Instability of Bingham fluids in Taylor-Dean flow between two concentric cylinders at arbitrary gap spacings

Stability of Bingham fluids is investigated numerically in azimuthal pressure-driven flow between two infinitely long concentric cylinders. An infinitesimal perturbation is introduced to the basic flow and its time evolution is monitored using normal mode linear stability analysis. An eigenvalue problem is obtained which is solved numerically using pseudo-spectral collocation method. Numerical results are obtained for two different cases: (i) the inner cylinder is rotating at constant velocity while the outer cylinder is fixed (i.e., the Taylor-Dean flow) and (ii) both cylinders are fixed (i.e., the Dean flow). The results show that the yield stress always has a stabilizing effect on the Taylor-Dean flow. But, for the Dean flow the effect of the yield stress is predicted to be stabilizing or destabilizing depending on the magnitude of the Bingham number and also the gap size.     

Interfacial flows in corrugated microchannels: Flow regimes,transitions and hysteresis

We report simulations of gas–liquid two-phase flows in microchannels periodically patterned with grooves and ridges. A constant effective body force is applied on both fluids to simulate a pressure-driven creeping flow, and a diffuse-interface model is used to compute the interfacial evolution and the contact line motion. Depending on the body force, capillary force and the level of liquid saturation, a number of flow regimes may appear in the corrugated microchannel: gas flow, blockage, liquid flow, bubble–slug flow, droplet flow, annular flow and annular-droplet flow. A map of flow regimes is constructed for a set of geometric and flow parameters starting from a prescribed initial configuration. Some of the regimes are new, while others have been observed before in straight tubes and pipes. The latter are compared with previous experiments in terms of the regime map and the holdup ratio. The transition among flow regimes shows significant hysteresis, largely owing to the pinning of the interface at sharp corners in the flow conduit. Hysteresis is reduced if the sharp corners are rounded. Under the same operating conditions, different flow regimes can be realized from different initial conditions. The roles of geometry and wettability of the channel walls are also elucidated.     

A blood-mimicking fluid for particle image velocimetry with silicone vascular models

For accurate particle image velocimetry measurements in hemodynamics studies, it is important to use a fluid with a refractive index (n) matching that of the vascular models (phantoms) and ideally a dynamic viscosity matching human blood. In this work, a blood-mimicking fluid (BMF) composed of water, glycerol, and sodium iodide was formulated for a range of refractive indices to match most common silicone elastomers (n = 1.40–1.43) and with corresponding dynamic viscosity within the average cited range of healthy human blood (4.4 ± 0.5 cP). Both refractive index and viscosity were attained at room temperature (22.2 ± 0.2°C), which eliminates the need for a temperature-control system. An optimally matched BMF, suitable for use in a vascular phantom (n = 1.4140 ± 0.0008, Sylgard 184), was demonstrated with composition (by weight) of 47.38% water, 36.94% glycerol (44:56 glycerol–water ratio), and 15.68% sodium iodide salt, resulting in a dynamic viscosity of 4.31 ± 0.03 cP.     

FTIR studies of plasticized poly(vinyl alcohol)-chitosan blend doped with NH4NO3 polymer electrolyte membrane

Fourier transform infrared (FTIR) spectroscopy studies of poly(vinyl alcohol) (PVA), and chitosan polymer blend doped with ammonium nitrate (NH(4)NO(3)) salt and plasticized with ethylene carbonate (EC) have been performed with emphasis on the shift of the carboxamide, amine and hydroxyl bands. 1% acetic acid solution was used as the solvent. It is observed from the chitosan film spectrum that evidence of polymer-solvent interaction can be observed from the shifting of the carboxamide band at 1660 cm(-1) and the amine band at 1591 cm(-1) to 1650 and 1557 cm(-1) respectively and the shift of the hydroxyl band from 3377 to 3354 cm(-1). The hydroxyl band in the spectrum of PVA powder is observed at 3354 cm(-1) and is observed at 3343 cm(-1) in the spectrum of the PVA film. On addition of NH(4)NO(3) up to 30 wt.%, the carboxamide, amine and hydroxyl bands shifted from 1650, 1557 and 3354 cm(-1) to 1642, 1541 and 3348 cm(-1) indicating that the chitosan has complexed with the salt. In the PVA-NH(4)NO(3) spectrum, the hydroxyl band has shifted from 3343 to 3272 cm(-1) on addition of salt from 10 to 30 wt.%. EC acts as a plasticizing agent since there is no shift in the bands as observed in the spectrum of PVA-chitosan-EC films. The mechanism of ion migration is proposed for the plasticized and unplasticized PVA-chitosan-NH(4)NO(3) systems. In the spectrum of PVA-chitosan-NH(4)NO(3)-EC complex, the doublet CO stretching in EC is observed in the vicinity 1800 and 1700. This indicates that there is some interaction between the salt and EC.     

