Elliptical Cavity Research Articles

Study on the Flow and Heat Transfer Performance of Microchannel Heat Exchangers With Different Elliptical Concave Cavities

AbstractEllipticity has a significant impact on the flow and heat transfer performance of microchannel heat exchangers (MHEs) with elliptical concave cavities. In this study, five types of MHEs with different elliptical concave cavities (ellipticities of 0.4, 0.6, 0.8, 1.0, and 1.2) were designed. The influence of ellipticity on the flow and heat transfer performance of MHEs was numerically investigated using ANSYS Fluent 21.0 R1. Moreover, MHEs with corresponding elliptical concave cavities structures were processed and manufactured, and then an experimental platform was designed and built for experimental verification. The results showed that the fluid velocity distribution in MHEs with elliptical concave cavities was symmetrical, and the formation of secondary flow in the elliptical concave cavities led to the continuous destruction and reconstruction of the flow and thermal boundary layer in the microchannel, which is conducive to mass and heat transfer in the MHEs with elliptical concave cavities. The inlet and outlet pressure drop of MHEs with elliptical concave cavities increased as the inlet flow rate increased. At the same inlet flow rate, the inlet and outlet pressure drop of the MHE with elliptical concave cavities first increased and then decreased with increasing ellipticity. At an ellipticity of 1.0, the inlet and outlet of MHE exhibited the lowest pressure drop indicating that the MHE with an ellipticity of 1.0 featured the highest pressure drop performance. The cold‐water outlet temperature of the MHEs with elliptical concave cavities first decreased and then increased as the inlet flow rate increased. At the same inlet flow rate, the cold‐water outlet temperature of the MHEs with elliptical concave cavities first increased and then decreased with increasing ellipticity, while the hot‐water outlet temperature of the MHEs first decreased and then increased with increasing flow rate. This indicated that the MHE with an ellipticity of 1.0 exhibited excellent heat transfer performance.

Expression of Concern for article entitled “Simultaneous application of active and passive methods in cooling of a cylindrical lithium-ion battery by changing the size of the elliptical cavity filled with nano phase change materials”

Expression of Concern for article entitled “Simultaneous application of active and passive methods in cooling of a cylindrical lithium-ion battery by changing the size of the elliptical cavity filled with nano phase change materials”

Does the capacitor analogy model in fracture mechanics of elastic dielectrics constitute an appropriate approximation?

The analytical solution of an elliptic dielectric cavity in an infinite dielectric plate is taken as basis to investigate a Griffith crack problem which is obtained by letting the semi-minor axis tend towards zero. In the course of this, an erroneous conformal mapping, commonly employed in literature and correctly reproducing the electric field only in a part of the physical space, is rectified. Interpreting the elliptic interface as faces of a mechanically opened crack which is exposed to an oblique remote electric field, surface charges and electrostatic tractions are calculated. In contrast to the established capacitor analogy model, approximately yielding electric charge densities and Coulombic tractions from displacements and electric potentials in the undeformed crack configuration, the work at hand provides exact solutions accounting for different implications of the crack curvature and for the inclination of the electric field. Crack weight functions are finally used to calculate stress and electric displacement intensity factors. As turns out, the surface charges of the capacitor analogy represent an excellent substitute for the exact electric boundary conditions within a relevant range of parameters, whereas inaccurate Coulombic tractions in the vicinity of crack tips may lead to a significantly overestimated mode I stress intensity factor.

Investigation of Electropolishing for High-Gradient 1.3 GHz and 3.9 GHz Niobium Cavities.

Electropolishing (EP) has become a standard procedure for treating the inner surfaces of superconducting radio-frequency (SRF) cavities composed of pure niobium. In this study, a new EP facility was employed for the surface treatment of both 1.3 GHz and 3.9 GHz single-cell cavities at the Wuxi Platform. The stable "cold EP" mode was successfully implemented on this newly designed EP facility. By integrating the cold EP process with a two-step baking approach, a maximum accelerating gradient exceeding 40 MV/m was achieved in 1.3 GHz single-cell cavities. Additionally, an update to this EP facility involved the design of a special cathode system for small-aperture structures, facilitating the cold EP process for 3.9 GHz single-cell cavities. Ultimately, a maximum accelerating gradient exceeding 25 MV/m was attained in the 3.9 GHz single-cell cavities after undergoing the cold EP treatment. The design and commissioning of the EP device, as well as the electropolishing and vertical test results of the single-cell cavities, will be detailed herein. These methods and experiences are also transferable to multi-cell cavities and elliptical cavities of other frequencies.

