Radiative effect on natural convection flows in porous media is studied

Lars Eivind Augland, Mohamed Ali Abu El-Rus, Gamal Yehia Boghdady, (2010): Repeated magmatic pulses in the East African Orogen of Central Eastern Desert, Egypt: an old idea supported by new evidence.

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A regular perturbation analysis is presented for the following laminar natural convection flows of Newtonian fluids

Propionic acid modified bagasse was used for the removal of reactive yellow 2 and reactive blue 4. The effects of pH, contact time, initial dye concentrations, adsorbent particle size and adsorbent dose on the adsorption of the two dyes were investigated. Additionally, the desorption process and intra-particle diffusion were studied. Acidic pH values were favorable for adsorption of both dyes. The equilibrium adsorption data were best fitted with the Freundlich isotherm for reactive yellow 2 and the Langmiur isotherm for reactive blue 4. The values of their corresponding constants were de-termined. The kinetic for dye adsorption is well described by a pseudo-first order kinetic model for the reactive yellow 2 and by pseudo-second order for the reactive blue 4. The investigation revealed that the hydroxyl groups of bagasse and the carboxylic group of propionic acid play a great role in the removal of both reactive dyes.

This research work involved the use of the low cost, available and renewable biosorbent propionic acid pretreated bagasse for the removal of the textile direct yellow 12 and direct red 81 dyes from aqueous solutions. Batch experiments were carried out for sorption kinetics and isotherms of the two dyes. The studied operating variables include initial pH, contact time, initial dye concentration, adsorbent dose and particle size. Maximum color removal was in acidic medium (pH 2.5-3.5) where a greater percentage removal was observed in this pH range. Equilibrium isotherms were applied using Langmuir and Freundlich models of adsorption and it was found that the Langmuir isotherm was the best model for adsorption of direct yellow 12 whereas the Freundlich model was suitable for adsorption of the direct red 81. The kinetics of adsorption of both dyes was consistent with a pseudo-first order kinetic for the direct yellow 12 and a pseudo-second order for the direct red 81. Desorption of both dyes is greatly dependent on the pH value of the solution with which the bagasse loaded dye in contact. The percent dye removal increases with the pH increase.

Raw sugarcane bagasse modified with propionic acid (RBMPA) was used as an efficient, low cost and eco-friendly adsorbent for the removal of methylene blue (basic) and orange II (acid) dyes from aqueous solutions. The effect of different system variables, namely contact time, dye concentration, adsorption dose, pH and particle size were investigated and optimal experimental conditions were ascertained. A greater percentage of dye removal was observed in acidic medium (pH=2) in case of orange II whereas in (pH=7) in case of methylene blue dyes and increases with the in-crease of the dosage of adsorbent. Maximum dye removal was attained after 60 min. Equilibrium isotherms were analysed by the Langmuir and Freundlich models of adsorption and it was found that the Langmuir isotherm provides a good model for the adsorption of methylene blue whereas the Freundlich isotherm is fit for the adsorption of orange II. The kinetics of the adsorption of both dyes was consistent with pseudo second-order kinetics with a good correlation (R2 > 0.99). Further-more, the amounts of dye adsorbed at equilibrium, qe (mg g-1) for methylene blue and orange II were 59.5 and 25.5, respec-tively.

Aregular two- parameter perturbation analysis based upon the boundary layer approximation is presented here to study the radiative effects of both firs- and second- order resistances due to a solid matrix on the natural convection flows in porous media