Perforated Plate Research Articles

Design and Characterization of an Upscaled Dielectric Barrier Discharge-Based Ten-Layer Plasma Source for High-Flow-Rate Gas Treatment

Dielectric barrier discharge (DBD)-based technology is considered a promising alternative for controlling indoor air pollutants. However, its limited processing capacity and lack of design techniques have restricted its use in practical applications. This paper introduces a methodology for designing upscaled DBD reactors with a processing capacity of up to 1000 L/min for treating high-flow-rate gases to mitigate indoor air pollution. A ten-layer high-flow-rate DBD reactor was constructed, with fundamental characterizations, including electrical and spectroscopic measurements, conducted to verify the feasibility of the proposed methodology. In particular, the flow paths of the ten-layer DBD reactor were optimized by incorporating an air diffuser and perforated metal plates, all without significant modifications. Computational fluid dynamics simulations showed a remarkably improved velocity uniformity (0.35 m/s to 0.04 m/s, as evidenced by the velocity standard deviation) in the 10 flow channels. These simulation results were consistent with the experimental results, wherein the velocity standard deviation reduced from 1.38 m/s to 0.13 m/s. Moreover, multi-gas plasma ignition for up to six gas species and high-flow-rate plasma generation of up to 1000 L/min were achieved. These results provide the foundation for developing DBD technologies for practical applications in high-flow-rate gas treatment, particularly for controlling indoor air pollution.

Shear resistance of perforated QN1803 high-strength stainless steel plate girders through experimental testing and numerical analysis

QN1803, a high-strength stainless steel, has been developed by steel industry recently. Its tensile yield strength can be approximately 40 % (or more) higher than that of the commonly-used EN1.4301, while its cost is 20 % lower due to its reduced nickel content. One obvious application for QN1803 is in plate girders, where web perforations are often required to accommodate building services. However, no research work has been reported in the literature that investigates the reduced shear buckling capacity of QN1803 plate girders as a result of web perforations. This issue is addressed herein. An experimental program comprising six plate girder tests is conducted in this study. Three different hole ratios were considered: 0.2, 0.4 and 0.6. The depths of web were selected as 700 mm and 500 mm, while the thickness of web was fixed as 4.0 mm. The initial geometric imperfections were determined from three-dimensional (3D) scanning prior to the plate girder tests. Finite element (FE) models incorporating the material non-linearity and initial geometric imperfections were then developed and validated against the experimental results. A parametric analysis including 62 FE models was performed to examine the influences of the critical parameters on the shear buckling capacity of such perforated members. The results suggest that for those members with a hole diameter - web height ratio of 0.6, the shear buckling capacity was reduced by 56 % on average due to the web perforation. The design rules for determining the shear buckling capacity of stainless steel plate girders as specified in Eurocodes (EN 1993–1–4 + A1) (2015) and American Specification (ANSI/AISC 370–21) (2021) were evaluated. Upon comparison, it was demonstrated that both EN 1993–1–4 + A1 (2015) and ANSI/AISC 370–21 (2021) cannot provide accurate and safe predictions for determining the shear buckling capacity of such members.

Analyzing free vibration and buckling of heated laminated plate with cutouts: A Nitsche-based isogeometric approach

In this research, a comprehensive Nitsche-based isogeometric analysis framework is presented for studying the free vibration and buckling characteristics of laminated plates with cutouts under uniform and non-uniform thermal loads. The approach utilizes non-overlapping non-uniform rational B-Splines patches to discretize the perforated plate and seamlessly connects them using the Nitsche method. The technique is then applied to investigate the free vibration and buckling behaviors of laminated plates with cutouts under varying thermal conditions. Three tests with different element sizes are used to analyze composite plate under uniform thermal load, demonstrating good convergence and accuracy of the present method. Rectangular laminated plates without cutouts, considering various boundary conditions, fiber orientations, and temperature variations under uniform or non-uniform thermal loads are analyzed. The natural frequencies and critical buckling temperatures are found to be in excellent agreement with existing literature. Additionally, the analysis is expanded for laminated plates with cutouts under diverse boundary conditions, considering variations in fiber orientations, cutout shapes and numbers, and types of thermal loads. Thorough investigations are carried out to understand the influence of these factors on the vibrational and buckling behaviors of the plates. Moreover, numerical study with non-conforming mesh demonstrates strong capability of the proposed method.

