A qualitative computational study of mass transfer in upward bubble train flow through square and rectangular mini-channels

In this paper we present a new method for numerical simulation of conjugate mass transfer of a dilute species with resistance in both phases and an arbitrary equilibrium distribution coefficient. The method is based on the volume-of-fluid technique and accounts for the concentration jump at the interface by transforming the discontinuous physical concentration field into a continuous numerical one. The method is validated by several test problems and is used to investigate the mass transfer in upward bubble train flow within square and rectangular channels. Computations are performed for a single flow unit cell and a channel hydraulic diameter of 2 mm. The simulations consider the transfer of a dilute species from the dispersed gas into the continuous liquid phase. Optionally, the mass transfer is accompanied by a first-order homogeneous chemical reaction in the liquid phase or a first-order heterogeneous reaction at the channel walls. The results of this numerical study are qualitative in nature. First, because periodic boundary conditions in axial direction are not only used for the velocity field but also for the concentration field and second, because the species diffusivity in the liquid phase is arbitrarily increased so that the liquid phase Schmidt number is 0.8 and the thickness of the concentration and momentum boundary layer is similar. Two different equilibrium distribution coefficients are considered, one where the mass transfer is from high to low concentration, and one where it is vice versa. The numerical study focuses on the influence of the unit cell length, liquid slug length and channel aspect ratio on mass transfer. It is found that for the exposure times investigated the liquid film between the bubble and the wall is saturated and the mass transfer occurs by the major part through the bubble front and rear so that short unit cells are more efficient for mass transfer. Similar observations are made for the homogeneous reaction and for the heterogeneous reaction when the reaction is slow. In case of a fast heterogeneous reaction and when the main resistance to mass transfer is in the gas phase, it appears that for square channels long unit cells are more efficient, while large aspect ratio rectangular channels are more efficient than square channels, suggesting that for these conditions they might be more appropriate for use in monolithic catalysts.     

Cavitation bubble dynamics in non‐Newtonian fluids

Cavitation phenomena play important roles in many areas of science and engineering. The most interesting effect of the non‐Newtonian properties of the liquid is the reduction of cavitation damage and noise. This article reviews experimental and theoretical efforts to understand such phenomena. Two major areas of research are described, namely the dynamics of cavitation bubbles oscillating in a liquid of infinite extent, and the behavior of bubbles collapsing near rigid walls. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Bioactive polymers LVII. A novel drug delivery system based on 5-nitro-2-furaldehyde-semicarbazone and poly(acrylic acid-co-vinyl alcohol)

The coupling of 5-nitro-2-furaldehyde-semicarbazone on to poly(acrylic acid-co-vinyl alcohol) copolymer by the use of dicyclohexylcarbodiimide as activator has been studied. On the basis of an experimental design, the influence of different parameters is studied (activator/support, drug/support, reaction time, solvent volume) in order to determine the optimum conditions for obtaining the maximum amount of the coupled drug on the support.     

Error estimation in the approximation of the solution of nonlinear fuzzy Fredholm integral equations

Using a fixed point technique, the sequence of successive approximations and a recent quadrature formula for fuzzy-number-valued functions, it is constructed a numerical method for the solution of nonlinear fuzzy Fredholm integral equations. Moreover, the error estimate of the method and a criterion to stop the corresponding algorithm are given.     

Improved Accuracy Pseudo-Exponential Function Generator With Applications in Analog Signal Processing

A new CMOS current-mode pseudo-exponential circuit based on the n-order Taylor series expansion will be presented. The most important advantage of the circuit with respect to the previously reported similar ones is the smaller value of the total computing error (under 0.3 dB), for a maximal output range of the proposed function generator greater than 40 dB. The total error could be very easily reduced by increasing the number of terms considered in the Taylor expansion. The circuit also presents the advantage of the independence of the output current on technological parameters. The frequency response is improved due to the strong inversion operation of all MOS transistors and to the current-mode operation of the circuit. The circuit area is relatively small due to the exclusively utilization of MOS transistors. The SPICE simulations confirm the theoretical estimated results. The proposed exponential function generator is designed in 0.12-mum CMOS technology and it consumes a reasonable power (less than 0.3 mW) for obtaining the previous mentioned computing error and has a low-voltage operation (a minimal accepted supply voltage under 1.2 V). The total silicon occupied area of the exponential function generator with third-order approximation is about 5.9 mum times 7.9 mum.     

Impact of Some Properties of Quaternized Polysulfone/Poly(Vinylidene Fluoride) Blend on the Potential Biomedical Applications

Blends of quaternized polysulfones with triphenylphosphonium pendant groups/poly(vinylidene fluoride) were analyzed to establish their impact on the rheological, morphological and surface properties, as well as their interactions with some blood compounds. The rheological functions reflect the influence of both polymers’ chemical structures. Blend compositions of the corresponding films influence the surface tension parameters, increase blend hydrophobicity and, implicitly, decrease the polar surface tension parameters. The specific surface characteristics of polymer blends are related to their interactions with some blood constituents and plasma proteins. Also, the specific microarchitecture of the blend represents an excellent scaffold for medical applications.     

Microstructure,mechanical properties,and corrosion resistance of Ti-20Zr alloy in undoped and NaF doped artificial saliva

The corrosion behavior of a new, advanced Ti-20Zr alloy with α+β microstructure (determined by optical microscopy, XRD, and SEM) and very good mechanical properties (obtained from the stress-strain curve) is studied in this paper. The composition of the alloy native passive film was determined from a XPS analysis and the long-term corrosion resistance in undoped and doped states with 0.05M NaF artificial Carter-Brugirard saliva of different pH values, simulating the severe functional conditions of a dental implant, was analyzed by electrochemical methods. This alloy possesses an advantageous balance between good mechanical resistance and plasticity and Young’s modulus and exhibits more favorable electrochemical parameters and corrosion resistance than CP Ti due to its more resistant passive layer containing Ti₂O₃, TiO₂, and ZrO₂ protective oxides. After 1000 h of immersion in saliva, the protective properties of the alloy were enhanced due to the deposited surface layer that incorporated protective phosphates (shown by SEM and XPS).     

Plasma parameters of argon and argon/molecular gas mixture plasmas produced in microwave discharge

The experimental results and their analysis are presented concerning electron density and temperature of the microwave discharge plasma (power range 100–500 W) produced in Ar gas and Ar–N₂ and Ar–N₂–NO gas mixture at the total pressure of 0.5 Torr. The triple probe method was primarily used in order to set-up a direct and on-time technique to measure electron temperature in complex plasma. The results were compared with those obtained using a cylindrical probe mounted in a circuit with reference electrode. Each probe was made of tungsten wires of 0.5 mm diameter and 3 mm in length each. When plasma contains only one maxwellian group of electrons, within the experimental errors, both the probes systems get comparable value of plasma parameters. When the characteristic of cylindrical probe shows two groups of thermal electrons within the microwave plasma the triple probe may show always results concerning one group but of which temperature depends on the ratio of the densities of those two groups of electrons.     

Expedient Immobilization of TEMPO by Copper‐Catalyzed Azide‐Alkyne [3+2]‐Cycloaddition onto Polystyrene Resin

TEMPO was readily grafted by copper(I)‐catalyzed azide‐alkyne cycloaddition onto polystyrene. Starting with commercially available Merrifield resin (4.3 mmol/ g) almost quantitative loading of TEMPO onto the polymer was achieved (≥ 4 mmol/ g). The so obtained PS‐CLICK‐TEMPO allowed the oxidation of alcohols to aldehydes with bleach or molecular oxygen as the terminal oxidant with high yields and selectivity in multiple cycles without loss of activity.