Total Mass Flux Research Articles

Condensation heat transfer coefficient during steam intermittent flows in a horizontal minichannel

Contents of the paper refer to experimental investigations and subsequent prediction of the heat transfer coefficient for condensation of steam flowing in the 2.13 mm i.d. horizontal smooth circular minichannel. Experimental data obtained cover comprehensive span of two-phase flow conditions such that total mass flux is in the range of 178 kg/(m2·s) ≤ G ≤ 885 kg/(m2·s), steam quality varies within 0.003 ≤ x ≤ 0.118 and saturation temperature is ranging between 120.2 °C ≤ Ts ≤ 151.8 °C. The flow patterns were observed visually and images of interest were recorded and subsequently identified based on a map from the literature. There are three basic two-phase flow patterns studied such as slug, slug-annular and churn occurring in the tested minichannel during intermittent flow. Measurements of the local peripherally averaged condensation heat transfer coefficient for each of the patterns considered were carried out using of a heat flux sensor.Based entirely on empirical results achieved the correlation equations specific to the patterns studied have been developed in terms of pertinent dimensionless numbers predicting values of the condensation heat transfer coefficient measured at deviation of ±15%. The correlations show that the condensation process studied combines contributions by gravity induced falling-film condensation with superimposed influence of the liquid phase axial flow, steam quality and interactions by capillarity and surface tension forces.Validity of the correlations proposed is presented in terms of variability ranges of the dimensionless numbers employed specific for each of the pattern studied such as slug, slug-annular and churn. The data predicted on the correlations developed are then compared against those computed on well recognized contributed relationships referenced to steam in flow condensation found in the literature and discrepancies between the predicted and contributed results are displayed and discussed. The comparison reveals some cases for which the results predicted on the correlations proposed can differ substantially from those computed on existing contributions particularly when referenced to intermittent flows at slug and churn patterns.

Droplet evaporation on pillar structured surface: A 3D lattice Boltzmann numerical study

In this paper, a three-dimensional symmetric lattice Boltzmann (LB) model is built up to investigate evaporation of a sessile droplet on pillar structured surfaces. Parametric effects on droplet evaporation, including pillar structure size, roughness, temperature and wettability, are studied comprehensively, with emphasis on the variations of contact angle, contact radius and velocity of triple-phase contact line (TPCL) as well as heat and mass fluxes during evaporation. Pillar structures are found to induce the droplet to split into spherical cap part and liquid film part, resulting in an evaporation mode different from that on a plain surface. The extent of pinning-depinning is strongly associated with structures when TPCL retracts between pillars. Increasing surface temperature can accelerate evaporation by breaking the constant contact angle (CCA) mode, and increasing surface roughness accelerates evaporation by decreasing the duration of CCA mode. The majority of heat and mass transfer takes place around TPCL. High wettability can facilitate the evaporation of spherical cap due to the meniscus at liquid–vapor interface in the vicinity of pillar top surface. The substrate heat flux directly affected by structure size is higher in the region where pillars are distributed, and the solid–liquid interfacial heat flux varies with the specific interface location within droplet. The total mass flux primarily depends on the TPCL length determined by the droplet evaporation mode. When the droplet evaporates by partial penetration in the Cassie state, the amount of evaporation at liquid–vapor interface between pillars is greater than that above pillars. This paper provides more details and insights for a deep understanding of droplet evaporation on pillar structured surfaces.

