Perforation Shape Research Articles

Numerical investigation of hydrodynamic performance and power consumption in stirred reactors with perforated Scaba 6SRGT impellers for non‐Newtonian fluid

AbstractThe present study aims to further understand the effect of perforated Scaba 6SRGT impellers on stirring performance and impeller power consumption by numerically investigating the hydrodynamic properties of non‐Newtonian fluids in a three‐dimensional stirred reactor. After model validation, the fluid velocity, stagnant region dimensionless volume, and impeller power consumption are quantitatively analyzed under the conditions of influencing parameters, including blade perforation pitch, ratio of distance between adjacent perforations, and perforation arrangement. The results reveal that the range of distribution of acceleration and peak velocity of the fluid along the radial appear in regions lower and larger than the dimensionless radius of the impeller (|r/R| = 0.45), respectively. Increasing the perforation pitch from 14 to 20 mm increases fluid velocity from 0.284 to 0.305 m/s and power consumption from 26.99 to 27.25 W, while reducing the stagnant region volume from 16.76% to 14.71%. The fluid velocity and impeller power consumption slightly increase with the ratio of distance between adjacent perforations. Circular‐shaped middle perforations yield higher fluid velocities and vorticity compared to lozenge‐shaped ones. The highest and lowest power consumptions are obtained by circular–circular–circular and lozenge–lozenge–lozenge perforation shape arrangements with values of 27.25 and 26.9 W, respectively.

Investigation of the Effect of Parametric Patterned Façade and Resulting Daylight Illuminance on Students’ Mood and Task Performance in Architecture Studio-Based Tutoring

Parametric design is one of the thriving contemporary architectural treatments that not only has an influence on the design of building envelopes but is capable of affecting the users physically and psychologically. The efficiency of the daylight resulting from the facade is greatly affected by the envelope’s perforation shapes, sizes, and distribution. This research builds upon a prior study which investigated the effect of Parametric Patterned Façade on daylight performance, quality, and visual comfort concluding with the choice of the highest-performing pattern for daylight metrics. The chosen pattern is the “Triangles Pattern” which was put in situ where the field experiment took place. The current study analyzed the effect of illuminance, and illuminance distribution resulting from the parametric patterned facade on architecture students’ mood and task performance in the setting of an architecture studio-based tutoring. Both quantitative and qualitative research methods were adopted; quantitative through the utilization of a Spatial Ability Test to assess students’ task performance, and qualitative through a self-reporting mood assessment, and subjective daylight perception questionnaire. The analysis was conducted through three types of tests to investigate the research hypothesis; statistical analysis of hypothesis (t-test), PANAS schedule for mood assessment, and comparative analysis of the subjective questionnaire between the base case condition and the parametric patterned façade condition. The results of paired sample study indicated that the students’ performance was enhanced after the exposure to the second condition (PPF condition) over the first (BC condition). Also, for the NA assessment, both PANAS assessment and t-test analysis results showed a difference in means between the two conditions indicating that there was an enhancement of the NA. Finally, a framework is proposed for the utilization of a Parametric Patterned façade in an educational setting. The implications of this experiment inform architects of the importance of daylighting techniques to enrich the educational environment, and how to establish a research methodology for the enhancement of daylight design using both technical and psychological approaches.

Local buckling behaviour of web perforated cold-formed steel lipped channel columns

