Surface Techniques Research Articles

Design of an auger thermo-radiation dryer for drying plant-derived pomace

This paper reports the improved model design of an auger thermo-radiation dryer for drying plant-derived pomace under a low-temperature mode (35...80 °C) to the resulting moisture content at the level of 8...13 % of solids. The dryer has an adjustable speed of auger rotation (3...4 min–1), of airflow (0.05...0.09 m/s), and is characterized by the uniform distribution of heat flux. It is equipped with an energy-saving two-circuit complex that utilizes secondary energy to heat primary air from 21.1 °C to 28.9 °C. The use of Peltier elements, installed at the heating technical surface of the dryer's auger, makes it possible to convert thermal energy into a low-voltage supply voltage for the autonomous supercharger and exhaust fans. The duration of pomace drying in the model structure of the auger thermo-radiation dryer has been determined, in particular tomato pomace, with an initial content of 75 % of solids, which is 107 min. For apple pomace whose starting content of solids is 65 %, it is 98 min. For comparison, the duration of the convective drying of tomato pomace (75 % of solids) is 120 minutes. The drying was carried out at a temperature of 60 °C to the resulting moisture content of 10...12 % of solids. Organoleptic evaluation on the example of tomato pomace confirms the effectiveness of structural solutions in the auger dryer compared to the convective technique. The results reported in this study could create conditions for the further design and implementation of the proposed structure of thermo-radiation dryer for drying plant-derived pomace involving an altered heat supply technique and the utilization of secondary energy. The designed structure of the device makes it possible to process and preserve the quality properties of plant-derived pomace, allowing the use of this product for a wide range of foodstuffs

Independent Variation of Reynolds Number, Wall Shear Stress and Flow Velocity for Cleaning Experiments: A Geometrically Flexible Parallel Plate Flow Cell

For a long time, determining the factors influencing the cleaning of technical surfaces in the food and beverage industry has been of significant interest. In this study, an innovative test setup with a newly designed parallel plate flow cell was implemented to assess the cleaning of soluble molecular fouling materials, which allows for the independent variation of flow parameters, such as the Reynolds number, velocity, and wall shear stress. The test setup used fluorescence spectroscopy; it was found to produce reliable measurements of cleaning, and the results were confirmed with the help of another fluorescent tracer. A comparison of cleaning times for both equipment revealed that the cleaning times tend to have a geometrically independent power-law relationship with the wall shear stress and velocity, and they were used to directly correlate the cleaning times of the used soluble fouling material. However, the Reynolds number showed a geometric dependence on cleaning times. Nevertheless, on dividing the Reynolds number with respective channel characteristic lengths, geometric independence was observed, and, therefore, a correlation was obtained. We also suggest that complex fouling materials should still be investigated to elucidate their cleaning mechanisms better and test for parameter influences on complex cleaning mechanisms.

Potential of Carvacrol and Thymol in Reducing Biofilm Formation on Technical Surfaces.

Polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), and stainless steel (SS) are commonly used in medicine and food production technologies. During contact with microorganisms on the surface of these materials, a microbial biofilm is formed. The biofilm structure is difficult to remove and promotes the development of pathogenic bacteria. For this reason, the inhibition of biofilm formation in medical and food production environments is very important. For this purpose, five naturally occurring compounds were used for antimicrobial screening tests. The two with the best antimicrobial properties were chosen to inhibit the biofilm formation of Staphylococcus aureus and Pseudomonas aeruginosa. After 3 days of exposure, thymol reduced the amount of biofilm of Pseudomonas aeruginosa within the range of 70–77% and 52–75% for Staphylococcus aureus. Carvacrol inhibited the formation of biofilms by up to 74–88% for Pseudomonas aeruginosa and up to 86–100% for Staphylococcus aureus. Those phenols decreased the enzyme activity of the biofilm by up to 40–100%. After 10 days of exposure to thymol, biofilm formation was reduced by 80–100% for Pseudomonas aeruginosa and by about 79–100% for Staphylococcus aureus. Carvacrol reduced the amount of biofilm by up to 91–100% for Pseudomonas aeruginosa and up to 95–100% for Staphylococcus aureus.

