Triangular Cross-sectional Shape Research Articles

Effect of nanocavity geometry on nanoscale nucleate boiling heat transfer

In recent years, surfaces with nanocavities have been identified to considerably improve boiling heat transfer, that is highly promising for advanced thermal energy systems. To boost developments in nanostructured boiling surfaces, effects of nanocavity geometry on nucleate boiling at the nanoscale are systematically studied for the first time by utilizing molecular dynamics simulation. Three typical nanocavities with rectangular, semicircular, and triangular cross-sectional shapes are constructed, which have the identical width and depth (8 nm and 4 nm). Moreover, three representative wetting conditions corresponding to different solid-liquid interaction strengths are further considered to provide a comprehensive understanding of geometry effects. The results manifest that nanocavity geometry effect on nucleate boiling can be attributed to the differences in their solid-liquid contact area and solid-liquid interactions play a vital role in reinforcement effectiveness. When the solid-liquid interaction is sufficiently strong (energy coefficient equals 1.5, termed ultra-superhydrophilicity), variations in nanocavity geometries will induce remarkable effects on boiling performance. Among three geometric configurations, the rectangular nanocavity exhibits the highest heat transfer efficiency and achieves maximum boiling enhancement, including significant improvements in bubble nucleation and growth, as well as critical heat flux. This study provides an essential insight into nanoscale boiling reinforcement mechanism.

Investigation into the Effects of Cross-Sectional Shape and Size on the Light-Extraction Efficiency of GaN-Based Blue Nanorod Light-Emitting Diode Structures

We investigated the effect of cross-sectional shape and size on the light-extraction efficiency (LEE) of GaN-based blue nanorod light-emitting diode (LED) structures using numerical simulations based on finite-difference time-domain methods. For accurate determination, the LEE and far-field pattern (FFP) were evaluated by averaging them over emission spectra, polarization, and source positions inside the nanorod. The LEE decreased as rod size increased, owing to the nanorods’ increased ratio of cross-sectional area to sidewall area. We compared circular, square, triangular, and hexagonal cross-sectional shapes in this study. To date, nanorod LEDs with circular cross sections have been mainly demonstrated experimentally. However, circular shapes were found to show the lowest LEE, which is attributed to the coupling with whispering-gallery modes. For the total emission of the nanorod, the triangular cross section exhibited the highest LEE. When the angular dependence of the LEE was calculated using the FFP simulation results, the triangular and hexagonal shapes showed relatively high LEEs for direction emission. The simulation results presented in this study are expected to be useful in designing high-efficiency nanorod LED structures with optimum nanorod shape and dimensions.

Enhanced tensile performance of ultra-high-performance alkali-activated concrete using surface roughened steel fibers

To improve the mechanical performance of ultra-high-performance alkali-activated concrete (UHP-AAC), the surface of steel fiber was modified using an electrolyte solution containing ethylenediaminetetraacetic acid (EDTA). The longer the steel fiber was exposed to the EDTA-electrolyte solution, the more the longitudinal peeling of the steel fiber surface was induced and the surface roughness increased. By exposing the specimens to the solution for up to 6 h, the highest fiber bond strength (11.96 MPa) and a maximum tensile strength of UHP-AAC (14.7 MPa) were obtained. The mechanical properties of UHP-AAC were also investigated using conventional long straight and twisted steel fibers. The increase in bond strength due to the triangular cross-sectional shape and untwisting torque of the twisted fiber had an overall positive effect on the mechanical properties of UHP-AAC. However, the best tensile performance of UHP-AAC, in terms of tensile strength and energy absorption capacity, was obtained when the straight steel fibers surface-refined by the EDTA-electrolyte solution for 6 h were adopted. Based on the Pearson correlation coefficient, the Weibull distribution was applied as a crack width prediction model. The results showed that the median microcrack widths formed in UHP-AAC were marginally influenced by the surface treatment using EDTA-electrolyte solution. However, the longer straight and twisted steel fibers produced wider microcracks than their counterparts. The greatly increased tensile strain capacity of UHP-AAC by using the surface-refined steel fibers was thus caused by the formation of more microcracks rather than the increase in the microcrack width.

