Wall Effects Research Articles

Isolated cassava cells: Comparison of structure and physicochemical properties with starch and whole flour

Individual cells are the smallest units of the plant tissue structure, and their structure and physicochemical properties are essential for whole food processing. In this study, cassava cells were isolated using acid-alkali, hydrothermal, and pectinase methods, and the differences in microstructure and physicochemical properties among the cells, starch, and whole flour were investigated. Cassava cells isolated using pectinase showed intact individual cells with a higher isolation rate and less damage to the cell wall structure and intracellular composition. The presence of cell walls in intact individual cells inhibited the swelling and leaching of starch, resulting in a lower peak viscosity and higher gelatinization temperature than those of starch. The intact cell structure and non-starch composition enhanced the shear resistance of the gels in the sample. Heat treatment led to the gelatinization of intracellular starch and increased the permeability of the cell wall, destroying the physical barrier function of the cell wall; however, the compact cell matrix and non-starch components can inhibit starch hydrolysis. This study suggests that cells isolated using pectinase can be used to investigate the effect of cell walls on the functional properties of intracellular starch in cassava. The isolated cells provide new insights into the cassava industry.

The mechanism of internal energy losses in double- suction centrifugal pumps under direct and reverse conditions

The double-suction centrifugal pump has gained extensive application in various hydraulic projects and industrial processes under direct and reverse operating conditions. However, the occurrence of unstable flow phenomena, such as flow separation, vortex and reflux, poses a significant challenge to its hydraulic performance. Therefore, this paper aims to analyze the energy loss and energy dissipation mechanisms in double-suction centrifugal pumps operating in both direct and reverse conditions. By utilizing the entropy production theory, a combination of numerical simulations and experimental methods are employed to investigate the energy loss of double-suction centrifugal pump compared to double-suction centrifugal pumps as turbines. The findings indicate that the turbulent entropy production loss and wall entropy production loss are the principal contributors, accounting for over 57 % and 33 % of the total entropy production loss, respectively, under different flow conditions of the pump and turbine. Conversely, the direct entropy production loss is not more than 1 %. This suggests that the main causes of energy losses are associated with wall effects in the near-wall region and unstable flow in the main flow region. Within the pump conditions, the main components responsible for energy loss are the volute and impeller. Conversely, under turbine conditions, the impeller and draft chamber are the main contributors to energy loss. The presence of a suction chamber rib proves beneficial under pump conditions as it diverts and optimizes internal flow. However, the draft chamber flow divider exacerbates energy losses under turbine conditions. This study not only provides insights into the energy loss characteristics of a double-suction pump operating under direct and reverse conditions but also offers a fresh perspective on the structural optimization of both the double-suction pump and double-suction pump as turbine.

Effect of partition walls on the vibration serviceability of cross-laminated timber floors

The current standards need more specific serviceability criteria for Cross-Laminated Timber (CLT) floors. This paper presents a comprehensive analysis of a relevant case study in Norway, which presented unexpectedly high accelerations in the CLT floors after construction. The lack of a sufficiently detailed design process resulted in the poor vibration performance of the floors, which partially compromised their functionality. The paper thoroughly investigates and discusses the experimental dynamic characterization of seven CLT floors within the considered building. The authors estimated the modal parameters and serviceability metrics based on both Eurocode 5 (EC5) and the new draft version of it. Specifically, the authors compared the analytical predictions of the fundamental frequency and the root mean square acceleration against the corresponding experimental estimations. Using a sensor-roving approach, a dense sensor configuration was adopted to describe seven floors’ mode shapes and serviceability metrics. These metrics include mean square acceleration and Vibration Dose Value. The scenarios examined in this study shed light on the significance of partition walls, a factor not considered in the practical design for serviceability verifications. The presence of partition walls can enhance the vibration comfort of timber floors by providing a stiffening effect, leading to a significant increase in the first fundamental frequency. A parametric finite element model was developed using OpenSeesPy to investigate this phenomenon further. The model, firstly validated against selected experimental results, is employed to assess the influence of partition walls on floor dynamics. The model predicts the increase in the first frequency caused by randomly generated partition walls. The paper proposes an empirical expression calibrated on the simulated data to estimate the relative increment of the floor’s fundamental frequency based on the partition walls’ layout. This formulation can be included in the analytical expression enclosed in the EC5 draft to predict the fundamental frequency of timber floors.

