Hexagonal Cross-section Research Articles

Optical and Structural Properties of Anisotropic ZnS Nanoparticle Suspensions.

We studied the optical and structural properties of highly ordered arrays of surfactant-capped ZnS nanowires (NWs) and nanorods (NRs) in organic suspensions. The photoluminescence (PL) emission measured under different concentrations and postsynthesis washing cycles interestingly showed increasing emission upon decreasing nanoparticle (NP) concentration. Synchrotron small angle X-ray scattering measurements elucidated the liquid-crystal-like structure of the NPs in suspension under different concentrations and temperatures. The NWs are stacked in a simple structure with a hexagonal cross-section, whereas the structure of the NRs is more complex, resembling a smectic-c liquid crystal, and shows unusual thermal expansion versus temperature. The results point out that a certain amount of bound surfactant must be present on the NP surface to maximize the PL intensity.

Manufacturing of hexagonal cross-section thermoplastic matrix composite parts with automatic filament winding system

Thermoplastic filament winding is a flexible manufacturing method typically used in the production of cylindrical composite structures, allowing for in-situ consolidation without the need for a second consolidation step. The objective of this study is to produce non-cylindrical geometries, typically manufactured using thermoset matrix composites according to the literature, using the thermoplastic filament winding process. For this purpose, glass fiber (GF) reinforced polypropylene (PP) prepreg tapes were used to produce hexagonal cross-section thermoplastic composite parts. The critical process parameters; hot-air heater nozzle temperature, compression roller pressure, the linear speed of mandrel rotation, and corner radius of the mandrel, were determined using the Taguchi experimental design method. The interlaminar shear strength (ILSS) and maximum compressive strength (σmax) values were obtained as 211 MPa and 49.40 MPa as maximum, respectively. ANOVA analysis showed that the corner radius had the most significant impact on ILSS, while mandrel rotation speed and temperature were critical for σmax.

Energy absorption performance of Kresling origami tubes under impact loading

Thin-walled tubes with an origami design, particularly the Kresling pattern, exhibit superior mechanical properties compared to traditional straight tubes, including a more constant reaction force and predictable deformation. Despite their potential, research on these patterned structures, especially when made from structural materials like metal and tested under dynamic conditions, remains limited. This study investigates the compressive performance of aluminium Kresling origami tubes (KOTs) under quasi-static and impact scenarios (up to 30 m/s) in the axial direction. Results show that increased impact velocity leads to more localized deformation and improved energy absorption metrics. A validated numerical model was used to analyze the influence of hierarchy rotation, sector angles, and loading velocity on mechanical performance. Comparisons with Miura-ori patterned tubes and hexagonal cross-section straight tubes of the same relative density revealed that KOTs have superior energy absorption performance. An empirical model was developed to effectively predict the mean crushing stress of KOTs. In addition. a generative machine learning model was introduced to synthesize a large dataset from initial simulations, providing an efficient and reliable solution for energy absorption analysis in origami structures, addressing the challenge of limited specimen datasets.

Antiskyrmions in Ferroelectric Barium Titanate.

Typical magnetic skyrmion is a string of inverted magnetization within a ferromagnet, protected by a sleeve of a vortexlike spin texture, such that its cross-section carries an integer topological charge. Some magnets form antiskyrmions, the antiparticle strings which carry an opposite topological charge. Here we demonstrate that topologically equivalent but purely electric antiskyrmion can exist in a ferroelectric material as well. In particular, our computer experiments reveal that the archetype ferroelectric, barium titanate, can host antiskyrmions at zero field. The polarization pattern around their cores reminds ring windings of decorative knots rather than the typical magnetic antiskyrmion texture. We show that the antiskyrmion of barium titanate has just 2-3nm in diameter, a hexagonal cross section, and an exotic topological charge with doubled magnitude and opposite sign when compared to the standard skyrmion string.