To connect beams and bracings with storage rack uprights, closely spaced perforations are provided along the web, flanges, and rear flanges of uprights. These perforations can significantly lower the ultimate capacity of such compression members with the possible influence of its natural buckling modes. This capacity reduction can depend on various parameters such as (a) geometrical shape, proportioning of cross-section, and stiffeners; (b) perforation shape, size, spacing, and location; (b) slenderness of member, cross-section, and elements of cross-section; and (d) material properties. A thorough understanding of the influence of the above-mentioned factors is necessary for the accurate strength prediction of perforated Cold-formed steel (CFS) compression members. Even though the current design standards are updated for the accurate strength prediction of unperforated CFS compression members, they do not collectively account for the influence of all the aforementioned factors on the load-carrying capacity of the perforated CFS members, particularly for the local buckling capacity. Though the Direct Strength Method (DSM) of design is the most accepted method for accurate strength prediction of CFS members even for complex cross-sectional shapes, recent research on the strength evaluation of perforated CFS members using DSM has emphasized the need for refinement in DSM. The Modified Direct Strength Method (MDSM), which accounts for the simultaneous buckling of flanges and web, includes the cross-section aspect ratio and cross-section slenderness to predict more accurately the local buckling design strength. However, it was developed only for unperforated specimens. Hence, a systematic experimental and numerical investigation was done to understand the influence of the perforation in the local buckling behavior of the lipped channel section. In total, 14 specimens, including 2 unperforated and 12 web perforated CFS lipped channel stub columns were physically tested with fixed support conditions. The Finite Element Analysis using ABAQUS software was used to conduct an extensive parametric numerical study. The results were used to compare the strength curves of DSM and MDSM and the modification in the design curves has been proposed by considering the erosion in strength due to the presence of perforation.

Assessing acoustic performance of building material: A finite element model for 3D printed multilayer micro-perforated panels with compressed earth blocks

This study deals with 3D printing multilayered micro-perforated panels (M-MPPs) coupled with buildings materials as compressed earth block for noise reduction applications. The sound absorption coefficient α is utilized as a metric to assess the sound insulation capabilities across a frequency range spanning from 10 to 3000 Hz, then evaluated and validated by numerical and experimental methods. The FEM model developed makes it possible to predict the acoustic absorption of M-MPPs by tuning the frequency range and varying optimized acoustics parameters, considering hole-hole interaction and taking into account visco-thermal effects that are present in compressed earth blocks. It is shown that the shape of perforations and material properties including the porosity rate, arrangement in the design of multilayer micro-perforated structures are identified to play a significant role in the sound performance of the entire structure. In addition, the application of MPP coupled with compressed earth blocks improve the sound absorption capacity of the composite structure. The developed FEM leads to accurate prediction of performance, efficient optimization, and cost effectiveness. Finally, the present study reveals the importance of M-MPPs combined with compressed earth blocks (CEBs) as viable noise reduction materials, particularly relevant for engineering applications and development initiatives in emerging economies.

Nasal Septal Perforation Dimensional Analysis.

To describe and illustrate septal perforation shape through the documentation and analysis of length and height measurements. A secondary objective is to correlate perforation size to surgical and nonsurgical etiologies. Retrospective case series. Tertiary academic medical center. Length and height of consecutively treated perforations over a 3-year period were measured directly or through computed tomography. Mean differences in length and height measurements were compared and regression analysis used to determine perforation shape and the effect of etiology on perforation size. Perforations were classified by length into small (1-5 mm), medium (6-15 mm), and large (>15 mm) and correlated to shape and etiology. One hundred twenty-four patients (mean age 50.4 years, 60.5% female) met study inclusion criteria. Height was less than length in 93% of perforations 5 mm or greater in length. Mean perforation height was significantly less than length for medium and large perforations (P < .001). Mean length and height measurements of nonsurgical perforations were greater than those for surgical perforations (P < .001). Height is less than length in over 90% of septal perforations. Most perforations assume an elliptical shape as they enlarge. Accurate measurement and presentation of length and height is relevant information to perforation management decisions and for the evaluation of treatment outcomes.

Seismic performance evaluation of exterior reinforced concrete beam-column connections retrofitted with economical perforated steel haunches

The exterior beam-column joint (BCJ) within reinforced concrete (RC) frame structures is acknowledged as a vulnerable component prone to seismic failure. This article proposes a practical and economical strengthening method for exterior BCJs using a perforated steel haunch system. This method is designed to mitigate damage in BCJs and improve the seismic performance of the structure. Employing finite element modeling (FEM) techniques, the study evaluates the impact of perforated steel haunches on the BCJs’ behavior and performance. The investigation involves creating nine distinct models, each representing a BCJ with a steel haunch system. These models include a control model without any perforations and eight variations with different levels of perforation (ranging from 10% to 50%) within the steel haunch system. Furthermore, the study analyzes the influence of perforation shapes on the connections’ performance, considering square, circular, hexagonal, and triangular shapes. The results reveal that utilizing a steel haunch without perforations significantly increases the load-carrying capacity of a BCJ by about 89%. Additionally, circular or square-shaped perforations, up to 30–35% within the steel haunch, effectively prevent the joints’ failure and promote the ductile behavior. These findings hold the potential to advance the design methodology for RC joints subjected to seismic loads, thereby enhancing the structural resilience in earthquake-prone regions.