Numerical study on the size effect on the mixing in 2×1, 3×3 and 5×5 rod bundle subchannels

Mixing Vane Grid (MVG) is considered as one of the most important components in the fuel assembly which not only plays the role of supporting the rod bundles but also improves the Critical Heat Flux (CHF) in the reactor core. Modeling and measuring the flow behavior accurately in the rod bundle is the key to understanding and learning complex grid performance in the fuel assembly and will develop high performance MVG. Usually, the fuel assembly in the reactor core consists of 17 × 17 or 16 × 16 rod bundles, it is hardly to use the original MVGs to perform study. The representative smaller prototypical grids are applied. Different bundle sizes are used including 1 × 1, 2 × 1, 3 × 3 and 5 × 5 et al. It is an absolute question of how the smaller size rod bundles are prototypical that could fully reflect the true flow and heat transfer behavior in a reactor core. In this paper, the effect of bundle size on flow and heat transfer is investigated under sizes of 2 × 1, 3 × 3 and 5 × 5. Firstly, the boundary settings in 2 × 1 are studied and the surface averaged secondary flow and local flow at the gap with 5 × 5 results are compared. Then the 3 × 3 and 5 × 5 bundle sizes are compared under subcooled flow. The center subchannels temperature and the void fraction distributions are analyzed. The effect of non-prototypical cold walls on heat transfer is discussed. The study shows that, different bundle sizes will produce different flow phenomena in the rod bundle, the flow pattern may not be the same with the reactor core fuel assembly, the typical bundle size selection should be based on the research purpose.

Restraint effect of partition wall on the tunnel floor heave in layered rock mass

Restraint effect of partition wall on the tunnel floor heave in layered rock mass

Wake transitions of flow past two tandem semi-circular cylinders near a moving wall

Wake transitions of flow past two tandem semi-circular cylinders near a moving wall were numerically investigated using the lattice Boltzmann method at the Reynolds number of 150 with various gap ratios (G/D, where G and D are the spacing between the cylinder and wall and the cylinder diameter, respectively) and spacing ratios (L/D, where L is the distance between the cylinder centers). The analysis aims to clarify the effects of L/D and G/D on wake structures, hydrodynamic forces, Strouhal number, and spectral energy of the flow exerted on both cylinders. This study reveals five distinct flow regimes in the L/D-G/D space, such as overshoot, continuous reattachment, pair-wise, quasi-coshedding, and coshedding. These regimes are identified using plots of vorticity contour, time history of drag and lift coefficients (CD and CL), power spectral density, and proper orthogonal decomposition of the vorticity fluctuation into deterministic spatial structures. Furthermore, the flow regime maps and diagrams of time-averaged pressure coefficients on the surface of the cylinders are given to analyze the influence of the moving wall. A significant change in CD and CL is observed for both cylinders, depending on the L/D and G/D ratios. The time-averaged drag coefficient of the downstream cylinder is remarkably lower than that of the upstream cylinder. A significant increase in the time-averaged lift coefficient of the upstream cylinder is observed when the G/D is small due to near-moving wall effects. The root-mean-squared value of the lift and drag coefficients of the downstream cylinder is lower than that of the upstream cylinder as a result of the proximity effect. Meanwhile, the Strouhal number for both cylinders remains mostly the same.

Seismic performance of underground subway station structure near the strike-slip fault by the developed hybrid IBE-FEM method

To investigate the influence of strike-slip faults on the seismic responses of underground structures, based on the single-layer potential theory of the boundary element concept and the fault-site-underground structure coupling mechanisms, we proposed a hybrid indirect boundary element-finite element numerical method (IBE-FEM) to simulate efficiently the seismic response of the entire process from the near seismogenic-fault to the underground structure. Initially, based on the kinematic finite-fault model, the seismic wavefield of an overlying soft-soil sedimentary-layer site subjected to strike-slip faults with source parameters, such as rupture velocity, dip-angle, and upper-boundary burial depth, was solved using the indirect boundary element method (IBE). Subsequently, the accuracy of the IBE-FEM in predicting the site seismic wavefield was verified. On this basis, the influence laws of the source parameters and the fault-site coupling effects on the seismic performance of the structure were preliminarily investigated by establishing a numerical model of the nonlinear dynamic interaction system of a soil-underground structure. The results showed that the seismic responses of the underground structure located in the footwall far-fault region were more strongly affected by variations in the rupture velocity. The lateral deformation of the structure under the rupture velocity condition of bedrock shear-wave velocity (vs) was dramatically increased compared to sub-vs, and the lowest amplification is 59 %. Furthermore, the hanging wall and seismic damage concentration effects significantly impacted the structure located in a strike-slip fault site with a shallow-burial. This study provides a reliable and efficient analytical method for the seismic design of underground structures in complex near-fault regions.

