Lateral Mass Transfer Research Articles

Application of generalized dispersion theory to vortex chromatography

Acoustically induced secondary flows are applied to enhance lateral mass transfer beyond the relatively slow diffusion. This has the goal to reduce convective axial dispersion and the resulting band broadening which, in turn, limits the performance of column chromatography. Traditional approaches based on Taylor-Aris model are limited to one-dimensional rectilinear (unidirectional) tube- or channel-flows. We therefore apply the generalized dispersion theory (GDT) allowing for prediction of the dependence of potentially improved performance on the characteristics of the induced secondary flow, channel geometry and solute properties as well as providing qualitative physical insight into the role of lateral flows. Results corroborate agreement with our experimental observations (residual standard deviation, Sres = 3.88) and demonstrate the advantage of applying GDT relative to 3D time-dependent simulations.

Matrimid substrates with bicontinuous surface and macrovoids in the bulk: A nearly ideal substrate for composite membranes in CO2 capture

Scalable fabrication of thin-film composite (TFC) membrane for post-combustion carbon capture is often limited by the availability of high-performance nanoporous substrate. Ideally, the substrate should allow for fast gas transport at the selective layer/substrate interface as well as in the bulk of the substrate. In this study, highly permeable Matrimid substrates were prepared via vapor- and nonsolvent-induced phase separations. The phase separation mechanism of the Matrimid®/N-methyl-2-pyrrolidone casting solution was modulated by the addition of LiCl to control the solution thermodynamic stability, and nanoporous Matrimid substrates were formed with a bicontinuous surface and macrovoids in the bulk. This hierarchically optimized structure resulted in a CO2 permeance of 2.60 × 105 GPU (1 GPU = 1 × 10−6 cm3(STP) cm−2 s−1 cmHg−1 = 3.349 × 10−10 mol m−2 s−1 Pa−1), which was ca. 11 times more permeable than a benchmark polyethersulfone substrate with cellular pores. The benefit of using this new substrate was demonstrated by coating a 170-nm amine-containing polymer to form a TFC facilitated transport membrane. The membrane exhibited a CO2 permeance of 932 GPU at 57 °C, which was 72 GPU higher than the counterpart coated on the benchmark substrate. Meanwhile, the CO2/N2 selectivity was remained at 158. This permeance improvement could be well explained by the resistance-in-series model, where the improved permeance was attributed to the reductions in substrate and lateral diffusion mass transfer resistances. The upper bound (UB) analysis indicates that the Matrimid substrate is nearly ideal for the state-of-the-art polymers for CO2/N2 separation. The substrate improvement could also reduce the parasitic energy associated with the membrane process due to the reduced membrane cost and flue gas compression requirement.

Experimental study of flame spread transition from chemistry to heat transfer controlled regime at sub-atmospheric pressure: The effect of sample width

Understanding the flame spread rate (FSR) is controlled by either chemistry or heat transfer is important for industrial process safety. In this study, we study the effect of width on flame spread transition from chemical to thermal regime at sub-atmospheric pressure using thin paper sample with widths from 10 mm to 90 mm. Results show that the transition boundary can be identified using not only reported FSR but also the flame image or radiation, as each of them has significantly different characteristics in different regimes. We find that the orientation significantly affects the flame spread in the thermal regime but has negligible influence in chemical regime. A width dependent characteristic Damkohler number coupled lateral heat and mass transfer has been developed to analyze this transition. The Damkohler number increases as the width increases only if the width is narrow. When the width is higher than a critical value, its effect on the Damkohler number can be neglected. For this reason, the transition pressure first shifts from 25kPa (10 mm and 20 mm width) to 20kPa (30 mm width), and then keeps unchanged at 15kPa (width>50 mm). This work strengthens our understanding on the effect of width on fire risks in aircraft.

Effects of chloroplast-cytoplasm exchange and lateral mass transfer on slow induction of chlorophyll fluorescence in Characeae.

