Showing papers on "Mass transfer coefficient published in 2020"

Nitrate green removal by fixed-bed columns packed with waste biomass: Modelling and friction parameter estimation

Abstract: Natural and waste waters pollution by nitrates is considered a major environmental problem due to the possible consequences on human health and on water bodies through eutrophication phenomenon. Hazelnut shell were employed as packing material in a large lab-scale column for the removal of nitrate from wastewaters, comparing the process performances with those obtained in batch system. A nitrate removal efficiency up to about 67% was observed in batch mode at low pH and with a sorbent mass concentration of 8 g/L with 0.5 mm size. A lower (62%) nitrate removal efficiency was observed at large lab-scale column, though notable volumes of effluents (60–200 L, depending on the inlet flow-rate) were successfully treated with a bed height of 30 cm and a sorbent mass of 590 g. Non-linear regression of batch equilibrium data using Langmuir, Freundlich and SIPS models allowed to estimate the isotherm parameters, subsequently used in a mass transfer dynamic model to fit the experimental data. The regressed film mass transfer coefficient kf, at six different inlet flowrate values were elaborated for the estimation of the characteristic parameters of the empirical correlation between Sherwood, Reynolds and Schmidt numbers. Furthermore, the pressure drop along the column was calculated and the Ergun and Carman equations were employed for the estimation of the empirical friction parameters.

Simultaneous NO and SO2 removal by aqueous persulfate activated by combined heat and Fe2+: experimental and kinetic mass transfer model studies.

Abstract: This study evaluates the chemistry, kinetics, and mass transfer aspects of the removal of NO and SO2 simultaneously from flue gas induced by the combined heat and Fe2+ activation of aqueous persulfate. The work involves experimental studies and the development of a mathematical model utilizing a comprehensive reaction scheme for detailed process evaluation, and to validate the results of an experimental study at 30–70 °C, which demonstrated that both SO2 and Fe2+ improved NO removal, while the SO2 is almost completely removed. The model was used to correlate experimental data, predict reaction species and nitrogen-sulfur (N-S) product concentrations, to obtain new kinetic data, and to estimate mass transfer coefficient (KLa) for NO and SO2 at different temperatures. The model percent conversion results appear to fit the data remarkably well for both NO and SO2 in the temperature range of 30–70 °C. The conversions ranged from 43.2 to 76.5% and 98.9 to 98.1% for NO and SO2, respectively, in the 30–70 °C range. The model predictions at the higher temperature of 90 °C were 90.0 and 97.4% for NO and SO2, respectively. The model also predicted decrease in KLa for SO2 of 1.097 × 10−4 to 8.88 × 10−5 s−1 (30–90 °C) and decrease in KLa for NO of 4.79 × 10−2 to 3.67 × 10−2 s−1 (30–50 °C) but increase of 4.36 × 10−2 to 4.90 × 10−2 s−1 at higher temperatures (70–90 °C). This emerging sulfate-radical-based process could be applied to the treatment of flue gases from combustion sources.

Dufour and Soret effects on Al2O3-water nanofluid flow over a moving thin needle: Tiwari and Das model

Abstract: This paper aims to examine the effect of Dufour and Soret diffusions on Al2O3-water nanofluid flow over a moving thin needle by using the Tiwari and Das model.,The governing equations are reduced to the similarity equations using similarity transformations. The resulting equations are programmed in Matlab software through the bvp4c solver to obtain their solutions. The features of the skin friction, heat transfer and mass transfer coefficients, as well as the velocity, temperature and concentration profiles for different values of the physical parameters, are analysed and discussed.,The non-uniqueness of the solutions is observed for a certain range of the physical parameters. The authors also notice that the bifurcation of the solutions occurs in which the needle moves toward the origin (λ < 0). It is discovered that the first branch solutions of the skin friction coefficient and the heat transfer coefficients increase, but the mass transfer coefficient decreases in the presence of nanoparticle. Additionally, the simultaneous effect of Dufour and Soret diffusions tends to enhance the heat transfer coefficient; however, dual behaviours are observed for the mass transfer coefficient. Further analysis shows that between the two solutions, only one of them is stable and thus physically reliable in the long run.,The problem of Al2O3-water nanofluid flow over a moving thin needle with Dufour and Soret effects are the important originality of the present study. Besides, the temporal stability of the dual solutions is examined for time.

Gas-liquid and gas-liquid-solid mass transfer model for Taylor flow in micro (milli) channels: A theoretical approach and experimental proof

Abstract: New theoretical approach to model Gas-Liquid and Gas-Liquid-Solid mass transfer for two-phase Taylor flows in milli and microchannels is proposed. The main idea of the proposed mathematical model is to take into account not only diffusion but the convection inside of liquid slugs caused by circulation within Taylor vortices and the convective transport from the film surrounding the bubble to the slug induced by the film movement. For that aim a three-layer model elaborated earlier by Abiev (CEJ, 2013) is used to decompose the liquid slug onto three interacting layers. Diffusion within the film around bubbles and the transit film belonging to the slug, as well as diffusion from the bubble caps was included in the model as well. Experimental data of Bercic & Pintar (CES, 1997), Butler et al. (CHERD, 2016; IJMF, 2018) and Haase et al. (TFCE, 2020) used for proof have shown quite better coincidence with the proposed model than the other available models. Special tests without convective term have demonstrated much less accuracy with the experimental data confirming the huge role of convection in the overall gas-liquid and gas-liquid-solid transport. The correlation between frequency of circulations within Taylor vortices and overall gas-liquid mass transfer coefficient found recently (Abiev et al., CEJ, 2019) was confirmed by use of Bercic & Pintar (CES, 1997) data. In the frame of the moving bubble the velocity of the transit film equals to the absolute value of two-phase velocity. That is why the convective term significantly influences the total mass transfer in the film and overall gas-liquid transport as well.

Nitrate removal from aqueous solutions by magnetic cationic hydrogel: Effect of electrostatic adsorption and mechanism

Abstract: Excessive nitrate (NO3−) is among the most problematic surface water and groundwater pollutants. In this study, a type of magnetic cationic hydrogel (MCH) is employed for NO3− adsorption and well characterized herein. Its adsorption capacity is considerably pH-dependent and achieves the optimal adsorption (maximum NO3−-adsorption capacity is 95.88 ± 1.24 mg/g) when the pH level is 5.2–8.8. The fitting result using the homogeneous surface diffusion model indicates that the surface/film diffusion controls the adsorption rate, and NO3− approaches the center of MCH particles within 30 min. The diffusion coefficient (Ds) and external mass transfer coefficient (kF) in the liquid phase are 1.15 × 10−6 cm2/min and 4.5 × 10−6 cm/min, respectively. The MCH is employed to treat surface water that contains 10 mg/L of NO3−, and it is found that the optimal magnetic separation time is 1.6 min. The high-efficiency mass transfer and magnetic separation of MCH during the adsorption–regeneration process favors its application in surface water treatment. Furthermore, the study of the mechanism involved reveals that both –N+(CH3)3 groups and NO3− are convoluted in adsorption via electrostatic interactions. It is further found that ion exchange between NO3− and chlorine occurs.