Optimization of Pin Fins Using Computational Fluid Dynamics and Machine Learning

This paper presents a two-part study focusing on the optimization of pin-fin arrays for gas turbine blade cooling. The first part of the study examines the thermal performance of various pin-fin shapes and sizes using computational fluid dynamics. The study investigates circular, elliptical, hexagonal, and rectangular cross sections, with emphasis on the hydraulic diameter and Reynolds number. Two-dimensional simulations mimicked a confined, staggered array of uniform-sized pins under different inlet conditions. For a hydraulic diameter of 0.053 m and a Reynolds number of 5500, the rectangular pins showed the highest Nusselt number 8.98, 16.01, and 20.62% larger than circular, elliptical, and hexagonal pins, respectively, but also a pressure increase 68.30% higher on average. For a hydraulic diameter of 0.046 m and a Reynolds number of 1000–15,000, it was shown that all shapes have an exponential increase in pressure and a logarithmic decay in the Nusselt number. Standing out was the rectangular shape, which, at a maximum Reynolds number of 15,000, had a pressure increase of 108% larger than the next in line, the hexagonal pin. In the same range of inlet conditions, the Gee–Webb coefficient was the highest for the circular pin, which was selected as the main shape for the following segment. In the second part of the study, a machine learning framework based on a neural network architecture is presented. The neural network predicts the thermal performance of different pin-fin array configurations. At the end, this framework is used in an optimization process that explores the advantages of nonuniform arrays consisting of differently sized circular pins as opposed to the standard uniform structures of the first part. The model proves to be capable of accurately predicting the characteristic thermal performance coefficients across a wide range of input parameters. The nonuniform array managed a 23% reduction in pressure rise at a 0.2% exit temperature increase compared to a reference standard array of the same hydraulic diameter.

The effect of axial–torsion coupling on the compressive collapse behavior of Kresling tubes

The coupled axial compressive and torsional response of thin-walled tubes, having Kresling geometric units in series, with hollow hexagonal cross-sections of similar wall thickness, is studied. The tubes are fabricated using multi-jet fusion technology with Polyamide-12 (PA12) material. Each tube is compressed under displacement-controlled quasi-static loading with roller boundary conditions to eliminate any reaction torque being induced in the tube. The tube’s deformation response is characterized by an initial load rise followed by a drop in the load past a load maximum. This load drop is caused by localized collapse within a single Kresling unit. The collapse mechanism is accompanied by relative rotation between the ends of the Kresling unit, indicating the presence of compression-twist coupling. After local densification in the collapsed Kresling unit is attained, the load rises and attains a peak followed by a second load drop causing the other Kresling unit to collapse. Finite Element (FE) simulations show that the nonlinearity of the material response influences the onset of the collapse of the Kresling unit. Results from the present study will be helpful in tailoring the geometry of the Kresling unit cells to attain desired energy absorption or to “tune” the end-displacement vs. rotation response of the structure.

Investigation of pin and perforated heatsink cooling efficiency and temperature distribution

The uneven temperature distribution resulting from thermal stresses in heat sinks is a significant issue in modern electronic devices. This numerical investigation utilizes fluid to analyze the cooling, flow, and heat transfer characteristics of eight different heat sink designs. These include pin–fin heat sinks with circular, triangular, square, and hexagonal cross-sections, as well as their perforated versions. The results show that the thermal resistance range for all geometries was between Rth = 0.29 and 0.51 K W−1. The circular cross-section pin structure was found to be the most efficient in terms of thermal resistance, while the triangular perforated structure was the least efficient. The narrow and low temperature distribution indicates a high cooling potential for the heat sink. It has been observed that the temperature range studied is between 308.732 and 315.273 K. The circular cross-section pin structure is most efficient in terms of homogeneous distribution between 308.73 and 311.306 K. The pin-type structure with a square cross-section attained the maximum Performance Evaluation Criteria (PEC) of 1.1872 at P = 689 Pa, while the pin-type structure with a triangular cross-section attained the lowest PEC of 0.67 at P = 2750 Pa. The investigation revealed that, in relation to PEC, perforated structures had superior performance compared to other pin designs, except for the square-section pin structure. This research found that measuring the efficiency of a heat sink based just on thermal resistance or average temperature distribution is not enough; the PEC criteria must also be taken into account.

VoCoRec

Open volumetric air receivers in solar tower systems are attractive for electricity generation as well as for process heat in chemical and other industrial applications. From the experience of past development stages, a new receiver concept was created with a conical cavity, with hexagonal cross-section for the modularity and a two-stage air heating. Several simulations have been performed. A prototype receiver module with approx. 175 kW thermal output has been manufactured and will be tested in DLR’s Synlight. For different module sizes the cost estimation for industrial fabrication was calculated as well as the performance, ranging from 89% to 78% at 700°C hot air temperature.

