Effects Of Surface Geometry Research Articles

Theoretical Insights into Methane C–H Bond Activation on Alkaline Metal Oxides

In this work, we investigate the role of alkaline metal oxides (AMO) (MgO, CaO, and SrO) in activating the C–H bond in methane. We use Density Functional Theory (DFT) and microkinetic modeling to study the catalytic elementary steps in breaking the C–H bond in methane and creating the methyl radical, a precursor prior to creating C2 products. We study the effects of surface geometry on the catalytic activity of AMO by examining terrace and step sites. We observe that the process of activating methane depends strongly on the structure of the AMO. When the AMO surface is doped with an alkali metal, the transition state (TS) structure has a methyl radical-like behavior, where the methyl radical interacts weakly with the AMO surface. In this case, the TS energy scales with the hydrogen binding energy. On pure AMO, the TS interacts with AMO surface oxygen as well as the metal atom on the surface, and consequently the TS energy scales with the binding energy of hydrogen and methyl. We study the activity of AMO ...

Investigation of the electrode surface geometry effects driven by nanosecond-pulsed surface dielectric barrier discharge

Nanosecond-pulsed surface dielectric barrier discharge (NS-DBD) plasma actuations with powered electrodes of different surface geometries were investigated numerically by solving the coupled plasma discharge equations, electron energy equations and the Navier–Stokes equations in quiescent air at atmospheric pressure. The plasma discharge characteristics and the air flow features were simulated numerically using a simple chemical kinetics plasma model for three powered electrodes with serrated, rectangular and semicircular surfaces, respectively. The results show that the reduced electric field of the serrated electrode is globally the strongest, while that of the rectangular electrode the second strongest, and that of the semicircular electrode the weakest. The maximum values of the reduced electric field, the mean electron energy and the electron density are found to occur immediately near the right upper tips of the powered electrodes, and the streamers of the mean electron energy and electron density in the serrated electrode case are larger in size and higher in value than in the rectangular and semicircular electrode cases. On the other hand, the pressure wave in the serrated electrode case is more intensive, and propagates slightly faster than in the other two electrode cases. Besides, the heated region in the serrated electrode case is greater with a higher temperature than in the other two electrode cases. The comparison results indicate that the performance of NS-DBD plasma actuators depends significantly on the powered electrode surface geometry, and the serrated surface design is a very promising means of flow control.

Bifurcation Analysis of Reaction Diffusion Systems on Arbitrary Surfaces.

In this paper, we present computational techniques to investigate the effect of surface geometry on biological pattern formation. In particular, we study two-component, nonlinear reaction-diffusion (RD) systems on arbitrary surfaces. We build on standard techniques for linear and nonlinear analysis of RD systems and extend them to operate on large-scale meshes for arbitrary surfaces. In particular, we use spectral techniques for a linear stability analysis to characterise and directly compose patterns emerging from homogeneities. We develop an implementation using surface finite element methods and a numerical eigenanalysis of the Laplace-Beltrami operator on surface meshes. In addition, we describe a technique to explore solutions of the nonlinear RD equations using numerical continuation. Here, we present a multiresolution approach that allows us to trace solution branches of the nonlinear equations efficiently even for large-scale meshes. Finally, we demonstrate the working of our framework for two RD systems with applications in biological pattern formation: a Brusselator model that has been used to model pattern development on growing plant tips, and a chemotactic model for the formation of skin pigmentation patterns. While these models have been used previously on simple geometries, our framework allows us to study the impact of arbitrary geometries on emerging patterns.

Evaluation of Nanoparticle Effect on Bubble Nucleation in Polymer Foaming

We present a density functional approach to calculate the free-energy barriers, critical radii, and nucleation rates of bubble nucleation in polystyrene and poly(methyl methacrylate) nanocomposites. In particular, the effects of surface geometry and chemistry of nanoparticles on bubble morphology and cell density have been evaluated with consideration of the local supersaturation of dissolved CO2 molecules and the local subsaturation of polymer chains. It is shown that addition of SiO2 or fluorinated SiO2 particles can improve the nucleation rates up to 4 or 5 orders of magnitude, and the critical radii shrink down to approximately half of the homogeneous nuclei, which are very helpful to fabricate low density foaming materials. The theoretical approach has been tested by the available experimental data and is expected to provide a reasonable explanation for the mechanism of inhomogeneous polymer foaming at the molecular level.