Study of the Electric Resistance of Contact of Frictional Technical Surfaces by Computer-Aided Simulation

Study of the Electric Resistance of Contact of Frictional Technical Surfaces by Computer-Aided Simulation

Independent estimation of sensible and latent fluxes in a vineyard using improved surface renewal analysis

Turbulent fluxes are key components of surface energy balance. Micrometeorological techniques, such as eddy covariance (EC), are commonly used to estimate sensible (H) and latent (LE) heat fluxes, because they provide direct measurements and do not interfere with the normal crop canopy development. However, EC has technical difficulties, strict size, and surface homogeneity requirements and is relatively expensive. Surface renewal analysis (SRA) is a promising alternative for turbulent flux estimation, because it is more economical, has less-stringent fetch requirements, and can be deployed in heterogeneous canopies or markedly sloped surfaces. Castellvi (SRACast) presented a methodology to estimate H using SRA, avoiding the high-frequency wind speed records that are necessary for determining stability and friction velocity, which are then used to calibrate the α parameter (a factor that corrects the nonuniform heating of an air parcel). Instead, an iterative procedure using wind speed recorded using a simple cup anemometer can be used. Here, we estimated sensible and latent heat fluxes and latent heat flux as residual from the energy–balance equation using SRACast during January 2018 and compared the results with EC measurements in a trilled vineyard (heterogeneous canopy), in Pirque, Santiago de Chile. Values of H and LE through SRACast present a high agreement with EC, with slopes (b) of 1.11 and 0.88 and coefficients of determination (R2) of 0.97 and 0.89, respectively. LEres_SRA showed values of 1.60 and 0.80 for b and R2, respectively. Energy balance closure was slightly better for SRA than for EC (b, 0.73 and 0.71; R2, 0.94 and 0.95), proving to be a reasonably good and simpler alternative for turbulent flux estimation.

An Optimised Surface Structure for Passive, Unidirectional Fluid Transport Bioinspired by True Bugs

Some true bug species use droplet-shaped, open-capillary structures for passive, unidirectional fluid transport on their body surface in order to spread a defensive fluid to protect themselves against enemies. In this paper we investigated if the shape of the structures found on bugs (bug-structure) could be optimised with regard to better performance in unidirectional fluid transportation. Furthermore, to use this kind of surface structure in technical applications where fluid surface interaction occurs, it is necessary to adapt the structure geometry to the contact angle between fluid and surface. Based on the principal of operation of the droplet-shaped structures, we optimised the structure shape for better performance in targeted fluid flow and increase in flexibility in design of the structure geometry. To adapt the structure geometry and the structure spacing to the contact angle, we implemented an equilibrium simulation of the, the structure surrounding, fluid. In order to verify the functionality of the optimised structure, we designed and manufactured a prototype. By testing this prototype with pure water used as fluid, the functionality of the optimised structure and the simulation could be proved. This kind of structure may be used on technical surfaces where targeted fluid transport is needed, e.g. evacuation of condensate in order to prevent the surface from mold growth, microfluidics, lab-on-a-chip applications and on microneedles for efficient drug/vaccine coating.

