Oval Cross Section Research Articles

A case study on effect of twisting technique on heat transfer characteristics in a twisted oval helical tube

Efficient transfer of energy is an important issue addressed by numerous scholars in the literature and various methods have been proposed for enhancing the heat transfer efficiency in heat exchangers. Among many different heat exchangers, helical tubes are one of the most prevalent types of heat exchangers which have many applications in industry. In a case study, effect of twisting technique on the heat transfer in a helical tube with oval cross section has been investigated numerically and the results have been compared with simple circular cross section helical tube. Effect of cross section aspect ratio and twisting ratio in different flow Reynolds numbers has been considered. Results have been presented in terms of Nusselt number, friction factor, PEC, entropy generation and contours of velocity, streamlines and temperature. Results indicate that twisting technique can significantly enhance the heat transfer and all cases have PEC values of above unit which indicates superiority of this method. Also the velocity contours and streamlines indicate that using twisting technique result in higher mixing in the flow which is the reason for higher heat transfer characteristics in twisted oval helical tubes.

Вплив форми дозвукової частини надзвукового вхідного пристрою на коефіцієнт збереження повного тиску

The subject of this study is the total pressure conservation coefficient. The object of this study is the channel of the subsonic part of a supersonic input device of rectangular and oval shape, equivalent in size. The purpose of this study is to study the shape of the subsonic part of a supersonic external compression input device. To achieve this purpose, the following tasks were solved: modeling the flow in the subsonic part of a supersonic inlet external compression input device of rectangular and oval shape; calculation of the total pressure conservation coefficient in the subsonic part of the rectangular and oval supersonic inlet external compression input device. When studying the shape of the subsonic part of the supersonic inlet external compression device, the method of numerical experiment was used. The studies were conducted at an estimated altitude of 12 km and an estimated Mach number M = 2.5. The influence of the fuselage on the operation of the input device was not considered. To study the influence of the cross-sectional shape of the studied subsonic parts of the inlet device, the coefficient of conservation of total pressure in 7 cross sections along the length of the inlet device was calculated. To obtain the initial data for modeling the flow in a subsonic channel, an analytical calculation of the flow parameters in the supersonic part of the input device was performed. The results of flow modeling showed that the total pressure conservation coefficient of the subsonic part of the studied inlet devices when operating at an altitude of 12 km was 0.982 in the subsonic part of the supersonic inlet device with oval sections and 0.993 in the subsonic part of the supersonic inlet device with rectangular sections. The resulting visualization of streamlines in the studied channels demonstrates the presence of a paired vortex formed in the initial section of the channel with oval cross-sections, which leads to significant losses in total pressure. The scientific novelty and practical significance of this study lie in the fact that new data were obtained regarding the comparison of the total pressure conservation coefficient for equivalent subsonic parts of a supersonic oval and rectangular inlet device. Recommendations on the rational form of the subsonic part of the supersonic inlet external compression device were obtained.

Osteology of the derived Therizinosaur Nothronychus with evidence for convergence in dinosaurian evolution

Abstract Therizinosaurs were a taxon of unusual theropods from North America and Asia. The derived therizinosaur Nothronychus graffami possessed a synsacrum and hip convergent with extant birds. The osteology is figured and described in detail supplemented with material from Nothronychus mckinleyi. Both species exhibit traits convergent with extant birds, ornithischian dinosaurs, and titanosaurs. As preserved, the ilia and sacrum are minimally distorted and apomorphically modified into a synsacrum. The pubes are modified into a mesopubic condition, wherein the pubes are partially retroverted. The femoral shaft has an oval cross-section. As these characters are absent from the basal therizinosaur Falcarius utahensis, they evolved more than once within the maniraptoran lineage. An herbivorous ecology is supported. Both specimens were skeletally mature, based on fusion of the neural spines and scapulocoracoid.