Effect of surface geometry on low-velocity impact behavior of laminated aramid-reinforced polyester composite

The aim of this study is to investigate the effect of surface geometry for low-velocity impact applications. To achieve this purpose, aramid fiber-reinforced laminated polyester composite with various geometries such as cylindrical, elliptical, and spherical were prepared, and low-velocity impact properties were investigated numerically and experimentally. All properties such as orientation, fiber volume fraction, matrix material, and average thickness are the same in all samples. Experimental low-velocity impact behaviors of structure were determined by drop weight tester at low velocity 2.012 m/s. Simulations were carried out by LS-Prepost 4.2 and LS-Dyna v971 software. By this way, results of impact tests were verified and modeled with finite element method. Results of the impact tests showed that the elliptical samples have the highest energy absorption capability due to effective stress transfer capacity. According to experimental results, maximum energy absorption rate difference is 17% between elliptical 10 mm and cylindrical 5 mm geometries.

Fabrication of micro-structured scaffold using self-assembled particles and effects of surface geometries on cell adhesion

Fabrication of micro-structured scaffold using self-assembled particles and effects of surface geometries on cell adhesion

The effects of metal surface geometry on the formation of uranium hydride

The present work examines the effect of surface geometry on the reaction between hydrogen gas and uranium metal, forming uranium hydride (UH3), a pyrophoric compound of significance to the civil nuclear industry. Hydride formation was initiated on uranium samples that had been patterned with a focused ion beam instrument to form surface arrays of triangular prisms and pillars with differing apex angles. Post reaction analysis indicated preferential hydride formation at the apex of these features. Additionally, once hydride formation had commenced the observed growth rate on the prisms appeared to accelerate in comparison to the rate exhibited on the surrounding surface.

Spreading dynamics of liquid droplet on gradient micro-structured surfaces

Designed microtextured surfaces have shown promising applications in tuning the wettability of a liquid droplet on the surfaces and attracted great attention over the past decade; unfortunately, the effect of surface geometry on wetting properties is still poorly understood. In this work, two- and multi-stage pillar microtextures are designed to construct gradient surfaces by altering pillar width and spacing. Then, the multi-phase lattice-Boltzmann method (LBM) is used to investigate the wetting dynamics of a liquid droplet on the gradient surface. Results show that for the two-stage gradient surface with variable pillar spacing, the contact angle hysteresis is found to be proportional to the roughness gradient when droplet/surface system is in the Cassie-Baxter state. However, this proportional relation is no longer correct when the system is in the transition state between the Wenzel and Cassie-Baxter states. For the two-stage gradient surface with variable pillar spacing, the contact angle hysteresis always increases linearly with increasing roughness gradient. Results also show that when a larger droplet is placed on the multi-stage gradient surface, stronger droplet motion is observed due to the smaller contact angle hysteresis. The present LBM simulations provide a guideline for the design and manufacture of the microtextured surfaces to tune the droplet wettability and motion.

Phase change heat transfer and bubble behavior observed on twisted wire heater geometries in microgravity

Phase change is an effective method of transferring heat, yet its application in microgravity thermal management systems requires greater understanding of bubble behavior. To further this knowledge base, a microgravity boiling experiment was performed (floating) onboard an aircraft flying in a parabolic trajectory to study the effect of surface geometry and heat flux on phase change heat transfer in a pool of subcooled water. A special emphasis was the investigation of heat transfer enhancement caused by modifying the surface geometry through the use of a twist of three wires and a twist of four wires. A new method for bubble behavior analysis was developed to quantify bubble growth characteristics, which allows a quantitative comparison of bubble dynamics between different data sets. It was found that the surface geometry of the three-wire twist enhanced heat transfer by reducing the heat flux needed for bubble incipience and the average wire temperature in microgravity. Simulation results indicated that increased local superheating in wire crevices may be responsible for the change of bubble behavior seen as the wire geometry configuration was varied. The convective heat transfer rate, in comparison to ground experiments, was lower for microgravity at low heating rates, and higher at high heating rates. This study provides insights into the role of surface geometry on superheating behavior and presents an initial version of a new bubble behavior analysis method. Further research on these topics could lead to new designs of heater surface geometries using phase change heat transfer in microgravity applications.

