Size Of Corrugations Research Articles

High Azimuthal Mode Selectivity of a Cavity with Mode-Joining Corrugations for High-Harmonic Gyrotrons

Mode-joining longitudinal corrugations are studied as a means of high azimuthal mode selectivity for cavities of high-harmonic terahertz gyrotrons. Their number dictates the choice of the jointed operating mode, which has a form of strongly coupled co- and counter-rotating azimuthal harmonics. It is found that the distinctive feature of this mode is a weak dependence of eigenvalue and ohmic losses on corrugation size. First, this favors the use of mode-joining corrugations with variable depth for efficient suppression of all competing modes by both diffractive and ohmic losses in the gyrotron cavity. Second, this provides a good robustness of gyrotron performance against manufacturing errors in the size of corrugations and only a minor conversion of the operating mode to spurious modes at junctions of the corrugated cavity with smooth-walled waveguides. The beneficial properties of mode-joining corrugations are demonstrated by a cavity design for a gyrotron operated in the second-harmonic TE±9,4 and third-harmonic TE±18,4 modes at 398 GHz and 593 GHz, respectively.

Research progress in insulating and thermal conductivity of fluorinated graphene and its polyimide composites

AbstractThe demand for innovative thermal management materials with superior thermal conductivity and electrical insulating properties has significantly increased with the development of portable and flexible electronic gadgets. Fluorinated graphene (FG) has recently attracted the attention of the scientific community because of its exceptional thermal conductivity and electrical insulating qualities. This work aims to provide a detailed analysis of the structure‐property relationships inherent in FG, including both chemical and physical properties, and to explain the FG manufacturing process. Special attention should be paid to a thorough analysis of the thermodynamic conduction mechanism exhibited by FG, including the effects of corrugation size, fluorine coverage, and fluorine atom distribution on its thermal conductivity. The essay also examines in‐depth the most current and cutting‐edge developments addressing the utilisation of FG as a functional filler in composite‐modified polyimide (PI) materials. Furthermore, it has been noted as a crucial component in answering the needs for possible applications by maximising thermal conductivity and mechanical qualities in FG/PI composites through particular FG structural engineering and increased FG‐PI interaction. As a result, these elements serve as the main focus of ongoing research projects, highlighting important directions for development and investigation.

Influence of Corrugation Size and Location on Sensitivity Enhancement for MEMS-Based Pressure Sensor

In this paper, a MEMS capacitive diaphragm-based pressure sensor is investigated. The main focus of this work is to analyze the effect of the geometry and configuration on the sensitivity of a sensor as a crucial parameter in sensor design. Finite element modelling using ABAQUS software is conducted to simulate the behaviour of the diaphragm with different geometries under the same condition. Three popular geometries including square, rectangular and circular shapes with similar areas are investigated and sensitivities of 0.3, 0.24, and 0.22 µm/MPa were obtained for circular, square, and rectangular shapes respectively. Corrugated structure is added to circular diaphragm and deflection and stress analysis are provided for various positions and wave radius of the corrugated region and the best configuration based on sensitivity analysis is proposed. Simulation proved the 17.62% improvement in sensitivity by using a corrugated structure in a circular diaphragm with a small wave radius at the circumference of the circle. An increasing number of corrugated wave regions was also simulated but could not enhance the sensitivity in comparison with a one-wave corrugated structure.

Experimental study on the hysteresis behavior of L-shaped double-skin composite wall with concrete-filled steel tubes

In this paper, the seismic behavior of L-shaped double-skin composite wall (DSCW) with concrete-filled steel tubes were investigated. The influence of different parameters, i.e., axial compression ratio, shear span-to-depth ratio, corrugation size, corrugated arrangement, flange size and CFST side column were discussed based on cyclic tests. The hysteresis behavior of DSCW specimens in terms of hysteresis curves, skeleton curves and rigidity deterioration were analyzed. The failure mechanism, as well as the composite effect between each component was also compared based on the strain analysis. It was concluded that the L-shaped DSCW has favorable seismic ductility and toughness with the maximum lateral drift angle of 3%. With the increase of axial compression ratio, the peak load of DSCW specimens increased while the post-peak ductility decreased. By contrast, the peak load of DSCW specimens decreased with the increase of shear span-to-depth ratio. More corrugations are effective to increase the seismic behavior of L-shaped DSCW and it was recommended that the corrugations should be arranged vertically. The flange size has limited influence on the failure processes and carrying capacity of DSCW specimens, while the stress distribution was highly dependent on the flange design of DSCW. The application of concrete-filled steel tubes (CFST) side column is effective to increase the seismic behavior of DSCW and also has significant influence on the composite effect between each component.

