Twin Cavities Research Articles

Analysis of applying fin for charging process of phase change material inside H-shaped thermal storage

An H-shaped Double thermal storage unit has been studied numerically. A middle wall is sandwiched between two twin thermal storage cavities which are charging. The fins are attached to the middle wall to enhance the charging process. The set of equations modeling the charging process were solved using the Finite Element Method. The effects of different main parameters, namely thermal Fourier number, fin angle (symmetric cases) (−60 ≤ λ ≤ 60), 15 cases related to non-symmetric fin angle (−60 ≤ λl ≤ 60) and ( − 60 ≤ λr ≤ 60), and aspect ratio of fins (AR = 0.5–32) on the melting process of phase change material have been numerically studied. The results indicate that using fins for the cavity enhances the melting rate in the neighboring region due to the conductive heat transfer through the fins. Also, faster phase change material melting can be achieved by directing the fins upwards.

Chemical effects in “hydrodynamic cavitation on a chip”: The role of cavitating flow patterns

Amongst the advanced oxidation processes (AOPs), hydrodynamic cavitation (HC) has emerged as one of the most cost-efficient, simple and ecologically friendly approaches in the recent decade. This type of the cavitation, in contrast to its counterpart (acoustic cavitation), has a huge potential to upscale to the industrial levels. In the recent years, the micro-scale HC (HC on a chip concept) has exhibited favorable efficacy in terms of nucleation type, surface effects and flow pattern dominancy. In this study, the chemical effects of the HC on a chip concept are shown for the first time by considering the effects of the cavitating flow patterns. So, this is the first attempt to understand the effects of the inception and developed cavitating flow patterns on the chemical reactions during the bubble collapse in the micro-scale. In addition, a particular attention is paid to the chemical reaction effects before the cavitation bubble observation in this investigation. Our results indicated that the triiodide releasing amount was interestingly maximum before the inception occurred, especially at the first cycle. The released amount decreased at the inception and increased for the case of the developed twin cavities. We also showed that, comparing to our previous studies, the cavitation arrived at a relatively lower upstream pressure in the open loop cavitation test rig. Therefore, the outcome of this approach reveals the significance of the in-depth investigations of the complex and very transient nature of the cavitation at different flow patterns. Furthermore, this study implied that reactors benefitting HC on a chip concept will be environmentally friendly tools for producing products from the wastes and worthless materials in the near future.

Dynamic Behaviour of Abandoned Underground Mines: Insights from Numerical Simulations

The Apulian region (south-east of Italy) is characterized by the presence of old underground cavities used for the extraction of soft calcarenite rocks and then abandoned over time. The assessment of stability of these caves represents a challenging problem, especially for the areas of possible interaction of the caves with overlying structures and infrastructures. The role of environmental factors in triggering disruption processes in the cave has been extensively studied in the literature, but the instability effect related to dynamic loads is often underestimated. Consequently, the purpose of the present work is to propose some advancements in this field by evaluating the effects of dynamic loads, consistent with the regional seismicity, on the stability of calcarenite underground cavities. A large number of two-dimensional parametric finite element analyses has been carried out on ideal cases of single rectangular cavities. The study allowed to detect appreciable instability effects caused by the dynamic input, depending on the cavity width, the thickness of the roof, and the energy content of the dynamic input. The interaction between twin cavities under dynamic conditions has been also studied from a numerical point of view. The results show that plastic failure in the septum is reached earlier under dynamic conditions than static and it is again dependent on the cavity width and the roof thickness. Lastly, a numerical procedure to calculate factor of safety against either shear failure or tensile failure mechanisms has been proposed, which allows to quantify the change of the stability conditions from static to dynamic conditions.

A class of organic cages featuring twin cavities

A variety of organic cages with different geometries have been developed during the last decade, most of them exhibiting a single cavity. In contrast, the number of organic cages featuring a pair of cavities remains scarce. These structures may pave the way towards novel porous materials with emergent properties and functions.We herein report on rational design of a three-dimensional hexaformyl precursor 1, which exhibits two types of conformers, i.e. Conformer-1 and -2, with different cleft positions and sizes. Aided by molecular dynamics simulations, we select two triamino conformation capturers (denoted CC). Small-sized CC-1 selectively capture Conformer-1 by matching its cleft size, while the large-sized CC-2 is able to match and capture both conformers. This strategy allows the formation of three compounds with twin cavities, which we coin diphane. The self-assembly of diphane units results in superstructures with tunable proton conductivity, which reaches up to 1.37×10-5 S cm-1.

