Impermeable Flow Research Articles

Effect of permeable spacer structure on energy loss and mass transfer in reverse osmosis membrane modules

This study used numerical simulation to investigate the effects of a novel permeable cylindrical-flow distributor on energy loss and mass transfer in reverse osmosis (RO) membrane modules. The analysis focused on variables, such as Reynolds number, inlet concentration and flow incidence angle, influencing the improvement of water production efficiency in RO membranes and the reduction of concentration polarisation on the membrane surface. The membrane surface shear stress, vorticity, permeate flux and concentration polarisation factor were used to describe these effects. To better explain the performance of the permeable flow distributor, the viscous resistance coefficient (Du) in the porous media model was used to measure the permeability of the flow distributor. Furthermore, a produced water energy consumption factor (JCP) was defined to represent the energy required for unit water production. The results indicate that the permeable flow distributor significantly reduces pressure loss in the membrane channels, avoiding the high energy consumption associated with traditional flow distributors in RO processes. The Du exhibits an optimal value in the range of 1e8 to 1e10, which maximises the JCP, leading to a 32.9 % improvement compared to traditional impermeable flow distributors. This achievement enables energy-efficient and effective desalination of seawater.

Assessing Potential Effects of Nature-Based Solutions (NBS) on Water Ecosystem Service in the Interurban Micro-Watershed Río Torres, Costa Rica

The implementation of green infrastructure (GI) as Nature-Based Solutions (NBS) generates positive effects on the water ecosystem service in an urban context. Practices such as bioretention cells, green roofs, rain gardens, permeable pavements, and infiltration trenches contribute to treating large volumes of runoff and providing safe spaces for populations living in highly urbanized areas. With the aim to simulate these effects, a hydrological modeling was carried out using the i-Tree Hydro Plus model, which quantified the runoff generated from precipitation events and effective transformations (NBS) to cope with runoff. Eight scenarios were developed: a baseline scenario, five future scenarios with green infrastructure, a scenario with increased tree coverage, and a scenario with increased urbanization. Our hypothesis is that NBS would reduce runoff and increase permeable flow. The analysis of the feasibility of implementing the modeled green infrastructures was carried out through consultation with local stakeholders in the micro-watershed. We found that bioretention cells decrease runoff by 5%, green roofs by 4%, rain gardens by 4%, permeable pavements by 4.5%, and infiltration trenches by 7.5% compared to the baseline scenario where runoff accounts for 32% of water balance flows. The scenario of increased tree coverage had a similar behavior to the baseline scenario, indicating that efforts in this alternative would generate a limited impact on the reduction of runoff. With increased urbanization, impermeable flow increases up to 78%, which would generate floods. Implementing NBS would be feasible since this type of initiative is included in the agenda of many regulatory instruments of urban planning in Costa Rica.

Numerical Study and Structural Optimization of Vehicular Oil Cooler Based on 3D Impermeable Flow Model

A non-uniform permeable flow numerical model of vehicular oil cooler was proposed to simulate the thermal performance of oil cooler, due to the complex internal structure of cooler and the anisotropy of coolant flow and heat transfer. By comparing the numerical simulation results with the experimental results, the maximum error of the simulation results under different working conditions is 9.2%, which indicates that the modelling method is reliable and can improve the development efficiency. On this basis, through the three-dimensional numerical simulation to establish and optimize the oil cooler’s parameters. The thermal performance under different structural oil cooler were compared using the comprehensive evaluation factor j/f. The results and the experimental data show that under the impermeable flow model can obtain good heat transfer efficiency with low flow resistance at the same time. When the cross-sectional area is 3 mm2, length of 90 mm, layer number of 11, the model accuracy was 0.6%, as the optimal structure parameters, the heat transfer increase by 47% and with the total pressure drop increased by only 30%.