Quasi-static crashworthiness behaviour of auxetic tubular structures based on rotating deformation mechanism

Auxetic materials have attracted significant interest due to their exceptional mechanical characteristics and distinctive deformation modes. Nevertheless, the practical use of these materials in engineering is constrained by their limited ability to absorb energy. Thus, enhancing the energy absorption (EA) capabilities of auxetic materials is crucial to expand their range of potential applications. In this study, the EA capabilities of auxetic tubular structures with rotating deformation mechanisms are examined, with a specific emphasis on three different perforation shapes: elliptic, peanut, and square, along with their modified versions incorporating stiffeners. The study employs a combination of experimental testing and numerical modelling, utilising ANSYS/LS-DYNA to evaluate various crashworthiness parameters. These parameters include total EA, specific EA, maximum crushing force, and crushing force efficiency, all of which are assessed under quasi-static compression conditions. The research highlights the importance of perforation shape and stiffener incorporation in enhancing crashworthiness. Results show that elliptic perforations exhibit superior EA and stiffened auxetic models outperform conventional ones in terms of crash absorber performance. The presence of stiffeners significantly improves the ability of tubular structures to withstand crushing forces. Furthermore, the study validates the numerical model against experimental findings, demonstrating a high level of agreement in terms of crushing force–displacement, EA, and failure modes. The research provides valuable insights into the design and performance of crashworthy structures and offers potential applications in various fields where impact resistance and EA are critical.

Studies on heat transfer performance of miniature cross-flow heat exchangers with perforated fins for direct methanol fuel cells

Despite the widespread industrial application of finned micro heat exchangers, there is still a need to enhance the heat transfer efficiency. This study focuses on fin perforation research to improve heat transfer efficiency. In this study, a miniature cross-flow heat exchanger (heat source is a heat stream at 351.35 K) was simulated. By employing a combination of experimental methods and numerical simulations, the investigation delves into the impact of mixed shapes and innovative spatial distributions of perforations on fin convective heat transfer characteristics. The findings demonstrate that square and square-and-diamond perforated fins exhibit a temperature drop increase of 10.1 % and 8.9 %, respectively, in comparison to unperforated fins during forced convection. Fin temperature drop is augmented by 12.3 % with differentially staggered perforations on adjacent fins (spatially staggered perforations) in contrast to parallel perforated fins, and by 23.6 % compared to non-perforated fins. Furthermore, the optimal performance of the fin heat transfer is observed at 5.74 % perforated area occupancy. The study reveals a positive correlation between the Nusselt and Reynolds numbers. Moreover, the spatial distribution of perforations significantly enhances the performance evaluation criteria compared to the perforation shape. Ultimately, the implementation of fin perforation technique is considered to offer more consistent power output and an extended range for direct methanol fuel cells.

Analysis of perforated fixed baffle at low filling ratio to reduce sloshing using SPH

Prismatic tanks are used widely in various industrial applications, including marine and petroleum, due to their ease in design and storage capacity. However, these tanks often experience sloshing issues that can affect vessel stability. Sloshing effects can cause undesirable motions and impact the system's overall performance. This study focuses on analyzing the effect of perforated shapes on fixed baffles as a solution to reduce the sloshing effect in prismatic tanks. Baffle or anti-sloshing is an internal partition used to minimize the movement of liquid in the tank. The analysis method uses Smoothed particle hydrodynamics (SPH), which is a particle method or can be referred to as mesh-free computational fluid dynamics. The parameters tested include the perforated shape and the filling ratio of the water filling in the tank. The analysis found that the perforated form of the baffles has a significant effect on reducing the sloshing effect. The perforated shape of the fixed baffles has the same impact on reducing the sloshing effect of the prismatic tank. There is no significant difference in the ability of each baffle shape to overcome the sloshing problem. The findings from this study can guide designers or engineers in designing prismatic tanks that are more stable and reduce the effects of sloshing. Using baffles with the right perforated shape can optimize tank performance in maritime and shipping.