On cavitation inception and cavitating flow patterns in a multi-orifice microfluidic device with a functional surface

During the last decade, hydrodynamic cavitation has been implemented in various applications such as energy harvesting and biomedical applications. Facile hydrodynamic cavitation methods are required for fulfilling the requirements in these applications. In this study, a new generation microfluidic device containing eight parallel micro-orifices with a new design was fabricated and tested with the purpose of intensifying the cavitating flows and early cavitation inception. The roughness elements in the micro-orifices facilitated cavitation inception. This study presents a general perspective of occurrence of different cavitating flow patterns in microscale and addresses the ambiguities about the conditions for the formation of a specific flow pattern. Cavitation inception occurred with the appearance of small bubbles emerging from roughness elements at a rather low upstream pressure in the open loop experimental setup. A reduction in the cavitation number resulted in the formation of different flow patterns such as cavitation clouds, twin cavities, sheet cavities, and bubbly flows. Having several flow patterns with different intensities all together within a single microfluidic device is the main advantage of the proposed device over the state of the art microfluidic devices. Generation of flow patterns with various released energy levels makes this proposed device a unique multi-functional platform, which can be implemented to a lab on a chip platform for applications such as nanoparticle synthesis and wound healing.

Twin-beam-enhanced displacement measurement of a membrane in a cavity

We report an experimental demonstration of quantum-enhanced displacement measurement of a membrane in an optical cavity by using bright quantum correlated light to surpass the shot-noise limit (SNL). The optical cavity enhances the displacement signal and the twin beams suppress the noise background 3 dB below the SNL at an equivalent optical power. Thus, the signal-to-noise ratio is significantly improved by simultaneously using optical cavities and twin beams, and a sensitivity of 200 am/Hz is achieved. The frequency fluctuations of twin beams are analyzed and reduced by using optical twin cavities. These results provide a useful method for precision measurements as well as to control cavity optomechanical systems with nonclassical light.

A Covering Type Extrusion Die with Twin Cavities for Semi-Hollow Al-Profiles

A new structure named covering type with twin cavities in a die for the semi-hollow aluminum profiles was present. The determination of structure parameters was introduced in detail. Mainly including the selection of the machine, the arrangement of portholes, the structure design of chamber and the selection of bearing. The method of checking the die strength was introduced. According to the extrusion results, the structure of the traditional solid die, the porthole die with single cavity and the covering type structure with twin cavities were compared. The characteristics of the latter structure were simple and easy to process. The practical application shows that the new die structure can enhance the die life, improve the production efficiency and reduce the cost. The high precision and the surface brightness of the profiles were obtained. The structure is worth promoting. The aim is to provide reliable data and reference for the further research and development of this technology on the extrusion die with multi-cavities in a die.

Effect of Twin Cavities on the Axially Loaded Pile in Clay

Effect of Twin Cavities on the Axially Loaded Pile in Clay

The Diffraction of Rayleigh Waves by Twin Circular Cavities in a Poroelastic Half-Space

ABSTRACTThe diffraction of Rayleigh waves by twin circular cavities in a poroelastic half-space is investigated using the indirect boundary integral equation method (IBIEM). To satisfy the boundary conditions on the free surface, Green’s functions of compressional and shear wave sources in a poroelastic half-space are derived based on Biot’s theory. It is verified that the IBIEM has great accuracy and numerical stability. Then, the influences of the drainage boundary condition, incident wave frequency, porosity, and cavity spacing on the dynamic responses are investigated by numerical examples. The results show that the amplification effect of the twin cavities is greater in the case of undrained boundary conditions, lower frequencies, and smaller cavity spacings. The porosity of the saturated medium also influences the dynamic responses because the velocity of the Rayleigh wave will change with the porosity of the saturated medium.

An Extrusion Die with Twin Cavities for Semi-hollow Al-Profiles

The importance of extrusion die with multi-cavities was elaborated. Through an actual case. A new structure for the semi-hollow Al-profiles was introduced. The structure named substituted type to solve the cantilever strength was presented. And the selection and the optimization of structure parameters were described in detail. Including the determination of extrusion machine ability, the layout for the die holes, the use of computer simulation software for analysis and comparison to determine the arrangement of portholes, the structure of chamber in female die, the selection of bearing etc. It was shown that the structure with twin cavities for semi-hollow profiles is effective, the structure can greatly improve the production efficiency and reduce the cost. It is worth promoting. The purpose is to provide reliable data and reference for the further research and development of this technology on the extrusion die with multi-cavities in a die.

