Equal Diameter Research Articles

Natural convection heat transfer over horizontal annular elliptical finned tubes

A numerical simulation of natural convection heat transfer from annular elliptical finned tubes was conducted. A parametric study was also carried out to explain the effect of fin shape change from circular to elliptical on the flow field and heat transfer. It was shown that there was an optimum value for the fin aspect ratio (ratio of main diameters) in which heat flux was maximised. Finally, a correlation was proposed to calculate the Nu number for the elliptical fin. This correlation approached the circular fin correlation for the case of equal main diameters. Finally, the optimum aspect ratio was presented graphically.

Thermohydraulic analysis of hybrid nanofluid in a multilayered copper foam heat sink employing local thermal non-equilibrium condition: Optimization of layers thickness

In the present study, fluid flow and heat transfer characteristics of a heat sink partially fitted with multilayered porous medium are analyzed. The multilayered copper foam contains three different layers placed at the bottom wall of the heat sink exposing to a uniform heat flux. The whole occupied volume of the porous region is 60% of the channel. The main objective of the current study is to reveal a layout for the porous medium with optimum thickness for each layer in two proposed models to maximize the heat transfer and minimize the pressure drop. In the constant particle diameter model, all three layers have an equal particle diameter of 1.5 cm with three porosities of 0.95, 0.85 and 0.75 from bottom to top. In the constant porosity model, all three layers have an equal porosity of 0.95 with three particle diameters of 0.5, 1 and 1.5 cm from bottom to top. To trade-off between the desirable (heat transfer) and undesirable (pressure drop) outcomes, the dimensionless number of performance evaluation criterion (PEC) is determined. Darcy–Brinkman–Forchheimer and local thermal non-equilibrium (LTNE) models are applied to solve the governing equations in the porous region. The CFD numerical simulations are conducted to analyze the effect of each layer thickness of the multilayered porous medium in the two proposed models on the thermohydraulic parameters such as friction coefficient, Nusselt number and PEC number. At the optimum layouts of the porous medium, water-graphene nanoplatelet/platinum hybrid nanofluid is applied to enhance the thermal performance of the heat sink. The obtained results reveal that the highest PEC number is achieved in the constant porosity model equal to 1.17 at the case in which the lower, middle and upper metal foam layer thicknesses are 0.6, 1 and 0.2 cm, respectively, resulting in 145% heat transfer enhancement. In constant particle diameter model, the highest PEC number equals to 1.26 at the case in which the lower, middle and upper metal foam layer thicknesses are 1, 0.6 and 0.2 cm, respectively, resulting in 191% heat transfer augmentation compared with the plain channel. Further increase in PEC number is observed by adding nanoparticles to the base fluid for nanofluid volume concentration of 0.1% in constant porosity and particle diameter models which are equal to 1.22 and 1.31, respectively.

Experimental study of internal flow structures in cylindrical rotating detonation engines

The internal flow structures of detonation wave were experimentally analyzed in an optically accessible hollow rotating detonation combustor with multiple chamber lengths. The cylindrical RDC has a glass chamber wall, 20 mm in diameter, which allowed us to capture the combustion self-luminescence. A chamber 70 mm in length was first tested using C2H4O2 and H2–O2 as propellants. Images with a strong self-luminescence region near the bottom were obtained, confirming the small extent of the region where most of the heat release occurs as found in our previous research. Based on the visualization experiments, we tested RDCs with shorter chamber walls of 40 and 20 mm. The detonation wave was also observed in the shorter chambers, and its velocity was not affected by the difference in chamber length. Thrust performance was also maintained compared to the longer chamber, and the short cylindrical RDC had the same specific impulse tendency as the cylindrical (hollow) or annular 70-mm chamber RDC. Finally, we calculated the pressure distributions of various chamber lengths, and found they were also consistent with the measured pressure at the bottom and exit. We concluded that the short-chamber cylindrical RDC with equal length and diameter maintained thrust performance similar to the longer annular RDC, further expanding the potential of compact RDCs.

Effectiveness and Technical Considerations of Solitaire Platinum 4×40 mm Stent Retriever in Mechanical Thrombectomy with Solumbra Technique.