Size control of InP nanowires by in situ annealing and its application to the formation of InAsP quantum dots

We carried out in situ annealing of InP nanowires (NWs) in a metal-organic vapor phase epitaxial (MOVPE) growth reactor to control and reduce the tip size of InP NWs. InP NWs were grown by selective-area (SA) MOVPE on partially masked (111)A InP substrates, and annealing was successively applied in tertiarybutylphosphine (TBP) ambient. Initially, the InP NWs had a hexagonal cross-section with {112¯} facets vertical to the substrates; they became tapered, and the edges were rounded by annealing. By appropriately selecting the annealing temperature and initial NW diameter, the tip size of the NW was reduced and NWs with a tip size of 20 nm were successfully formed. Subsequently, a thin InAsP layer was grown on the annealed NWs and their photoluminescence was investigated at low temperatures. The characterization results indicated the formation of InAsP quantum dots (QDs) emitting in the telecom band. Our approach is useful for reducing the size of the NWs and for the controlled formation of InAsP QDs embedded in InP NWs in photonic devices compatible with telecom bands.

Synthesis of zinc oxide nanoflower using egg shell membrane as template

In this study, the nanocomposite of eggshell membrane is synthesized with ZnO by the chemical bath deposition (CBD) method, and eggshell membrane, which is used as a template, and decomposed. The end product obtained is nanoflowers of zinc oxide (ZnFs). The petals of nanoflowers obtained are of hexagonal cross-section similar to the unit cell structure of zinc oxide. The CBD parameters of temperature, reaction time, and solution pH were varied extensively during this study to obtain optimized parameters for the growth of ZnFs. The obtained nanoflower structure was analyzed using various characterization techniques of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), X-Ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR).

Thermal performance enhancement of a micro-jet heat sink via parametric investigated micro pin fin arrays

The thermal management issue of high electronic chips with heat flux is one of the most challenge during the development of electronic devices. In this work, the design of micro pin fin arrays (MPFA) of micro-jet heat sink was proposed to achieve effective cooling of electronic chips. The MPFA with different cross-sectional shapes were used to improve the thermal performance of the heat sink. The results show that heat sink design with MPFA exhibit excellent cooling performance while consuming approximately the same amount of power as smooth surface. In addition, the hexagonal cross-section has better thermal performance, the temperature uniformity of the heating surface can be improved by up to 70 % and the average temperature can be reduced by 7–20K. Moreover, the manufacturing cost and cooling performance per unit cost were investigated and the results show that the square cross-section is the most commercially viable. Based on this, the square cross-section was parametrically studied, including the length to height ratio and fins number. It was founded that the heat sink exhibits better thermal performance for a length-to-height ratio of 1.4 and a number of fins of 169. Finally, the ultimate heat flux of the electronic chip can be withstood was also tested, and the optimal heat sink design can handle heat flux of 400W/cm2. Therefore, the heat sink with MPFA design can significantly improve the thermal performance without consuming the pump power, which can be used to cooling the high electronic chips with high heat flux in the future.

Analytical and finite element analyses on axial tensile behaviour of origami bellows with polygonal cross-section

The mechanical behaviour and energy absorption (EA) of origami bellows with polygonal cross-sections under quasi-static axial tension were numerically and theoretically investigated. The finite element analysis results showed that the plateau force increased with the number of polygon sides N, leading to increases in the mean tensile force (Pm) and specific energy absorption (SEA). Two types of basic deployment elements during the tensile process of hexagonal cross-section bellows were defined based on two corresponding deployment modes, namely non-rigid deployment mode I and non-rigid deployment mode II. The bellows exhibiting deployment mode II had approximately 60 % greater SEA and Pm than those exhibiting mode I. Theoretical predictions of the mean tensile force for each mode were derived based on a rigid, perfectly plastic material model and superfolding elements. The predicted results showed reasonable agreement with the finite element analysis results in terms of force – displacement history and Pm. This work reveals the fundamental mechanics involved and can facilitate design of origami bellows with optimized geometric and material parameters for desired EA behaviour.

Hydrothermal and energy-saving performances in a mini-channel heat sink under different wire coil inserts induced swirling flow