Experimental study of spatial frequency transition of laser induced periodic surface structures

This study shows the influence of laser fluence and pulse number on the spatial frequency distribution of laser induced periodic surface structures (LIPSS) on a stainless steel surface. Also the transition of LIPSS to larger self organized, periodic, cone-like structures has been investigated. The experiments were carried out using a Ti:Sapphire femtosecond laser system with 800 nm centre wavelength, a pulse duration of 30 fs and a repetition rate of 1 kHz. Experiments have been carried out on flat, cold-rolled stainless steel surfaces (1.4301) by variation of the laser output power and feed rate. It could be shown, that the transition of low spatial frequency LIPSS (LSFL) to high spatial frequency LIPSS (HSFL) is a continuous process, strongly depending on the laser single pulse fluence and the pulse number. At higher accumulated fluences the transition of LIPSS to larger self organized structures could be observed. As a result, hierarchical structures were created with micrometer-sized cones at the bottom and nanometer-sized LIPSS on top. By further increasing the accumulated fluence, the grooves between the micro structures are widened until the ablation threshold of the alloy is reached. These hierarchical structures could be of considerable value in improving wetting properties of technical surfaces.

Evaluation on Ground Surface Accuracies of Large-Depth and Steeply Micro-Structured SiC Surfaces

Microstructures can be used to enhance technical surfaces with additional functionalities, which are driving advances in many fields of industrial applications. However, it is difficult to obtain 3D valid information about large-depth and steeply micro-structured surfaces owing to the limitation of the white light interferometric measurements. Therefore, the registration of bisection-measured micro-topographies is proposed using the interactive closest point (ICP) method combined with the genetic algorithm, with the objective of evaluating the micro-form and micro-profile accuracies of a micro-structured surface. First, a diamond grinding-wheel V-tip was employed to fabricate micro-pyramid-structured SiC; subsequently, 3 ideal point models were constructed to match the measured point clouds using the ICP method; finally, the non-dominated sorting genetic algorithm-II (NSGA-II) was used to micro-alignment the bisection-measured point clouds with regard to micro-form and micro-profile errors. It is shown that the registration accuracy is dominated by the ideal profile point number, but the registration efficiency depends on the ideal point number. The the NSGA-II could improve the registration accuracy of micro-profile by 42.6% compared with traditional ICP matching. It is confirmed that the micro-grinding is able to control the micro-form and the micro-profile accuracies within 4%.

A Novel Camera-Based Measurement System for Roughness Determination of Concrete Surfaces.

Determining the roughness of technical surfaces is an important task in many engineering disciplines. In civil engineering, for instance, the repair and reinforcement of building component parts (such as concrete structures) requires a certain surface roughness in order to ensure the bond between a coating material and base concrete. The sand patch method is so far the state-of-the-art for the roughness measurement of concrete structures. Although the method is easy to perform, it suffers from considerable drawbacks. Consequently, more sophisticated measurement systems are required. In a research project, we developed a novel camera-based alternative, which comes with several advantages. The measurement system consists of a mechanical cross slide that guides an industrial camera over a surface to be measured. Images taken by the camera are used for 3D reconstruction. Finally, the reconstructed point clouds are used to estimate roughness. In this article, we present our measurement system (including the hardware and the self-developed software for 3D reconstruction). We further provide experiments to camera calibration and evaluation of our system on concrete specimens. The resulting roughness estimates for the concrete specimens show a strong linear correlation to reference values obtained by the sand patch method.

Film flows with recirculation: hydrodynamics and heat transfer

Hydrodynamics and heat transfer in film flows along solid surfaces are analyzed by numerical simulation. The current version of the Kolmogorov-Prandtl turbulence model is used to obtain a compact mathematical description focused on engineering applications in power engineering and other heat technologies. Film flows with recirculation are studied as special modes of condensing (or evaporative) devices of power plants. Other possible applications are the problems of evaporative cooling, problems of hydraulic roughness of technical surfaces, technologies of thin-film materials and – in the field of large linear scales - modeling of some natural catastrophic phenomena, such as mudflows. The mathematical description is presented as a system of three ordinary first-order nonlinear differential equations - for distributions of turbulent energy, turbulent energy flux density, flow velocity. The phenomena of laminar – turbulent transition and special modes of “flooding” of the flow are diagnosed. Temperature distributions are calculated and heat fluxes are determined. The Reynolds number of the film and the Stanton number are presented as functions of two dimensionless determining parameters specifying the film thickness and the ratio of the friction stresses at the boundaries.