Drag, lift, and torque correlations for axi-symmetric rod-like non-spherical particles in linear wall-bounded shear flow

This paper presents novel correlations to predict the drag, lift, and torque coefficients of axi-symmetric non-spherical rod-like particles in a wall-bounded linear shear flow. The particle position and orientation relative to the wall are varied to systematically investigate the influence of the wall on the hydrodynamic forces. The newly derived correlations for drag, lift, and torque on the particle depend on various parameters, including the particle Reynolds number, the orientation angle between the major axis of the particle and the main local flow direction, the aspect ratio of the particle, and the dimensionless distance from the particle centre to the wall. The impact of the wall on the hydrodynamic forces is accounted for as a function of a multiplication factor on the drag force in case of locally uniform flow, and an additional force contribution for the lift and the torque, modifying the resultant forces experienced by a particle in a locally uniform flow. The changes in the hydrodynamic forces prove to be substantial, emphasizing the necessity of accounting for wall effects across all particle types and flow conditions investigated in this study. The coefficients of the correlations are determined through a fitting process utilizing the data generated from our previous study on the interaction forces between a locally uniform flow and an axi-symmetric non-spherical rod-like particles, as well as from data of novel direct numerical simulations (DNS) performed in this work of flow past axi-symmetric rod-like particles near a wall. The proposed correlations exhibit a good agreement compared to the DNS results, with median errors of 2.89%, 5.37%, and 11.00%, and correlation coefficients of 0.99, 0.99, and 0.96 for the correlations accounting for the drag, lift, and torque coefficients of a non-spherical particle in wall-bounded linear shear flow profile, respectively. These correlations can be used in large-scale simulations using an Eulerian–Lagrangian or a CFD/DEM framework to predict the behaviour of axi-symmetric rod-like non-spherical particles in wall-bounded shear flow to locally uniform flow conditions.

Temporal Characteristics Based Outlier Detection and Prediction Methods for PPP-B2b Orbit and Clock Corrections

The BeiDou Global Navigation Satellite System (BDS-3) provides real-time precise point positioning (PPP) service via B2b signals, offering real-time decimeter-level positioning for users in China and surrounding areas. However, common interruptions and outliers in PPP-B2b services arise due to factors such as the Geostationary Orbit (GEO) satellite “south wall effect”, Issue of Data (IOD) matching errors, and PPP-B2b signal broadcast priorities, posing challenges to continuous high-precision positioning. This study meticulously examines the completeness, continuity, and jumps in PPP-B2b orbit and clock correction using extensive observational data. Based on this analysis, a two-step method for detecting outliers in PPP-B2b orbit and clock corrections is devised, leveraging epoch differences and median absolute deviation. Subsequently, distinct prediction methods are developed for BDS-3 and GPS orbit and clock corrections. Results from simulated and real-time dynamic positioning experiments indicate that predicted corrections can maintain the same accuracy as normal correction values for up to 10 min and sustain decimeter-level positioning accuracy within 30 min. The adoption of predicted correction values significantly enhances the duration of sustaining real-time PPP during signal interruptions.

