Transport Of Mass Research Articles

Ambient acidic ultrafine particles in different land-use areas in two representative Chinese cities

The adverse effects of acidic ultrafine particles (AUFPs) have been widely recognized in scientific communities. However, a handful of studies successfully acquired the concentrations of AUFPs in the atmosphere. To explore the AUFPs pollution, six extensive measurements were for the first time conducted in the roadside, urban and rural areas in Hong Kong, and the urban area in Shanghai between 2017 and 2020. The concentrations of AUFPs and UFPs, and the proportions of AUFPs in UFPs were obtained. The concentration of UFPs was the highest at the roadside site, followed by the urban site and the rural site, while the proportion of AUFPs in UFPs showed a contrary trend. The difference, on one hand, indicated the potential transformation of AUFPs from non-acidic UFPs during the transport and aging of air masses, and on the other hand, suggested the minor contribution of anthropogenic sources to the emission of AUFPs. In addition, the urban area in Hong Kong suffered from heavier pollution of UFPs and AUFPs than that in Shanghai. As for size distribution, the proportion of AUFPs in UFPs peaked in the size range of 35–50 nm and 50–75 nm in roadside and urban area, respectively. In rural area, the peak was observed in the size range of 5–10 nm, which might indicate the stimulation of new particle formation with the AUFPs as seeds. Furthermore, in the urban areas of Hong Kong and Shanghai, no significant difference was found for the geometric mean diameters of UFPs and AUFPs (p > 0.05). At last, the sulfuric acid proxy was positively correlated with the proportions of AUFPs in UFPs but not well correlated with the AUFPs levels. The results suggested the important roles of interaction between sulfuric acid vapor and non-acidic UFPs in AUFPs formation. Due to the significant reduction of sulfur dioxide in China during the last decade, the pollution of AUFPs in urban areas was alleviated.

Characterization of transport from the Asian summer monsoon anticyclone into the UTLS via shedding of low potential vorticity cutoffs

Abstract. Air mass transport within the summertime Asian monsoon circulation provides a major source of anthropogenic pollution for the upper troposphere and lower stratosphere (UTLS). Here, we investigate the quasi-horizontal transport of air masses from the Asian summer monsoon anticyclone (ASMA) into the extratropical lower stratosphere and their chemical evolution. For that reason, we developed a method to identify and track the air masses exported from the monsoon. This method is based on the anomalously low potential vorticity (PV) of these air masses (tropospheric low PV cutoffs) compared to the lower stratosphere and uses trajectory calculations and chemical fields from the Chemical Lagrangian Model of the Stratosphere (CLaMS). The results show evidence of frequent summertime transport from the monsoon anticyclone to midlatitudes over the North Pacific, even reaching the high-latitude regions of Siberia and Alaska. Most of the low PV cutoffs related to air masses exported from the ASMA have lifetimes shorter than 1 week (about 90 %) and sizes smaller than 1 % of the Northern Hemisphere (NH) area. The chemical composition of these air masses is characterized by carbon monoxide, ozone, and water vapour mixing ratios at an intermediate range between values typical for the monsoon anticyclone and the lower stratosphere. The chemical evolution during transport within these low PV cutoffs shows a gradual change from the characteristics of the monsoon anticyclone to characteristics of the lower stratospheric background during about 1 week, indicating continuous mixing with the background atmosphere.

Particulate Matter Pollution in Urban Cities of India During Unusually Restricted Anthropogenic Activities

