Changes In Roughness Parameters Research Articles

Computational fluid dynamics based numerical study to determine the performance of triangular solar air heater duct having perforated baffles in V-down pattern mounted underneath absorber plate

In the current analysis, the effect of perforated baffles in V-down pattern as artificial roughness on the thermal and hydraulic response of a solar air heater having equilateral triangular passage has been examined. A thorough numerical investigation has been done using ANSYS FLUENT-19.0. Effect of change in roughness parameters, viz., baffle height (e) and open area ratio (β) on thermo-hydraulic performance has been explored. Flow Reynolds number is systematically varied. Study reveals that upon varying the baffle height from 5 mm to 11 mm and open area ratio from 20% to 29%, maximum heat transfer rate is attained at e = 9 mm and β = 20%, respectively. Axial Velocity and Turbulence Kinetic Energy have been plotted for clear view of change in variables. Also, the correlations have been developed for Nusselt number and Friction factor. The thermo-hydraulic performance factor of proposed perforated baffle geometry has been observed to be 2.54 at e = 9 mm and β = 20%. Performance of the SAH with suggested roughness is found to be advantageous than other type of roughness elements studied in recent times.

Ciliated columnar epithelium pathomorphosis in children with upper and lower respiratory infections: ultrastructural and nanoscopic analysis

The cytomorphological profile of nasal epithelium in children with acute and chronic respiratory disorders was characterized. The redistribution of nasal ciliary epithelial cells in favor of the mucus-secreting (goblet) cells was observed (group with acute respiratory infection – ratio 2.3:1; group with chronic lung disease – 1:2.4) with normal values of these indicators 5:1 (control group). The mucosal metaplasia, against a background of local leukocyte infiltration, was detected among 28 patients (64.29 %). Using atomic force microscopy, the pathomorphosis of the cytoplasmic membrane ciliated epithelium was described, which characterized by the changes in roughness parameters (Ra, Rq, Rsk, Rmax, Rsk) and waviness (Wa) in group with chronic lung disease (Ra – 34.94 ± 7.8 nm, Rq – 41.26 ± 7.5, Rmax – 225.55 ± 44.43, Rsk – 1,2, Wa – 43.23 ± 12.4 nm) compared with control group (Ra – 7.22 ± 1.94 nm, Rq – 11.43 ± 1.83, Rmax – 111.83 ± 29.26, Rsk – 0.33, Wa – 83.81 ± 29.55 nm). Several deviations in microgeometry of the cilia form factor were revealed, which associated with formation of abnormally long cilia (10–12 μm), decreasing (0.095–0.15 μm) and/or a thickening (0.3–0.4 μm) of their diameter, as well as spatial disorientation like the “corkscrew twisting”. Based on the electron microscopic analysis, anomalies in external dynein arms of the cilia axoneme were revealed, which made it possible to confirmed in two patients the hereditary respiratory pathology.

Prediction of behavior of triangular solar air heater duct using V-down rib with multiple gaps and turbulence promoters as artificial roughness: A CFD analysis

In the current study, duct of equilateral triangular cross section having V-down ribs with multiple gaps and turbulence promoters as artificial roughness is analyzed and thermo-hydraulic response of duct is measured. For in depth analysis computational fluid dynamics analysis has been carried out using ANSYS FLUENT 19.0. Under the parametric variation part, effect of change in roughness parameters, viz., relative roughness pitch and angle of attack on thermohydraulic performance has been explored. Flow Reynolds number (Re) is systematically varied from 4,000 to 20,000. Proposed roughness proves its worth as its attachment over the absorber leads to an enhancement in Nusselt number and friction factor both, because of enhanced level of interaction among the fluid particles. Study reveals that upon varying the relative roughness pitch (P/e) from 8 to 14 and angle of attack from 45⁰ to 60⁰, maximum heat transfer rate is attained at P/e = 10 and α = 45⁰, respectively, irrespective of Reynolds number. Performance of the SAH with proposed roughness is found to be better than other type of roughness elements studied in recent past.

Microstructural and corrosion resistance characterisation of NiTi shape memory alloy modified at low-temperature plasma with carbon coatings produced via RFCVD and IBAD methods

ABSTRACTNiTi shape memory alloy, both before and after low-temperature oxynitriding under glow discharge conditions combined with the production of a nano-sized outer carbon coating, was investigated. The study compares two types of carbon coatings: produced via the RFCVD (radio frequency chemical vapour deposition) and IBAD (ion beam-assisted deposition) methods. The latter was also enriched by randomly distributed silver nanoparticles. The study showed slight changes in roughness parameters and increased corrosion resistance after surface treatment processes. The largest impedance module and corrosion potential and the smallest density of corrosion current were achieved for samples with a carbon coating produced via the RFCVD process. The presented surface modifications using hybrid processes can extend the use of NiTi alloy in medicine due to the increased biocompatibility.

