Wall Effects Research Articles

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 & 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>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.

Contrastive Investigation of High rise building with distinctive infill wall by Pushover analysis

Pushover analysis is a method that uses simple nonlinear techniques to predict seismic structural deformations. Today, we use masonry infill in reinforced concrete (R/C) frames for architectural, aesthetic or economic reasons. In this project, we need to study the effect of backfill on the damage structure of the reinforced concrete frame. The main purpose of this study is to show that adding walls to the reinforced concrete frame can increase the strength and stiffness of seismic resistant structure loads and increase the feedback for strength and stiffness analysis.These instructions strictly comply with FEMA-356. In this project, we use three types of bricks: red brick, fly ash brick, deep brick and siporex brick. Taking the output of non-linear analysis, we compare layer V/S i) Base Shear, ii) Storey Displacement, iii) Floor Shift Base Shear V/S Attack and Observe Spectrum Acceleration V/S spectral function . We also use ETABS 2017 software to study the effects of bare shear walls.. Key Words: Pushover Examination, Brick infill, FEMA-356, Displacement, Float, Shear Divider, ETAB-2017

Experimental Study on the Horizontal Bearing Characteristic of a Strip-Walled Underground Diaphragm Wall

Researching and developing a new type of diaphragm wall foundation can solve the probl em that the traditional diaphragm wall structure may not meet the high standards of safety and stability of underground structures in some specific engineering environments. This paper focuses on the horizontal bearing characteristic of a new form of foundation, a strip-walled underground diaphragm wall, through a series of model tests. In the tests, nine plexiglass models with different section sizes, wall spacings and wall heights, as well as loading strategies (horizontal loads along and against the wall in the model), were conducted. The influence of the above factors on the horizontal bearing performance of the foundation and the soil resistance distribution around the wall was studied. The results show that when the horizontal load applied along the wall is greater than 50 N, the growth rate of total displacement at the top of the wall gradually decreases; when a horizontal load is applied against the wall, with a uniform change in wall height, the optimal wall spacing is 11 cm. When the same displacement occurs, the bearing performance of the model under the former loading strategy is generally 10% higher than that under the later loading strategy. In addition, the depth where the maximum bending moment along the wall occurred gradually moves downward with the increase in horizontal load, and the increase in wall spacing and wall height has a positive effect on the horizontal bearing characteristic. With the application of load, the maximum bending moment of the wall will gradually decrease along the depth. The increase in wall spacing and wall height can improve the overall flexural stiffness and horizontal bearing performance of the foundation. Lastly, the group wall effect coefficient, β, is put forward, and a simplified formula for calculating the horizontal bearing capacity of a strip wall foundation is proposed. In the formula, β is negatively correlated with the buried depth of the wall and positively correlated with the distance between the walls, and its coefficient is greater than 1.

Influence of particle stacking modes on the fluidization characteristics of biomass particles in binary particle systems

Spouted bed is widely used in biomass combustion and other industrial production due to the advantages of good heat transfer performance and sufficient gas–solid mixing. In order to achieve higher heat and mass transfer performance and conversion efficiency, inert particles are often added to assist in the fluidization of biomass particles. However, the stacking patterns of different particles in a binary particle system can have some effects on particle flow, distribution, and bed stability. Therefore, in this study, the computational fluid dynamics–discrete element method was used to analyze the particle fluidization characteristics under four different particle stacking modes in a spouted bed. The results show that the average bed height of larger spherocylindrical particles is prioritized in binary particle systems. The void fraction of spherocylindrical particles tends to increase in the near-wall region, whereas spherical particles tend to decrease. When the binary particles are mixed at the initial moment, the change rule of vertical velocity of the two particles remains consistent. In addition, the vertical velocities of two kinds of particles when layered stacking is used are gradually close to each other only after a period of time. In addition, the orientation angle of the spherocylindrical particles in the spouted bed tends to be horizontal for both the single-component spherocylindrical particle system and the wall effect attenuates this phenomenon.

