Smooth Corrugations Research Articles

Effects of corrugation cross section shape on thermal-hydraulic performance in outward corrugated tube

The corrugation cross-section shape is an important parameter that affects the thermal-hydraulic performance of corrugated tubes. In this study, the three-dimensional models of corrugated tubes are established to study the influence of corrugation cross-section shapes on the thermal-hydraulic performance of corrugated tubes in the range of 10,000–40,000 Reynolds numbers. The influence mechanism of corrugation cross-section shapes on thermal-hydraulic performance is analyzed in terms of the distributions of flow field, turbulence characteristics and temperature, etc. The research results point out that the corrugated tube with a smooth corrugation inlet cross-section shape and a large enough secondary flow zones can provide better thermal-hydraulic performance. Conversely, the steeper corrugation outlet cross-section shape is beneficial to induce a stronger impact between the fluid and the corrugation wall, thereby improving the thermal-hydraulic performance of the corrugated tube. Besides, the maximum THP = 1.41 is obtained at Re = 40,000 for Case 3 with R1 = 24.8 mm and R2 = 1.5 mm.

Contact line motion in axial thermocapillary outward flow

We study the contact line dynamics of a viscous droplet deposited at the centre of a substrate subject to an axial thermal gradient. The temperature of the substrate decreases with distance from the centre, so the Marangoni stress induced at the liquid–air interface displaces the liquid radially outward. The flow experiences two stages. In the first stage, the droplet evolves towards an axially symmetric ring whose radius increases with time as . Using the lubrication approximation, we perform numerical simulations that confirm this law for the motion of the front and show that the maximum thickness of the profile decreases as . We explain the evolution law of the contact line by balancing Marangoni and viscous stresses. In the second stage, the contact line becomes unstable and develops smooth corrugations whose amplitude increases with time and that eventually become long fingers. The temporal evolution of the Fourier spectra of the contour shows a shift of the most unstable mode from smaller to larger azimuthal wavenumbers.

Corrugated silicon metasurface optimized within the Rayleigh hypothesis for anomalous refraction at large angles

We optimize optical performance of metasurfaces based on periodically corrugated silicon layers by adjusting the Fourier coefficients of their surface profile. For smooth corrugations, we demonstrate an excellent quantitative accuracy of semi-analytical approach based on the Rayleigh hypothesis. We employ the approach to design metasurfaces with anomalous refraction due to dominant first order diffraction. Unlike conventional Huygens' dielectric metasurfaces, corrugated silicon layers are capable of efficient anomalous refraction in grazing directions: we obtain corrugation shapes allowing to deflect 70-80% of the energy of normally incident green light into the range of 68{\deg}-85{\deg} of angles with respect to the normal.

Graphene Plasmon Reflection by Corrugations

Graphene plasmons (GPs) exhibit extreme confinement of the associated electromagnetic fields. For that reason, they are promising candidates for controlling light in nanoscale devices. However, despite the ubiquitous presence of surface corrugations in graphene, very little is known on how they affect the propagation of GPs. Here we perform a comprehensive theoretical analysis of GP scattering by both smooth and sharp corrugations. For smooth corrugations, we demonstrate that scattering of GPs depends on the dielectric environment, being strongly suppressed when graphene is placed between two dielectrics with the same refractive indices. We also show that sharp corrugations can act as effective GP reflectors, even when their dimensions are small in comparison with the GP wavelength. Additionally, we provide simple analytical expressions for the reflectance of GPs valid in an ample parametric range. Finally, we connect these results with potential experiments based on scattering scanning near-field optical microscopy (s-SNOM) showing how to extract the GP reflectance from s-SNOM images.