Energy conservation and emission reduction are crucial international policies. For micro/mini-channel heat exchangers, improving their thermal performances while consuming as little energy as possible is essential for implementing these policies. Swirling flow stands out as one of the most effective methods for heat transfer enhancement in channel. The wire coil insert, known as an effective swirling flow device, has been widely applied in traditional heat exchangers. However, the effects of different wire coil inserts on hydrothermal and energy-saving performances in the square micro/mini-channel remain unclear. Actually, some wonderful swirling flow generators achieve excellent thermal performance at the cost of sacrificing flow performance and energy conservation. This violates the primary intention of energy conservation and emission reduction. Therefore, this study designs several wire coil inserts with various shapes (square, circle, obverse or reverse trapezoidal, observe or reserve triangular, and hexagonal cross-section shapes) and different pitches (p=3–10.5 mm). Also, a numerical investigation on effects of these wire coil inserts on performances in mini-channels (a single mini-channel with 2×2 mm2 cross-section) at Reynolds number (Re) of 523–1120 is conducted. The results show that the square wire coil insert yields the best heat transfer and comprehensive thermal performance. This is attributed to the fact that wire coil inserts induce swirling flow, which promotes the separation and redevelopment of the flow and thermal boundary layers. Based on this, the effect of wire coil pitch is analyzed thoroughly. Increasing the pitch leads to an increasing first and then decreasing tendency in the comprehensive thermal performance. Overall, the mini-channel with a square wire coil insert at p=6 mm obtains the optimal comprehensive thermal performance factor (∼2.0) for Re = 1120. Moreover, it also presents an acceptable energy-saving performance. In addition, the comparison of this study and several other studies suggests that, square coil insert has great potential to improve comprehensive performance of mini-channel heat exchanger at higher Reynolds number.

Computational Framework Development for Heat Transfer Studies in Liquid Metal-Cooled Small-Scale Heat Sinks With Non-Circular Cross Sections

Abstract The present work provides a reliable computational framework to investigate the laminar and turbulent forced convection of sodium and sodium–potassium (Na, NaK) in small-scale heat sinks with hydraulic diameters between 1 mm and 5 mm. Na and NaK flow and heat transfer are studied numerically for a wide range of Reynolds numbers from 600 to 9000 in three sharp-cornered miniature heat sinks with rectangular, pentagonal, and hexagonal cross sections. For a fixed surface area to volume ratio, it is observed that the rectangular minichannel heat sink provides the highest convective heat transfer rates. The rectangular miniature heat sink is shown to provide 280% higher convective heat transfer rates in comparison with the pentagonal heat sink. Moreover, the obtained convective heat transfer coefficients for NaK are almost 20% higher than the ones for Na in the investigated pentagonal heat sink. For the same flow Peclet number in the rectangular and hexagonal heat sinks, both Na and NaK provide nearly identical average Nusselt numbers. However, NaK shows greater local and average Nusselt numbers compared to Na at the same Reynolds number.

Preparation and Immunofluorescence Staining of Bundles and Single Fiber Cells from the Cortex and Nucleus of the Eye Lens.

The lens is a transparent and ellipsoid organ in the anterior chamber of the eye that changes shape to finely focus light onto the retina to form a clear image. The bulk of this tissue comprises specialized, differentiated fiber cells that have a hexagonal cross section and extend from the anterior to the posterior poles of the lens. These long and skinny cells are tightly opposed to neighboring cells and have complex interdigitations along the length of the cell. The specialized interlocking structures are required for normal biomechanical properties of the lens and have been extensively described using electron microscopy techniques. This protocol demonstrates the first method to preserve and immunostain singular as well as bundles of mouse lens fiber cells to allow the detailed localization of proteins within these complexly shaped cells. The representative data show staining of the peripheral, differentiating, mature, and nuclear fiber cells across all regions of the lens. This method can potentially be used on fiber cells isolated from lenses of other species.

Cross-Wind Aeroelastic Effects of Tall Buildings with a Hexagonal Cross-Section

This research investigates the cross-wind aeroelastic effects of tall buildings with hexagonal cross-sections by using aeroelastic models with multiple-degree-of-freedom (MDOF). Cross-wind displacement and acceleration responses at the top of each model are measured using the wind tunnel test. The aerodynamic damping ratios for the two representative wind directions are identified by analyzing the measured responses using the random decrement technique. Results show that large-amplitude vortex-induced vibrations occur for one of the representative wind directions where the vertex of the hexagonal model is against the approaching wind, while there is no significant VIV observed for the other representative wind direction where the face of the hexagonal model is perpendicular to the approaching wind. The most dangerous wind direction is then identified based on the discussion. Two expressions for the cross-wind aerodynamic damping ratio are established for the two wind representative wind directions. The two equations can be used in engineering practice to estimate the cross-wind aerodynamic damping ratio of hexagonal tall buildings.

Flux-periodic oscillations in proximitized core–shell nanowires

Flux-periodic oscillations of the superconducting gap in proximitized core–shell nanowires are explored. Periodicity of oscillations in the energy spectrum of a cylindrical nanowire is compared with nanowires having hexagonal and square cross-section geometry, along with the effects of Zeeman and Rashba spin–orbit interaction. A transition between h/e and h/2e periodicity is found and shown to be dependent on the chemical potential, with correspondence to degeneracy points of the angular momentum quantum number. For a thin shell of a square nanowire, solely h/e periodicity is found in the infinite wire spectrum and shown to result from energy separation between the lowest groups of excited states.

