Advective Flow Research Articles

Balance model of dissolved nitrogen and phosphorus transportation and metabolism in the Dniester estuary system

In order to obtain quantitative estimates of water and nutrient fluxes into the Dniester estuary system, the biogeochemical modeling approach recommended by the international program LOICZ was used. The integral (reservoir) model of the system consists of balance equations for water, salinity and dissolved forms of nitrogen and phosphorus. The research involves the information of the annual cycle (from November 2003 to October 2004) of hydrochemical studies at the mouth of the Dniester River and at the exit of the estuary to the Black Sea carried out within the framework of the international project GEF/BSERP, as well as the data of hydrometeorological observations at Belgorod-Dniestrovsky hydrometeorological station, Tzargorod Gyrlo hydrometeorological post and Odesa State Environmental University training base.
 The water balance equation takes into account the flows of river runoff, precipitation and evaporation. Uncertainty associated with the failure of taking into account the underground runoff still remained. The use of an independent empirical assessment of the advective water flow through the Tzargorod Strait made it possible to estimate the degree of non-stationarity of the model equations on the scale of variability from a month to a year. The flow of turbulent exchange between the estuary and the adjacent sea is estimated by means of the salt balance equation and is determined by the difference between the estuary and marine water salinity.
 By calculating the monthly and yearly values it was established that, for the Dniester estuary and similar systems, the water balance equation can be considered as stationary while the precipitation and evaporation flows can be neglected: compared to the river runoff, advective and turbulent water exchange flows they are several orders of magnitude lower, that is, below the limit of errors of horizontal water flows.
 The joint action of the advective and diffusion flows ensured the overall removal of nutrients from the estuary ecosystem. During the annual cycle of 2003-2004 observations 73% of total dissolved phosphorus and 92% of total dissolved nitrogen entered the sea from the estuary compared to the amount reaching the estuary with the Dniester River runoff.
 Stoichiometric analysis of biogeochemical residuals showed that, for most of the year, the ecosystem of the Dniester estuary produced organic matter and consumed dissolved phosphorus, while the nitrogen fixation in the ecosystem outweighed the denitrification process.

Heat, noble gases and CO2 sources in geothermal fields of Mexico

The Trans-Mexican Volcanic Belt (TMVB) and the Gulf Extensional Province (Baja California) are the regions in Mexico with the highest heat flow and where the main geothermal energy resources are currently exploited. Here, previously published and newly collected heat and volatile species (He, Ar and CO2) data from 132 fluid samples of four geothermal areas belonging to TMVB (Los Azufres, Los Humeros, Acoculco and Cerritos Colorados) and two in Baja California (Cerro Prieto and Las Tres Vírgenes) were analyzed. The goal was to identify heat sources, understand how heat is transported into the geothermal reservoirs and how the multiple fluid sources (meteoric, magmatic and crustal) in the reservoir might impact the heat in each field. Distinct R/Ra ratios (where R is the measured 3He/4He ratio and Ra is the atmospheric ratio) are observed in the TMVB and Baja California geothermal fields, with those in the TMVB displaying significantly higher R/Ra values (7.14–7.27) than those in Baja California (1.21–6.62), indicating a higher contribution of mantle helium from possibly younger, active magmatic heat sources. Lower R/Ra values in Baja California might reflect local tectonic features, where reservoirs are primarily affected by crustal contributions from an old, subducted fossil slab related to the Farallon Plate. The analysis of heat to 3He ratios (or Q/3He) together with information provided by 4He/36Ar ratios suggest that heat and volatiles are transferred into the hydrothermal system by advection. The magma bodies beneath the geothermal areas of interest are sufficiently voluminous to provide aqueous fluids by exsolution to sustain this advective flow. The release of He and Ar from magma, during its degassing, appears to be controlled by their diffusivities, fractionating the pristine mantle 4He/36Ar ratio toward higher values, while advection transfers volatiles more rapidly than heat, fractionating the pristine mantle Q/3He ratios toward lower values. The Q/3He vs. 4He/3He relationship shows that boiling and dilution by meteoric water led to further fractionation of heat and volatiles, particularly in Los Azufres and Los Humeros fields, while Cerro Prieto has Q/3He ratios close to those at mid-ocean ridges or fractionated by circulation of low-heat, 4He-rich fossil waters. Distinct sources of heat and volatiles are also reflected in the CO2 content, the major dry gas component in these geothermal fields. Main sources of CO2 are mantle carbon (1%-51%) and limestone (34%–100%) from local sources and the subducting slab, although expected fractionation of the C isotopic composition and CO2/3He during magma ascent and degassing introduce uncertainties on the precise estimation of each source contributing C to the studied geothermal reservoirs. Yet, contribution of carbon from sediments might be minor (0%–35%), and mainly found in Cerro Prieto and Las Tres Virgenes fields located in Baja California, which are affected by the release of volatiles from the subducted Farallon plate and presence of connate waters in the reservoir of Cerro Prieto.