Minimum Weight Design of Sinusoidal Corrugated Web Beam Using Real-Coded Genetic Algorithms

Fundamental advantage of using corrugated web girder rather than plate girder reinforced with stiffeners is securing stability against shear buckling of web and unnecessary stiffeners despite the thinner web. Nonetheless, because shear buckling behavior of corrugated web is very complex, the design mechanism for beams and local, global, and interactive buckling problems should be considered in designing of its structural optimization for better economics and reasonableness. Therefore, this paper proposes a mathematical model for minimum weight design of sinusoidal web girder for securing better stability with smooth corrugation and aims at developing its optimum design program. The constraints for the optimum design were composed on the basis of the standards of EN 1993-1-5, DASt-R015, and DIN 18800, and the optimum program was coded in accordance with the standards based on Real-Coded Genetic Algorithms. The genetic operators for the developed program resulted in a stable solution with crossover probability between 12.5 and 50%, and the perturbation vector for outbreeding could obtain the best result with the model being applied of feasible design variable space of 20–30%. Additionally, the increase of yield strength resulted in decreased value of the objective function, and it was found through the change of the value of the constraint function that the thickness of web was an important factor in the optimum structural design.

Heat transfer enhancement in two-start spirally corrugated tube

Various techniques have been tested on heat transfer enhancement to upgrade the involving equipment, mainly in thermal transport devices. These techniques unveiled significant effects when utilized in heat exchangers. One of the most essential techniques used is the passive heat transfer technique. Corrugations represent a passive technique. In addition, it provides effective heat transfer enhancement because it combined the features of extended surfaces, turbulators and artificial roughness. Therefore, A Computational Fluid Dynamics was employed for water flowing at low Reynolds number in spiral corrugated tubes. This article aimed for the determination of the thermal performance of unique smooth corrugation profile. The Performance Evaluation Criteria were calculated for corrugated tubes, and the simulation results of both Nusselt number and friction factor were compared with those of standard plain and corrugated tubes for validation purposes. Results showed the best thermal performance range of 1.8–2.3 for the tube which has the severity of 45.455×10−3 for Reynolds number range of 100–700. The heat transfer enhancement range was 21.684%–60.5402% with friction factor increase of 19.2–36.4%. This indicated that this creative corrugation can improve the heat transfer significantly with appreciably increasing friction factor.

Low-loss plasmon-triggered switching between reflected free-space diffraction orders.

Surface plasmon coupling of a TM polarized free space incident beam by means of the + 1st or the -2nd order of a smooth corrugation grating at a metal surface causes the cancellation of the diffracted -1st order free space beam and a maximum of the 0th order Fresnel reflection whereas the converse occurs midway between these two conditions. This implies that angular tilting of the element or wavelength scanning provokes the switching between the -1st and 0th reflected orders. This plasmon-mediated effect on propagating free-space beams exhibits remarkably low absorption losses.

Effect of Triangular Corrugations on Dynamic Characteristics of Film Flow

Thick film flow in a narrow channel is investigated by simulations and experiments. The influence of obstacle and corrugations on liquid film flow is studied in simulations. LIF (light induced fluorescence) method is applied to visualize the flow field close to the substrate in the experiments. With the validated 3-D simulations, numerical investigation of film flow over triangular corrugations can be done. The results indicate that eddies in the trough of corrugations are generated in two ways. Eddies generated in the first way are mainly induced by the geometry of the substrate with strong undulated corrugations. On corrugations with a small steepness, eddies generated in the second way are primarily induced by inertia force and their formulation are depended on Reynolds number. Whenever corrugations are steep or smooth, eddies in the troughs always have two variation periods with regard to Reynolds number. In the first period, the eddy size enlarges dramatically with increasing Reynolds number. In the second period, increasing Reynolds number has little influence on the eddy transformation. A smooth corrugation will delay the transition point of the two periods, and reduce the difference between them. Film flow over arbitrary geometric corrugations is simulated and the stagnant point movement is investigated. Similarity theory in fluid dynamics is verified, which proves that results of this study with relatively large scale model provides basic knowledge that can be used to predict flow behavior in small scale corrugated plates in industry.