Structural performance of perforated arched self-compacted reinforced concrete beams under concentrated static loading

Arched reinforced concrete (RC) beams are a viable solution for use as the main supporting system for large-span halls. This is because of the developed normal force owing to the curvature, which approaches the line of pressure under loading, leading to a balance of the resulting bending moment. Therefore, the curved beam can sustain more applied loads than the ordinary straight beam for the same span. However, providing web openings along the entire span of the arched beam can compromise the ultimate capacity. Thus, the behavior of two-hinged perforated arched RC beams made of self-compacting concrete was investigated experimentally and numerically. The experimental program consisted of 11 RC beams, one straight and 10 arched beams, divided into five groups to study the effects of arching, perforation shape and size, and reinforcement configuration around the perforations. In addition, a parametric numerical study using the ABAQUS program was conducted to investigate the relevant parameters in detail. It was found that the arched beam exhibited remarkable ultimate capacity compared to that of the straight beam; however, the strength gains due to the arching effect reduced significantly due to providing web openings. In addition, it was found that providing additional web reinforcement in both the circular and cross-bar configurations around the perforations significantly enhanced the overall behavior. Furthermore, it was found that the best rise-to-span ratio of arched beams was 0.18 for both solid and perforated ones.

Modeling and Design Enhancement of Electrothermal Actuators for Microgripping Applications

Microgrippers are miniature tools that have the capability to handle and manipulate micro- and nano-scale objects. The present work demonstrates the potential impact of the incorporation of perforations on a ‘hot and cold arm’ electrothermal actuation mechanism in order to improve the operation of microgrippers in terms of arm opening and operating temperature. By applying a voltage to one arm and setting the other as a ground, the current passes through the electrothermal actuator and induces its displacement along the in-plane direction. The difference in the geometry of the two arms causes one arm to expand more than the other and this results in transverse bending. A computational model was developed using a finite element analysis tool to simulate the response of the thermal actuators with varying geometries and investigate the impact of incorporating perforations on the arms of the thermal actuators to enhance its performance in terms of deflection and operating temperature. The simulation results were compared to their experimental counterparts reported in the literature. A good agreement between the numerical and experimental data was obtained. A novel design of a microgripper, made of perforated electrothermal actuators, was introduced. Its main characteristics, including the tip opening of the gripper arms, the applied voltage, and the stress and temperature distributions, were analyzed using the developed computational model. Different perforation shape and distribution were investigated. The present study demonstrates the capability of perforations to enhance the operation of microgrippers as manifested by the obtained higher tip displacement and lower tip temperature in comparison to conventional microgripper designs made of non-perforated thermal actuators. Furthermore, the highest stress generated on the microgripper elements was found to be much lower than the yield strength of the constituent material, which indicates proper functioning without any mechanical failure.

Finite Element Analysis of Upper Limb Splint Designs and Materials for 3D Printing.

Three-dimensional (3D) printed splints must be lightweight and adequately ventilated to maximize the patient's convenience while maintaining requisite strength. The ensuing loss of strength has a substantial impact on the transformation of a solid splint model into a perforated or porous model. Thus, two methods for making perforations-standard approach and topological optimization-are investigated in this study. The objective of this research is to ascertain the impact of different perforation shapes and their distribution as well as topology optimization on the customized splint model. The solid splint models made of various materials have been transformed into porous designs to evaluate their strength by utilizing Finite Element (FE) simulation. This study will have a substantial effect on the designing concept for medical devices as well as other industries such as automobiles and aerospace. The novelty of the research refers to creating the perforations as well as applying topology optimization and 3D printing in practice. According to the comparison of the various materials, PLA had the least amount of deformation and the highest safety factor for all loading directions. Additionally, it was shown that all perforation shapes behave similarly, implying that the perforation shape's effect is not notably pronounced. However, square perforations seemed to perform the best out of all the perforation shape types. It was also obvious that the topology-optimized hand splint outperformed that with square perforations. The topology-optimized hand splint weighs 26% less than the solid splint, whereas the square-perforated hand splint weighs roughly 12% less. Nevertheless, the user must choose which strategy (standard perforations or topology optimization) to employ based on the available tools and prerequisites.

