Dependence Of Moisture Diffusivity Research Articles

Mathematical modeling of the effects of thickness and temperature on thin-layer drying kinetics of oven-dried cooking bananas (Musa spp., sub. grp. ABB) slices

Cooking bananas is a major beneficial food in developing countries that is involved in improving human well-being and health. However, owing to its high moisture content, it quickly deteriorates. Understanding the dehydration mechanism of raw banana slices is important for subsequent processing, preservation, transportation, and product quality. Thus, this study investigates the influence of slice thickness (5, 10, and 15 mm) at varying temperatures (45, 55, and 65 °C) in a convective oven dryer on thin-layer drying kinetics and extrapolates their effect on the drying kinetics of cooking banana slices. As the temperature and slice thickness increased, the drying time also increased. Midilli’s model was found to be the best for explaining the experimental data. The effective moisture diffusivity ranged from 1.393 × 10 −8 to 8.889 10 −8 m2/s. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation, and the activation energies were found to be 23.599, 24.804, and 24.223 kJ/mol for thicknesses of 5, 10, and 15 mm, respectively.

Mathematical modelling of roselle seeds (Hibiscus sabdariffa L.) drying kinetics

Roselle seeds (Hisbiscus sabdariffa L.) are among the seeds that are high in nutrients and can be useful in several applications. Through the drying process, the seeds can be preserved for a long time. The roselle seeds were oven-dried at different temperatures 55, 60, 65 and 70oC, giving different outlet values for yield and final moisture. A total of five empirical mathematical models (Newton, Henderson and Pabis, Logarithmic, Diffusion approach and Page) were selected to describe and compare the drying characteristics of roselle seeds at respective drying temperatures. The adequately suitable drying temperature was found to be 70oC with a drying time of 4 hrs. The effective moisture diffusivity was calculated using the Fick diffusion equation. The results showed that the moisture content of the seeds gradually decreased with time. The effective diffusivity coefficient of moisture transfer varied from 5.4262×10-10 to 1.074×10-9 m2/s over the temperature range investigated. Mathematical models were fitted to the experimental data and by statistical comparison, the Page model represented drying characteristics better than the other equations with the highest R2 (0.998) and the lowest values of χ2 (0.00033) and RMSE (0.00023) observed for drying air temperature of 70°C. The dependence of moisture diffusivity on temperature was described by the Arrhenius equation, with the estimated activation energy being 43.08 kJ/mol within 55 to 70oC. Based on the selected model, it is possible to predict the moisture change during the drying of roselle seeds and thereby better control the process.

Three-dimensional orthotropic nonlinear transient moisture simulation for wood: analysis on the effect of scanning curves and nonlinearity

This paper introduces, with the development of user-subroutines in the finite-element software Abaqus FEA®, a new practical analysis tool to simulate transient nonlinear moisture transport in wood. The tool is used to revisit the calibration of moisture simulations prior to the simulation of mechanical behaviour in bending subjected to climate change. Often, this calibration does not receive sufficient attention, since the properties and mechanical behaviour are strongly moisture dependent. The calibration of the moisture transport simulation is made with the average volumetric mass data experimentally obtained on a paired specimen of Norway spruce (Picea abies) with the dimensions 30times 15times 640, {mathrm{mm}}^{3}. The data, from a 90-day period, were measured under a constant temperature of 60 °C and systematic relative humidity cycles between 40 and 80%. A practical method based on analytical expressions was used to incorporate hysteresis and scanning behaviour at the boundary surface. The simulation tool makes the single-Fickian model and Neumann boundary condition readily available and the simulations more flexible to different uses. It also allows for a smoother description of inhomogeneity of material. The analysis from the calibration showed that scanning curves associated with hysteresis cannot be neglected in the simulation. The nonlinearity of the analysis indicated that a coherent set of moisture dependent diffusion and surface emission coefficient is necessary for the correct description of moisture gradients and mass transport.

Modelling of moisture migration during convective drying of pineapple slice considering non-isotropic shrinkage and variable transport properties.

The present work aims to develop a 3-dimensional finite element (FE) model to analyze moisture migration during drying of pineapple ring considering moisture dependent diffusion coefficient (D) and mass transfer coefficient (hm) along with radial and longitudinal shrinkage. Pineapple rings were dried at 70°C temperature and 0.6m/s air velocity to study the moisture loss and shrinkage kinetics during drying. Thickness, outer radius and inner radius of hollow cylindrical pineapple slices were reduced by 79.3%, 32.2%, and 51.2%, respectively due to the occurrence of shrinkage during drying. Non-linear regression analysis showed the quadratic model to best fitted to the experimental moisture ratio data for explaining the shrinkage phenomenon in pineapple slice during drying. Shrinkage was accommodated into FE modelling using the arbitrary lagrange-eulerian method. Consideration of variable D showed better agreement with the experimental data than consideration of constant D, however constant and variable hm predicted similar results. Incorporation of shrinkage phenomena during modelling led to prediction of more accurate result showing 0.06% deviation from experimental curve, but neglecting the shrinkage resulted in a 17% deviation. Hence, model developed with consideration of shrinkage along with variable D and hm presented best fit with experimental drying curve. Developed model allowed the visualization of spatial moisture profile within the sample during drying, which would be useful for estimating the correct drying time, optimizing and designing of drying process.