Flux and spectral variability of Mrk 421 during its moderate activity state usingNuSTAR: Possible accretion disc contribution?

Context.The X-ray emission in BL Lac objects is believed to be dominated by synchrotron emission from their relativistic jets. However, when the jet emission is not strong, one could expect signatures of X-ray emission from inverse Compton scattering of accretion disc photons by hot and energetic electrons in the corona. Moreover, the observed X-ray variability can also originate in the disc, and get propagated and amplified by the jet.Aims.Here, we present results on the BL Lac object Mrk 421 using the Nuclear Spectroscopic Telescope Array data acquired during 2017 when the source was in a moderate X-ray brightness state. For comparison with high jet activity state, we also considered one epoch of data in April 2013 when the source was in a very high X-ray brightness state. Our aim is to explore the possibility of the signature of accretion disc emission in the overall X-ray emission from Mrk 421 and also examine changes in accretion parameters considering their contribution to spectral variations.Methods.We divided each epoch of data into different segments in order to find small-scale variability. Data for all segments were fitted using a simple power-law model. We also fitted the full epoch data using the two component advective flow (TCAF) model to extract the accretion flow parameters. Furthermore, we estimated the X-ray flux coming from the different components of the flow using the lowest normalisation method and analysed the relations between them. For consistency, we performed the spectral analysis using models available in the literature.Results.The simple power-law function does not fit the spectra well, and a cutoff needs to be added. The spectral fitting of the data using the TCAF model shows that the data can be explained with a model where (a) the size of the dynamic corona at the base of the jet is from ∼28 to 10 rs, (b) the disc mass accretion rate is from 0.021 to 0.051ṀEdd, (c) the halo mass accretion rate is from 0.22 to 0.35ṀEdd, and (d) the viscosity parameter of the Keplerian accretion disc from 0.18 to 0.25. In the assumed model, the total flux, disc and jet flux correlate with the radio flux observed during these epochs.Conclusions.From the spectral analysis, we conclude that the spectra of all the epochs of Mrk 421 in 2017 are well described by the accretion-disc-based TCAF model. The estimated disc and jet flux relations with radio flux show that accretion disc can contribute to the observed X-ray emission, when X-ray data (that cover a small portion of the broad band spectral energy distribution of Mrk 421) are considered in isolation. However, the present disc-based models are disfavoured with respect to the relativistic jet models when considering the X-ray data in conjunction with data at other wavelengths.

On the onset of advective flow in a stratified medium induced by weak symmetry breaking of horizontal translations

In this paper, we analytically study the mechanism of the onset of the liquid/gas flow in a non-isothermal stratified medium. The flow is induced by small spatial inhomogeneities of the exchange coefficients. In a statically stable stratified medium heated strictly from above, as is known, there is heat diffusion directed from top to bottom. We consider the system, which is slightly non-invariant with respect to translations along with horizontal directions. It may occur, for example, due to the dependence of the thermal conductivity coefficient on horizontal coordinates. In this case, we show that it could result in the rise of horizontal inhomogeneity in the distributions of buoyancy and hydrostatic pressure and, consequently, in the onset of the horizontal advection. We consider harmonic variations of the thermal conductivity of small amplitude. By applying a linear approximation to a set of governing equations, we derive explicit analytical expressions for temperature perturbations and velocity components. Finally, we investigate the possibility of an intense response of the system on slight initial symmetry breaking in a definite range of parameter values.

