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Abstract The experimental study for the melting processes of phase change material (paraffin) inside a cylindrical container under different boundary conditions of the cylindrical outside surface was carried out. In the experiments paraffin was heated by the heating rod installed in the center of the cylindrical container. The interpolation method was employed to calculate phase front and liquid fraction during the melting process by the reading of the thermocouples in an array arrangement. Paraffin near the heating rod firstly melted due to heat conduction in the initial melting stage, and then the generation and intensification of natural convection led to the acceleration of phase changes, resulting in obvious temperature stratifications in the upper region of the cylinder container. Moreover, flat temperature phenomena are described and discussed in detail. The effect of different heating powers, boundary conditions and the temperatures of water bath on melting rates is evaluated as well. Highlights • Conduct paraffin melting experiments in cylindrical cavity with an electric heating rod. • Analyze the effect of different heating powers and boundary conditions on the melting rate. • Record the paraffin melting process. • Temperatures of the molten liquid show a significant stratification. • Lower undercooling or higher boundary temperature accelerate the melting process. [ABSTRACT FROM AUTHOR]

We developed an approach to determine characteristics of the wave process in a cylindrical cavity filled with a viscous compressible liquid excited by a vibrating spherical body placed on the axis of the cavity. The solution to this problem is reduced to an infinite system of algebraic equations. [ABSTRACT FROM AUTHOR]

• Three top boundary conditions are analyzed in a cylindrical microfluidic cavity. • Particles' stable trapping positions change with the boundary conditions. • The effect of boundary condition should be considered for acoustic manipulation. Precise manipulation of microparticles in microchannels is a primary technique for numerous lab-on-a-chip bioengineering research and applications, as it determines the chip's functions and analytical results. Acoustic manipulation, using the acoustic radiation force, is a compact, versatile and contactless manipulation technique, which can be easily integrated with other microfluidic components. It is our main purpose to report the effect of boundary condition of a cylindrical microfluidic cavity on the acoustic particles' manipulation. A device consisting of a cylindrical cavity in a silicon wafer with three kinds of top boundary conditions (rigid, soft, and imperfect rigid boundary) has been built. The corresponding distributions of acoustic radiation force are analyzed analytically and numerically. Experiments are performed with 2.5 μm radius polystyrene microspheres in the cavity covered by three reflective layers (340 μm-thick glass, 400 μm-thick PDMS, and 660 μm-thick glass film), respectively, which specify the three different boundary conditions at the top of the cavity. It is demonstrated that the boundary condition of a cavity influences the acoustic radiation force and the stable positions of particles, and this is in agreement with the theoretical predictions. Thus, the effects of boundary conditions need to be considered for precise acoustic manipulation. [ABSTRACT FROM AUTHOR]

Graphical abstract Dividing sample into multi-subsample, further improving distribution measurement resolution. Highlights • The established multisection model for measuring the permittivity distribution. • Field analysis and the perturbation technology is combined to analyze and calculate the permittivity in the slotted cylindrical cavity. • Measuring the sample horizontally, and designing the corresponding test setup for more stable measurement. • Analyzing the results by the established partial error equations. Abstract There are few papers to introduce the distribution measurement of material's permittivity in the previous work, but the measurement is an important effort to effectively evaluate the inhomogeneity of material's permittivity. In order to measure the distribution of the relative permittivity with small interval along sample rod, a multisection measurement model has been introduced. The sample is horizontally inserted into the slotted cylindrical cavity with TM 0 n 0 working modes and passes through it to improve the measurement stability. During the measurement, the sample is divided into many sections, and each section is treated as a subsample for the distribution measurement of the permittivity. The traditional perturbation technology is combined with the field analysis of two subsamples in the cavity to calculate the permittivity of all subsamples from the effective permittivity. Based on the theoretical analysis of the simulation results from HFSS, partial error equation is established, and the absolute error of the multisection measurement model is less than 0.1. Besides, the horizontal movement device for the sample movement, support platform with a groove for the sample placement, and vertical cylindrical cavity for the measurement are employed to make up the test setup. Meanwhile, it can provide a stable and rapid measurement. Thus, a fiber reinforced plastic rod has been measured to verify the feasibility of the developed test setup. [ABSTRACT FROM AUTHOR]