Fluctuating characteristics of streamwise wind speed and total saltation mass flux in the near-neutral atmospheric surface layer

Eolian sand transport in the atmospheric surface layer (ASL) is a typical kind of gas–solid two-phase flow at a very high Reynolds number that fluctuates over a wide range of spatial and temporal scales. Based on the high-frequency time series of streamwise wind speed (u) and total saltation mass flux (q) measure at three different observation sites, the fluctuating characteristics of u and q in the near-neutral ASL have been analyzed. Our study suggests that the probability density function (PDF) of the normalized streamwise wind speed fluctuations at the height of approximately 0.5 m follows a standard normal distribution, and the PDF of the q presents a lognormal distribution in the near-neutral ASL during strong and steady wind-blown sand. The investigations on the premultiplied spectral of q and u show that, as the energy of very large-scale motions (VLSMs) increases, the influence of the VLSMs on q becomes more significant. In addition, the stochastic couplings between u and q have been analyzed by using space–time correlations and linear coherence spectrum. Our results suggest that the VLSMs have a significant effect on the low-frequency fluctuations of q in the near-neutral ASL.

Acclimation of phenology relieves leaf longevity constraints in deciduous forests.

Leaf phenology is key for regulating total growing-season mass and energy fluxes. Long-term temporal trends towards earlier leaf unfolding are observed across Northern Hemisphere forests. Phenological dates also vary between years, whereby end-of-season (EOS) dates correlate positively with start-of-season (SOS) dates and negatively with growing-season total net CO2 assimilation (Anet). These associations have been interpreted as the effect of a constrained leaf longevity or of premature carbon (C) sink saturation-with far-reaching consequences for long-term phenology projections under climate change and rising CO2. Here, we use multidecadal ground and remote-sensing observations to show that the relationships between Anet and EOS are opposite at the interannual and the decadal time scales. A decadal trend towards later EOS persists in parallel with a trend towards increasing Anet-in spite of the negative Anet-EOS relationship at the interannual scale. This finding is robust against the use of diverse observations and models. Results indicate that acclimation of phenology has enabled plants to transcend a constrained leaf longevity or premature C sink saturation over the course of several decades, leading to a more effective use of available light and a sustained extension of the vegetation CO2 uptake season over time.

EFFECT OF NON-UNIFORMLY DISTRIBUTED POROSITY OF GAS DIFFUSION LAYERS ON MASS TRANSFER IN PROTON EXCHANGE MEMBRANE FUEL CELLS

Gas diffusion layer porosity can affect mass and charge transfer inside proton exchange membrane fuel cells and influence cell performance. Moreover, the electrochemical reaction rate distribution in various regions inside the cell is not uniform. Proper porosity distribution is very important to improve cell performance. In this paper, a three-dimensional fuel cell model with three steps porosity along the gas flow direction is established. Four cases of non-uniformly distributed porosity, both in anode and cathode gas diffusion layers are simulated, which are compared with uniform porosity distribution to study the effect of these structures on mass transfer inside the cell. Then, an optimization calculation is carried out to obtain the optimal porosity distribution along gas flow direction at 0.2 V and 0.6 V. The numerical results indicate that non-uniformly distributed porosity can change cell performance, and porosity increasing along the gas flow direction makes cell performance be better. Porosity increasing along the gas flow direction can improve the uniformity of current density distribution at low voltage. Diffusive mass flux plays a dominant role in reactant mass transfer. Higher porosity near the outlet region increases total mass flux at the interface, and the proportion of diffusion mass flux in total mass flux also increases.

Quantification of Magnesia Dissolution in Silicate Melts and Diffusivity Determination Using Rotating Finger Test

Refractories exposed to corrosive melts at high temperatures experience wear due to dissolution. The presented work deals with the dynamic corrosion of magnesia fine ceramics in a CaO–Al2O3–SiO2–MgO silicate slag with a CaO/SiO2 weight ratio of 0.65. Finger tests at 200 rpm at three different temperatures, 1450, 1500, and 1550 °C, were performed. A contemporary rotary finger test (RFT) device with in-situ wear profile measurement using a laser device was used. The precise dimension measurements with high-resolution facilitate the determination of total mass flux densities, which allow for determination of effective binary diffusivities. Thereby, two methods based on Sherwood relations were applied. The comparison shows the benefit to better consider deviations from pure cylinder shape. The use of contemporary RFT devices and magnesia fine ceramics allows reliable determination of the effective binary diffusivity.

