Straight Walls Research Articles

Numerical assessment of hydrodynamic and mixing characteristics for mixed electroosmotic and pressure-driven flow through a wavy microchannel with patchwise surface heterogeneity

The micromixing of two fluids plays a vital role in lab-on-a-chip devices. For obtaining better mixing efficiency, we propose a micromixer using patchwise surface potential heterogeneity and wavy wall. We numerically investigate the hydrodynamic and mixing characteristics for flow through a microchannel with a straight top wall and wavy bottom wall. The primary flow is actuated by an external pressure-gradient and patches are placed at the top wall with positive zeta potential, such that the reversed electroosmotic actuation forms the recirculation zones close to the top wall. The streamlines, flow velocity, recirculation zone velocity, species concentration, flow rate, and mixing efficiency are investigated by varying the relative pressure-gradient strength, Debye parameter, zeta potential and wavy surface amplitude. Two different configurations are considered by placing the patches at the top wall, opposite to the peaks and valleys of the bottom wavy surface, respectively. It reveals that the recirculation zone velocity increases with the increase in both Debye parameter and surface amplitude, whereas it decreases with relative pressure-gradient strength near the patch surfaces. The flow rate decreases with the increase in zeta potential and we also identify the values of zeta potential for chocking of flow in the microchannel. It reveals that the mixing efficiency monotonically increases with surface amplitude, and the variation with zeta potential is non-monotonic. We also identify the range of zeta potential for which the value of mixing efficiency is higher than 90% for different configurations of the channel.

Effect of interlayer temperature on microstructure evolution and mechanical performance of wire arc additive manufactured 300M steel

The 300M steel straight wall parts (SWPs) are fabricated by wire arc additive manufacturing based on cold metal transfer technology. The effects of interlayer temperature on microstructure evolution and mechanical performance in the different regions of the SWPs are investigated. The results show that the surface waviness of the SWP first decreases and then increases with the increase of interlayer temperature, and the lowest surface waviness is controlled in 0.47 mm at the interlayer temperature of 200 °C. In the top region, the microstructure mainly consists of untempered martensite and slightly changes with the increase of interlayer temperature. In the middle and bottom regions, the microstructure is mainly composed of tempered martensite as the interlayer temperature is 100 or 200 °C. However, when the interlayer temperature is increased above 400 °C, the needle-like bainite and feather-like bainite are gradually formed due to the slow cooling rate and long dwell time in the bainite transformation zone. The microhardness and ultimate tensile strength in the top region are significantly higher than those in the middle and bottom regions, which are attributed to the enhanced solid solution strengthening effect of untempered martensite. The tensile fracture morphology is transformed from the quasi-cleavage fracture mode to the ductile mode with the increase of interlayer temperature or the decrease of distance from the substrate.

Non-Newtonian nanofluid natural convective heat transfer in an inclined Half-annulus porous enclosure using FEM

In this paper, by means of the finite element method, the MHD free convection flow of non-Newtonian nanoliquid inside a halved annulus enclosure considering a constant heat flux is being applied to the straight walls has been analyzed. The enclosure is loaded with water and nanoparticles of alumina (Al2O3) the combination of these tows produces a liquid that shows shear-thinning behavior. The governing parameters of this study are the Rayleigh number (103 ≤ Ra ≤ 106), inclination angle (0 ≤ α ≤ 90), power-law index (0.6 ≤ n ≤ 1) and Hartmann number (0 ≤ Ha ≤ 100). The outcomes indicate that the inclination angle of the cavity and the Hartmann number can be considered as effective control parameters at different Rayleigh numbers. While the magnetic field is applied the velocity field retarded and hence convection heat transfer and the Nusselt number diminished, and the increment of power-law index prompts the heat transfer to drop. It is shown that the power-law index and Hartmann reduces the local Nusselt number. Also, the average Bejan numbers corresponding of active parameters are discussed in this study.