Morphological controls on surface runoff: an interpretation of steady-state energy patterns, maximum power states and dissipation regimes within a thermodynamic framework

Abstract. Recent research explored an alternative energy-centred perspective on hydrological processes, extending beyond the classical analysis of the catchment's water balance. Particularly, streamflow and the structure of river networks have been analysed in an energy-centred framework, which allows for the incorporation of two additional physical laws: (1) energy is conserved and (2) entropy of an isolated system cannot decrease (first and second law of thermodynamics). This is helpful for understanding the self-organized geometry of river networks and open-catchment systems in general. Here we expand this perspective, by exploring how hillslope topography and the presence of rill networks control the free-energy balance of surface runoff at the hillslope scale. Special emphasis is on the transitions between laminar-, mixed- and turbulent-flow conditions of surface runoff, as they are associated with kinetic energy dissipation as well as with energy transfer to eroded sediments. Starting with a general thermodynamic framework, in a first step we analyse how typical topographic shapes of hillslopes, representing different morphological stages, control the spatial patterns of potential and kinetic energy of surface runoff and energy dissipation along the flow path during steady states. Interestingly, we find that a distinct maximum in potential energy of surface runoff emerges along the flow path, which separates upslope areas of downslope potential energy growth from downslope areas where potential energy declines. A comparison with associated erosion processes indicates that the location of this maximum depends on the relative influence of diffusive and advective flow and erosion processes. In a next step, we use this framework to analyse the energy balance of surface runoff observed during hillslope-scale rainfall simulation experiments, which provide separate measurements of flow velocities for rill and for sheet flow. To this end, we calibrate the physically based hydrological model Catflow, which distributes total surface runoff between a rill and a sheet flow domain, to these experiments and analyse the spatial patterns of potential energy, kinetic energy and dissipation. This reveals again the existence of a maximum of potential energy in surface runoff as well as a connection to the relative contribution of advective and diffusive processes. In the case of a strong rill flow component, the potential energy maximum is located close to the transition zone, where turbulence or at least mixed flow may emerge. Furthermore, the simulations indicate an almost equal partitioning of kinetic energy into the sheet and the rill flow component. When drawing the analogy to an electric circuit, this distribution of power and erosive forces to erode and transport sediment corresponds to a maximum power configuration.

Dynamical processes controlling the evolution of early-summer cut-off lows in Northeast Asia

Cut-off lows are crucial extratropical circulation systems that can bring weather extremes over large areas, but the mechanism responsible for the life cycle of cut-off lows remains elusive. From a perspective of regional eddy-mean flow interaction, this study investigates the dynamical processes controlling the evolution of early-summer cut-off lows over Northeast Asia using the 6-hourly reanalysis data. Through the diagnostic of local wave activity (LWA) budget, we show that the cut-off low is initialized by a Rossby wave train originated from the subpolar North Atlantic, and then reinforced rapidly by zonal LWA flux convergence and local baroclinic eddy generation, and eventually decayed through energy dispersion by zonal wave activity advection. Furthermore, we show that the evolutions of the above dynamical processes are strongly modulated by the changes of background flow. In early summer, Northeast Asia is located at the eastern exit of the midlatitude jet to the north of the subtropical jet and exhibits a weak meridional gradient of potential vorticity, which favors frequent formation of cyclonic anomaly and energy accumulation. Prior to the onset of cut-off lows by several days, a Rossby wave train propagates along the Eurasian midlatitude jet, which initializes a cyclonic anomaly over Northeast Asia. With the aid of mean flow advection of anomalous zonal momentum, the zonal winds are then decelerated at the midlatitude jet exit and accelerated at the subtropical jet center. The former obstructs the wave packet proceeding downstream and the latter favors stronger baroclinic eddy generation below the subtropical jet. The two processes together maintain and strengthen the cyclonic anomaly in Northeast Asia rapidly.

Characterizing the Advective Hot Flows of Nova-like Cataclysmic Variables in the X-Rays: The Case of BZ Cam and V592 Cas

We present a joint spectral analysis of ROSAT PSPC, Swift X-ray Telescope, and Nuclear Spectroscopic Telescope Array Focal Plane Module A/B (FPMA/B) data of the nova-like (NL) cataclysmic variables (CVs) BZ Cam and V592 Cas in the 0.1–78.0 keV band. Plasma models of collisional equilibrium fail to model the 6.0–7.0 iron line complex and continuum with larger than 2.0. Our results show nonequilibrium ionization (NEI) conditions in the X-ray plasma with temperatures of 8.2–9.4 keV and 10.0–12.9 keV for BZ Cam and V592 Cas, respectively. The centroids of He-like and H-like iron ionization lines are not at their equilibrium values as expected from NEI conditions. We find power-law spectral components that reveal the existence of scattering and Comptonization with a photon index of 1.50–1.87. We detect a P Cygni profile in the H-like iron line of BZ Cam translating to outflows of 4500–8700 km s−1 consistent with the fast winds in the optical and UV. This is the first time such a fast collimated outflow is detected in the X-rays from an accreting CV. An iron Kα line around 6.2–6.5 keV is found revealing the existence of reflection effects in both sources. We study the broadband noise and find that the optically thick disk truncates in BZ Cam and V592 Cas consistent with transition to an advective hot flow structure. V592 Cas also exhibits a quasiperiodic oscillation at mHz. In general, we find that the two NLs portray spectral and noise characteristics as expected from advective hot accretion flows at low radiative efficiency.

