Cavitating nozzle flows in micro- and minichannels under the effect of turbulence

The cavitation phenomenon inside micro- and minichannel configurations was numerically investigated. The simulations for each channel were performed at different upstream pressures varying from 1 to 15 MPa. Two microchannel configurations with inner diameters of 152 and 254 μm and two minichannel configurations with inner diameters of 504 and 762 μm were simulated. To validate the numerical approach, micro-jet impingement from a microchannel with an inner diameter of 152 μm was first simulated at different Reynolds numbers. Then, the mixture model was used to model the multiphase flow inside the channels. The results of this study present major differences in the cavitating flows between the micro- and miniscale channels and show that the pressure profile and vapor phase distribution exhibit different features. The static pressure drops to negative values (tensile stress) in microchannels, while the minimum static pressure in minichannels is found to be equal to vapor saturation pressure, and higher velocity magnitudes especially at the outlet are visible in the microchannels. It is shown that for higher upstream pressures, the cavitating flow extends over the length of the micro/minichannel, thereby increasing the possibility of collapse at the outlet. The effect of energy associated with turbulence was investigated at high Reynolds numbers for both micro/minichannels and its impact was analyzed using wall shear stress, turbulence kinetic energy and mean velocity at various locations of the micro/minichannels.     

Structural and Optical Properties of New Naphthalene and Perylene Imide Imidazoles

ABSTRACT

New unsymmetrically substituted naphthalene and perylene imide imidazoles, N-(2-ethylhexyl)-naphthalene-3,4-(4,5-dicyano-1,2-benzimidazole)-9,10-dicarboxyimide and N-(1-heptyloctyl)-perilene-3,4-(4,5-dicyano-1,2-benzimid-azole)-9,10-dicarboxyimide, were synthesized via condensation reactions of diaminophthalonitrile and aromatic monoimide monoanhydride derivatives. Their structural analyses have been conducted by using general spectroscopic methods including FT-IR, ¹H- and ¹³C-NMR, mass and elemental analysis. The molecular structure of naphthalene derivative was also determined by single crystal x-ray diffraction. Electronic absorption and emission properties were investigated on comparison. For studied compounds, both DFT and TDDFT calculations were carried out with the 6-311G(d,p) basis set, taking into account solvation effects by means of polarizable continuum model as implemented in the Gaussian 09 package.     

Preparation and characterization of phosphine oxide based polyurethane/silica nanocomposite via non-isocyanate route

A novel carbonate-modified bis(4-glycidyloxy phenyl) phenyl phosphine oxide (CBGPPO) was synthesized to prepare phosphine oxide based polyurethane/silica nanocomposites. Spherical silica particles were prepared according to Stöber method and modified with cyclic carbonate functional silane coupling agent (CPS) to improve the compatibility of silica particles and organic phase. The cyclic carbonate-modified epoxy resins and silica particles were used to prepare hybrid coatings using hexamethylene diamine as a curing agent. The cupping, impact and gloss measurements were performed on aluminum panels, and the tensile test, gel content, thermal and morphological analyses were conducted on the free films. No damage was observed in the impact strength of the coatings. Incorporation of silica and CBGPPO into formulations increased modulus and hardness of the coating making the material more brittle. It was also observed that, the thermal stability of hybrid coatings enhanced with the addition of silica and CBGPPO.     

Power reclamation efficiency of a miniature energy‐harvesting device using external fluid flows

This study represents experimental results related to the energy‐harvesting capability of a miniature power reclamation device based on external liquid flows. The device's reclamation principle depends on the conversion of mechanical energy into electrical energy. The mechanical energy in the device was generated by capturing vibrations caused by external liquid flows via the device's tails, which were designed by taking inspiration from the body shape of the black ghost knife fish, Apteronotus albifrons. The reclaimed power was obtained through magnetic polarization, which was generated by rotating circular waterproof magnet structures as a result of rotating movements of the mentioned tails and is transferred to 3.76 V (Ni‐Mg) batteries. Power reclamation was also simulated using COMSOL 4.2a software in order to compare the maximum reclaimable theoretical energy‐harvesting capacity with the experimental results. Experimental tests were performed within a range of flow velocities (1.0 ~ 5.0 m/s) for various fluid densities (plain water, low‐salt water and high‐salt water) in order to obtain extensive experimental data related to the device in response to external fluid flows. According to experimental results, the device could generate powers up to 17.2 W. On the other hand, the maximum reclaimable power was obtained at 25.7 W from COMSOL Multiphysics 4.2a simulations. Promising energy harvesting results imply that the output from this device could be used as a power source in many applications such as in lighting and global positioning system (GPS) devices. Copyright © 2014 John Wiley & Sons, Ltd.     