The Effect of Surface Geometry of Copper on Dehydrogenation of Benzotriazole. Part II

Dehydrogenation of benzotriazole (BTAH)—an outstanding corrosion inhibitor for copper—on low Miller index surfaces of copper and under-coordinated defects thereon has been characterized using density functional theory calculations. The issue of dehydrogenation is of importance, because benzotriazole bonds strongly to copper surfaces—a requirement for successful competition with corrosive species—only in dehydrogenated (or deprotonated) form. The calculated dehydrogenation activation energy of weakly chemisorbed BTAH—oriented with the molecular plane perpendicular to the surface—is about 1.1 eV on Cu(111), whereas, on more open Cu(100) and step-edges, the activation energy decreases to values closely below 1.0 eV. On the other hand, dehydrogenation activation energies of physisorbed BTAH—oriented with the molecular plane parallel to the surface—are found to be considerably smaller; the smallest calculated value is 0.73 eV. We also find that dehydrogenation barriers decrease with increasing molecular covera...

The Effect of Surface Geometry of Copper on Adsorption of Benzotriazole and Cl. Part I

The adsorption of benzotriazole and Cl on low Miller index surfaces of copper and under-coordinated defects thereon was characterized using density functional theory calculations; the former is an outstanding corrosion inhibitor and the latter a corrosion promoter. We find that adsorption bonding of intact benzotriazole (BTAH), dehydrogenated benzotriazole (BTA⊙), and Cl becomes stronger as the coordination number of surface Cu atoms involved in the adsorption site decreases, whereas the adsorption energy of H—considered as a side-product of BTAH dehydrogenation—is rather insensitive to surface geometry. The Cl binds the strongest, and the binding energy ranges from −3.3 eV on Cu(111) to −3.9 eV on very low-coordinated defects, and BTA⊙ binds somewhat weaker, from −2.8 to −3.8 eV, whereas BTAH binds considerably weaker, from −0.6 to −1.3 eV. The bonding enhancement due to reduced coordination of surface Cu atoms is hence the strongest for BTA⊙, which indicates its ability to passivate the reactive under-c...

A Comparative CFD Study on Solar Dimple Plate Collector with Flat Plate Collector to Augment the Thermal Performance

It is well known that surface enhancements play an important role in augmenting the thermal performance of flat plate solar collector. In this paper, an attempt is made to explain in a comparative way the effect of surface geometry of solar collector having dimple geometry with that of a flat plate solar collector of the same size. A CFD analysis was carried out for the two cases,subjected to a constant heat flux of 600W/m2 and 1000W/m2. It can be inferred from the study that the absorber plate temperature shows a rise of average surface temperature of about 50C for the dimple solar collector when compared to a flat plate solar collector. Most importantly, the average exit water temperature shows a marked improvement of about 5.50C for a dimple solar collector as compared to that of a flat plate solar collector.

Analysis of Heat Transfer, Friction Factor and Exergy Loss in Plate Heat Exchanger Using Fluent

Exergy analysis and energy saving are very important parameters in the heat exchanger design. The effects of surface geometry on heat transfer, friction factor and exergy loss were investigated analytically using fluent software for a flat plate heat exchanger. The analysis was carried out for a 1-1 pass heat exchanger under parallel and counter flow situations, for turbulent flow conditions. Both the heat exchanging fluids were water. It is found that the exergy loss increases with increase in the mass flow rate. Heat transfer rate increases while friction factor and thereby pressure loss decreases with increase in Reynolds number. The various correlations for a flat PHE obtained using fluent are Nu/Pr<SUP>1/3</SUP>= 0.0108 Re<SUP>0.895</SUP> and friction factor f = 55Re<SUP>-0.87</SUP>. Pressure drop greatly increases the capital cost though heat transfer has larger effect on the exergy loss. For improving the heat transfer between the plates and minimizing the exergy loss, the analysis with the software may prove useful in the optimization method for selecting parameters of the plate heat exchangers.

