Simulation of a Hydrogen-Air Diffusion Flame under Consideration of Component-Specific Diffusivities

This work deals with the numerical investigation of a three-dimensional, laminar hydrogen-air diffusion flame in which a cylindrical fuel jet is surrounded by in-flowing air. To calculate the distribution of gas molecules, the model solves the species conservation equation for N-1 components, using infinity fast chemistry and irreversible chemical reaction. The consideration of the component-specific diffusion has a strong influence on the position of the high-temperature zone as well as on the concentration distribution of the individual gas molecules. The calculations of the developed model predict the radial and axial species and temperature distribution in the combustion chamber comparable to those from previous publications. Deviations due to a changed burner geometry and air supply narrow the flame structure by up to 50% and the high-temperature zones merge toward the central axis. Due to the reduced inflow velocity of the hydrogen, the high-temperature zones develop closer to the nozzle inlet of the combustion chamber. As the power increases, the length of the cold hydrogen jet increases. Furthermore, the results show that the axial profiles of temperature and mass fractions scale quantitatively with the power input by the fuel

Static Wettability of Differently Mechanically Treated and Amphiphobic-Coated Aluminium Surfaces

Wettability, roughness and surface treatment methods are essential for the majority of practical applications, where liquid–solid surface interactions take place. The present study experimentally investigated the influence of different mechanical surface treatment methods on the static wettability of uncoated and amphiphobic-coated aluminium alloy (AlMg3) samples, specially focusing on the interaction between surface finishing and coating. Five different surfaces were prepared: as-received substrate, polished, sandpapered, fleece-abraded and sandblasted. After characterisation, the samples were spray-coated using an amphiphobic coating. The characterisation of the uncoated and coated samples involved measurements of the roughness parameters and the apparent contact angles of demineralized water and rapeseed oil. The coating was initially characterised regarding its adhesion to the sample and elevated temperature stability. The applied surface treatments resulted in the scattered sample roughness in the range of Sa = 0.3–15.8 µm, water contact angles of θap,w = 78°–106° and extremely low oil contact angles. Coating the samples more than doubled the surface roughness to Sa = 13.3–29 µm, whereas the initial surface treatment properties (structure, anisotropy, etc.) were entirely repressed by the coating properties. Coating led the water contact angles to increase to θap,w_coated = 162°–173° and even more pronounced oil contact angles to increase to θap,o_coated = 139°–150°, classifying the surfaces as superhydrophobic and oleophobic

Influence of Non-Thermal Plasma Treatment on Structural Network Attributes of Wheat Flour and Respective Dough

Due to its “generally recognized as safe status” (GRAS) and moderate treatment temperatures, non-thermal plasma (NTP) has lately been considered a suitable replacement for chemicals in the modification of food properties and for preserving food quality. One of the promising areas for the application of NTP is the treatment of wheat flour, leading to improved flour properties and product quality and consequently to higher customer satisfaction. In the present research, the German wheat flour type 550, equivalent to all-purpose flour, was treated using NTP in a rotational reactor to determine the influence of short treatment times (≤5 min) on the properties of flour (moisture and fat content, protein, starch, color, microbial activity, and enzymes), dough (visco-elastic properties, starch, wet and dry gluten, and water absorption), and baking products (color, freshness, baked volume, crumb structure, softness, and elasticity). Based on the properties of NTP, it was expected that even very short treatment times would have a significant effect on the flour particles, which could positively affect the quality of the final baking product. Overall, the experimental analysis showed a positive effect of NTP treatment of wheat flour, e.g., decreased water activity value (8% after 5 min. treatment); dough extensibility increased (ca. 30% after 3 min treatment); etc. Regarding the baking product, further positive effects were detected, e.g., enhanced product volume (>9%), improved crumb whiteness/decreased crumb yellowness, softening of breadcrumb without a change in elasticity, and limited microorganism and enzymatic activity. Furthermore, no negative effects on the product quality were observed, even though further food quality tests are required. The presented experimental research confirms the overall positive influence of NTP treatment, even for very low treatment times, on wheat flour and its products. The presented findings are significant for the potential implementation of this technique on an industrial level

Strukturiranje i primena materijala na osnovu biopolimera hitozana

Derived from chitin, chitosan is a unique biopolymer that exhibits, beside biocompatibility and biodegradability, outstanding adsorption properties. The layer-by-layer (LBL) deposition technique is based on the alternated adsorption of materials bearing complementary charged or functional groups, in aqueous medium. As a consequence of the polycationic nature of chitosan, chitosan-based films can be used as sensors, drug delivery systems and in tissue engineering. The goal of work was to obtain innovative nano-composites beads based on hitosan, alginate and iron-oxide prepared using LBL deposition method, as magnetic adsorbents used for the separation of dyes from solutions and suspensions.Hitozan je jedinstveni biopolimer koji, pored biokompatibilnosti i biodegradabilnosti, pokazuje i odlična adsorpciona svojstva. Sloj po sloj tehnika (layer-by-layer, (LBL)) se zasniva na naizmeničnoj adsorpciji materijala sa komplementarno naelektrisanim ili funkcionalnim grupama, u vodenoj sredini. Polikatjonska priroda hitozana omogućava njihovu primenu u LBL procesima, i zbog toga se filmovi na osnovu hitozana koriste kao senzori, nosači lekova i u inženjerstvu tkiva. Cilj rada je strukturiranje inovativnih nanokompozitnih granula na osnovu hitozana, alginata i Fe2O3 primenom LBL tehnike radi njihove primene kao magnetnih adsorbenata za uklanjanje boja iz rastvora i iz suspenzija