Field, frequency, and temperature dependencies of the surface resistance of nitrogen diffused niobium superconducting radio frequency cavities

We investigate the rf performance of several single-cell superconducting radio-frequency cavities subjected to low temperature heat treatment in nitrogen environment. The cavities were treated at temperature 120–165 °C for an extended period of time (24–48 h) either in high vacuum or in a low partial pressure of ultrapure nitrogen. The improvement in Q0 with a Q rise was observed when nitrogen gas was injected at ∼300 °C during the cavity cooldown from 800 °C and held at 165 °C, without any degradation in accelerating gradient over the baseline performance. The treatment was applied to several elliptical cavities with frequency ranging from 0.75 to 3.0 GHz, showing an improved quality factor as a result of low temperature nitrogen treatments. The Q rise feature is similar to that achieved by nitrogen alloying Nb cavities at higher temperature, followed by material removal by electropolishing. The surface modification was confirmed by the change in electronic mean free path and tuned with the temperature and duration of heat treatment. The decrease of the temperature-dependent surface resistance with increasing rf field, resulting in a Q rise, becomes stronger with increasing frequency and decreasing temperature. The data suggest a crossover frequency of ∼0.95 GHz above that the Q rise phenomenon occurs at 2 K. Some of these results can be explained qualitatively with an existing model of intrinsic field-dependence of the surface resistance with both equilibrium and nonequilibrium quasiparticle distribution functions. The change in the Q slope below 0.95 GHz may result from masking contribution of trapped magnetic flux to the residual surface resistance. Published by the American Physical Society 2024

Scattering of SH waves by elliptical cavity and type-III crack in deep anisotropic geology

Most of the underground rock formations are anisotropic, and the study of the dynamic response of anisotropic geology containing internal defects is necessary for the development of underground tunnels or caverns. In this paper, the wave function expansion method, the complex function method, and the Green's function method are used to solve the problem of scattering of SH waves in anisotropic rock in the presence of elliptical cavity and type-III crack. Boundary conditions for solving the problem are given using the conformal transformation method, and crack in the medium is constructed using the "crack cutting" technique. The scattered wave field generated by the crack is constructed based on the Green function method, and the displacement and stress fields in the model are obtained by the wave field superposition principle in the case of SH wave incidence. The dynamic stress concentration factor (DSCF) on the boundary of the elliptical cavity and the dynamic stress intensity factor (DSIF) at the crack tip are derived. The correctness of the method is verified by degenerating it to a classical analytic solution. Finally, the effects of the anisotropic strength of the rock mass, the dimensions of the cavern, and the incidence angle and wave number of the SH wave on the DSCF and DSIF are analyzed by numerical calculations in both the frequency and time domains. The results show that the anisotropy of the rock mass, the shape of the cavern and the defects of the surrounding medium have a great influence on the dynamic response of the underground structures, which should be given enough attention in the development and design of deep underground caverns or tunnels.

A high-gain circularly polarized magnetoelectric dipole antenna array with metallic radiating structure for millimeter-wave applications

A high-gain circularly polarized (CP) magnetoelectric (ME) dipole antenna with metallic radiating structure is presented. The proposed CP antenna element consists of two pairs of metallic posts with a supporting metallic plate, a metallic air-filled elliptical cavity, and a feeding slot on the bottom substrate integrated waveguide (SIW). The two pairs of modified rectangular metallic posts combined with the gaps between them act as radiating ME-dipoles which are surrounded by a metallic air-filled elliptical cavity. The above-mentioned radiating structures are fed by a modified cross-shaped coupling slot etched on the bottom feeding SIW to generate CP radiation, where loading the elliptical metallic cavity significantly improve the CP performance of the antenna element. Then, a 4 × 4 antenna array with full-corporate feeding network is designed, fabricated, and measured, which has an impedance bandwidth of 18.9 % from 37.4 to 45.2 GHz and a 3-dB axial ratio (AR) bandwidth of 14.2 % from 36 to 41.5 GHz. Thanks to the all-metal radiating structures, a maximum measured gain of 20.4 dBic has been achieved. The measured and simulated results are in good agreement.

