Semicircular Cavities Research Articles

Numerical investigation of the effect of rectangular and semicircular cavities filled with phase change materials installed on the solar wall

The use of alternative energy sources, particularly solar energy, in buildings is rising and spreading around the globe. In this paper, a solar wall is analyzed using a numerical method. On the wall, a number of obstacles are placed in two shapes, rectangular (REC) and semicircular (SEC). The cavities are filled with organic phase-change materials. This study was performed in 7 h in the absence of solar radiation on the wall for different dimensions of obstacles in 5 different modes. Various temperatures have been investigated, including exhaust air temperature (TAR), Trombe wall temperature (TWL), and mean volume % of molten PCM in cavities. COMSOL software is used to carry out this numerical study. The results of this study showed that the use of SECs compared to RECs causes the TWL to be higher. In the most extreme case, at a 16 cm aspect ratio, the use of SECs gives a 2.1 °C increase in TWL relative to the REC one. The outlet TAR is also increased by the usage of SECs. The use of larger dimensions of the cavities has increased the TAR leaving the wall so that the TAR after 7 h of the absence of solar radiation, in the most significant case of SECs, was more than 295.5 K. The use of SECs also increases the PCM freezing time. In the largest case of cavities, using SECs increases the freezing time by 15 min compared to RECs.

Bandwidth-Controllable Third-Order Band Pass Filter Using Substrate-Integrated Full- and Semi-Circular Cavities

The article presents a novel circular substrate-integrated waveguide (SIW) bandpass filter (BPF) with controllable bandwidth. The proposed BPF was configured using two microstrip feed lines, semi-circular SIW cavities, capacitive slots, and inductive vias. The circular cavity was divided into two halves, and the two copies were cascaded. The resulting bisected and cascaded structures were then connected back-to-back. Finally, by introducing two inductive vias to the circular center cavity, a transmission zero was generated. In order to examine the design concept, a coupling matrix was generated. To demonstrate the theory, a third-order BPF was realized, fabricated, and experimentally validated. The BPF prototype features a wide passband of 8.7%, a low insertion loss of 1.1 dB, and a stopband of 1.5 f0 with a rejection level better than 20 dB, which makes it a potential candidate for microwave sensing and communication industries.

Mechanical activation with Easy Clean device enhanced organic tissue removal from simulated internal root resorption in a laboratory evaluation

BackgroundConsidering the irregular shape of the root canal, removing inflamed pulp and granulation tissue completely from internal resorption cavities during chemomechanical preparation can be challenging. This study aimed to evaluate the effectiveness of passive ultrasonic irrigation (PUI) compared to mechanical activation with Easy Clean in the removal of organic tissue from simulated areas of internal root resorption.MethodsThe root canals of 72 extracted single-rooted teeth with oval canals were instrumented with Reciproc R25 instruments. After root canal preparations, the specimens were split longitudinally, and semicircular cavities were prepared using a round bur on each half of the roots. Samples obtained from bovine muscle tissue were weighed and adapted into semicircular cavities. The roots were reassembled and joined, and the teeth were divided into six groups (n = 12) according to the irrigation protocol: Sodium hypochlorite (NaOCl) without activation; NaOCl + PUI; NaOCl + Easy Clean; distilled water without activation; distilled water + PUI; and distilled water + Easy Clean. After irrigation protocols, the teeth were disassembled, and the remaining organic tissue was weighed. Data were analyzed by two-way ANOVA and Tukey’s post hoc test (p < 0.05).ResultsNone of the experimental protocols totally removed the bovine tissue from simulated cavities. Tissue weight reduction was significantly affected by the activation method (p < 0.05) and by irrigation solution (p < 0.05). Groups with NaOCl irrigation presented higher tissue weight loss when compared to distilled water, for all irrigation methods (p < 0.05). The use of Easy Clean resulted in the greatest tissue weight loss (42.0%—Distilled water/45.5%- NaOCl) compared to those of PUI (33.3%—Distilled water/37.7%- NaOCl) and no activation (33.4%—Distilled water/38.8%- NaOCl) (p < 0.05). However, no differences were observed between PUI and no activation groups (p > 0.05).ConclusionsMechanical activation with Easy Clean enhanced organic tissue removal from simulated internal resorption more effectively than PUI. Easy Clean for agitation of the irrigating solution is effective in removing simulated organic tissues from artificial internal resorption cavities, being an alternative to the use of PUI.