Hydrodynamics of a novel 3D printed structured packing–SpiroPak

Hydrodynamic performance of an ultra low-pressure drop and high surface area, 3D printed structured packing (SpiroPak) was investigated in this study. Computational fluid dynamics (CFD) modelling combined with single-phase (dry) and irrigated (multiphase) experiments were carried out to validate the CFD modelling results. Experiments were conducted to measure the dry and wet pressure drop at a range of liquid load (0–38.2 m3/m2∙h) and F-factor (0–1.2 Pa0.5). Liquid distribution was measured using Wire Mesh Sensor (WMS) for SpiroPak and compared with a commercial and 3D printed replica of Mellpak 250X and Montzpak B1–500. The topology of the packing was analysed to calculate the specific surface area that could be available for mass transfer. It was found that the SpiroPak can have up to 50~200% more surface area per unit volume when compared with commercial packing. Experimental and modelling results showed that SpiroPak could reduce the dry pressure drop by approximately 50%. Parametric study found that reducing corrugation size to increase surface area and increasing the gap size to reduce the pressure drop were key design parameters of SpiroPak. Finally, scale-up and scale-out (tessellation) techniques were compared to determine the optimum element size for the application of SpiroPak on a large scale.

Hydraulic parameters of culverts from pipes with normal and spiral form of corrugation

The research paper is devoted to study of culverts from metal corrugated pipes (CMP) and helically corrugated steel pipes (HCSP). Modern design solutions of culverts from CMP and HCSP are differ as compared with used before (bottom with various types of roughness, inlet and outlet heads, type and size of corrugation) and there is not enough experimental data for their design. The aim of the study is to test CMP and HCSP models to determine their hydraulic parameters, such as roughness and resistance coefficient, critical bias and so on. The laboratory equipment and method of experimental study as well as results of the tests of CMP and HCSP with protective tray at the pipe bottom and without it under different operation modes are given in the research paper. The results of the study show that roughness coefficient under pressure hade mode can be determined using Norton equation only for HCSP, Norton and Einstein-Banks equations are corrected for CMP.

Hollow fiber membranes with different external corrugated surfaces for desalination by membrane distillation

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were prepared using the phase inversion spinning technique under a wet gap mode. Different corrugated outer surfaces were obtained by means of a micro-engineered spinneret, spraying the external coagulant on the nascent fiber along gap, and different spinning parameters, namely, the gap distance and the external coagulant flow rate. A quantitative evaluation of the corrugation size and shape was carried out by electron scanning microscopy and atomic force microscopy. The effect of the corrugation size and shape on the direct contact membrane distillation (DCMD) performance has been studied. The corrugated outer surface acted as micro-turbulence promoters mitigating the temperature polarization effect and enhanced the external effective surface area for condensation. Both factors improved the DCMD permeability of the hollow fiber membranes. However, corrugations with V-shaped valleys depths greater than about 30μm did not always improve the DCMD permeate flux. It was found that the membrane prepared with the spray wetting mode exhibited the best desalination performance. The salt rejection factor of all prepared hollow fiber membranes was greater than 99.9% and the highest DCMD permeate flux of this study was greater than those reported so far for the PVDF-HFP hollow fiber membranes.