Rapid cytoplasmic streaming in characean algae mediates communications between remote cell regions exposed to uneven irradiance. The metabolites exported from brightly illuminated chloroplasts spread along the internode with the liquid flow and cause transient changes in chlorophyll fluorescence at cell areas that are exposed to dim light or placed shortly in darkness. The largest distance to which the photometabolites can be transported has not yet been determined. Neither is it known if lateral transport has an influence on the induction of chlorophyll fluorescence. In this study, the relations between spatial connectivity of anchored chloroplasts in characean internodes and fluorescence induction curves were examined. Connectivity between remote cell parts was pronounced upon illumination of a cell spot at a distance up to 10 mm from the area of fluorescence measurement, provided the spot was located upstream in the cytoplasmic flow. Spatial interactions between distant cell sites were also manifested in strikingly different slow stages of fluorescence induction caused by narrow- and wide-field illumination. Cytochalasin D, cooling of bath solution, and inactivation of light-dependent envelope transporters were used to disturb cyclosis-mediated spatial interactions. Although fluorescence induction curves induced by narrow- and wide-field illumination differed greatly under control conditions, they became similar after the inhibition of cyclosis with cytochalasin D. The results indicate that cytoplasmic streaming not only drives the lateral translocation of photometabolites but also promotes the export of reducing power from illuminated chloroplasts due to flushing the chloroplast surface and keeping sharp concentration gradients.

Positively charged nanofiltration membranes mediated by a facile polyethyleneimine-Noria interlayer deposition strategy

The development of the positively charged nanofiltration (NF) membrane is of great importance for water softening. The relative low water permeance restricts its widespread application. Up to now, numerous efforts on the interlayer technologies have been implemented to manipulate the interfacial polymerization (IP) process of the negatively charged NF membrane. However, there are few reports on the interlayer-mediated positively charged NF membrane. Herein, an interlayer-mediated positively charged NF membrane is fabricated via an IP process between polyethyleneimine (PEI) and trimesoyl chloride. A facile interlayer is deposited based on the interaction of a macrocycle polyphenol of Noria and PEI. The fabricated NF membrane possesses a unique surface morphology, less intrusion of the polyamide layer, a low lateral mass transfer resistance and adequate separation layer thickness. Consequently, the interlayer-mediated NF membrane exhibits a high water permeance of 110.4 L·m−2·h−1·MPa−1, which is ~2.6 times over the control group of 41.6 L·m−2·h−1·MPa−1, while preserves a considerable rejection of 95.4% towards MgCl2 solution. More importantly, the water permeance is enhanced not at the expense of membrane thickness, which is conducive to the long-term running stability. This study paves a new way to fabricate a high performance positively charged NF membrane through an interlayer manipulation strategy.

Microstructural response of the fuel phase in U-7Mo dispersion fuel irradiated at different powers

Irradiation conditions such as fission power, fission rates, and temperature are important parameters for nuclear fuels because they influence the microstructural behavior and ultimate irradiation performance. Two U-7Mo/Al-3.5 wt.% Si dispersion fuel plates were irradiated in the Advanced Test Reactor edge-on to the core in the RERTR-9B experiment at different powers to study the effects of power on fuel phase swelling behavior. The results of non-destructive measurements have been reported in a previous paper [1], and the destructive examination results are being reported here. In particular, the microstructural evolution of the U-Mo fuel phase in irradiated fuel plates has been investigated by cutting transverse cross-sections, using generated scanning electron microscopy micrographs, and image processing methods to assess the changes in microstructural features, such as fission gas pore growth and non-recrystallized grain fraction. In this study, the focus was to examine the evolution of fission gas pores from both the constrained and unconstrained regions of U-Mo fuels irradiated at different powers. Based on an estimated linear gradient, the rate of change of fission gas pore size with locally calculated fission densities is more prominent in the higher power specimen. As such, the average porosity and pore area is approximately 11% and 2 × larger in the fuel irradiated at higher power than that of the lower power specimen. The growth of fission gas pores can accelerate the pore interconnectivity and thus fission gas outside the fuel kernel (FGO), which are two precursors for swelling in U-Mo fuels. The influence of increased power, internal plate stresses, and fission-induced creep on fuel kernel deformation and lateral mass transfer is also highlighted.

Patterned Surfaces for Solar-Driven Interfacial Evaporation.

