Bottom Of Cavity Research Articles

Integrated studies of convection and ice layer formation during cooling of the bottom of a rectangular cavity

Experimental studies of the processes of crystallization of water as a liquid — simulator of melts with an inverse dependence of the density of melts on temperature — were carried out on two flat models. With the rapid cooling of the bottom of the cavity, substantial undercooling of the bottom layer of the liquid can be observed. The hydrodynamics in the process of growth of the ice layer at the bottom of the cavity was investigated. The effect of convective flow on the rate of crystallization and on the forms of the crystallization front has been studied. The evolution of the temperature field in the process of crystallization of water at the lower cooled boundary of the cavity is studied. It is shown that the evolution of temperature fields tracks the development stages of instability of the bottom layer of a liquid and the development of Rayleigh-Benard convection observed in a hydrodynamic experiment.

Numerical simulation of the crystallization front propagation during the bottom cooling of a flat layer of water

The process of crystallization of water after a sudden cooling of the bottom of a rectangular cavity is investigated by numerical simulation of conjugate convective heat exchange using the finite element method. Detailed information has been obtained on hydrodynamics, temperature fields, and the forms of the crystallization front. The crystallization of water is studied by taking into account the dependence of the density on the temperature and heat of the phase transition. Numerical studies are carried out using a proprietary software package. Adaptive triangular grids are used to track the position of the crystallization front at each time step.

Double Resonant Cavity of Oxides/Metal/Nitrides for Long Wavelength Infrared Sensing

Sub wavelength double resonant cavity structures of oxides/metal/nitrides (OMN) for bolometric detection in the long wavelength infrared (LWIR) range are studied for the first time. An optimized OMN structure allows for a significant enhancement in effective absorbance (50%-70%) with respect to that of the bare film on an amorphous Al2O3 substrate (1-30%) in the LWIR atmospheric transparent window (8-14 μm). Remarkable improvement in the response range and sensitivity have been achieved by designing the double cavity OMN structure, where the bottom cavity originates from the high reflectance between the transition metal oxide film and the Al2O3 substrate, while the silicon nitride film on the top serves as a quarter wavelength anti-reflection cavity centered at about 8 μm. The OMN structured LWIR detector can be realized by cost effective methods of chemical solution deposition (CSD) or radio frequency (RF) sputtering deposition. A detectivity of 0.18-0.2×108 cm·Hz0.5/W@6-10 Hz was achieved by using the O...

Quintuple-mode wideband bandpass filters with improved out-of-band rejection

AbstractThis paper presents design of quintuple-mode wideband bandpass filters, implemented with off-centered perturbed metallic cylinders in a rectangular waveguide cavity. Three perturbation cylinders are placed at the bottom of the rectangular waveguide cavity, along with a pair of perpendicularly fed coaxial lines; excite five quasi-transverse magnetic modes to realize the desired passband. The height of the waveguide cavity and the shape of the perturbation cylinders are exploited to shift the resonant modes far away from the passband and achieve a good out-of-band rejection and sharp skirt selectivity. The filter operates at the center frequency of 2.68 GHz with a wide fractional bandwidth of 43%. The proposed filter is fabricated with aluminum. The measured and simulated results are in good agreement with each other.

MODELING THE THERMO-HYDRODYNAMICS OF A SHALLOW BOREAL LAKE: 3D MODEL VERIFICATION

3D modelled results were verified against observed data obtained along three transects in a shallow boreal lake Vendyurskoe several times during the ice season. It was revealed that 1) the model overestimates ice thickness; at the same time, modelled ice-on and iceoff dates are very close to those observed; 2) in general, the model underestimates the water temperature by 8–10 %; 3) comparison of modelled currents with observed data on mean currents revealed qualitative compliance of current direction (coincidence of quadrants) and modulus of velocity (coincidence of the order of magnitude and a slow decrease of velocity over time during the ice season 1994–1995). Underestimated water temperature may affect the quality of simulation of chemical-biological processes. For instance, one may expect overstated absolute values of dissolved oxygen content in the bulk of the water column. Overestimated modelled water temperature for layers near the bottom of local cavities may influence the rates of the chemical-biological processes occurring there. Despite the model errors found in the course of verification, the model quite realistically describes the hydrodynamic processes in a shallow ice-covered lake, and can therefore be regarded as a useful tool for further research after the diagnosed defects are removed from the computer code. As an option of the code improvement, the authors consider further elaboration of the module of heat/salt flux to/from bottom sediment, development of parameterisations facilitating heat transfer along the water column on sub-grid scale.