Effects of Surface Geometry on Film Cooling Performance at Airfoil Trailing Edge

Cooling at the trailing edge of a gas turbine airfoil is one of the most difficult problems because of its thin shape, high thermal load from both surfaces, hard-to-cool geometry of narrow passages, and at the same time demand for structural strength. In this study, the heat transfer coefficient and film cooling effectiveness on the pressure-side cutback surface was measured by a transient infrared thermography method. Four different cutback geometries were examined: two smooth cutback surfaces with constant-width and converging lands (base and diffuser cases) and two roughened cutback surfaces with transverse ribs and spherical dimples. The Reynolds number of the main flow defined by the mean velocity and two times the channel height was 20,000, and the blowing ratio was varied among 0.5, 1.0, 1.5, and 2.0. The experimental results clearly showed spatial variation of the heat transfer coefficient and the film cooling effectiveness on the cutback and land top surfaces. The cutback surface results clearly showed periodically enhanced heat transfer due to the periodical surface geometry of ribs and dimples. Generally, the increase of the blowing ratio increased both the heat transfer coefficient and the film cooling effectiveness. Within the present experimental range, the dimple surface was a favorable cutback-surface geometry because it gave the enhanced heat transfer without deterioration of the high film cooling effectiveness.

Falling liquid films on longitudinal grooved geometries: Integral boundary layer approach

Falling thin liquid film on a substrate with complex topography is modeled using a three equation integral boundary layer system. Linear stability and nonlinear dynamics of the film in the framework of this model are studied on a topography with sinusoidal longitudinal grooves aligned parallel in the direction of the main flow. The linear stability theory reveals the stabilizing nature of the surface tension force and the groove measure on the film, and the pronounced destabilizing effects of inertia. The evolution of the film thickness is tracked numerically for a vertically falling film on a grooved geometry by choosing wavenumbers corresponding to the unstable mode where the growth rate of instability is maximum. The effect of surface geometry on the temporal evolution of the film dynamics is analyzed on a periodic domain. Numerical investigations agree with the linear stability predictions and show that the longitudinal grooves exert a stabilizing effect on the film and the waviness is suppressed when the steepness of the longitudinal groove measure increases.

Adhesion models: From single to multiple asperity contacts

This review presents a summary of the current adhesion models available to date, between real rough surfaces, starting from single asperity models and expanding to multiple asperity contacts. The focus is made on multi-asperity contact interactions. Both van der Waals and contact mechanics approaches have been considered and relevant adhesion models are reviewed and discussed. The influence of the meniscus forces on adhesion has been considered, along with a summary of the various meniscus models. The effect of surface geometry, its topography and environmental conditions on meniscus action are also discussed along with its integration into multi-asperity adhesion models.

Impact of Soil Microstructure Geometry on DRIFT Spectra: Comparisons with Beam Trace Modeling

Fourier‐transformed infrared spectroscopy in diffuse reflectance mode (DRIFT) has been proposed as a tool for the characterization of organic matter (OM) composition at intact soil surfaces; however, the local properties and the geometry of intact structural surfaces (e.g., biopores and cracks) affect the reflection in as yet unknown ways. Our goal was to develop an approach to correct for surface geometry effects. The objectives were to analyze the effects of (i) particle size, (ii) porosity, and (iii) specific surface shapes on the infrared signal intensity by comparing measured with simulated reflectance data. Mid‐infrared DRIFT spectra were obtained from differently textured quartz samples and from gypsum blocks with defined surface shapes as models for soil porous systems. A beam tracing model (BTM) was used for the numerical description of the infrared beam propagation in such model soils. The measured DRIFT signal intensity and the simulated bihemispherical reflectance both decreased with increasing quartz particle size; the resolution of the DRIFT spectra decreased with particle size. The geometric effects of the microtopography can be explained by the local variations in the distance between the collection mirror of the DRIFT device and the sample surface. The DRIFT‐measured effects of particle size and surface topography on the signal intensity agreed with the BTM simulation results. The results suggest that a radiative transfer model is useful for interpretations of DRIFT data obtained at intact structural surfaces. The OM properties can be analyzed with DRIFT for surfaces that consist of particles &lt;70 μm and have relatively small, i.e., &lt;1‐mm, relief differences.