Based on complex function methods and a multipolar coordinate system, the scattering induced by a cylindrical cavity in a radially inhomogeneous half-space is investigated. Mass density of the half-space varies depending on the distance from the centre of the cavity while the shear modulus is always constant. The wave velocity is expressed as a function of radius vector and the Helmholtz equation is a partial differential equation with a variable coefficient. By means of a conformal mapping technique, the Helmholtz equation with a variable coefficient is transferred into its normal form. Then, displacement fields and corresponding stress components are deduced. Applying the boundary conditions, dynamic stress concentration factors around the cavity are obtained and analyzed. Typical numerical results are presented to demonstrate the distribution of dynamic stress concentration factors when influencing parameters are assumed. [ABSTRACT FROM AUTHOR]

In this paper for the first time we have discovered and studied the analogy of the second order phase transition in spheri-cal microwave cavities with heterogeneity in the form of a metal ball. The transition occurs between the state when the ball is sym-metrically disposed relative to the side walls and the state with asymmetric arrangement of the ball. For these states the spectra of oscillations in 8-mm range were measured and on the basis of the obtained data the correlation coefficients of inter-frequency inter-vals were determined. It has been established that an integrable system of spherical symmetric cavity with an inner ball has a cor-relation coefficient close to zero, while for non-integrable systems with asymmetric arrangement of the ball, the correlation coeffi-cient C(1) > 0.2. Phase transition between these states occurs in a narrow range of eccentricity. The dependence of the distribution of inter-frequency intervals on the mean distance between the natural frequencies were determined and it was found that for an integrable system, this dependence is described by the Poisson function, and for non-integrable by Wigner distribution, which is typical for states with repulsion resonance lines and quantum chaos. Thus, it was found that a change in the symmetry of the microwave resonator leads to the second order phase transition, when the system becomes non-integrable cavity and is accompa-nied by quantum chaos.

Highlights • We enhance reforming performance of a plate-type MSR by cylindrical cavities. • We study how depth and diameter of cylindrical cavity affects net power of PEMFC. • We study methanol conversion, hydrogen yield and CO of an original plate-type MSR. • The original MSR obtains the best augmentation of 22.46% in PEMFC net power. • The MSR raises methanol conversion up to 22.65% and hydrogen yield up to 64.52%. Abstract The plate-type methanol steam reformer (MSR) designed for improving its reforming performance is integrated with proton exchange membrane fuel cells (PEMFCs) regarded as a hopeful miniature power source. This study then uses computational fluid dynamics (CFD) through SIMPLE-C algorithm and Arrhenius form of reaction model to study the reforming performance of a plate-type MSR with the cylindrical cavities installed on the bottom of reformer channels. The influences of depth and diameter of cavities, and heated-wall temperature on reforming performance of reformer and estimated net power output of PEMFC have been examined with the same catalyst and inlet conditions in various flow channels of plate-type MSR. The results display that the installation of cylindrical cavities obviously improves the methanol conversion rate and hydrogen yield of a plate-type MSR. Compared with the traditional plate-type MSR, installing the cylindrical cavities of D C = 1.4 mm and H C = 1.5 mm on the plate-type MSR channels leads to the best enhancement in the methanol conversion rate by 22.65% and in the hydrogen yield by 64.52% at T heater = 250 °C. Moreover, the novel plate-type MSR with the cylindrical cavities of D C = 1.4 mm and H C = 1.5 mm acquires the best augmentation of 22.46% in the estimated net power output of PEMFC at T heater = 250 °C. [ABSTRACT FROM AUTHOR]

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Cavity modification is proposed with the aim of enhancing the continuous frequency tunability of a gyrotron. The modification can be applied to both uniform and tapered gyrotron cavities and involves just using an additional cavity section. It ensures larger effective cavity length and thus lower starting current for higher order axial modes. As a consequence, the frequency tuning band of the gyrotron can be increased significantly. Moreover, the proposed cavity modification is beneficial for smoothing the variations of output power within the tuning band. [ABSTRACT FROM AUTHOR]