ObjectiveThe Solitaire Platinum 4×40 mm stent retriever contains radiopaque markers with a long length. We evaluated the effect of Solitaire Platinum 4×40 mm stent retriever in Solumbra technique thrombectomy, and compared it with shorter Solitaire stent retrievers. MethodsA total of 70 patients who underwent Solumbra technique thrombectomy with equal diameter (4 mm) and different length (40 vs. 20 mm) Solitaire stent retrievers were divided into two groups : the Solitaire Platinum 4×40 mm stent (4×40) group and the Solitaire FR 4×20 mm stent or Solitaire Platinum 4×20 mm stent (4×20) group. The clinical outcomes, Thrombolysis in Cerebral Infarction score, the first pass reperfusion status, and complications were evaluated and compared between the two groups. Multivariate analysis was performed to evaluate the predictive factors for reperfusion and complete reperfusion from the first pass. ResultsHigher first-pass reperfusion and complete reperfusion were achieved in the 4×40 group (68.0% and 48.0%) than in the 4×20 group (46.7% and 33.3%; p=0.004 and 0.007, respectively). In multivariate analysis, radiopaque device and longer stent retriever were correlated with first-pass reperfusion (p=0.014 and 0.008, respectively) and first-pass complete reperfusion (p=0.022 and 0.012, respectively). ConclusionOur study demonstrated the usefulness of the Solitaire Platinum 4×40 mm stent retriever, which led to higher first-pass reperfusion and complete reperfusion rates than the Solitaire FR 4×20 mm stent or the Solitaire Platinum 4×20 mm stent, especially in Solumbra technique thrombectomy.

Fatigue resistance of welded steel tubular X-joints

High-cycle fatigue experiments are performed on welded tubular steel X-joints, with braces and chord of equal diameter. They are scaled-down joints, used extensively in offshore wind platforms. Three different welding procedures are considered in specimen fabrication: manual, fully-automatic and manual with HFMI post-weld treatment. Τwo possible locations for crack initiation were identified: chord “crown” and “in-between location”, also verified by numerical calculations and fractography of failed specimens. Monotonic loading tests on fatigue-cracked specimens showed good performance in terms of ultimate strength and deformation capacity, despite the presence of through-thickness cracks. The results are compared with predictions from relevant design standards.

Fully Integrated Time-Gated 3D Fluorescence Imager for Deep Neural Imaging.

This paper presents a device for time-gated fluorescence imaging in the deep brain, consisting of two on-chip laser diodes and 512 single-photon avalanche diodes (SPADs). The edge-emitting laser diodes deliver fluorescence excitation above the SPAD array, parallel to the imager. In the time domain, laser diode illumination is pulsed and the SPAD is time-gated, allowing a fluorescence excitation rejection up to O.D. 3 at 1ns of time-gate delay. Each SPAD pixel is masked with Talbot gratings to enable the mapping of 2D array photon counts into a 3D image. The 3D image achieves a resolution of 40, 35, and 73μm in the x, y, and z directions, respectively, in a noiseless environment, with a maximum frame rate of 50 kilo-frames-per-second. We present measurement results of the spatial and temporal profiles of the dual-pulsed laser diode illumination and of the photon detection characteristics of the SPAD array. Finally, we show the imager's ability to resolve a glass micropipette filled with red fluorescent microspheres. The system's 420μm-wide cross section allows it to be inserted at arbitrary depths of the brain while achieving a field of view four times larger than fiber endoscopes of equal diameter.

Experimental Assessment of the Flow Resistance of Coastal Wooden Fences

Wooden fences are applied as a nature-based solution to support mangrove restoration along mangrove coasts in general and the Mekong Delta coast in particular. The simple structure uses vertical bamboo poles as a frame to store horizontal bamboo and tree branches (brushwood). Fence resistance is quantitatively determined by the drag coefficient exerted by the fence material on the flow; however, the behaviour of drag is predictable only when the arrangement of the cylinders is homogeneous. Therefore, for more arbitrary arrangements, the Darcy–Forchheimer equations need to be considered. In this study, the law of fluid flow was applied by forcing a constant flow of water through the fence material and measuring the loss of hydraulic pressure over a fence thickness. Fences, mainly using bamboo sticks, were installed with model-scale and full-scale diameters applying two main arrangements, inhomogeneous and staggered. Our empirical findings led to several conclusions. The bulk drag coefficient ( C D ¯ ) is influenced by the flow regime represented by Reynolds number. The drag coefficient decreases with the increase of the porosity, which strongly depends on fence arrangements. Finally, the Forchheimer coefficients can be linked to the drag coefficient through a related porosity parameter at high turbulent conditions. The staggered arrangement is well-predicted by the Ergun-relations for the Darcy–Forchheimer coefficients when an inhomogeneous arrangement with equal porosity and diameter leads to a large drag and flow resistance.

