Spherical nanoparticle effects on the lower critical solution temperature phase behavior of poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blends: Separation of thermodynamic aspects from kinetics

The effects of spherical nanosilica particles on the lower critical solution temperature (LCST) phase diagram of poly(ε-caprolactone) (PCL)/poly(styrene-co-acrylonitrile) (SAN) blends are investigated by using isochronal dynamic temperature sweep tests at different cooling rates. A stronger dependency of the rheologically determined phase-transition points on the cooling rate is observed in the presence of nanoparticles, which results from the large contribution of entropic surface tension of chains in the Gibbs free energy of mixing and much slower rate of PCL/SAN phase dissolution. By alleviating the effects of kinetic factors, it is found that the drop in the LCST-type phase boundary of PCL/SAN blends by adding nanofiller is more apparent than real. However, the closest LCST phase diagram to the real steady-state thermodynamic diagram shows an unexpected shift to lower temperatures by adding nanosilica. The migration of nanosilica particles to the SAN domains especially at lower cooling rates in the dynamic measurements is the most likely explanation of these observations. The findings that prove the profound impact of kinetic factors in dynamic temperature measurements are reached in a hybrid system, wherein the SAN chains are preferentially absorbed on the surface of a nanofiller having very small primary particle size. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48679.     

Material characterization and interfacial boundary identification by solving an inverse elasto statics boundary elements problem

An inverse geometry problem of identifying simultaneously two irregular interfacial boundaries along with the mechanical properties of the interface domain located between the components of multiple (three) connected regions is investigated. A discrete number of displacement measurements obtained from a uniaxial tension test are used as extra information to solve this inverse problem. A unique combination of global and local optimization method is used, that is, the imperialist competitive algorithm (ICA) to find the best initial guesses of the unknown parameters to be used by the local optimization methods, that is, the conjugate gradient method (CGM) and the simplex method (SM). The CGM and SM are used in series. The performance of these local optimization methods is dependents on the initial guesses of the unknown boundaries and the mechanical properties, that is, Poisson’s ratio and Young’s modulus, so ICA provides the best initial guesses. The boundary elements method is employed to solve the direct two-dimensional (2D) elastostatics problem. A fitness function, which is the summation of squared differences between measured and computed displacements at identical locations on the exterior boundary, is minimized. Several example problems are solved and the accuracy of the obtained results is discussed. The influence of the value of the material properties of the subregions and the effect of measurement errors on the estimation process are also addressed.     

Impact of impeller type on methyl methacrylate emulsion polymerization in a batch reactor

The emulsion polymerization of methyl methacrylate (MMA) was carried out in a lab‐scale reactor, which was equipped with a top‐entry agitator, four wall baffles, a U‐shaped cooling coil, and a temperature controller. Potassium per sulfate and sodium dodecyl sulfate as were used as the initiator and the surfactant, respectively. The experimental investigation demonstrated the impact of the impeller type (45° six pitched‐blade turbine and Rushton impeller), number of impellers (single and double impellers), and impeller speed (100–350 rpm) on the monomer conversion, polymer particles size, molecular weight, and glass transition temperature. The results revealed that the effect of the impeller speed on the characteristics of the polymer attained using the pitched‐blade turbine was more prominent than that for the Rushton turbine. It was also found that the impact of the impeller speed on the polymer characteristics was much more pronounced for the double pitched‐blade turbines rather than for the double Rushton turbines. However, more uniform size distribution was achieved with the Rushton turbine. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40496.     

Experimental study of thermo-hydraulic and fouling performance of enhanced heat exchangers

The present study investigated the effect of two tube inserts (wire coil and wire mesh) on the heat transfer enhancement, pressure drop and mineral salts fouling mitigation in tube of a heat exchanger. A 3/4-in. tube that is heated by band heaters, is used which simulated a tube of heat exchanger. Working fluid is water with certain quality. The heat transfer rate averagely increased by 22–28% for wire coil (p/d = 0.125, e/d = 0.00375) and 163–174% for wire mesh (medium density) over a plain tube value, depending on type of tube insert, density of wire torsion and flow velocity. However, the pressure drop also increased substantially by 46% for wire coil and 500% for wire mesh. Wire coil insert with vibration mitigate mineral salts fouling (scaling) about 34%, and wire mesh have no effect on scaling, however it sometimes increased deposit rate.     