Droplet generation by the oscillation of two spark-generated bubbles near a confined opening

Cavitation bubbles can be both beneficial and detrimental. One of their beneficial applications is to produce droplets as they oscillate near a confined free surface. In this paper, the oscillation of two spark-generated bubbles beneath a confined free surface and the resultant droplet generation are studied numerically using boundary element method. Three different configurations are considered: (i) a vertical cylinder (θ = 0°), (ii) a vertical nozzle (θ = 45°) and (iii) a perforated horizontal flat plate (θ = 90°). The influences of the effective parameters, including the initial pressure and locations of the bubbles, and the configuration geometry on the dynamics of the bubbles, the free surface and the resultant droplet are studied. It was found that by decreasing the inter-bubble distance, the droplet size increases and its pinch-off occurs earlier. In general, the effect of the distance of the upper bubble from the free surface on the droplet behavior is much more significant than that of the inter-bubble distance. Furthermore, through the augmentation of the upper bubble's strength parameter, the droplet size is reduced and the moment of droplet pinch-off is postponed. Finally, the droplet size and its pinch-off time increase from the vertical cylinder to the flat plate case.

Experimental study on large deflections of perforated composite plates

Experimental study on large deflections of perforated composite plates

The effect of triangular shutter type flow deflector perforated baffle plate on the thermofluid performance of a heat exchanger

AbstractThe study aimed to investigate the heat transfer (HT) properties of a tubular heat exchanger (HX) by using innovative baffle plate arrangements. The newly designed baffle plate was circular with triangular openings and adjustable triangular flow deflectors. These deflectors were strategically placed at the inlet of the HX to create a swirling flow downstream. Three baffle plates were installed along the flow direction with different length‐to‐diameter ratios (pitch ratios) to assess their impact on HT, pressure drop, and thermal enhancement factor. The study compared these results with a smooth channel under varying Reynolds numbers (16,500–29,500). The findings revealed that both the pitch ratio (0.6–1.2) and the inclination angle of the deflectors (30⁰–50⁰) significantly affected the HX's performance. Notably, the baffle plate with a deflector inclination angle of 30° and a pitch ratio of 1 showed a remarkable average improvement of 36.5% compared to other angles and ratios.

Experimental Investigations on Single-Phase Heat Transfer Enhancement in an Air-To-Water Heat Exchanger with Rectangular Perforated Flow Deflector Baffle Plate

Experimental analysis was conducted to investigate the turbulent heat transfer behaviors within a tubular heat exchanger, incorporating a novel baffle plate design. The new design includes a perforated circular baffle plate with a rectangular flow deflector that can be adjusted to different inclination angles. The baffle plate is strategically positioned at the entrance of the heat exchanger, resulting in a swirling flow downstream. To assess the impact of the baffle plate design, three baffle plates were placed longitudinally along the flow, with varying pitch ratios (l/D). The effects of pitch ratio (ranging from 0.6 to 1.2), deflector inclination angle (ranging between 30⁰ to 50⁰), and Reynolds numbers (ranging between 16000 to 29000) were examined. The outcomes highlighted the substantial impact of pitch ratio and inclination angle on the thermal enhancement factor. In particular, compared to single segmental baffle plates working under similar operating conditions. The result indicates that an inclination angle of 30° and a pitch ratio of 1 exhibited an average 41.49% augmentation in thermal-fluidic performance compared with an exchanger with a segmental baffle plate.

Visualization of a jet stream group influencing the noise increase phenomena in generated by airflow through a perforated metal plate

The perforated plate is made by a punching process. Because of this manufacturing process, the cross section of holes in a perforated plate varies in the direction of the thickness of the plate. When an airflow passes through a group of holes in a perforated plate, the noise characteristics change depending on the direction of passage. In the case where the cross-sectional area of holes increases in the downstream direction, the aerodynamic noise generated by airflow through holes in perforated plates increases. The cause of the noise increase is considered to be the lock-in phenomenon between the vibration of the plates and the outflow of the vortex. For this to occur, at least seven closely spaced groups of holes are required. In this study, flow visualization using the fog method was performed to clarify the behavior of the jet stream group during the noise increase. The results showed that the vortex outflows at each hole were in opposite phase when the lock-in phenomenon did not occur, but that the vortex outflows at adjacent holes were synchronized when the lock-in phenomenon occurred.

Experimental investigation of the effect of material on the non-linear properties of perforated plates

Perforated plates are one of the effective passive noise controllers in the aeroacoustics system and industry. Effective absorption, resistant in harsh environment and easy maintenance are main reasons for perforated plates having several applications. Literature shows that even though perforated plates are common sound absorbers, they can be relatively easy non-linear. There are many reasons for this, for instance, temperature, and high level sound pressure. High sound pressure level can have non-linear impact at fairly low levels. Therefore, identification and understanding of this phenomenon is important. This is an essential reason for this study to experimentally investigate perforated plates with different material and study the non-linear properties of them. Two perforated plates with different material, fiberglass and steel, have been studied. The results illustrate that the geometry such as perforation, its thickness and the perforated plate material affect the non-linear properties of the perforated plate.

