Computational study of buoyancy effects in a laminar starting jet

Vortical structures formed in evolving jets are important in applications such as fuel injection in diesel engines and fuel leaks. When the jet fluid is different from the ambient fluid, the buoyancy can play an important role in determining the jet flow structure, and hence, the entrainment and fluid mixing processes. In the present study, a jet of helium injected in air is investigated, with emphasis placed on delineating the buoyancy effects on vector–scalar fields during the starting phase. We utilize a computational model, previously validated to predict the flow field of low-density gas jets. The model incorporates finite volume approach to solve the transport equation of helium mass fraction coupled with conservation equations of mixture mass and momentum. Computations were performed for a laminar jet to characterize the advancing jet front, and to capture the formation and propagation of vortex rings and the related pinch-off process. Results show significant effects of buoyancy on jet advancement, as well as on vorticity and helium concentration in the core of the vortex rings.     

<Emphasis Type="Italic">P. psyllium</Emphasis>-<Emphasis Type="Italic">g</Emphasis>-polyacrylonitrile: synthesis and characterization

P. psyllium mucilage, an anionic natural polysaccharide consisting of pentosan and uronic acid obtained from the seeds of Plantago psyllium (Plantago family), was grafted with acrylonitrile (AN). Graft copolymers were prepared by grafting acrylonitrile onto P. psyllium mucilage (PSY) using ceric ion initiated solution polymerization technique for the very first time. The influence of varying concentration of (AN) and ceric ammonium nitrate (CAN) on graft copolymerization was studied. The percent grafting was found to be affected by the concentrations of AN and CAN in the reaction mixture. The prepared copolymers were not soluble in any common solvent or mixture of solvents. The prepared copolymers were characterized by FTIR.     

Acidic Peroxo Salts: A New Class of Initiators for Vinyl Polymerization. IV. Kinetics of Polymerization of Methyl Methacrylate Initiated by Potassium Monopersulfate Catalyzed by Ag(l)

Abstract

Kinetics of vinyl polymerization of methyl methacrylate (MMA) initiated by an acidic peroxo salt, such as potassium monopersulfate coupled with silver nitrate, have been investigated in aqueous medium over the temperature range from 35 to 50°C. The rates of polymerization (R_p) have been computed for various concentrations of the monomer and initiator. The effectiveness of various metal salts in catalyzing the polymerization reaction has been determined from the observed R_p values. The effects of the catalyst (AgNO₃), initiator, monomer, and various secondary aliphatic and aromatic amines on R_p and percentage conversion have been studied. The endgroups of the resultant polymers have been studied using standard methods. From the observed endgroups and kinetic results, a reaction scheme has been proposed involving initiation by ′OH or SO₄ ^? radicals, generated by the interaction of the initiator with silver nitrate and termination by mutual combination.     

PLANTAGO PSYLLIUM-GRAFTED-POLYACRYLONITRILE： SYNTHESIS,CHARACTERIZATION AND ITS USE FOR SOLID REMOVAL FROM SEWAGE WASTEWATER

Plantago psyllium mucilage (PSY), an anionic natural polysaccharide consisting of pentosan and uronic acid obtained from the seeds of Plantago psyllium (Plantago family), was grafted with acrylonitrile (AN). Graft copolymers were prepared by ceric ion initiated solution polymerization technique and were characterized by FT-IR spectroscopy, scanning electron microscopy and differential scanning calorimetry. These copolymers are good flocculating agents for removal of suspended (SS) and total dissolved solid (TDS) in sewage wastewater treatment. The effects of copolymer dose, pH and contact time on flocculation capacity of one selected copolymer sample were studied by jar test method. The suitable pH range for maximum solid removal was 7.0 to 9.2 and the optimum copolymer dose was 1.2mg/L. The overall process for solid removal took 4h. X-ray diffraction (XRD) patterns of grafted copolymer, PSY grafted polyacrylonitrile (PSY-g-PAN) and solid waste, before and after treatment are used to suggest the interaction of the solid waste with PSY-g-PAN copolymer.     

A rapid densitometric method for simultaneous quantification of gallic acid and ellagic acid in herbal raw materials using HPTLC

Gallic acid and ellagic acid are two widely occurring phenolic compounds of plant origin, to which many biological activities including anticancer and antiviral activity have been attributed. A simple HPTLC method has been developed for the simultaneous quantification of gallic acid and ellagic acid. The method was validated for precision, repeatability, and accuracy. Instrumental precision was found to be 0.083 and 0.78, and the repeatability of the method was found to be 1.07 and 1.50 (% CV) for gallic acid and ellagic acid, respectively. The accuracy of the method was checked by a recovery study conducted at two different levels and the average percentage recovery was found to be 101.02% for gallic acid and 102.42% for ellagic acid. The above method was used for the quantification of gallic acid and ellagic acid content in seeds of Abrus precatorius Linn., whole plant of Phyllanthus maderaspatensis Linn., and flowers of Nymphaea alba Linn. The proposed HPTLC method for the simultaneous quantification of gallic acid and ellagic acid was found to be simple, precise, specific, sensitive, and accurate and can be used for routine quality control of herbal raw materials and for the quantification of these compounds in plant materials.     

Catalytic Effect of Cetyltrimethylammonium Bromide on the Oxidation of Oxalic Acid by N-Bromophthalimide in Acidic Medium

The kinetics of micellar catalyzed oxidation of oxalic acid [OA] by N-bromophthalimide was studied in the presence of perchloric acid at 308 K. The orders of reaction with respect to [Oxalic acid], [oxidant], and [H⁺] were found to be fractional, first and negative fractional order respectively. Cationic micelles of cetyltrimethylammonium bromide increased the reaction rate. The effect of phthalimide, mercuric acetate and inorganic salts, that is, [Cl^?][Br^?] has also been done. The rate reaction decreases with increasing dielectric constant of the medium. The results are treated quantitatively in terms of Piszkiewicz and Berezin models. The rate constant (K_obs), cooperatively index (n), binding constant (k_s + k_o), and corresponding activation parameters (E_a, ΔH^#, ΔS^#, and ΔG^#) were determined. A suitable mechanism consistent with the experimental finding has been proposed.