Parametric study of methane catalytic combustion in a micro-channel reactor: Effects of porous washcoat properties

A washcoat resolved numerical model of catalytic micro combustor fueled by methane is developed. Detailed gas phase mechanism and alumina dioxide supported Pt-based surface mechanism are adopted. This model proves to capture flow, temperature and species fields precisely including impermeable flow and products accumulation in porous washcoat layer. The novelty and superiority of this research compared to traditional modeling method in which instantaneous diffusion onto catalytic wall is assumed lies in that: it is possible to investigate effects of porous washcoat properties with this full-scale numerical model. Computational results show that homogeneous reactions (HR) are impaired and heterogeneous reactions (HTR) are strengthened as channel confinement increases. Da number analysis reveals that the micro combustor works under a mixed controlled mode in which catalytic reaction rate and internal mass diffusion rate are comparable. When washcoat layer thickness increases from 15 μm to 75 μm, overall catalyst usage roughly decreases from 0.34 to 0.05. It is concluded washcoat thickness can’t be too thin in order to maintain HTR intensity and too thick since catalyst usage is extremely low. Porous washcoat properties impact combustion characteristics in a similar mechanism: modifying effective mass diffusion coefficient. In general, increasing porosity, average pore diameter and decreasing tortuosity will enhance HTR and impair HR. In real application, these parameters can be utilized to modify combustion temperature, emission performance and stability operation map.

Particle accumulation in high‐Prandtl‐number liquid bridges

AbstractParticle accumulation in high‐Prandtl‐number (Pr = 68) thermocapillary liquid bridges is studied numerically. Randomly distributed small rigid non‐interacting spherical particles are found to cluster in particle accumulation structures. The accumulation is found to be caused by a finite‐particle‐size effect when the particles move close to the impermeable flow boundaries. The extra drag force experienced by a particle near the boundaries creates a dissipation in the dynamical system describing the particle motion. This causes particles to be attracted to regions in or near Kolmogorov‐Arnold‐Moser tori of the unperturbed flow field.

The Effect of Curvature and Confinement on Gas-Phase Detonation Cellular Stability

We examine the evolution of cellular detonation patterns in a two-dimensional channel with yielding confinement on one side. It is shown that in a narrow channel of fixed width the number of cells first increase with decreasing level of confinement. Subsequently, with increasingly weaker confinement, the cells then grow in size and the total number of cells in the channel decreases. For sufficiently weak confinement, the flow becomes laminar with no detonation cells. We examine the relative importance of two fluid mechanisms underlying the observed evolution: global curvature of the detonation shock front due to induced flow divergence caused by the yielding confinement, and energy loss associated with transverse shock wave transmission to the confining material. In order to determine which effect is dominant, we compare two types of numerical calculations. One involves specialized calculations in which the explosive boundary, along which impermeable flow conditions are applied, is deflected through a range of specified angles upon detonation arrival. This set-up mimics the effect of yielding confinement in terms of induced flow divergence, but removes the transverse wave energy loss that would otherwise occur due to wave transmission into the confiner material. The second involves multi-material simulations which can account for transverse wave energy loss into the confining material. Shock polar theory is used to select confiner densities in the multi-material calculations that provide equivalent material interface deflection angles at the detonation shock to the angles imposed in the deflected solid wall calculations. We determine that the induced global curvature of the wave primarily drives both the evolution of the cellular pattern and eventual stabilization of the detonation front, characterized by laminar flow solutions. In wider channels, we show that the detonation front will likely remain unstable even for very weak confinement, as the mean curvature of the front only becomes significant near the edge of the explosive domain.

The flow of magnetohydrodynamic Maxwell nanofluid over a cylinder with Cattaneo–Christov heat flux model

A theoretical analysis is performed for studying the flow and heat and mass transfer characteristics of Maxwell fluid over a cylinder with Cattaneo–Christov and non-uniform heat source/sink. The Brownian motion and thermophoresis parameters also considered into account. Numerical solutions are carried out by using Runge–Kutta-based shooting technique. The effects of various governing parameters on the flow and temperature profiles are demonstrated graphically. We also computed the friction factor coefficient, local Nusselt and Sherwood numbers for the permeable and impermeable flow over a cylinder cases. It is found that the rising values of Biot number, non-uniform heat source/sink and thermophoresis parameters reduce the rate of heat transfer. It is also found that the friction factor coefficient is high in impermeable flow over a cylinder case when compared with the permeable flow over a cylinder case.