OPTIMIZATION OF HEAT CONDUCTION FOR TREELIKE NETWORK WITH ARBITRARY CROSS-SECTIONAL SHAPE

To minimize the thermal resistance of the fractal treelike heat conduction network and develop an optimization principle applicable for the network with an arbitrary cross-sectional shape, this paper first establishes a theoretical model regarding the total thermal resistance of the symmetric treelike network with arbitrary cross-sectional shapes and then studies the effects of the geometric and structural parameters of the network on its total thermal resistance. The numerical simulations are also performed to analyze the influences of the geometric and structural parameters of symmetric treelike networks with circular, rectangular and triangular cross-sectional shapes on the total thermal resistance. Both the theoretical model and the numerical simulation show that the total thermal resistance of the network with an arbitrary cross-sectional shape first decreases and then increases with increasing cross-sectional area ratio but always increases with increasing length ratio of branches at two successive branching levels when the total branch volume is constant. When the cross-sectional area ratio is equal to the reciprocal of the branching number, the treelike network has the minimum total thermal resistance. This scaling law is applicable for the treelike network with an arbitrary cross-sectional shape to achieve the minimum total thermal resistance.

The aerodynamics of flying snake airfoils in tandem configuration.

Flying snakes flatten their body to form a roughly triangular cross-sectional shape, enabling lift production and horizontal acceleration. While gliding, they also assume an S-shaped posture, which could promote aerodynamic interactions between the fore and the aft body. Such interactions have been studied experimentally; however, very coarse models of the snake's cross-sectional shape were used, and the effects were measured only for the downstream model. In this study, the aerodynamic interactions resulting from the snake's posture were approximated using two-dimensional anatomically accurate airfoils positioned in tandem to mimic the snake's geometry during flight. Load cells were used to measure the lift and drag forces, and flow field data were obtained using digital particle image velocimetry (DPIV). The results showed a strong dependence of the aerodynamic performance on the tandem arrangement, with the lift coefficients being generally more influenced than the drag coefficients. Flow field data revealed that the tandem arrangement modified the separated flow and the wake size, and enhanced the lift in cases in which the wake vortices formed closer to the models, producing suction on the dorsal surface. The downforce created by the flow separation from the ventral surface of the models at 0deg angle of attack was another significant factor contributing to lift production. A number of cases showing large variations of aerodynamic performance included configurations close to the most probable posture of airborne flying snakes, suggesting that small postural variations could be used to control the glide trajectory.

Mitigating the Effect of Nanoscale Porosity on Thermoelectric Power Factor of Si

The addition of porosity to thermoelectric materials can significantly increase the figure of merit, ZT, by reducing the thermal conductivity. Unfortunately, porosity is also detrimental to the thermoelectric power factor in the numerator of the figure of merit ZT. In this manuscript we derive strategies to recoup electrical performance in nanoporous Si by fine tuning the carrier concentration and through judicious design of the pore size and shape so as to provide energy selective electron filtering. In this study, we considered phosphorus doped silicon containing discrete pores that are either spheres, cylinders, cubes, or triangular prisms. The effects from these pores are compared with those from extended pores with circular, square and triangular cross sectional shape, and infinite length perpendicular to the electrical current. A semiclassical Boltzmann transport equation is used to model Si thermoelectric power factor. This model reveals three key results: The largest enhancement in Seebeck coefficient occurs with cubic pores. The fractional improvement is about 15% at low carrier concentration ($< 10^{20}\ \mathrm{1/cm^3}$) up to 60% at high carrier population with characteristic length around $\sim 1\ \mathrm{nm}$. To obtain the best energy filtering effect at room temperature, nanoporous Si needs to be doped to higher carrier concentration than is optimal for bulk Si. Finally, in $n$-type Si thermoelectrics the electron filtering effect that can be generated with nanoscale porosity is significantly lower than the ideal filtering effect; nevertheless, the enhancement in the Seebeck coefficient that can be obtained is large enough to offset the reduction in electrical conductivity caused by porosity.

A Study on the Deformation Behavior of a Microstructure Depending on Its Shape and the Cutting Section in the Precision Cutting of a Functional Part

The shape accuracy of microstructures is an important factor that directly affects the quality and performance of products. Nevertheless, it is difficult to find a study for the shape accuracy of microstructures below several microns. This study aimed to reduce the shape error in the precision machining of microstructures with a repeated triangular cross-sectional shape with a width of 5 µm or less. Two important factors in this study were the morphological features of the microstructure to be fabricated and the cross-sectional shape of the chip. The tool path was modified in consideration of these two factors. Before the tool path change, the shape error due to the deformation of the triangular micropattern in a DOC (depth of a cut) of 1 µm was about 0.39 µm. However, after the tool path was modified, the shape error due to deformation did not occur while maintaining the DOC at 1 µm.

