Modelling of packed bed adsorption columns for the separation of green tea catechins

Green tea is a rich source of catechins, which when purified have a high economic value as they can be used as a supplement in several products, to increase their health benefits. Catechins are regarded as desired components with several applications in a variety of areas such as foods, cosmetics and pharmaceuticals. A multicomponent sorption model has been developed for the separation of catechins from liquid tea streams, with macroporous resins in a packed bed column. Two commercially available food grade resins were considered: Amberlite XADHP and Diaion HP20. For the desorption step, two food grade solvents are used: water and ethanol. The adsorption and desorption behaviour is subsequently mathematically described with one-dimensional axial dispersed plug flow model that can accurately simulate the dynamics of the solvent swing sorption columns. The model parameters were regressed from experimental data. Five components are modelled in the competitive sorption: the main four catechins present in green tea and caffeine. The model was used for the process design and optimization for the recovery of catechins from green tea.     

Numerical Modeling of Ti Deformation for the Development of a Titanium and Stainless Steel Transition Joint

Finite element analysis (FEA) was used to model the joining of titanium grade 2 (Ti) to AISI 321 stainless steel (SS) transition joint of lap configuration with grooves at the interface on SS side. The hot forming of Ti for filling the grooves without defects was simulated. FEA involving large plastic flow with sticking friction condition was initially validated using compression test on cylindrical specimen at 900 °C. The barreled shape and a no-deformation zone in the sample predicted by FEA matched with those of the compression experiments. For the joining process, FEA computed the distribution of strain and hydrostatic stress in Ti and the minimum ram load required for a defect-free joint. The hot forming parameters for Ti to fill the grooves without defects and any geometrical distortion of the die were found to be 0.001 s^?1 at 900 °C. Using these conditions a defect-free Ti-SS joint was experimentally produced.     

Numerical and Experimental Studies of Parasitic Heat Losses in Coldfinger of a Pulse Tube Cryocooler in Off-State Condition

A pulse tube cryocooler (PTC) for future metrological satellites has been developed at one of the lead centers of the Indian Space Research Organisation in Bangalore, India for cooling on-board Infrared (IR) detectors to 80 K.A study has been conducted on the coldfinger of PTC to understand the off-state heat loads on the cooler by varying the value of gravity numerically in ANSYS FLUENT and experimentally by orienting the setup with respect to gravity. The off-state parasitic losses represent a major heat load in on-board applications that include redundant, viz. nonoperating coolers. To find out the amount of off-state parasitic heat losses in a nonoperating coldfinger of the PTC experimentally, transient warm-up technique was used. Various heat loads were applied experimentally on the cryo-tip at temperatures ranging from 80 to 100 K for determining the parasitic losses. The effect of orientation of PTC on the off-state parasitic heat load with respect to gravity is studied and presented in this paper. Enhancement due to free convection heat flow normalized by gas molecular conduction in pulse tube is analyzed using computational fluid dynamics to verify and compare with experimental results. The best orientation angle where the parasitic is low is when the cold end of the coldfinger of pulse tube cryocooler faces down (0^°) and high when the cold end of the coldfinger is oriented to 135^°.     

Growth and properties of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin films prepared by multiple metallic layer stacks as a function of sulfurization time

In this paper, we report the two stage growth of Cu₂ZnSnS₄ (CZTS) thin films as a function of sulfurization time. First, magnetron sputtered metallic precursors were deposited sequentially (Zn/Cu/Sn/Cu) over rotating glass substrates held at 230?°C. Later, the sputtered precursors were heat treated at 500?°C in the ambiance of sulfur for various time durations in the range, 10–120 min. The sulfur treated samples were examined using various analytical tools to understand the role of sulfurization time on the CZTS growth and properties. From composition and structural analysis, Zn/Cu/Sn/Cu precursors sulfurized for shorter duration (10 and 20 min) revealed severe deficiency of sulfur that resulted in several metallic, bi-metallic and metal sulfide phases. With the increase of sulfurization time to 30 min, sulfur incorporation was enhanced and reached stoichiometric ratio (~50% S) for CZTS growth, however, samples were poorly crystalline in nature and consisted of prominent Cu_2?xS phase as well. The Zn/Cu/Sn/Cu precursors sulfurized for 60 min exhibited prominent CZTS phase without Cu_2?xS phase. Further, rise in sulfurization time to 120 min enabled drastic improvement in crystallinity of CZTS phase. Raman mapping over 60 µm × 60 µm for these films confirmed the homogeneous phase growth of CZTS. XPS study revealed the oxidation states of Cu¹⁺, Zn²⁺, Sn⁴⁺ and S^2? in CZTS films. The optimized films showed high absorption coefficient of 10⁵ cm^?1 with an optical band gap of 1.51 eV. These films showed leaf like grain morphology with high mobility and low resistivity of 18.2 cm²/V-s and 0.7 Ω-cm, respectively.     