An Investigation on Ventilation of Building-Integrated Photovoltaics System Using Numerical Modeling

Abstract This study numerically investigates the thermal behavior and airflow characteristics of the building-integrated photovoltaic (BIPV) façade. A three-dimensional model is developed based on the typical BIPV façade. Computational fluid dynamics (CFD) with the shear stress transport (SST) κ-omega turbulent model is used in the study. The effects of geometric configurations on the BIPV cell temperature in steady state are evaluated including the sizes of the bottom and top openings and the depth of the back air cavity (or so-called cavity depth). When the sizes of the inlet and outlet openings are the same, the effects on the decrease of cell temperature are limited. By enlarging the bottom (inlet) opening, the impact of ventilation in the cavity behind is more significant and the cell temperature decreases. Cavity depth is also a vital factor affecting BIPV cell temperature. The paper identifies the optimal cavity depth of approximately 100–125 mm. Flow disturbance and a vortex may be observed at the bottom and top of the air cavity, respectively, as the cavity depth increases which negatively affects the ventilation causing these flow disturbances to increase the cell temperature. Thermal effects of environmental conditions are compared with regard to two selected BIPV configurations. The wind velocity and the attack angle also have an obvious impact on cell temperature. Ambient temperature and solar irradiance exhibit a linear relationship with BIPV cell temperature as expected.

Experimental Study of Air Layer Drag Reduction with Bottom Cavity for A Bulk Carrier Ship Model

Air lubrication by means of a bottom cavity is a promising method for ship drag reduction. The characteristics of the bottom cavity are sensitive to the flow field around the ship hull and the effect of drag reduction, especially the depth of the bottom cavity. In this study, a ship model experiment of a bulk carrier is conducted in a towing tank using the method of air layer drag reduction (ALDR) with different bottom cavity depths. The shape of the air layer is observed, and the changes in resistance are measured. The model experiments produce results of approximately 20% for the total drag reduction at the ship design speed for a 25-mm cavity continuously supplied with air at Cq = 0.224 in calm water, and the air layer covers the whole cavity when the air flow rate is suitable. In a regular head wave, the air layer is easily broken and reduces the drag reduction rate in short waves, particularly when λ/Lw1 is close to one; however, it still has a good drag reduction effect in the long waves.

Factors affecting irradiation of nano & micro materials by laser treatment industrial unit

This work presents an industrial unit for hardening and treatment of nano-materials and micrometers to improve their physical, chemical and mechanical properties by exposing them to laser radiation. The treatment process is carried out through the laser treatment industrial unit. It is composed of circular metal base with motor, rectangular holder, moving sides. The sample installation cavities which are metal joints that widen and shrink according to sample dimensions by incorporating the cavities vertically and moving the sides, the unit has black front and back barrier to prevent lasers with bottom cavity to store the black barrier. Scaling must be compatible with laser diameter or width; the unit has partition barriers and fixing arms to control the process. Laser and unit are operated to complete the treatment, method is physical process, the laser beam go through treated material without being absorbed or interact by transparent material, the treated nanomaterials or short fibres were collected. The samples were exposed to Nd -YAG third harmonic generation and Argon ion CW laser. The hardness was measured before and after laser irradiation. The current work will present an application on the hardening of E-fibre glass 731ED 1/32″.The change in hardness were explained by raman spectroscopy. The research end with conclusions and recommendation for the expected application of the new treatment unit and method.

Numerical study of the effect of ship attitude on the perform of ship with air injection in bottom cavity

Air lubrication by means of a bottom cavity is a promising way for ship drag reduction. The characteristics of air layer under the bottom cavity and effect of drag reduction are sensitive to the attitude of ship model. To investigate the stability of air layer under different navigation condition of air cavity ship, a method with the combination of RANS equations and VOF model is proposed for the viscous-flow calculation of a large flat bottom ship, which is verified by the model-test result. The effect of heeling and trim on the formation and stability of air layer is investigated. Present numerical results show that there is a critical value of heeling arctan(h/Bc) with the definition the cavity depth and width of the h/Bc. The air layer would be stable if ship heeling is less than the critical value. The air layer broke when the heeling is greater than the critical value, and heeling increase, broken phenomenon aggravate. The trim angle of the ship is unfavorable to the stability of the air layer and it should be avoided as much as possible in the course of navigation.