Investigating the crosslinking effects on surface characteristics of vinyltrimethoxysilane‐grafted moisture‐cured low‐density polyethylene/ethylene vinyl acetate blend

ABSTRACTIn this article, the adhesion attributed characteristics of vinyltrimethoxysilane‐grafted moisture‐cured low‐density polyethylene/ethylene vinyl acetate (VTMS‐grafted LDPE/EVA) blend have been investigated before, during, and after crosslinking process. Characterization of the changes due to the moisture‐induced crosslinking has been carried out as a function of vapor exposure (crosslinking) duration. Fourier transform infrared (FTIR) spectroscopy was used for identification of compounds based on functional groups and also for identification of any modification in the chemical structure of the compounds. In addition, contact angle measurement was performed to calculate the surface energy and its components. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were utilized to study the surface morphology changes. The results demonstrated that the moisture‐induced crosslinking was not causing significant changes in roughness parameters and surface energy values of the samples after crosslinking. For instance, the Ra parameter, which shows the arithmetic average height of the surface, changed from 278 nm to 280 nm and the surface free energy decreased from 30.90 to 27.63 mJ/m2 after 16 hours of vapor exposure. However, surface relative elastic modulus approximately doubled, indicating a stiffer surface. The findings confirmed that the adhesion‐related surface properties of the VTMS‐grafted LDPE/EVA blend were not affected impressively by the crosslinking. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47147.

Laser assisted finishing process for improved surface finish of fused deposition modelled parts

Fused deposition modelling (FDM) is a popular Additive Manufacturing (AM) technology. AM based FDM process allows the fabrication of prototypes, tools and direct parts without any geometrical constraints. However, finishing issues such as visible rough patterns are inherent fabrication constraints of FDM parts, which limits the industrial scopes. The aim of this work is to provide the in-depth investigation of the finishing of fused deposition modelled polymer parts by the laser process. This research provided a novel strategy of coupling the FDM process and laser finishing. Empirical models have been developed for average surface roughness, skewness and kurtosis by which average and spatial properties (i.e., relative and combined) of profile distribution over the finished parts have been measured and analyzed. Practical parts have been dealt with in this paper and the change in roughness parameters have been analyzed before and after laser process. Empirical analysis has been used to understand main and interaction effects of different finishing parameters, namely the resolution and laser power, and the part build orientation during FDM. Empirical analysis presented that the interaction have more significant effects than main effects of laser power which is one of the individual parameters of the coupled operation. The experimental result of coupled operation shows that the developed laser assisted finishing process completely eliminates the visible rough patterns, thereby improving surface finish of FDM parts. This research also discussed importance of post finishing techniques and established the quantitative comparison between the published FDM finishing work and present technique to show the effectiveness of the proposed technique in relation to them.

Growth kinetics and morphology of plasma electrolytic oxidation coating on aluminum

Plasma electrolytic oxidation (PEO) was carried out on AA1190 aluminum alloy in mixed silicate-phosphate-based electrolyte in order to fabricate ceramic coating under constant current density. The variations of PEO coating duration with kinetics, surface roughness, amount and size of discharge channels were studied with respect to PEO processing time. The growth mechanism of the ceramic coating was described considering a variation of volume and diameters of discharge channels and pancakes during the PEO. Scanning electron microscope (SEM), atomic force microscope (AFM), and roughness tester were used to study the plasma discharge channels of the PEO coatings. In addition, the effect of alumina nanoparticles in the electrolyte as the suspension was studied on the geometric parameters of discharge channels. It seems that the nanoparticles are adsorbed to the locations of erupted molten oxide, where the dielectric breakdown occurs. Nanoparticles were embedded in the dense oxide layer and were adsorbed at the walls of voids and coatings surface. As a result, they caused significant changes in roughness parameters of the samples containing nanoparticles compared to those without nanoparticles. The obtained results showed that growth kinetics followed a linear trend with respect to PEO coating duration. It was also observed that in the absence of alumina nanoparticles, the average volume of the pancakes is 150% greater than the ones fabricated in the suspension of nanoparticles. Besides, increasing the PEO coating duration leads to adsorbing more nanoparticles on the coating surface, filling the voids, and flattening the surface, and alterations in Rv, Rsk, and Rlo parameters. Correlation between the diameter of discharge channel (dc) and thickness of the pancake (h) also showed a linear relation.

