Study on the diffusion coefficients for ammonia nitrogen and nitrite and nitrate in PVA gels

2016 ◽  
Vol 74 (8) ◽  
pp. 1773-1779 ◽  
Author(s):  
Hong Yang ◽  
Qingkun Guan
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Polynomial Equation ◽  
Ammonia Nitrogen ◽  
Test Device ◽  
Surface Method ◽  
Cubic Polynomial ◽  
Addition Amount

In order to quantify the proliferation of polyvinyl alcohol (PVA) gels in a matrix and optimize the performance of mass transfer, activated carbon (AC) and CaCO3 were selected as adding materials in this experiment. For the performance of mass transfer, the optimal conditions were analyzed using response surface method (RSM) considering the inter-correlated effects of the amount of AC and CaCO3. For RSM, 13 trials resulted in a partial cubic polynomial equation, which best predicted the amount of residual debris after homogenization. The results of the study show that the effective diffusion coefficient test device can analysis the diffusion rate nitrogen, nitrite and nitrate within the PVA gels quantitatively; adding appropriate amounts of AC and CaCO3 in the biological active filter can improve the performance of mass transfer effectively; the maximum effective diffusion coefficient of nitrogen and nitrite and nitrate in the packing were 1.3637 × 10−9 and 1.0850 × 10−9 and 1.0199 × 10−9 m2/s, respectively, at optimal addition amount.

scholarly journals Heat and mass transfer coefficients and modeling of infrared drying of banana slices

Revista CERES ◽  
2017 ◽  
Vol 64 (5) ◽  
pp. 457-464 ◽  
Author(s):  
Fernanda Machado Baptestini ◽  
Paulo Cesar Corrêa ◽  
Gabriel Henrique Horta de Oliveira ◽  
Fernando Mendes Botelho ◽  
Ana Paula Lelis Rodrigues de Oliveira
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Shelf Life ◽  
Heat And Mass Transfer ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Infrared Drying ◽  
Ripening Stages

ABSTRACT Banana is one of the most consumed fruits in the world, having a large part of its production performed in tropical countries. This product possesses a wide range of vitamins and minerals, being an important component of the alimentation worldwide. However, the shelf life of bananas is short, thus requiring procedures to prevent the quality loss and increase the shelf life. One of these procedures widely used is drying. This work aimed to study the infrared drying process of banana slices (cv. Prata) and determine the heat and mass transfer coefficients of this process. In addition, effective diffusion coefficient and relationship between ripening stages of banana and drying were obtained. Banana slices at four different ripening stages were dried using a dryer with infrared heating source with four different temperatures (65, 75, 85, and 95 ºC). Midilli model was the one that best represented infrared drying of banana slices. Heat and mass transfer coefficients varied, respectively, between 46.84 and 70.54 W m-2 K-1 and 0.040 to 0.0632 m s-1 for temperature range, at the different ripening stages. Effective diffusion coefficient ranged from 1.96 to 3.59 × 10-15 m² s-1. Activation energy encountered were 16.392, 29.531, 23.194, and 25.206 kJ mol-1 for 2nd, 3rd, 5th, and 7th ripening stages, respectively. Ripening stages did not affect the infrared drying of bananas.

The Influence of Grain Form on Effective Diffusion Coefficient of Polycrystalline

2015 ◽  
Vol 756 ◽  
pp. 529-533
Author(s):  
Marija V. Chepak-Gizbrekht ◽  
Anna G. Knyazeva
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Effective Diffusion Coefficient ◽  
Effective Properties ◽  
Mass Transfer Rate ◽  
Effective Diffusion ◽  
High Mass ◽  
Know How ◽  
Nonlinear Character

To study the behavior of materials with special properties, such as micro and nanograin structure, it is necessary to know how the size and the form of grain influences on the effective properties of the material. In particular, for materials with fine-dispersed structure characterized by high mass transfer rate, which could be due to several reasons. To study this kind of materials is necessary to build mathematical models taking into account the peculiarities that arise from the transition to the micro structure of the macrostructure. This paper presents a method of calculating the effective diffusion coefficient, which takes into account the influence of the size and form of grains. This method could be useful for the construction of multilayer models of mass transfer. On the example of hexagonal polycrystalline material shown that the dependence of the effective diffusion coefficient of the angle at the grain boundary acquires nonlinear character with the increase of grain boundary layer.