The outbreak of COVID-19 is a global public health challenge and has affected many countries, including India. The nationwide lockdown was imposed in India from March 25 to May 31, 2020 to prevent the transmission of COVID-19. The study intends to assess the impact of the absence of major anthropogenic activities during the various phases of the COVID-19 lockdown (LDN) period on the daily mean concentrations of PM2.5 and PM10 in six populated cities of Jaipur, Jodhpur, Kota, Udaipur, Ajmer, and Alwar in the state of Rajasthan. Investigation has been done for the different periods, including the pre-lockdown—PRELD (January 1–March 4, 2020), partial lockdown—PLDN (March 5–24, 2020), COVID-19 lockdown—LDN (March 25–May 31, 2020), and unlocking—ULC (June 1–August 31, 2020) phases. We have also compared the mean concentrations of PM2.5 and PM10 with the same period of the year 2019. A significant improvement in air quality during the COVID-19 LDN period was noticed in all cities compared to 2019 and for the same period of the year 2020. However, the levels of PM2.5 and PM10 were seen to rise during the second, third, and fourth LDN phases compared to the first LDN, indicating that the subsequent lockdowns started with some relaxations and dusty conditions. On the other hand, wind-blown dust is another vital source of PM10, resulting in high concentrations in the summer months (April–May). Significant reductions in PM2.5 (~25–50%) and PM10 (20–37%) in all six cities during the LDN period compared with PRELD were estimated. However, with significant variations from city to city, the lowest reductions in PM2.5 (~25%) and PM10 (~20%) were measured in Jodhpur and Ajmer, respectively. It was noticed that the episodes of rainfall and transport of oceanic air masses resulted in a reduction of particles during the ULC period compared to the LDN period. The air quality index was, more or less, in the “good to satisfactory” category during the first 3 LDN periods, whereas it was moderate for Jodhpur, Jaipur, and Ajmer during the last LDN period. The study will be helpful to determine mitigation policies to minimize air pollution, especially in developing regions.

Assessing diffusion model impacts on enstrophy and flame structure in turbulent lean premixed flames

Diffusive transport of mass occurs at small scales in turbulent premixed flames. As a result, multicomponent mass diffusion, which is often neglected in direct numerical simulations (DNS) of premixed combustion, has the potential to impact both turbulence and flame characteristics at small scales. In this study, we evaluate these impacts by examining enstrophy dynamics and the internal structure of the flame for lean premixed hydrogen-air combustion, neglecting secondary Soret and Dufour effects. We performed three-dimensional DNS of these flames by implementing the Stefan–Maxwell equations in the code NGA to represent multicomponent mass transport, and we simulated statistically planar lean premixed hydrogen-air flames using both mixture-averaged and multicomponent models. The mixture-averaged model underpredicts the peak enstrophy in the multicomponent simulation by up to 13% in the flame front. Comparing the enstrophy budgets of these flames, the multicomponent simulation yields larger peak magnitudes compared to the mixture-averaged simulation in the reaction zone, showing differences of 17% and 14% in the normalised vortex stretching and viscous effects terms. In the super-adiabatic regions of the flame, the mixture-averaged model overpredicts the viscous effects by up to 13%. To assess the effect of these differences on flame structure, we reconstructed the average local internal structure of the turbulent flame through statistical analysis of the scalar gradient field. Based on this analysis, we show that large differences in viscous effects contribute to significant differences in the average local flame structure between the two models.

THE SOUTHERN OCEAN: OUR BEST OPPORTUNITY?

The Southern Ocean has a significant importance in global climate regulation because its great potential to sequester atmospheric carbon and its enormous contribution to the transport of heat and mass in the global ocean. Antarctic benthos presents unique characteristics developed after millions of years of evolution and greatly contribute to the maintenance of the global biodiversity and genetic pool. Ongoing anthropogenic pressure seriously threaten Southern Ocean’s current characteristics and the ecosystems services they provide. In my opinion, individual actions toward environmental protection emergesas the fastest alternative to ameliorate the current situation.
 Keywords: Antarctica, climate change, anthropogenic impacts, social behavior.

Chemical Reaction and Internal Heating Effects on the Double Diffusive Convection in Porous Membrane Enclosures Soaked with Maxwell Fluid.