The effect of surface geometry on soccer ball trajectories

Two different measurement techniques are used to examine the effect of surface geometry on soccer ball trajectories. Five professional players are observed using high-speed video when taking curling free kicks with four different soccer balls. The input conditions are measured and the average launch velocity and spin are found to be approximately 24 m/s and 106 rad/s. It is found that the players can apply more spin (~50%) on average to one ball, which has a slightly rougher surface than the other balls. The trajectories for the same four balls fired at various velocities and spin rates across a sports hall using a bespoke firing device are captured using high-speed video cameras, and their drag and lift coefficients estimated. Balls with more panels are found to experience a higher lift coefficient. The drag coefficient results show a large amount of scatter, and it is difficult to distinguish between the balls. Using the results in a trajectory prediction programme it is found that increasing the number of panels from 14 to 32 can significantly alter the final position of a 20 m-curling free kick by up to 1 m.

Effects of surface geometry and non-newtonian viscosity on the flow field in arterial stenoses

Hemodynamics including flow pattern, shear stress, and blood viscosity characteristics has been believed to affect the development and progression of arterial stenosis, but previous studies lack of realistic physiological considerations such as irregular surface geometry, non-Newtonian viscosity characteristics and flow pulsatility. The effects of surface irregularities and non-Newtonian viscosity on flow fields were explored in this study using the arterial stenosis models with 48% arterial occlusions under physiological flow condition. Computational flow dynamics based on the finite volume method was employed for Newtonian and non-Newtonian fluid. The wall shear stresses (WSS) in the irregular surface model were higher compared to those in the smooth surface models. Also, non-Newtonian viscosity characteristics increase the peak WSS significantly. The dimensionless pressure drop and the time averaged WSS in pulsatile flow were higher than those in steady flow. But pulsatility effects on pressure and WSS were less significant compared to non-Newtonian viscosity effects. Therefore, irregular surface geometry and non-Newtonian viscosity characteristics should be considered in predicting pressure drop and WSS in stenotic arteries.

Sports ball aerodynamics: A numerical study of the erratic motion of soccer balls

The application of the commercial CFD code, FLUENT, to sports ball aerodynamics was assessed and a validated 3D analysis technique was established for balls that have been scanned with a 3D laser scanner or drawn in CAD. The technique was used to examine the effects of surface geometry on the aerodynamic behaviour of soccer balls by comparing the flow around different balls and predicting the aerodynamic force coefficients. The validation process included performing CFD studies on 3D smooth spheres and various soccer balls, and comparing the results to wind tunnel tests and flow visualisation. The CFD technique used a surface wrapping meshing method and the Reynolds Averaged Navier–Stokes approach with the realizable k-ε turbulence model, which was found to be able to predict the drag, lift and side force coefficients ( C D , C L and C S ) reliably, to compare the wake behaviour, and to give good pressure distributions near the stagnation point. The main limitations of the technique with the available computational resources were its inability to accurately predict boundary layer transition or growth, but despite this, several conclusions could be drawn regarding soccer ball aerodynamics. C D was not significantly different between balls. C L and C S were found to be significantly affected by the orientation of the ball relative to its direction of travel, meaning that balls kicked with low amounts of spin could experience quasi-steady lift and side forces and move erratically from side-to-side or up and down through the air. For different balls, C D , C L and C S were predicted and their variation with orientation entered into a modified trajectory simulation program. The erratic nature of this type of kick was found to vary with details of the surface geometry including seam size, panel symmetry, number, frequency and pattern, as well as the velocity and spin applied to the ball by the player. Exploitation of this phenomenon by players and ball designers could have a significant impact on the game.