Mixing sensitivity to the inclination of the lateral walls in a T-mixer

One of the simplest geometries for micro-mixers has a T-shape, i.e., the two inlets join perpendicularly the mixing channel. The cross-sections of the channels are usually square/rectangular, as straight walls facilitate experimental and modeling analysis. On the contrary, this work investigates through Computational Fluid Dynamics the effect of a cross-section with lateral walls inclined of an angle α as such an inclination may stem from different microfabrication techniques. Considering water as operating fluid, the same mixing performance as square/rectangular cross-sections is obtained for inclinations α≤3°; this indicates the maximum admissible error on the perpendicularity of the walls in the manufacturing process. Above this value, the presence of inclined walls delays the onset of the engulfment regime at higher Reynolds numbers, and for α≥23°the mixing is hampered dramatically, as the flow is unable to break the mirror symmetry and enter in the engulfment regime. At low Reynolds numbers, the mixing is moderately improved for α≥10°, because the vortex regime presents a lower degree of symmetry than that of T-mixers with straight walls.

Study of hydraulic resistance of tangential swirlers

This article presents the results of experimental research and simulation of the hydraulic drag of tangential swirlers. Three types of swirler devices made with straight, profiled, and circular channel walls were studied within a wide range of design and process parameters. Simulation modelling on the Comsol Multiphysics platform was used to calculate hydraulic drag and determine the velocity and pressure fields. This allowed obtaining a dependence of the hydraulic drag coefficient of the investigated swirlers and identifying parameters affecting their hydraulic drag.

Study on turbulent flow in wave wall tube heat exchanger

The traditional straight wall tube heat exchanger has low heat exchange efficiency, in order to solve this problem, the turbulent flow in wave wall tube heat exchanger was studied by numerical simulation. It is found that the unique corrugated structure of the heat exchange tube in the wave wall tube heat exchanger can improve the flow state of the fluid in the heat exchanger. The average pressure drop of heat exchanger gradually increases with the increase of Reynolds number Re. Under the same conditions, the average pressure drop of wave wall tube heat exchanger is lower than that of straight wall tube heat exchanger. The improvement of heat exchange performance of heat exchanger can not be realized only by increasing the inlet flow of heat exchanger. The wave wall tube heat exchanger can strengthen the heat exchange of the fluid in the heat exchanger.

Numerical research of a new vortex double wall cooling configuration for gas turbine blade leading edge

In order to explore new cooling methods to further improve the cooling performance for the gas turbine blade leading edge, a vortex double wall cooling configuration is established and studied. The numerical simulation was conducted after grid independence validation and turbulence model validation. Four groups of different combined cooling methods, different disturbing objects, different rows of bridge holes and the existence of film holes were studied in detail. Results showed that the vortex double wall cooling method could improve the cooling performance by more than 3 times than the basic straight passage double wall cooling. And compared to impingement double wall cooling, the vortex double wall cooling has better cooling behavior with larger inner surface Nusselt number and globally-averaged Nusselt number. Different disturbing objects on the outer surface could improve the local heat transfer performance without affecting the overall cooling performance, and protrusions are found to be a good kind of disturbing objects. When rows of bridge holes increase to 3, its thermal performance factor is 23.6% higher than case with 1 bridge hole row. It is regarded that increasing bridge hole rows could bring considerable cooling improvements. For the condition with film holes, it is found the overall flow and heat transfer performance is 6.2% higher than case without film holes. Generally, the vortex double wall cooling method proves to be a potential cooling method for the leading edge, and the configuration with protrusions and more rows of bridge holes could further improve its cooling behavior.

Cochlear Implant Electrode Tip Fold-Over: Our Experience With Long and Flexible Electrode.

