Rectangle Cavity Research Articles

Effect of baffle length on mixed convection coupled to surface radiation in a rectangle cavity

In this study, we numerically investigated the influence of the baffle length and emissivity of the walls on heat transfer in a mixed convection coupled with radiation in a rectangular cavity ventilated. The baffle length is used Lb = 0.3, 0.5 and 0.7. The cavity walls are gray. The left vertical wall is heated to a constant heat flux and the other walls are adiabatic. The finite volume method is used to solve the governing equations. At the input of the cavity whose opening height w =H/10, the fluid velocity is determined from the number of Reynolds Re between 50 and 500. The Grashof number Gris fixed to 104 and the Prandtl number Pr is kept constant 0.71. The results obtained in this study show that the heat transfer enhancement depends on the increase in emissivity; However, the increase in total Nusselt number NuT depends on the increase of the baffle length.

Peak modulation in multicavity-coupled graphene-based waveguide system

Plasmonically induced transparency (PIT) in a multicavity-coupled graphene-based waveguide system is investigated theoretically and numerically. By using the finite element method (FEM), the multiple mode effect can be achieved, and blue shift is exhibited by tunable altering the chemical potential of the monolayer graphene. We find that the increasing number of the graphene rectangle cavity (GRC) achieves the multiple PIT peaks. In addition, we find that the PIT peaks reduce to just one when the distance between the third cavity and the second one is 100 nm. Easily to be experimentally fabricated, this graphene-based waveguide system has many potential applications for the advancement of 3D ultra-compact, high-performance, and dynamical modulation plasmonic devices.

Numerical investigation of turbulent flow and heat transfer over partially open cavities: Effect of opening ratio

Partially open cavities are encountered in various engineering systems such as electronic cooling devices and cooling for gas turbine blades, instead of conventional film cooling slots. Flow is to be imparted over the partially open cavity where it induces a shear layer and a shear driven vortex within the cavity, which is subjected to cooling effect at its wall. Depending on the opening ratio, heat and mass transfer occur between the main flow and the trapped vortex through the shear layer. In the present study, RANS simulations of such flow have been conducted for circular and square cavities to investigate the effect of opening ratio on the heat and mass transfer characteristics. The simulations were established on a rigorous numerical approach and proper validation with laser Doppler velocimetry measurements of turbulent flow in circular cavity. Based on the hydraulic diameter of the cavity, opening ratios ranging from 0.2 to 1.0 were investigated for a Reynolds number of 3?105. Generally, the maximum Nusselt number was achieved at higher opening ratios for both circular and rectangle cavities. On the other hand, the maximum dimensionless temperature gradient, ?, inside the cavity was achieved at L/D = 0.2 for both cavity configurations.

A Complex Variable Solution for Rectangle Pipe Jacking in Elastic Half‐Plane

In mechanics, the solution of soil stresses and displacements field caused by shallow rectangular jacking pipe construction can be simplified as half‐plane problem. Both the boundary conditions of the surface and the cavity boundary must be taken into account. It is the essential prerequisite for mechanical analysis of the pipe jacking with the complex variable theory that the mechanical boundary must be transformed from the half‐plane with a rectangle cavity to the concentric ring. According to Riemann’s existence theorem and basic complex variable theory, a conformal mapping function is established. Both sides of boundary conditions equation are developed into Laurent series, and then the coefficients of complex stress function are solved by power series method. The derived solution is applied to an example and a comparison is made using FEM method to show the accuracy of the methods. The result shows the following: (1) the method presented in this paper is applicable to a shallow‐buried rectangular tunnel; (2) the complex function method proposed in this paper is characterized by clear steps, fast convergence, and simple operation.

Tunable power splitter based on MIM waveguide-rectangle cavity system with Kerr material

A tunable power splitter based on metal-dielectric metal (MDM) waveguide coupled with rectangle cavity with Kerr nonlinear material is proposed. The power splitter properties are simulated by the finite-difference time-domain (FDTD) method [Y. H. Guo et al., Opt. Express 19 (2011) 13831–13838]. Simple theoretically analysis and numerically calculation demonstrate that the waveguide-rectangle cavity coupled system performs a tunable plasmonic power splitter. Additionally, the output power ratio can be efficiency tuned by varying the control light intensity. Results obtained by the coupled mode theory are consistent with those from the FDTD simulation. The plasmonic splitter may become a choice for the highly integrated optical circuits.