Reparative potentials of commensal-derived cellular components in juvenile Lateolabrax maculatus fed high soybean meal diet: Insight into growth performance, immunity, antioxidant capacity and liver health

An eight-week feeding trial was designed to estimate the effects of commensal Bacillus siamensis LF4-derived whole cell wall (CW), cell wall protein (CWP), lipoteichoic acid (LTA) and peptidoglycan (PGN) supplementation in a high soybean meal (SM) diet on the growth, immunity and liver health of spotted seabass (Lateolabrax maculatus). Fish continuously fed low SM (containing 16 % SM) and high SM (containing 40 % SM) diets were served as positive (LSM) and negative (HSM) control, respectively. After feeding high SM diet for 28 days, fish were fortified with B. siamensis LF4-derived CW, CWP, LTA or PGN until 56 days. The results showed that CW, LTA, and PGN application significantly increased FBW, WGR, and SGR (P<0.05), but not affect CF, VSI, HSI, IFR, ILI, and ISI (P＞0.05) in spotted seabass (L. maculatus) fed with high SM diet. Distal intestinal protease activity reduction caused by dietary high SM inclusion was significantly repaired when spotted seabass (L. maculatus) fortified with LTA and PGN (P<0.05). CW, LTA and PGN administration effectively increased serum immunity by enhancing ACP activity and C3, C4, IgM contents and reduced IL-1β content in serum of spotted seabass (L. maculatus) fed high SM diet (P<0.05). Significantly decreased serum MDA content in groups CW, LTA and PGN and significantly increased liver GSH content in group CWP were observed as compared to those in group HSM (P<0.05). Dietary CW, LTA and PGN supplementation, rather than CWP, repaired SM-induced liver injury by improving liver morphology and significantly reducing GOT and GPT activities (P<0.05). In summary, CW, LTA and PGN derived from B. siamensis LF4 effectively repaired SM-induced growth, feed utilization, immunity suppression and liver injury in spotted seabass (L. maculatus).

Magnetic resonance imaging of a stream of bubbles injected into liquid suspensions

Magnetic resonance imaging (MRI) is a powerful tool for characterizing opaque multiphase flows non-invasively. However, MRI has often (i) had low temporal resolution and thus not captured transient dynamics, (ii) only provided 2D slice images of 3D flows and (iii) been limited to flows in narrow (∼30 mm) tubes with significant wall effects. Here, we apply multi-band echo planar imaging (MB-EPI) with a custom-built radiofrequency coil in a full-body MRI scanner to provide fully 3D images of the dynamics of a stream of bubbles rising through a dense suspension with 151 ms resolution in a 178 mm diameter system. Image processing demonstrates that bubble rise and coalescence dynamics vary significantly with (a) initial spacing between bubbles and (b) particle volume fraction. The ability to image bubble dynamics in dense suspensions as well as in full 3D provides future opportunities to characterize complex, non-axisymmetric, multiphase flows.

Experimental and numerical investigation of iron ore pellet firing using coupled CFD-DEM method

Iron ore pellets are the main feedstock in ironmaking processes. While extensive research has addressed numerical modeling of the iron ore pellet induration process, little effort has been made to describe the intricate thermochemical processes occurring within the reactor starting from the pellet and particularly at the intra-particle scale. In this regard, discrete-continuous methods like CFD-DEM can generate more realistic, irregular particle assemblies, which leads to significantly more accurate predictions of voidage variation, wall effects, temperature distribution, and associated mass transfer phenomena. This study presents a numerical model based on computational fluid dynamics (CFD) coupled with the discrete element method (DEM) to simulate the thermal induration process of iron ore pellets. The presented model solving heat, mass, and momentum conservation equations for both continuous and discrete phases, provides detailed information on the thermochemical aspects of the process. Pilot-scale induration experiment was conducted to validate model predictions in terms of thermal history and final conversion fraction. It was found that inlet charge specifications, such as particle and pellet size, significantly impact the productivity of pelletizing plants, highlighting the potential of the presented model to optimize the process and improve plant productivity.

Virtual wall: Numerical model on interaction between trees and building façade to quantify heat exchange and microclimate in urban context

When simulating a building's energy demand, the tree surroundings should be accounted in their shade and reshaping microclimate, just representing an envelope layer as a virtual wall. This study delves into the effects of such tree-induced virtual walls on building energy dynamics, with a dataset derived from 24 distinct samples of building façades and adjacent trees within a campus environment. An experiment was designed to validate microclimate simulation that captures variations in sheltered radiation and temperature reductions. The study introduces and calculates the dynamic and static equivalent heat transfer coefficients and thermal resistances for the virtual wall. The findings reveal significant correlations between the calculated coefficients and resistances, and various factors such as seasonality, weather conditions, and façade orientation. The equivalent thermal resistance value for south façade is highest on sunny days, reaching up to 3.7 m2·K/W, and on cloudy days, east façade has the highest equivalent heat transfer coefficient and thermal resistance values, at around 8.5 W/m2·K and 10.3 m2·K/W, respectively. Moreover, the study reveals that the tree's impact is primarily determined by its height and canopy area, with the equivalent heat transfer coefficient negatively correlated with tree height and canopy area, and positively correlated with building height.