Relation between Acoustic Absorption Performance and Flow Field around Perforated Plate with Cross Flow

The present paper focuses on the relationship between the acoustic absorption performance and the flow field around a perforated plate with cross-flow. The normal incidence absorption coefficient was calculated from the measured transfer function using transfer function methods. As the flow velocity passing through the orifices increased, the peak level of the acoustic absorption coefficient increased in some cases. We observed the flow field around a perforated plate by flow visualization using a laser. The vortices were clearly formed downstream of the orifices due to the incident sound of pure tone. We discussed the relationship between the vortex and the acoustic absorption performance of perforated plate with a cross flow.

Experimental investigation of the effect of absorption material on the non-linear properties of perforated plates

Combinations of perforated plate and porous material are used in numerous applications for noise reduction at high sound pressure level, such as in aircraft engines and automotive mufflers. Therefore, it is important to have a better understanding of the acoustic property of these systems. A semi-empirical model is a common way to calculate and understand the sound absorption of these systems. Previous studies show that the interface between a perforated plate and porous material have direct effect on the non-linear property of the perforated plate and sound absorption. Therefore, in this study two conditions of perforated plate and porous material combinations was considered. First, when the perforated plate has direct contact to the porous material and second, when there is air gap between them. Results of this research shows that the variation of non-linear acoustic resistance in case either with or without a cavity gap of air is relatively small.

Mass-air-mass resonance for multiple leaf partition using perforated plate

In an exchange counter, a taxi cabin, and so on, there is a partition between the user and the staff to secure safety. In contrast, the partition prevents speech communication between them. Thus, it is necessary to decline the sound insulation performance of the partition for their comfortable communication. Therefore, we have proposed producing mass-air-mass resonances by applying multiple leaf partitions to decrease the performance. The partition needs to be comprised of very thin sheets and very thin air layers to cause resonances in the frequency range of approximately 500 to 2000 Hz, which is included in voice frequency. In this study, we have realized the sound insulation decline using perforated plates instead of very thin sheets. The formulae of the resonance frequencies were derived for triple or quadruple leaf partitions when using perforated plates as partition components. Moreover, we have verified experimentally that the resonances can occur in the frequencies calculated from the formulae.

Flexural behavior of modular steel channel–concrete composite floor systems with bolted connections

This paper presents an innovative modular steel channel–concrete composite floor system designed for rapid assembly. This system, compared to traditional steel–concrete composite floors, connects adjacent modules solely through the use of high-strength bolts. This design eliminates the need for on-site wet construction, thereby yielding superior economic benefits. To investigate the proposed system’s mechanical behavior, bending tests were conducted on four composite floors with various support conditions, the numbers of bolts, and the degrees of shear connection. The load–displacement responses, torsional behavior of the channel beams, interfacial slip, and strain development of the composite floor systems were analyzed. The test results show that the simply supported composite floor, without bolted connections, undergoes flexural failure. In contrast, the semi-continuous composite floors, with bolted connections, display punching shear-flexural failure. The pre-tension forces applied to the bolts can effectively mitigate the torsional deformation of the channels and module separation, ensuring that the system maintains excellent structural integrity, sufficient load-bearing capacity, and adequate ductility. The semi-continuous composite floors, when fitted with high-strength bolts, demonstrate an increase in ultimate load-bearing capacity by 13–15%. However, there is a corresponding decrease in ductility by 18–23% when compared to the simply supported composite floor without bolts. The use of perforated steel plates as shear connectors offers efficient shear resistance between the steel channels and concrete slabs, facilitating full composite action of the system throughout the loading process. The paper concludes with the development of a model that calculates the flexural strength and punching shear strength of the composite floors based on the yield-line theory.

Aerodynamic performance test and flow visualization for reducing acoustic liner drag in grazing flow

We aim to reduce aerodynamic drag over an acoustic liner, which comprises of a perforated plate, a honeycomb core, and a rigid backplate, for aero-engine applications through both performance testing and flow visualization. Whereas the acoustic liner can attenuate engine noise, the structural characteristic of the liner surface causes the additional drag in grazing flow, resulting in deterioration of engine fuel efficiency. In this work, acoustic liner test pieces with various hole geometries are tested in the flow duct rig capable of generating sound wave and grazing air flow inside the duct. The static pressure drop measurement reveals that the perforation in the grazing flow direction wound increase the drag despite the same overall perforation for all test pieces. We further conduct the flow visualization using the test rig designed for water flow to be analogous to the air flow of the flow duct rig, and the analogy is based on Reynolds number defined with the friction velocity and the representative size of an acoustic liner. The result via particle image velocimetry represents the flow patterns causing the drag.