The effect of surface tension on laminar natural convection in a vertical cylindrical cavity filled with a weak evaporating liquid has been analyzed numerically. The cylindrical enclosure is insulated at the bottom, heated by a constant heat flux from the side, and cooled by a non-uniform evaporative heat flux from the top free surface having temperature-dependent surface tension. Governing equations with corresponding boundary conditions formulated in dimensionless stream function, vorticity, and temperature have been solved by finite difference method of the second-order accuracy. The influence of Rayleigh number, Marangoni number, and aspect ratio on the liquid flow and heat transfer has been studied. Obtained results have revealed that the heat transfer rate at free surface decreases with Marangoni number and increases with Rayleigh number, while the average temperature inside the cavity has an opposite behavior; namely, it growths with Marangoni number and reduces with Rayleigh number. [ABSTRACT FROM AUTHOR]

Numerous engineering applications involve low Mach number flow in cavity aperture geometries, which can generate flow-excited acoustic oscillations and hence high amplitudes of noise and vibration. This is caused by the instability of the shear layer interacting with the acoustic modes of the system. In this study, we experimentally investigate ducted cylindrical cavities with aspect ratios (Depth/Diameter) of 0.5, 1, and 1.5 up to flow velocities of Mach 0.4. We examine the influence of the cavity confinement (Cavity Width/Duct Width) on the aeroacoustics response, as well as the downstream impingement behaviour of the shear layer. Rectangular and square cavities bearing similar geometric parameters are also investigated to compare the effect of the cavity shape on the shear layer dynamics and the aeroacoustics response. The results confirm resonance behaviour at frequencies well predicted by the theory, as well as Strouhal periodicities that agree with reported literature. However, cylindrical and square cavities with aspect ratio of 0.5 exhibit stronger dependence on the aspect ratio due to the interference of the recirculation region by the cavity floor, ultimately modifying the symmetry of the shear layer. This asymmetric flow pattern affects the velocity-dependent tones, generating much lower Strouhal numbers than the estimated values, and must be accounted for in equipment design. Moreover, Particle Image Velocimetry (PIV) measurements further illustrate the spatial characteristics of the shear layer dynamics for the various shaped cavities. The visualizations demonstrate enhanced flow modulation at higher acoustic pressure amplitudes, as well as reveal the flow asymmetry and the three-dimensional shear layer topology in cylindrical and square cavities. [ABSTRACT FROM AUTHOR]

The present numerical research studies the effect of nano-materials in a lid-driven cylindrical cavity with rotation of circumferential top wall. The heat is transferred from two lateral walls to the domain by constant temperature conditions while other walls are kept isolated. The non-dimensional equations are solved by Finite Volume Method (FVM) and SIMPLEC method. The effect of Reynolds (Re = 100, 400, 1000), Ryleigh (Ra = 104, 105, 106) numbers are studied. In addition, the effect of concentration of nano materials ( ϕ = 0%, 1%, 5%), the Height Ratio (HR = 1, 0.5, 2) on Nusselt number, isotherm lines and streamlines are studied. The results show that Reynolds number also can change the effect of nano particles on the heat transfer rate. It is observed that the height ratio increase can improve the Nusselt number since the number and the size of vortices inside the cavity changes. In addition, increase of Ra number can change the flow structure inside the cavity which can help in increasing of Nusselt number.

A 2.45 GHz microwave-plasma chemical-vapor deposition (MPCVD) reactor was designed and built in-house by collaborating with Guangdong TrueOne Semiconductor Technology Co., Ltd. A cylindrical cavity was designed as the deposition chamber and a circumferential coaxial-mode transformer located at the top of the cavity was adopted as the antenna. Two quartz-ring windows that were placed far away from the plasma and cooled by water-cooling cavity walls were used to affix the antenna to the cavity and act as a vacuum seal for the reactor, respectively. This design improved the sealing and protected the quartz windows. In addition, a numerical simulation was proposed to predict the electric-field and plasma-density distributions in the cavity. Based on the simulation results, a microwave-plasma reactor with TM021 mode was built. The leak rate of this new reactor was tested to be as low as 1 × 10−8 Pa·m3·s−1, and the maximal microwave power was as high as 10 kW. Then, single-crystal diamond films were grown with the morphology and crystalline quality characterized by an optical microscope, atomic force microscope (AFM), Raman spectrometer, photoluminescence (PL) spectrometer, and high-resolution X-ray diffractometer. It was shown that the newly developed MPCVD reactor can produce diamond films with high quality and purity.