Global Surface Pressure Pattern for a Compressible Elliptical Cavity Flow Using Pressure-Sensitive Paint

The flow field in a cavity depends on the properties of the upstream boundary layer and the cavity geometry. Comprehensive studies for rectangular cavities have been conducted. This experimental study determines the global surface pressure pattern for elliptical cavities (eccentricities of 0, 0.66 and 0.87) in a naturally developed turbulent boundary layer using pressure-sensitive paint. The ratio between the length (major axis) and the depth is 4.43–21.5, and the freestream Mach number is 0.83. The mean surface pressure distribution of an elliptical cavity resembles that of a rectangular cavity. A change in the value of eccentricity (wall curvature) affects the region for an adverse pressure gradient in an open cavity, an extension of the plateau in a transitional–closed cavity and flow expansion near the front and rear edges. The boundaries between an open, transitional and closed cavities vary.

Modeling Microwave Heating of Molten Salt for Thermal Storage Systems

With the aim of affordably storing energy produced by photovoltaic and wind power plants, Power-to-heat-to-power (or Carnot batteries) are proposed as an outstanding system capable of transforming this energy into heat through existing commercial thermal storage systems for thermosolar plants, and again produce electricity by connecting these storage systems to available power blocks that can come from dismantled carbon plants or any other such as gas plants, or even nuclear. On this basis, microwave heating is studied as feasible to store energy in molten solar salt: 60%w NaNO3, 40%w KNO3. This study is expected to provide some key points for the design of microwave systems for molten solar salt, analysing different simulated cases with numerical modeling: continuous flow microwave heating in an elliptical cavity with different flow rates – 1 l/min and 1.6 l/min – and different positions of the fluid carrier tube, and in a microwave oven with helical tubes.

Multi-band perfect absorber based on an elliptical cavity coupled with an elliptical metal nanorod.

We proposed a triple-band narrowband device based on a metal-insulator-metal (MIM) structure in visible and near-infrared regions. The finite difference time domain (FDTD) simulated results illustrated that the absorber possessed three perfect absorption peaks under TM polarization, and the absorption efficiencies were about 99.76%, 99.99%, and 99.92% at 785 nm, 975 nm, and 1132 nm, respectively. Simulation results matched well with the results of coupled-mode theory (CMT). Analyses of the distributions of the electric field indicated the "perfect" absorption was due to localized surface plasmon polaritons resonance (LSPPR) and Fabry-Perot resonance. We developed a multi-band absorber with more ellipsoid pillars. The four band-absorbing device presented perfect absorption at 767 nm, 1046 nm, 1122 nm, and 1303 nm, and the absorption rates were 99.45%, 99.41%, 99.99%, and 99.94%, respectively. By changing the refractive index of the surrounding medium, the resonant wavelengths could be tuned linearly. The maximum sensitivity and Figure of Merit were 230 nm RIU-1 and 10.84 RIU-1, respectively. The elliptical structural design provides more tuning degrees of freedom. The absorber possessed several satisfactory performances: excellent absorption behavior, multiple bands, tunability, incident insensitivity, and simple structure. Therefore, the designed absorbing device has enormous potential in optoelectronic detection, optical switching, and imaging.