Balance of total mass and nitrogen fluxes through consecutive digestate processing steps: Two application cases

The high water content and low nutrient concentration of digestate complicate its storage, transportation, and utilization. Subsequent digestate processing can effectively remove water and influence nutrient partitioning among digestate fractions and final products.The current study was carried out to evaluate the performance of two typical digestate processing chains, solid and liquid ones, respectively, and to give practical recommendations for optimization. Two fully operating biogas plants with advanced heat utilization were considered as data sources. The digestate mass flow balance of dry matter (DM), water, total N (TN), and ammonium-N mass flows was performed and the efficiency of the examined processing units was calculated.It was found that solid-liquid separation of raw digestate shifted 73–87% of TN and 60–93% of NH4–N to the liquid phase. Subsequent drying of separated solid fraction removed about 6% of the initial water and required 84% less thermal energy per kg N recovered than the processing of separated liquid. The final product, pellets, contained 14% of initial TN, but only 2% of initial NH4–N as a result of microbial conversion of inorganic N during drying.Vacuum evaporation of separated liquid fraction removed 34% of the initial water and left a DM-rich concentrate. At the same time, an ammonium sulfate solution (ASS) containing 21% of initial TN and 34% of initial NH4–N was produced.Both evaluated processing chains showed specific advantages and challenges. Solid products were characterized by a high share of recalcitrant organic compounds and could serve as a soil improver. Liquid processing concentrated plant-available N in ASS, which could be used as valuable inorganic fertilizer.

The observable properties of cool winds from galaxies, AGN, and star clusters – II. 3D models for the multiphase wind of M82

ABSTRACT Galactic winds are a crucial player in galaxy formation and evolution, but observations of them have proven extraordinarily difficult to interpret, leaving large uncertainties even in basic quantities such as mass outflow rates. Here we present an analysis of the wind of the nearby dwarf starburst galaxy M82 using a semi-analytic model that is able to take advantage of the full three-dimensional information present in position–position–velocity data cubes measured in the H i 21-cm line, the CO J = 2 → 1 line, and the Hα line. Our best-fitting model produces position-dependent spectra in good agreement with the observations, and shows that the total wind mass flux in the atomic and molecular phases is ≈10 M⊙ yr−1 (corresponding to a mass loading factor of ≈2–3), with less than a factor of 2 uncertainty; the mass flux in the warm ionized phase is more poorly constrained, and may be comparable to or smaller than this. At least over the few kpc off the plane for which we trace the outflow, it appears to be a wind escaping the galaxy, rather than a fountain that falls back. Our fits require that clouds of cool gas entrained into the wind expand only modestly, suggesting they are confined by magnetic fields, radiative cooling, or a combination of both. Finally, we demonstrate that attempts to model the wind using simplifying assumptions such as instantaneous acceleration and a constant terminal wind speed can yield significantly erroneous results.

Review of the Observed Energy Flow in the Earth System

The energy budget imbalance at the top of the atmosphere (TOA) and the energy flow in the Earth’s system plays an essential role in climate change over the global and regional scales. Under the constraint of observations, the radiative fluxes at TOA have been reconstructed prior to CERES (Clouds and the Earth’s Radiant Energy System) between 1985 and 2000. The total atmospheric energy divergence has been mass corrected based on ERA5 (the fifth generation ECMWF ReAnalysis) atmospheric reanalysis by a newly developed method considering the enthalpy removing of the atmospheric water vapor, which avoids inconsistencies due to the residual lateral total mass flux divergence in the atmosphere, ensuring the balances of the freshwater fluxes at the surface. The net surface energy flux (Fs) has been estimated using the residual method based on energy conservation, which is the difference between the net TOA radiative flux and the atmospheric energy tendency and divergence. The Fs is then verified directly and indirectly with observations, and results show that the estimated Fs in North Atlantic is superior to those from model simulations. This paper gives a brief review of the progress in the estimation of the observed energy flow in the Earth system, discusses some caveats of the existing method, and provides some suggestions for the improvements of the aforementioned data sets.

