Using electrocoagulation-electroflotation technology to treat synthetic solution and textile wastewater, two case studies

The purpose of this study was to investigate the effects of the operating parameters, such as pH, initial concentration (C_i), duration of treatment (t), current density (j), interelectrode distance (d) and conductivity (κ) on the treatment of a synthetic wastewater in the batch electrocoagulation (EC)-electroflotation (EF) process. The optimal operating conditions were determined and applied to a textile wastewater. Initially a batch-type EC-EF reactor was operated at various current densities ranging from 11.55 to 91.5 mA/cm² and various electrode gaps (1, 2 and 3 cm). For solutions with 300 mg/L of silica gel, good turbidity removal (89.6%) was obtained without any coagulant when the current density was 11.55 mA/cm², and with initial pH at 7.6, conductivity at 2.1 mS/cm: the treatment time was hold for 10 min and the electrode gap was 1 cm. Application of the optimal operating parameters on a textile wastewater showed a high removal efficiency for the following variables: suspended solid (SS) 85.5%, turbidity 76.2%, biological oxygen demand (BOD₅) 88.9%, chemical oxygen demand (COD) 79.7%, and color over 93%.     

Adaptive neural network output feedback control for flexible multi-link robotic manipulators

In this paper, a novel approach for adaptive control of flexible multi-link robots in the joint space is presented. The approach is valid for a class of highly uncertain systems with arbitrary but bounded dimension. The problem of trajectory tracking is solved through developing a stable inversion for robot dynamics using only joint angles measurement; then a linear dynamic compensator is utilised to stabilise the tracking error for the nominal system. Furthermore, a high gain observer is designed to provide an estimate for error dynamics. A linear in parameter neural network based adaptive signal is used to approximate and eliminate the effect of uncertainties due to link flexibilities and vibration modes on tracking performance, where the adaptation rule for the neural network weights is derived based on Lyapunov function. The stability and the ultimate boundedness of the error signals and closed-loop system is demonstrated through the Lyapunov stability theory. Computer simulations of the proposed robust controller are carried to validate on a two-link flexible planar manipulator.     

Relation of mechanical power to gas holdup and mass transfer in an agitated vessel

Two devices were developed, mechanical and electrical, to measure the mechanical power relative to superficial gas velocity and stirring speed in a mechanically agitated reactor. Two bubble regimes were demonstrated. The study of gas holdup, obtained from the residence time distribution, and the bubble size, determined by interfacial area measurement, confirm these two regimes of flow. Our results show that the gas holdup, the interfacial area, and the liquid-side mass transfer coefficient are increasing functions of the energy dissipated in the solution.     

Relativistic Coulomb wave functions in momentum space

Thirty-six 3-month-old female Wistar rats were labelled with a single intraperitoneal tetracycline injection. Twenty-four animals were subsequently ovariectomized, while the control group of 12 animals underwent sham operations. All animals received the basal Ewos R3 diet and half of the ovariectomized animals (n = 12) were given an additional 5% dietary xylitol supplementation. Three months later, following the collection of blood and urine, the animals were killed by decapitation. The tibiae were detached and prepared for chemical and other studies. The weight and density of the tibiae were measured. The right tibiae were dried and pulverized for chemical analysis of calcium, phosphorus and citric acid. The total inorganic fraction was determined by ashing the powdered bone. The left tibiae were cross-sectioned at the tibio-fibular junctions for the measurement of the width of periosteally formed bone, which was identified by tetracycline fluorescence. The examination of mineral content of bone was performed by scanning electron microscopy, using an electron probe microanalytic technique. The results indicate that the supplementation of the diet with 5% xylitol had a protective effect against the loss of bone mineral after ovariectomy in the rat. This was clearly seen in tibial density and in the inorganic fraction of the bone, and in the concentrations of bone Ca and phosphorus. Ovariectomy caused a doubling in periosteal bone formation relative to the controls, whereas the growth of the periosteally formed bone was somewhat reduced following xylitol supplementation as compared with ovariectomy alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prediction of two-phase pressure gradients of refrigerants in horizontal tubes