Structural Analysis of Composite Aircraft Wing Ribs Designed with Elliptical Cavities

Geleneksel malzemelerle üretilen kanat kaburgalarına kıyasla farklı fiber açılarıyla tasarlanan kompozit kanat kaburgalarının havacılık endüstrisine katkıda bulunulacağı düşünülmektedir. Bu çalışmada, insansız hava aracı olan MQ-1B Predator’ün kanat kök kaburgaları için farklı oryantasyon açılarına sahip Karbon-Epoksi, Aramid-Epoksi ve Kevlar-Epoksi kompozit malzemeleri kullanılmıştır. Kaburga yapıları üç boyutlu tasarımları için Solidworks programı kullanılmış, ağırlığının azaltılması için üzerinde farklı boyutlarda eliptik boşaltmalar yapılmıştır. Uçak kanat kaburgalarının modellemesi ve yapısal analizleri için ANSYS Workbench sonlu elemanlar programı kullanılmıştır. İncelenen kompozit kaburga yapılarının tabaka kalınlıkları 0,25 mm olup, altı tabakalı kompozit plakadan oluşturulmuştur. Modellerde fiber oryantasyon açıları ise sırasıyla 0°, 15°, 30°, 45°, 60°, 75° ve 90° olacak şekilde kullanılmıştır. Aerodinamik yük altında modellenen kanat kök kaburgaların yapısal analizlerinde kanat kök kaburgalarında meydana gelen eş değer (von Mises) gerilme ve toplam deformasyon değerleri incelenmiştir. Yapılan analizler sonucunda, farklı kompozit malzeme ve oryantasyon açılarına sahip kaburga yapıları uygulanan yükün altında farklı davranışlar sergilediği tespit edilmiştir. Kaburgalar üzerindeki en düşük deformasyon 0° fiber açılı Karbon-Epoksi malzemeli kaburgada modelinde 0,0084515 mm ve en düşük gerilme ise 90° fiber açılı Kevlar-Epoksi malzemeli kaburga modellerinde 0,59402 MPa olarak meydana geldiği tespit edilmiştir.

Experimental demonstration on detonation initiation by laser ignition and shock focusing in elliptical cavity

As a method of initiating detonation in a short distance with a small amount of energy, the combination of laser ignition and shock focusing in an elliptical cavity was proposed and experimentally demonstrated with a C2H4-O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}\\hbox {H}_{4}{-}\\hbox {O}_{2}$$\\end{document} mixture at 100 kPa and 297 K. In the experiment, an elliptical cavity and single rectangular cavities of different heights were used, and their flow-field patterns were visualized using high-speed schlieren imaging. Detonation initiation was achieved in the case of the elliptical cavity, and based on the Mach number change of the leading shock wave, two propagation phases were verified: the deceleration and acceleration phases. The deceleration phase was driven merely by the gasdynamic effect, wherein the initial shock wave (ISW) expanded spherically, and the acceleration phase began when the ISW shifted to planar propagation. In the acceleration phase, although gradual acceleration was observed in rectangular cavities, rapid acceleration occurred in the elliptical cavity. From the schlieren images, the second acceleration was caused not only by the concave reflected shock wave’s catching up with the ISW, but also by the fast-flames that were generated along the cavity corners and engulfed the ISW in the converging section of the elliptical cavity.

ON CONTACT PROBLEMS FOR TWO STAMPS AND A NEW TYPE OF CRACK MODEL

In this work, for the first time, an exact solution of the contact problem of interaction with a multilayer base of two semi-infinite stamps, the ends of which are parallel to each other, is constructed. Stamps are assumed to be absolutely rigid, and the distance between them can have any finite value. The task is an important stage in the algorithm for constructing models of a new type of crack in materials of different rheologies. The mechanism of destruction of the medium by cracks of a new type is radically different from the mechanism of destruction of the medium by Griffiths cracks, and has so far been poorly studied. Griffiths formed his cracks with a smooth border as a result of compression from the sides of an elliptical cavity in the plate. Cracks of a new type have a piecewise smooth border, resulting from the replacement of an ellipse with a rectangle compressed from the sides. The problem considered in the article can be considered as the result of the formation of a new type of crack with absolutely rigid banks and deformable lower boundary. Thanks to it, after the solution, it becomes possible to switch to deformable stamps and a crack of a new type in the rheological medium. The solution of this problem turned out to be possible due to the construction of exact solutions of the Wiener–Hopf integral equations on a finite segment. The paper shows how the solution of one of the previously unsolved problems allows us to investigate and solve exactly other problems, to identify previously unknown properties and resonances. As a result of constructing an exact solution to the problem, the fact that the solution of dynamic contact problems for stamp systems is not unique was confirmed and a dispersion equation for finding resonant frequencies was constructed.