Aerodynamic Characteristics of Circular and Noncircular Cross-Sectional Missile Configurations

This paper summarizes an investigation of the aerodynamic performance of missile configurations with axisymmetric and nonaxisymmetric cross sections. Configurations have either a circular, oval, pentagonal, triangular, or square cross section and were tested at three different flight conditions: Ma=1.17 and Reynolds number per inch of 3.88×105, Ma=2.49 and Reynolds number per inch of 6.88×105, and Ma=4.33 and Reynolds number per inch of 8.74×105. The influence of Mach number, shape, and fin deflection was investigated. A prescribed body motion was used to expedite the prediction of the missile aerodynamic forces and moments at different angles of attack compared to many static computational fluid dynamics simulations. The results show that the oval missile model is the most aerodynamically efficient body at all the tested speeds. At higher speeds, all nonstandard configurations produce more normal force and better aerodynamic efficiency than the circular body. The triangular configuration is much less stable than the other models.

Full-Endoscopic Technique for Posterior Fossa Decompression in Chiari Malformation.

Full-endoscopic techniques are well-described for spinal procedures. Although endoscopic-assisted techniques are reported for posterior fossa decompression (PFD) in Chiari malformation (CM), a full-endoscopic technique is yet to be reported in these patients. The aim of this study was to present and describe a full-endoscopic technique for PFD in patients with CM. Two patients diagnosed with CM were operated on by the full-endoscopic PFD technique. The patients consented to the procedure and to the publication of their image. An endoscope with an oval shaft cross-section with a diameter of 9.3 mm, a working length of 177 mm, a viewing angle of 20°, and a working channel of 5.6 diameters were used. Operative videos were recorded. The surgical steps were easily applied after the clear anatomic landmarks, such as the C1 posterior tubercle and the rectus capitis posterior minor muscles. The patients were followed up for 6 months. Both patients were symptom-free with a significant decrease in Visual Analog Scale score and a good functional outcome assessed by Chicago Chiari Outcome Scale after surgery without any complications. All the steps of the full-endoscopic technique for PFD described by the authors in their previous human cadaveric study were also feasible on patients with CM.

Effects of bipolar plate flow channel configuration on thermal-electric performance of direct ammonia solid oxide fuel cell: Part I - Numerical study of channel section geometry

Direct ammonia SOFCs (DA-SOFCs) are numerical studied to investigate the effects of bipolar plate flow channel configuration on thermal-electric performance. This study establishes a planar DA-SOFC model and investigates triangular, quadrangular, and oval flow channel configurations’ impact using numerical simulations. Results reveal oval cross-section channels outperform trapezoidal and triangular ones, achieving power density increases of 15.6%, 16.1%, and 18.6%, respectively, compared to rectangular channels at 0.6V. The oval channel displays superior velocity and vorticity, enhancing mass transfer between the main flow and reaction zone. Increasing channel width reduces rib width, promoting O2 distribution, temperature improvement via exothermic reactions, NH3 decomposition into H2, and improved cell performance. Rib width increase shortens diffusion and reduces concentration polarization, but increases ion transport and ohmic polarization. A theoretical formula for optimal rib width (Wrib0) to minimize polarization loss is provided. These findings offer a comprehensive reference for optimizing DA-SOFC design.

A novel oval-shaped coaxial ground heat exchanger for augmenting the performance of ground-coupled heat pumps: Transient heat transfer performance and multi-parameter optimization