The aim of this study was to retrospectively investigate if there is any incidence of electrode tip fold-over with 31.5 mm long and flexible lateral wall electrodes implanted in two high-volume Cochlear Implant (CI) centers in Germany. In addition, a detailed literature review was performed to capture all the peer-reviewed publications reporting on tip fold-over with CI electrodes from different CI brands for comparison. Post-operative X-ray images of FLEX SOFT electrode from MED-EL in Stenver's view were retrospectively investigated for the presence of electrode tip fold-over from 378 consecutive cases in two high-volume CI centers in Germany. All patients were implanted between 2010 and 2018 by three individual experienced CI surgeons using round window and extended round window approach for CI electrode insertion. A literature review was performed following a thorough PubMed (https://www.ncbi.nlm.nih.gov/pubmed/) search using the keywords "cochlear implant electrode tip fold-over" or "cochlear implant electrode tip roll-over" to capture articles that were published until December 2020 in English language only. Articles selection was based on electrode-related issues investigated only in-patient cases applying imaging modality. Those studies investigated tip fold-over in cadaveric temporal bones and cases with inner-ear malformation excluded. No single case of tip fold-over was clinically detected from the retrospective investigation of post-operative X-ray images from 378 consecutive cases. The electrode angular insertion depth as measured applying the cochlear coordinate system, varied from a minimum of 560° to a maximum of 720°. The literature review on the tip fold-over issue resulted in 24 peer-reviewed published articles in total. Tip fold-over with pre-curved modiolar-hugging electrodes was reported in 85 cases out of 1,606 implantations making an incidence rate of 5.3%. With the straight lateral wall electrodes, the tip fold-over was reported in four cases out of 398 implantations making an incidence rate of 1%, not including the number of implantations reported in the current study. Otherwise it would be 0.5%. Electrode tip fold-over with 31.5 mm long flexible lateral wall electrodes is highly exceptional and this can be generalized to any of the straight lateral wall electrodes from any CI brand. The literature review on tip fold-over revealed an incidence rate of 5.3% with pre-curved or modiolar-hugging electrodes and 1% with straight lateral wall electrodes from CI brands. Including this series of 0% tip fold-over, the incidence rate of electrode tip fold-over with LW electrode type would be 0.5%.

Correlation Between Cochlear Length, Insertion Angle, and Tonotopic Mismatch for MED-EL FLEX28 Electrode Arrays.

To investigate the relationship between cochlear length, insertion angle, and tonotopic mismatch and to compare the tonotopic mismatches with respect to the spiral ganglion and the organ of Corti. Retrospective. Tertiary referral center with cochlear implant program. Analyses of patients' computed tomography images after cochlear implant surgery. Cochlear implantation with 28-mm-long straight lateral wall electrode arrays. Cochlear length, insertion angle, and insertion depth were assessed using the OTOPLAN software. Tonotopic mismatch for each electrode contact was estimated using the Greenwood (organ of Corti) and the Stakhovskaya (spiral ganglion) maps and compared. 106 cochleae were analyzed. 99% of the electrode arrays were located in the tympanic ramp. The insertion was complete in 96% of cases. The mean cochlear length was 34.5 mm and the mean insertion angle of the apical electrode was 545°. Cochlear length was negatively correlated with the insertion angle of the contacts E1 to E9 (all p < 0.004). The tonotopic mismatch was greater at the organ of Corti than at the spiral ganglion. It was also greater at the organ of Corti in larger cochleae (correlation with mismatch for E1 r = 0.421, p < 0.0001) and in the apical than in the middle and basal regions of the cochlea. Small cochlea size corresponded to higher insertion angle and reduction of tonotopic mismatch on a 28-mm-long straight lateral wall electrode array. Tonotopic mismatch could be minimized preoperatively by choosing electrode arrays according to the individual cochlear morphology and postoperatively by appropriate frequency fitting.

Comparative morphoanatomical studies of south eastern Nigerian representatives of Oldenlandia L. (Rubiaceae)

Leaf and stem anatomical structure of the four Oldenlandia L. (O. affinis (Roem. &amp; Schult.) DC., O. corymbosa L., O. herbacea (Linn.) Roxb., and O. lancifolia (Schumach) DC.) from some parts viz. Ogbokor (Edo State), Obiga-Asa (Abia State), IITA staion Onne (Rivers State), and Agricultural farm Uniport (Rivers State) Nigeria were examined by light microscopy. The epidermal cells are pentagonal to polygonal with straight, curved or wavy anticlinal walls, and paracytic stomata. All the species have dorsiventral leaf with the leaf vein vascular bundles embedded in the spongy mesophyll. The midribs vascular bundles form an arc enclosed by parenchymatous endodermal cells. O. herabcea is amphistomatic while the other species are hypostomatic. Raphide bundles were seen only in the lamina of O. corymbosa. Tuft hair is absent in O. herbacea but occurred on the adaxial leaf surfaces of O. affinis, O. corymbosa, and O. diffusa. The stem of O. diffusa is terete while other species have quadrangular stem. Papillae occurred on the adaxial epidermis of O. affinis and O. corymbosa. The stem pith thickness (PT)/cortical thickness (ET) ratio varied among the species. Notable diagnostic features in these species include the PT/ET ratio, layers of cortex in the stem, occurrence of tuft hairs on the leaf veins and surface, presence or absence of raphides and papillose, layer of abaxial and adaxial cortex in the midrib, and amphistomatatic or hypostomatic leaf.