High Dispersive Electrostatic Mirrors of Rotational Symmetry with the Third Order Time-of-Flight Focusing by Energy

Expressions describing the time of flight of charged particles taking into account time-of-flight chromatic aberrations in electrostatic mirrors with rotational symmetry are presented. By numerical calculations, the conditions of time-of-flight focusing of particles by energy up to the third order inclusively in the three-electrode mirrors, the electrodes of which are coaxial cylinders of equal diameter, are determined. Various operating modes of such mirrors are considered: (1) spatial time-of-flight focusing in the Gaussian plane of the mirror; (2) spatial time-of-flight focusing in the focal plane of the mirror; (3) time-of-flight focusing in the telescopic mode; (4) time-of-flight focusing in the collimator mode. The results of calculations are presented as a function of two fundamental solutions to the equation of paraxial trajectories. One of these solutions describes trajectories whose direct and reverse branches coincide, and the second solution describes trajectories whose direct and reverse branches are symmetric with respect to the axis of symmetry of the field. It is shown that for all modes of operation the time-of-flight dispersion of the mirror by mass, determined on the basis of the second solution, is several times higher than that obtained on the basis of the first solution.

Enhanced photoelectrochemical properties of NiO nanoparticles-decorated TiO2 nanotube arrays for water splitting

Vertically oriented titanium dioxide nanotube arrays (TNTAs) decorated with NiO nanoparticles (NPs) were successfully fabricated using two-step electrochemical anodization. An ultrasound-assisted deposition method was used to homogeneously loading the NiO NPs into the TNTAs, resulting in a NiO/TNTAs junction electrode. X-ray diffraction reveals that the TNTAs and NiO/TNTAs showed anatase structures. Also, SEM images confirm that the nanotubes have a nominal length of 3.57 µm and approximately equal wall thickness and diameters; 55.51 nm and 17.64 nm, respectively. The NiO/TNTAs junction electrode exhibited high visible light photo-response that enhances the photoelectrochemical activity. Accordingly, the incident photon-to-current conversion efficiency of NiO/TNTAs was estimated to be 86.89% in comparison to the pure TNTAs whose efficiency was equal to 29.62%. In conclusion, the NiO/TNTAs junction fabricated by a simple, cost-effective, and applicable cell is a promising clean renewable source for the water-splitting applications.

Controllable fabrication of pico/femtoliter pipette sampling probes and visual sample volume determination

We propose a hydraulically assisted eddy-current etching method for the controllable fabrication of pico/femtoliter sampling probes with equal inner diameters along the length of the probe. The relative standard deviations of the outer and inner diameters (O.D. and I.D., respectively) of several 1.07-μm-I.D. sampling probe tips fabricated in a single batch using this method were 2.2% and 2.8%, respectively, and the average O.D./I.D. ratio of these probes was 1.17. The probe fabrication method has high reproducibility, and sharp tips are produced, which is advantageous for the transfer of ultra-small sample volumes. Further, the narrow, equal diameter, cylindrical inner bore allows the online, visual determination of the pipetted sample volume by utilizing a microscopic imaging system to measure the liquid length. This value is converted linearly to the pipetted volume, whose measurement error is on a sub-pixel level. Image-based sampling using the fabricated probes was achieved by connecting the probe to an electroosmotic pump, which allowed the controlled pipetting of pico/femtoliter samples. Because the pipette allows samples of the same volume to be measured accurately, the pipette was applied for the semiquantitative mass spectrometry analysis of the metabolites in individual epidermal cells sampled from different parts of Portulaca oleracea plants. The results show that different types of cells have distinct metabolite profiles. Further, the experiments showed that, in dopamine-rich leaves, the content of dopamine in the petioles is higher than that in the foliage. The probe fabrication strategy opens new avenues for the controllable pipetting of ultra-small volume samples and the realization of the visual pipetting of pico/femtoliter samples.