Enhanced boundary scavenging of 241Am on the continental margin of the East China sea

The 241Am concentrations were determined by sector field high-resolution inductively coupled plasma mass spectrometry for settling particles and surface sediments collected on the continental margin in the East China Sea to discuss the behavior of 241Am in the studied area. A large and regular increase was noted from 97 m depth to 592 m depth in 241Am concentrations in settling particles from the cylindrical sediment traps, whereas only a slight increase in 239+240Pu concentrations was evident. The gradual increase in 241Am/239+240Pu activity ratios from the cylindrical trap settling particles also was observed. These results were attributed to 241Am being scavenged by settling particles at a more rapid scavenging rate than 239+240Pu. There was an obvious tendency for 241Am fluxes to increase linearly with depth with the highest fluxes at near-bottom, and these fluxes were due to large advective import to the near-bottom. There was a tendency for 241Am concentrations in surface sediments to increase almost linearly with depth, showing the same tendency as 210Pb concentrations, and this tendency indicated that the enhanced boundary scavenging of 241Am as well as 210Pb occurred in the East China Sea continental slope region due to the greater abundance of reactive finer particles. The 241Am concentrations in settling particles from the time-series sediment trap ranged from 1.05 to 4.20 mBq g−1, showing large variation. The 241Am concentrations from the time-series trap varied inversely with the total mass fluxes, indicating that 241Am concentrations were diluted by particles when mass flux increased. The 241Am fluxes showed large time-series variations and these variations were primarily controlled by mass flux variation. It seems that the high total mass flux events are due to resuspension of the underlying surface sediments and episodic lateral transport of particles that flow down the continental slope in the East China Sea.

Response of planktonic foraminifera to seasonal and interannual hydrographic changes: Sediment trap record from the northern South China Sea

Foraminifera play an important role in the organic and inorganic carbon pumps of the ocean. Understanding their responses in seasonal and interannual time scales to the climate and seawater chemistry changes is important for studying carbon cycles and paleoclimatology. This study examined about 5.1-year continuous mass fluxes in 2013/9-2019/8 and 1.8-year planktonic foraminiferal shell fluxes in 2016/8-2019/8 census from ten and four sets of sediment traps, respectively, moored at the South East Asia Time-series Study (SEATS) site in the northern South China Sea (SCS), the world’s largest marginal sea. A total of four sets of sediment trap mooring with 11 common species were identified, spanning from August 2016 to August 2019 with 8-day and 16-day collecting periods, which provided access to evaluate the impact of the prevailing monsoon system and interannual climatic conditions. Our results show that the winter monsoon enhances the nutrient inventories in the euphotic zone, supporting the productivity and the mass and shell fluxes. In addition to seasonal cycles, the variation of chlorophyll-a concentration in the SCS shows a strong response to wind speed under the influence of El Niño–Southern Oscillation (ENSO). The reduction in wind speed and the intensification of Kuroshio intrusion during the ENSO warm phases reduces the productivity and mass and shell fluxes, and vice versa in the case of the ENSO cold phases. The imprint of an ENSO cold phase (La Niña event) in 2017 was signified by 2–3-fold higher values than the 3-year average of total mass and foraminiferal shell fluxes. Instead of the common dominance of Trilobatus sacculifer and Globigerinoides ruber among species composition, Neogloboquadrina dutertrei was the predominant species comprising over 40%–60% of total shells greater than 212 μm. Furthermore, the interval with an elevated abundance of N. dutertrei lasted throughout January 2018 (four collecting intervals). Foraminifera shell fluxes were the lowest during warm months (March-August) in 2019, which was coeval with the increase in proportions of Orbulina universa and Globigerinella calida. The unusual species composition might signify a weak ENSO warm phase (A weak El Niño event) between September 2018 and August 2019.