Effects of cavity shapes and sizes on rarefied hypersonic flows

Cavity structures are frequently encountered on hypersonic vehicle surfaces, which change the aerodynamic heat flux and force (pressure) compared with flat vehicle surfaces. The effects of the cavity length-to-depth ratio, cavity rounded corners, Maxwellian accommodation coefficient, and free-stream Knudsen number on the heat flux and pressure loaded on the vehicle surface with rectangular cavities have been studied extensively. Still, the influence of the cavity shape and size remains. In this study, the effects of cavity shape and size on the flow field characteristics and aerodynamic surface quantities on the surface are analyzed using the direct simulation Monte Carlo method. The rectangular cavities with sidewall angles (α) of 0°, 15°, 30°, and 45° are selected to investigate the shape influence, and the semicircular cavities with radii (R) of 3, 6, 9, and 12 mm are chosen for size effect. The results indicate that the gas flows over the cavity configurations specified in our study hold the “open-cavity” characteristics. The vortexes formed inside the cavity are shrunk as α increases from 0° and 45°, but they are similar under the R-range explored. The pressure, skin friction, and heat transfer coefficients over the surface display complex trends as varying α and R. In addition, the effect of cavities on the overall aerodynamic heat flux and force, which are vital for practical applications, are explored. The results reveal that the aerodynamic heat flux is dramatically influenced by α and R, while the aerodynamic force is mildly affected. Overall, the larger the α and R, the greater the effect of the cavity on the rarefied hypersonic flows. Our research is beneficial to the protection and optimal design of hypersonic vehicles.

Effects of wall temperature on separation structures in supersonic flow over a semi-circular cavity

The influence of wall temperature on the vortex structure and flow characteristics of flow in semi-circular cavities is numerically investigated in this paper. The results show that the separation and reattachment points move downstream, and the secondary vortex increases with increases in wall temperature. In the secondary vortex section, normalized wall shear stress in the polar map has good consistency at different wall temperatures, and the flow properties of the three extreme points on the map are similar to Couette flow. In addition, the secondary vortex region can be regarded as an isobaric high-pressure region, while the pressure gradients slowly vary as the wall temperature increases. We confirm the independence of separation pressure for the wall temperature using pressure distribution and find that the peak and inflection points are at the reattachment points and separation points, respectively. Moreover, using a series of numerical calculations of the positions of the vortex center at different wall temperatures, explicit empirical formulas for estimating the positions of the primary vortex center are put forward. Using a topological mapping method, cavity flow is converted into quasi-one-dimensional steady-state compressible viscous flow through a variable cross-section pipe, and the flow parameter distribution, including the Mach number and pressure, conforms to the rule of quasi-one-dimensional flow.

Efficacy of Combined Use of XP-endo shaper and XP-endo Finisher in Cleaning Simulated Internal Root Resorption Defects: An In-Vitro Comparative Study

Aim: Evaluate the efficacy of the combined use of XP shaper and finisher in cleaning simulated internal root resorption defects in comparison to the conventional passive ultrasonic irrigation using stereomicroscope.Materials and methods: The root canals of 90 freshly extracted human mandibular premolars were prepared using Protaper up to F4 and the teeth were split longitudinally and semicircular cavities (simulated internal root resorption cavities) were prepared in the canal wall on each half of the roots, then randomly assigned into two experimental groups (n=40) according to the cleaning technique groups (A) cleaned using passive ultrasonic irrigation , group (B) cleaned using XP-endo shaper followed by XP-endo finisher , five specimens were assigned to serve as negative control and five more were assigned to serve as positive control. Colored gelatin material (CGM) was prepared and applied into the semicircular cavities except for the negative control which did not receive (CGM). The root halves were reassembled creating a circular simulated resorption cavity within the root canal. Specimens were cleaned according to the group they were assigned to except for the positive control which did not receive any further treatment. All the specimens were disassembled and the residual CGM was examined under a stereomicroscope at 10x magnification and calculated as percentage of residual CGM to total area of the IRR cavity by using image analysis software and the data were statistically analyzed with one- way ANOVA test and significance level was set at P> 0.05.Results: None of the tested methods could completely remove the CGM from the simulated IRR cavities. Group B showed lower mean percentage of residual CGM than did group A (P> 0.041).Concussion: within the limitations of this study XP-endo shaper followed by XP-endo finisher was more effective in cleaning inaccessible internal root resorption defects than PUI.