Experimental and Numerical Studies on Bearing Characteristics of Hexagonal-Section Composite Foundation Element

Hexagonal-section composite foundation is a new method of foundation reinforcement. The load–settlement characteristic and load-transfer mechanism play a critical role in the bearing capacity of pile composite foundation. The quantitative assessment of the hexagonal-section composite foundation element (Trilobal Pile for short) under vertical load was carried out through experimental and numerical studies. The variation rules and the influencing factors of stress and displacement of trilobal pile were compared and analyzed in ten model tests. And the numerical approach with trilobal pile (composite foundation) and equal diameter pile composite foundation were also conducted to simulate the loading process and the stress variation. The results show that the load–settlement curve of trilobal pile changed slowly and its ultimate bearing capacity was about 150 kN. Compared with the equal diameter pile, the ultimate bearing capacity of trilobal pile was increased by almost 275%, and the settlement was reduced by nearly 104.2%. The pile–soil stress ratio of trilobal pile was always greater than 1, and the maximum was about 7. And the axial force and lateral friction resistance of the trilobal pile changed abruptly at the variable cross section. The maximum axial force abrupt change rate of the trilobal pile was about 10%, and the abrupt change rate of the lateral frictional resistance of each test pile was about 65.2–82%. These results provide useful theoretical references for further development and optimization of the trilobal pile.

Improvement of the optical method for researching the contact stresses during the forging

Dobrov I. V., Semichev A. V. Improvement of the optical method for researching the contact stresses during the forging. Material working by pressure. 2020. № 1 (50). Р. 24-27.
 The analysis of the results of experimental resarch of contact normal stresses during the forging of a symmetrical workpiece under conditions of plane deformation performed by the tensometric method is carried out. It is shown that when comparing the combined graphs of the distribution of contact normal stresses along the symmetry axis of the workpiece, depending on the position of the considered section of the workpiece relative to the length (diameter) of the contact surface, presented in the technical literature, it is necessary to take into account the real change in the dimensions of the contact surface during forging of the initial workpiece with different degrees of deformation. An optical method for research of the distribution of contact normal stresses during forging under conditions of plane deformation of a symmetric workpiece made of a material with high plastic properties, which during forging, flows into holes of equal diameter, located along the axis of symmetry at an equal distance from each other in the diaphanous puncheon of new design. The results of experimental expand the physical understanding of the nature of the redistribution of normal contact stresses during forging and qualitatively coincide with the results of load cell measurements of normal contact stresses in real conditions presented in the scientific and technical literature.

Pressure loss and heat transfer characterisation of intersecting hole heat exchangers

Intersecting cooling holes allow very high density heat exchangers to be implemented in the cooling systems of gas turbine blades. The pressure loss and heat transfer characteristics caused by the highly turbulent flow at intersections are poorly understood. These are characterised experimentally and numerically for a single intersection of two equal diameter holes at 90∘ or 60∘/120∘ angles of intersection, 0%, 10%, 49% and 88% offset. Large variations in pressure loss occur for a given intersection geometry; dependent on the mass flow splits, and the level of offset. Pressure losses range from 4 to more than 30 inlet dynamic heads. This allows the flow distribution in an engine application to be tuned, allowing for manufacturing uncertainties. Heat transfer coefficient (HTC) distributions measured in single intersections are reported. These show clear enhancement associated with stripping the fluid boundary layer and mixing of the bulk flow. High local heat transfer gradients were observed at the intersections and circumferentially averaged Nusselt number enhancement of up to 5 found where the degree of pipe intersection is significant. The HTC distributions allow the required packing of hole intersections while controlling the pressure margin. The experimental data are replicated in CFD studies which show good agreement within experimental uncertainty. Thus more detailed numerical models can be relied on for a full range of intersection angles and offsets. Extending the modelling to include multiple linked intersections confirmed that data measured in single intersections are applicable to a matrix of multiply intersecting holes.