Ground-coupled heat pumps (GCHP) are highly impactful and promising systems for extracting geothermal energy. Nevertheless, the effectiveness of GCHP can be further improved by reshaping and optimizing the configuration of the coaxial ground heat exchanger (CGHE), which represents the core component of the GCHP and has a significant influence on the heat extraction performance of the system. This paper introduces a detailed comparative numerical study on a novel CGHE with an oval cross-section for enhancing the performance of the GCHP. The proposed design's simplicity stems from altering the outer tube to an oval shape, compared to the commercially used circular CGHE. The conjugate fluid flow and heat transfer are simulated utilizing a three-dimensional numerical model. Heat flux, GHE thermal resistance, and pressure drop within the tube are computed and analyzed. A comparison between circle and oval cross-sections is carried out. The adopted 3-D model shows a fit verification with their experimental pairs via a field experiment. Parametric study and sensitivity analysis are performed, and the effect of groundwater flow on heat transfer is also examined. An optimization approach is developed to explore the optimal inner tube position and incorporate multi-inner tubes that attain the maximum heat transfer efficiency of the oval-CGHE. The results reveal that oval-CGHE significantly surpasses the conventional circle-CGHE, improving the maximum and average heat transfer by 21.03% and 10.24%, corresponding to a reduction in thermal resistance by 28.83% and 9.06%, respectively. Additionally, optimizing the inner tube position and incorporating multi-inner tubes further enhances the performance of oval-CGHE by maximum and average heat transfer rates of 33.01% and 22.91% for inner tube position optimization and 39.08% and 28.84% for multi-inner tube optimization, respectively.

Buckling analysis of laminated composite elliptical shells using the spline finite strip procedure

According to the first order shear deformation plate assumption, current paper numerically investigates the buckling problem of cylindrical shells with oval cross-section under simply supported boundary condition subjecting to uniform and non-uniform loads via spline finite strip method. Equilibrium governing equations are generated based upon the virtual work's principle. Shell displacement function is assumed to be as dual development of degree 3 spline functions and Lagrange polynomial functions. The analysis method used at any time with any type of loading can calculate deformation and buckling. The step-by-step critical load is calculated using the determinant of the stiffness matrix. In the present paper, it is supposed that the applied linear elastic materials consist of isotropic and non-isotropic materials. Numerical studies are performed to indicate the effects of shell geometry, materials, and layered materials on the buckling load. For the validation purpose, the results of current research are compared with those of previous researches and ABAQUS software.

Evaluasi Efisensi Riser Untuk Bentuk Riser Samping yang Berbeda Menggunakan Metode Simulasi Casting

As the solidification reaches the hot spot area, no molten metal remains and shrinkage is formed. To anticipate the shrinkage, a riser is added to the casting system. An optimal riser design would produce free shrinkage components. One of the factors that affect riser efficiency is the riser shape. This study aims to find the most efficient side riser shape by using simulation software. The riser shape of tubes, tubes with a half sphere on top, hemispheres, conical tubes, tubes with an oval cross-section, and cubes are used in this experiment, with the volume of all risers kept constant. The most efficient shape of the riser is the tube. The tube riser produces a larger modulus. The tube riser generated directional solidification. The same pattern can be seen in the niyama criteria and solidification temperature, where the tube riser has a more continuous pattern compared to other riser shapes.

Incidence and contributing factors of non-root canal treated teeth with chronic fatigue root fracture: A cross-sectional study

Chronic fatigue root fracture describes a root fracture in a non-root canal treated (non-RCT) tooth. This study aimed to report the incidence and contributing factors of non-RCT teeth with chronic fatigue root fracture in a Taiwanese population. This cross-sectional study included teeth extracted at Taipei Veterans General Hospital in Taiwan between 2018 and 2019. The reasons for extractions were recorded and included vertical and horizontal root fractures (VRF and HRF). Comparisons of clinical factors between teeth with fatigue VRF and teeth with fatigue HRF were performed by chi-square or Fisher exact test, where appropriate. Of the 4207 extracted teeth examined, 263 (6.25%) had tooth fracture. Thirty-two non-RCT teeth had chronic fatigue root fracture, including 16 with VRF and 16 with HRF. The incidence was 0.76% (32/4207). The occurrence of chronic fatigue root fracture was higher in males (83.9%). The mean age of the 31 patients with chronic fatigue root fracture was 71.7±13.1 years. More than half of these teeth had intact crowns with severe attrition. The fatigue VRF occurred more frequently in molars (P=0.003), in roots with a long oval cross-section (P=0.037), and in terminal teeth (P=0.013) than the fatigue HRF. The incidence of chronic fatigue root fracture is 0.76%. Both VRF and HRF occur mainly in aged males, in posterior teeth with attrition, and in teeth without restoration. Tooth position, cross-section root morphology, and terminal tooth are contributing factors related to chronic fatigue root fracture.

