundary conditions are noted to have considerable effects on simulation results. The second example verifies the model for cross-sectional analyses involving LNAPL and DNAPL migration. Finite-difference (5-point) and finite-element (9-point) spatial approximations are compared for different grid aspect ratios. Unless corrected, negative-transmissivity conditions were found to have undesirable impact on the finite-element solutions. The third example provides a model validation against laboratory experimental data on 5-spot water-flood treatment of oil reservoirs. The sensitivity to grid orientation is noted for the finite-difference schemes. The fourth example demonstrates model utility in characterizing the 3-D migration of LNAPL and DNAPL from surface sources. The final example present a modeling study of air sparging. Critical parameters affecting the performance of air-sparging system are examined. In general, the modeling results indicate sparging is more effective in water-retentive soils, and larger values of sparge influence radius may be achieved for certain anisotropic conditions.

Modeling pumping tests in weathered glacial till

Three multiple well pumping tests were performed in low-permeability Wisconsin-age weathered glacial till in Iowa, USA. A radial flow model based on the Dupuit assumptions and a radial and vertical flow model were used to estimate flow parameters. A numerical solution to the Dupuit equation and an analytical solution to the Dupuit equation using Jacob's correction gave similar parameter estimates but both showed a trend of increasing hydraulic conductivity with distance from the pumped well. The trend most likely indicated a weakness in the modeling. When a radial and vertical flow model was used to estimate parameters, the trend disappeared though the parameter estimates were similar. The field site consisted of 15 fully penetrating observation wells fanning out in three rays from a central fully penetrating pumping well. Of the four parameters ( K r, K z, S y, and S s) estimated using the Neuman radial and vertical flow delayed yield model, K z varied the most between rays. The anisotropy ratio ( K z K r ) varied from 0.05 to 5 among the three rays. Representative parameter values for the till can be summarized: K r and K z are 4 × 10 −4 cm s −1, S y is 0.04, and S s is 6 × 10 −5 cm −1.

Basement Tectonics of the Southem Termination of the Santander Massif, Eastern Cordillera, Colombian Andes

The Santander Massif is a broad, basement cored antiform which, where fully developed, is limited toward its eastern and western foreland basins by two oppositely dipping reverse faults, which involve minor thrusting within the foreland sediments. More internal faults, however, accommodated an east-west extension by limiting sedimentary wedges which have the structure of half-grabens. Both marginal and internal faults impart a near symmetrical fan structure to the massif. The alternating compressional and extensional deformation regimes are taken as evidence for a vertical flow model, in which laminar parts of the massif rose along slightly divergent movement paths, following the fan array of the faults, and triggered the extensional deformation at higher levels. Evidence for a steep attitude of the faults is provided by (1) normal faults which, when bordering secondary basement highs, become reverse faults of an opposed dip, and (2) by the Bucaramanga fault, which between the Santander Massif on its eastern side and the more southerly Mogotes-Arcabuco Massif on its western side inverts both dip and displacement. A further internal deformation, which controlled the massif's structural evolution, consists of a longitudinal stretch. This was mitigated within the basement itself by an internal arching, and, where transmitted to themore » foreland, was absorbed by minor transcurrent faults or by east-west trending normal faults, as is the case of the displaceD plateaus in the Bucaramanga area. Considering the deep-seated origin of the structures of the Santander Massif, it is suggested that the imbricate sheets of the Guaicaramo fold and thrust belt at the eastern foothills of the Cocuy Massif evolved out of steeply inclined synclines. Folding of these imbricate sheets reflects uplift of more foreland oriented basement blocks.« less

Mathematical modeling of vertical flow of gas suspensions

Mathematical modeling of vertical flow of gas suspensions