Archangelskyoxylon carlquistii gen. et sp. nov. Taxonomy and phylogeny of an unequivocal gnetoid Jurassic fossil wood from Argentina

Archangelskyoxylon carlquistii gen. et sp. nov. is based on anatomical secondary xylem from the Lower Jurassic (Sinemurian–Toarcian) in the Roca Blanca Formation of Santa Cruz Province, Patagonia, Argentina. The woods are preserved as siliceous permineralization and examined by light and scanning electron microscopy. The new fossil wood shows a set of anatomical features of the secondary xylem (e.g., vessels with simple, scalariform, foraminate, and modified foraminate perforation plates; vessel with bordered pits with outer aperture vestured or non-vestured, and inner aperture vestured; tracheids with bordered pits; septate fiber-tracheids, and uni to biseriate parenchyma rays), that are related to the Gnetidae and closely resembles those of Gnetum. The new taxon was compared with existing Gnetidae species and included in a phylogenetic analysis to test its relationships with fossil and extant genera of Gnetidae. In the resulting phylogenetic hypothesis, Archangelskyoxylon is placed into a clade that is closely related to Weltwitschia and Gnetum. This finding supports the existence of this lineage in the south of Gondwana during the Jurassic and reinforces the hypothesis that lineages related to the Gnetaceae diverged earlier in South America.

The Effect of Ignition Procedure on Flashback of Hydrogen-Enriched Flames

Abstract The impact of different ignition sequences on the ignition dynamics of CH4-H2 flames in a bluff body burner is investigated at atmospheric conditions. Experiments are performed over a wide range of operating conditions covering pure methane injection (PH0) to pure hydrogen injection (PH100). A perforated plate of total porosity σ=0.17 is positioned at the outlet of the combustion chamber to increase the chamber back pressure and trigger transient flashback during ignition. Time-series of pressure, OH* chemiluminescence and OH-PLIF images of the propagating flame branch are recorded simultaneously to characterize the ignition process. Two ignition procedures are investigated. For ignition procedure A, designated as an early ignition procedure, the spark is initiated before fuel injection. For ignition procedure B, designated as a late ignition, the spark is only activated after the fuel injection. The impact of the fuel air mixing on the final stabilization state is investigated by changing the fuel delivery time (dt) before the initial spark. Three different time delays are considered dt = 1, 3, and 5 s. The final state of the flame is found to be highly sensitive to the selected ignition procedure and increasing dt favors the occurrence of flashback. At constant power, the magnitude of the pressure peak is driven by a competition between the fuel mass flowrate at the moment of ignition and the high reactivity of hydrogen, which shifts the flammability limit toward lower equivalence ratios, hence generating a lower reaction rate. For procedure A, the peak of the chamber over pressure shows a nonmonotonic growth for increasing levels of H2 in the fuel blend, while it linearly increases for procedure B. Experiments are then conducted at a fixed injection flow velocity Ub = 5 m s–1 and fixed laminar burning velocity Sl0=0.25 m s–1 by varying the level of hydrogen enrichment. For procedure A, the over pressure amplitude decreases with increasing the hydrogen enrichment leading to a soft ignition for all CH4-H2 blends. Under ignition procedure B, the amplitude of the over pressure reached during ignition is found to be relatively unaffected by the hydrogen concentration, but the flame stabilization mode shows a strong dependence to both the level of H2-enrichment and fuel delivery time dt. OH* as well as OH-PLIF images reveal that the trajectory of the flame leading point changes as dt increases. The different dynamics of the flame leading points is likely to be the cause the different types of stabilization modes observed.