In this paper, the joint impact of the interior heating and chemical reaction on the double diffusive convective flow in porous membrane enclosures soaked by a non-Newtonian Maxwell fluid is investigated applying linear and nonlinear stability techniques. The porous enclosures are square, slender and rectangular. Using the linear stability analysis, the expression for the critical thermal Rayleigh–Darcy number, above which the convective movement occurs, is derived analytically in terms of associated physical parameters. A nonlinear stability examination reliant on the Fourier double series is executed to calculate the convective heat and mass transports of the arrangement. It is observed that the pattern of convective activity is oscillatory only in the occurrence of a relaxation parameter and the threshold value of the relaxation parameter for the occurrence of the oscillatory pattern depends on the other physical parameters. The onset of convective instability accelerates with the increasing chemical reacting parameter, the interior heating parameter, the solute Rayleigh–Darcy number, the Lewis number, the Vadasz number, and the relaxation parameter, while it delays with the heat capacity ratio. The convective heat and mass transfers increase with the solute Rayleigh–Darcy number, the Vadasz number, the relaxation parameter, and the aspect ratio (for rectangular enclosure), while it decreases with the heat capacity ratio and the aspect ratio (for slender enclosure). Additionally, the convective heat transfer enhances with the interior heating parameter, while the convective mass transfer enhances with the chemical reacting parameter and the Lewis number. The effects of Vadasz number, heat capacity ratio, and relaxation parameter are witnessed only on the oscillatory pattern of convection and unsteady convective heat and mass transfers. Further, some existing literature results are compared with the current findings.

TAP analysis of single and double peak responses during CO oxidation over Pt

Critical phenomena in heterogeneous catalysis have attracted a considerable interest throughout history due to their intriguing dynamical complexity. The coordinated interplay of various phenomena, such as surface interactions, nonlinear reaction mechanisms and the transport of energy and mass, determine the likelihood of dynamic patterns in certain catalytic systems. In this work, pulse experiments performed with a Temporary Analysis of Products (TAP) reactor showcase the complex dynamic behavior of CO oxidation over a Pt catalyst and exhibit its dependence on the pulsed CO/O2 ratio and the local bed temperature. Pulse responses exhibit a dynamic transition between two critical values of the reaction rate for feed mixtures richer in O2 due to the controlled interactions of the adsorbed species on the surface of the catalyst.

Modeling the Effects of Sedimentation on Natural Occurrences of CH4 Hydrates in Marine Sediments

This study explores the relationships that sedimentation rate and transport properties have with the formation and evolution of hydrates in fine-grained marine sediments and their corresponding bottom simulating reflector (BSR) responses. Using a series of one-dimensional simulations of multiphase, multicomponent flow and transport of mass and heat through porous media, a slab of sediments through sedimentation is modeled. The boundary conditions are set to emulate the pressure and geothermal gradients and its resulting gas hydrate stability zone (GHSZ). Hydrates are formed by injecting methane gas through the bottom of the grid and letting it migrate and reach the boundary of stability. The resulting hydrate accumulation is subjected to different sedimentation rates and replicated with different intrinsic permeability. With sedimentation, the geothermal gradient is displaced upward and the boundary of stability shoals. Through methane recycling, the distribution of phases changes through cycles of slow melting and rapid reformation. This results in a dynamic flow barrier that relocates the base of the GHSZ over geological time, in response to the variations of both pressure and salinity. The characteristics of a BSR response will be tied to the stage of the melting cycle.