Influence of Corrugation Profile on the Thermalhydraulic Performance of Cross-Corrugated Plates

This article presents a numerical investigation on the thermalhydraulic performance of cross-corrugated plates, commonly employed in plate and compact heat exchangers. Three-dimensional numerical predictions were obtained using a finite volume method and a validated low Reynolds number k-ϵ turbulence model. The influences of Reynolds number, corrugation inclination angle, and especially corrugation profile on flow and heat transfer were studied and discussed. The velocity, temperature, local Nusselt number distribution, and the path line were presented for cross-corrugated plates with sinusoidal, isosceles triangular, trapezoidal, rectangular, and elliptic corrugations. The average Nusselt number Nu and the friction factor f were calculated and correlated with the Reynolds number. Thermalhydraulic performance was evaluated in terms of the heat transfer and pressure drop. Nu and f are about 1–4 times higher for the trapezoidal channel than for the elliptic channel, indicating significant influence of the corrugation profile. Optimal structures are among those with smooth corrugation shapes and small inclination angles.

Complete transformation of a normally incident wave to the −1st diffraction order by a smooth echelette

We study the regime of complete transformation of a wave, which is incident normally on a corrugated metal surface, to the −1st diffraction order (to one side) for rather simple smooth corrugation profiles without losses. The study is based on the numerical solution of the integral equation by using an interactive computer code developed by the author. It is shown that the regimes under consideration can take place only in the case of asymmetric corrugation profiles. Realization of such regimes requires a comparatively great number of parameters in the profile description. One can develop the profiles which ensure the specified regimes for both H- and E-polarized waves. Several examples of such profiles are presented and illustrated with detailed graphical descriptions of their diffraction properties.

Convective heat transfer enhancement in low Reynolds number flows with wavy walls

The present work reports the analysis of combining low Reynolds number flows and channels with wall corrugation and the corresponding thermal exchange intensification achieved. The proposed model involves axial heat diffusion along the fluid and adiabatic regions both upstream and downstream to the corrugated heat transfer section, in light of the lower values of Reynolds numbers (and consequently Peclet numbers) that can be encountered in the present class of problems. Aimed at developing a fast and reliable methodology for optimization purposes, the related laminar velocity field is obtained by an approximate analytical solution valid for smooth corrugations and low Reynolds numbers, typical for instance of micro-channel configurations, locally satisfying the continuity equation. A hybrid numerical-analytical solution methodology for the energy equation is proposed, based on the Generalized Integral Transform Technique (GITT) in partial transformation mode for a transient formulation. The hybrid approach is first demonstrated for the case of a smooth parallel-plates channel situation, and the importance of axial heat conduction along the fluid is then illustrated. Heat transfer enhancement is analyzed in terms of the local Nusselt number and dimensionless bulk temperature along the heat transfer section. An illustrative sinusoidal corrugation shape is adopted and the influence of Reynolds number and corrugation geometric parameters is then discussed.

An Investigation into the Interactions Between Self‐Assembled Adenine Molecules and a Au(111) Surface

Two molecular phases of the DNA base adenine (A) on a Au(111) surface are observed by using STM under ultrahigh-vacuum conditions. One of these phases is reported for the first time. A systematic approach that considers all possible gas-phase two-dimensional arrangements of A molecules connected by double hydrogen bonds with each other and subsequent ab initio DFT calculations are used to characterize and identify the two phases. The influence of the gold surface on the structure of A assemblies is also discussed. DFT is found to predict a smooth corrugation potential of the gold surface that will enable A molecules to move freely across the surface at room temperature. This conclusion remains unchanged if van der Waals interaction between A and gold is also approximately taken into account. DFT calculations of the A pairs on the Au(111) surface show its negligible effect on the hydrogen bonding between the molecules. These results justify the gas-phase analysis of possible assemblies on flat metal surfaces. Nevertheless, the fact that it is not the most stable gas-phase monolayer that is actually observed on the gold surface indicates that the surface still plays a subtle role, which needs to be properly addressed.