A reduction of settlement probability of Chlorella vulgaris on photo-chemically active ceramics with hierarchical nano-structures

Biofouling is defined by the adsorption of biomolecules or microorganisms on technical surfaces, which are causing adverse effects on the functionality (decrease of ship speed) and safety (infections of implants) of quite a number of industrial products. Conventional, anti-biofouling in marine environments is done by coating a technical surface with highly poisonous tin-organic, which have already been banned for environmental protection. Therefore, the developing of biologically benign coatings becomes a long-term pursue for the industry. Here, we study the Chlorella vulgaris settlement on self-disinfecting titanium dioxide surfaces with three different micro-structures: a flat surface, a light harvesting surface with nano-structure and a hierarchical surface structure, spanning over 5 orders of magnitude (from 0.1 nm to 10 μm). These titanium dioxide surfaces were prepared by Ostwald ripening. This sample manufacturing process gains new catalytic properties as a self-cleaning effect, especially for the light harvesting surface with nano-structure (bulk metallic glass). Chlorella vulgaris dispersions were growing in glass flasks together with the different surface samples over the full time of the experiments. Therefore, this study was made as part of a laboratory scale test. It was found, that bulk metallic glass structures made by Ostwald ripening are showing the highest catalytic and at the same time the best self-cleaning effects. Additionally, the Chlorella vulgaris settlement probability was found to depend on the Wenzel roughness. The surfaces with a high Wenzel roughness were the ones with the lowest Chlorella vulgaris settlement. A semi-field test is proving the comparable antibiofouling performance of our surfaces with existing polymeric or sharkskin like structures on the timescale of one month.

Electron flux and pressure dynamic in the LHC vacuum pilot sector as a function of beam parameters and beam pipe properties

The Large Hadron Collider (LHC) is affected by the electron cloud (EC) phenomenon that can provoke beam instabilities, detrimental heat loads and pressure increases in the vacuum system. An innovative dedicated system called vacuum pilot sector (VPS) provides a continuous monitoring of the electron flux and of the pressure signals thanks to electron pickup and vacuum gauges. The VPS system is installed in a room temperature, field-free part of the LHC storage ring. Several technical surfaces, such as ex situ nonevaporable getter (NEG), amorphous carbon coating and copper, are simultaneously tested. The main outcomes of this study show that the EC signals have: (1) a linear dependence upon the number of bunches and upon the bunch population in the multipacting regime, (2) a multipacting threshold at a given bunch population, (3) a reduction under beam conditioning, (4) a strong dependence on the filling pattern and beam energy. The comparison between different surfaces shows that amorphous carbon coating reduces drastically the EC buildup, thanks to its low secondary electron yield (SEY) and photoelectron yield (PY), while copper and ex situ NEG coated surfaces suffer of EC multipacting, even after several months of operation. The multipacting rate coefficients are higher for copper than for ex situ NEG, as predicted from the SEY estimation. Other detailed experimental observations are discussed in this paper.

Influence of synthetic wastewater on entrapped air on the isotactic and atactic polypropylene microplastic surfaces.