Numerical investigation of mixing performance in spiral micromixers based on Dean flows and chaotic advection

In this work, we propose three innovative spiral micromixers viz., a simple spiral (SS) micromixer, SE micromixer designed by modifying the center part of the spiral one with straight walls, and RS micromixer designed by modifying the whole spiral part with straight walls. Numerical investigations are performed to analyze the strength of Dean vortices and chaotic advection, the mixing and pressure drop characteristics in the micromixers for Reynolds number (Re) in the range of 0.1 to 100 and for different depth and width of the mixers. It reveals that at Re=0.1, all the micromixers show almost similar mixing index and for 0.1<Re≤10 the mixing index decreases with Re. Further increasing Re beyond 10, the mixing index increases due to the formation of Dean vortices and chaotic advection. In SE and RS micromixers, 24% and 25% more mixing are obtained respectively than that of SS micromixer. The maximum pressure drop is observed in RS micromixer followed by SE and SS micromixers. The mixing performance representing the combined mixing index and pressure drop is maximum for SE micromixer among all three micromixers. The effect of change in width in altering the mixing index is more than that of the depth.

Application of the Saint‐Venant theory to thin‐walled sections warping

AbstractThe Saint‐Venant theory proposes an exact solution to the elastic equations for beams including warping strains due to shear force and torsion. It has been at the centre of recent developments in the field of beam theory: normal stress may at first be determined as if plane sections would remain plane but under torsion and shear force, restrain warping introduces secondary normal stress.For thin‐walled sections, the analysis of warping due to torsion is conventional and uses the concept of sectorial area. However, the problem of shear flows due to shear force is generally solved by using an energy approach in which warping only appears indirectly. By introducing a static moment function, similar to the sectorial function used for torsion, this paper proposes to take explicit account of the warping of thin‐walled sections under the effect of shear force. In the case of sections with straight walls, it is convenient to use third degree polynomials. The proposed method can easily be calculated with a spreadsheet and may be extended to any type of arch, in particular those which consist of B‐spline functions or NURBS.Different examples are analyzed.

Increasing Boiling Fluid Flowing Efficiency from Motive Nozzles of Two-Phase Ejectors

The article contains the possibility of increasing boiling fluid flowing efficiency from expanding channels. This process takes place in the motive flow nozzle of a liquid-vapor ejector, working on the principle of thermal stream compression. Efficiency increasing by profiling the diffuser part of the nozzle. Modern industry uses nozzles, which are like de Laval nozzles, with straight walls of the diffusers. The authors suggest paying closer attention to profiling these nozzles, which might increase their efficiency and improve their gas-dynamic characteristics. For comparison, we choose a channel of a traditional form (with straight walls of the diffuser) and a channel of parabolic shape. The article contains a mathematical model to calculate the process of flowing the boiling fluid from the authors-designed channels – the peculiarities of this model that appear after changing the geometry of its streaming part. We obtain comparative analysis calculation results based on the mathematical model and the Ansys CFX workflow model. As a result of numerical calculation using the authors mathematical model and modelling in the Ansys CFX software package, it concludes that the parabolic shape of the diffuser is the most favourable. In the boiling process, the liquid central core is boiling at the optimum distance from the nozzle throat, and the flow of a stable vapor structure with the required pressure value for each regime forming at the outlet.

Deformation Failure and Support Test of Surrounding Rock in Deep Arched Roadway with Straight Wall