On the origin of core radio emissions from black hole sources in the realm of relativistic shocked accretion flow

ABSTRACT We study the relativistic, inviscid, advective accretion flow around the black holes and investigate a key feature of the accretion flow, namely the shock waves. We observe that the shock-induced accretion solutions are prevalent and such solutions are commonly obtained for a wide range of the flow parameters, such as energy (${\cal E}$) and angular momentum (λ), around the black holes of spin value 0 ≤ ak < 1. When the shock is dissipative in nature, a part of the accretion energy is released through the upper and lower surfaces of the disc at the location of the shock transition. We find that the maximum accretion energies that can be extracted at the dissipative shock ($\Delta {\cal E}^{\rm max}$) are $\sim 1{{\ \rm per\ cent}}$ and $\sim 4.4{{\ \rm per\ cent}}$ for Schwarzschild black holes (ak → 0) and Kerr black holes (ak → 1), respectively. Using $\Delta {\cal E}^{\rm max}$, we compute the loss of kinetic power (equivalently shock luminosity, Lshock) that is enabled to comply with the energy budget for generating jets/outflows from the jet base (i.e. post-shock flow). We compare Lshock with the observed core radio luminosity (LR) of black hole sources for a wide mass range spanning 10 orders of magnitude with sub-Eddington accretion rate and perceive that the present formalism seems to be potentially viable to account LR of 16 Galactic black hole X-ray binaries (BH-XRBs) and 2176 active galactic nuclei. We further aim to address the core radio luminosity of intermediate-mass black hole (IMBH) sources and indicate that the present model formalism perhaps adequate to explain core radio emission of IMBH sources in the sub-Eddington accretion limit.

Flow capacity characterization of unconventional natural gas bearing rocks using digital rock physics: A comparison between advection and diffusion

Experimental flow capacity characterization of unconventional rocks is a nontrivial task, and the relative contribution of advective vs. diffusive flow mechanisms remains illusive. Herein we apply a digital rock physics workflow to systematically compare the advection and diffusion behavior of supercritical methane in two 3D reconstructed unconventional shale and coal core samples. Nitrogen sorption experiments and scanning electron microscope observations are combined to inform the construction of representative pore network models. For advection modeling, we consider the nanometer-scale confinement effect and pore shape effect, while for diffusion modeling the contributions of Fick diffusion, transitional diffusion, and Knudsen diffusion are considered separately based on the Knudsen number. The effect of pore size, shape, pressure, and temperature on methane flow capacity in a single nanopore is first studied. Then the apparent permeability and effective diffusivity of the two reconstructed nanoporous media are calculated and compared. We demonstrate that at reservoir pressure and temperature conditions, diffusion contributes to mass flux (above 10%) only in micropores and small mesopores (< 10 nm). For most realistic unconventional rocks, the contribution of bulk diffusion can be neglected when estimating the flow capacity.

Customized Woven Carbon Fiber Electrodes for Bioelectrochemical Systems—A Study of Structural Parameters

Commercial carbon fiber (CF) fabrics are popular electrode materials for bioelectrochemical systems (BES), but are usually not optimized for the specific application. This study investigates BES-relevant material characteristics on fabric level, such as weave types and weave parameters. The two contrasting weave types plain and leno weave were characterized with respect to their envisaged application types: 1) BES with mainly advective flow regimes and 2) stirred systems, which could benefit from fluid flow through a fabric electrode. Experiments with batch and continuously fed pure cultures of Geobacter sulfurreducens PCA and Shewanella oneidensis MR-1 reveal that µm-scale electrode topologies are of limited use for the thick biofilms of G. sulfurreducens, but can boost S. oneidensis’ current generation especially in batch and fed-batch reactors. For advective flow regimes, deeper layers of biofilm inside microporous electrodes are often mass transport limited, even with thin biofilms of S. oneidensis. Therefore, low porosity plain weave electrodes for advective flow operation as in wastewater treating BES should be thin and flat. A trade-off between maximized current density and electrode material utilization exists, which is optimized exemplarily for an advective flow operation. For stirred BES of biotechnological applications, a flow-through of electrolyte is desired. For this, leno weave fabrics with pores at cm-scale are produced from 100% CF for the first time. In a preliminary evaluation, they outperform plain weave fabrics. Mass transfer investigations in stirred BES demonstrate that the large pores enable efficient electrode utilization at lower power input in terms of stirring speed.