The municipal wastewater collection system is recognized as an initial point of interaction between microplastics (MPs) and the urban wastewater matrix. The raw wastewater contains a wide variety of organic and inorganic substances including chemicals and heavy metals. However, the fate of MPs in urban sewer systems is not yet well understood. In this work two types of virgin polypropylene (PP) samples, isotactic (iPP) and atactic (aPP), were exposed to two synthetic wastewater solutions in order to study their effects on the physical properties of the hydrophobic polymer surfaces. Particular attention was paid to the pollution adhesion at the air-liquid-solid interfaces of the surface air pockets entrapped on the polymer surfaces. The first wastewater solution consists of mixed fat, oil and grease (FOG) - surfactant and another which is an exclusively contained wastewater surfactant. The interaction experiment over a period of 10min between the polymer's air pocket and solutions indicated that the size of the bubble in the mixed FOG-surfactant solution increased more pronouncedly for iPP (%152) in contrast to aPP (%31) and was also compared with the greater surface roughness of the polymers. The size variation of the spherical cap on the immersed polymer surfaces were measured between 17µm and 85µm using image processing techniques while the data was analyzed by the Young-Laplace equation. The corresponding technical surface roughness of the polymers, the surface tension of the liquids and their air/water contact angle on the flat polymer surfaces were also measured. The results of this study indicated that surface air pockets influence the adsorption capacity of MPs and thus their buoyancy and contamination potential.

Memo Akten’s Learning to See: from machine vision to the machinic unconscious

This article uses Memo Akten’s art installation Learning to See (Akten https://www.memo.tv/portfolio/learning-to-see/ , 2017) to challenge the belief that machine learning and machine vision are neutral and objective technologies. Furthermore, this article follows Bernard Stiegler to contend that not only machine vision but also human vision is the result of constant training processes that rely directly on technology (understood as a technical surface of inscription). From this perspective, human vision is always already technical. Likewise, in an age dominated growingly by machine learning technologies, it is possible to speak not only of machine vision but also of a machinic imagination and a machinic unconscious, two notions that can be illustrated through Akten’s art installation.

Clove Oil (Syzygium aromaticum L.) Activity against Alicyclobacillus acidoterrestris Biofilm on Technical Surfaces.

Acidotermophilic bacteria Alicyclobacillus acidoterrestris is one of the main contaminants in the fruit industry forming biofilms which are difficult to remove from the production line by conventional methods. An alternative approach aims for the use of essential oils to prevent Alicyclobacillus biofilm development. The effect of clove essential oil on A. acidoterrestris biofilms on glass and polyvinyl chloride surfaces under static and agitated culture conditions was investigated by atomic force microscopy and the plate count method. The medium-flow and the type of technical surface significantly influenced A. acidoterrestris biofilm. The PVC was colonized in a greater extent comparing to glass. Clove essential oil in 0.05% (v/v) caused 25.1–65.0% reduction of biofilms on the technical surfaces along with substantial changes in their morphology by a decrease in the biofilm: height, surface roughness, and surface area difference. The oil also induced alteration in individual bacterial cells length and visible increase of their roughness. Clove essential oil seems to release EPS from biofilm and thus induce detachment of bacteria from the surface. Due to anti-A. acidoterrestris biofilm activity, the clove oil may be used in the juice industry to hinder a development of A. acidoterrestris biofilms on production surfaces.

Characterization of Rough PTFE Surfaces by the Modified Wilhelmy Balance Technique

The wetting of rough polymer surfaces is of great importance for many technical applications. In this paper, we demonstrate the relationship between the mean roughness values and the fractal dimension of rough and self-affine PTFE surfaces. We have used white light interferometry measurements to obtain information about the complex topography of the technical surfaces having different height distributions. Two different methods for the calculation of the fractal dimension were used: The height difference correlation function (HDC) and the cube counting method. It was demonstrated that the mean roughness value (Ra) correlates better with the fractal dimension Df determined by the cube counting method than with the Df values obtained from HDC calculations. However, the HDC values show a stronger dependency by changing the surface roughness. The advancing and receding contact angles as well as the contact angle hysteresis of PTFE samples of different roughness were studied by the modified Wilhelmy balance technique using deionized water as a liquid. The modified Wilhelmy balance technique enables the possibility for future analysis of very rough PTFE surfaces which are difficult to investigate with the sessile drop method.