Flow control in a confined supersonic cavity flow using subcavity

The effects of the front wall and aft wall sub-cavities in the flow field of a confined supersonic deep cavity are numerically investigated. The turbulent simulations are carried out by deploying a finite volume-based explicit density-based solver in the OpenFOAM framework in conjunction with the k − ω SST (Shear Stress Transport) turbulence model. A cavity with a length-to-depth ratio of three placed in a confined passage is considered in the study. The freestream Mach number at the entrance of the passage is approximately 1.71. The addition of the sub-cavity of lengths ranging between 0.2 and 0.3 times the length of the main cavity in the front wall and the aft wall, significantly affects the frequencies of cavity oscillations as obtained from the spectral signature. The front wall sub-cavity of length ratio 0.2 reduces the dominant frequency by almost 60 percent as compared to the baseline cavity. The analysis and comparison of the flow field using the numerical schlieren in both configurations reveal a significant alteration in the flow field. The flow visualization provides a distinct understanding of the attenuation and enhancement of pressure oscillations obtained through spectral analysis in the presence of sub-cavities.

Structure effect of wall cooling channel on liquid metal heat transfer in aero-engines

In this study, a model of the cooling channel and an experimental system for heat transfer involving liquid metal are studied, to investigate the influence of the wall cooling channel structure of combustor on the heat transfer process. The error between the experimental and simulated outcomes fall is within 3 %, suggesting that the accuracy of the simulation is satisfactory. The simulation results found that the temperature non-uniformity coefficient can be reduced by 13 % and 7 % through adjusting the aspect ratio under the heat flux of 3 MW/m2 and 1.5 MW/m2 respectively, and the wall temperature of gas side can be reduced by 89 K and 47 K respectively. A smaller aspect ratio is favorable for homogenizing the liquid metal temperature distribution. Longer widths, however, can lead to horizontal thermal stratification, which can be unfavorable for heat transfer. With an aspect ratio and rib thickness of about 0.5 and 0.4 mm, respectively, the cooling channel outlet has the lowest non-uniformity coefficient of temperature and enthalpy, which is conducive to the improvement of the wall energy recovery rate. The optimal cooling channel effectively improves the thermal stratification in channel, and provides theoretical guidance for the suitable application of liquid metal to the combustor wall cooling channel.

Analysis of the influence of uneveneity of the sintering process of the barch on the operation of the sintering machine

Literature data on the unevenness of temperature and composition of the gas leaving the sintering bed across the width and length of it and their influence on the productivity of sinter machines are considered. An analysis of the technologies reasons for the unevenness of the sintering process was carried out. It is shown that the reasons for the width of the pallets include the distribution of the mix bed in the loading bin, air leaks into the ignition hearth, the wall effect at the side plates of the pallets, the shape and angle of inclination of the sides relative to the grates. Along the length of the sinter machine, the unevenness of gas flow and composition is due to a decrease in the gas-dynamic re-sistance of the bed during the sintering process, segregation of the mix and fuel along the height of the bed, completion of bed drying and gaps between pallets. Using an adapted mathematical model of the sintering process, a comparison was made of the parameters of the basic (non-uniform) and calculated uniform operating modes of the AKM-312 sinter machine of the Steel Plant NLMK. I It has been established that with the vertical installation of the pallet sides accepted in the calculations that an increased gas flow rate at the periphery of the bed is accompanied by an increase in gas temperature with a corresponding decrease in the suction before exhausters. It was found that during the transition from the base to the uniform mode of operation of the sinter machine, the gas temperature in front of the exhausters decreased from 99.6 to 85.1 °C, the suction increased from 13.54 to 14.26 kPa, and in the collecting collector – by 1.15 kPa. The productivity of the sinter machine increased by 4.1%. When installing pallet sides vertically, the effectiveness of increasing the height of the layer on its periphery instead of compacting it and constructive solutions has been justified. Its increase provided an additional productivity of the sinter machine by 1.8%, a total of 5.9%. It has been shown that due to the simultaneous increase in gas temperature over the entire width of the bed in the final period of the sintering process, with a uniform operating mode of the sinter machine, the maximum gas temperature at the end of the process increases with a lower one – in front of the exhausters. From the point of view of the capabilities of exhausters in terms of the created suction, the accepted representation of their gas-dynamic characteristics at a temperature of 150 °C, which is possible only with a high level of unevenness of the sintering process, is not reasoned

