Assessment of k–ε models using tetrahedral grids to describe the turbulent flow field of a PBT impeller and validation through the PIV technique

In turbulence modeling, the RNG and Realizable models have important improvements in the turbulent production and dissipation terms in comparison to the Standard. The selection of the appropriate turbulence model has an impact on the convergence and solution in STRs, and they are used in mixing, multiphase modeling or as starting solution of transient models as DES and LES. Although there are several studies with the pitched blade turbine(PBT) impeller, most of them used the Standard model as representative of all k–ε models, using structured hexahedral grids composed of low number of cells, and in some cases under axial symmetry assumptions.Accordingly, in this work the assessment of the Standard, RNG and Realizable models to describe the turbulent flow field of this impeller, using the Multiple Reference Frame(MRF) and Sliding Mesh(SM) approaches with tetrahedral domains in dense grids, is presented. This kind of cell elements is especially suitable to reproduce complex geometries. Flow velocities and turbulent parameters were verified experimentally by PIV and torque measurements. The three models were capable of predicting fairly the pumping number, the power number based on torque, and velocities. Although the RNG improved the predictions of the turbulent kinetic energy and dissipation rate, the Realizable model presented better performance for both approaches. All models failed in the prediction of the total dissipation rate, and a dependence of its value on the number of cells for the MRF was found.     

Physicochemical and Bioactive Compounds of ‘Cantaloupe’ Melon: Effect of Ozone Processing on Pulp and Seeds

Melon seeds are an important source of bioactive compounds, which are considered to be health beneficial. Therefore, the objective of this work was to assess the impact of gaseous ozone treatments (30 and 60 min) on melon seeds paste (nonedible part) and compare with the effect on pulp (edible part). Ozone treatments were evaluated in terms of physicochemical (color, pH, and soluble solids content) and nutritional profiles (total phenolics, total carotenoids, and total antioxidant capacity) of processed material. Results indicate that ozone has a different impact on the two fruit matrices, being seeds less affected by this preservation treatment.     

Properties of polyamide 6/clay nanocomposites processed by low cost bentonite and different organic modifiers

Nanocomposites based on polyamide 6 have been directly prepared by melt compounding, using modified low cost bentonites by three selected quaternary ammonium cations, in particular quaternized octadecylamine (ODA), dimethyl benzyl hydrogenated tallow quaternary ammonium (B2MTH) and dimethyl hydrogenated ditallow quaternary ammonium (2M2TH). Thermal stability of organic modifiers and organoclays has been studied by TGA and results allow evaluating the degree of modifier incorporation into clay galleries. The influence of the organic modifier on the morphology and properties of the obtained nanocomposites has been studied by X-ray diffraction and TEM analysis. Depending on the degree of bentonite modification, different mechanisms were reported to explain the improved mechanical properties of the resulting nanocomposites.     

Neutral lipids of chickpea flour and protein isolates

The neutral lipids composition of defatted chickpea flour and two types of protein isolates has been studied. The main compounds in neutral lipids are triacylglycerols, free fatty acids, and diacylglycerols. Other compounds present are wax esters, free fatty alcohols, and free sterols. The main fatty acids in neutral lipids are C_18:2 and C_18:1 among the unsaturated, and C_16:0 and C_18:0 among the saturated acids. Free and esterified alcohols range from C_16:0 to C_28:0, the majority being those with an even number of carbon atoms. Sterols observed are β-sito-sterol, campesterol, stigmasterol, and δ-5-avenasterol. Triacyl-glycerols are partially hydrolyzed, and the amounts of unsaturated sterols and unsaturated fatty acids are reduced as a result of the chemical treatment during production of the protein isolates.     

Microbiological assessment of the Gouda-type cheese-making process in a Venezuelan industry

The adoption of the Hazard Analysis and Critical Control Point (HACCP) system is necessary to assure the safety of the product in the cheese-making industry. The compliment of pre-requisite programs as Good Manufacture Practices (GMPs) and Sanitation Standard Operating Procedures (SSOPs) are required before the implementation of the HACCP plan. GMPs are the standards related to equipments, tools, personnel, etc. SSOPs are the procedures related to hygiene and sanitation of the plant and workers. The aim of this study was to assess the compliment of the pre-requisite programs and the microbiological conditions of the Gouda type cheese-making process in a Venezuelan processing plant before designing a HACCP plan. Samples were: (a) raw milk, pasteurized milk, curd and ripened cheese, (b) water, (c) environment of the production areas and ripening premises, (d) equipments before and after sanitation, (e) food handlers. Microbiological analyses were done according to COVENIN standards. This study showed that even though pasteurization process was effective to kill pathogen bacteria of the raw milk and the water was safe, however there are deficient manufacture practices in the hygiene as well as in sanitation of the plant and food handlers. Prerequisite programs (GMP-SSOP) of this industry need to be well established, controlled and evaluated.     