The landslide velocity

Abstract. Proper knowledge of velocity is required in accurately determining the enormous destructive energy carried by a landslide. We present the first, simple and physics-based general analytical landslide velocity model that simultaneously incorporates the internal deformation (nonlinear advection) and externally applied forces, consisting of the net driving force and the viscous resistant. From the physical point of view, the model represents a novel class of nonlinear advective–dissipative system, where classical Voellmy and inviscid Burgers' equations are specifications of this general model. We show that the nonlinear advection and external forcing fundamentally regulate the state of motion and deformation, which substantially enhances our understanding of the velocity of a coherently deforming landslide. Since analytical solutions provide the fastest, most cost-effective, and best rigorous answer to the problem, we construct several new and general exact analytical solutions. These solutions cover the wider spectrum of landslide velocity and directly reduce to the mass point motion. New solutions bridge the existing gap between negligibly deforming and geometrically massively deforming landslides through their internal deformations. This provides a novel, rapid, and consistent method for efficient coupling of different types of mass transports. The mechanism of landslide advection, stretching, and approaching the steady state has been explained. We reveal the fact that shifting, uplifting, and stretching of the velocity field stem from the forcing and nonlinear advection. The intrinsic mechanism of our solution describes the fascinating breaking wave and emergence of landslide folding. This happens collectively as the solution system simultaneously introduces downslope propagation of the domain, velocity uplift, and nonlinear advection. We disclose the fact that the domain translation and stretching solely depend on the net driving force, and along with advection, the viscous drag fully controls the shock wave generation, wave breaking, folding, and also the velocity magnitude. This demonstrates that landslide dynamics are architectured by advection and reigned by the system forcing. The analytically obtained velocities are close to observed values in natural events. These solutions constitute a new foundation of landslide velocity in solving technical problems. This provides practitioners with key information for instantly and accurately estimating the impact force that is very important in delineating hazard zones and for the mitigation of landslide hazards.

Variability in the meridional overturning circulation at 32°S in the Pacific Ocean diagnosed by inverse box models

The meridional circulation and transport at 32°S in the Pacific Ocean in 1992 and 2017 are compared with analogous data from 2003 and 2009 computed by Hernández-Guerra and Talley (2016). The hydrographic data come from the GO-SHIP database and an inverse box model has been applied with similar constraints as in Hernández-Guerra and Talley (2016). In 1992, 2003 and 2017 the pattern of the overturning streamfunction and circulation are similar, but in 2009 the pattern of the circulation changes in the whole water column. The horizontal distribution of mass transports at all depths in 1992 and 2017 resembles the familiar shape of the “classical gyre” also observed in 2003 and is notably different to the “bowed gyre” found in 2009. The hydrographic data have been compared with data obtained from the numerical modelling outputs of ECCO, SOSE, GLORYS, and MOM. Results show that none of these models properly represents the “bowed gyre” circulation in 2009, and this change in circulation pattern was not observed during the entire length of model simulations. Additionally, the East Australian Current in the western boundary presents higher mass transport in the hydrographic data than in any numerical modelling output. Its poleward mass transport ranges from −35.1 ± 2.0 Sv in 1992 to −54.3 ± 2.6 Sv in 2003. Conversely, the Peru-Chile Current is well represented in models and presents an equatorward mass transport from 2.3 ± 0.8 Sv in 2009 to 4.4 ± 1.0 Sv in 1992. Furthermore, the Peru-Chile Undercurrent presents a more intense poleward mass transport in 2009 (−3.8 ± 1.2 Sv). In addition, the temperature and freshwater transports in 1992 (0.42 ± 0.12 PW and 0.26 ± 0.08 Sv), 2003 (0.38 ± 0.12 PW and 0.25 ± 0.02 Sv), and 2017 (0.42 ± 0.12 PW and 0.34 ± 0.08 Sv) are similar, but significantly different from those in 2009 (0.16 ± 0.12 PW and 0.50 ± 0.03 Sv, respectively). To clarify the causes of these different circulation schemes, a linear Rossby wave model is adopted, which includes the wind-stress curl variability as remote forcing and the response to sea surface height changes along 30°S.

The influence of the summer tropospheric circulation on the observed ozone mixing ratios at a coastal site in the Eastern Mediterranean

This study combines surface ozone (O3) measurements at the Finokalia site (Eastern Mediterranean) with backward trajectory modeling results, reanalysis, and satellite data to investigate how the summer tropospheric circulation affects the O3 mixing ratios in the Eastern Mediterranean. The whole dataset covers the summer months (June, July, August) of 2011–2018. Our findings show that north-northeastern flow, known as the Etesians, is a high frequent wind system over the Eastern Mediterranean during the summer period. Under this flow regime, polluted air masses from the continental central and Eastern Europe reach the monitoring site, increasing the O3 mixing ratios of the area. Contrary, western flows carrying maritime air masses from the Mediterranean Sea, though less frequent, have a central role in controlling the annual O3 mixing ratios in the Eastern Mediterranean. Furthermore, the vertical O3 profile analysis over the Finokalia site indicates enhanced O3 mixing ratios in the middle troposphere when northern flows prevail, confirming the significant relationship between the low-level summer atmospheric circulation and the downward transport of O3-rich air masses to the lower troposphere over Finokalia station, Eastern Mediterranean.