Chaos in a stadium-shaped acoustic cavity

A numerical scheme has been developed to solve wave equations for chaotic systems such as stadium-shaped cavity. The same numerical method can also be used for finding wave properties of rectangle cavities with randomly placed obstacles. About 30,000 eigenvalues have been obtained accurately on a normal circumstance. For comparison, we also initiated an experimental study which determines both eigenfrequencies and eigenfunctions of a stadium-shaped cavity using pulse and normal mode analyzing techniques. The acoustic cavity was made adjustable so that the transition from nonchaotic (circle) to chaotic (stadium) waves can be investigated.

Two kinds of double Fano resonances induced by an asymmetric MIM waveguide structure

Asymmetric plasmonic waveguides with a shoulder-coupled rectangle cavity are proposed and investigated numerically by using the finite-difference time-domain (FDTD) method. The symmetry breaking of the structure results in a new discrete mode supported by the cavity. The extreme interference between two discrete states and an intrinsic wide continuous state gives rise to novel double Fano resonances with symmetric and anti-symmetric configurations. Coupled-mode theory (CMT) further confirms that two Fano profiles originate from the different coupling conditions of the cavity modes with the waveguides. Moreover, the sensing characters are performed. The Fano responses with the higher sensitivity and figure of merit (FOM) up to 57 are realized. Undoubtedly, the studied structure will play an important role in the nano-integrated plasmonic devices for optical switching and sensing.

Fano resonance in a symmetric waveguide system with different filled insulators

Anti-symmetric waveguide mode is firstly excited in a symmetric plasmonic structure by filling different materials. This waveguide system consists of a rectangle cavity, which is divided into two parts by a silica strip. Simulation results show that by filling different materials in the two parts of the cavity, both of the symmetric and anti-symmetric waveguide modes can be excited in the cavity. The interaction of the different waveguide modes, gives rise to the Fano resonances. Because of different origins, these Fano resonances exhibit different dependence on the parameters of the structure and can be easily tuned. This has important applications in highly sensitive and multiparameter sensing in the complicated environments. The mechanism based on different filled materials paves a new route to exciting anti-symmetric waveguide mode, and the utilization of the anti-symmetric mode in the MIM waveguide provides a new possibility for inducing Fano resonances.

Tunable multiple plasmon-induced transparency with side-coupled rectangle cavities

The tunable multiple plasmon-induced transparency (PIT) effect is investigated numerically in a metal-insulator-metal (MIM) waveguide with three side-coupled rectangular resonators. The system exhibits dual-mode PIT effects in the visible and near-infrared regions. By adjusting the geometrical parameters of the structure, we can manipulate not only each single PIT window, but also the double PIT windows simultaneously. Our structures may have potential applications for optical communication, integrated optics, and optical information processing. The finite element method (FEM) illustrates our theoretical design.

Plasmon-Induced Transparency in a Surface Plasmon Polariton Waveguide with a Right-Angled Slot and Rectangle Cavity

The phenomenon of plasmon-induced transparency (PIT) is realized a in surface plasmon polariton waveguide at near-infrared frequencies. The right-angled slot and rectangle cavity placed inside one of the metallic claddings are respectively utilized to obtain bright and dark modes in a typical bright-dark mode waveguide. A PIT transmission spectrum of the waveguide is generated due to the destructive interference between the bright and dark modes, and the induced transparency peak can be manipulated by adjusting the size of the bright and dark resonators and the coupling distance between them. Subsequently, spectral splitting based on the PIT structure is studied numerically and analytically. Simulation results indicate that double electromagnetically induced transparency (EIT)-like peaks emerge in the broadband transmission spectrum by adding another rectangle cavity, and the corresponding physical mechanism is presented. Our novel plasmonic structure and the findings pave the way for new design and engineering of highly integrated optical circuit such as nanoscale optical switching, nanosensor, and wavelength-selecting nanostructure.