Quantifying the Direct Influence of Diffusive Mass Transfer in Rarefied Gas Mixing Simulations

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Masoud Darbandi ◽  
Moslem Sabouri
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Effective Diffusion Coefficient ◽  
Rarefied Gas ◽  
Effective Diffusion ◽  
Mass Diffusion ◽  
Mixing Length ◽  
Gas Mixing ◽  
Diffusive Mass Transfer ◽  
Mixing Problem

This work utilizes the direct simulation Monte Carlo (DSMC) calculations and examines the influence of rarefication on the mixing length and effective diffusion coefficient in a two-species mixing problem. There have been efforts in past rarefied mixing flow studies to bridge between the mixing evolution rate and Knudsen number. A careful review of those efforts shows that the past derived relations did not determine the weights of Reynolds (or Peclet) number in the rarefaction influences. Although they indicated that an increase in Knudsen would decrease the mixing length, such reductions were primarily due to the Reynolds (or Peclet) reduction. Therefore, those studies could not explicitly appraise the contribution of rarefaction in the total mass diffusion magnitude. This work focuses specifically on the role of rarefaction in the total diffusive mass transfer magnitude in rarefied gas mixing problems. It excludes the contributions of momentum and heat to the mass diffusion via imposing suitable velocity, pressure, and temperature fields in the mixer domain. The results show that there will be some decreases in the diffusive mass fluxes and some increases in the mixing length as Knudsen increases. Using the Fick’s law, the effective diffusion coefficient is then calculated in the mixer zone. The results show that this coefficient may vary considerably throughout the mixer zone due to the local rarefaction level variation. The results of all investigated cases indicate that the trends of their effective diffusion coefficient variations approach to a limiting value as the rarefaction level decreases.

Evaluation of Moisture Diffusion Coefficient of Cylindrical Bodies Considering Shrinkage During Natural Convection Drying

2011 ◽  
Vol 7 (1) ◽  
Author(s):  
Najmur Rahman ◽  
Subodh Kumar
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Natural Convection ◽  
Moisture Content ◽  
Model Evaluation ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Empirical Relation ◽  
Marquardt Algorithm ◽  
Drying Kinetic

An analytical diffusion model which considers the influence of the external resistance to mass transfer, sample finite geometry and shrinkage is proposed to simulate drying kinetic curves of cylindrical bodies. The convective mass transfer coefficients, hm at air-solid interface obtained from natural convection drying experiments on potato cylinders of length 0.05m and diameter 0.01m at different air drying temperatures were used for the model evaluation. Using Levenberg-Marquardt algorithm for optimization, an empirical relation describing effective diffusion coefficient of potato as a function of air temperature and material moisture content is proposed for finite and infinite cylinders with and without considering shrinkage. The significance of material moisture content in the proposed diffusion coefficient relation is demonstrated through a comparison between the predicted and experimental moisture content ratios. The mean effective diffusion coefficient, Deff for finite shrinking cylindrical bodies is found to vary from 3.93 to 8.63 x 10-10 m2/s for the temperature range of 40 to 60°C. In addition, the assumption of infinite geometry instead of finite one in the model evaluation results in an overestimation of Deff. However, lower values of Deff are obtained when shrinkage effect is taken into account in the analysis, irrespective of the product size considered.

scholarly journals Dehydration of infrared ginger slices: heat and mass transfer coefficient and modeling

2019 ◽  
Vol 43 ◽  
Author(s):  
Paulo Cesar Corrêa ◽  
Fernanda Machado Baptestini ◽  
Juliana Soares Zeymer ◽  
Marcos Eduardo Viana de Araujo ◽  
Rita Cristina Pereira de Freitas ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Heat And Mass Transfer ◽  
Effective Diffusion Coefficient ◽  
Diffusion Theory ◽  
Effective Diffusion ◽  
Heat Transfer Process ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
And Storage

ABSTRACT Dehydration of plant products extends its shelf life and reduces its mass and volume, which increases transport and storage efficiency and adds value to food. However, it is an intensive process in energy and time, making necessary the search for more efficient technologies, Thus, this study aimed to investigate the infrared ginger dehydration process by approaching the constant period of dehydration to the theory of mass and heat transfer process to the wet bulb thermometer and the decreasing period of dehydration to liquid diffusion theory. We submitted 5.0 mm thickness and 2.0 cm diameter slices to a dryer with infrared radiation at 50, 60, 70, 80, 90 and 100 °C until constant mass. Heat and mass transfer coefficients, and effective diffusion coefficient increased linearly with temperature increasing, resulting in values ranging from 69.40 to 92.23 W m-2 °C-1, 0.062 to 0.089 m s-1 and 3.81 x 10-9 to 1.13 x 10-8 m2 s-1. Variation of heat and mass transfer coefficients was described by a linear model and the variation of effective diffusion coefficient with the temperature was described with the Arrhenius relation, whose activation energy was 22.07 kJ mol-1. The modified Henderson and Pabis model was able to satisfactorily describe the period of decreasing drying rate.

Diffusive Mass Transfer during Drying of Grinded Sunflower Stalks

2016 ◽  
Vol 10 (4) ◽  
pp. 459-463 ◽  
Author(s):  
Roman Hosovkyi ◽  
◽  
Diana Kindzera ◽  
Volodymyr Atamanyuk ◽  
◽  
...  
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Temperature Effect ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Diffusive Mass Transfer ◽  
Sunflower Stalks ◽  
Diffusive Processes

Diffusive mass transfer has been studied during drying of grinded sunflower stalks to produce fuel briquettes. Theoretical aspects of diffusive processes during filtration drying have been analyzed. The process of diffusive mass transfer during drying of grinded sunflower stalks particles of prismatic shape has been mathematically described. The temperature effect on effective diffusion coefficient has been examined.