Exact solution of a geometrically nonlinear problem for a long three-layer cylindrical panel of oval section

A statement is given and an exact solution of a geometrically nonlinear problem is given for a long open three-layer cylindrical shell of an oval cross-section susceptible to transverse shear under the action of a uniform surface load. The main equations are written according to the geometrically nonlinear theory of smooth shells in the quadratic approximation, in which Tymoshenko's hypotheses hold for the entire package of shell layers. The solution of the problem is obtained in a parametric form with the value of the tangential force as a parameter. For a shell with hinged longitudinal edges, the exact values of the components of the stress-strain state were obtained, the limit values of the generalized geometric parameter were determined, and a system of equations for finding the critical load was constructed. As partial cases, the obtained solution yields the corresponding results for the Kirchhoff–Leav model, the shell of a circular cross-section, and the single-layer shell. The obtained results can be a reference for approximate and numerical methods.

Normal reference values for magnetic resonance imaging measurements of the fetal internal jugular veins in middle and late pregnancy

BackgroundAt present, there is a lack of normal magnetic resonance imaging (MRI) morphometric reference values for fetal internal jugular veins during middle and late pregnancy.ObjectiveWe used MRI to assess the morphology and cross-sectional area of the internal jugular veins of fetuses during middle and late pregnancy and to explore the clinical value of these parameters.Materials and methodsThe MRI images of 126 fetuses in middle and late pregnancy were retrospectively analysed to determine the optimal sequence for imaging the internal jugular veins. Morphological observation of the fetal internal jugular veins in each gestational week was carried out, lumen cross-sectional area was measured and the relationship between these data and gestational age was analysed.ResultsThe balanced steady-state free precession sequence was superior to other MRI sequences used for fetal imaging. The cross section of fetal internal jugular veins was predominantly circular in both the middle and late stages of pregnancy, however the prevalence of an oval cross section was significantly higher in the late gestational age group. The cross-sectional area of the lumen of the fetal internal jugular veins increased with increasing gestational age. Fetal jugular vein asymmetry was common, with the right jugular vein being dominant in the high gestational age group.ConclusionWe provide normal reference values for fetal internal jugular veins measured by MRI. These values may form the basis for clinical assessment of abnormal dilation or stenosis.

Numerical analysis of a heat exchanger with curved segmental baffle and Cassini oval cross-section tubes in various bundle arrangements

Numerical analysis of a heat exchanger with curved segmental baffle and Cassini oval cross-section tubes in various bundle arrangements

Full-endoscopic technique for posterior fossa decompression in Chiari malformation type I: An anatomical feasibility study in human cadavers.

Although endoscope-assisted techniques have been described, a full-endoscopic approach is yet to be performed for posterior fossa decompression (PFD) in Chiari malformation type I (CM-I). This study aims to describe the full-endoscopic PFD technique and evaluate its feasibility. Five fresh-frozen anonymized adult human cadavers were operated on using an endoscope with an oval shaft cross-section with a diameter of 9.3 mm, a working length of 177 mm, and a viewing angle of 20°. It also had an eccentric working channel with a diameter of 5.6 mm, a light guide, a sheath for continuous irrigation, and a rod lens system. The instruments were introduced from the working channel. Posterior craniocervical structures were dissected, and PFD was achieved. The planned steps were performed in all five cadavers. The endoscope was introduced to the posterior craniocervical region, dissecting the structures to easily expose the suboccipital bone and C1 posterior arch. Important structures, such as the C1 posterior tubercle, rectus capitis posterior minor muscles, and posterior atlantooccipital membrane, were used as landmarks. PFD was feasible even with the dural opening. Using the full-endoscopic approach, posterior craniocervical structures can be reached, and PFD can be performed successfully. The instruments used are well-defined for spinal usage; thus, this full-endoscopic technique can be widely used in the surgical treatment of patients with CM-I.