Admittance of the Earth Rotational Response to Zonal Tide Potential

AbstractThis study is devoted to the determination of the admittance parameters describing the Earth rotational response to the components of the zonal tide potential. First, in order to better grasp the physical content of those admittance coefficients, we revisit the theoretical description of the length of day (LOD) changes at sub‐decadal time scale, where forcing is dominated by zonal tides and hydro‐atmospheric mass transports. This theoretical reminder specifies the rheological coefficients permitting to apply the hydro‐atmospheric corrections to isolate the tidal part of the LOD. Then, the admittances are determined from the LOD series corrected from hydro‐atmospheric contributions at the frequencies of the dominant zonal tidal terms between 7 and 365 days. In contrast of the former kindred studies, we both address the discrepancy of the results brought by various EOP series and the hydro‐atmospheric corrections on the LOD. Our study forwards the complementary corrections brought by the ocean, the land water and sea level changes. Below 32 days, removing the atmospheric‐oceanic excitation from LOD allows to much better constraint the admittance complex coefficients κ than applying the atmospheric correction only: the discrepancy with respect to modeled values is reduced up to 70%, and the frequency dependence of the imaginary part brought by the ocean dynamical response is confirmed. A systematic effect with respect to the values modeled by Ray and Erofeeva (2014), https://doi.org/10.1002/2013jb010830 has been detected and hints a defect of this model. Moreover, the role of land water and associated sea level variation is notable at the semi‐annual period.

Chemical species mixing during direct energy deposition of bimetallic systems using titanium and dissimilar refractory metals for repair and biomedical applications

Direct energy deposition (DED) is one of the additive manufacturing technologies where the metal powder is laser-melted by the nozzle and then deposited onto the metal substrate layer-by-layer. DED allows dissimilar metals to be fabricated in order to produce high-performance and intricate parts, and to utilise as a repair method of different metals as well. Refractory metals – high-density, high-melting point materials – are used for repair as a thermal shielding of titanium for high-temperature or biomedical applications. Chemical species mixing of the joint interface between Ti and Zr, Nb, Mo, Hf, Ta and W is induced by transport of species, heat and mass during the DED process. In this work, chemical species mixing, solute profile, and thermal-fluid characteristics are studied using the high-fidelity modelling of coupled powder and thermal-solutal-fluid flow dynamics to elucidate the dissimilar mixture of metals and provide insights into the manufacturability of the refractory metals using DED. It is found that low viscosity metals such as Zr and Nb show good repairability indicated by internal species mixing. Other metals also exhibit enhanced mixing when the temperature is properly set to reduce the viscosity. Therefore, consideration of convection and species mixing in the liquid metal phase is significant. Cooling rate, related to cracking, is also discussed and controlling the local cooling and subsequent solidification behaviour should be properly done by setting proper process conditions. This indicates that the computational tool is capable of predicting causal relationship between materials and processing route for DED applications. • Direct energy deposition is simulated for dissimilar Ti and refractory metals. • Powder and fluid flow simulation is used with multi-metal formulations. • Viscosity significantly affects the mixing behaviour. • Viscosity is linked with local temperature determined by process parameters. • Local temperature also affects cooling rate and thus solidification behaviour.