Optimal cooling of an internally heated disc.

Motivated by the search for sharp bounds on turbulent heat transfer as well as the design of optimal heat exchangers, we consider incompressible flows that most efficiently cool an internally heated disc. Heat enters via a distributed source, is passively advected and diffused, and exits through the boundary at a fixed temperature. We seek an advecting flow to optimize this exchange. Previous work on energy-constrained cooling with a constant source has conjectured that global optimizers should resemble convection rolls; we prove one-sided bounds on energy-constrained cooling corresponding to, but not resolving, this conjecture. In the case of an enstrophy constraint, our results are more complete: we construct a family of self-similar, tree-like 'branching flows' whose cooling we prove is within a logarithm of globally optimal. These results hold for general space- and time-dependent source-sink distributions that add more heat than they remove. Our main technical tool is a non-local Dirichlet-like variational principle for bounding solutions of the inhomogeneous advection-diffusion equation with a divergence-free velocity. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 1)'.

Angular momentum transport and thermal stabilization of optically thin, advective accretion flows through large-scale magnetic fields

ABSTRACT Outward transport of angular momentum, as well as viscous and thermal stability, are the necessary criteria for the formation of an accretion disc and to radiate steadily. Turbulent motions originating from magneto-rotational instability or hydrodynamic instability can do the required transport. We explore the effect of a large-scale magnetic field (LSMF) over the turbulent transport in an optically thin advective accretion disc. In this work, turbulent transport is represented through the usual Shakura–Sunyaev α-viscosity. The evolution of the magnetic field and other variables is found by solving vertically integrated height-averaged magnetohydrodynamic equations. Depending on its configuration, the LSMF can support or oppose α in outward transport of angular momentum. Once outward transport of angular momentum is assured, i.e. formation of the disc is confirmed through the combined effect of α-viscosity and the LSMF, we explore the impact of the LSMF in thermally stabilizing the disc. As found earlier, we also find that the advection of heat energy becomes zero or negative with an increasing accretion rate. That is why, at or above a critical accretion rate, the optically thin advective disc becomes thermally unstable. We show, however, that with the addition of a strong enough magnetic field, the disc regains its thermal stability and Joule heating turns out to play the key role in that. Throughout our analysis, the plasma-β (βm) remains within the range of 5–103, which does not impose any restriction in the simultaneous operation of the LSMF and the turbulent transport.

Stability of Advective Flow in a Rotating Horizontal Incompressible Fluid Layer Heat-Insulated from Below with Rigid Boundaries at Low Prandtl Number

Stability of Advective Flow in a Rotating Horizontal Incompressible Fluid Layer Heat-Insulated from Below with Rigid Boundaries at Low Prandtl Number

Convective heat transfer of spring meltwater accelerates active layer phase change in Tibet permafrost areas