Solar-driven interfacial evaporation, as one of the most effective ways to convert and utilize solar energy, has attracted lot of interest recently. Most of the previous research studies, however, mainly focused on nonpatterned solar absorbers by improving the structural and chemical characteristics of the solar absorbers used in the interfacial evaporation systems. In this work, we investigated the influence of patterned surface on the evaporation performance of solar absorbers. The patterned surfaces studied, which include black patterns and white patterns, were achieved by selectively printing carbon black on the air-laid paper. Such a design leads to the lateral temperature differences between adjacent patterns of the solar absorber under solar illumination. The temperature differences result in the lateral heat and mass transfer between those patterns, which can effectively accelerate solar-driven vapor generation. With similar patterns and same coverage of carbon black, the increase in the circumference of the surface patterns leads to the increase in the evaporation performance. Additionally, we found that the evaporation performance can be optimized through the design of surface patterns, which demonstrates the potential in reducing the usage of the light-absorbing materials in the solar absorber. The findings in this work not only expand the understanding of the interfacial evaporation systems but also offer additional guidelines in designing interfacial evaporation systems.

Water Flow in Soils with Heterogeneous Macropore Geometries

Core Ideas Increasing macropore volume may decrease the final cumulative outflow. Heterogeneous macroporous geometries can be represented explicitly or implicitly. HYDRUS‐1D and SWAP performed well in soils with heterogeneous macroporous geometries. Dead‐end macropores are included by changing lateral transfer parameters with depth. Heterogeneous macroporous geometries (HMGs) comprise unevenly distributed macropores with depth. A large variety of macropore distributions produce fast water flow and chemical transport that deviate from uniform flow. We analyzed the measured pressure head and outflow in column experiments with a uniform matrix (Exp. I), one central macropore (main bypass) (Exp. II), and HMG (Exp. III) and evaluated the performance of the models HYDRUS‐1D and SWAP under these conditions. Two replicate soil columns were prepared with a 62‐cm silty loam layer above a 5‐cm sandy loam layer. Well‐defined infiltration and drainage conditions were applied to top and bottom boundaries, respectively. Pressure head and outflow were measured at short time intervals, and calibration was performed by PEST. Experiment I was conducted to calibrate the matrix parameters and Exp. II to calibrate macropore parameters. In Exp. III, four dead‐end macropores were created around the main bypass, and the models were run using the previously calibrated parameters, updating only the macropore geometry parameters. The results indicated that HMGs increased total macropore influx, especially in the internal catchment domain. Interaction between the internal catchment, main bypass, and matrix domains was necessary for explaining the change in cumulative outflow and outflow onset observations. The simulations with both models were accurate for HMG regarding pressure head and outflow. The implicit representation of HMGs by HYDRUS‐1D improved outcomes for cumulative outflow, whereas the explicit representation by SWAP improved results for lateral mass transfer. The ability to model the effects of HMGs is essential for environmental and agricultural studies.

Mechanism of the Impact of Particle Size Distribution to Bed-Inventory Overturn for Pant-Leg Circulating Fluidized Bed

An improved two particle sizes numerical model based on a uniform size model was established to investigate the influence of the average particle size on bed-inventory overturn inside a pant-leg circulating fluidized bed (CFB). The new model successfully simulated the dynamic performance of a pant-leg CFB that as average particle size shrank, the pant-leg CFB tended to overturn, while the uniform size model showed a contradicted trend. The success was attributed to the difference of the flow pattern with different particle size. The smaller particles tend to stay the upper furnace after fluidized by the primary air flow while the larger particles tend to fall back to the bottom soon after being carried to upper furnace by the primary air flow and smaller particles. As pointed out in our previous work, the lateral mass transfer resulted in a lateral pressure difference at the upper finance and inhibited further lateral mass transfer, which was regarded as a self-balancing process. The quick fall down of the large particles somehow weaken the lateral pressure different built-up at the upper furnace. Therefore, as the average particle size shrink, the weaken effect of the large particles on self-balancing ability of the pant-leg CFB increase, resulting a more tendency for bed-inventory overturn. It was such a characteristic behavior of the large particles, which was neglected in the uniform particle size model, caused the difference between the results of the two models described above.

Two dimensional mass transfer in flat layers and lateral diffusion effect in permeability determination

For investigation of diffusion, such experimental setup geometry arrangement is preferred, where as soon as possible homogeneous concentration field takes place in flat material samples. However, lateral mass transfer may play significant role. Here, this effect was solved for twodimensional diffusion through a layer of finite thickness to a circular target with an insulating ring. Simple formula has been suggested fitting the numerical results in a wide range of variables including asymptotic cases as well. The formula is suitable for determination of permeability using data received by electrodiffusion measurement under the conditions of limiting diffusion current to a circular electrode with a guard ring.