Research on the heat transfer and 3-dimensional characteristics of natural convection in a small cavity with heat sources

Taking compact electronic equipments cooling problem as the background, the numerical simulation were conducted by SIMPLE algorithm with a QUICK scheme. The program was conducted by FOTRAN language. The natural convection was numerically studied in a small cavity with heat sources. The fluent of the cavity geometry, geometry of the heat sources, the local and number of the heat transfers on heat transfer and 3-dimensional characteristics were analyzed. The results showed that The heat transfer enforced firstly, and got weak when the geometry of the cavity increased. The influence of the heat sources was in a certain range. The length was 4 time width of the heat resources and the height was 2 time height of the heat resources. The heat transfer enforced when the geometry of the heat sources increased. The number of the rolls increased and air temperature rose when the number of the heat sources increased. The effect of heat transfer was better in a square cavity than rectangle cavity when the Rayleigh number was lower. The average Nusselt number at the top plate increased when the heat source was around center than around the boundary. The flow and heat transfer enforce.The effect of heat transfer was better when the heat source was around center than around the boundary. The temperature fields of X = L x /2 were similar as 2-dimensional temperature fields. The 3-dimensional model could be replaced by 2-dimensional model in influence range of heat source.

Numerical simulation of macrosegregation during solidification of binary alloys

Macrosegregation as a consequence of solidification of a binary Pb–48 wt% Sn alloy in two-dimensional rectangle cavity was investigated by two-phase model instead of the common used continuum model. The macroscopic transport of mass, momentum, species and energy was coupled with the microscopic descriptions of grain nucleation and growth. The mathematic equations of the two-phase model were discretized on staggered grids and solved by the finite volume method. The final tin concentrations along different heights over the bottom face were compared with the experiment measurements. Simulations with different microstructure parameters (second dendrite arm spacing (SDAS)) were conducted to ascertain the influence of microstructure on the final macrosegregation. The results show that with the decrease in SDAS value, the drag force as the resistance to relative motion between solid and liquid phase increases, and the macrosegregation during solidification is alleviated.

РЕЗОНАНСНОЕ СКВИД-ДЕТЕКТИРОВАНИЕ АКСИОНОВ ТЕМНОЙ МАТЕРИИ В ПРЯМОУГОЛЬНОМ РЕЗОНАТОРЕ

РЕЗОНАНСНОЕ СКВИД-ДЕТЕКТИРОВАНИЕ АКСИОНОВ ТЕМНОЙ МАТЕРИИ В ПРЯМОУГОЛЬНОМ РЕЗОНАТОРЕ

A band-pass plasmonic filter with dual-square ring resonator

In this paper, we show the simulation of a plasmonic band-pass filter which consists of two surface plasmon polaritons (SPPs) waveguides and a resonator in metal–insulator–metal (MIM) structure. The resonator is formed by two square rings and a patch between them. The patch is a tiny rectangle cavity in order to transfer the SPPs from one ring to the other. The finite element method (FEM) method is employed in simulation. The results show that the dual-ring resonator performs better than a single ring does. The 3 dB bandwidth near the peak wavelength λ = 1054 nm is merely 31.7 nm. The resonant wavelength can be shifted by changing the side length of the square ring. This narrow band-pass filter is easy to fabricate and has potential applications in future integrated optical circuits.

Plasmon induced transparency in a surface plasmon polariton waveguide with a comb line slot and rectangle cavity

The phenomenon of electromagnetically induced transparency (EIT) is demonstrated in a surface plasmon polariton waveguide at infrared frequencies. The comb line slot and rectangle cavity are placed inside one of the metallic claddings, and their coupling intensities among them are utilized to obtain bright and dark states. The destructive interference between the bright and dark states leads to an EIT-like transmission spectrum of the waveguide. The induced transparency peak can be manipulated by adjusting the coupling distance between the bright and dark states. Finally, the influence of Joule loss on the EIT-like effect is investigated. It is found that the EIT-like transmission contrast is sensitive to the variation in the metallic damping factor.

Numerical Simulations of Macrosegregation: A Comparison between Orthogonal Grids and Non-Orthogonal Grids

Macrosegregation predictions have been performed for the alloy solidification in regular and irregular geometries. The continuum model is used to describe the mass, momentum, species, and energy transportation. Based on the same conservation equations, different discretization forms are derived for the orthogonal grids and non-orthogonal grids. Comparisons are made between the results with orthogonal grids and non-orthogonal grids for different cases. Firstly, simulations are conducted for the Pb-48%Sn alloy solidified in a rectangle cavity, i.e., the H-H benchmark. Then, simulations are applied to a 53t steel ingot. Prediction results are compared with concentration measurements along different transverse sections. Although both prediction results are in good agreements with the measurements or results in references, some differences can be observed due to the different boundary fitness. It is advised to adopt the non-orthogonal grids in macrosegregation simulations instead of the orthogonal grids for complex computation domains.