Concrete ablation analysis for molten corium-concrete interaction mitigation strategy

The molten corium-concrete interaction (MCCI) has been receiving increased attention because it can cause the direct release of core melt into the environment via basemat melt-through (BMT). The MCCI analysis has high uncertainty and it is not fully understood according to the current level of knowledge. However, since there is a possibility that MCCI may occur, nuclear power plants (NPPs) must take action to mitigate the MCCI based on quantitative analysis. Therefore, in this study, an analysis model was proposed and MCCI analysis was conducted for NPPs using the model to provide database for establishment of MCCI mitigation strategy of real NPPs. First, the CORQUENCH code was selected as the analysis tool to conduct the MCCI analysis for NPPs, which was released in August 2018 (version 4.1b). The analysis model was proposed and validated for both small and large MCCI experiments. The validation results confirmed that the analysis model predicts the experimental results well regardless of experimental scale within a reasonable range. Second, MCCI analysis was conducted for the NPPs under a conservative assumption to consider the uncertainties in the initial conditions. The results showed that continuous ablation occurs when water is not injected into the reactor cavity and the containment liner plate is damaged by the core melt at 916 min after the melt pouring time. To verify the analysis results, sensitivity analyses were conducted for the initial corium temperature, total corium mass, melt eruption model, void fraction model, and time step. Third, possible MCCI mitigation strategies were proposed based on additional analyses. One strategy is adding new concrete at the bottom of the reactor cavity. In this case, the analysis results showed that the additional concrete should have a thickness of 40 cm or more to secure extra time for the core melt cooling. The other is injecting water into the reactor cavity. The analysis results confirmed that the core melt is effectively cooled down when the water is injected in the early phase.

Convective heat transfer enhancement: effect of multi-frequency heating

PurposeThis study aims to enhance natural convection heat transfer for a porous thermal cavity. Multi-frequency sinusoidal heating is applied at the bottom of a porous square cavity, considering top wall adiabatic and cooling through the sidewalls. The different frequencies, amplitudes and phase angles of sinusoidal heating are investigated to understand their major impacts on the heat transfer characteristics.Design/methodology/approachThe finite volume method is used to solve the governing equations in a two-dimensional cavity, considering incompressible laminar flow, Boussinesq approximation and Brinkman–Forchheimer–Darcy model. The mean-temperature constraint is applied for enhancement analysis.FindingsThe multi-frequency heating can markedly enhance natural convection heat transfer even in the presence of porous medium (enhancement up to ∼74 per cent). Only the positive phase angle offers heat transfer enhancement consistently in all frequencies (studied).Research limitations/implicationsThe present research idea can usefully be extended to other multi-physical areas (nanofluids, magneto-hydrodynamics, etc.).Practical implicationsThe findings are useful for devices working on natural convection.Originality/valueThe enhancement using multi-frequency heating is estimated under different parametric conditions. The effect of different frequencies of sinusoidal heating, along with the uniform heating, is collectively discussed from the fundamental point of view using the average and local Nusselt number, thermal and hydrodynamic boundary layers and heatlines.

Detection of Simulated Periradicular Lesions in Porcine Bone by Optical Coherence Tomography

IntroductionThe accurate detection of periradicular lesions located under a nonperforated cortical plate poses a challenge in endodontic microsurgery. Optical coherence tomography (OCT) is a noninvasive imaging method that has been successfully used in many dental applications. In this study, we investigated if spectral-domain OCT (SD-OCT) could be used to determine simulated periradicular lesions. MethodsTwenty-eight cavities with different depths were prepared on bone plates obtained from 5 porcine mandibles. Both 3-dimensional SD-OCT imaging and micro–computed tomographic (micro-CT) imaging were used to image the bottom of the air-filled cavity and the cavity filled with soft tissue for comparison. The residual bone thickness under the cavity was measured by SD-OCT and micro-CT imaging and compared using the Pearson correlation. ResultsThe air-filled lesions were readily detected; yet, filling of the cavity with soft tissue diminished the appearance of the lesion boundaries in the SD-OCT images. The optical values of residual bone thickness obtained from SD-OCT ranged from 0.14–2.11 mm, which corresponded to the range of 0.26–1.18 mm from micro-CT imaging. A strong correlation was found between the 2 imaging modalities (r = 0.96; range, 0.94–0.98). The slope (1.56) of the linear regression matched the bulk refractive index of bone tissues. ConclusionsSD-OCT allows for visualization of the lesion boundaries via intact bone surfaces and may be a promising, practical, and nonirradiating adjunct tool for chairside localization of periradicular lesions in bone.