Study of the influence of cross section sizes of the rod shock system on the efficiency of shock pulse energy transfer to the deformation center

Using the finite element model of the shock system, the efficiency of the shock pulse energy transfer to the deformation zone under wave strain hardening is studied. It was established, that conducting research from the point of view of the efficiency of transferring the shock pulse energy to the deformation zone, and from the point of view of the design of the shock pulse generator, is advisable on shock systems in which the contacting ends of the striker and the waveguide have equal diameters. Studies showed that with ratios 1<L1/L2<10; 5<L1/d1<10, an increase in the fraction of the shock pulse energy transmitted to the deformation zone n exceeds 80% for the striker and waveguide with diameters of 30, 48, 60, 90 mm. According to the adopted optimization criteria, the geometrical dimensions of the striker and the waveguide are determined, which ensure the transfer of the largest amount of shock pulse energy to the deformation zone.

Mechanism of Continuous Melting and Secondary Contact Melting in Resistance Heating Metal Wire Additive Manufacturing.

Resistance heating metal wire materials additive manufacturing technology is of great significance for space environment maintenance and manufacturing. However, the continuous deposition process has a problem in which the metal melt is disconnected from the base metal. In order to study the difference between the second contact melting of the disconnected metal melt and the continuous melting of the metal wire as well as eliminate the problem of the uneven heat dissipation of the base metal deposition on the melting process of the metal wire, the physical test of melting the metal wire clamped by the equal diameter conductive nozzle was carried out from the aspects of temperature distribution, temperature change, melting time, dynamic resistance change, and the microstructure. The current, wire length, and diameter of the metal wire are used as variables. It was found that the dynamic resistance change of the wire can be matched with the melting state. During the solid-state temperature rise, due to the presence of the contact interface, the continuous melting and secondary contact melting of metal wires differ in dynamic resistance and the melting process. The continuous melting of the metal wire was caused by the overall resistance of the wire to generate heat and melt, and the temperature distribution is “bow-shaped”. In the second contact melting, the heat generated by the contact interface resistance was transferred to both ends of the metal wire to melt, and the temperature distribution is “inverted V”. The microstructure of the metal wire continuous melting and secondary contact melting solidification is similar. The continuous melting length of the metal wire is greater than the melting length of the secondary contact.

Net flow generation in closed-loop valveless pumping

Net flow generation in valveless pumping, met in many physiological applications and recently in micropumping devices, constitutes an open fluid dynamics issue due to the complex interaction between the fluid medium and the flexible walls of the pump. In the context of the present experimental work, the conditions of the net flow generation are examined in a closed-loop horizontal valveless pump, which consists of a rigid and an elastic tube of equal diameters and lengths, and a pincher that forces the liquid within the tube to oscillate at Reynolds and Womersley numbers up to 7800 and 48, respectively. Pinching off as well as at the mid-length of the pump flexible tube, net flow is generated at certain pinching frequencies for which details are presented based on simultaneous recording of the pressure at the two tube junctions, the flow rate and the displacement of the pincher. Pinching off the mid-length of the pump at low pinching frequencies, net flow rate is practically null due to the almost identical pressure waveforms at the tube junctions, which vary in phase with the pincher motion. However, close to the first natural frequency of the hydraulic loop, the reflection of the pressure waves at the tube junctions combined with their increased phase difference cause high axial pressure gradients, which when they increase simultaneously with the squeezing of the tube, net flow rate maximization occurs. Pinching at the flexible tube mid-length area, nonzero net flow rates can also be generated, the sign of which changes when the pincher mid-point crosses the tube mid-length without being nullified.

A simplified boundary condition method for conducting shock resistance analyses of ship piping systems

The shock resistance of ship piping systems is very difficult to study owing to the large scales of such systems, and the high level and variability of the impact loading involved. To address these issues, the present work establishes a numerical model of pipe systems based on multi-span beam bending moment theory. An analysis of the bending moments of different multi-span continuous beams under static loading demonstrates that the simplified model employing just five spans provides a bending moment for target equal diameter straight tube (EDST) segments that deviates from theoretical calculations by less than 1%. Moreover, the bending moments obtained by the five-span model for a target EDST segment deviate by only about 4% from corresponding results obtained by the finite element (FE) method under both uniformly distributed static loading and complex static loading. The proposed simplified five-span model is then employed to calculate the stress responses obtained at individual critical points in a complex piping system under impact loading. The results obtained deviate at most by less than 15% from corresponding results obtained from the FE method based on the overall piping system model. Moreover, the average deviation for all critical points considered was only 5.87%. The results show that the shock response obtained using the simplified five-span model is essentially equivalent to that of the complex model. The proposed simplified five-span method is thereby demonstrated to be reasonable for simplifying large-scale complex piping systems when conducting shock resistance research.