Development of Curved Shape Diffuser Duct for Aero Engines With a Backend Centrifugal Compressor

In the present study, a design of the curved shape diffuser-duct is proposed to apply to the compressor stage for aero-engines with a backend centrifugal compressor. For these configurations, the flow exiting radially from the centrifugal impeller needs to be changed from radial-to-axial direction to meet downstream combustion chamber requirements. Hence, the specially designed exit duct with a curved shape to manage the flow from the radial-to-axial direction was later diffused using the diffuser-shaped exit duct. This study aims to design and develop an efficient diffuser-duct for the adequate deceleration of flow in the exhaust diffuser and, as a result, a uniform and low-velocity flow at the exit. This configuration comprises a radial-to-axial turning annular passage at the centrifugal impeller exit. Then, the passage is directed to either a purely axial direction or is inclined to the axial direction by a slight angle. The results indicate a uniform total pressure at the stage exit with marginal variation along the span. It shows equivalent end wall effects near both the shroud and hub surfaces. This endwall effect may be occurring mainly due to the growth of the boundary layer across the diffuser passage.

Molecular Orientation Behavior of Lyotropic Liquid Crystal-Carbon Dot Hybrids in Microfluidic Confinement.

Lyotropic liquid crystals represent an important class of anisotropic colloid systems. Their integration with optically active nanoparticles can provide us with responsive luminescent media that offer new fundamental and applied solutions for biomedicine. This paper analyzes the molecular-level behavior of such composites represented by tetraethylene glycol monododecyl ether and nanoscale carbon dots in microfluidic channels. Microfluidic confinement allows for simultaneously applying multiple factors, such as flow dynamics, wall effects, and temperature, for the precise control of the molecular arrangement in such composites and their resulting optical properties. The microfluidic behavior of composites was characterized by a set of analytical and modeling tools such as polarized and fluorescent microscopy, dynamic light scattering, and fluorescent spectroscopy, as well as image processing in Matlab. The composites were shown to form tunable anisotropic intermolecular structures in microchannels with several levels of molecular ordering. A predominant lamellar structure of the composites was found to undergo additional ordering with respect to the microchannel axis and walls. Such an alignment was controlled by applying shear and temperature factors to the microfluidic environment. The revealed molecular behavior of the composite may contribute to the synthesis of hybrid organized media capable of polarized luminescence for on-chip diagnostics and biomimetics.

Study on flame quenching characteristics inside the Tesla valve structure flame arrester unit

Flame arrester is a kind of safety device designed to prevent the spread of flames. In order to achieve a more efficient flame arrester unit structure, this paper proposes a flame arrester unit based on the Tesla valve structure. A comparative study of the quenching characteristics of deflagration flames of propane-air premixtures in traditional crimped ribbon and Tesla valve structure flame arrester units is conducted through numerical simulations and experiments. The results indicate that the flame arrester unit based on the Tesla valve structure exhibits more efficient flame quenching performance compared to the crimped ribbon flame arrester unit. The flame quenching process fusion image shows that the flame quenching length of Tesla valve flame arrester unit with the same cross-sectional area is only 61% of the crimped ribbon flame arrester unit. In addition to heat transfer and wall effect, the collision of airflow in the branched pipe and main pipe within the Tesla valve structure flame arrester unit also plays a significant role in hindering the further advancement of flames. The quenching process of the Tesla valve structure flame arrester unit can be divided into four stages: expansion, diversion, convergence, and contraction stages. Among the five structural parameters that make up the Tesla valve structure flame arrester unit, the angle is the most critical factor affecting quenching performance, with the angle and entrance structure having a significant impact on flow performance. Furthermore, experimental evidence confirms the typical morphological changes the flame front structure undergoes during flame propagation: spherical (hemispherical),finger-shaped and tulip-shaped. However, tulip-shaped flames do not always propagate continuously to the end of the pipeline.