Projection-based Embedded Discrete Fracture Model (pEDFM)

This work presents a new discrete fracture model, namely the Projection-based Embedded Discrete Fracture Model (pEDFM). Similar to the existing EDFM approach, pEDFM constructs independent grids for the matrix and fracture domains, and delivers strictly conservative velocity fields. However, as a significant step forward, it is able to accurately model the effect of fractures with general conductivity contrasts relative to the matrix, including impermeable flow barriers. This is achieved by automatically adjusting the matrix transmissibility field, in accordance to the conductivity of neighboring fracture networks, alongside the introduction of additional matrix-fracture connections. The performance of pEDFM is investigated extensively for two- and three-dimensional scenarios involving single-phase as well as multiphase flows. These numerical experiments are targeted at determining the sensitivity of the model towards the fracture position within the matrix control volume, grid resolution and the conductivity contrast towards the matrix. The pEDFM significantly outperforms the original EDFM and produces results comparable to those obtained when using DFM on unstructured grids, therefore proving to be a flexible model for field-scale simulation of flow in naturally fractured reservoirs.

Finite Element Model of Oxygen Transport for the Design of Geometrically Complex Microfluidic Devices Used in Biological Studies.

Red blood cells play a crucial role in the local regulation of oxygen supply in the microcirculation through the oxygen dependent release of ATP. Since red blood cells serve as an oxygen sensor for the circulatory system, the dynamics of ATP release determine the effectiveness of red blood cells to relate the oxygen levels to the vessels. Previous work has focused on the feasibility of developing a microfluidic system to measure the dynamics of ATP release. The objective was to determine if a steep oxygen gradient could be developed in the channel to cause a rapid decrease in hemoglobin oxygen saturation in order to measure the corresponding levels of ATP released from the red blood cells. In the present study, oxygen transport simulations were used to optimize the geometric design parameters for a similar system which is easier to fabricate. The system is composed of a microfluidic device stacked on top of a large, gas impermeable flow channel with a hole to allow gas exchange. The microfluidic device is fabricated using soft lithography in polydimethyl-siloxane, an oxygen permeable material. Our objective is twofold: (1) optimize the parameters of our system and (2) develop a method to assess the oxygen distribution in complex 3D microfluidic device geometries. 3D simulations of oxygen transport were performed to simulate oxygen distribution throughout the device. The simulations demonstrate that microfluidic device geometry plays a critical role in molecule exchange, for instance, changing the orientation of the short wide microfluidic channel results in a 97.17% increase in oxygen exchange. Since microfluidic devices have become a more prominent tool in biological studies, understanding the transport of oxygen and other biological molecules in microfluidic devices is critical for maintaining a physiologically relevant environment. We have also demonstrated a method to assess oxygen levels in geometrically complex microfluidic devices.

Utilization of percolation approach to evaluate reservoir connectivity and effective permeability: A case study on North Pars gas field

Reservoir characterization, especially during early stages of reservoir life, is very uncertain, due to the scarcity of data. Reservoir connectivity and permeability evaluation is of great importance in reservoir characterization. The conventional approach to addressing this is computationally very expensive and time consuming. Therefore, there is a great incentive to produce much simpler alternative methods. In this paper, we use a statistical approach called the percolation theory, which considers a hypothesis wherein the reservoir can be split into either permeable (i.e. sand/fracture) or impermeable flow units (i.e. shale/matrix), and assumes that the connectivity of permeability contrasts controls the flow. We developed master curves for the reservoir connectivity and its associated uncertainty, as well as the effective permeability and its associate uncertainty curves. To validate the approach, we have used the data set of the North Pars gas field located at the North of the South Pars field in the Persian Gulf. We have shown that the percolation approach gives reliable predictions when compared with results from a conventional reservoir modeling approach. Moreover, the first approach, as obtained from algebraic manipulation, is very fast, whereas the latter is very costly and time consuming.