Two-phase pressure drop data were obtained for evaporation in two horizontal test sections of 10.92 and 12.00 mm diameter for five refrigerants (R-134a, R-123, R-402A, R-404A and R-502) over mass velocities from 100 to 500 kg/m² s and vapor qualities from 0.04 to 1.0. These data have then been compared against seven two-phase frictional pressure drop prediction methods. Overall, the method by Müller-Steinhagen and Heck (Müller-Steinhagen H, Heck K. A simple friction pressure drop correlation for two-phase flow in pipes. Chem. Eng. Process 1986;20:297–308) and that by Grönnerud (Grönnerud R. Investigation of liquid hold-up, flow-resistance and heat transfer in circulation type evaporators, part IV: two-phase flow resistance in boiling refrigerants. Annexe 1972-1, Bull. de l'Inst. du Froid, 1979) were found to provide the most accurate predictions while the widely quoted method of Friedel (Friedel L. Improved friction drop correlations for horizontal and vertical two-phase pipe flow. European Two-phase Flow Group Meeting, paper E2; June 1979; Ispra, Italy) gave the third best results. The data were also classified by two-phase flow pattern using the Kattan-Thome-Favrat (Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 1: development of a diabatic two-phase flow pattern map. J. Heat Transfer 1998;120:140–7; Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 2; new heat transfer data for five refrigerants. J Heat Transfer 1998;120:148–55; Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 3: development of a new heat transfer model based on flow patterns. J. Heat Transfer 1998;120:156–65) flow pattern map. The best available method for annular flow was that of Müller-Steinhagen and Heck. For intermittent flow and stratified-wavy flow, the best method in both cases was that of Grönnerud. It was observed that the peak in the two-phase frictional pressure gradient at high vapor qualities coincided with the onset of dryout in the annular flow regime.     

Decoupled estimation of angular parameters for coherently distributed sources

In this paper, we consider the problem of estimating the direction-of-arrivals (doas) and angular spreads of uncorrelated coherently distributed sources. The proposed methods enable a decoupled estimation of the doas from that of the angular spreads of sources. Compared with existing algorithms, the proposed algorithms improve the robustness to the mismodeling of the spatial distribution of the scatterers. They allow an unambiguous doas estimation and don’t need the a priori knowledge of the azimutal power distribution. Furthermore, the proposed techniques work even in the case where the different sources have different angular distribution shape.     

Prediction of grain boundary stress fields and microcrack initiation induced by slip band impingement

Slip localization is widely observed in metallic polycrystals undergoing cyclic deformation or post-irradiation tensile deformation, whatever their crystallographic structure. Hence, strong strain localization occurs in thin slip bands (SBs) inducing by the way local stress concentrations at their intersections with grain boundaries (GBs). Many GB stress field formulae based on the dislocation pile-up theory have been proposed since the pionnering work of Stroh and others. These allow the use of the Griffith criterion for prediction GB fracture initiation. However, recent observations show that assuming that slip is localized on a single atomic plane leads to unrealistic results. In fact, a large number of slip planes are plastically activated and then finite slip band thickness should be accounted for. Numerous crystalline finite element (FE) computations have been carried out using considering a slip bands with low critical resolved shear stress embedded in an elastic matrix. The computed GB normal and shear stress fields:

are considerable lower than the pile-up ones and exhibit strong dependency on the slip band thickness close to the SB corner

but are in fair agreement with the solution predicted by the pile-up theory far away.

Since the pile-up theory leads to the overestimation of the local GB stress fields, the main goal of the current paper is to perform analytical model of GB stress components based upon FE calculations. The effect of various parameters can be understood in the framework of matching asymptotic expansions which is usually applied to cracks with V notches of finite thickness. Finally, the predicted remote stresses to GB fracture in pre-irradiated austenitic stainless steels subjected to tensile loading in various environment are compared to experimental data and the pile-up based predictions.