Hidden Upwelling Systems Associated With Major Western Boundary Currents

AbstractWestern boundary currents (WBCs) play an essential role in regulating global climate. In contrast to their widely examined horizontal motions, less attention has been paid to vertical motions associated with WBCs. Here, we examine vertical motions associated with the major WBCs by analyzing vertical velocity from five ocean synthesis products and one eddy‐resolving ocean simulation. These data reveal robust and intense subsurface upwelling systems, which are primarily along isopycnal surfaces, in five major subtropical WBC systems. These upwelling systems are part of basin‐scale overturning circulations and are likely driven by meridional pressure gradients along the western boundary. Globally, the WBC upwelling contributes significantly to the vertical transport of water mass and ocean properties and is an essential yet overlooked branch of the global ocean circulation. In addition, the WBC upwelling intersects the oceanic euphotic and mixed layers, and thus likely plays an important role in ocean biological and chemical processes by transporting nutrients, carbon and other tracers vertically inside the ocean. This study calls for more research into the dynamics of the WBC upwelling and their role in the ocean and climate systems.

Abstract P1-06-04: Spatial, temporal and therapy dependent heterogeneity in transport phenotype of multiple liver metastases in murine breast cancer model

Abstract Introduction: Inter- and intra-tumor heterogeneities in response of tumors to systemic anti-cancer therapy are the major source of therapeutic resistance. Cancer cells from bulk tumors and cancer cell lines are not clonal but are composed of subclones, creating heterogeneous tumor microenvironment. Furthermore, metastasis can evolve during the disease progression as well as in response to systemic therapies. These spatial and temporal heterogeneities in tumors can affect blood perfusion and vascular permeability which determine the transport of various masses and chemotherapeutic (we refer to as “transport phenotype”). Insufficient drug transport to the tumor in vivo can generate transport-based therapeutic resistance even for agents with proven efficacy against the target cells in vitro. Our goal is to understand spatial and temporal heterogeneity in the transport of mass/anti-cancer drugs to metastatic tumors to leverage novel strategies for improving therapeutic efficacy using mouse tumor models. The study of bulk tumors will provide a mixture of different functions from heterogeneous sets of various clones. We sought to establish single cell-derived clones from the parental murine breast cancer cell line to dissect and simplify tumor heterogeneity. Methods: Single cells were isolated via aliquoting 4T1-luc-tomato red cell suspension (polyclonal) in single-cell concentration into 96 well plate. To evaluate the phenotype of the clonal and parental cells, we performed clonogenic assay, proliferation and growth inhibition assay using pegylated liposomal doxorubicin (PLD), and angiogenic protein production assay using membrane array. Among the established clones, we selected 2 clones and parental cells for further experiments. Experimental liver metastases were created by injecting cell suspension into the spleen of BALB/c mice. Then, the window chamber was implanted above the liver of anesthetized mice and fluorescently labeled dextran tracers with different molecular weights were intravenously (iv) injected. To determine transport phenotype, circulation and diffusion of tracers inside/around individual metastasis were imaged and quantified through the window using Intravital Microscopy (IVM) at various time points. In another set of experiment, PLD was iv injected, and change in the transport phenotype was monitored. Results: While parental cells formed heterogeneous colonies, clonal cells created each cell line dependent uniform colonies in petri dish. Also, parental and selected two clonal cells exhibited different growth, response to PLD, and protein production in vitro. IVM imaging of individual liver metastasis over time using different cell lines revealed that relative fluorescent intensity of tracers transported inside/around tumor compared to that in the uninvolved tumor-free liver was more heterogeneous among parental cell derived tumors compared to clonal cells. Interestingly, these “transport phenotypes” evolved and increased their heterogeneity as tumors progressed regardless of cell type. Furthermore, transport phenotype was modulated from one to another after PLD therapy, creating possible mechanisms of transport based on drug resistance. Discussion: These data suggest that transport phenotype cannot be determined solely by genotype of tumors but modulated as a function of tumor growth and therapy response to become more heterogeneous. The intrinsic heterogeneity of transport phenotype and its acquired transformation suggests a more complicated scenario of tumor drug-resistance mechanism. The clinical implication of our findings is that the transport of therapeutics to the tumor and its efficacy may not be predicted by DNA-based assay and transport-based therapeutics resistance will eventually occur in every tumor type. Citation Format: Thao Nguyen, Yan ting Liu, Arturas Ziemys, Shen Haifa, Kenji Yokoi. Spatial, temporal and therapy dependent heterogeneity in transport phenotype of multiple liver metastases in murine breast cancer model [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-06-04.