Electrochemical study on the natural and chemical preservatives antibacterial effect against S. aureus PTCC 1112 and its determination at low levels

Journal of the Iranian Chemical Society - Pathogen microorganisms detection, such as Staphylococcus aureus (S. aureus), is so critical because it can be dangerous for public health. In this...     

Improvement of size-based particle separation throughput in slanted spiral microchannel by modifying outlet geometry

The inertial microfluidic technique, as a powerful new tool for accurate cell/particle separation based on the hydrodynamic phenomenon, has drawn considerable interest in recent years. Despite numerous microfluidic techniques of particle separation, there are few articles in the literature on separation techniques addressing external outlet geometry to increase the throughput efficiency and purity. In this work, we report on a spiral inertial microfluidic device with high efficiency (>98%). Herein, we demonstrate how changing the outlet geometry can improve the particle separation throughput. We present a complete separation of 4 and 6 μm from 10 μm particles potentially applicable to separate microalgae (Tetraselmis suecica from Phaeodactylum tricornutum). Two spiral microchannels with the same cross section dimension but different outlet geometry were considered and tested to investigate the particle focusing behavior and separation efficiency. As compared with particle focusing observed in channels with a simple outlet, the particle focusing in a modified outlet geometry appears in a more successful focusing manner with complete separation. This simple approach of particle separation makes it attractive for lab-on-a-chip devices for continuous extraction and filtration of a wide range of cell/particle sizes.     

Study of mechanism and kinetic modeling of CO hydrogenation reaction over the impregnated Co-Ni/Al2O3 catalyst

An investigation of the kinetic and mechanism of CO hydrogenation reaction was performed on impregnated Co-Ni/Al₂O₃. Determination of kinetic parameters from the experiments was carried out in a micro fixed-bed reactor. Kinetic evaluations were performed under various operational conditions of T = 473–673 K, p = 1–14 bar, H₂/CO = 1–3, and GHSV = 4,500 hr⁻¹. Kinetic models and rate equations for CO consumption were obtained by using two main-type rate equations of Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER). Estimation of various kinetic parameters was performed using a nonlinear regression method. According to the obtained experimental results and using statistical criteria, one kinetic expression based on the LHHW mechanism (-r_CO = k_p.b_CO.P_CO. b_H2. P_H2/[1+ b_CO.P_CO + b_H2.P_H2]²) was chosen as the best-fitted model. For this fitted model, the activation energy was found to be 109.2 kJ/mol. Characterization of the catalyst was also performed using X-ray diffraction (XRD), BET, scanning electron microscopy (SEM), and energy-dispersive x-ray spectrometer (EDS) techniques.     

Synthesis and Complexing Properties of Novel Crown Ethers and Thiacrown Ethers Incorporating New Heterocyclic Moieties

The synthesis of some novel crown and thiacrown ethers via the reaction of 2,3-bis(4-hydroxyphenyl) or 2,3-bis(4-mercaptophenyl)quinoxalines and pyridopyridazine with diethylene and triethylene glycol ditosylate is described. The complexing ability of compounds 5b and 5h, as the representatives of both groups of compounds, with alkali and alkali earth metal cations were measured by the solvent extraction method. The results showed that crown ether 5b comparatively had more affinity towards the Mg²⁺ cation, while thiacrown ether 5h had greater affinity towards the Ca²⁺ cation.     

SYNTHESIS OF [1,3,4]THIADIAZOLO[2,3-C][1,2,4]TRIAZIN-4-ONES USING SULFURIC ACID SUPPORTED ONTO SILICA GEL IN SOLVENTLESS SYSTEM

[1,3,4]Thiadiazolo[2,3-c][1,2,4]triazin-4-ones were prepared by one pot condensation and cyclization of 4-amino-[1,2,4]triazine-3-thione-5-ones with various aromatic carboxylic acids in the presence of silica gel sulfuric acid in solventless condition.     

Electrochemical Oxidation of Catechols in the Presence of Pyrimidine-2-thiol: Application to Electrosynthesis

The electrooxidation of catechols (1a–d) in the presence of pyrimidine-2-thiol (3) as a nucleophile in aqueous solution is described. The mechanistic investigations using cyclic voltammetry and controlled potential coulometry indicate that the quinone derived from catechols participates in a Michael addition reaction with pyrimidine-2-thiol to form corresponding catechol derivatives of 6a–d (ECEC). The efficient electrosynthesis of 6a–d has been performed at carbon rod electrodes in an undivided cell in good yield and purity.