Impact of web perforation size and shapes on structural behavior: a finite element analysis

Purpose Various designs of corrugated webs include trapezoidal, sinusoidal, triangular and rectangular profiles. The increasing use of curved plates has prompted the creation of I-sections made of steel with a corrugated web design. This study aims to examine the effectiveness of an I-beam steel section that features a perforated-triangular web profile. Design/methodology/approach In the current study, finite element analysis was conducted on corrugated-perforated steel I-sections using ANSYS software. The study focused on inspecting the design of the perforations, including their shape (circle, square, hexagon, diamond and octagon), size of perforations (80 mm, 100 mm and 120 mm) and layout (the position of web perforation), as well as examining the geometric properties of the section in term of bending, lateral torsional buckling, torsion and shear behavior. Findings The study revealed that perforations with diamond, circle and hexagon shapes exhibit good performance, whereas the square shape performs poorly. Moreover, the steel section’s performance decreases with an increase in perforation size, regardless of loading conditions. In addition, the shape of the web perforations can also influence its stress distribution. For example, diamond-shaped perforations have been found to perform better than square-shaped perforations in terms of stress distribution and overall performance. This was because of their ability to distribute stress more evenly and provide greater support to the surrounding material. The diagonal alignment of the diamond shape aligns with principal stress directions, allowing for efficient load transfer and reduced stress concentrations. Additionally, diamond-shaped perforations offer a larger effective area, better shear transfer and improved strain redistribution, resulting in enhanced structural integrity and increased load-carrying capacity. Originality/value Hence, the presence of lateral-torsional buckling and torsional loading conditions significantly impacts the performance of corrugated-perforated steel I-sections.

Factors Affecting the Surgical Outcome in Nasal Septal Perforation Repair.

Nasal septal perforation (NSP) repair is challenging surgery considered in patients with symptomatic NSP intractable to conservative treatments. This study aimed to assess the success rate and identify factors affecting the surgical outcome of NSP by analyzing consecutive series of NSP repairs by a single surgeon. We enrolled 84 patients diagnosed with NSP and who underwent surgical repair of NSP by a single surgeon (Y.J.J.) between November 2007 and July 2022. Medical records were retrospectively reviewed regarding variables involving preoperative symptoms, rhinologic history, etiology, surgical techniques, and the outcome of surgery. In addition, features of NSP were objectively evaluated using computed tomography scans. The overall success rate of NSP repair was 64.3% (54 of 84). Nasal obstruction (79.8%), crusting (34.5%), and epistaxis (27.4%) were frequent preoperative symptoms. Iatrogenic injury from previous nasal surgery (70.2%) was the most common cause. The average size of NSP on preoperative CT was 9.53 ± 6.68 mm. Patients with incomplete NSP closure had significantly larger perforations (12.21 ± 7.92 mm) than those with successful closure (8.04 ± 5.41 mm) preoperatively (P = .005). Patients with smoking history (OR = 2.971, 95% CI 1.170-7.548, P = .020) and NSP repair with combined rhinoplasty (OR = 3.811, 95% CI 1.401-10.370, P = .007) were more likely to experience incomplete closure. Patients whose perforations were reinforced with interposition graft were more likely to result in successful repair (OR = 6.752, 95% CI 2.496-18.262, P < .001). The bilaterality of mucosal flap coverage, surgical approach, types of mucosal flap and interposition graft, perforation shape, mucosal thickness around perforation, and distance from the nasal floor were not significantly related to the surgical outcome. Significant factors affecting the outcome of NSP repair were patient's smoking status, combined rhinoplasty, application of interposition graft, and perforation size.