Experimental study of flow boiling characteristics of open microchannels with elliptical cavities and elliptical ribs

Open microchannel heat sinks (O-MCHS) stand out among many thermal management technologies due to their extra open gaps that reduce pressure drop and mitigate flow instability. Recently, there has been a growing trend of incorporating microstructures onto microchannels in order to enhance the hydrothermal performance of heat sinks. However, the heat transfer characteristics and bubble behavior of O-MCHS with microstructures are still rarely studied. In this study, open copper-based microchannel heat sinks with elliptical cavities and elliptical central ribs (O-EC-ECR) and elliptical cavities and elliptical side ribs (O-EC-ESR) were designed and manufactured; the flow patterns, heat transfer performance and pressure drop were systematically studied and compared with those of rectangular open microchannel heat sink (R O-MCHS). The working fluid was degassed DI water and the experiments were performed with the inlet subcooling of 75 ℃ at efficient heat fluxes of 668.00–2416.16 kW/m2 under various mass fluxes ranging from 421 to 801 kg/m2·s. The experimental results demonstrated that the O-EC-ECR exhibited the best two-phase heat transfer performance among three structures at all mass fluxes. The average two-phase heat transfer coefficient of O-EC-ECR was increased by 12.2 % compared to R O-MCHS at the mass flux of 801 kg/m2·s. The average wall temperature of O-EC-ECR was found to be 10.1 ℃ lower than that of R-O-MCHS and 6.7 ℃ lower than that of O-EC-ESR at the mass flux of 801 kg/m2·s. This should be attributed to the dramatically increased convective heat transfer area as well as the separating and breaking effect of the central ribs on the bubbles, which was manifested by the increase in heat transfer coefficient and critical heat flux (CHF). In addition, the central ribs improved the flow boiling stability by effectively suppressing the generation of confined bubbles and the formation of slugs. The arrangement of the side ribs and cavities made bubbles easier to condense, which facilitated the mixing of hot and cold fluid. At low to medium mass fluxes, the O-EC-ESR only showed superior heat transfer performance during the bubbly flow dominated nucleate boiling regime. Whereas high mass flux can improve the boiling heat transfer performance; the average heat transfer coefficient of O-EC-ESR was increased by 6.1 % compared to R O-MCHS. The average pressure drop of O-EC-ESR was decreased by 21.8 % compared to R O-MCHS and 25.6 % compared to O-EC-ECR at the mass flux of 801 kg/m2·s.

Mid-T heat treatments on BCP’ed coaxial cavities at TRIUMF

Mid-T heat treatments in the range from 250°C to 400°C on superconducting radio-frequency (SRF) cavities have been shown to provide high quality factors that rise with applied rf field strength in high frequency, electro-polished (EP), elliptical cavities operating at 2 K, similar to nitrogen doped cavities. The rise in quality factor is attributed to a decrease in the temperature dependent part of the surface resistance RBCS. Until now, no results have been reported for these new treatments on quarter-wave resonators (QWR) and half-wave resonators (HWR). The TRIUMF multi-mode coaxial cavities are dedicated test cavities that allow frequency and temperature resolved performance characterization of treatments without changing environments, therefore providing an excellent test vehicle to test these new treatments with rf frequencies ranging from 200 to 1,200 MHz. In this paper, performance measurements from both QWR and HWR cavities are reported and their performance compared with four different treatments: baseline, a conventional 120°C low temperature bake for 48 h, and two mid-T bakes at 300°C and 400°C for 3 h. In addition, sample analysis using SEM, EDX and SIMS of witness samples is also shown. It is found that the mid-T bakes are not directly transferable to low frequency cavities. In the fundamental modes of the two test cavities, no performance gain over the baseline treatment nor a decreasing temperature dependent component with rising rf amplitude was observed. At frequencies above 1 GHz and low temperatures, the mid-T bakes show a reduced field dependence of RBCS compared to both the baseline and 120°C treatments.