Effects of incipient pairing on nonequilibrium quasiparticle transport in Fermi liquids

Abstract The low-temperature properties of a wide range of many-fermion systems spanning metals, quantum gases and liquids to nuclear matter are well understood within the framework of Landau’s theory of Fermi liquids. The low-energy physics of these systems is governed by interacting fermionic quasiparticles with momenta and energies near a Fermi surface in momentum space. Nonequilibrium properties are described by a kinetic equation for the distribution function for quasiparticles proposed by Landau. Quasiparticle interactions with other quasiparticles, phonons, or impurities lead to internal forces acting on a distribution of nonequilibrium quasiparticles, as well as collision processes that ultimately limit the transport of mass, heat, charge, and magnetization, as well as limiting the coherence times of quasiparticles. For Fermi liquids that are close to a second-order phase transition, e.g., Fermi liquids that undergo a superfluid transition, incipient Cooper pairs—long-lived fluctuations of the ordered phase—provide a new channel for scattering quasiparticles, as well as corrections to internal forces acting on the distribution of nonequilibrium quasiparticles. We develop the theory of quasiparticle transport for Fermi liquids in the vicinity of a BCS-type superfluid transition starting from Keldysh’s field theory for nonequilibrium, strongly interacting fermions. The leading corrections to Fermi-liquid theory for nonequilibrium quasiparticle transport near a Cooper instability arise from the virtual emission and absorption of incipient Cooper pairs. Our theory is applicable to quasiparticle transport in superconductors, nuclear matter, and the low-temperature phases of liquid 3He. As an implementation of the theory we calculate the pairing-fluctuation corrections to the attenuation of zero sound in liquid 3He near the superfluid transition and demonstrate quantitative agreement with experimental results.

Numerical study on heat and mass transport enhancement in MHD Williamson fluid via hybrid nanoparticles

Fundamental laws are used for modeling of transport characteristics in Williamson fluid with Cu and Al2O3. Models are solved numerically using the finite element method (FEM). study is conducted on the effects of hybrid nanoparticles on heat and mass transfer during homogeneous and heterogeneous chemical reactions. The Williamson parameter can play significant influence on momentum transport. Based on simulations, the Lorentz force for the flow of Cu-Al2O3–Williamson fluid is greater than the Lorentz force acting on Cu-Williamson fluid. Thus momentum BL thickness for Cu-Al2O3-Williamson fluid is less than that for the flow of Cu-Williamson fluid. An increase in curvature parameter makes the fluid to decelerate. However, this decelerating effect for flow of Cu-Williamson fluid is more than that in Cu-Al2O3– Williamson fluid. Mass transport in the fluid is slow down by an increase in when Schmidt number is increased. However, this decrease in transport of mass in Cu-Al2O3– Williamson fluid is greater than that in Cu-Williamson fluid. Concentration related to the products of species taking part in homogeneous-heterogeneous chemical reaction strength.

Numerical study on dual‐region mass transport at wave flow field of proton exchange membrane fuel cell

AbstractThe performance and stability of proton exchange membrane fuel cells are mainly dependent on mass transports in the gas diffusion layer (GDL). The mass transports in dual‐region including the regions of under‐channel and under‐rib are one of the factors that cause mass uneven distribution. Therefore, the wave structure and the auxiliary flow channel are introduced to enhance these mass transports. Auxiliary conventional parallel flow field (ACPFF), wave flow field (WFF), and auxiliary WFF (AWFF) are transferred into ANSYS MESHING for meshing, then imported into Fuel Cell and Electrolysis module on FLUENT for the solution. This comprehensive AWFF has important influences on mass even distribution and performance. The results reveal that dual‐region forced convections can be made by the periodic waved structure and the auxiliary flow channel. More reactants are forced to appear in GDL of under‐channel and under‐rib. Based on the simulation results, the distributions of oxygen, water, temperature are more even in AWFF. Specifically, the cell performance at high current density is improved obviously. Compared to CPFF, the max power density is increased by more than 4% in this novel flow field (AWFF), which will provide a new trial for the design of a comprehensive flow field.