A study of finding empirical correlation for the Nusselt number and the factors influencing it for perforated fin array of different shapes

An experimental investigation of three-dimensional steady state forced convection heat transfer through perforated rectangular fins with three different materials were carried out. The experimental procedure has been done in turbulent region with Reynolds number range of (6200 ≤ Re ≤ 18,700) and (Pr = 0.71) and constant inlet air temperature of (Tin≈17°C) with a constant power input of (20 W ≤ Q ≤ 70 W) step 10 W. The current study used a rectangular fin array with three materials (stainless steel 430, aluminum 2014-T6, yellow brass), with various perforation shapes and patterns which includes [Rectangular, Circular, and V-shape, all (Inline, staggered)]. It is found that the mean deviation of average Nusselt number taken for previously published results to the experimental result of all specimens have been found to be ∓ 8 %. A general correlation has been derived based on average Nusselt number with an error of ± 5 % which is described with the formula (Nu¯=βRe¯αδRAFPrRAF). It is concluded that the general correlation equation derived has reasonably acceptable degree of accuracy and it’s more general and considers many materials with a wide range of RAF compared with the other equations. The average error found between the general correlation and previously published result is ± 9.8 %.

Application of residence time distribution (RTD) to enhance the performance of perforated baffled constructed wetland under unsteady flow

The perforated baffle can significantly enhance the performance of the constructed wetland. In the present study, the effects of perforation shape, number of baffles, baffle position and perforation location on the flow pattern of wetlands were investigated using NaCl impulse-response tracer test, and perforated baffles were used to improve the nitrogen removal rate of the constructed wetland. The perforated baffle optimizes the flow pattern by reducing the peak height of the RTD curve and delaying the peak occurrence time. Triangle perforation exhibits better flow pattern optimization due to its smaller area. When the inlet flow rate is 100 mL/min, the mean residence time (Tm) increases by 0.25 h. The position of the perforated baffle has a more significant effect on the flow pattern, being able to better extend hydraulic residence time (HRT) when located at the height of H/2 substrate. In addition, the perforation locations of two adjacent baffles are not on the same vertical line, which can increase the horizontal water flow velocity and improve the space utilization of the wetland. Compared to the control check constructed wetland (CKCW) without baffles, the perforated baffled constructed wetland (PBCW) exhibited a higher NH4+-N removal rate of 84.53 ± 7.48 % during stable operation. This is mainly because the perforated baffle improves the utilization of dissolved oxygen (DO) while improving the water flow distribution and extending the HRT. In conclusion, perforated baffles have considerable potential to alleviate shock loading and enhance the performance of constructed wetlands.

Experimental parametric study of perforated steel plate fuses for mass timber seismic force resisting systems

The lack of practical connections with reliable desired energy dissipation capacity as the main components of a seismic force resisting system (SFRS) is a major obstacle in using mass timber in tall buildings located in seismically active regions. A common method to dissipate seismic energy in timber structures is through the yielding of steel material found in the mechanical connections. Under the induced seismic motions, these dissipative connections are intended to yield while the rest of the structure remains intact with minimum damage. In this research, the focus is on the use of perforated steel plate as a dissipating energy device and a seismic fuse. Previous tests have demonstrated the potential use of perforated steel plates as seismic fuses in mass timber SFRS and confirmed their scalability and predictability. Despite promising results under monotonic loading, their behavior under cyclic loading can be improved. This paper presents an experimental parametric study investigating the effects of the number of rows, shape, and size of perforations, the steel plate thickness, and the steel link size on the mechanical performance of the perforated plates. The obtained hysteresis responses and envelope curves are compared. It is found that the ellipse and stagger patterns possess the largest ultimate displacement and stiffness, respectively. In addition, no significant enhancement in the ultimate deformation was observed in the cyclic response of the fuse, beyond three rows of perforations. Within the range of the configurations considered, the reduced ultimate deformation under cyclic loading remains a technical challenge that needs to be addressed if this type of seismic fuse is to be installed in SFRS. The results will assist with the design of future test programs on full-size mass timber connections consisting of such fuses.