Gas sensing properties of silicon nanowires with different cross-sectional shapes toward ammonia: a first-principles study

Nanostructure-based sensors working based on the adsorption-desorption mechanism received much attention in a wide variety of applications as a way to achieve both ultrasensitive sensing and small dimensions. In this paper, the adsorption of ammonia molecule on silicon nanowire surface with square, circular, and triangular cross-sectional shapes, which has almost similar cross-sectional area (1.2 nm2), is studied. The effects of various adsorption configurations are considered on the sensing properties, utilizing first-principles ab initio density functional theory calculations. Structural properties such as bond lengths and bond angles are obtained along with electronic properties such as band structure, charge transfer, and projected density of states for several adsorption configurations. The most stable and most sensitive structure is calculated to be the triangular nanowire considering formation enthalpy as a stability factor. For this nanowire, adsorption energy, covalent bond length, and charge transfer between ammonia and nanowire are calculated to be 1.296 eV, 3.124 A, and 0.227 |e|, respectively. We also consider nanowires with fully hydrogen-passivated surface and nanowires with a dangling bond. It has been shown that nanowires with a dangling bond are more sensitive toward ammonia than fully passivated nanowires.

Analiza protočnosti kanala različitih oblika poprečnih presjeka i obloženosti

U ovome radu prikazane su hidrauličke analize protočnosti pod utjecajem različitih oblika poprečnih presjeka i vrste obloženosti kanala. Prilikom analize različitih oblika poprečnih presjeka izrađen je hidraulički proračun za jednoliko stacionarno tečenje za trokutni, pravokutni, trapezni i polukružni oblik poprečnog presjeka kanala. Prvom provedenom hidrauličkom analizom uspostavilo se da je, u pogledu protočnosti kanala, najpovoljniji polukružni oblik poprečnog presjeka kanala. U drugoj hidrauličkoj analizi promatrane su različite vrste obloženosti stijenki kanala te se u tu svrhu također proveo hidraulički proračun za jednoliko stacionarno tečenje u kojem su promatrane različite obloge kanala, odnosno koeficijenta hrapavosti na protočnost. Provedena analiza pokazala je kako veći koeficijenti hrapavosti daju manju protočnost u kanalu i obrnuto. Samim time, prilikom dimenzioniranja kanala, odnosno hidrauličkog proračuna, potrebno je uzeti u obzir odgovarajući poprečni presjek kanala te vrstu obloženosti kanala kako bi dimenzionirani kanal bio najpovoljniji u pogledu što manjih hidrauličkih gubitaka i što veće propusne moći.

Moisture Sorption and Desorption in Epoxy Composites Reinforced with Triangular and V-Shaped Bars: Determination of Diffusion Coefficient and Effect of Varied Factors

Sorption and desorption of moisture in epoxy composites reinforced with triangular and V-shaped bar fillers were studied. Epoxy was reinforced with vinyl ester bar assemblies fabricated according to 4 varied factors: bar orientation relative to diffusion direction (pointed or base side), bar alignment (parallel or staggered), spacing between bars (1 or 5 mm), and bar cross-sectional shape (triangular or V-shaped). Unlike previous studies, the bar fillers were initially coated with small amount of epoxy resin to improve wetting during fabrication of composites. Moisture uptake and loss of composites during one-side exposure to water vapor (50% relative humidity at 60°C) and hot air (60°C), respectively, were monitored with time. Experimental results show weight change of composites during moisture sorption and desorption varies linearly with square root of exposure time. Diffusion coefficients of composites were determined by assuming the material to be semi-infinite and fitting a mathematical solution to Fick’s second law of diffusion to weight change data. Results show diffusion coefficient of composites during moisture sorption is increased when bars are oriented pointed relative to diffusion direction, aligned parallel, spaced at 1 mm, and has triangular cross-sectional shape. However, during desorption, the diffusion coefficient is increased when base side of bars are exposed and when the bars are aligned staggered. The observed effects of factors on moisture diffusion coefficients of epoxy composites during sorption and desorption are discussed in relation to path length, available diffusion area, and status of epoxy/vinyl ester interphase before and after moisture sorption in composites.