PGM-Free Oxygen-Reduction Catalyst Development for Proton-Exchange Membrane Fuel Cells: Challenges, Solutions, and Promises

ConspectusProton-exchange membrane fuel cells (PEMFCs) are efficient and clean hydrogen energy technologies for transportation and stationary applications. Highly active and durable low-cost cathode catalysts for the oxygen-reduction reaction (ORR) under challenging acidic environments are desperately needed to address the cost and durability issues of PEMFCs. The most promising platinum group metal (PGM)-free catalysts for the ORR in acidic media are atomically dispersed and nitrogen-coordinated metal site catalysts denoted as M–N–C, M = Fe, Co, or Mn. Due to significant efforts in the past few decades, these catalysts have demonstrated much-improved ORR activity and promising initial fuel cell performance approaching traditional Pt/C catalysts. However, the insufficient long-term stability (up to 5000 h) under PEMFC operation represents a primary technical barrier to making current PGM-free catalysts less viable yet in PEMFCs. In this Account, we highlight recent advances in synthesizing efficient PGM-free catalysts for the ORR in PEMFCs, emphasizing effective strategies to improve mass and intrinsic activity and the possible degradation mechanisms. In particular, a chemical doping method based on the zeolitic imidazolate framework (ZIF)-8 represents the key to developing efficient M–N–C catalysts containing atomically dispersed and nitrogen-coordinated single metal active sites (i.e., MN4). The newly acquired understanding of the formation mechanism of MN4 active sites during the thermal activation and its correlation to catalytic properties guide the rational catalyst design rather than relying on current trial-and-error approaches. Considerable efforts have further been invested in increasing the active site density and enhancing intrinsic activity by regulating carbon-phase structures and the local coordination environment. These highly active catalysts usually suffer from significant activity loss during the ORR. Therefore, breaking the activity–stability trade-off is the key to simultaneously achieving activity and stability in one catalyst, which is discussed on the basis of our recent successes in regulating local carbon structures surrounding active single metal sites. Significant research efforts toward understanding the degradation mechanisms and improving the lifetime of PGM-free catalysts are still crucial for viable applications in the future. Novel electrode designing strategies are needed to translate the PGM-free catalysts’ ORR activity to solid-state electrolyte-based membrane electrode assemblies (MEAs) with robust three-phase (i.e., gas–liquid–solid) interfaces for efficient charge and mass transports for performance improvement. On the basis of our effort at the University at Buffalo supported by ElectroCat Consortium associated with U.S. DOE’s Hydrogen and Fuel Cell Technologies Office, we provide a perspective on PGM-free cathode catalysts concerning remaining bottlenecks and future opportunities, aiming to inspire the community in both mechanistic understanding and technological development.

Thermodiffusion and chemical reaction on MHD free convective flow past a rotating vertical porous plate with constant heat and mass discharge

Simultaneous heat and mass transport have played significant roles in different substantial chemical, and biomedical processes. Heat and mass transports happen in absorptions, distillations, extractions, drying, melt along with crystallizations, moreover, evaporations, and condensations. Mass flows due to the temperature gradients are recognized as the Soret effect. The Soret effects on the unsteady hydromagnetic liberated convective flow of a non-incompressible electrically performing gelatinous liquid over the rotating perpendicular absorbent plate in the incidence of temperature amalgamation have been investigated. The effects of the first order chemical reaction along with heat radiation are considered. The scheme of partially differential equalities is rendered into ordinarily differential equalities and therefore solved systematically with the Laplace transforms methodology. The impacts of different pertinent flow parametrics on velocities, temperature as well as concentration distributions, in addition, the shear stress is examined through the graphical profiles along with tables accordingly. This is established that resultant velocity field is ascending through an increase in the Soret parameter and chemically reacting parameter. The temperature distribution is increased by an increasing heat absorption parameter. Also, when the Soret parameter increases, then concentration increases throughout the fluid region.