Degradation of Low Concentrated Perfluorinated Compounds (PFCs) from Water Samples Using Non-Thermal Atmospheric Plasma (NTAP)

Perfluorinated compounds (PFCs) are manmade chemicals, containing the covalent C-F bond, which is among the strongest chemical bonds known to organic chemistry. Abundant use of these chemicals contaminates air, water, and soil around the world. Despite recent initiatives and legal regulations set to reduce their omnipresence, conventional water purification processes are either inefficient or very expensive, especially for low PFC contamination levels. This research is focused on the non-thermal atmospheric plasma (NTAP) decomposition of very low concentrations (<1 µg/L) of PFCs (especially perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS)), present in the wastewater produced during the process of PFCs removal from contaminated soil. The efficiency of the decomposition process was investigated for air, oxygen, and nitrogen plasma, with exposure times of 1–10 min and different plasma nozzle- and reactor sizes. Experiments demonstrated that the NTAP treatment is an efficient alternative method for degradation of more than 50% of the initial PFC concentration in the water samples, in less than 200 s. The final concentration of PFC showed strong dependency on the tested parameters. The treatment effect showed to be strongly non-linear with time, followed by the reduction of the pH-value of the treated sample, which might present a limiting factor for further PFC decomposition

Strukturiranje ekološki prihvatljivih elastomernih kompozitnih materijala

For the waste rubber recycling, it is obligative to know the chemical composition of the waste products, if it is to be used in the new composite elastomeric material formulation. The composite elastomeric materials obtained from the waste rubber powder have a very diverse application (farm floors, sports stadiums, tyres production, in construction as a vibration protection material). The aim of this work was to prepare elastomeric composites based on recycled elastomer powder (REP). A few types of elastomeric materials were synthesized based on natural rubber, polybutadiene rubber, styrene-butadiene rubber, (NR/BR/SBR, 40/40/20 phr), carbon black and recycled elastomer powder were synthesized. It was assessed that composites NR/BR/SBR/REP have shorter optimum curing time tc90 than samples without REP. By increasing the REP content the tc90 value and tensile strength are decreasing, but the abrasion resistance is increasing.Kod recikliranja otpadne gume neophodno je poznavati hemijski sastav otpadnog proizvoda, ukoliko će se on koristiti u recepturama za nove hibridne elastomerne materijale. Kompozitni elastomerni materijali dobijeni od praha otpadne gume imaju veoma raznovrsnu primenu (podovi na farmama, sportski stadioni, dobijanje pneumatika, u građevinarstvu kao materijali za zaštitu od vibracija itd). Cilj ovog rada je bio da se dobiju elastomerni kompoziti na osnovu reciklirane gume. Sintetisano je nekoliko tipova elastomernih materijala na osnovu prirodnog kaučuka, stiren-butadienskog kaučuka i polibutadienskog kaučuka (NR/BR/SBR, 40/40/20 phr), čestica čađi i recikliranog gumenog praha. Ustanovljeno je da kompoziti NR/BR/SBR/REP imaju kraće optimalno vreme umrežavanja u poređenju sa uzorcima NR/BR/SBR bez REP. Porastom količine REP smanjuje se vreme optimalnog umrežavanja i prekidna črstoća, a povećava se otpornost na abraziju

Degradation of Low Concentrated Perfluorinated Compounds (PFCs) from Water Samples Using Non-Thermal Atmospheric Plasma (NTAP)

Perfluorinated compounds (PFCs) are manmade chemicals, containing the covalent C-F bond, which is among the strongest chemical bonds known to organic chemistry. Abundant use of these chemicals contaminates air, water, and soil around the world. Despite recent initiatives and legal regulations set to reduce their omnipresence, conventional water purification processes are either inefficient or very expensive, especially for low PFC contamination levels. This research is focused on the non-thermal atmospheric plasma (NTAP) decomposition of very low concentrations (&lt;1 &micro;g/L) of PFCs (especially perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS)), present in the wastewater produced during the process of PFCs removal from contaminated soil. The efficiency of the decomposition process was investigated for air, oxygen, and nitrogen plasma, with exposure times of 1&ndash;10 min and different plasma nozzle- and reactor sizes. Experiments demonstrated that the NTAP treatment is an efficient alternative method for degradation of more than 50% of the initial PFC concentration in the water samples, in less than 200 s. The final concentration of PFC showed strong dependency on the tested parameters. The treatment effect showed to be strongly non-linear with time, followed by the reduction of the pH-value of the treated sample, which might present a limiting factor for further PFC decomposition