Visualization study on the ignition and combustion characteristics of methane/hydrogen ignited by diesel

Nowadays, internal combustion engine fuels need to shift from diesel and gasoline to clean fuels. As a low-carbon fuel, methane has attracted widespread attention. Diesel ignition of premixed methane is one of the measures to achieve effective application. However, limited by the equipment and the active reactivity of methane, there are few basic visualization studies on that, resulting in a lack of deep understanding of ignition and flame propagation processes. Therefore, this paper studies the diesel ignition and combustion characteristics of diesel-ignited methane and the promotion of 10 and 20% (volume fraction) hydrogen on combustion performance based on the rapid compression and expansion machine. The experimental results indicate that methane has a suppressive effect on the ignition of diesel. The combustion process can be mainly divided into the diesel ignition stage, the premixed combustion stage, and the fuel burnout stage. Blending 10% and 20% hydrogen has little effect on the diesel ignition stage, but has a relatively great impact on the premixed combustion stage. The flame propagation can be improved with hydrogen blending, but that is limited due to the effects of ignition and wall. The combustion duration can be shortened with hydrogen blending, mainly for the CA50-90, especially at a lower equivalence ratio. The combustion efficiency can be improved with hydrogen blending. Overall, the strategy of blending hydrogen is considered more suitable for large bore engines and the results can deepen the understanding of the combustion process of diesel-ignited methane/hydrogen/air mixtures and have value for the relevant engine development so that the energy shortage and environment pollution issues can be alleviated.

A logarithmic law for the velocity- and retention-dependency of the eddy dispersion in chromatographic columns

Applying the recently introduced patchwork model for porous media, we present a new step forward in the modelling of eddy dispersion in chromatographic columns. The logarithmic law describing the velocity dependency emerging from this patchwork model is supplemented with a retention factor dependency via first principles modelling of the variations in flow resistance and retention capacity caused by the packing disorder. Furthermore, it is shown the derived expression is also able to fit the eddy dispersion originating from the wall effect on the packing. When applied to literature data of eddy dispersion, the newly introduced logarithmic law has a goodness of fit that is at least equal to that of Knox’ empirical power law (R2>0.98). The main difference is that, whereas Knox’ power law requires a separate fit for each component due to the retention factor dependency, the present model simultaneously fits all plate height curves measured on one chromatographic column, using only two parameters with a clear physical meaning.

Advancing Methodologies for Investigating PM2.5 Removal Using Green Wall System.

Combustion processes are the primary source of fine particulate matter in indoor air. Since the 1970s, plants have been extensively studied for their potential to reduce indoor air pollution. Leaves can retain particles on their surfaces, influenced by factors such as wax content and the presence of hairs. This study introduces an innovative experimental approach using metal oxide particles in an office-like environment to evaluate the depolluting effect of plant walls. Two plant walls were installed in a controlled room, housing three plant species: Aglaonema commutatum 'Silver Bay', Dracaena fragrans, and Epipremnum aureum. Metal oxide particles were introduced via a compressed air blower positioned between the two walls. The concentration of these particles was monitored using PM2.5 sensors, and the deposition of iron (Fe) on the leaves was quantified through Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This novel methodology effectively demonstrated the utility of both real-time sensors and ICP-MS in quantifying airborne particle concentrations and leaf deposition, respectively. The results revealed that Dracaena fragrans had a 44% higher Fe particle retention rate compared to the control (wallpaper). However, further validation through methodological replication is necessary to confirm the reproducibility of these findings.

Effect of perforated wall in controlling the separation due to SWBLI at Mach no. 5 to 9

Abstract The mixed compression scramjet engine intake was numerically simulated to study the characteristic of shock wave induced boundary layer separation leading to the formation of the separation bubble (SB). The analysis employed a 2D-RANS method with SST k-ω turbulence model at different Mach numbers. The intake is designed as a three-ramp intake for improved performance. As the Mach number varies, the size of the separation bubble formed due to the interaction of oblique shock waves with the boundary layer also varies, affecting both intake the efficiency and overall efficiency of the engine. Apart from traditional control techniques, the most preferred bleed technique is incorporated. Localised &amp; distributed bleed techniques are designed and analysed within the intake at different locations. These techniques result in a reduction in the size of the separation bubble within the intake. Establishing perforation in the engine intake also increases the intake efficiency and overall engine performance.