Magnetoelectric coupling in multiferroic BiFeO3 by co-doping with strontium and nickel

We report the effects of the Sr²⁺ and Ni²⁺ co-doping of BiFeO₃ on the crystal structure and multiferroic properties of Bi_1?xSr_xFe_1-yNi_yO₃ (x?=?0.05, 0.0?≤?y?≤?0.10, and Δy?=?0.05) that is synthesized using assisted high-energy ball milling. The mixtures of Bi₂O₃, Fe₂O₃, SrO and NiO were milled for 5?h, pressed at 900?MPa, and sintered at 800?°C in order to obtain cylindrical test pieces. X-ray diffraction and Rietveld refinement elucidated the effects of Sr²⁺ and Ni²⁺ on the crystal structure. Co-doping with SrNi in suitable proportions stabilizes rhombohedral BiFeO₃. High contents of Ni²⁺ promote the precipitation of secondary phases in the forms of NiFe₂O₄ and Bi₂₅FeO₄₀. The magnetic behavior was examined by means of vibrating sample magnetometry. The results showed a change in the magnetic order from antiferromagnetic for the undoped sample to the ferromagnetic order for the co-doped samples. This change is attributed to the modulations in the magnetic moment due to crystal structure distortions. All samples show high relative permittivity values, which were enhanced by doping with Sr²⁺. Ni²⁺ cations increase the dielectric dissipation factor; this enhancement is related to their interactions with cations of a different oxidation state, such as Fe³⁺, Fe²⁺, Ni²⁺, Bi³⁺ and Sr²⁺ in the crystal structure of BiFeO₃. The magnetoelectric coupling that was evaluated using magnetodielectric measurements was above 4% at 1?kHz for the higher applied magnetic field of 18?kOe.     

Improved Palladium and Nickel Catalysts Heterogenised on Oxidic Supports (Silica,MCM‐41, ITQ‐2, ITQ‐6)

Two series of solid catalysts in which a chiral palladium or nickel complex with Schiff bases as ligands have been immobilized on ordered mesoporous silica supports (MCM‐41), delaminated ITQ‐2, ITQ‐6 zeolites and amorphous silica have been prepared. Hydrogenation of alkenes and imines was studied with the homogeneous as well as with the counterpart heterogenized catalysts. The high accessibility introduced by the structure of the supports allows the preparation of highly efficient immobilized catalysts with TOFs of 1,000,000 h⁻¹. A moderate acidity in the support increases the catalytic activity considerably, and the easy recoverable immobilized catalysts can duplicate the activity of the homogeneous analogues. No deactivation of the catalysts was observed after repeated recycling.     

Design of tailored biodegradable implants: The effect of voltage on electrodeposited calcium phosphate coatings on pure magnesium

Magnesium, as a biodegradable metal, offers great potential for use as a temporary implant material, which dissolves in the course of bone tissue healing. It can sufficiently support the bone and promote the bone healing process. However, the corrosion resistance of magnesium implants must be enhanced before its application in clinical practice. A promising approach of enhancing the corrosion resistance is deposition of bioactive coating, which can reduce the corrosion rate of the implants and promote bone healing. Therefore, a well-designed substrate-coating system allowing a good control of the degradation behavior is highly desirable for tailored implants for specific groups of patients with particular needs. In this contribution, the influence of coating formation conditions on the characteristics of potentiostatically electrodeposited CaP coatings on magnesium substrate was evaluated. Results showed that potential variation led to formation of coatings with the same chemical composition, but very different morphologies. Parameters that mostly influence the coating performance, such as the thickness, uniformity, deposits size, and orientation, varied from produced coating to coating. These characteristics of CaP coatings on magnesium were controlled by coating formation potential, and it was demonstrated that the electrodeposition could be a promising coating technique for production of tailored magnesium-CaP implants.