Fluorinated graphene suspension for inkjet printed technologies

The possibility to control the size of the flakes of graphene suspension in the course of their fluorination in an aqueous hydrofluoric acid solution was demonstrated. The effect of the suspension composition, the fluorination time, temperature and thermal stress on the fragmentation process was investigated. The corrugation of suspension flakes, which occurs at fluorination due to a difference in the constants of graphene and fluorographene lattices, leads to the appearance of nonuniform mechanical stresses. The fact that the flake size after fragmentation is determined by the size of corrugation allows the assumption that the driving force of fragmentation is this mechanical stress. This assumption is confirmed by the break of the corrugated layers from flakes under thermal stress. Moreover, fluorination treatment at elevated temperatures (∼70 °C) significantly accelerates the fragmentation process. Suspensions of fluorinated graphene with nanometer size flakes are of interest for the development of 2D ink-jet printing technologies and production of thermally and chemically stable dielectric films for nanoelectronics. The printed fluorinated graphene films on silicon and flexible substrates have been demonstrated and the charges in metal–insulator–semiconductor structures have been estimated as the ultra low values of (0.5–2) × 1010 cm−2.

Electron beam energy chirp control with a rectangular corrugated structure at the Linac Coherent Light Source

Electron beam energy chirp is an important parameter that affects the bandwidth and performance of a linac-based, free-electron laser. In this paper we study the wakefields generated by a beam passing between flat metallic plates with small corrugations, and then apply such a device as a passive dechirper for the Linac Coherent Light Source (LCLS) energy chirp control with a multi-GeV and femtosecond electron beam. Similar devices have been tested in several places at relatively low energies ($\ensuremath{\sim}100\text{ }\mathrm{MeV}$) and with relatively long bunches ($g1\text{ }\text{ }\mathrm{ps}$). In the parameter regime of the LCLS dechirper, with the corrugation size similar to the gap between the plates, the analytical solutions of the wakefields are no longer applicable, and we resort to a field matching program to obtain the wakes. Based on the numerical calculations, we fit the short-range, longitudinal wakes to simple formulas, valid over a large, useful parameter range. Finally, since the transverse wakefields---both dipole and quadrupole---are strong, we compute and include them in beam dynamics simulations to investigate the error tolerances when this device is introduced in the LCLS.

The effect of corrugated skins on aerodynamic performance

Corrugated skins provide a good solution to morphing wings due to their highly anisotropic behavior. If the low stiffness corrugation plane is aligned in the chordwise direction, the airfoil shape change is possible. In contrast to the traditional smooth skin of an airfoil, a corrugated skin influences both the local and global aerodynamics of a wing. The aim of this study is to investigate the effect of a corrugated skin on the global aerodynamics of an airfoil, particularly lift and drag characteristics. First, the aerodynamic analysis of a NACA 0012 airfoil with a smooth profile is conducted, both in the wind tunnel and by computational fluid dynamics, at different Reynolds numbers and compared to the data in the literature. The lift and drag coefficients at different angles of attack, between −10° and 10°, are considered. Next, two NACA 0012 airfoils with different sized corrugated profiles are investigated both experimentally and by numerical simulation. The effects of corrugation size and Reynolds number are analyzed and quantified relatively to the standard NACA0012 airfoil with a smooth skin. Preliminary numerical results are validated using the experimental data.

3‐D Milk Fouling Modeling of Plate Heat Exchangers with Different Surface Finishes Using Computational Fluid Dynamics Codes

ABSTRACTMilk fouling and self‐cleanability of the heat exchanger surface during the pasteurization process has gained attention from industries as well as academia. In particular, the antifouling mechanism associated with plate corrugation profiles causing the extreme turbulent flow scheme and surface coatings to reduce the surface energy is uncertain. This study was aimed to develop a computational fluid dynamics (CFDs) model in three‐dimensional (3‐D) environment, which could estimate antifouling performances of plate heat exchangers (PHEs) during milk pasteurization process. It was the first attempt to simulate the fouling and temperature distribution patterns on realistic corrugated surfaces of PHE unit with different surface treatments. The conventional stainless steel surface and stainless steel plates coated with Lectrofluor 641 and graded Ni‐P‐polytetrafluoroethylene were compared for their antifouling performances. A transient 3‐D fouling model was developed based on heat and mass transfer equations, and fouling kinetics involving diffusion and protein adhesion mechanisms. Pattern and size of corrugations of actual PHE were measured and subsequently used to build 3‐D solid geometry using AutoCAD (Autodesk, San Rafael, CA). The geometry file was meshed using Gambit software (Fluent Inc., Lebanon, NH) and further transferred to CFD codes. Fouling predictions based on chemical kinetics and the temperature‐dependent parameters accounting for different surface energy values were close to experimental data within a maximum prediction error of 7%. The developed 3‐D fouling model is expected to meet the demand of food industries to correlate the surface energy with the self‐cleanability of food thermal process equipments and seek the theoretical solution.PRACTICAL APPLICATIONSMilk‐fouling phenomena of plate heat exchangers (PHEs) result in an increase of energy consumption, extra maintenance, higher labor costs and a decrease in the productivity. In addition, fouling deposits can cause the growth of unwanted microorganisms on the corrugated surfaces of PHEs. In this study, the transient three‐dimensional computational fluid dynamics model was developed to describe fouling phenomena in consideration of realistic corrugation profiles and estimate the amount of surface fouling based on the hydrodynamic and thermodynamic performances of the PHEs and surface characteristics (conventionally uncoated stainless steel [SS‐316] and stainless steel surfaces with Lectrofluor 641 and graded Ni‐P‐polytetrafluoroethylene).