Temporal variation of particulate organic carbon flux at the mouth of Tokyo Bay.

A sediment trap experiment was conducted at a depth of 750 m at the mouth of Tokyo Bay to clarify the quantity and transport process of particles from the bay to the open ocean. The high total mass flux (8.7 ± 4.5 g m–2 d–1) suggests that the particles not only originate in the surface layer right above the trap, but are also focused in Uraga Channel and discharged into the bay mouth. The organic carbon and nitrogen isotope ratios (δ13Corg, δ15N) of the trapped particles were like those of the surface sediment in the bay, that is, a mixture of particles in rivers and suspended particles in the surface layer of the bay. Compared with the results of the experiment conducted in 1995–2002, the average total mass flux was reduced by 70% and organic carbon content was reduced by 50%. The δ13Corg values of trapped particles were also lower than those observed in the previous experiment, indicating a lower contribution from surface-suspended particles with high δ13Corg values in the bay. These results could partly reflect a decrease of the concentration of the suspended particulate carbon in the bay by half over 20 years. Another factor contributing to the decrease of the flux at the bay mouth would be that the intrusion of Kuroshio coastal water into the bay, which pushes particles out to the bay mouth, has not occurred in recent years.

National characterization of pesticide runoff and erosion potential to put USEPA standard ecological scenarios in context for pyrethroids.

Decision-making for pesticide registration by the US Environmental Protection Agency (USEPA) relies upon crop-specific scenarios in a tiered framework. These standard modeling scenarios are stated to represent "…sites expected to produce runoff greater than would be expected at 90% of the sites for a given crop/use." This study developed a novel approach to compare the pesticide runoff + erosion (SumRE ) mass flux potential of a hydrophobic chemical using 36 of these ecological regulatory scenarios with national-scale distributions of modeled SumRE from over 750 000 USA-wide agricultural catchments to provide real-world context for the simulated transport predictions used for regulatory decision-making. For the standard scenarios and national scale modeling, "edge of field" SumRE mass flux was estimated using regulatory guidance for a hypothetical pyrethroid. The national-scale simulations were developed using publicly available soil, hydrography, and crop occurrence /regional timings databases. Relevant soil and crop combinations identified by spatial overlay along with weather data were used in a regulatory model to generate daily SumRE estimates, which were assigned to the catchments. The resulting average annual total SumRE mass fluxes were ranked to produce distributions to compare with the standard regulatory scenario outputs. These comparisons showed that SumRE flux from 25 of the 36 USEPA ecological regulatory crop-specific scenarios modeled ranked above the 99th percentile of pyrethroid runoff + erosion vulnerability from any catchment growing that crop; SumRE flux from six scenarios was more severe than any catchment. For 12 USEPA regulatory scenarios, the resulting eroded sediment corresponds to highly erodible land (HEL), which the US Department of Agriculture mandates should not be cropped without substantial additional erosion prevention controls for sustainability. Since the pesticide regulatory framework already incorporates many acknowledged assumptions to ensure it conservatively meets protection goals, these HEL observations suggest that the standard scenarios overestimate potential aquatic exposure and that the regulatory process is more protective than intended.Integr Environ Assess Manag 2023;19:175-190. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Effect of sorption-induced deformation on methane flow in kerogen slit pores