Abstract. Convective heat transfer (CHT) is one of the important processes that control the near-ground surface heat transfer in permafrost areas. However, this process has often not been considered in most permafrost studies, and its influence on freezing–thawing processes in the active layer lacks quantitative investigation. The Simultaneous Heat and Water (SHAW) model, one of the few land surface models in which the CHT process is well incorporated into the soil heat–mass transport processes, was applied in this study to investigate the impacts of CHT on the thermal dynamics of the active layer at the Tanggula station, a typical permafrost site on the eastern Qinghai–Tibet Plateau with abundant meteorological and soil temperature and soil moisture observation data. A control experiment was carried out to quantify the changes in active layer temperature affected by vertical advection of liquid water. Three experimental setups were used: (1) the original SHAW model with full consideration of CHT, (2) a modified SHAW model that ignores CHT due to infiltration from the surface, and (3) a modified SHAW model that completely ignores CHT processes in the system. The results show that the CHT events occurred mainly during thaw periods in melted shallow (0–0.2 m) and intermediate (0.4–1.3 m) soil depths, and their impacts on soil temperature at shallow depths were significantly greater during spring melting periods than summer. The impact was minimal during freeze periods and in deep soil layers. During thaw periods, temperatures at the shallow and intermediate soil depths simulated under the scenario considering CHT were on average about 0.9 and 0.4 ∘C higher, respectively, than under the scenarios ignoring CHT. The ending dates of the zero-curtain effect were substantially advanced when CHT was considered due to its heating effect. However, the opposite cooling effect was also present but not as frequently as heating due to upward liquid fluxes and thermal differences between soil layers. In some periods, the advection flow from the cold layer reduced the shallow and intermediate depth temperatures by an average of about −1.0 and −0.4 ∘C, respectively. The overall annual effect of CHT due to liquid flux is to increase soil temperature in the active layer and favor thawing of frozen ground at the study site.

High helium reservoirs in the Four Corners area of the Colorado Plateau, USA

Radiogenic 4He is naturally produced in Earth's crust due to alpha decay of Uranium (U) and Thorium (Th). Helium has unique thermodynamic properties required for the medical imaging industry, aerospace and other fields of high-tech manufacturing, and currently is in increasingly high demand. Despite its economic value, the mechanisms of helium migration and retention in sedimentary basins remain poorly understood.Oil and gas fields with economic helium (>0.3%) concentrations have been discovered in Paleozoic intervals in the Colorado Plateau, southwestern USA. Here we report new noble gas isotope and abundance data for gas samples (n = 31), from actively producing Paleozoic formations within five fields: Ratherford, Tocito Dome, Navajo Springs, Pinta Dome, and Dineh-Bi-Keyah. Helium concentrations range from 0.01% to 7.9% with varying amounts of liquid and gaseous hydrocarbons, N2, and CO2. We present multi-stage gas, water, and oil equilibration models to account for the observed noble gas elemental and isotopic signatures. Oil-dominated systems are explained by a closed system oil/water equilibration and subsequent admixture of air. He-rich dry gas samples exhibit uniform 4He/N2 ratios consistent with the regional mean values, suggesting a common crustal source and no subsequent fractionation. In contrast, air-derived 20Ne/36Ar ratios are highly fractionated. These observations are consistent with a tectonically controlled crustal gas release from the basement, groundwater saturation with 4He and N2, and subsequent degassing. Extensive gas-water interaction (i.e., migration) leads to extreme fractionation of 20Ne/36Ar, but does not affect 4He/N2 due to water saturation with crustal gases released from the basement.We show the volume of rock required to have produced helium in the reservoir to be significantly larger than the current reservoir volume immediately beneath the field. Therefore, the reservoir helium concentration cannot be sourced by in-reservoir decay of U and Th and instead requires a process to incorporate exogenous sources of helium in the reservoir without significant dilution from hydrocarbons. For helium-rich fields, excess helium is sourced from the Precambrian granitic basement likely utilizing a large area beneath the field area (i.e., crustal gas mobilization and transport via fracture zones), consistent with the degree of water contact. Deep crustal faults in the Precambrian basement are in close proximity to the high helium fields, indicating that these structures are potentially serving as primary migration conduits via advective fluid flow.

Modeling particulate matter concentration in indoor environment with cellular automata framework

This study attempts to develop a new 3D approach for modeling concentration of airborne particulate matter (PM) in indoor environment with cellular automata (CA) framework. So far numerical simulations of transient 3D indoor PM transport and distribution are mostly using the Lagrangian and Eulerian approaches. Each approach has its own advantages and drawbacks. For the purpose of increasing numerical efficiency without losing necessary accuracy, a new 3D CA-based approach for transient PM concentration estimation is proposed by considering four major PM transport mechanisms (flow advection, turbulent diffusion, gravitational settling, and boundary deposition). This CA approach enables us to use simple explicit algebraic equations to simulate the above four mechanisms without adopting numerical iteration and/or matrix solving, so that the numerical efficiency can be enhanced. Two test cases having reliable measured PM concentration profiles in indoor chambers are used to verify the accuracy and efficiency of the proposed approach with two Eulerian drift flux models and two Lagrangian particle tracking models for comparison. The simulated results indicate that the proposed approach can simulate as accurate as the two Eulerian drift flux models with significant reduction on its execution time. For the present two test cases, it can be at least 483.4%–564.6% faster than the other Eulerian drift flux models. Thus, it has considerable potentials as a useful tool for 3D numerical simulations of indoor PM transport and distribution.