Performance analysis and mathematical modelling of banana slices in a heat pump drying system

In this study, banana slices were dried at different temperatures in a closed-loop heat pump drying system. As the temperature and the slice thickness increased, the drying time also increased. Midilli & Kucuk model was found to be the best model to explain the experimental data. The effective moisture diffusivity ranged from 1.12 × 10−10 to 1.64 × 10−10 m2/s. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation and the activation energy was found to be -51.45 kJ/mol. The highest mean specific moisture extraction ratio (SMER) and coefficient of performance (COP) of HPD system were obtained as 0.212 kg/kWh and 3.059, respectively, at the highest drying air temperature.

Moisture Dependent Diffusion and Shrinkage in Yam during Drying

Abstract Crank’s analytical approximations for Fick’s diffusion equation were used to investigate the effect of moisture dependent sample thickness and diffusivity on the behavior of yam (Dioscoreaceae rotundata) cubicles during drying processes. Drying and shrinkage experiments were separately conducted at temperatures of 30, 40 and 50 °C in a cabinet drier. The comparative study of moisture dependent shrinkage and moisture dependent diffusivity justifies the interdependence of diffusivity and shrinkage due to water loss during drying. The behavior for yam is best explained by a combination of fractal moisture dependent shrinkage and moisture dependent diffusion, describing both the drying and rate curves better with good prediction of the high moisture regions. This assertion was reached as a result of low mean square error, standard error, percentage relative deviation, Akaike’s Information Criterion and high coefficient of determination. The results may indicate a varying mobility of water in food matrix of different moisture content in the multilayer and monolayer regimes.

Moisture movement in early-age concrete under cement hydration and environmental drying

This paper focuses on improving the knowledge of moisture movement and simulation of concrete at early age. In the modelling, self-desiccation due to cement hydration and the non-linear moisture capacity of cementitious materials are considered. A model based on the degree of cement hydration is used to model the reduction in internal relative humidity due to cement hydration. A three-parameter model that is suited to a wide range of water-to-binder ratios of concrete is used to simulate moisture capacity. To verify the model, a series of tests to measure the internal relative humidity of three kinds of concrete under drying and sealing conditions is conducted. Through comparing the model and test results of humidity profiles, the moisture-dependent diffusivity of the three concretes is obtained. Owing to adequate consideration being given in the model to both moisture loss resulting from cement hydration and moisture capacity, the moisture diffusivity of the concrete obtained is less than that determined in previous investigations. The developed moisture movement model and finite-difference method can predict well the moisture distribution and its variations with time.

Simulation of moisture field of concrete with pre-soaked lightweight aggregate addition

Use of pre-soaked lightweight aggregate (PSLWA) as an internal reservoir to provide water as the concrete dries is an effective method to reduce shrinkage of concrete. In this paper, a moisture distribution model of concrete internal cured with PSLWA is developed based on the experimental measurement on internal relative humidity of concrete with and without internal curing under sealing status. The function of internal curing with PSLWA is considered in the model through a parameter called critically released water, Wc, that was experimentally determined from experiments. Meanwhile, self-desiccation and moisture capacity are taken into account in development of the diffusion equation. To verify the model, a series tests to measure the internal relative humidity of three kinds of internal cured concrete under drying and sealing conditions were conducted. Through comparing the model and test results of humidity profiles, the moisture dependent diffusivity of the three internal cured concretes is obtained. The developed moisture movement model and finite differential method can well predict the moisture distribution as well as its variations with time of concrete internal cured with PSLWA.

An Observer Based Methodology for Estimating Concentration-Dependent Diffusion Coefficients in Drying Considering Shrinkage

Abstract In this work, we present a method for estimating the diffusion coefficient in isothermal drying processes in those cases in which the associated shrinkage cannot be neglected. We assume that the drying process is described by the diffusion equation and depart of a numerical solution of reduced order to the corresponding problem. The method chosen for identifying the parameter in question is based in a high gain filter. As an example for showing the proposed method we take a solid presented by Aguerre et al. (Latin American Applied Research 2008;38:345–9). First, we solve the direct problem for generating an average moisture content profile and the corresponding radius profile. Taking the radius evolution as known data and the average moisture evolution as the innovation term in the filter, we solve the inverse problem and as a result a moisture-dependent diffusion coefficient is obtained, which is refined in a posterior and final optimization step.