Novel non-planar ring cavity for enhanced beam quality in high-pulse-energy optical parametric oscillators

A novel non-planar ring cavity is presented. It is shown that by using a fractional image rotation, i.e. a rotation whose angle cannot be expressed as 2π/n, where n is a small integer, the number of modes that can oscillate in the cavity is greatly reduced. This Fractional Image Rotation Enhancement (FIRE) cavity can thus be used to increase the beam quality in cases of low transversal mode discrimination, such as lasers with large pump and beam size and high-pulse-energy optical parametric oscillators (OPOs), especially when compactness and efficiency are key parameters. The experimental results obtained with a FIRE OPO for mid-IR (3–5 μm) generation based on a ZnGeP2 crystal pumped by a Ho3+:LiLuF4 MOPA system at 2.05 μm are compared to those realized with the same crystal and pump arrangement using a standard Rotated Image Singly-Resonant Twisted RectAngle (RISTRA) cavity. An increase of the beam quality from M2 of 2.08–2.29 to M2 of 1.88–1.99 is reached at 20 mJ pulse energy when the FIRE cavity is used.

Fabrication of Diamond-Structure Alumina Photonic Crystal with Rectangle Cavity Defect and its Microwave Properties

A diamond-structure alumina photonic crystal with a rectangle cavity defect has been fabricated combining stereolithography (SL) and gel-casting. In transmission spectra a resonance peak of transmission of 70% is observed in the band gap of 10.48Ghz-12.21Ghz, by comparing with the measured result of the perfect structure and theoretical calculations. Experimental results showed that the peak of photonic band gap was caused by the rectangle cavity defect of the diamond structural photonic crystal. The method provides us with a novel approach to fabricate ceramic microwave photonic crystals with point defect.

Resonant Mode Analysis of the Nanoscale Surface Plasmon Polariton Waveguide Filter with Rectangle Cavity

The resonant mode characteristics of the nanoscale surface plasmon polaritons (SPP) waveguide filter with rectangle cavity are studied theoretically. By using the finite difference time domain method, both the band-stop- and band-pass-type rectangle SPP filters are analyzed. The results show that the whispering gallery mode (WGM) and the Fabry–Perot (FP) mode can be supported by the rectangle SPP resonator. Furthermore, both traveling-wave mode and standing-wave mode can be realized by the WGM, while only standing-wave mode can be introduced by the FP mode. The traveling-wave mode can only be realized by the square-shaped SPP resonator, and the traveling-wave mode is splitted into two standing-wave modes by transforming the cavity shape from square to rectangle. Also, the effects of the cavity shape, cavity size, and coupling gap size on the transmission spectra of the SPP resonators are analyzed in detail. This simple SPP waveguide filter is very promising for the high-density SPP waveguide integrations.

Entropy generation of turbulent double-diffusive natural convection in a rectangle cavity

Abstract Turbulent double-diffusive natural convection is of fundamental interest and practical importance. In the present work we investigate systematically the effects of thermal Rayleigh number (Ra), ratio of buoyancy forces (N) and aspect ratio (A) on entropy generation of turbulent double-diffusive natural convection in a rectangle cavity. Several conclusions are obtained: (1) The total entropy generation number (Stotal) increases with Ra, and the relative total entropy generation rates are nearly insensitive to Ra when Ra ≤ 109; (2) Since N > 1, Stotal increases quickly and linearly with N and the relative total entropy generation rate due to diffusive irreversibility becomes the dominant irreversibility; and (3) Stotal increases nearly linearly with A. The relative total entropy generation rate due to diffusive and thermal irreversibilities both are monotonic decreasing functions against A while that due to viscous irreversibility is a monotonic increasing function with A. More important, through the present work we observe a new phenomenon named as “spatial self-copy” in such convectional flow. The “spatial self-copy” phenomenon implies that large-scale regular patterns may emerge through small-scale irregular and stochastic distributions. But it is still an open question required further investigation to reveal the physical meanings hidden behind it.