Simulation Study on Geometric Parameters Influencing the Flow Coefficient of Perforated Plate

Natural ventilation is one of the vital means for passive energy-efficient design in green buildings. As a widely used building façade, the perforated plate is mostly utilized for appearance decoration, noise absorption, and sun shading, but its impact on the natural ventilation effect has rarely been paid attention to. In this study, the influence of the perforation rate, the perforation size, and the perforation shape on the flow coefficient of the perforated plate were simulated using the commercial CFD software Fluent, and the correlation between the flow coefficient and these geometric parameters was then regressed. The results show that the flow coefficient of perforated plate increases with the increase in perforation rate, which is slightly greater than that of ordinary building openings, and the corresponding flow coefficients of different holes rank as circle &gt; square &gt; triangle under the same conditions. The flow coefficient increases with the increase in the perforation size, and this effect is greater when the size is small. In addition, the flow coefficient is less affected by the size of round holes compared to triangular and square holes. The regression model indicates that both the perforation rate and the perforation size have a considerable positive influence on the flow coefficient, while the square and triangle holes have a negative influence on the flow coefficient compared with the circular hole. Moreover, the geometric parameters of perforated plates that have the greatest influence on flow coefficient are perforation rate, perforation shape, and size, in descending order.

Perforations in Columbellidae shells: Using 3D models to differentiate anthropogenic piercing from natural perforations

Perforated shells are often used to study socially mediated behaviour in past hunter-gatherer groups. One of the key issues regarding empty shells from beaches or fossil outcrops is determining human agency in the accumulation and modification of an assemblage. Here we investigate anthropogenic mediation in Initial Upper Palaeolithic and Early Ahmarian assemblages of Columbella rustica at Ksâr ‘Akil (Lebanon). We compare perforations in the archaeological specimens with data from newly gathered Columbellidae modern death assemblages from Tenerife (Spain) using three-dimensional shell-thickness models as templates. This approach, using micro-CT scans of pristine shells to map robust and fragile zones on shell outer-surfaces, allows us to contextualise the two datasets within their natural morphology. Our results show that in natural death assemblages the vast majority of perforations occur in structurally weak zones, and their distribution can be explained by shell morphology in combination with predator activity and other post-mortem damage. In our archaeological dataset we found a higher frequency of perforations in more robust zones and a higher uniformity in their location, size and shape. This suggests human mediation in either the selection or manufacture process of C. rustica beads at Ksâr ‘Akil from as early as the Initial Upper Palaeolithic and throughout the Early Ahmarian. Standardisation in perforation shape, size and distribution have been argued to be indicative of formalised manufacture processes and our results are thus more congruent with intentional bead manufacture than the selection of naturally-holed specimens.

Effect of pitch and hole-hydraulic depth of perforated V-shaped baffles on the heat transfer and thermohydraulic performance of an air heater duct

The introduction of V-shaped or inclined perforated baffles in a heat exchanger duct influences the flow dynamics significantly and enhances its thermal performance. The appropriate spacing and perforation shape of baffles further improve the heat transfer mechanism. This work aims to experimentally compare the thermal attributes of a smooth air heater duct with those by incorporating perforated V-shaped baffles with staggered non-circular openings of a constant perforation ratio in the flow passage. The effects obtained on the Nusselt number (Nu), friction factor (f) and the thermohydraulic performance parameter (η) of the duct are studied under the turbulent airflow Reynolds number (Re) range of 5500 to 15,000 by modifying three different values of pitch ratio (p/H) and hole-hydraulic depth-to-baffle height ratio ([Formula: see text]) for both V-down and V-up arrays. The investigation also encompasses developing the correlations of criteria Nu, f and η. The results show that the Nu ameliorates by increasing [Formula: see text] at reduced p/H, whereas the f value increases by reducing the hole-hydraulic depth. The maximum Nusselt number ratio ([Formula: see text]) obtained for V-down and V-up baffles, respectively, are 3.36 and 3.58 at p/H of 1 and [Formula: see text] of 0.84 with the Re range of around 13,600. The V-down and the V-up array at p/H of 1 shows the maximum friction factor ratio ([Formula: see text]) as 11.9 and 13.14, respectively, for [Formula: see text] values of 0.74 and 0.79 at the extreme Re range. The V-up array at p/H of 3 with increased [Formula: see text] (0.84) outperforms obtaining the highest η value of 1.67. The correlations developed show good agreement between the experimental and predicted data.