Faraday waves produced by periodic substrates: Mimicking the alligator water dance.

Male alligators use surface waves to attract their mates. This phenomenon is colloquially known as the alligator’s water dance. Male alligators vibrate their lungs at very low frequencies, creating unique wavy patterns and fountains on the surface of the water. We hypothesize that the water dance phenomena are an expression of Faraday waves, arising from the instability of the plane fluid interface to wavy perturbations above a threshold vibration amplitude. We performed laboratory experiments to study how the corrugations covering the skin of an alligator affect the onset, efficiency, and pattern of Faraday waves. A three-dimensional (3-D) printed plate was modeled after a molding of an alligator’s back, mimicking the corrugation size, shape, and spacing. An electromagnetic induction transducer was used to vibrate this model plate normal to the water surface. Frequency sweep data were collected for a variety of amplitude settings. Sweeps were performed for different plate depths, with and without corrugations. Three diagnostics were employed: a piezoelectric hydrophone, an out-of-plane laser vibrometer, and a high-speed video. Onset, frequency, and pattern data will be presented as a function of driving parameters, and as a function of depth. Implications of this work for an eventual field experiment will be discussed.

Bose–Einstein condensate flow in a corrugated magnetic waveguide

The flow of a Bose–Einstein condensate through smooth and corrugated waveguides is studied by direct numerical solution of the time-dependent Gross–Pitaevskii equation. One end of each waveguide has a teacup longitudinal potential, which when lowered generates a quasi-continuous supersonic flow. As the nonlinear strength factor, which is proportional to the scattering length times the number of atoms, becomes more positive, we find that the condensate broadens and moves more rapidly down a smooth waveguide. For a given nonlinear strength factor, an increase in the size of corrugations in the waveguide, used to simulate imperfections in experimental structures, has a noticeable effect on condensate flow. However, for a given corrugation size, an increase in the condensate flow is always observed when the nonlinear strength factor is increased.

Scattering from edge corrugations of SAW .DELTA.v/v waveguide on LiNbO3.

The SAW energy is concentrated into the SAW waveguide and is propagating along it without radiation. However the energy can radiate from the waveguide if there are corrugations at waveguide edges. This paper described the radiation characteristics from the rectangular edge corrugations of SAW Δν/ν waveguide on YZ-LiNb03. The theoretical characteristics is derived from the perturbation method and it is found that the SAW energy radiates toward only one side of the waveguide, if the corrugation size and position at the both edges of the waveguide are suitably designed. The experimental results are qualitatively in agreement with theoretical predication.

Scattering from the SAW Waveguide with Edge Corrugations

SAW energy radiates to both sides from a SAW waveguide which has rectangular corrugations at one edge. In this paper we present theoretical results of propagation and radiation characteristics of the SAW waveguide with edge corrugations on both sides by the equivalent transmission line approach. Numerical results are shown for thin ribbon waveguide of gold on fused quartz and Δv/v waveguide on YZ-LiNbO3. As a result, it is found that SAW energy radiates toward only one side of the waveguide, if the corrugation size and position are suitably designed.