Shale gas production relies on the movement of methane through nanopores which are characterized by extra-low permeability in shale formations. However, there is a lack of understanding on methane transport in realistic organic nanopores, especially in relation to sorption-induced swelling. Here, using Monte Carlo and molecular dynamics simulations, the effect of kerogen deformation on gas transport is investigated by comparing the flow rate differences in slit pores with rigid (non-deformable) and flexible (deformable) kerogen matrices, constructed from 27 type II-D kerogen units. Simulation results show that sorption-induced swelling reduces methane mass flux significantly in large slit pores (20–40 Å) as pressure increases. By incorporating kerogen deformation into a diffusive-viscous gas flow model, it is concluded that the observed mass flux decrease is likely attributed to the narrowing pore size which mainly suppresses the viscous flux component. Further calculations suggest that kerogen swelling may decrease the apparent permeability of the slit pore by up to ∼40% within pore pressure of 50 MPa. Additional findings show that diffusion can enhance the maximum gas velocity in the slit pores threefold compared with the Hagen-Poiseuille equation when pore pressure is ∼2 MPa, and the diffusion and the viscous flow dominate the total mass flux when Kn > 10 and Kn < 0.1, respectively.

Linking soil phosphorus with forest litterfall resistance and resilience to cyclone disturbance: A pantropical meta-analysis.

While tropical cyclone regimes are shifting with climate change, the mechanisms underpinning the resistance (ability to withstand disturbance-induced change) and resilience (capacity to return to pre-disturbance reference) of tropical forest litterfall to cyclones remain largely unexplored pantropically. Single-site studies in Australia and Hawaii suggest that litterfall on low-phosphorus (P) soils is more resistant and less resilient to cyclones. We conducted a meta-analysis to investigate the pantropical importance of total soil P in mediating forest litterfall resistance and resilience to 22 tropical cyclones. We evaluated cyclone-induced and post-cyclone litterfall mass (g/m2 /day), and P and nitrogen (N) fluxes (mg/m2 /day) and concentrations (mg/g), all indicators of ecosystem function and essential for nutrient cycling. Across 73 case studies in Australia, Guadeloupe, Hawaii, Mexico, Puerto Rico, and Taiwan, total litterfall mass flux increased from ~2.5 ± 0.3 to 22.5 ± 3 g/m2 /day due to cyclones, with large variation among studies. Litterfall P and N fluxes post-cyclone represented ~5% and 10% of the average annual fluxes, respectively. Post-cyclone leaf litterfall N and P concentrations were 21.6 ± 1.2% and 58.6 ± 2.3% higher than pre-cyclone means. Mixed-effects models determined that soil P negatively moderated the pantropical litterfall resistance to cyclones, with a 100 mg P/kg increase in soil P corresponding to a 32% to 38% decrease in resistance. Based on 33% of the resistance case studies, total litterfall mass flux reached pre-disturbance levels within one-year post-disturbance. A GAMM indicated that soil P, gale wind duration and time post-cyclone jointly moderate the short-term resilience of total litterfall, with the nature of the relationship between resilience and soil P contingent on time and wind duration. Across pantropical forests observed to date, our results indicate that litterfall resistance and resilience in the face of intensifying cyclones will be partially determined by total soil P.

A novel analytical model of solute transport in a layered aquifer system with mixing processes in the reservoirs.

Analytical models of solute transport have been widely used to aid the understanding of the physical and chemical processes undergone by substances introduced in a layered aquifer system. However, in previous studies, the advection component of transport was assumed to be one dimensional, while also ignoring the mixing processes that occur in the inlet and the outlet reservoirs. In this study, new sets of models describing those mixing processes are presented. Beyond that, these models were integrated into already existing models and the result is a novel analytical model of solute transport in aquifer-aquitard systems. The novel analytical solution was derived by the Laplace transform method and the finite-cosine Fourier transform method under the mobile-immobile (MIM) framework. The calculations take into account: the longitudinal and vertical dispersion, the molecular diffusion and the horizonal and vertical advection components of solute transport, as well as first-order chemical reaction, in both the aquifer and the aquitard. A finite-difference solution of the model is tested against experimental data in order to critique its reliability. Results indicate that the numerical and analytical solutions of the new model match well with experimental data. This new model outperforms the previous models in terms of interpreting experimental data. The mixing old and new water in the reservoirs during solute transport in aquifer-aquitard systems is important. Global sensitivity analysis demonstrates that the output concentration of solute in the aquifer-aquitard system is most sensitive to the volume of water in the inlet reservoir. The contribution of the molecular diffusion effect to the total mass flux of the tracer cross the aquifer-aquitard interface is much smaller than the contribution of the dispersive and advective effects.