Using Tomography to Characterize the Mixing of Non‐Newtonian Fluids with a Maxblend Impeller

The flow field inside a cylindrical mixing vessel was visualized by electrical resistance tomography (ERT), a non‐intrusive measurement technique. Six tomography planes, each containing 16 sensing electrodes, measured the mixing time in the agitation of pseudoplastic fluid exhibiting yield stress. The effects of various parameters such as impeller types, impeller speed, fluid rheology, power consumption, Reynolds number, and absence of baffles on the mixing time were investigated. The Maxblend impeller was able to improve the mixing performance of non‐Newtonian fluids in a batch reactor. The mixing quality could be further enhanced by decreasing the xanthan gum concentration and using baffles in the mixing vessel.     

Hybrid mathematical modeling and multi-objective optimization of mechanical properties of green composites based on starch and modified rice straw fillers

A hybrid mathematical modeling/optimization approach based on the response surface methodology (RSM) and desirability function (DF) capabilities was applied here to imitate and optimize the mechanical properties of thermoplastic starch-based biocomposites. In order to prepare the biodegradable and renewable biocomposites, rice straw (RS) was chemically modified to obtain more effective sustainable reinforcing fillers for starch, having semi-thermoset and core-shell structures. A combination of different RS products was used in the biocomposites and the composition of RS-based fillers was chosen as control variable. A series of experiments, by using RSM, were designed to assess the effects of filler loading and composition on the Young modulus, tensile strength, ultimate strain, and absorbed energy of the biocomposites. The best-fitting regression functions were identified via RSM statistical analysis and transformed into DF to optimize the desired responses concurrently. The findings demonstrate that the starch/RS product biocomposites with optimum elastic modulus (339.3 MPa), tensile strength (9.8 MPa), elongation at break (13.8%), and absorbed energy (1831.2 kJ/m²) were obtained by incorporating RS-based fillers with both semi-thermoset and core-shell structures in combination with each other at loadings of 13.5 and 6.5 phr, respectively.     

Measuring Mixing Time in the Agitation of Non‐Newtonian Fluids through Electrical Resistance Tomography

Electrical resistance tomography (ERT), which is a non‐invasive and robust measurement technique, was employed to visualize, in three dimensions, the concentration field inside a cylindrical mixing vessel equipped with a radial‐flow Scaba 6SRGT impeller. The ability of ERT to work in opaque fluids makes this technique very attractive from an industrial perspective. An ERT system with a 4‐plane assembly of peripheral sensing rings, each containing 16 electrodes, was used to measure the mixing time in agitation of xanthan gum solution which is a pseudoplastic fluid with yield stress. An image reconstruction algorithm was used to generate images of the tracer distribution within the sensing zone. In this study, the effect of impeller speed, fluid rheology, power consumption, and Reynolds number on the mixing time was investigated.     

Dynamic and local gas holdup studies in external loop recirculating airlift reactor with two rolls of fiberglass packing using electrical resistance tomography

BACKGROUND: Airlift bioreactors have been used extensively in biotechnology industries in recent years in a variety of arrangements and applications. The insertion of packing inside the bioreactors has the potential to provide high productivity within a compact size through utilizing immobilized species. RESULTS: A novel recirculating external loop airlift bioreactor that has two rolls of fiberglass packing and a gas distributor in between was designed and built. Electrical resistance tomography (ERT) images showed that the gas holdup increased after installing the packing and the gas distributor. Gas holdup in the riser increased with decreasing static liquid height in the bioreactor. This decreased the liquid superficial velocity, which contributed to a higher gas holdup in the bioreactor. Results also showed that riser gas holdup varied slightly with different sparger configurations. Higher gas holdup increases the oxygen mass transfer rate by increasing the residence time and interfacial mass transfer area. CONCLUSION: ERT results showed that fiberglass packing with an installed gas distributor in bioreactors can achieve higher gas holdup at higher superficial gas velocity. This can contribute to improved conversion in bioreactors with packing through utilizing higher biomass concentrations and higher oxygen concentration. © 2012 Society of Chemical Industry     

Selected Mapping Technique for PAPR Reduction Without Side Information Based on m-Sequence

Selected mapping (SLM) is a technique for reducing the high peak-to-average power ratio (PAPR) in which a suitable signal is selected among a set of alternative signals which all indicate alike information. The chief drawback existing in this method is that transmitter is compelled to send several additional bits called side information (SI) for each data block in order that recovering at the receiver side can be possible. In this paper, we present a novel SLM scheme by using the linear feedback shift register circuit and m-sequence named MSLM technique by which any side information bit is not explicitly sent. In MSLM, The basic idea is to fit the side information into transmitted symbols based upon which some special locations in the transmitted data block are expanded, i.e. some transmitted symbols are extended. In the receiver side, by using some properties of m-sequence the SI bits can be detected. We present the example of our method for an OFDM system through the use of 16-QAM modulation and different m-sequences and finally, concerned results are illustrated from the view point of bit error rate, probability of detection failure and PAPR reduction.