The deformation and failure of the uphill roadway on the 3rd horizontal track in the No. 6 Mine of Pingdingshan Coal Group was taken as the engineering background. The similar simulation material of the roadway surrounding rock with quartz sand as the aggregate, cement as the cementing agent, and gypsum powder as the regulator was selected. Through mechanical tests on 25 sets of specimens with different proportions, the best proportion of similar simulated materials for simulating the deformation and failure of the surrounding rock of the roadway was obtained. Later, a large-scale deep mine roadway simulation test system independently developed by the company was used to carry out the roadway deformation and failure test. First, load the test body to the set initial stress state, and then carry out the full-face excavation and unloading of the roadway; finally, load it in the vertical direction until the roadway wall is damaged. It can realize the actual effect of simulation of roadway deformation and failure under the path of “high stress + internal unloading + stress adjustment.” The results showed that after the deep roadway is excavated with preload and high stress, the surrounding rock deformation, failure, and instability of the roadway mainly experience 3 periods: the first period is the period of uniform deformation of the roadway surrounding rock, the second period is the development period of the roadway surrounding rock slab structure, and the third period is the period of instability of the roadway surrounding rock slab structure. Combined with the time period of deformation and failure of the surrounding rock of the roadway, the damage scope of the surrounding rock and the actual situation of the site engineering. A step-by-step combined roadway repair and support plan of “bolt mesh + shotcrete + full-face hollow grouting anchor cable” with hollow grouting anchor cable as the core was determined. The stability of the repaired roadway has been significantly improved, ensuring the long-term use of the roadway.

Microstructure and Mechanical Properties of Additively Manufactured Ni-Al Bronze Parts Using Cold Metal Transfer Process

In this paper, the microstructure and mechanical properties of the SG-CuAl8Ni6 Ni-Al bronze straight wall were studied, which was fabricated by the cold metal transfer (CMT) arc additive manufacturing technology. This Ni-Al bronze cladding layer of SG-CuAl8Ni6 is composed mainly of α-Cu, residual β phase, rich Pb phase and κ phase. The microstructure of this multilayer single-channel Ni-Al bronze straight wall circulating presents the overall periodic law, which changes from fine cellular crystals, columnar crystals to dendritic crystals with the increase of the distance from the substrate. The Vickers hardness value of the Ni-Al bronze straight wall decreases with the distance of substrate are between 155 and 185 HV0.5. The microhardness and elastic modulus of the Ni-Al bronze specimen are 1.57 times and 1.99 times higher than these of the brass matrix, respectively. The ultimate tensile strength (UTS) of the straight wall in the welding direction and 45° downward-sloping is greater than that of about 550 MPa in the stacking direction, and the elongation value in the welding direction is the highest. With the increase in interlayer temperature, the grain size increased gradually, and the tensile strength decreases slightly.

Toolpath Planning and Generation for Multi-Stage Incremental Forming Based on Stretching Angle.

To solve the problems that exist in the multi-stage forming of the straight wall parts, such as the sheet fracture, uneven thickness distribution, and the stepped feature sinking, a new forming toolpath planning and generation method for the multi-stage incremental forming was proposed based on the stretching angle. In this method, the parallel planes that were used for forming toolpath generation were constructed by using the stretching angle so that the distances between the parallel planes and the forming angles were gradually reduced. This makes the sheet material flow become changed and the thickness thinning is relieved. The software system for the toolpath generation was developed by using C++, VC++, and OpenGL library. In order to verify the feasibility of the proposed method, numerical simulation and forming experiments were carried out for the single stage forming, the traditional multi-stage forming, and multi-stage forming based on the proposed forming toolpath, using 1060 aluminum sheets. The comparative analysis of the thickness distribution, profile curve, strain curve, and sheet material flow shows that the proposed method is feasible, and the profile dimension accuracy is better, the thickness distribution is more uniform, and the sinking and bulging are significantly reduced. The formed sheet part with the stretching angle of 15° has higher dimensional accuracy, smaller bottom subsidence, and larger thickness than that of the stretching angle 5°.

Macroscopic and Mesoscopic Characteristics of a Small-Span Metro Tunnel in the Development of a Disaster Under Load