DPSM Modeling for Studying Interaction Between Bounded Ultrasonic Beams and Corrugated Plates with Experimental Verification

Periodically corrugated structures play an important role in the field of vibration control and for designing structures with desired acoustic band gaps. Analytical solutions for corrugated plates are available for well-defined, smooth corrugations, such as sinusoidal corrugations that are not very common in the real world. Often corrugated plates are fabricated by cutting grooves at regular intervals in a flat plate. No analytical solution is available to predict the wave propagation behavior in such a periodically corrugated plate in which the equation of the plate surface changes periodically between a planar fiat surface and a nonplanar parabolic groove. This problem is solved here for steady-state case by a newly developed semianalytical technique called distributed point source method (DPSM), and the theoretical predictions are compared with the experimental results generated by reflecting a bounded 2.25 MHz ultrasonic beam by a fabricated corrugated plate. The main difference that is observed in the reflected beam profile from a flat plate and a corrugated plate is that the back-scattering effect is much stronger for the corrugated plate, and the forward reflection is stronger for the flat plate. The energy distribution inside the corrugated plate also shows backward propagation of the ultrasonic energy.

On the onset of InAs islanding on InP: influence of surface steps

We investigate the transition from two- to three-dimensional growth of thin InAs films on InP by chemical beam epitaxy. This transition is shown to strongly depend on growth temperature and on the misorientation-or the presence of surface steps — on the InP surface where the InAs film is deposited. Low temperature photoluminescence measurements on InP-InAs-InP quantum well structures and atomic force microscopy analysis of InAs-InP structures indicate different islanding behaviors for substrates with different misorientations, the onset of islanding process occurring earlier for misoriented than for nominal substrates. The shape and distribution of the islands indicate the existence of a step edge barrier altering the diffusion dynamics on the surface. Low growth temperature is shown to delay islanding for a fixed deposition time and also limit island formation to certain regions of the sample where smooth corrugations (slope ∼1°) are observed.

Guided-mode interactions in thin films with surface corrugation

The guided modes in a thin-film planar dielectric waveguide sandwiched between a cover and a substrate (two different dielectrics) are considered. The interface between the cover and the film has a smooth corrugation in the longitudinal direction. For weak corrugations, the guided-mode interactions are investigated using the expansion in terms of ideal normal modes. A corresponding treatment is given for the not-so-weak corrugations using the expansion in terms of local normal modes. The coupling coefficients are evaluated and reduced to simple forms. The theories are specialized for the treatment of contradirectional coupling between two guided modes taking place selectively in the neighborhood of the Bragg frequency. The coupled-mode equations governing the contradirectional interaction obtained from the local normal mode expansion procedure, in the limit of weak periodic corrugations, are identical to those deduced directly using the ideal normal mode expansion technique. The treatments for both the transverse electric and the transverse magnetic modes are included.

An effective procedure to determine corrugation functions from atomic beam-diffraction intensities

A computational method is described, which, starting from given difraction intensities, approaches effectively the best-fit corrugation function ζ( R) . Because of the approximations involved, the procedure works well for smooth corrugations with amplitudes not exceeding ∼10% of the lattice constant. The method rests on two crucial observations: (i) With the full knowledge of the scattering amplitudes A G = ¦A G¦ exp( iϑ G) (absolute values plus phases), the corrugation function can be calculated to a high degree of accuracy from ζ( R) = (2 ik i) −1 In ¦−ΣA G exp( i G·R)¦ which is derived easily from the hard corrugated wall scattering (HCWS) equation by approximating k G by − k i ( k i and k G being the wavevectors of the incoming and diffracted beams, respectively), (ii) With only the ¦A G¦'s (or intensities) known, approximate solutions of the HCWS equation can be obtained with a rough estimate of the relative phases of only a few intense diffraction beams; the estimate is readily performed by investigating systematically a coarse mesh of phases. In this way, approximate corrugations are found with which a full set of phases can be generated, which allows the calculation of an improved ζ( R ); this step is repeated in a loop, until optimum agreement between calculated and given intensities is obtained. The effectiveness of the procedure is demonstrated for three one-dimensional model corrugations described by several Fourier coefficients. The method is finally applied to the case of H 2 diffraction from the quasi-one-dimensional adsorbate corrugation Ni(110) + H(1 × 2).