Understanding the Past-Present-Future Hydrogeologic System Through Numerical Groundwater Modeling of South Bengal Basin, India

The quaternary hydrogeologic system of the South Bengal Basin in India with low natural topographic gradients, such as deltas and floodplains, is complex. This research elaborates the hydrogeologic system in and around the twin megacities of Kolkata and Howrah located on this complex delta of the South Bengal Basin and the rapid urbanization pattern during the past 30 years to understand the past, present (2016), and future (2030) behavior of the aquifer system and the advective flow paths of contaminants (wastewater, arsenic, and heavy metals) through hydrogeological simulations and field data. The groundwater model has been calibrated and validated by using the observed and simulated head. The root mean square error of the model is 1.07 m. The built-up area has increased from 142 to 243 km2 between 1985 and 2016, resulting in over-pumping of groundwater. About 93% of the available groundwater is abstracted, and as a result, the piezometric surface is declining at a rate of 13–37 cm/year and the groundwater trough in Kolkata is expanding at the rate of 8.60 km2/year. At places, the confined aquifer is behaving as an unconfined one, increasing the threat of land subsidence. The water quality is deteriorating in parts of Kolkata city where the groundwater is contaminated with wastewater, arsenic, and heavy metals, particularly in boroughs VIII and X. Contaminants from industrial sites may reach the strainer depth (100–120 m bgl) of pumping wells within a period of 20–25 years. The maximum simulated drawdown with respect to the predevelopment head is 22 m. If over-pumping continues, then simulation indicates that the head may drop by another 1.94–2.20 m by 2030. All this may endanger the health and well-being of millions of people living in the area in the near future.

Solid Electrolyte Interphase Growth in Lithium Metal Cells With Normal Electrolyte Flow

In high energy density lithium metal batteries (LMBs), dendrite and solid electrolyte interphase (SEI) growth reduce safety and longevity, respectively. A stable SEI layer enables high efficiency cycling but continued SEI growth can lead to reduced capacity and coulombic efficiency. In this paper, we develop a steady-state model that predicts the effect of small advective electrolyte flow towards the lithium metal electrode on SEI growth during charging. For a fixed current density, increasing the electrolyte flow rate improves the coulombic efficiency and decreases SEI layer growth rate. Decreasing the charging current density at a constant flow rate also decreases the SEI layer growth rate. Low flow rates (μm/s) can increase coulombic efficiency by up to 6%. The sensitivity of the coulombic efficiency to plating and SEI layer reaction rates is also explored.

Viscoelastic RNA entanglement and advective flow underlies nucleolar form and function

The nucleolus is the largest membrane-less intracellular condensate, which facilitates transcription, processing, and assembly of ribosomal RNA (rRNA), the most abundant RNA in the cell. Nucleolar function is thought to be facilitated by its biophysical nature as a multiphase liquid, whose fluidity enables dynamic processing of rRNA within a reactive fluidic environment. Despite compelling evidence for nucleoli exhibiting liquid-like behaviors, no precise measurements of native nucleolar rheology have been achieved.

Coolant Wetting Simulation on Simplified Stator Coil Model by the Phase-Field Lattice Boltzmann Method.

Stator coils of automobiles in operation generate heat and are cooled by coolant poured from above. The flow characteristic of the coolant depends on the coil structure, flow condition, solid–fluid interaction, and fluid property, which has not been clarified due to its complexities. Since straight coils are aligned and layered with an angle at the coolant-touchdown region, the coil structure is simplified to a horizontal square rod array referring to an actual coil size. To obtain the flow and wetting characteristics, two-phase fluid flow simulations are conducted by using the phase-field lattice Boltzmann method. First, the flow onto the single-layered rod array is discussed. The wetting area is affected both by the rod gap and the wettability, which is normalized by the gap and the averaged boundary layer thickness. Then, the flow onto the multi-layered rod arrays is investigated with different rod gaps. The top layer wetting becomes longitudinal due to the reduction of the flow advection by the second layer. The wetting area jumps up at the second layer and increases proportionally to the below layers. These become remarkable at the narrow rod gap case, and finally, the dimensionless wetting area is discussed at each layer.