Hysteretic behavior of prestressed high-strength bolt joint subject to combined flexure and axial forces for prefabricated prestressed spatial structures

A novel prestressed high-strength bolt (PHSB) joint applied in the prefabricated large-span ridge tube cable dome with annular struts (PLRTCDAS) was proposed. Firstly, the hysteretic behavior of the PHSB joint under combinations of bending moment and axial compression was studied by experiments. Four parameters of the PHSB joint, including the disc thickness, perforated cross plate thickness, perforated angle steel thickness, and outer sleeve height, were considered in the test. The effects of these parameters on the hysteretic curves, skeleton curves, bearing capacity, failure modes, energy dissipation behavior, and ductility were analyzed and discussed in detail. Secondly, a three-dimensional finite element (FE) model of the PHSB joint considering geometric, material, and interaction nonlinearities was established by ABAQUS. The accuracy of FE model was verified by comparing the test and numerical results. Finally, the hysteretic behavior of the PSHB joint under different combinations of axial forces and bending moments was investigated by the proposed FE model. The research indicates that the PHSB joint exhibits perfect energy dissipation capacity and higher ductility. Reducing the perforated angle steel thickness or increasing the outer sleeve height can improve the hysteretic behavior of the PHSB joint without significantly reducing its bearing capacity. The verified FE model is an effective method to simulate PHSB joint hysteretic behavior.

Seismic behavior of self-centering precast segmental bridge piers with external auxetic steel shear panel dampers

Precast self-centering segmental bridge piers have gained significant attention in bridge construction. Among them, development of the energy dissipation devices that are applicable for the self-centering bridge piers has been a major focus over the past three decades. This study develops a novel post-tensioned precast segmental bridge piers (SC-PSBPs), incorporating replaceable external auxetic steel shear panel dampers (ASSPDs) at the bottom and connecting steel plates at the intermediate segments. The seismic behavior of the SC-PSBPs is investigated through experiments and numerical simulations. Auxetic metamaterials are utilized to develop two kinds of perforated steel plates, including elliptical and peanut-shaped perforations, for the ASSPDs. Eight SC-PSBP specimens are tested to study failure patterns, hysteresis response, residual displacement, segment gap opening behavior, and local response of steel components. Test results show that the proposed SC-PSBP, equipped with unbonded post-tensioning (PT) tendons and ASSPDs, exhibits stable hysteresis response and self-centering capacity with minimal concrete damage. Plastic deformation is concentrated in the ASSPDs, while the intermediate connecting steel plates behave elastically throughout the loading history. A numerical model is developed to investigate the influence of design parameters on the hysteresis behavior of SC-PSBPs. Parametric analyses using the validated FE models explore the seismic behavior of SC-PSBPs with different geometries of ASSPDs, connecting steel plates, and initial PT forces. Numerical results show that both the ASSPDs and the connecting steel plates are imperative to achieve the desired rocking and damage concentration mechanisms of SC-PSBPs. The numerical findings also indicate that decreasing the porosity of ASSPDs effectively enhances the bearing and energy dissipation capacity of SC-PSBPs, as well as increases their residual displacement.

On the effect of aeration on laser ranging measurements of free water surface

Aerated flows pose both challenges and opportunities in the measurement of free water surface. In this study, an amplitude-modulated continuous wave scanning LIDAR device was used to measure a distance from the device sensor to the water column surface subjected to different degrees of aeration, while reference measurements were performed by high-speed imaging. Different aeration conditions were generated by variation of the air flow rate supplied to the liquid and by using perforated plates with different hole arrangements. The LIDAR device was shown to produce level readings consistently below visible water levels. The measurement error of the LIDAR method is largely determined by the volume fraction of air in water and was lowest at about 0.1 air volume fraction. The error increases linearly until a very high air volume fraction (i.e., above 0.55), while the LIDAR method also performs poorly in unaerated water. Although the measurement uncertainty of LIDAR in the range of aerated water is by at least an order of magnitude higher than in the case of measuring dry solid surfaces, the method is viable for free surface measurement under low to moderate aeration conditions that don't produce excessive foaming.

Improvement of airflow uniformity and noise reduction with optimized V-shape configuration of perforated plate in the air distributor

The air distributor is the end component of the ventilation system, and its performance directly determines the comfortable and pleasant feeling of the residence. A perforated plate can be added to the air distributor to convert dynamic pressure into static pressure first and then distribute the air flow, which provides better self-adjustment compared with the embedded guide vane structure. However, the perforated plate can lead to a contradiction between head loss, noise and distribution uniformity. To reconcile this problem, a novel V-shape configuration of the perforated plate was put forward in this study. The internal flow and aeroacoustic properties of different types of perforated plates were systematically studied, and a full-scale test platform was built to verify the flow characteristics. The effects of hole size and installation position of the perforated plate on the uniform distribution of air flow were analyzed by the parametric analysis method. Then, the sound pressure level of the optimized perforated plate air distributor was further analyzed. The results show that, with the optimized perforated plate structure, the uniform flow performance was improved by about 30% and the overall sound pressure level was reduced by up to 12 dB.