A Reservoir Conductivity Evaluation Using Percolation Theory

Oil reservoirs are very complex with geological heterogeneities that appear on all scales. Proper modeling of the spatial distribution of these heterogeneities is crucial, affecting all aspects of flow and, consequently, the reservoir performance. Reservoir connectivity and conductivity evaluation is of great importance for decision-making on various possible development scenarios including infill drilling projects. This can be addressed by using the percolation theory approach. This statistical approach considers a hypothesis that the reservoir can be split into either permeable (good sands) or impermeable flow units (poor sands) and assumes that the continuity of permeability contrasts controls the flow. The approach uses an object-based technique to model the spatial distribution of both isotropic and anisotropic sand bodies in two dimensions. Recently the application of the percolation approach in evaluating reservoir connectivity for both conventional and fracture reservoirs has been reported. This article concentrates on analyzing the conductivity behavior of petroleum reservoirs. In particular, the percolation approach is used to develop the universal curves of the average reservoir permeability and its associated uncertainties. To validate the approach, we used the Burgan reservoir dataset of Norouz offshore oil field in the south of Iran. Core and palynological data analysis indicated that the Burgan consists of a series of incision-fill sequences occurring in an estuarine/coastal plain/deltaic environment. Consequently, the Burgan consists of a thick stack of excellent quality sands incising into each other with few remaining shalier sediments locally separating these sequences. We have shown that the effective permeability, as a measure of reservoir conductivity, from the percolation approach gives reliable prediction once compared with exact numerically obtained results from the modeling of real field data. Moreover, the first approach as obtained from algebraic manipulation is very fast whereas the latter is so costly and time consuming.

History-matching flow simulations and time-lapse seismic data from the Sleipner CO 2 plume

Abstract Since its inception in 1996, the CO 2 injection operation at Sleipner has been monitored by 3D time-lapse seismic surveys. Striking images of the CO 2 plume have been obtained showing a multi-tier feature of high reflectivity. In the medium to longer term, the topmost layer of CO 2 , accumulating and migrating directly beneath the topseal, is the main determinant of storage site performance. Fortunately it is this topmost layer that can be most accurately characterized, its rate of growth quantified, and CO 2 flux arriving at the reservoir top estimated. The latter is mostly controlled by pathway flow through thin intra-reservoir mudstones. This has increased steadily with time, suggesting either that pathway transmissivities are increasing with time and/or the pathways are becoming more numerous. Detailed 3D history-matching of the topmost layer cannot easily match the observed rate of spreading. Isotropic permeabilities result in a stronger radial component than observed and a degree of anisotropic permeability, higher in a north–south direction, is possible. The main contributor to the mismatch, however, is likely to be small but significant uncertainty in the depth conversion. Irrespective of uncertainty, the observed rate of lateral migration seems to require very high permeabilities, and is, moreover, suggestive of a topseal which behaves like a ‘hard’ impermeable flow barrier. Detailed studies such as this will provide important constraints on longer term predictive models of plume evolution and storage performance which are key regulatory requirements.

Seismic tremor at the 9°50′N East Pacific Rise eruption site

Ocean bottom seismic observations within the 9°50′N region of the East Pacific Rise indicate persistent, low‐amplitude tremor activity throughout the October 2003 through February 2007 period of monitoring. These signals exhibit either monochromatic or polychromatic spectral characteristics, with a ∼6 Hz fundamental frequency and up to two harmonics. Individual events cannot be correlated between nearby (<1 km) stations, implying the presence of multiple, small‐amplitude sources positioned within the shallow crust. Tremor exhibits a semidiurnal periodicity, with some stations recording activity during times of increasing tidal extension and others detecting tremor signals during times of increasing compression. The amplitude, duration, and rate of activity also correlate positively with fortnightly changes in the amplitude of the tides. These spatiotemporal patterns are consistent with tremor generation in response to tidally modulated fluid flow within a network of shallow cracks. Tremor energy flux is spatially and temporally heterogeneous; however, there are extended periods of greater and lesser activity that can be tracked across portions of the array. Despite their shallow crustal origin, changes in tremor amplitude and spectral character occur in the months prior to a major microearthquake swarm and inferred seafloor spreading event on 22 January 2006, with an increase in the degree of correlation between tremor activity and tidal strain in the weeks leading up to this event. After the spreading event, two eruption‐surviving stations near the axis continue to show high rates of tremor activity, whereas these signals are suppressed at the single station recovered from the near‐axis flanks. This off‐axis quiescence may result from the dike‐induced closing of cracks or perhaps from the emplacement of impermeable flows near the station.