Heat Transfer in a Rotating, Blade-Shaped, Two-Pass Cooling Channel With Various 45-Deg Rib Turbulators and a Tip Turning Vane

Abstract This work experimentally studied a rotating, blade-shaped, two-pass cooling channel with various 45-deg rib turbulators and a tip-turning vane. The first passage of the cooling channel has an aspect ratio (AR) = 4:1 with the coolant moving radially outward. After a 180-deg blade-shaped tip turn, the coolant flows radially inward into the second passage with an AR = 2:1. The first and second passages are oriented at 50 deg and 105 deg from the rotation direction, respectively. In the tip-turn portion, a tip-turning vane with an oval cross section connects the mid-lines of the two passes. Two orientations of 45 deg angled ribs were considered in this work: unusual and criss-cross. The ribs have a profiled cross section and were placed in-line (P/e = 10, e/H = 0.16) on the leading and trailing surfaces of the channel. Five inlet Reynolds numbers (10,000–45,000) and five rotational speeds (0−400 rpm) were considered in this study, with a maximum rotation number of Ro = 0.38 achieved in the first pass. The results showed that the effect of the turning vane on heat transfer and pressure loss for the 45-deg unusual rib case was insignificant. The overall heat transfer for the criss-cross rib case was slightly increased by the turning vane. For pressure loss, the turning vane provided approximately an 8% reduction in the 45-deg criss-cross rib case, which was the highest in the rib cases. The 45-deg criss-cross ribs presented the highest thermal performance with the turning vane.

Morphologic clustering of earcanals using deep learning algorithm to design artificial ears dedicated to earplug attenuation measurement.

Designing earplugs adapted for the widest number of earcanals requires acoustical test fixtures (ATFs) geometrically representative of the population. Most existing ATFs are equipped with unique sized straight cylindrical earcanals, considered representative of average human morphology, and are therefore unable to assess how earplugs can fit different earcanal morphologies. In this study, a methodology to cluster earcanals as a function of their morphologies with the objective of designing artificial ears dedicated to sound attenuation measurement is developed and applied to a sample of Canadian workers' earcanals. The earcanal morphologic indicators that correlate with the attenuations of six models of commercial earplugs are first identified. Three clusters of earcanals are then produced using statistical analysis and an artificial intelligence-based algorithm. In the sample of earcanals considered in this study, the identified clusters differ by the earcanal length and by the surface and ovality of the first bend cross section. The cluster that comprises earcanals with small girth and round first bend cross section shows that earplugs induced attenuation significantly higher than the cluster that includes earcanals with a bigger and more oval first bend cross section.

Heat Transfer in a Rotating Blade-Shaped Two-Pass Channel with a Turning Vane

The effect of adding a tip turning vane on the heat transfer and pressure loss of a blade-shaped two-pass cooling channel was experimentally investigated in this work. In the first passage with an aspect ratio (AR) of , the coolant traveled radially outward to a 180 deg blade-shaped turn. After the turn, the coolant flowed radially inward in the second passage with . The cooling channel was positioned such that the first and second passes were angled 50 and 105 deg from the direction of rotation, respectively. The turning vane was designed with an oval cross section to connect the midlines of the two passages. A 45 deg angled ribbed case (inline, ) was studied in addition to the smooth surface case. The Reynolds number ranged from 10,000 to 45,000 in the first pass and 16,000 to 73,000 in the second pass. In this study, five rotational speeds (0–400 rpm) were considered, and the maximum inlet rotation number was . The results showed that the turning vane decreases both heat transfer and pressure loss in the cooling channel. The average overall heat transfer for the entire channel was reduced 6 and 4% by the turning vane in the smooth and ribbed cases, respectively. However, with the presence of the turning vane, the tip wall heat transfer was increased in the range of 10–20% in both the smooth and ribbed cases. The rotational effect on heat transfer was found to be reduced with the presence of the vane. On the other hand, the turning vane provided 10 and 5% pressure loss reductions in the smooth and ribbed cases, respectively.