In this paper, we present the RF behavior of conventional cylindrical interaction cavity for 240 GHz, 1 MW gyrotron for futuristic plasma fusion reactors. Very high-order TE mode is searched for this gyrotron to minimize the Ohmic wall loading at the interaction cavity. The mode selection process is carried out rigorously to analyze the mode competition and design feasibility. The cold cavity analysis and beam-wave interaction computation are carried out to finalize the cavity design. The detail parametric analyses for interaction cavity are performed in terms of mode stability, interaction efficiency and frequency. In addition, the design of triode type magnetron injection gun is also discussed. The electron beam parameters such as velocity ratio and velocity spread are optimized as per the requirement at interaction cavity. The design studies presented here confirm the realization of CW, 1 MW power at 240 GHz frequency at TE mode. [ABSTRACT FROM AUTHOR]

The characteristics of flow over rectangular cavities have been well documented. However, few studies have considered cylindrical cavity flows. For compressible cylindrical cavity flows, the type of cavity flowfield is dependent on the diameter-to-depth ratio ( D / H ), which is similar to the length-to-depth ratio for a rectangular cavity flow. For an open-type cavity flow ( D / H ≤ 6.14 ), there is a slight upstream influence and uniform static pressure distributions are observed inside the cavity; a small adverse pressure gradient ahead of the rear face and a downstream expansion. The leading- and rear-edge expansions are more significant for transitional- ( D / H = 8.60 – 21.00 ) and closed-type ( D / H = 43.00 ) cavities. The amplitude of surface pressure fluctuations increases toward the rear face, for all of the test cases, whereas an additional peak near the middle of cavity floor is observed for a closed-type cavity. Notably, the effect of freestream Mach number is pronounced only on the amplitude of peak pressure fluctuations near the rear wall. Similarities between a cylindrical cavity and a rectangular cavity for a compressible flow are also highlighted in this study. [ABSTRACT FROM AUTHOR]

The model of fractional time-derivative of generalized magneto–thermo–viscoelasticity equations for isotropic media in the presence of a constant magnetic field is considered. Some essential theorems on the linear coupled and generalized theories of thermo-viscoelasticity can be easily obtained. This model is applied to solve a problem of an infinite body with a cylindrical cavity in the presence of an axial uniform magnetic field. The boundary of the cavity is subjected to a combination of thermal and mechanical shock acting for a finite period of time. Laplace transform techniques are used to derive the solution in the Laplace transform domain. The inversion process is carried out using a numerical method based on Fourier series expansions. Numerical computations for the temperature, the displacement and the stress distributions as well as for the induced magnetic and electric fields are carried out and represented graphically. Comparisons are made with the results predicted by the generalizations, Lord–Shulman theory, and Green–Lindsay theory as well as to the coupled theory. [ABSTRACT FROM AUTHOR]

The theory of coupled plasma, thermal, and elastic waves was used to investigate the wave propagation on semiconductor material with cylindrical cavity during photo-thermoelastic process. An unbounded material, elastic semiconductor containing a cylindrical cavity with isotropic and homogeneous thermal and elastic properties has been considered. The inner surface of cavity is constrained, and the carrier density is photogenerated by an exponentially decaying pulse boundary heat flux. The eigenvalue approach, together with Laplace transform techniques, was used to obtain the analytical solutions. Numerical computations have been done for a silicon-like semiconductor material, and the results are presented graphically to estimate the effect of the coupling between the plasma, thermal, and elastic waves. The graphical results indicate that the thermal activation coupling parameter is an important phenomenon and has a great effect on the distribution of field quantities. [ABSTRACT FROM AUTHOR]

A thin-film grating on a curved substrate functions as a highly reflective and wavelength sensitive mirror for a diverging wave that has the same curvature as the substrate. In this paper we propose a cylindrical cavity surrounded by a curved resonant grating wall, and describe its resonance characteristics. Through finite-difference time-domain (FDTD) simulation we have clarified that this type of cavity supports two resonance modes: one is confined by Fresnel reflection and the other by resonance reflection of the wall. We have also demonstrated that the latter mode exhibits a Q factor several orders of magnitude higher than that of the former mode.