Modified hexagonal pin fins for enhanced thermal-hydraulic performance of micro-pin fin heat sinks

PurposeThis numerical study aims to investigate the modification of the hexagonal pin fin geometry to enhance both the thermal and hydraulic performance of the copper micropin fin heat sink with single-phase water coolant in a laminar regime. The heat sink performance evaluation criteria have been investigated for the parametric effects of vertex angle θ (10–120) and relative length (RL) (0.25–9) of hexagonal pin fins.Design/methodology/approachTo carry out research and reduce the computational cost, only one heat sink unit is simulated and analyzed using periodic boundary conditions on the side walls and includes a hexagonal pin fin and half channel on both sides to reflect the structural characteristics completely. The governing equations are also solved using finite volume method.FindingsThe results reveal that θ = 60 and RL = 1 yield the optimum thermal performance and heat sink performance is significantly influenced by the vertex angle and RL. The modified hexagon geometry improves fluid flow behavior by reducing the volume of the recirculation region behind the pin fin, preventing its effects on the downstream pin fins and restricting the thermal boundary layer development on its straight side. At Re = 1,000, the modified geometry enhances the average Nusselt number by 24.46% and the thermal performance factor by 23.89%, demonstrating the potential of modified hexagonal pin fins to enhance micropin fin heat sink performance.Originality/valuePrior studies suggest using the pin fins with a regular hexagonal cross-section to obtain better thermal performance. However, this comes with a higher pressure drop penalty. The modification of the hexagonal pin fin geometry has been investigated in this numerical study to enhance both the thermal and hydraulic performance of the micropin fin heat sink. Because little attention has been paid to the modification of the regular hexagonal pin fins, as a geometry inspired by natural honeycomb structures, its design optimization is relatively scarce, and a gap was felt in this field.

Twin thickness-dependent tensile deformation mechanism on strengthening-softening of Si nanowires

Twin thickness-dependent deformation and the transition from strengthening to softening in twinned silicon nanowires are investigated using molecular dynamics simulations with cylindrical and hexagonal cross sections. The results show that the transition from strengthening to softening occurs at critical twin thicknesses of 8.1 nm (11.0 TB s) with cylindrical cross section and 11.0 nm (8 TBs) with hexagonal cross section with decreasing twin thickness, and that the strongest twin thickness originates from a transition in the initial plasticity mechanism from full dislocation nucleation and interaction with the TBs to partial dislocation nucleation and gliding parallel to the TBs. Moreover, it is found that the relationship between peak stress and twin thickness can be divided into two regions. Several full and partial dislocations are formed in the regions with strengthening twin thickness range. The accumulation and pile-up of these dislocations and their interaction with the TBs at high density cause the Hall-Petch strengthening behavior. In contrast, few full and partial dislocations are formed with softening twin thickness range. These dislocations are nucleated and propagate parallel to the TBs, resulting in TB migration that causes inverse Hall-Petch softening behavior. Our simulation results provide sufficient insight into the mechanical behavior of twinned silicon nanowires with cylindrical and hexagonal cross sections. The study will be helpful to the further understanding of CTB-related mechanical behaviors of non-metallic materials and non-metallic system.

A model for a set of porous fins on a long rotating cylinder considering thermal radiation and natural convection

This article proposes a method to estimate the heat transfer and temperature distribution from a porous fin placed on a constantly rotating long cylinder with a hexagonal cross section. Moreover, both radiation and natural convection are considered, as well as radiation interchange between the cylinder and the fin and among the porous fins themselves, giving rise to an Integro-Differential problem. Time-averaged thermal properties are employed since the proposed problem is periodic. The numerical simulation is validated by comparing three different numerical methods: Finite Difference Method (FDM), Finite Volumes Method (FVM), and Spectral Collocation Method with Chebyshev interpolation polynomials (CGL). The three methods demonstrated good agreement among themselves. They provided results according to the existing literature concerning heat transfer and temperature distribution on porous fins, such as showing that convection, as the convective parameter grows from 0 to 10, can quickly become the dominant mode of heat transfer instead of the radiation parameter, which ranged from 0 to 50. The impact on the temperature at the tip ranged from less than 4% to 18.9%, depending on the changes made to thermal and physical parameters under similar conditions. The dimensionless temperature stayed in the stipulated variation from 0 to 1.