Layer‐by‐layer assembly of halogen‐free polymeric materials on nylon/cotton blend for flame retardant applications

Thin films of environmentally safe, halogen free, anionic sodium phosphate and cationic polysiloxanes were deposited on a Nyco (1:1 nylon/cotton blend) fabric via layer‐by‐layer (LbL) assembly to reduce the inherent flammability of Nyco fabric. In the coating process, we used three different polysiloxane materials containing different amine groups including, 35–45% (trimethylammoniummethylphenythyl)‐methyl siloxane‐55‐65% dimethyl siloxane copolymer chloride salt (QMS‐435), aminoethylaminopropyl silsesquioxane‐methylsilsesquioxane copolymer oligomer (WSA‐7021) and aminopropyl silesquioxane oligomers (WSA‐991), as a positive polyelectrolyte. Thermo‐gravimetric analysis showed that coated fabric has char yield around 40% at 600 °C whereas control fabric was completely consumed. The vertical flame test (VFT) on the LbL‐coated Nyco fabric was passed with after flame time, 2 s, and the char length of 3.81 cm. Volatile and nontoxic degradation products of flame retardant‐coated fabric were analyzed by pyrolysis gas chromatography mass spectroscopy (Py‐GCMS). Surface morphology of coated fabrics and burned fabric residues were studied by scanning electron microscopy. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimization of shock response within a military vehicle space frame

Space frames are usually used to enhance the structural strength of a vehicle while reducing its overall weight. The space frame of a military vehicle is subjected to significantly different loading than what is experienced in civilian vehicles, such as projectile impact or mine blast. In this work, a finite element (FE) model for the upper half of an armored vehicle with internal space frame is developed. The behavior of the vehicle is studied when subjected to a high impact load that simulates a projectile impact. The objective of this work is to minimize shocks at identified critical locations on the space frame while maintaining the overall structural integrity of the vehicle. Several variables that can affect shock propagation are identified including, the cross-sectional parameters of the internal space frame and outer armor. The optimization problem is solved using the Successive Heuristic Quadratic Approximation (SHQA) technique, which combines successive quadratic approximation with an adaptive random search while varying the bounds of the search space. The entire optimization process is carried out within the MATLAB environment. The results show that a significant reduction in the shock can be achieved using this approach.     

Palladium(II)‐Catalyzed Sequential Aminopalladation and Oxidative Coupling with Acetylenes/Enones: Synthesis of Newly Substituted Quinolines from 2‐Aminophenyl Propargyl Alcohols

Palladium catalyzed conversion of 1‐(2‐aminophenyl)‐propargyl alcohols to 3‐alkynyl quinolines is realized via a cascade that involves aminopalladation, oxidative coupling with alkynes and dehydration. The method is shown to have a broad substrate scope with respect to propargyl alcohols as well as alkynes. Vinyl ketones as coupling partners in the same reaction afforded 3‐alkenyl quinolines with equal ease.

     

Comparison of corrosion performance of various conversion coatings on magnesium alloy using electrochemical techniques

Comparative studies on some of the important chemical conversion coatings, namely, phosphate–permanganate, galvanic black anodizing, dichromate treatment, and micro arc oxidized and modified acid fluoride anodizing on magnesium alloy AZ31B have been conducted. The surface morphology and composition of the coatings were examined through SEM and EDX techniques. Corrosion resistances of these coatings were compared using electrochemical impedance spectroscopy (EIS) and linear polarization studies. The corrosion resistances of the coatings investigated were found to be according to the order as follows: modified acid fluoride > micro arc oxidized phosphate > micro arc oxidized silicate > dichromate > galvanic black anodizing > phosphate-permanganate > bare magnesium.