In search of efficient energy utilization and superior thermal performance, the present study is aimed at understanding the positional effect of discrete heaters and coolers on a cylindrical thermal system. This system undergoes a magneto-thermal convective process using Cu-Al 2 O 3 H 2 O hybrid nanofluid. Four options are investigated by altering the position of four heater and cooler segments mounted centrally on the wall of four quadrants of the cylinder. The equations of motion and energy are solved in nondimensionalized form by employing the finite element technique. The effects of operating parameters on the thermal transport are investigated systematically for a fixed nanoparticle volume fraction (φ) and a range of the Rayleigh number (signifying the buoyant forces), Hartmann number (signifying the magnetic field strength), and the magnetic field inclination (γ). The study shows that heat transfer, as well as entropy production, is markedly influenced by the heater-cooler positions and flow-controlling parameters. Among all the studied configurations, two cases show the optimum value of the Nusselt number. The cross heater-cooler arrangement affirms as the most effective heating-cooling option to obtain enhanced heat transfer. Higher heat transfer corresponds to greater entropy production. Higher magnetic field intensity dampens the heat transfer rate and thermodynamic irreversibility. The innovative identification of superior cross-wise heating-cooling over the usual side-side or bottom-top heating-cooling is the major outcome of this study. The experimental hybrid nanofluid properties are considered for this study. [Display omitted] [ABSTRACT FROM AUTHOR]

Diffraction of plane harmonic SH waves by a cylindrical cavity in a homogeneous, isotropic and linear elastic infinite wedge is investigated. Analytical closed form solution is obtained by utilizing Wave Function Expansion Method and Image Technique. Governing equation of this two dimensional steady-state wave motion problem is the Helmholtz equation. Helmholtz equation for polar coordinates is solved by using Separation of Variables Method. Displacement fields are expressed in terms of Fourier-Bessel series in complex form. Complex coefficients of Fourier-Bessel series are to be determined from boundary conditions. Zero-stress boundary condition at cavity inner surface is satisfied directly since polar coordinate systems are used. Free stress conditions at flat surfaces of the infinite wedge are satisfied in closed form via imaging method. In this technique, imaginary cavities symmetric with respect to flat surfaces are considered. With this consideration, scattered waves from imaginary cavities would represent reflections from flat surfaces so that stress free boundary condition on flat surfaces would be automatically satisfied. This technique would generate two additional displacement fields with two additional set of unknown complex Fourier-Bessel constants. These unknowns could be determined from boundary conditions of imaginary cavities. The cylindrical scattered waves from each cavity are defined in different polar coordinate systems. Addition Theorems are used for adequate coordinate transformation. Since Image Technique is used, to maintain angular symmetry, analytical solutions are obtained for a specific wedge whose internal angle is 120 degrees. Also, direction of incident waves has to be either horizontal or on the symmetry line of the wedge and cavity center has to be on the symmetry line. In numerical results, parameters in length dimension are normalized with respect to cavity radius. [ABSTRACT FROM AUTHOR]

The differential quadrature method (DQM) has been so far applied to a wide variety of fluid and/or structural problems. The results of many researchers reveal that the DQM is computationally efficient and is applicable to a large class of boundary value problems. However, there is little information about its applications to fluidstructure interaction problems. Therefore, the purpose of this paper is to provide some information in this area and to develop procedures based on the DQM for the numerical solution of fluidstructure interaction problems. First, the governing partial differential equations of motion of the structure and fluid are discretized separately using the DQM. Then, by applying the boundary condition at fluid-structure interface, the governing eigenvalue equations of the coupled system are obtained which can then be solved for the eigenvalues of the system. The applicability of the proposed procedures is shown herein through the free vibration analysis of thin circular plates in contact with a cylindrical fluid-filled cavity. Issues related to the implementation of the regularity conditions at the center of the circular plate and the central line of the cylindrical cavity are addressed. Two new regularity conditions are proposed for the circular cylindrical fluid domain. The accuracy and efficiency of the proposed procedures are demonstrated by comparing the obtained results with those available in the literature. It is shown that highly accurate converged results can be obtained by the proposed procedures using a small number of grid points. Three new dimensionless parameters and variables are also introduced for the free vibration of the coupled system. The influences of these parameters on dynamic behavior of the system are studied. [ABSTRACT FROM AUTHOR]

In this work, we apply Green and Naghdi's generalized thermoelasticity theory to a one-dimensional problem of an infinitely long cylindrical cavity. Laplace transform techniques are used to solve the problem. A comparison of generalized thermoelasticity theory with one relaxation time is made. Numerical results are computed and represented graphically for the temperature,displacement, and stress distributions. [ABSTRACT FROM AUTHOR]