Fabrication of an Anisotropic Superhydrophobic Polymer Surface Using Compression Molding and Dip Coating

Many studies of anisotropic wetting surfaces with directional structures inspired from rice leaves, bamboo leaves, and butterfly wings have been carried out because of their unique liquid shape control and transportation. In this study, a precision mechanical cutting process, ultra-precision machining using a single crystal diamond tool, was used to fabricate a mold with microscale directional patterns of triangular cross-sectional shape for good moldability, and the patterns were duplicated on a flat thermoplastic polymer plate by compression molding for the mass production of an anisotropic wetting polymer surface. Anisotropic wetting was observed only with microscale patterns, but the sliding of water could not be achieved because of the pinning effect of the micro-structure. Therefore, an additional dip coating process with 1H, 1H, 2H, 2H-perfluorodecythricholosilanes, and TiO2 nanoparticles was applied for a small sliding angle with nanoscale patterns and a low surface energy. The anisotropic superhydrophobic surface was fabricated and the surface morphology and anisotropic wetting behaviors were investigated. The suggested fabrication method can be used to mass produce an anisotropic superhydrophobic polymer surface, demonstrating the feasibility of liquid shape control and transportation.

Analysis of cross-sectional shapes of borehole

The studies are known to indicate the effect of the shape of a bore-hole cross-section on the results of the explosion including elliptical, square, triangular cross-sectional shapes as well as bore-holes with stress raisers applied to their side surfaces. The parameters of the indicated shapes can affect not only the process of crushing by explosion, but also the design of the drilling tool. Therefore, it is necessary to carry out generalization of the parameters of the cross-sectional shapes, and the article proposes criteria for estimating the shapes of the cross-section of a cavity completely filled with an elongated charge of an explosive. The criteria are considered from the point of view of the effectiveness of the explosive impact on the rock and can be used to create and justify the design of the drilling tool. The analysis is made of the geometric shapes of the cross sections of the explosion cavity using examples of biangular, triangular, and quadri-angular shapes. The specific value of the criteria can be determined for the existing designs of the drilling tool. The interrelations of the considered criteria are shown.

Solidity effect on crashworthiness characteristics of thin-walled tubes having various cross-sectional shapes

ABSTRACTIn this paper, effects of solidity and cross-sectional shape on crashworthiness characteristics of thin-walled tubes under dynamic axial impact load are examined. For this purpose, explicit finite element analyses are conducted for tubes having triangular, square, circular, hexagonal, octagonal and multi-cell cross-sectional shapes. The FE model is validated with analytical and experimental results that were reported in literature. It is found that FE solutions agree well with analytical and experimental results presented in the literature. To compare the tubes having different geometric dimensions and shapes on the same ground, the tubes are selected such that they have the same mass and length, and the striker mass and velocity are identical for all tubes as well. By changing solidity of tubes between 0.05 and 0.25, the cross-sectional dimensions of tubes are specified. The crushing force efficiency, crushing strain, total efficiency, structural efficiency and dynamic energy absorbing effectiveness parameters are calculated for various tubes as a function of the solidity parameter. It is concluded that crashworthiness performance of thin-walled tubes is significantly influenced by the solidity and cross-sectional shape. Results about the most effective solidity values and cross-sectional shapes are presented.

Band Structure Effects in Extremely Scaled Silicon Nanowire MOSFETs With Different Cross Section Shapes

A multiscale simulation package based on ab initio calculation is used to study the band structure effects in extremely scaled gate-all-around silicon nanowire (SNW) MOSFETs with different cross-sectional shapes. All the interactions are computed directly from ab initio method without semiempirical parameters, and the effects of crystal atom relaxations and boundary atom dangling bond saturations are included intrinsically. The tight-binding Hamiltonian is obtained from ab initio results with maximally localized Wannier functions. The device performances are obtained with nonequilibrium Green’s function method. With this simulation flow, the band structure and its impacts on the device performance of SNWs with different cross-sectional shapes are studied. Simulation results show that the crystal relaxation has notable effects on the band structure with different cross-sectional shapes and sizes. The SNWs with triangular cross-sectional shape are very competitive due to a smaller average conductivity effective mass ascribed to the valley splitting at extremely scaled size.