Evaluation of the band-shaped isthmuses in the mesiobuccal root canal system using micro-computed tomography.

This micro-computed tomography (micro-CT) study analyzed band-shaped isthmuses having their floor at the apical third of the mesiobuccal roots of maxillary molars in terms of 2D and 3D morphological parameters. A total of 199 maxillary first molars were scanned with micro-CT. Twenty-seven specimens, confirmed to have a band-shaped isthmus, were further examined in terms of the isthmus length, volume, structure model index (SMI), and surface area. The distance of apical foramina of mesial canals from the isthmus floor and major-minor diameters, roundness, perimeter, and area of the isthmus roof and floor were compared. Statistical analyses were performed with descriptive statistics and t-test with a 5% significance threshold. The band-shaped isthmus frequency was 13.5% and its length reached up to 5.5mm. The distances of the apical foramina of mesiobuccal canals (MB1 and MB2) from the isthmus floor were similar (p > .05). Isthmus roof and floor showed significant differences in terms of their major diameter and area (p < .05), whereas their minor diameter, roundness, and perimeter values were similar (p > .05). The band-shaped isthmuses are not rare and can reach through the half of the root length with oval cross-sections in the floor and roof anatomy. The distance between the isthmus floor and apical foramina did not differ between MB1 and MB2. The band-shaped isthmus morphology contributes to the complexity of the apical anatomy of maxillary first molar teeth with various lengths and diameters.

Non-conventional tube shapes for lifetime extend of solar external receivers

In this work, several novel tube shapes of solar tubular receivers that differ from the classical circular shape are analysed aiming to reduce the stresses of the receiver tubes, without penalizing its thermal efficiency. The analysis is performed using analytical thermal and mechanical models of the literature adapted for their use with non-circular tube shapes, verifying the assumptions made with FEM simulations due to the lack of experimental data available.Among the geometries studied, the results show that oval cross-section tubes improve the thermal efficiency of the receiver at the expense of increasing the stresses considerably. Ovoidal tubes show worse thermal and mechanical behaviour when the frontal part becomes peakier. Semicircle tubes reduce the stress by 10.9%, while keeping constant or even slightly improving the thermal performance. The last ones, increase the lifetime of the receiver and reduces the receiver costs if the manufacturing of the new geometries does no overpass 3.5 times the present price of production of the circular tubes. Therefore, the use of asymmetric cross-section tubes with low rear-front surface ratios, and smooth front surfaces can be considered a good alternative for substituting traditional circular cross-section tubes in central receivers.

Numerical simulation of the effects of superhydrophobic coating in an oval cross-sectional solar collector with a wavy absorber filled with water-based Al2O3-ZnO-Fe3O4 ternary hybrid nanofluid

Thermo-hydrodynamic assessments of solar collectors equipped with superhydrophobic coating have been rarely reported in the literature, while such surfaces can offer low cost and improved hydrodynamic performances. Hence, the current numerical work aims at evaluating a solar collector with considering superhydrophobic coating. The assessed quantities include the average Nusselt number, friction factor, performance evaluation criteria, and entropy generation variations against slip length in a fully turbulent flow. The collector, having an oval cross-section and wavy or flat absorber, is filled with a ternary nanofluid whose thermophysical properties are included in the simulations by empirical temperature-dependent correlations. To apply the slip conditions in the commercial solver, which is not as straight as importing a particular slip length to an open-source computational code, a trial procedure is used. It is found that the superhydrophobic coating can reduce the friction factor by about 45%, while only a little decrement in the average Nusselt number is observed (an average of 4.5%). Overall, the values of performance evaluation criteria indicate that the coating can be thermo-hydrodynamically beneficial in the solar collectors, along with practical worthiness to subside the power demand. The results add weight to the technical applications of hydrophobic coating in solar systems.