Comparison between the use of thermoplasticized gutta-percha and a polydimethyl siloxane-based material in filling internal resorptive cavities using spiral computed tomography.

To evaluate the fill of internal resorption cavities obturated with thermoplasticized gutta-percha and GuttaFlow2 using CT scan. Twenty human maxillary anterior teeth were selected and root canals were prepared using ProTaper system to size F3. Irrigation was performed with 5 ml of 2.5% sodium hypochlorite (NaOCl) and 5 ml of 17% ethylenediaminetetraacetic acid (EDTA). Each root was then sectioned horizontally into two halves and semicircular cavities were prepared around the periphery of the root canal opening of each root half, using a round bur. Both the root halves were then fixed using cyanoacrylate glue. All the specimens were subjected to preoperative CT scan analysis to determine the volume of internal cavities. The samples were then randomly divided into two groups. In Group 1, the specimens were obturated with thermoplasticized gutta-percha (E&Q system) and specimens in Group 2 were obturated using GuttaFlow2. All specimens were then subjected to postoperative CT scan analysis. The volume of voids in internal resorptive cavities were calculated, which was then used to estimate the amount of gutta-percha filled. There was no significant difference in volume of internal resorptive cavities between thermoplasticized gutta-percha and GuttaFlow2 groups before obturation (p = 0.466). However, after obturation there was a significant difference between both the groups, in which GuttaFlow2 demonstrated better fill (p = .014). Thermoplasticized gutta-percha filled 81% of internal resorptive cavity while GuttaFlow2 filled 91%, respectively. GuttaFlow2 showed better fill than thermoplasticized gutta-percha in the filling of internal resorptive cavities.

Transient mixed convection in a channel with two facing discretely heated semicircular cavities: Buoyancy, inclination angle, and channel aspect ratio effects

ABSTRACTSpace-averaged surface temperature distributions and overall Nusselt number measurements have been carried out to study the transient mixed convection heat transfer in a channel with two facing and symmetrically heated semicircular cavities. Effects of buoyancy, channel orientation, and channel aspect ratio on thermal behavior have been investigated from Re 500 to 1,500. Depending on the parametric set, steady, oscillatory, and irregular thermal regimes have been identified. The natural frequencies and time scales of the oscillatory regimes have been obtained using spectral analysis. Results show that with increase in channel aspect ratio, the heat transfer performance reduces for all inclination angles.

H&lt;sup&gt;3&lt;/sup&gt;TRB Test on 650 V SiC JBS Diodes

Reliability characterization of SiC devices is an ongoing activity. For this work, 650 V SiC JBS diodes in TO247 housings were tested in H3TRB. After a test period of 4000 hours none of the devices had failed during the test and only two out of sixteen devices had failed during blocking curve measurements performed at intermediate time steps. This is significantly better performance than many silicon devices offer today. The failure spots of the failed devices were detected at the edge of the main junction appearing as semi-circular cavities in the aluminum metallization. All other devices did not even show deviations from their original blocking curves.

The effectiveness of various irrigation protocols on organic tissue removal from simulated internal resorption defects.

To evaluate the effectiveness of NaOCl, NaOCl-EDTA and NaOCl+HEBP activated by ultrasonics and XP-endo Finisher on organic tissue removal from simulated internal root resorption cavities. The root canals of 144 single-rooted teeth were instrumented. The teeth were split longitudinally, and semicircular cavities were prepared in the canal walls on each half of the roots. Samples obtained from ground bovine muscle tissue were weighed and adapted into the semicircular cavities. The root fragments were reassembled and cemented to create a circular simulated resorption cavity within the canal. Teeth were divided into twelve groups (n=12) according to the irrigation protocols: group 1: NaOCl, no activation; group 2: NaOCl, passive ultrasonic irrigation (PUI); group 3: NaOCl, XP-endo Finisher; group 4: NaOCl-EDTA, no activation; group 5: NaOCl-EDTA, PUI; group 6: NaOCl-EDTA, XP-endo Finisher; group 7: NaOCl+HEBP, no activation; group 8: NaOCl+HEBP, PUI; group 9: NaOCl+HEBP, XP-endo Finisher; group 10: distilled water, no activation; group 11: distilled water, PUI; and group 12: distilled water, XP-endo Finisher. The teeth were disassembled, and the tissue remaining inside the resorption cavities were weighed. The data were analysed statistically using two-way anova and Fisher's LSD tests with a significance level of 0.05. The use of XP-endo Finisher with the experimental solutions resulted in the greatest tissue weight loss compared to the other activation protocols (P<0.001). There was no significant difference between NaOCl and NaOCl+HEBP in terms of tissue removal. The use of a NaOCl+HEBP mixture activated with XP-endo Finisher was an effective irrigation regimen for removing simulated organic tissues from artificial internal root resorption cavities in the straight root canals of single-rooted teeth.