The effect of hybridization and geometry of polypropylene fibers on engineered cementitious composites reinforced by polyvinyl alcohol fibers

In the present study, the hybridization effect of polypropylene (PP) with polyvinyl alcohol (PVA) fibers in engineered cementitious composites (ECCs) was investigated. For this purpose, PVA reinforcing fiber was partially replaced by PP fibers with different circular, triangular, and trilobal cross-sectional shapes. The flexural behaviors of the ECCs containing hybrid fibers including first-crack strength, post-crack strength, and toughness were studied under three-point bending test. It was found that hybridization with nonround cross-sectional shape PP fibers had positive effect on the ductility but decreased the flexural strength of resultant ECCs. The greater reduction in toughness and post-peak strength was observed for composite containing circular PP fibers. The results indicated that partially replacement of PVA fibers with nonround cross-sectional shape PP fibers can be considered to be promising method to reduce the costs of ECC production along with attaining improved deformability.

Short-Channel Structured Reactor as a Catalytic Afterburner

Short-channel structures of triangular and sinusoidal channel cross-sectional shape were examined experimentally to find their heat (or mass) transfer and flow friction (flow resistance) characteristics. A particular emphasis was placed on influence of the channels length (referred to its hydraulic diameter) on transport and hydrodynamic characteristics. The transport and friction properties were correlated in terms of dimensionless channel length with satisfactory accuracy. The dimensionless channel length was proved to be a key factor that determines the transport and friction coefficients. Comparison with ceramic monolith has shown possibility of using the structures in automotive catalytic converters.

Effects of corner angle of trapezoidal and triangular channel cross-sections on electrical performance of silicon nanowire field-effect transistors with semi gate-around structure

Structural effects, especially corner angle of upper-corners of trapezoidal and rectangular, and triangular cross-sectional shapes of silicon nanowire field-effect transistors on effective carrier mobility and normalized inversion charge density have been investigated. 〈100〉-directed silicon nanowire field-effect transistors with semi-gate around structure fabricated on (100)-oriented silicon-on-insulator wafers were evaluated. As the upper-corner angle decreased from obtuse to acute angle, we observed an increased amount of inversion charge using split-CV measurement. On the other hand, the effective carrier mobility dependence on the upper-corner angle seems to have an optimized point near 100° at 296K. Although normalized inversion charge density was the largest with acute angles, effective carrier mobility with acute upper-corner angle was severely degraded. Considering the intrinsic delay time of SiNW FET, SiNW FETs with trapezoidal cross-section with upper-corner angle of 100° is more suitable in this work to achieve high electrical performance. We believe these findings could represent guidelines for the design of high-performance SiNW FETs.

Short-channel structured reactor: Experiments versus previous theoretical design

The study deals with the so-called short-channel structures (very short monoliths) that were introduced by Kołodziej and Łojewska [1] on the theoretical basis. The structures are very short so the entrance (mixing) section occupies majority of the channel length. This leads to highly enhanced heat and mass transfer, but the flow resistance is increased as well. The article presents experimental results of flow resistance, heat and mass transfer for short-channel structures of sine and triangular cross-sectional channel shape. The results presented in terms of dimensionless quantities confirmed theoretical consideration presented in [1]. The efficiencies of the structure have been derived that show the structures as more efficient when compared to classic monoliths or packed bed reactors.

Uncombable Hair Syndrome

A 4-year-old boy was noted to have unruly, spangled hair, which could not be combed flat. His mother reported that his hair had always had that texture and that it seemed to grow slowly. A hair pull test demonstrated that hairs could not be easily extracted, and light microscopic examination of the hair revealed pathognomonic characteristics of uncombable hair syndrome, including a triangular cross-sectional shape and canal-like longitudinal depressions.

Effect of Geometry on the Melting Rates of Iron Rods Burning in High Pressure Oxygen

Abstract The effect of sample geometry on the melting rates of burning iron rods was assessed. Promoted-ignition tests were conducted with rods having cylindrical, rectangular, and triangular cross-sectional shapes over a range of cross-sectional areas. The regression rate of the melting interface (RRMI) was assessed using a statistical approach which enabled the quantification of confidence levels for the observed differences in RRMI. Statistically significant differences in RRMI were observed for rods with the same cross-sectional area but different cross-sectional shape. The magnitude of the proportional difference in RRMI increased with the cross-sectional area. Triangular rods had the highest RRMI, followed by rectangular rods, and then cylindrical rods. The dependence of RRMI on rod shape is shown to relate to the action of molten metal at corners. The corners of the rectangular and triangular rods melted faster than the faces due to their locally higher surface area to volume ratios. This phenomenon altered the attachment geometry between liquid and solid phases, increasing the surface area available for heat transfer, causing faster melting. Findings relating to the application of standard flammability test results in industrial situations are also presented.