Role of Individual Heat Transfer Mechanisms Within a Model Baking Oven Heated by Porous Volumetric Ceramic Burners

The baking process demands a high amount of energy, but only one-third of the total energy supply to the baking oven is actually used for baking, while the rest is dissipated to the environment. This implies that the energy input to the baking process can be significantly reduced, e.g., by enabling a more efficient heat transfer to the product, compared to commercially available ovens. Application of highly radiative, gas-fired heat sources, with a wide power modulation range, such as porous volumetric ceramic burners (VCB), can lead to a reduction in both the baking time and the energy input to a baking oven. In order to optimize energy input to a wide variety of baking products, the role of individual mechanisms in heat transfer between a heat source and a baking product needs to be determined. In the scope of this work, the analysis of the heat transfer within a baking oven model, heated by porous VCBs, was conducted. Contribution of heat transfer mechanisms (heat conduction, convection, thermal radiation) to the total heat transfer was determined by the difference method, where two aluminum cubes of different surface characteristics were used as target objects. Further, the influence of water, commonly added to the baking chamber in form of steam or aerosol, on the heat transfer characteristics within the oven was investigated. Without water addition, the heat transfer between the porous VCBs and the test object occurred mainly through thermal radiation (~45%), followed by heat conduction and convection (~27.5% each). Compared to the reference, commercially available electrical deck baking oven, the share of thermal radiation in the model oven was increased (+ 10%), whereas the share of heat conduction was reduced (−20%). With water addition, the heat transfer to the test object through heat conduction, convection, and thermal radiation declined, as an additional heat transfer through condensation took place. Results of this research provide necessary understanding of the heat transfer mechanisms within the novel baking oven, heated by porous VCBs. They are the base for optimization of the heat transfer from the VCBs to different baking goods, through changing the VCB's operating parameters

Enhancement of Wheat Flour and Dough Properties by Non-Thermal Plasma Treatment of Wheat Flour

Demand to improve food quality attributes without the use of chemicals has risen exponentially in the past few years. Non-thermal plasma (NTP) (also called ‘cold plasma’) is becoming increasingly popular for this purpose due to its unique low-temperature and non-chemical nature. In the present research, the concept of in situ dielectric barrier discharge (DBD) plasma treatment inside a rotational reactor for the direct treatment of wheat flour was experimentally analyzed. The primary research goal was to determine the effects of short-period NTP treatment of DBD type on flour and dough properties. For this purpose, the influence of different operating parameters was tested, i.e., treatment time, the amount of flour placed in the reactor and the environmental (air) temperature. Changes in the structural attributes of the most commonly used flours (type 550 and 1050) and their respective doughs were studied using a set of analytical techniques. Rheological analysis demonstrated the ability of NTP to significantly intensify the visco-elastic properties of dough produced from wheat flour type 550 that was treated for less than 180 s. This indicated that plasma treatment enhanced intermolecular disulphide bonds in gluten proteins, which resulted in stronger protein–starch network formations. However, longer treatment times did not result in a significant increase in the visco-elastic properties of wheat dough. The obtained results showed a 6–7% increase in flour hydration due to NTP treatment, which also makes a contribution to hydrogen bonding due to changes in the bonded and free water phase. Experimental findings further confirmed the dependence of NTP treatment efficiency on environmental air temperature

Hydrocarbons conversion to syngas in inert porous media combustion

Experimental combustion in inert porous media of Liquefied Petroleum Gas (LPG), Butane, Propane, Diesel Fuel and Heavy Fuel Oil (HFO) is presented to assess the syngas production within different stages of refinement of fuels, considering light gases up to a residual oil. The porous media is composed by a fixed bed of alumina spheres and temperatures and gas composition were acquired while stable combustion waves under rich fuel conditions were produced. The results of this study showed that it is possible to partially oxidize HFO producing up to a 10% of H-2 and CO in the products for the equivalence ratio of phi = 1.3, with a superior performance than any other fuel tested in this work. The behavior of the recorded temperature results showed good agreement with the available literature. Upstream regimes of propagation of the combustion wave are observed for the experiments with liquid fuels, while gaseous fuels presented downstream regimes for phi > 2 up to phi = 4. Results suggest that in order to efficiently transform the fuels into syngas, it is convenient to operate the reactor under an upstream regime considering the chemical energy at inlet and outlet. Furthermore, liquid fuels, regardless of its refining level, have the potential to produce syngas in inert porous media in promising volumes.CONICYT-Chile (FONDECYT) 1121188 CONICYT-Chile PCHA/Doctorado Nacional/2013-21130165 CONICYT-Chile (FONDAP) 15110019/SERC-Chil