Analytical solution of a spatially variable coefficient advection–diffusion equation in up to three dimensions

Analytical solutions are provided for the two- and three-dimensional advection–diffusion equation with spatially variable velocity and diffusion coefficients. We assume that the velocity component is proportional to the distance and that the diffusion coefficient is proportional to the square of the corresponding velocity component. There is a simple transformation which reduces the spatially variable equation to a constant coefficient problem for which there are available a large number of known analytical solutions for general initial and boundary conditions. These solutions are also solutions to the spatially variable advection–diffusion equation. The special form of the spatial coefficients has practical relevance and for divergent free flow represent corner or straining flow. Unlike many other analytical solutions, we use the transformation to obtain solutions of the spatially variable coefficient advection–diffusion equation in two and three dimensions. The analytical solutions, which are simple to evaluate, can be used to validate numerical models for solving the advection–diffusion equation with spatially variable coefficients. For numerical schemes which cannot handle flow stagnation points, we provide analytical solution to the spatially variable coefficient advection–diffusion equation for two-dimensional corner flow which contains an impermeable flow boundary. The impermeable flow boundary coincides with a streamline along which the fluid velocity is finite but the concentration vanishes. This example is useful for validating numerical schemes designed to predict transport around a curved boundary.

On The Performance Of Horizontal Wells In Reservoirs Containing Discontinuous Shales

Abstract To fully utilize the potential of horizontal wells, the well planning team must have a clear understanding of both vertical and lateral reservoir characteristics. In many instances, a major uncertainty is the degree to which the horizontal well productivity will be affected by the presence of discontinuous shales. Previous studies concerned with this problem have reported horizontal well productivity as a function of effective vertical permeability, which offers no direct indication of the effects of shale lateral extent, preferential orientation and vertical frequency on well performance. With a numerical model study and an explicit stochastic shale generation algorithm, the influence of shale frequency, size and areal alignment, with respect to the horizontal well direction, on the well productivity was systematically investigated. The result shows that for any given frequency, well productivity is not monotonically related to shale size. Owing to the inclined flow path to the horizontal well, a local minimum in productivity exists as the shale barriers increase in size. The orientation of the horizontal well with respect to the alignment of the shale bodies was found to influence well productivity. Additionally, the productivity of a shorter horizontal well was found to be less affected by the shale bodies. Finally, an empirical correlation based on simulation results is presented. The observations presented in this paper provide new insight into vertical reservoir characterization from horizontal well pressure data, as well as horizontal well planning in reservoirs with a known directional bias in sedimentary structures. Introduction The last decade witnessed a substantial increase in the activities of horizontal wells mainly due to advances in drilling technology which improved the economics of drilling horizontal wells. A horizontal well can typically produce reservoir fluids at a rate two to six times that of a vertical well. The productivity of horizontal wells depends largely on the vertical permeability of the formation. The constituents that reduce the vertical permeability of a reservoir are impermeable flow barriers, such as shales, distributed throughout the formation. Since shales are the most common type of vertical permeability barriers, the term "shales" is used in the remainder of this paper to designate all the impermeable reservoir facies. Through this study we make an attempt to quantify the effect of discontinuous shales on the productivity of horizontal wells. Two types of shale distributions affect fluid flow in the reservoir(1)- continuous shales and discontinuous shales. The shale barriers with known lateral extent and distribution within the formation are termed as continuous shales. Discontinuous shales are those which cannot be correlated between wells and are usually distributed randomly within the porous media. The spatial distribution and the dimension of the discontinuous shales cannot be determined accurately. In order to account for the uncertainty in their lateral extent and distribution within the reservoir, stochastic modelling techniques(2) are generally used to represent the discontinuous shale barriers in reservoir simulation models. There are two different ways to represent discontinuous shales in simulation models: explicit and implicit representation.

Measurement of slope runoff in a permafrost region

Installations at a High Arctic experimental site that is underlain by continuous permafrost allowed the measurement of slope runoff. Surface flow was collected near the base of the slope and the water was led to a flume with a V-notch weir. The water level in the flume was recorded and subsequently converted to discharge measurements. Subsurface flow was intercepted by an impermeable flow barrier set in a trench dug down to the permafrost table and later back-filled by the excavated slope materials. Water draining from above the flow barrier was fed into another flume unit similar to that for surface runoff. During the operational period, regular inspection of the flumes was required to ensure the prevention of ice formation or evaporative losses from the water in the flumes. Keywords: surface flow, subsurface flow, slope hydrology, permafrost.