Comparison of the induced flow obtained with 2D and 3D CFD simulations of a solar chimney at different width-to-gap ratios

Solar chimneys are among the most common methods for natural ventilation of buildings. Computational Fluid Dynamics (CFD) has been widely applied in research and design of solar chimneys. Most of the previous studies are based on 2D CFD models which ignore the effects of the width (the third dimension) of the air channel. In addition, the applicability of 2D models for the solar chimneys with a low width-to-gap ratio is still questionable. This study investigates both 2D and 3D CFD models for window-sized vertical solar chimneys. The 2D model is applied to the domain comprising the central plane of the channel gap ( G) and height ( H) while the 3D model is applied to the domain consisting of the channel gap, height, and width ( W). The flow fields, flow rates and thermal efficiencies computed with the 2D and 3D models at different heights, gaps, and widths are compared. The results show that W/ G is the most crucial factor. The effects of the side walls are significant at a low W/ G but gradually diminishes as W/ G increases. At W/ G = 15, the side wall effects are confined to a region of about 2.6% W. Particularly, for W/ G&gt;8, the differences between the 2D and 3D flow rates and thermal efficiencies are within ±5%. These findings offer a reference for researchers and engineers to select between 2D and 3D CFD models for a specific solar chimney.

Light‐Induced Ferroelectric Modulation of p‐n Homojunctions in Monolayer MoS2

AbstractThe association of 2D materials and ferroelectrics offers a promising approach to tune the optoelectronic properties of atomically thin Transition Metal Dichalcogenides (TMDs). In this work, the combined effect of ferroelectricity and light on the optoelectronic properties of monolayer (1L)‐MoS2 deposited on periodically poled lithium niobate crystals is explored. Using scanning micro‐photoluminescence, the effect of excitation intensity, scanning direction, and domain walls on the 1L‐MoS2 photoluminescence properties is analyzed, offering insights into charge modulation of MoS2. The findings unveil a photoinduced charging process dependent on the ferroelectric domain orientation, in which light induces charge generation and transfer at the monolayer‐substrate interface. This highlights the substantial role of light excitation in ferroelectrically‐driven electrostatic doping in MoS2. Additionally, the work provides insights into the effect of the strong, nanometrically confined electric fields on LiNbO3 domain wall surfaces, demonstrating precise control over charge carriers in MoS2, and enabling the creation of deterministic p‐n homojunctions with exceptional precision. The results suggest prospects for novel optoelectronic and photonic application involving monolayer TMDs by combining light‐matter interaction processes and the surface selectivity provided by ferroelectric domain structures.

Numerical study on the smoke temperature distribution beneath the ceiling of a single-ended sealing tunnel under the condition of double fire sources

As a special tunnel structure, the single-ended sealing tunnel has only one evacuation port, which increases greatly the risk of fire. Numerical modeling of a double source fire in a single-ended sealed tunnel was developed based on FDS 6.7. The effects of double-source spacing and end walls on ceiling smoke temperature were analyzed and discussed. The results show that when the double fire sources are considered as a whole, there are varying degrees of smoke backflow throughout the tunnel, with the upstream smoke backflow phenomenon being more pronounced under the influence of the end wall. In this study, the dimensionless separation distance φ is introduced and divided into two regions to quantify the effect of the spacing of the double fires. When 0 ≤ φ < 0.625, the maximum smoke temperature beneath the ceiling falls exponentially with increasing separation distance. On the other hand, when 0.625 < φ ≤ 1, the maximum smoke temperature under the ceiling rises exponentially. Furthermore, we suggest empirical formulas for forecasting the longitudinal distribution of downstream temperatures as well as the maximum smoke temperature of the ceiling. The predictive equations’ dependability was further confirmed by contrasting the predicted equations with simulated and historical experimental data. The study results serve as a reference for fire prevention and rescue in similar special tunnel structures, such as single-end sealing.