The Effective Diffusion Coefficient and Mass Transfer Coefficient of Nordic Softwoods as Calculated from Direct Drying Experiments

Holzforschung ◽  
1999 ◽  
Vol 53 (5) ◽  
pp. 534-540 ◽  
Author(s):  
Antti Hukka
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Transfer Coefficients ◽  
Medium Temperature ◽  
Whole Process ◽  
Moisture Profiles

Summary The effective diffusion coefficient and mass transfer coefficient of Scot's pine and Norway spruce heartwood are calculated from the measured development of the internal moisture profiles of sawn timber during drying. Measurement is made using the oven-dry method. Calculation of both coefficients is based on using an existing timber drying simulation model to iteratively optimise the parameter values for the diffusion and mass transfer coefficients of prescribed functional form. The results show that the procedure employed is a feasible method to obtain numerical values for the internal and external transfer coefficients as functions of wood moisture content and temperature. The resulting diffusion coefficient and mass transfer coefficient are applicable in the whole moisture range between green and dry states in temperatures 20–80°C thus covering the whole process of medium-temperature wood drying.

scholarly journals Sorption behavior and mechanism of oxytetracycline from simulated wastewater by Amberlite IR-120 resin

2020 ◽  
Vol 82 (11) ◽  
pp. 2366-2380
Author(s):  
Rechidi Yousef ◽  
Chabani Malika
Keyword(s):  
Aqueous Solution ◽  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Transfer Coefficient ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Transfer Model ◽  
Mass Transfer Model ◽  
External Mass Transfer ◽  
Pseudo Second Order

Abstract The adsorption of oxytetracycline from aqueous solution by the resin Amberlite IR 120 was studied. The effect of different experimental parameters such as contact time, initial concentration of OTC 40–200 mg/l, initial pH 2–12 of aqueous solution, adsorbent dose 0.5–3 g/l, and stirring speed 100–700 rpm on the adsorption of OTC were investigated. The kinetic adsorption experimental results were analyzed using pseudo-first order, pseudo-second order and Elovich kinetic models. The adsorption process was found to follow a pseudo-second order kinetic model and the corresponding rate constants were obtained. A film-pore diffusion (FPD) mass transfer model has been developed to predict the concentration distribution in the fluid phase, based on the external mass transfer coefficient and the effective diffusion coefficient. The values of the external mass transfer coefficient (βL) and effective diffusion coefficient (Deff) were found to decrease with increasing OTC concentration. The comparison between the experimental and the theoretical curves allowed us to note that the film-pore diffusion mass transfer model gave a good agreement with the experimental data for all the values of initial OTC concentration.

Diffusion of Heavy Oil in SiO2 Model Catalyst and FCC Catalyst

2012 ◽  
Vol 550-553 ◽  
pp. 158-163 ◽  
Author(s):  
Zi Yuan Liu ◽  
Sheng Li Chen ◽  
Peng Dong ◽  
Xiu Jun Ge
Keyword(s):  
Diffusion Coefficient ◽  
Pore Size ◽  
Effective Diffusion Coefficient ◽  
Pore Diameter ◽  
Effective Diffusion ◽  
Model Catalyst ◽  
Average Pore ◽  
Diffusion Factor ◽  
Fcc Catalyst ◽  
Fcc Catalysts

Through the measured effective diffusion coefficients of Dagang vacuum residue supercritical fluid extraction and fractionation (SFEF) fractions in FCC catalysts and SiO2model catalysts, the relation between pore size of catalyst and effective diffusion coefficient was researched and the restricted diffusion factor was calculated. The restricted diffusion factor in FCC catalysts is less than 1 and it is 1~2 times larger in catalyst with polystyrene (PS) template than in conventional FCC catalyst without template, indicating that the diffusion of SFEF fractions in the two FCC catalysts is restricted by the pore. When the average molecular diameter is less than 1.8 nm, the diffusion of SFEF fractions in SiO2model catalyst which average pore diameter larger than 5.6 nm is unrestricted. The diffusion is restricted in the catalyst pores of less than 8 nm for SFEF fractions which diameter more than 1.8 nm. The tortuosity factor of SiO2model catalyst is obtained to be 2.87, within the range of empirical value. The effective diffusion coefficient of the SFEF fractions in SiO2model catalyst is two orders of magnitude larger than that in FCC catalyst with the same average pore diameter. This indicate that besides the ratio of molecular diameter to the pore diameter λ, the effective diffusion coefficient is also closely related to the pore structure of catalyst. Because SiO2model catalyst has uniform pore size, the diffusion coefficient can be precisely correlated with pore size of catalyst, so it is a good model material for catalyst internal diffusion investigation.

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