Effect of finite width cavity in axisymmetric supersonic flow field

In this research, the effect of finite width cavities in supersonic flow field is experimentally investigated. The test facility consists of a supersonic nozzle, which provides flow Mach number of 1.9. A circular cross-sectional test section is fastened at the exit of the nozzle. Cavities are incorporated in the test section at a distance of 20 mm from the inlet. Cavities of constant length and width, and varying depth are used for the study. Entrainment of flow in the main stream is observed immediate downstream of the cavity aft edge due to three dimensional effect. As the depth of the cavity is increased, residence time of the fluid as well as the mixing characteristics are enhanced and stagnation pressure loss also increased. Twin cavities are also arranged symmetrically, which further leads to an improvement in mixing with marginal rise in stagnation pressure loss.

Twin Cavities: An Unusual Radiological Finding in Pulmonary Tuberculosis

Twin Cavities: An Unusual Radiological Finding in Pulmonary Tuberculosis

Collective Dark States Controlled Transmission in Plasmonic Slot Waveguide with a Stub Coupled to a Cavity Dimer

We report collective dark states controlled transmission in metal-dielectric-metal waveguides with a stub coupled to two twin cavities, namely, plasmonic waveguide-stub-dimer systems. In absence of one individual cavity in the dimer, plasmon-induced transparency (PIT) is possible when the cavity and the stub have zero detuning in the resonance frequencies. However, it is shown that the hybridized modes in the dimer collectively generate two dark states which make the stub-dimer “invisible” to the straight waveguide, splitting the original PIT peak into two in the transmission spectrum. Simultaneously, the original PIT peak becomes a dip due to dark state interaction, yielding anti-PIT-like modulation of the transmission. With full-wave electromagnetic simulation, we demonstrate that this transition is controlled by the dimer-stub separation and the dimer-stub relative position. All results are analytically described by the temporal coupled mode theory. Our results may be useful in designing densely integrated optical circuits and in optical sensing and switching applications.

The combination of high Q factor and chirality in twin cavities and microcavity chain.

Chirality in microcavities has recently shown its bright future in optical sensing and microsized coherent light sources. The key parameters for such applications are the high quality (Q) factor and large chirality. However, the previous reported chiral resonances are either low Q modes or require very special cavity designs. Here we demonstrate a novel, robust, and general mechanism to obtain the chirality in circular cavity. By placing a circular cavity and a spiral cavity in proximity, we show that ultra-high Q factor, large chirality, and unidirectional output can be obtained simultaneously. The highest Q factors of the non-orthogonal mode pairs are almost the same as the ones in circular cavity. And the co-propagating directions of the non-orthogonal mode pairs can be reversed by tuning the mode coupling. This new mechanism for the combination of high Q factor and large chirality is found to be very robust to cavity size, refractive index, and the shape deformation, showing very nice fabrication tolerance. And it can be further extended to microcavity chain and microcavity plane. We believe that our research will shed light on the practical applications of chirality and microcavities.

3D Diffraction of obliquely incident SH waves by twin infinitely long cylindrical cavities in layered poroelastic half-space

This paper studies three-dimensional diffraction of obliquely incident plane SH waves by twin infinitely long cylindrical cavities in layered poroelastic half-space using indirect boundary element method. The approach is validated by comparison with the literature, and the effects of cavity interval, incident frequency, and boundary drainage condition on the diffraction are studied through numerical examples. It is shown that, the interaction between two cavities is significant and surface displacement peaks become large when two cavities are close, and the surface displacement may be significantly amplified by twin cavities, and the influence range with large amplification can be as wide as 40 times of the cavity radius. Surface displacements in dry poroelastic case and saturated poroelastic cases with drained and undrained boundaries are evidently different under certain circumstances, and the differences may be much larger than those in the free-field response.