Investigation on the effects of an elliptical wall on the dynamic behaviors of a bubble restricted by two parallel plates

The present paper investigates the dynamic behaviors of a bubble restricted by two parallel plates near an elliptical wall. The typical experimental phenomena of the bubble are recorded employing the high-speed photography and a theoretical Kelvin impulse model is established. The impacts of the spatial position and the curvature of the wall on the bubble collapse behaviors are quantitatively investigated through the theoretical model and verified against the experimental results. The Kelvin impulse intensity and the direction during the bubble collapse process are compared and discussed for different elliptical-shaped walls. The main conclusions include: (1) During the bubble collapse process, the phenomenon of the bubble uneven splitting is discovered. (2) At different spatial positions and wall curvatures, the bubble collapse jet angle, movement distance, and velocity are in good agreement with the theoretical Kelvin impulse predictions. (3) As the short-to-long axis ratio increases, the differences in the distributions of the Kelvin impulse intensity and the direction near the elliptical wall gradually become larger, and the range of the influence of the impulse intensity expands.

Wake Structures and Hydrodynamic Characteristics of Flows around Two Near-Wall Cylinders in Tandem and Parallel Arrangements

To clarify the hydrodynamic interference characteristics of flows around multiple cylinders under the wall effect, the two-dimensional (2D) flows around the near-wall single, two tandem and parallel cylinders are simulated under different gap ratios (0.15 ≤ G/D ≤ 3.0) and spacing ratios (1.5 ≤ T/D ≤ 4.0) at a Reynolds number of Re = 6300. We also examine the wake patterns, the force coefficients, and the vortex-shedding frequency with emphases on the wall effect and effects of the two-cylinder interference. A critical wall gap of G/D = 0.6 is identified in the single-cylinder case where the wall can exert significant influences. The two near-wall tandem cylinders exhibit three wake states: stretching mode, attachment mode, and impinging mode. The force coefficients on the upstream cylinder are significantly affected by the wall for G/D ≤ 0.6. The downstream cylinder is mainly influenced by the upstream cylinder. For G/D &gt; 0.6, the force coefficients on the two cylinders exhibit a similar variation trend. In the parallel arrangement, the two cylinders exhibit four wake states in different G/D and T/D ranges: double stretching mode, hetero-vortex scale mode, unilateral vortex mode, and free vortex mode. Moreover, the two parallel cylinders in the hetero-vortex scale or free vortex mode have two states: synchronous in-phase state and synchronous out-of-phase state. The mean drag coefficients on the two cylinders decrease, while the mean lift coefficients exhibit opposite variation trends, as the T/D grows.

Half canal wall down tympanomastoidectomy.

The purpose of this study is to analyse the effect of half canal wall down tympanomastoidectomy in the treatment of chronic otitis media or cholesteatoma. In this retrospective study, the half canal wall down tympanomastoidectomy technique was used at our hospital for chronic otitis media or cholesteatoma removal in 265 adult patients, representing 271 operated ears, with an average follow-up time of 8.4 years. The post-operative cavities were slightly wider and straighter in 91.9 per cent of the ears. Fifteen per cent of the patients needed cavity cleaning every six months, 25 per cent of them needed cavity cleaning every year and 60 per cent of the patients had a self-cleaning cavity. Only one patient with a cleft palate experienced cholesteatoma recurrence in the mesotympanum. The half canal wall down tympanomastoidectomy technique showed a low-recurrence rate and satisfying operative cavities. The half canal wall down tympanomastoidectomy technique is a good choice for middle ear surgery.

Symbolic Regression for the Wall Effect on a Settling Sphere in a Circular Cylinder

Symbolic Regression for the Wall Effect on a Settling Sphere in a Circular Cylinder