Spline-based surfaces in architecture and civil engineering

Spline is the most convenient approximation tool widely used for designing curvilinear technical surfaces in various branches of technology, architecture and civil engineering. To solve such problems, bicubic splines are used. The spline function as a polynomial of the third degree contains differential coefficients. Most often, this is the first derivative in the spline nodes. These coefficients entirely determine its shape. We propose using a fourth order integro-differential spline with additional integral coefficients to construct the surface. These coefficients characterize the shape of the spline curve and the surface between the nodes. As far as computing goes, this spline is not more complicated than traditional one, since it is constructed by solving tridiagonal linear equation system. However, additional coefficients are convenient for local modifications of the curve and surface shapes. This reduces the number of pieces of a composite spline surface. In the practice of constructing geometric shapes in architecture, there are problems when the surface is more complex in one direction than in another. For modeling such surfaces, instead of bicubic spline, we propose using a heterogeneous integro-differential spline. The latter is cubic in one direction of the grid of nodes, and the fourth order polynomial in another direction.

Development, Characterisation and High-Temperature Suitability of Thin-Film Strain Gauges Directly Deposited with a New Sputter Coating System.

New sensor and sensor manufacturing technologies are identified as a key factor for a successful digitalisation and are therefore economically important for manufacturers and industry. To address various requirements, a new sputter coating system has been invented at the Institute of Micro Production Technology. It enables the deposition of sensor systems directly onto technical surfaces. Compared to commercially available systems, it has no spatial limitations concerning the maximum coatable component size. Moreover, it enables a simultaneous structuring of deposited layers. Within this paper, characterisation techniques, results and challenges concerning directly deposited thin film strain gauges with the new sputter coating system are presented. Constantan (CuNiMn 54/45/1) and NiCr 80/20 are used as sensor materials. The initial resistance, temperature coefficient of resistance and gauge factor/k-factor of quarter-bridge strain gauges are characterised. The influence of a protective layer on sensor behaviour and layer adhesion is investigated as well. Moreover, the temperature compensation quality of directly deposited half-bridge strain gauges is evaluated, optimised with an external trimming technology and benchmarked against commercial strain gauges. Finally, the suitability for high-temperature strain measurement is investigated. Results show a maximum operation temperature of at least 400 °C, which is above the current state-of-the-art of commercial foil-based metal strain gauges.

Crossing-The-Line Segmentation as a Basis for Rsm and Rc Evaluation

Feature characterization of rough surfaces is of growing interest in terms of a function oriented description of technical surfaces. Feature characterization requires a segmentation of significant hills and dales of the measured profile. The segmentation can be done in several ways. One method is the so called crossing-the-line segmentation which will be part of ISO 16610 part 45 and ISO 21920 part 2. The crossing-the-line segmentation described in this publication represents an extension of the algorithm proposed by Scott (Scott P, 2006, Meas. Sci. Technol. 17, 559–564) and is based on new knowledge gathered over the last ten years. As an example, the feature parameters and according to ISO 4287:1997 are evaluated.

Characterization of self-cleaning properties on superhydrophobic aluminum surfaces fabricated by direct laser writing and direct laser interference patterning

Self-cleaning ability on technical surfaces can increase the added value of a product. A common path to achieve this property is making the surface superhydrophobic so that water droplets can roll down, picking up dirt particles. In this contribution, the self-cleaning efficiency of Al surfaces structured with direct laser writing (DLW), direct laser interference patterning (DLIP) and a combination of both technologies was quantitatively determined. This was performed by developing a characterization method, where the treated samples are firstly covered with either MnO2 or polyamide micro-particles, then tilted by 15° and 30° and finally washed applying up to nine water droplets (10 µl) over the contaminated surfaces. Then, an optical analysis by image processing of the remaining contamination particles on the textured surfaces was realized after each droplet rolled over the surface. The DLIP textures showed the best performance, allowing the removal of more than 90% of the particles after just three droplets were released. High-speed videos and scanning electron microscopy characterization allowed a deeper understanding on the cleaning behavior and on the relationship between surface microstructure and particle size and shape.