Mixed convective heat transfer in rectangular enclosures driven by a continuously moving horizontal plate

The fluid flow and heat transfer induced by the combined effects of the mechanically driven lid and the buoyancy force within rectangular enclosures were investigated in this work. The fluid filled enclosures are heated and lid-driven either on the upper or on the lower horizontal wall, thermally isolated on the right vertical wall, and cooled on the other walls. The basis of the investigation was the numerical solutions of the equations for the conservation of mass, momentum, and energy transport using the finite difference method. The effects of the flow governing parameters including the Richardson and the Prandtl numbers, and the length-to-height aspect ratio, respectively, in the range 10⁻²  Ri  10², 10⁻³  Pr  10, and 1  AR  4 for a fixed Reynolds number, Re = 100, were studied. The results are presented in the form of the hydrodynamic and thermal fields, and the profiles for vertical and horizontal components of velocity, temperature, and the local heat flux. The fluid flow and energy distributions within the enclosures and heat flux on the heated wall are enhanced by the increase in the Richardson number. While an increase in the Prandtl number improves the heat flux on the heated wall, an increase in aspect ratio suppresses it. The results can be used as base line data in the design of systems in which mixed convection heat transfer in rectangular enclosures occurs.     

Adsorption and Precoat Filtration Studies of Synthetic Dye Removal by Acid Mine Drainage Sludge

Adsorption tests of Congo Red, a commercial azo dye, by acid mine drainage (AMD) sludge were carried out at different pH, temperature, dye concentration, contact time, and adsorbent dosage. Precoat filtration was conducted to test if the dye could be removed during continuous filtration by a precoated AMD sludge layer. Adsorption of Congo Red onto AMD sludge followed the Langmuir isotherm model with a maximum adsorption capacity of 389.1?mg/g. Based on thermodynamic studies, adsorption was found to be exothermic, and an increase in temperature led to a decline in dye removal. Dye removal decreased with an increasing pH. Through metal leaching tests, it was observed that most metals associated with AMD sludge remained insoluble when adsorption occurred at pH 6–10. A rather rapid process was observed for the adsorption of Congo Red onto AMD sludge with more than 80% adsorption taking place within 5?min. Adsorption kinetics followed pseudo-second-order model. Precoat filtration continuously removed Congo Red from aqueous solution with success, and dye removal mechanism via precoat filtration was adsorption. The adsorption and precoat filtration studies showed dye removal could be a beneficial use of AMD sludge prior to its final disposal.     

Retardation of Nonlinearly Sorbed Solutes in Porous Media

The impact of the assumption of linear sorption on retardation of nonlinearly sorbed solutes in porous media is numerically explored in this paper. Breakthrough data of nonlinearly sorbed solutes are generated using the BIO1D simulation code along with the Freundlich-type nonlinear sorption model. Retardation coefficients (R) from generated breakthrough curves are estimated using first-moment analysis. Variations of R with experimental conditions revealed that R of a nonlinearly sorbed solute is a function of the input concentration, the injection period, and the pore–water velocity but is independent of the length scale. This study also showed that it is appropriate to estimate R of a nonlinearly sorbed solute using a linearized isotherm if all soil particles experience sorption with liquid concentration equal to the induced concentration. Otherwise, the estimated linearized R will be either under- or overestimated depending on the applied experimental conditions and Freundlich parameters. The study further revealed that inability to account for sorption nonlinearity may in some cases erroneously be interpreted as evidence of the presence of transport nonequilibrium. A method is suggested to determine nonlinear sorption parameters from miscible displacement experiments.     

Photocatalytic degradation of phenol and phenolic compounds: Part I. Adsorption and FTIR study

With the goal of predicting the photocatalytic behaviour of different phenolic compounds (catechol, resorcinol, phenol, m-cresol and o-cresol), their adsorption and interaction types with the TiO₂ Degussa P-25 surface were studied.     

Phosphate adsorption on chemically modified sugarcane bagasse fibres

Integral sugarcane bagasse fibres of about 2 cm length that were pre-treated for removal of greases and sugars were carboxymethylated on their surface, retaining about 20% of impurities (as insoluble material and water). The fibres were doped with Fe²⁺ ion, by dipping in aqueous iron chloride solutions of different concentrations. This material was used to remove phosphate from water. Thermal analyses (differential scanning calorimetry – DSC) and infrared spectroscopy – FTIR show the occurrence of important changes on carboxymethylated fibres after incorporation of Fe²⁺ and PO₄^3-. Non-carboxymethylated fibres, also treated with the iron solutions, also showed a good level of capture of phosphate from an aqueous solution. The chemical modification increases Fe²⁺ ion adsorption on the fibre surface, increasing the efficiency of phosphate adsorption. Apparently, the process of modification, without incorporation of Fe²⁺, also improves phosphate retention. When about 4% of iron is adsorbed on the fibres, 97% of phosphate is captured on the carboxymethylated material and 94% on the non-carboxymethylated material. The absorption data fit both the Langmuir and Freundlich isotherm. When quantified by measuring the monolayer adsorption in the Langmuir isotherm model, the presence of Fe²⁺ ions on the surface fibres increases the phosphate adsorption capacity by about 45%. Our results (Q max = 152 mg/g) are far superior or in the same order of magnitude, when compared with literature data, with the advantage be the raw material, waste of biomass, only somewhat changed chemically and even after the modifications compose materials harmless to the environment.     