Development of hybrid resonator antennas using elliptical cavity and microstrip patch radiator

This paper presents a few linearly polarized (LP) Hybrid Resonator Antennas (HRAs) using half mode SIW-based semi-elliptical cavity provide wideband capability. Considering the resonate modes of an elliptical cavity, field distribution and resonate frequency are studied at the dominant mode of operation using HFSS; the cavity is halved along its major and minor axis to create an aperture led to obtaining two HMSIW semi-elliptical cavity-based aperture antennas. A 50 Ω feed line is applied to stimulate the cavity and to facilitate compatibility with planar circuitry. To increase the impedance bandwidth, one and two patch radiators are added in front of the aperture to excite the TM010 mode of the patch. The proposed structures are simulated using HFSS software, and the antenna parameters are adjusted for maximum bandwidth. Two prototypes of the HRAs are implemented for verification. The proposed structures are tested, and the radiation characteristics are reported. The results show that one HRA offers 15% bandwidth with a peak gain of 6.8 dBi, whereas the other antenna offers 20% impedance bandwidth with a 7.2 dBi gain. The introduced HRAs are low profile providing attractive features, and are good candidate as a single antenna or as an element of array.

Analytical solution of the temperature-dependent thermoelastic problem induced by Joule heating and the presence of an elliptic cavity

Joule heat induced by electric current may well lead to thermal stress and contribute to structural failure and crack evolution in a range of modern materials. In this paper, we use complex variable methods to obtain the thermoelastic fields around an elliptic cavity in a plate subjected to remote electric and thermal loads. Of particular interest is the fact that we consider the temperature dependency of the corresponding thermoelastic coefficients. We introduce an analytical method which is verified by the fact that it leads to results which reduce to the classical analytical results in the literature when the thermoelastic coefficients are taken to be temperature-independent. We find that when the elliptic cavity is reduced to the representation of a linear crack, the corresponding stress intensity factor increases to a greater extent under the temperature-dependent assumption versus the corresponding classical results. Our findings are significant in forming the basis for the analysis of the evolution of crack growth under severe temperature gradients such as those occurring as a result of Joule heat loading.

Construction of a New MgB2 Coating System for 1.3-GHz Superconducting RF Cavities at LANL

After many years of evaluating MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films prepared with various techniques for the application to superconducting radio-frequency (SRF) cavities, we have decided to build a system to coat full-size 1.3-GHz elliptical cavities. This paper describes the design and construction of the system. Additionally, we briefly describe experimental results with a small system and first tests with the new large system. We were able to obtain superconducting samples with a T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of up to 38 K with the small system, but we have not been able to get any superconducting samples with the new system yet.

Diffraction of Harmonic Shear Waves on an Elliptical Cavity Located in a Viscoelastic Medium

Diffraction of Harmonic Shear Waves on an Elliptical Cavity Located in a Viscoelastic Medium

Application of triangular duct in solar-assisted air-heating system with surface roughness: a numerical investigation.

The device called solar air heater (SAH) is used to collect and transfer solar-thermal energy to air that can further be used for space heating, drying, etc. The conventional air heater (solar-assisted) has poor performance, and with this work, an attempt has been made to improve its performance by providing surface roughness over the heated surface. The roughness employed over the surface has an elliptical cavity, and its distribution over the heated surface is defined with the three parameters (dimensionless): relative flow-wise distance (ranging from 6 to 14), relative cavity depth (ranging from 0.016 to 0.038), and relative crosswise distance (ranging from 6 to 14). A CFD code has been developed and validated with experimentation to do the parametric study for understanding the effect of the proposed surface roughness on the performance of the air heater. It is concluded that the proposed surface roughness promotes the local turbulence, flow separation, and strong vortices in the flow field resulting in comparatively higher thermal performance in the proposed air heater. But this higher thermal performance is achieved at the expense of higher-pressure loss in the passage. A substantial change in heat augmentation by 2.57 times (with 2.3 times higher pressure loss) which results in 1.75 times higher thermo-hydraulic performance has been noticed over conventional designs at a relative flow-wise distance of 10, relative cavity depth 0.038, and relative crosswise distance of 10.