Effectiveness of four different gutta percha techniques in filling experimental internal resorptive lesions - An in vitro study

Background and Objectives: The objective of thisstudy was to compare the efficacy of four different obturation techniques in obturating artificially created internal resorptive lesions. Materials and Methods: Forty extracted,human maxillary central incisor teeth were collected for the study. Access cavity was prepared in each tooth. The teeth were instrumented to apical size 50. The roots were sectioned horizontally 7 mm from the apex. Semicircular cavities were created using a No 6 round diamond bur. The sections were joined together using cyanocrylate glue. The teeth were radiographed to visualize the internal resorption cavity. The teeth were randomly divided into four groups of ten teeth each as follows Group I:Lateral condensation. Group II :Obtura II. Group III: System B. Group IV:Thermafil. After obturation, they were stored at room temperature for 7 days. The specimens were then removed from the plaster cast, each tooth was sectioned. The teeth were photographed under a stereomicroscope. The photographs were transferred to a computer and an image analysis program was be used to calculate the percentage of sealer, gutta percha and voids. The results were evaluated statistically by usingOne way ANOVA and Newman-Keuls test. Results: The Obtura II group showed significantly more gutta percha in the internal resorptive lesions as compared to the other systems with significantly less amount of sealer and voids.

The method of lines for the computation of incompressible viscous flows

AbstractA common approach to finding numerical solutions of the time‐dependent incompressible Navier‐Stokes equations is considered within the method of lines framework [1]. For the determination of viscous incompressible flows the stream‐function formulation for the fourth‐order equation [2, 3], an artificial compressibility method [4], and a modified velocity correction method [5] are designed. Some improved and extended results of numerical simulations obtained by the author in the previous works are presented. Test calculations have been done for various flows inside square, triangular and semicircular cavities with one moving wall, the backward‐facing step, double bent channels and for the flow around an aerofoil at large angle of attack. An alternative and practical methodology for resolving the Navier‐Stokes equations in arbitrarily complex geometries using Cartesian meshes is proposed. Some of complex geometrical configurations can be decomposed into a set of subdomains. The simplest approach for specifying boundary conditions near curved or irregular boundaries is to transfer all the variables from the boundaries to the nearest grid knots. (© 2009 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

An Efficient Equal-Order Finite-Element Method for Natural Convection in Complex Enclosures

In this article, an efficient and accurate equal-order finite-element method is developed and then incorporated into the finite-element program, ANSYS/FLOTRAN, release 6.0. In this method the systems of linear algebraic equations resulting from the finite-element formulation of the momentum and energy equations are solved implicitly using a fast and robust preconditioned BiCGStab( l ) algorithm. Further, the linkage between the momentum and continuity equations is enhanced through improved pressure-velocity coupling. As a result, no under-relaxation is needed for the pressure equation and large values of under-relaxation are possible for the momentum and energy equations, resulting in a marked improvement in convergence. Both efficiency and accuracy of this method are demonstrated for buoyancy-driven flows in square, semicircular, and triangular cavities at various Rayleigh numbers.

Coupled saturated‐unsaturated quasilinearized steady state flows from buried and surface cavities

The coupled saturated‐unsaturated flow that results from water‐filled cavities in soils is studied, under the assumption of quasilinearization for the unsaturated flow, using a combined boundary element‐finite element method. Buried two‐dimensional circular cylindrical cavities and two‐dimensional semicircular cavities are examined in detail. The effect of the size of the cavity and the soil type on the flux from the cavity and the size of the saturated zone and effectively wetted region is illustrated. Comparisons with previous analytical and numerical results, in which the depth of water in the cavity was neglected, are also made. These comparisons indicate the severe errors that are introduced into the calculation of the flux and the flow field when the depth of water is neglected. In particular, it is shown that the percentage error in the flux from a buried circular cylinder with water depth neglected increases from 20% to 220% as the dimensionless cavity size s increases from 0.1 to 1, and that the saturated zone extends to a depth of approximately 7.9 times the cavity radius for s = 1.