Human mitochondrial carnitine acylcarnitine carrier: Molecular target of dietary bioactive polyphenols from sweet cherry (Prunus avium L.)

The effect of polyphenols, recognized as the principal antioxidant and beneficial molecules introduced with the diet, extracted from sweet cherry (Prunus avium L.) on the recombinant human mitochondrial carnitine/acylcarnitine transporter (CACT) has been studied in proteoliposomes. CACT transport activity, which was strongly impaired after oxidation by atmospheric O2 or H2O2, due to the formation of a disulfide bridge between cysteines 136 and 155, was restored by externally added polyphenols. CACT reduction by polyphenols was time dependent. Spectroscopic analysis of polyphenolic extracts revealed eight most represented compounds in four cultivars. Molecular docking of CACT structural omology model with the most either abundant and arguably bio-available phenolic compound (trans 3-O-feruloyl-quinic acid) of the mix, is in agreement with the experimental data since it results located in the active site close to cysteine 136 at the bottom of the translocation aqueous cavity.

Evolution of the Fine Structure of the Matter Distribution of a Free-Falling Droplet in Mixing Liquids

In this paper we study the evolution of the matter distribution pattern of ink droplets falling freely into calm water and forming a cumulative back jet by tracing with high-speed video recording. In the phase of primary contact and immersion, the matter of a drop merging with the receiving liquid is distributed in the form of fine fibers forming a regular striped pattern on the surface of the growing crown and a net pattern consisting of three-, four-, and pentagonal cells at the cavity bottom. The fibrous distributions of the colored liquid remain at all subsequent stages of the flow evolution until the formation of a vortex cascade. Then the picture is blurred due to molecular diffusion in a practically quiescent liquid. The formation of a discrete (fibrous) pattern of the drop matter distribution is associated with the compactness of the region of release of the available potential surface energy during the confluence of liquids that initiates a fast movement of a thin layer. Subsequent fiber preservation is provided by the slowness of molecular diffusion.

Interior jump and piecewise regularity for compressible Stokes equations in the T-shaped cavity domain

In the T-shaped cavity domain the fluid flows consist of three essential phenomena that are the flows in the top region with inflow and outflow, the ones in the bottom (cavity) region and the interface fluctuation between two flows. We consider a simple modeling problem of compressible Stokes flows to illustrate them. The domain is split by the interior curve connecting the upstream and downstream corners. The transport equation is directed by the vector field having jump discontinuity with respect to the curve. So the continuity equation shows the pressure jump solution across the curve and the velocity vector by the momentum equations has the singular behaviors due to the pressure gradient plus the corner singularities at the non-convex corners. We establish a piecewise maximal regularity by constructing a vector function corresponding to the pressure jump on the interior curve, without subtracting the corner singularities.

Compact differential dual‐band bandpass filter using single quad‐mode metal‐loaded dielectric resonator

This letter presents a novel miniaturized differential dual-band bandpass filter (BPF) using a single quad-mode metal-loaded dielectric resonator (DR). The differential dual-band BPF is designed in a single-cavity configuration with one quad-mode DR and four feeding probes, featuring compact size. The rectangular DR is directly mounted on the bottom of the metal cavity and covered by a metal plate on the top surface. It allows two pairs of orthogonal modes (LSE10 and LSM10), which can be differentially excited and coupled by introducing proper perturbation for constructing dual-band differential-mode frequency response. To validate the proposed idea, a compact differential BPF with good performance using a quad-mode DR cavity is designed, fabricated, and measured. The simulated and measured results with good agreement are presented.

Biomechanical behavior of cavity design on teeth restored using ceramic inlays: An approach based on three-dimensional finite element analysis and ultrahigh-speed camera

Ceramic fracture and debonding are the primary failures that follow ceramic inlay and can lead to stress and tooth fracture. In this study, we examined two designs—concave and flat—of the gingival cavity bottom for tooth cavities restored using ceramic inlays. We investigated the biomechanical behavior of ceramic inlay–restored teeth (concave and flat) through three-dimensional finite element analysis (FEA) and experimentally validated the results using an ultrahigh-speed camera. We conducted in vitro real-time recording of the deformation of a restored tooth during loading using an ultrahigh-speed camera. This technique enables further image registration to observe deformation variation and vector fields. The deformation vector fields revealed that the concave design moved the deformation toward the buccal side of the cavity bottom, whereas the flat design moved it toward the palatal side. These findings correlated with the FEA results, which indicated that the concave design constrained stress in the dentin cavity and relieved palatal stress. Our results suggest that incorporating a concave design in cavity preparation can improve the fracture resistance of ceramic inlay–restored teeth, preventing unrestorable fractures. The current study is the first to utilize an ultrahigh-speed camera in dental biomechanics, and such cameras are useful for nondestructive and dynamic analysis. Statement of SignificanceFirst utilize ultrahigh-speed cameras in dental biomechanics analysis. Tooth fracture videos captured by ultrahigh-speed camera helps us learn fracture mechanics in between tooth cavity design and ceramic inlay. Concave design leads to stress in safer areas that causes a less damaging fracture. Minimal invasive preparation by concave design strengthens tooth fracture resistance. Non-destructive data from ultrahigh-speed cameras combined with FEA can get more insight into how the stress and strain derived in biomaterials.