Nonlinear Amplification of Seismic Ground Motion by Twin Cavities

This paper presents nonlinear amplification of seismic ground motion by twin cavities in layered sites. The equivalent linear method is used in the dynamic analysis and Lysmer-Kuhlemeyer transmitting boundary is used at the left and right boundaries of the computation region. It is shown that, cavities have significant effect on seismic ground motion, and soil nonlinearity has significant effect on seismic ground motion around cavities. The PGAs in linear and nonlinear analysis may be increased by 24.4% and 19.2%, compared with those in the free-field response. The PGA in nonlinear analysis may be decreased by 44.6%, compared with that in the linear analysis.

Influence of dimensional fluctuations on the optical coupling between nanobeam twin cavities

In this paper, we study the influence of fabrication uncertainties on silicon-on-insulator optical nanosystems performances. The considered structure consists in near-field coupled twin nanobeam cavities. We have performed experiments on a given population of samples, and noticeable changes in light propagation and localization were observed. Thanks to an analytic coupled-mode-based method supported by three-dimensional numerical computations, we quantitatively explain these experimental observations. We have indeed noticed that a few percent variation of the system nominal dimensions is enough to significantly change the optical coupling conditions between the cavities. Particularly, we show that, under specific conditions, light can stay locked in one of the two cavities. This result highlights the issues of reproducibility and reliability concerning future industrial application, like nano-optical electromechanical systems.

On the Stability of Unsaturated Loess Slope under Tunneling Condition

As a unique mode of soil erosion, loess cavities often act as the critical factor to the stability of the highway slopes of unsaturated loess. In this paper, the unsaturated loess slope stabilities are comparatively studied in different cases through the developed program of the strength reduction FEM, such as loess cavities in different position, single- & twin cavities, occurrence and loss of matric suction etc. The work done in this paper revealed the mechanism how the tunneling and the matric suction have effect on the stability of unsaturated loess slope to some extent. The results not only indicate that the loess cavities favor to maintain the stability of slope with the cavities located near the slope's crest, while the loess cavities reduce the stability of slope with the cavities located near the slope's toe, but also disclose that the safety factor of the unsaturated loess slope increases and the potential sliding surface move downward with considering the matric suction and vice versa. In addition, the twin cavities near the slope's toe have the obvious negative effects on slope's stability.

Instrumentation with polarized neutrons

Neutron scattering with polarization analysis is an indispensable tool for the investigation of novel materials exhibiting electronic, magnetic, and orbital degrees of freedom. In addition, polarized neutrons are necessary for neutron spin precession techniques that path the way to obtain extremely high resolution in space and time. Last but not least, polarized neutrons are being used for fundamental studies as well as very recently for neutron imaging. Many years ago, neutron beam lines were simply adapted for polarized beam applications by adding polarizing elements leading usually to unacceptable losses in neutron intensity. Recently, an increasing number of beam lines are designed such that an optimum use of polarized neutrons is facilitated. In addition, marked progress has been obtained in the technology of 3 He polarizers and the reflectivity of large- m supermirrors. Therefore, if properly designed, only factors of approximately 2–3 in neutron intensity are lost. It is shown that S-benders provide neutron beams with an almost wavelength independent polarization. Using twin cavities, polarized beams with a homogeneous phase space and P > 0.99 can be produced without significantly sacrificing intensity. It is argued that elliptic guides, which are coated with large m polarizing supermirrors, provide the highest flux.

Development of Cavitation in Refrigerant (R-123) Flow Inside Rudimentary Microfluidic Systems

The existence of hydrodynamic cavitation in the flow of refrigerant (R-123) through micro-Venturis has been viewed in the form of a bubbly cavitating regime. Flow visualization discloses inchoate cavitation bubbles/bubble clouds emerging from the inside of the micro-Venturi throat egress. The bubble density decreases when the flow passes through the diffuser section and further downstream into the microchannel owing to the collapse of the vapor filled bubbles caused by a rise in the static pressure. An increase in the flow rate beyond cavitation inception results in the formation of twin cavities. The elongated cavities emerge from inside the Venturi boundaries and amalgamate further downstream sending out thick and dense vapor/bubble clouds. The discharge is affected by the aggressive cavitation and flow rate choking has been observed at different backpressures. The physical properties of the liquid (wettability, small contact angle, etc.) assist in the inhibition of cavitation by modifying the surface nuclei population. The liquid is able to endure significant tension and remains in a metastable state before sudden rupture. Flow visualization reveals considerable differences between cavitating flow patterns observed in refrigerant (R-123) and water flows through a micro-Venturi system.1575