Adsorption of Cd and Cr ions from industrial wastewater using Ca doped Ni–Zn nanoferrites: Synthesis,characterization and isotherm analysis

Removal of heavy metals (Cd and Cr) from industrial wastewater by adsorption onto a series of Ca substituted nickel zinc nanoferrites (Ca_xNi_0.4Zn_0.6-xFe₂O₄ (x = 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6)) (CNZNFs) was studied in detail. The effect of calcium doping and contact time over adsorption of cadmium and chromium ions was investigated and maximum uptake of Cd (98.25%) and Cr (51%) ions were marked by prepared nanoadsorbents. Structural studies confirmed the formation of spinel structured nanoparticles with crystallite size ranging from 24 to 38 nm while porosity was observed to vary from 52% to 58% with calcium concentration. Pseudo second order (PSO) kinetic model for adsorption of both heavy metals (cadmium and chromium) was observed to be better fitted with adsorption data. Maximum adsorption efficiencies for Cd (128.20 mg/g) and Cr (23.54 mg/g) were found by the data fit of Langmuir isotherm model. Additionally, the adsorption data was found to obey Langmuir isotherm model for both heavy metals due to higher values of correlation coefficients (R² = 0.94131 for cadmium and 0.91091 for chromium) than Freundlich isotherm model (R² = 0.5865 for cadmium and 0.4599 for chromium).     

Comparative analysis of the hydriding kinetics of LaNi5, La0.8Nd0.2Ni5 and La0.7Ce0.3Ni5 compounds

In two-phase domains, the plateau pressure of hydride forming materials (such as intermetallic compounds or IMCs) depends markedly on the operating temperature (Van’t Hoff relationships). Therefore, for practical applications, it is necessary to select hydrogen storage materials by considering the thermal environment of the hydride tank. The thermodynamic properties (absorption and desorption pressure plateaux) of IMCs can be adjusted to some extend by chemical alloying with foreign metals and substitution on different crystallographic sites. In this paper, we report on the hydriding kinetics of substituted AB₅ compounds. Isotherms have been measured at different temperatures on La_xNd_1−xNi₅ (x ≈ 0.2) and La_xCe_1−xNi₅ (x ≈ 0.3) compounds. Pneumato-chemical impedance spectroscopy has been used to analyze the hydriding kinetics and to determine microscopic rate parameters associated with surface dissociation of molecular hydrogen, diffusion-controlled transport of atomic hydrogen to bulk regions and hydride formation. Results have been compared to those measured on LaNi₅ and the interest of using such substituted compounds for application in auxiliary power units is discussed.     

Physico-chemical study for zinc removal and recovery onto native/chemically modified Aspergillus flavus NA9 from industrial effluent

Zinc biosorption characteristic of locally isolated Aspergillus flavus NA9 were examined as a function of pH, temperature, pulp density, contact time and initial metal ion concentration. The maximum zinc uptake was found to be 287.8 ± 11.1 mg g^?1 with initial metal concentration 600 mg L^?1 at initial pH 5.0 and temperature 30 °C. The equilibrium data gave good fits to Freundlich and Florry models with correlation coefficient value of 0.98. The contribution of the functional groups and lipids to zinc biosorption as identified by chemical pretreatment was in the order: carboxylic acids > hydroxyl > amines > lipids. The mechanism of biosorption was also studied using Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The biosorbent was regenerated using 0.01 M HCl with 83.3% elution efficiency and was reused for five sorption–desorption cycles with 23.5% loss in biosorption capacity. The order of co-cations showing increased inhibitions of zinc uptake by A. flavus NA9 was Pb > Cu > Mn > Ni. The biosorption assays conducted with actual paint industry effluents revealed efficiency of 88.7% for Zn (II) removal by candidate biomass.     

A chromatographic theory based on the concept of a layer of equilibrium adsorption

The LEA model has been analyzed by comparing to other Chromatographic theoretical approaches. In the LEA model a layer of equilibrium adsorption, L_e, serves as an effective kinetic constant. For the layer L_e the concentration issuing from this layer is in equilibrium with the average value of adsorption on the whole layer at any moment of time. The value of L_e is determined from all factors which broaden the Chromatographie zone. Such an approach permits us to combine the features of the mass balance (solute continuity in a Chromatographie column), of the mass transfer phenomenon, and of the adsorption isotherm into a single first order differential equation. Apart from other layer-by-layer models, the LEA model supposes that over the whole column a continuous (real) distribution of adsorption a (L, t) and concentration c (L, t) is observed. The usefulness of the LEA model in developing a Chromatographic theory has been discussed.