Estimating Mass Flux From Size‐Fractionated Filtered Particles: Insights Into Controls on Sinking Velocities and Mass Fluxes in Recent U.S. GEOTRACES Cruises

AbstractWe compile full ocean‐depth size‐fractionated (1–51 and &gt;51 μm) particle concentration and composition of suspended particulate matter from three recent U.S. GEOTRACES cruises, and exploit detailed information of particle characteristics measured to give insights into controls on sinking velocity and mass flux. Our model integrates the concept of fractal scaling into Stokes' Law by incorporating one of two porosity‐size power law relationships that result in fractal dimensions of 1.4 and 2.1. The medians of pump‐derived total (&gt;1 μm) mass flux in the upper 100 m of gyre stations are 285.1, 609.2, and 99.3 mg/m2/d in the North Atlantic, Eastern Tropical South Pacific, and Western Arctic Ocean cruises, respectively. In this data set, variations in particle concentration were generally more important than sinking velocity in controlling variations in mass flux. We examine different terms in a Stokes' Law model to explore how variations in particle and water column characteristics from these three cruises affect mass flux. The decomposition of different aspects of the Stokes' relationship sheds light on the lowest total mass flux of the three cruises in the Western Arctic, which could be explained by the Arctic having the lowest particle concentrations as well as the lowest sinking velocities due to having the smallest particle sizes and the most viscous water. This work shows the importance of both particle characteristics and size distribution for mass fluxes, and similar methods can be applied to existing and future size‐fractionated filtered particulate measurements to improve our understanding of the biological pump elsewhere.

Numerical investigation of the effect of ultrasound on paper drying

The paper drying process is very energy inefficient. More than two-thirds of the total energy used in a paper machine is for drying paper. Novel drying technologies, such as ultrasound (US) drying, can be assessed numerically for developing next-generation drying technologies for the paper industry. This work numerically illustrates the impact on drying process energy efficiency of US transducers installed on a two-tiered dryer section of a paper machine. Piezoelectric transducers generate ultrasound waves, and liquid water mist can be ejected from the porous media. The drying rate of handsheet paper in the presence of direct-contact US is measured experimentally, and the resultant correlation is included in the theoretical model. The drying section of a paper machine is simulated by a theoretical drying model. In the model, three scenarios are considered. In the first scenario, the US modules are positioned in the dryer pockets, while in the second scenario, they are placed upstream of the drying section right after the press section. The third case is the combination of the first and second scenarios. The average moisture content and temperature during drying, enhancement of total mass flux leaving the paper by the US mechanism, total energy consumption, and thermal effect of heated US transducers are analyzed for all cases. Results show that the application of the US can decrease the total number of dryer drums for drying paper. This numerical study is based on the US correlation obtained with the US transducer in direct contact with the paper sample. Thus, future work should include US correlation based on a non-contact US transducer.

Continuum-Scale Gas Transport Modeling in Organic Nanoporous Media Based on Pore-Scale Density Distributions