Formulation and properties' evaluation of PVC/(dioctyl phthalate)/(epoxidized rubber seed oil) plastigels

Epoxidized rubber seed oil (4.5% oxirane content, ERSO) was prepared by treating the oil with peracetic acid generated in situ by reacting glacial acetic acid with hydrogen peroxide. The thermal behavior of the ERSO was determined by differential scanning calorimetry. The effect of the epoxidized oil on the thermal stability of poly (vinyl chloride) (PVC) plastigels, formulated to contain dioctyl phthalate (DOP) plasticizer and various amounts of the epoxidized oil, was evaluated by using discoloration indices of the polymer samples degraded at 160°C for 30 min and thermogravimetry at a constant heating rate of 10°C/min up to 600°C. The thermal behavior of the ERSO was characterized by endothermic peaks at about 150°C, which were attributed to the formation of network structures via epoxide groups, and at temperatures above 300°C, which were due to the decomposition of the material. Up to 50% of the DOP plasticizer in the PVC plastisol formulation could be substituted by ERSO without a marked deleterious effect on the consistency of the plastigel formed. In the presence of the epoxidized oil, PVC plastigel samples showed a marked reduction in discoloration and the number of conjugated double bonds, as well as high temperatures for the attainment of specific extents of degradation. These results showed that the ERSO retarded/inhibited thermal dehydrochlorination and the formation of long (n > 6) polyene sequences in PVC plastigels. The plasticizer efficiency/permanence of ERSO in PVC/DOP plastigels was evaluated from mechanical properties' measurements, leaching/migration tests, and water vapor permeability studies. The results showed that a large proportion of DOP could be substituted by ERSO in a PVC plastisol formulation without deleterious effects on the properties of the plastigels. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Coupled nonparametric shape and moment-based intershape pose priors for multiple basal ganglia structure segmentation

This paper presents a new active contour-based, statistical method for simultaneous volumetric segmentation of multiple subcortical structures in the brain. In biological tissues, such as the human brain, neighboring structures exhibit co-dependencies which can aid in segmentation, if properly analyzed and modeled. Motivated by this observation, we formulate the segmentation problem as a maximum a posteriori estimation problem, in which we incorporate statistical prior models on the shapes and intershape (relative) poses of the structures of interest. This provides a principled mechanism to bring high level information about the shapes and the relationships of anatomical structures into the segmentation problem. For learning the prior densities we use a nonparametric multivariate kernel density estimation framework. We combine these priors with data in a variational framework and develop an active contour-based iterative segmentation algorithm. We test our method on the problem of volumetric segmentation of basal ganglia structures in magnetic resonance images. We present a set of 2-D and 3-D experiments as well as a quantitative performance analysis. In addition, we perform a comparison to several existent segmentation methods and demonstrate the improvements provided by our approach in terms of segmentation accuracy.     

Photocurable cyanate ester containing hybrid coatings by an anhydrous sol–gel technique

This work reports the synthesis and characterization of hybrid coatings obtained by UV curable anhydrous sol–gel process. Chemical structure of the products was confirmed using spectroscopic methods such as infrared and nuclear magnetic resonance spectroscopy. The properties of the hybrid coatings such as thermal and mechanical properties were investigated in detail by scanning electron microscope, thermogravimetric analysis, and mechanical measurement. Cure kinetics of the coating formulations was investigated by differential scanning photo-calorimetry (Photo-DSC). Cross cut adhesion, pendulum hardness, gloss, pencil hardness, MEK rub test were also performed to measure the coating performance of the hybrid coatings. The results indicate that the addition of the appropriate amount of CPM and sol–gel can effectively improve the thermal and mechanical properties.     

Silver and fluoride doped hydroxyapatites: Investigation by microstructure,mechanical and antibacterial properties

Hydroxyapatite co-doped with Ag⁺ and F^? ions was synthesized by the precipitation method and sintered at 1100 °C for 1 h. Samples were characterized by density, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy to investigate their microstructure, phase formation and bonding characteristics. Moreover, samples were also characterized by microhardness and antibacterial tests. Small amount of dopings resulted in high densities and fine grain microstructures. In most of the samples, hydroxyapatite was the main phase with a minor amount of β-TCP. Presence of fluoride and small amount of TCP was verified with all characteristic FTIR bands of hydroxyapatite for most of the samples. Compared to the pure hydroxyapatites, much higher microhardness values were measured in samples co-doped with Ag⁺ and F^? ions. Antibacterial activity of the materials related to Escherichia coli was also observed in hydroxyapatite samples with high amount of Ag⁺ ions.