Quadruple-Mode Wideband Bandpass Filter with Improved Out-of-Band Rejection

This paper proposes a method for designing a quadruple-mode wideband bandpass filter using off-centered perturbed metallic cylinders in a rectangular waveguide cavity with compact size and improved out-of-band rejection. Two off-centered perturbation cylinders were placed at the bottom of the rectangular waveguide cavity along with a pair of perpendicularly-fed coaxial lines, which excited four quasi-transverse magnetic (TM) modes to realize the desired passband. The height of the waveguide cavity and the shape of the perturbation cylinders were exploited to achieve an all quasi-TM modes filter with good out-of-band rejection and sharp skirt selectivity. The proposed filter operates at 2.93 GHz center frequency with 38% wide fractional bandwidth (FBW). The proposed filter is fabricated using aluminum. The measured and simulated results are in good agreement with each other.

Computational study of axisymmetric divergent bypass dual throat nozzle

A bypass dual throat nozzle (BDTN) is a fluidic thrust-vectoring nozzle (FTVN) that is based on the conventional dual throat nozzle (DTN). The BDTN provides high thrust vectoring (TV) efficiency with low thrust loss and does not consume additional secondary flow. A fixed-geometry axisymmetric divergent BDTN (ADBDTN) that has flow adaptive capability and can provide high TV efficiency in the pitch and yaw directions without substantially changing the working state of the engine is investigated in this study. In addition, the TV mechanism and the effects of the expansion ratio, bypass width, and rounding radii at the nozzle throat and cavity bottom on the nozzle performance under the vectored state are presented in detail. Results show that the TV mechanism of the ADBDTN is similar to that of the DTN, which deflects the primary flow through the separation zone inside the recessed cavity. Larger expansion ratios and rounding radii at the nozzle throat contribute to the large pitch thrust-vector angle and high discharge coefficient. Decreasing the expansion ratio and increasing the rounding radius at the nozzle throat can improve the thrust coefficient. As the bypass width increases, the thrust and discharge coefficients increase and the pitch thrust-vector angle reaches its maximum. The effect of the rounding radius at the cavity bottom on the nozzle performance is relatively small. For the configuration with flow adaptive capability, the largest pitch thrust-vector angle is 25.37∘ and the highest thrust and discharge coefficients are 0.957 and 0.983, respectively.

Effects of receiver parameters on the optical performance of a fixed-focus Fresnel lens solar concentrator/cavity receiver system in solar cooker

To facilitate building integration with solar cooker for household, a solar cooker based on a fixed-focus Fresnel lens solar concentrator/cavity receiver system was proposed. To increase the system optical efficiency, the cavity receiver with bottom reflective cone was used as a fixed receiver. Expecting to optimize the system and receiver of better optical performance, the effects of receiver parameters on it were studied. To evaluate the effects, a significance test of key factors was conducted. Comparative analysis of fixed-focus food cooking system was undertaken. The analysis shows that average optical efficiencies using cavity receiver with bottom reflective cone of spherical, cylindrical, conical are 72.23%, 68.37% and 76.40%, respectively, while that of their corresponding conventional cavity receivers are 68.49%, 31.91% and 74.61%. The former significantly increased 3.74%, 36.46% and 1.79%, respectively. Moreover, cavity receiver with bottom reflective cone angle 90° is able to hold a higher amount of incoming energy from concentrator, compared to other three angles. Increasing the bottom reflective cone reflectivity and cavity receiver surface absorptivity can improve optical efficiency. In addition, the cavity receiver surface absorptivity and concentrated sunlight incidence angle have the most significant influence on the optical efficiency and flux uniformity, respectively. The conical cavity receiver with bottom reflective cone is the most suitable one for system. This work is expected to be useful for further optimization of solar concentrator/cavity receiver system.