SummaryWe present a continuum-scale mass transport model informed by pore-scale density distribution for gas diffusion through organic nanoporous media. A diffusion model and a sorption model are developed by considering multiple transport and storage mechanisms, including bulk diffusion and Knudsen diffusion for free phase, and surface diffusion and multilayer adsorption for sorbed phase. The continuum-scale diffusion equation is derived based on the free-phase concentration for the overall mass conservation of free and sorbed phases, carrying a newly defined effective diffusion coefficient and capacity factor to account for multilayer adsorption. Diffusion in free and sorbed phases is coupled with the sorption model, which provides pore-scale multilayer adsorption properties by utilizing a pore-scale simplified local density (SLD) method combined with the modified Peng-Robinson equation of state (PR-EOS) for confinement effect. The model was first implemented to analyze adsorption data from a krypton (Kr) adsorption experiment on graphite. Then, we applied the developed diffusion model to conduct the sensitivity analysis of the effects of pore size on gas transport for Kr-graphite and methane-coal systems. The model was finally used to study Kr diffusion profiles through a coal matrix obtained by using X-ray micro-computed tomography (microCT) imaging. The results show that the sorbed phase occupies most of the pore space in organic nanopores with less than 10 nm due to multilayer adsorption, and surface diffusion contributes significantly to the total mass flux. Therefore, neglecting the volume of sorbed phase and surface diffusion in organic nanoporous rocks may result in considerable errors in the prediction of hydrocarbon production. We also compared Brunauer-Emmett-Teller (BET) and Langmuir models by analyzing adsorption data for the wide pressure range up to the saturation pressure. The comparison between BET and Langmuir models shows that the Langmuir model can only match the adsorption isotherm at low pressure and yield lower effective surface diffusion coefficients. Therefore, implementing a Langmuir model may be erroneous for organic nanoporous media with strong adsorption capacity, particularly when pore pressure is high.

Particle fluxes in submarine canyons along a sediment-starved continental margin and in the adjacent open slope and basin in the SW Mediterranean Sea

Investigating the transfer of particulate matter from the continental shelf to the deep basin is critical to understand the functioning of deep sea ecosystems. In this paper we present novel results on the temporal variability of particle fluxes to the deep in three physiographic domains of a 240 km long margin segment and nearby basin off Murcia and Almeria provinces in the SW Mediterranean Sea, which are submarine canyons forming a rather diverse set (namely Escombreras, Garrucha-Almanzora and Almeria), the adjacent open slope and the deep basin.This margin is located off one of the driest regions in Europe and, therefore, its study may help understanding how mainland aridity translates into the export of particles to deep margin environments. Five mooring lines equipped with currentmeters, turbidity-meters and sediment traps were deployed for one entire annual cycle, from March 2015 to March 2016. We combine oceanographic, hydrological and meteorological data with grain size and bulk elemental data (organic carbon, opal, CaCO3, lithogenic) from the collected sinking particles to understand what drives particle transfers in such an under-studied setting, and to quantify the resulting fluxes and assess their spatio-temporal variability.Weighted total mass fluxes in canyons range from 1.64 g m−2 d−1 in Almeria Canyon to 7.33 g m−2 d−1 in Garrucha-Almanzora Canyon system, which are rather low values compared to other submarine canyons in the Western Mediterranean Sea. This results from the absence of extreme wind-storm events during the investigated time period combined with the reduced sediment input to the inner shelf by river systems in the study area. Our results also show that wind-storms are the main trigger for off-shelf particle transport to the deep margin, both within submarine canyons and over the open slope. The most significant transfer period is associated to a set of north-eastern storms in early spring 2015, when the off-shelf transport likely was promoted by storm-induced downwelling. However, the prevailing oceanographic conditions restricts the advection of water down the canyon heads to a few hundred meters, thus promoting a bottom-detached transport of particles seaward. Overall physiography, canyon head incision into the continental shelf and the distance of the canyon head to the shoreline (e.g. very short in Garrucha Canyon) play a key role in particle trapping capability and, therefore, in easing downslope particle transport. Further, bottom trawling activities around the Garrucha-Almanzora Canyon system, feed a nepheloid layer at depths in excess of 400 m, subsequently enhancing particle fluxes throughout the study period. In contrast, maximum particle fluxes in the deep basin respond to seasonal phytoplankton blooms.Our study shows that particle export from the shallow inner margin to the deep outer margin in sediment-starved settings, even if limited, does occur as dominated by atmosphere and ocean driven short-lived events. However, that export does not reach too far as at several tens of kilometres from the shelf edge advective fluxes are replaced by vertical ones impelled by phytoplankton dynamics.