Electrochemical study of liquid-solid mass transfer in packed bed electrodes with upward and downward co-current gas-liquid flow

Hydrodynamic and mass transfer parameters (pressure drop, gas and liquid hold-up, liquid-solid mass transfer coefficients) have been measured for porous electrodes with upward or downward co-current gas-liquid flow by means of several electrochemical techniques. The influence of the most important parameters (packing diameter, gas and liquid flow rates) and of the hydrodynamic flow regimes, has been studied. It is found that in the trickle flow regime the limiting current densities depend only on the liquid flow rates (with no measurable influence of the gas). In the upward flow configuration, the strong turbulence generated by the ascending gas bubbles leads to a sharp increase of current densities with the gas flow rate. A comparison between both configurations is presented.     

Sep: A Fixed Degree Regular Network for Massively Parallel Systems

We propose a family of regular Cayley network graphs of degree three based on permutation groups for design of massively parallel systems. These graphs are shown to be based on the shuffle exchange operations, to have logarithmic diameter in the number of vertices, and to be maximally fault tolerant. We investigate different algebraic properties of these networks (including fault tolerance) and propose a simple routing algorithm. These graphs are shown to be able to efficiently simulate or embed other permutation group based graphs; thus they seem to be very attractive for VLSI implementation and for applications requiring bounded number of I/O ports as well as to run existing applications for other permutation group based network architectures.     

High temperature water gas shift reaction over Fe-Cr-Cu nanocatalyst fabricated by a novel method

Fe-Cr-Cu nanocatalyst was synthesized through an inorganic-precursor thermolysis approach and exploited for high temperature water gas shift reaction. The results demonstrated that the method used for the nanocatalyst fabrication led to smaller crystallite size (32.9 nm) and higher BET surface area (127.3 m²/g) compared to those of a reference sample (65.5 nm, 78.6 m²/g) prepared by co-precipitation conventional method. Furthermore, the obtained data for catalytic activity showed that the catalyst prepared via inorganic precursor has better activity than the reference sample in all studied temperatures (350-500 °C) and also exhibited higher catalytic activity than a commercial Fe-Cr-Cu catalyst in higher temperatures (more than 450 °C).     

Investigation of β phase formation in piezoelectric response of electrospun polyvinylidene fluoride nanofibers: LiCl additive and increasing fibers tension

As a piezoelectric polymer, poly (vinylidene fluoride) (PVDF) is attractive in energy conversion applications between electrical and mechanical forms because of its low cost, high flexibility, and biocompatibility. The piezoelectricity of electrospun PVDF polymer is due to changes in the crystalline structure (e.g., creating the β‐phase) during the electrospinning process. This research focuses on two approaches for investigation of β Phase formation: (1) addition of LiCl in different concentrations (0.001, 0.00133, 0.002, 0.004 wt%) as inorganic salt to the polymer solution, (2) increasing tension along the fiber axis by increasing the collector drum speed during the aligning process. Performances of these structures were evaluated by using X‐ray diffraction (XRD), Fourier Transform Infrared (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). A one‐step nano‐generator and cost‐effective package based on electrospun nanofibers was presented to measure output voltages as a performance factor. Results show that the addition of LiCl leads to β Phase formation in the crystalline structure, decreasing fiber diameter to 65 nm, and increment in the work of rupture and piezoelectric output. Moreover, the results show that increasing collector drum speed causes the alignment of β‐crystallites along the fiber axis and subsequently no considerable effect on the formation of β‐phases and output voltage. POLYM. ENG. SCI., 56:61–70, 2016. © 2015 Society of Plastics Engineers     

Advances in electrospinning: The production and application of nanofibres and nanofibrous structures

The use of electrospun nanofibres in applications such as medical products, fuel cells, photocatalysis, filtration, sensors and actuators is reviewed. Yarn production is classified into two types, namely hollow and core-shell structures; the methods used for producing the two structures for different polymers are discussed. Explanations are given for the various arrangements for producing nanofibre yarns and bundles in non-twisted or twisted forms to suit their end use. Natural and synthetic polymer products for biomedical uses and their applications in the form of polymer nanofibres are reviewed and polymeric optical fibres for use in photonic devices and optical circuits are evaluated. The production and development of nanofibrous filtration devices is explored with specific reference to water treatment and the control of air pollution. Particular attention is then given to the evaluation of different electrospinning methods for PVDF (polyvinylidene fluoride), a piezoelectric polymer widely used in sensor applications in terms of their ability to harvest more energy after agitation of the sensor and the effects of different additives on the piezoelectric properties of PVDF. Priorities for further research are then outlined.     

Modelling and measurements of the velocity gradient and local flow direction at the pore scale of a packed bed

In a packed bed with single phase liquid flow, velocity gradient and local flow direction are measured at the pore scale using tri-segmented microelectrodes flush mounted at the surface of a sphere equator area. The experimental measurements are compared to numerical predictions deduced from the solution of a 3D model based on continuity and momentum balance equations.     

Evaluation of most similar neighbour and random forest methods for imputing forest inventory variables using data from target and auxiliary stands

We report the results from modelling standing volume, above-ground biomass and stem count with the aim of exploring the potential of two non-parametric approaches to estimate forest attributes. The models were built based on spectral and 3D information extracted from airborne optical and laser scanner data. The survey was completed across two geographically adjacent temperate forest sites in southwestern Germany, using spatially and temporally comparable remote-sensing data collected by similar instruments. Samples from the auxiliary reference stands (called off-site samples) were combined with random, random stratified and systematically stratified samples from the target area for prediction of standing volume, above-ground biomass and stem count in the target area. A range of combinations was used for the modelling process, comprising the most similar neighbour (MSN) and random forest (RF) imputation methods, three sampling designs and two predictor subset sizes. An evolutionary genetic algorithm (GA) was applied to prune the predictor variables. Diagnostic tools, including root mean square error (RMSE), bias and standard error of imputation, were employed to evaluate the results. The results showed that RF produced more accurate results than MSN (average improvement of 3.5% for a single-neighbour case with selected predictors), yet was more biased than MSN (average bias of 5.13% with RF compared to 2.44% with MSN for stem volume in a single-neighbour case with selected predictors). Combining systematically stratified auxiliary samples from the target data set with the reference data set yielded more accurate results compared to those from random and stratified random samples. Combining additional data was most influential when an intensity of up to 40% of supplementary samples was appended to the reference set. The use of GA-selected predictors resulted in reduced bias of the models. By means of bootstrap simulations of RMSE, the simulations were shown to lie within the applied non-parametric confidence intervals. The achieved results are concluded to be helpful for modelling the mentioned forest attributes by means of airborne remote-sensing data.     

An experimental study of the frequency response of electrochemical sensors in nonhomogeneous flow in packed beds

Circular electrochemical probes were mounted flush with the wall of a packed bed operating either in single-phase liquid flow or in gas-liquid downflow. Frequency analysis of the measured diffusion current indicated that the recently determined mass transfer function of the probes is approximately valid, even under spatially nonhomogeneous flow conditions, provided that the relative fluctuation intensity of the current does not exceed 0.15. Correction of the current measurements in the frequency domain by means of the mass transfer function was necessary in order to determine the fluctuating characteristics of the velocity gradient. This paper was presented at the International Workshop on Electrodiffusion Diagnostics of Flows held in Dourdan, France, May 1993.