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.

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.

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.

The Effects of Gas Mixture Composition on the Mass Transfer and Individual Diffusion Coefficient in CH4-CO2-Light Oil Systems

2021 ◽  
Author(s):  
Taiyi Zheng ◽  
Yongcheng Luo ◽  
Yu Shi ◽  
Xiangui Liu ◽  
Zhengming Yang ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Mass Transfer Rate ◽  
Molar Fraction ◽  
High Mass ◽  
Gas Mixture ◽  
Light Oil ◽  
The Individual ◽  
Tight Formation

Abstract Limited CO2 resources considerably narrow down the field application of CO2 EOR for improving oil recovery in tight formation. Considering that CH4 and CO2 have similar EOR mechanisms, CH4, as a by-product of produced oil, is a relatively cost-efficient agent to be injected into the tight formation with CO2. In this work, experimental and mathematical methods are proposed to probe the effect of CH4 composition on the mass transfer between a CO2-CH4 gas mixture and crude oil collected from a tight oil reservoir. Experimentally, the pressure-decay tests for different CH4-CO2-light oil systems are conducted at a constant temperature in a pressure / volume / temperature (PVT) setup. Also, the gas mixtures’ compositions before and after the experiments are analyzed with gas chromatography to investigate the mass transfer of different components. Theoretically, mathematical formulations are developed to describe the mass transfer between the gas mixture and light oil based on translated Peng Robinson equation of state (PR-EOS), a real gas equation, and one-dimensional convection-diffusion equations. The individual diffusion coefficients of CH4 and CO2 as well as the concentrations distribution can be obtained by minimizing the deviation between the calculated pressure and the measured ones. The results indicate that the higher the content of CO2 in the initial gas phase, the faster the pressure drops are and less time it takes for the oil and gas phases to reach a stable pressure, which implies a high mass transfer rate with an increase in CO2 composition. In particular, the diffusion coefficient of CO2 is found to be about 2 times larger than that of CH4 the same composition condition. However, it is noted that the individual diffusion coefficients of CH4 or CO2 are not constants. A high molar fraction in the initial gas sample will lead to a large diffusion coefficient in different CH4-CO2-light oil systems.

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.

scholarly journals Computing and Comparing Effective Properties for Flow and Transport in Computer-Generated Porous Media

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-24 ◽  
Author(s):  
Rebecca Allen ◽  
Shuyu Sun
Keyword(s):  
Porous Media ◽  
Diffusion Coefficient ◽  
Effective Diffusion Coefficient ◽  
Stokes Equations ◽  
Effective Properties ◽  
Effective Diffusion ◽  
Pore Geometry ◽  
Flow And Transport ◽  
Scale Modeling ◽  
Line Array

We compute effective properties (i.e., permeability, hydraulic tortuosity, and diffusive tortuosity) of three different digital porous media samples, including in-line array of uniform shapes, staggered-array of squares, and randomly distributed squares. The permeability and hydraulic tortuosity are computed by solving a set of rescaled Stokes equations obtained by homogenization, and the diffusive tortuosity is computed by solving a homogenization problem given for the effective diffusion coefficient that is inversely related to diffusive tortuosity. We find that hydraulic and diffusive tortuosity can be quantitatively different by up to a factor of ten in the same pore geometry, which indicates that these tortuosity terms cannot be used interchangeably. We also find that when a pore geometry is characterized by an anisotropic permeability, the diffusive tortuosity (and correspondingly the effective diffusion coefficient) can also be anisotropic. This finding has important implications for reservoir-scale modeling of flow and transport, as it is more realistic to account for the anisotropy ofboththe permeability and the effective diffusion coefficient.

Stationary d.c. streaming due to shape oscillations of a droplet and its effect on mass transfer in liquid–liquid systems

2001 ◽  
Vol 444 ◽  
pp. 321-342 ◽  
Author(s):  
A. L. YARIN
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Effective Diffusion ◽  
Passive Scalar ◽  
Immiscible Liquid ◽  
Capillary Waves ◽  
Droplet Radius ◽  
Streaming Flows

The work is devoted to stationary streaming flows resulting from standing capillary waves at interfaces between two immiscible liquids and their effect on the mass transfer rate of a passive scalar. In particular, oscillating liquid droplets immersed in another immiscible liquid are considered. Secondary streaming flows in the Stokes layers near the interface are calculated, as well as the corresponding vortical flows arising in the bulk. It is shown that the vortices can drastically enhance the mass transfer rate of a passive scalar which is to be extracted by one liquid from the other. The corresponding Sherwood number is of the order of [[mid ]uint[mid ]a/[Dscr ]1]1/2, where [mid ]uint[mid ] is the magnitude of the interfacial streaming velocity, a is the droplet radius, and [Dscr ]1 is the diffusion coefficient in liquid 1 (inside the droplet). This means that the effective diffusion coefficient is of the order of [Dscr ]1[[mid ]uint[mid ]a/ [Dscr ]1]1/2, which is two orders of magnitude higher than [Dscr ]1. The results obtained show that such flows can be of potential interest for novel bioseparator devices.

scholarly journals The mechanism of mass transfer in the process of fish salting

2019 ◽  
Vol 81 (1) ◽  
pp. 42-46
Author(s):  
Y. A. Fatykhov ◽  
M. V. Shumanova ◽  
V. A. Shumanov
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Theoretical Model ◽  
Transfer Rate ◽  
Critical Concentration ◽  
Separation Of Variables ◽  
Mass Transfer Rate ◽  
Effective Diffusion ◽  
Temporal Distribution ◽  
Correlation Spectroscopy

The process of fish salting is based on patterns associated with the diffusion of salt in the fish tissue and the diffusion-osmotic transfer of water from the tissues of fish to the brine or in the opposite direction. Atlantic herring is an object of research. The character of the spatial-temporal distribution of salt within the product (herring) was established. As a method of experimental research was used a modern method of non-destructive testing, called photon correlation spectroscopy. The theoretical model of the process was obtained on the basis of the second Fick's law as a solution of a differential equation by the method of separation of variables. The qualitative nature of the mathematical model is interpreted as an exponential approach to the equilibrium value of salt concentration in the process of fish salting. Experimental dependences of the diffusion coefficient on the depth of salt penetration into the muscle tissue of fish were obtained. The mass transfer rate of salt in the first stage of the salting process is about 3·10-4 mm/s. The experimental value of the mass transfer rate is compared with the theoretical value of the proposed model. A satisfactory coincidence is obtained. The qualitative character of the advancement of the salt critical concentration (8.0%) in the form of a front has been established. This is consistent with the theory of P.B. Crean. The causes associated with the apparent increase in the diffusion coefficient at the second stage of the fish salting process are analyzed, which have been noted by many researchers. The expediency of using the effective diffusion coefficient in studies was expressed, which to a greater extent corresponds to the actual course of the process of mass transfer of salt and moisture. It is noted that the most recognized modern theoretical and empirical models of the process of salting fish are models that reflect an exponential approach to the equilibrium of substances involved in the process The acceptability of using the empirical model of salting fish Zugarramurdi and Lupine was confirmed as qualitatively corresponding to the theoretical model proposed in the article..

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