Correlation between multiple cerebral aneurysms and a rare type of segmental duplication of the middle cerebral artery

BackgroundConnection between the duplication of the middle cerebral artery (DMCA) and the presence of multiple aneurysms has been described in a small number of cases.Case presentationThe presence of a rare type of DMCA associated with cerebral aneurysms was diagnosed in 56 year old woman after a rupture of an aneurysm on the dorsal segment of the DMCA. .. The presence of equal diameters of branches of the DMCA and anterior cerebral artery (ACA) could be recorded as trifurcation of the carotid internal artery (ICA). However, due to the anastomosis of the DMCA branches in the area of the M2 segment, the recorded anatomical change represented a segmental duplication of MCA. Three aneurysms that were directly related to the segmental DMCA were diagnosed.ConclusionsAnatomical variation by type of segmental DMCA is a rare subtype of DMCA. The presence of multiple aneurysms associated with this type of anatomical variation in MCA indicates their high hemodynamic instability.

On the fatigue improvement of railways superstructure components due to cold expansion – Part I: Experimental analysis

The fatigue strength improvement of materials and structures has always been the subject of studies, as a consequence of the rapid development of technologies and strictive safety requirements. In the railway field the fatigue resistance problem is thoroughly studied due to high transportation safety standard. Fatigue cracking is a major issue, in particular at rail-end-bolt holes. Cold Expansion is a common technique to induce beneficial residual compressive stresses around the holes, with the aim to improve the fatigue life of the rail. This paper is the first of a two part-series dealing with the study of the residual stress-strain field induced by the cold expansion process around rail-end-bolt holes. In Part I of this series, a contribution to better understanding the whole strain field distribution arising around rail-end-bolt holes during and after cold expansion is presented. Strains were experimentally measured using both electrical strain gauges and 2D-Digital Image Correlation. Contrary to common literature, strain-time history during the entire cold expansion process was investigated, in order to capture the highly non-linear elasto-plastic response of the material; the results of this study has been used in Part II of this series for the validation of the finite element model described there. The cold expansion process was applied to three rail holes, having equal nominal diameter. At first, the experimental results concerning each expanded hole are analysed. Then, all the results are compared, in order to evaluate the repeatability: - of the measurements; - of the Cold Expansion process; - of the adopted experimental technique, and, above all, to extrapolate the distribution of the hoop and radial residual strains as a function of the distance from the hole edge. At the end, results obtained by strain gauges and 2D-Digital Image Correlation are compared: a good agreement is found on the central flat surface of the rail web, which guarantees the availability of a robust and valuable highly non-linear reference result that has been used for the validation of the finite element model presented in Part II of this series.

Application of Improved Single‐Hole Superposition Theory in Nonequal Cross‐Section Tunnel Intersection

With the excavation towards the intersecting tunnels’ direction, the impact on the surrounding rock stress between the two tunnels will gradually decrease, but how it decreased is not clear. At present, engineers often directly superimpose the stress in the triangular area of the crossing tunnel when calculating the stress in this area (single‐hole superposition theory). The theory is also used as the main theory to consider the surrounding rock stress for support which is difficult to explain the situation of nonuniform cross‐section centers not in the same plane. The safety level of support is mainly determined by construction experience which is unable to determine how to adjust the support level with the increase in the horizontal distance of intersecting tunnel, causing the insufficient utilization of materials. This paper derives theoretically the stress calculation of the triangular area of circular cross tunnels with different cross sections and analyzes the surrounding rock stress law of the intersecting tunnels triangular area from different cross‐section dimensions (the difference in diameter between the two tunnels is twice, 3 times, and 4 times) and different intersection angles. And the results show that, compared with the case of equal tunnel diameters, the stress influence area of the surrounding rock in the triangle area mainly expands to the side of the small section with the increase of the cross‐section difference of the intersecting tunnels; the dangerous area of the surrounding rock in the triangle area moves vertically to the small section; the safest condition is the two tunnels with 90° intersecting angle. The theoretical calculation model of this paper is verified by the previous research results.