Flow characteristics of vortex based cavitation devices

Vortex based hydrodynamic cavitation (HC) devices offer various advantages over conventional linear flow devices, such as early inception, low erosion risk, and higher cavitational yield. Despite several promising applications, the key underlying flow characteristics are not yet adequately understood. This article presents results of a computational investigation into cavitation in vortex devices. Multiphase computational fluid dynamics results are presented and compared with experimental data on pressure drop over a range of flow rates. The results highlight the unique hydrodynamic characteristics of this type of device in relation to conventional linear flow reactors; cavitation inception occurs in the liquid bulk away from sold surfaces, and rapid pressure recovery rates are achieved. The models were used to simulate detailed time–pressure histories for individual vapor cavities, including turbulent fluctuations. The developed approach, models and results will provide a sound and useful basis for comprehensive multiscale modeling of vortex-based devices for HC.     

Dissolution of semicrystalline polymer fibers: Numerical modeling and parametric analysis

The solvent processing of polymers is significantly constrained by polymer chain crystallinity. A phenomenological model is developed here that captures the phenomena governing the dissolution of semicrystalline polymers, for example, solvent penetration, transformation from crystalline to amorphous domains, specimen swelling, and polymer chain untangling. The model is validated for the case of cellulose fiber swelling and dissolution in an ionic liquid. A parametric sensitivity analysis is performed to assess the impact of decrystallization rate constant, disentanglement rate, concentration dependence of solvent diffusivity, disentanglement threshold, and thickness of external boundary layer on the swelling and dissolution of semicrystalline polymer fibers. The rate of dissolution after attaining maximum swelling is found to be mainly controlled by the polymer chain disentanglement rate. The insights obtained from this study would facilitate the design of efficient solvent systems and processing conditions for the dissolution of semicrystalline polymers such as cellulose, polyglycolic acid, and polyesters. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1368–1383, 2017     

Effect of electrode material on thermally stimulated discharge and dark current in polystyrene

Thermally stimulated discharge (TSD) currents excited at 110°C by 117 V in 20 μm thick polystyrene (PS) films in contact with Al, Zn, Pb, Cd, Cu and Ni have been measured keeping the other electrode as Al. TSC parameters are observed to change with the choice of electrode material. Maximum charge is stored by PS films in contact with Cu. The observed polarization is explained in terms of detrapping of charges injected from the electrodes with subsequent space-charge formation. The dependence of dark current at 50°C in metal-PS-Al systems on applied voltage in the range 3–117 V has also been investigated. Current density-square root voltage plots are observed to have straight portions at high field values. Zero field current density extrapolated from these plots and TSC activation energy are found to vary with metal work function qualitatively in a similar manner.     

Role of AgNPs in the enhancement of seed germination and its effect on plumule and radicle length of Pennisetum glaucum

The authors have investigated beneficial effects of 1 mM of silver nanoparticles (AgNPs) on agriculturally important plant Pennisetum glaucum (Bajara). The extracellular AgNPs were synthesised using Bacillus subtilis spizizenni and characterised using ultraviolet–visible absorption spectroscopy, Fourier transform infrared spectroscopy (FT‐IR) and transmission electron microscopy (TEM). Optical absorption spectrum showed characteristic peak of AgNPs at 423 nm. FT‐IR analysis of AgNPs showed peak at 3435 cm⁻¹, which indicates the presence of N–H group (primary, secondary amines and amides) on the surface of AgNPs. TEM studies indicate that synthesised AgNPs have average size of ∼2 nm. Energy dispersive X‐ray spectroscopy showed strong signal of Ag at 3 keV. Treatment of 1 mM AgNPs to the bajara seeds was found to be sufficient for excellent germination of seeds within 3 days. There was also significant increase in radicle and plumule length as compared with control bajara seeds according to statistical analysis by one‐way analysis of variance, followed by Tukey''s test. The percentage of AgNPs detected in root samples was 0.003% (by inductively coupled plasma atomic emission spectroscopy), which is negligible. There is still need to study the bioavailability and the type of interaction of AgNPs with plants, necessary for application in agriculture.Inspec keywords: transmission electron microscopy, ultraviolet spectra, scanning electron microscopy, nanofabrication, X‐ray diffraction, nanoparticles, visible spectra, silver, atomic emission spectroscopy, X‐ray chemical analysis, Fourier transform infrared spectra, statistical analysis, agricultureOther keywords: ultraviolet–visible absorption spectroscopy, transmission electron microscopy, Pennisetum glaucum, Bacillus subtilis spizizenni, energy dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy, optical absorption spectrum, plumule length, radicle length, silver nanoparticles, Tukey''s test, inductively coupled plasma atomic emission spectroscopy, statistical analysis, Bajara seeds, scanning electron microscopy, X‐ray diffraction, analysis of variance, electron volt energy 3.0 keV, time 3.0 d, Ag     

Position and hop-count assisted full coverage control in dense sensor networks

In recent years, wireless sensor networks (WSN’s) have gained much attention due to its various applications in military, environmental monitoring, industries and in many others. All these applications require some target field to be monitored by a group of sensor nodes. Hence, coverage becomes an important issue in WSN’s. This paper focuses on full coverage issue of WSN’s. Based on the idea of some existing and derived theorems, Position and Hop-count Assisted (PHA) algorithm is proposed. This algorithm provides full coverage of the target field, maintains network connectivity and tries to minimize the number of working sensor nodes. Algorithm works for communication range less than root three times of sensing range and it can be extended for arbitrary relation between communication range and sensing range. By using hop-count value, three-connectivity in the network is maintained. Also, neighbors information is used to create logical tree structure which can be utilized in routing, redundant data removal and in other areas. Simulation results show that PHA algorithm outperforms layered diffusion-based coverage control algorithm by providing better area coverage and activating fewer nodes.     

Photo-polarisation in pure and doped polystyrene

Depolarisation currents have been measured of the photo-electrets of pure and copperphthalocyanine doped polystyrene films using UV-radiation. A hyperbolic decay law is observed suggesting bimolecular recombination process. Doped films show strong saturation with the applied field supporting a trap filling mechanism.     

Thermally stimulated discharge current studies in copper phthalocyanine - doped polystyrene films

To improve the electret characteristics, TSD current studies of copper phthalocyanine - doped polystyrene films of about 20 microns thickness have been made as a function of doping concentration, poling temperature and field. Generally the thermograms observed exhibit α and ρ peaks. The activation energy is found to decrease as the concentration of the dopant in the polymer is increased. It is established that keeping the forming field constant and by increasing the concentration of the dopant, the same polarisation can be obtained at a lower poling temperature. A Maxwell-Wagner two-phase model with space - charge build-up seems to provide a possible mechanism for the polarisation.     

Hydrodynamics and liquid phase residence time distribution in mesh microreactor

This paper is focused on the experimental analysis of residence time distribution and phase hold-up in a mesh microreactor. A microreactor, where a finely weaved mesh is sandwiched between two flat plates with specific inlets for gas and liquid, is proposed. The microvolumes formed upon sandwiching the mesh are totally connected and thus it yields a view of several interconnected microvolumes. This system is easy to build and does not need precision micromachining. A high-speed photographic analysis yielded the phase distribution for different mesh types over a wide range of operating gas and liquid flow rates. The RTD was studied by measuring the liquid phase conductivity at the outlet of the reactor. Channeling prevailed for mesh with smaller open area. The ADEM was used for fitting the tracer curves with tailing ends. The RTD and the image analysis for all the mesh types showed hysteresis when the gas flow rate was maintained constant and the liquid flow rate was gradually increased and then decreased.