Effect of some yarn properties on surface roughness and friction behavior of woven structures

This paper focused on the effect of some constructional parameters of woven fabrics on surface roughness and on fabric-to-fabric friction coefficients. Fabrics under test differed from each other in their weft yarn counts, weft yarn properties and weft yarn density. Seven surface roughness parameters and static and kinetic coefficients of friction were assessed according to the changes in fabric constructional properties. The results showed that roughness parameters of amplitude, spacing and hybridity changed in different manners in the measurement directions of warp, weft and diagonal. Static and kinetic coefficients of friction changed with surface roughness values in opposite ways in warp and weft directions. Experimental results were also assessed with fabric thickness and fabric balance values. The anisotropic structure of textile surfaces was discussed by the changes in roughness parameters and friction coefficients. Skewness and kurtosis, being roughness parameters, were found to be important in the discussion of the relation between surface roughness and friction coefficients.

A quantitative AFM analysis of nano-scale surface roughness in various orthodontic brackets

In orthodontics, the surface roughnesses of orthodontic archwire and brackets affect the effectiveness of arch-guided tooth movement, corrosion behavior, and the aesthetics of orthodontic components. Atomic force microscopy (AFM) measurements were used to provide quantitative information on the surface roughness of the orthodontic material. In this study, the changes in surface roughness of various orthodontic bracket slots before and after sliding movement of archwire in vitro and in vivo were observed through the utilization of AFM. Firstly, we characterized the surface of four types of brackets slots as follows: conventional stainless steel (Succes ®), conventional ceramic (Perfect ®), self-ligating stainless steel (Damon ®) and self-ligating ceramic (Clippy-C ®) brackets. Succes ® and Damon ® brackets showed relatively smooth surfaces, while Perfect ® had the roughest surface among the four types of brackets used. Secondly, after in vitro sliding test with beta titanium wire in two conventional brackets (Succes ® and Perfect ®), there were significant increases in only stainless steel bracket, Succes ®. Thirdly, after clinical orthodontic treatment for a maximum of 2 years, the self-ligating stainless steel bracket, Damon ®, showed a significant increase in surface roughness. But self-ligating ceramic brackets, Clippy-C ®, represented less significant changes in roughness parameters than self-ligating stainless steel ones. Based on the results of the AFM measurements, it is suggested that the self-ligating ceramic bracket has great possibility to exhibit less friction and better biocompatibility than the other tested brackets. This implies that these bracket slots will aid in the effectiveness of arch-guided tooth movement.

Structure and magnetism of Ni/Ti multilayers on annealing

Neutron reflectometry study has been carried out in unpolarized (NR) and polarized (PNR) mode to understand the structure and magnetic properties of alloy formation at the interfaces of Ni/Ti multilayers on annealing. The PNR data from annealed sample shows a noticeable change with respect to the as-deposited sample. These changes are: a prominent shift of the multilayer Bragg peak to a higher angle and a decrease in the intensity of the Bragg peak. The PNR data from annealed sample revealed the formation of magnetically dead alloy layers at the interfaces. Changes in roughness parameters of the interfaces on annealing were also observed in the PNR data.

Turbulent boundary layers on rough surfaces

The influence of three-dimensional, stochastic roughness on the properties of turbulent boundary layers has been investigated experimentally in order to obtain an improved understanding and description of such effects on the boundary-layer flow over turbomachinery blading. Four rough surfaces were examined: a surface representative of newly-finished turbo-machinery blading, a variant of this surface with different roughness parameters, a sand-cast surface and a mesh surface with a deterministic roughness geometry. A skin-friction correlation has been obtained, and trends in this correlation and the roughness function caused by changes in roughness parameters have been identified.

Influence of initial surface damage on the final texture of chemically etched quartz plates

Various AT-cut quartz plates, mechanically lapped or polished prior to etching are etched at a constant temperature. The variations in the dissolution rate with the time of etching are found to depend on the surface damage in the initial stages of the chemical attack, but with prolonged etching all the dissolution rates tend to a common limiting value. Lapped and polished quartz plates exhibit opposite changes in roughness parameters with the depth of etch for short etching times. Subsequent dissolution leads, whatever the original surface preparation of the quartz plate, to equilibrium values of the roughness parameters characterized by the direction of the profilometry traces. Scanning electron micrographs are in agreement with these observations and reveal that pits of the same shape develop on polished and lapped quartz plates. Thus the initial surface damage has no influence on the final surface texture of deeply etched quartz plates which is determined primarily by the crystal orientation.