Fission induced swelling and creep of U–Mo alloy fuel

Tapering of U–Mo alloy fuel at the end of plates is attributed to lateral mass transfer by fission induced creep, by which fuel mass is relocated away from the fuel end region where fission product induced fuel swelling is in fact the highest. This mechanism permits U–Mo fuel to achieve high burnup by effectively relieving stresses at the fuel end region, where peak stresses are otherwise expected because peak fission product induced fuel swelling occurs there. ABAQUS FEA was employed to examine whether the observed phenomenon can be simulated using physical–mechanical data available in the literature. The simulation results obtained for several plates with different fuel fabrication and loading scheme showed that the measured data were able to be simulated with a reasonable creep rate coefficient. The obtained creep rate constant lies between values for pure uranium and MOX, and is greater than all other ceramic uranium fuels.

Bed-inventory overturn mechanism for pant-leg circulating fluidized bed boilers

A numerical model was established to investigate the lateral mass transfer as well as the mechanism of bed-inventory overturn inside a pant-leg circulating fluidized bed (CFB), which is of great importance to maintain safe and efficient operation of the CFB. Results show that the solid loading along the central line of the pant-leg CFB is promotional to the lateral mass transfer across the central line as well as the bed-inventory overturn. Although the lateral pressure difference generated from lateral mass transfer inhibits continuing lateral mass transfer, providing the pant-leg CFB with self-balancing ability to some extent, the primary flow rate change due to the outlet pressure change often disable the self-balancing ability by continually enhancing the flow rate difference. As the flow rate of the primary air fan is more sensitive to its outlet pressure, it is easier to lead to bed inventory overturn. While when the solid particle is easier to follow the surrounding air flow, the self-balancing ability can be more active.

Simulations of lateral mixing in cross-channel flow

Cross flow phenomena between connected sub-channels are studied by means of numerical simulations based on lattice-Boltzmann discretization. The cross (that is lateral) transfer is largely due to macroscopic instabilities developing at two shear layers. The characteristic size and advection velocity of the instabilities favorably compare with experimental results from the literature on a geometrically similar system. The strength of the cross flow strongly depends on the Reynolds number, with cross flow developing only for Reynolds numbers (based on macroscopic flow quantities) larger than 1360. Mass transfer between the sub-channels has been assessed by adding a passive scalar to the flow and solving its transport equation. As a result of the intimate connection of cross flow and lateral mass transfer, also the mass transfer coefficient is a pronounced function of Re.

Initiation of slip along the Xianshuihe fault zone, eastern Tibet, constrained by K/Ar and fission-track ages

The Xianshuihe fault zone (XFZ) forms a boundary that accommodates crustal movement eastwards from central Tibet. The lack of well-defined time constraints has hampered the reconstruction of the geometric and kinematic evolution of the fault zone, and inhibited the development of a consistent regional tectonic model. New geochronological investigations of mica K/Ar and apatite fission-track ages on the Ganzi–Yushu segment of the XFZ indicate that fault activity started ca. 13 Ma before present, which considerably precedes the 5 Ma initiation of offset on the Xiaojiang fault (XjF) segment. Different initiation times for different fault segments clearly demonstrate that the geometric and kinematic evolution of the XFZ can be divided into two periods. The XFZ cut through the Dangjiang, Ganzi, and Gongga Shan areas, and reached the Qinghe–Yanyuan area during an early stage, from ca. 13 to 5 Ma, as a boundary fault with lateral mass transfer from the interior to southeast Tibet. At the southern edge of the XFZ, the movement took advantage of the southern segment of the Longmen Shan thrust fault – the Jinhe–Qinghe thrust fault. During the late stage, from 5 Ma to present, the fault zone passed through the Yushu, Ganzi, and Gongga Shan areas, then offset the Longmen Shan thrust fault belt and reached the Kunming area. The Jinhe–Qinghe fault was abandoned in the later period as the southern part of the XFZ, and the XjF became active because of continuous clockwise rotation of the crust around the eastern syntaxis.