A similarity model with a volumetric similarity ratio of 1:100 and a granular flow model for the tunnel were designed. By comparing macroscopic and mesoscopic information (such as fracture process, strain evolution, stress transfer, crack propagation, and stress distribution) of the tunnel models under load, the failure mechanism of the metro tunnel under load was investigated. The result showed that: 1) under the loading path, the instability area of the tunnel is mainly distributed in the straight wall on both sides. When the load is 1.5 MPa, a large number of cracks on both sides of the straight wall run through, resulting in the initial failure of the rock mass; 2) the surface rock mass of arch bottom is under tensile stress and the deep rock mass is under pressure stress, therefore, the fracture does not develop continuously. The surface of straight wall produces continuous development crack under the action of tensile stress; 3) the arch bottom first responds during the stress redistribution of the small-span tunnel; the top and middle parts of the side walls of the running tunnel with greatest potential for damage respond most; 4) in the process of stress redistribution, the peak stress of the deep measuring points of the straight wall is greater than that of the free surface; 5) at the initial stage of loading, tensile cracks account for a high proportion of all cracks found. When the load is 1.5 MPa, the proportion of shear cracks increases to 28%, and when the load is 1.6 Mpa, the proportion of shear cracks increases to 31%. Finally, the tensile-shear effect triggers the failure of the tunnel.

Effect of Alloying Powders on Microstructure and Mechanical Properties of Aluminum Alloy Arc Additive Manufacturing.

Cold metal transfer arc additive manufacturing technique was used to produce 5356 aluminum alloy by adding refining agents to solve the problems of coarse grains and poor performance. Metallic powders (Ti, TiH, and Ti+B4C) were used to refine the grain size and promote the mechanical properties of the alloy. The effects of refining agents on the microstructure and mechanical properties of straight wall samples (SWSs) were studied. Samples with Ti+B4C addition had a profound impact on morphology. However, the TiH added sample revealed uneven transition between sediment layers, unstable precipitation process, unstable wall height and wall width, poor morphology, and defects. All SWSs with powder addition revealed the formation of the Al3Ti phase. Moreover, the columnar grains between the layers were transformed into equiaxed grains and finer grains at the center of the layers. There was a significant effect of TiH on the grain refinement. The samples with Ti demonstrated superior mechanical properties. The tensile strength and elongation of the SWSs increased by 28 MPa and 4.6% in the parallel additive direction and by 37 MPa and 8.9% in the vertical direction. The addition of Ti also contributed to the even distribution of the mechanical properties in both directions.

Behavior of Curved Double Steel-Concrete Composite Shear Walls Under Cyclic Loading

In this study, effects of different curved structures on mechanical behavior of curved double steel-concrete composite shear (SC) walls under cyclic loading were investigated numerically. Firstly, the experimental results of a straight SC wall under cyclic loading were used to validate numerical result. After then, curved SC walls were designed in ABAQUS according to different radius-thickness (R/t) ratios (5,10,15,20,25,30,40). In numerical studies, in-plane monotonic response, cycling response, and out-of-plane monotonic response were investigated by changing the loading. The results showed that among all parameters, the R/t ratio:5 has better seismic performance by 11.87% than straight SC wall under cyclic loading. In addition, it was found that when the ratio of the radius of curvature to the section thickness values were greater than 10, curved SC walls behaved as straight SC walls. When the R/t ratio was bigger than 10, the ultimate load and damage of wall load dropped consistently. According to in-plane monotonic response results, R/t ratio:5 has a 13.6% better peak force than straight wall when it is compared with other R/t ratio values. Calculated results showed that although there is no effect in bearing capacity when R/t ≥ 10, it increased by 35.4% when R/t is 5.

Taxonomic studies of two trifoliate legumes of high economic importance in Ebonyi State, South-eastern Nigeria

Taxonomic studies of Sphenostylis stenocarpa and Centrosema pubescens based macro-morphology and foliar epidermises were carried out to determine their similarities and differences. The taxa are of high economic values as they are used as food and medicine in Nigeria. Standard methods were used to carry out the studies as qualitative and quantitative macromorphological characters of the taxa were obtained by visual observation and measuring with metre rule while foliar epidermal study followed standard methods previously used by other researchers. The taxa studied have trifoliate leaf type with leaf and leaflet arrangement alternate and opposite respectively. From the foliar epidermises, Sphenostylis stenocarpa possesses paracytic stomata on the abaxial surface and anisocytic stomata on the adaxial. The abaxial surface of Centrosema pubescens possesses anomocytic and paracytic stomata and anomocytic stomata on the adaxial surface. Cell shapes of the foliar epidermal surfaces are irregular with undulate anticlinal wall patterns except on the adaxial surface of Sphenostylis stenocarpa with pentagonal cell shape and straight anticlinal wall. The two taxa are similar in their leaf type and arrangement but differ greatly in their stomatal types.