20 Ma of lateral mass transfer around the western Himalayan syntaxis

20 Ma of lateral mass transfer around the western Himalayan syntaxis

Flow in Compound Channel with Abrupt Floodplain Contraction

Flooding rivers usually present transition reaches where the floodplain width can significantly vary. The present study focuses on an abrupt floodplain contraction (mean angle 22°) in order to determine whether one-dimensional (1D) models, developed for straight and slightly converging geometry, are equally valid for such a geometry. Experiments on a contraction model were carried out in an asymmetric compound channel flume. Severe mass and momentum transfers from the floodplain towards the main channel were observed, giving rise to a noteworthy transverse slope of the water surface and different head loss gradients in the two subsections. Three 1D models and one 2D simulation were compared to experimental measurements. Each 1D model incorporates a specific approach for the modeling of the momentum exchange at the interface boundary between the main channel and the floodplain. The increase of the lateral mass transfer generates moderate errors on the water level values but significant errors on the discharge distribution. Erroneous results arise because of incorrect estimations of both momentum exchange due to lateral mass transfers and boundary conditions which are imposed by the tested 1D models.

Interfacial tension measurement at a flat liquid–liquid interface under electrochemical instability

The electrocapillary curve and temporal stability of the interfacial tension were measured for a polarized flat water–dichloroethane interface under electrochemical instability. The interfacial tension was measured on the basis of capillary wave spectra obtained by means of the heterodyne detection of the light scattered at the interface. Anomalous behavior of the electrocapillary curve was observed in the potential range in which the electrochemical instability was expected. The correlation between the interfacial tension and the current spike observed in the chronoamperometry was examined. Despite the presence of the anomalous current spikes and other phenomena showing thermodynamic instability, the results revealed that the interfacial tension was stable and did not show any correlation with the anomalous current. The results were explained by a structure formation by the lateral mass transfer to avoid the instability, in addition to the vertical interfacial ion transfer which is apparently observed by the current measurement.

Combined Effect of Magnetic Field and Lateral Mass Transfer on Non-Darsy Axisymmetric Free Convection in a Power-Law Fluid Saturated Porous Medium

Combined Effect of Magnetic Field and Lateral Mass Transfer on Non-Darsy Axisymmetric Free Convection in a Power-Law Fluid Saturated Porous Medium

Lithospheric Electrical Structure of the Qinling Orogen and its Geodynamic Implication

AbstractStudying in detail three‐dimensional electrical structural features of lithospheres and combining with other geophysical and geological data in the Qinling orogenic belt, we find that since Mesozoic‐Cenozic eras, particularly late‐geological time, as a result of continuous intracontinental subduction beneath the Qinling orogen by the North China block (NCB) southward and the Yangtze block (YZB) northward, the present Hinterland fault‐bounded fold zone (HLZ) and North Qinling thick‐skinned imbricated thrust zone (NQZ), owing to the lithosphere of the South Qinling zone (SQZ) wedging into that of the NQZ, has a superimposed and thickened lithosphere and is simultaneously in initial delamination period. In contrast, the SQZ is undergoing delamination and underplating to cause mass‐energy recycling between crust and mantle, and around the Foping region probably developing a new plume. In addition, between southern and northern as well as internal lithospheric boundaries of the Qinling orogen also accompany intensive lithospheric strike‐slip faulting with different properties to lead to lateral mass transfer. Finally, we probe and discuss geodynamic implication of the coexistence of the thickened lithosphere and a large‐scale tectonic delamination as well as strike‐slip faulting.

Screening model for volatile pollutants in dual porosity soils

This paper develops mass fraction models for transport and fate of agricultural pollutants in structured two-region soils. Mass fraction index models, based on a semi-infinite domain solution, are derived that describe leaching at depth, vapor losses through soil surface, absorption, and degradation in the dynamic- and stagnant-water soil regions. The models predict that leaching is the result of the combined effect of the upward vapor-phase transport relative to downward advection, residence time relative to half-life, dispersion, and lateral diffusive mass transfer. Simulations show that leached fraction of volatile compounds does not always decrease monotonically with increased residence time relative to the pollutant half-life, as a result of complex interactions among the different physical and biochemical processes. The results show that leaching, volatilization, and degradation losses can be affected significantly by lateral diffusive mass transfer into immobile-water regions and advection relative to dispersion (i.e. Peclet number) in the mobile-water regions. It is shown that solute diffusion into the immobile phase and subsequent biochemical decay reduces leaching and vapor losses through soil surface. Potential use of the modified leaching index for the screening of selected pesticides is illustrated for different soil textures and infiltration rates. The analysis may be useful to the management of pesticides and the design of landfills.