Hygric, thermal and durability properties of autoclaved aerated concrete

The hygric and thermal properties of autoclaved aerated concrete (AAC) given in the manufacturers’ lists include mostly just the thermal conductivity in dry state and generic data for the specific heat capacity and water vapor diffusion resistance factor. Durability characteristics are not listed at all. This greatly limits any service life assessment studies of AAC-based building envelope systems. In this paper, complete sets of hygric and thermal properties of three commercially produced AAC with different bulk density and compressive strength are measured, together with the basic physical characteristics and durability properties. Experimental results show that the thermal conductivity can be as much as six times higher in capillary water saturation state than in dry conditions. Thermal conductivity is also found to increase up to 50% when temperature is increased from 2°C to 40°C. The dependence of moisture diffusivity on moisture content is remarkable; the differences as high as one order of magnitude are observed if its values obtained for low and high moisture contents are compared. The freeze/thaw resistance of capillary saturated samples is found satisfactory up to 25cycles and increases with compressive strength. For the moisture content lower than 10% by volume AAC in the range of compressive strength of 1.8–4MPa can successfully resist to 50cycles.

Prediction of Drying Characteristics of Pomegranate Arils

The thin-layer drying characteristics of pomegranate arils were investigated at the temperature of 55, 65 and 75°C, and the thin-layer drying models were used to fit the drying data. The increase in drying air temperature resulted in a decrease in drying time. Five different thin-layer drying models were used to predict the drying characteristics. The Midilli et al. model showed a better fit to experimental drying data as compared to other models. Effective moisture diffusivities were calculated based on the diffusion equation for a spherical shape using Fick’s second law, and varied from 9.373 × 10−11 to 3.429 × 10−10 m2/s over the temperature range. Moisture diffusivity values increased as air temperature was increased. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation. The activation energies of control and pre-treated samples were determined to be 49.7 and 40.1 kJ/mol, respectively.

Thin layer drying characteristics of rapeseed ( Brassica napus L.)

This study was performed to determine the most appropriate thin layer drying model and the effective moisture diffusivity of rapeseed. The thin layer drying tests were conducted at three different combinations of drying air temperature levels of 40, 50, and 60 °C and relative humidity levels of 30, 45, and 60%. The thin layer drying characteristics of rapeseed were determined. The Page (1949) model was the most adequate model for describing the thin layer drying of rapeseed. Drying occurred in the falling rate period and the rate of moisture removal from rapeseed was governed by the rate of water diffusion to the surface of the seed. Effective moisture diffusivities were calculated based on the diffusion equation for a spherical shape using Fick’s second law. Effective moisture diffusivity during drying varied from 1.72 × 10 −11 to 3.31 × 10 −11 m 2 s −1 over the temperature range. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation. The activation energy for moisture diffusion during drying was 28.47 kJ mol −1.

Drying Kinetics of Lima Bean (Phaseolus lunatus L.) Experimental Determination and Prediction by Diffusion Models

This article aims at determining thin-layer drying curves for grains of lima bean, variety olho-de-peixe and to predict them using diffusion models. Samples of lima bean (110.0 g) with initial moisture content of 66.0% (wet basis, wb) were dried at temperatures of 40.0, 50.0 and 60.0°C. The effective diffusivity of moisture was determined by analytical solutions of the mass diffusion equation (Fick’s second law) with prescribed boundary condition for spherical, cylindrical, and infinite slab at each temperature. Comparison with the experimental data showed that the infinite slab with constant diffusivity predicted more accurately, but statistical indicators of the goodness of fit were not completely satisfactory. Thus, a model for the infinite slab with constant volume, moisture-dependent diffusivity and convective boundary condition was numerically integrated. This model was solved by the numerical method of finite volumes with fully implicit formulation. The values obtained for the diffusivity were between 5.58 x 10-9 and 6.39 x 10-8 m2 min-1, being the activation energy 28.4 kJ mol-1. The model satisfactorily describes the drying process of this lima bean cultivar under all conditions investigated.

Calculation of Moisture Distribution in Early-Age Concrete

The moisture content in concrete pores is a critical parameter for most of the degradation processes suffered by concrete, such as concrete shrinkage and related cracking. The objective of this paper is to present the formulation of a general moisture distribution model for young-age concrete. In the modeling, both cement hydration and moisture diffusion resulted humidity variations are taken into account synchronously. The effect of initial water distribution (after concrete casting) on the development of moisture distribution is considered by introducing a critical time parameter. The simulation of humidity reduction produced from self-desiccation is based on cement hydration degree that taking the effect of temperature into account by using the equilibrant age concept. During modeling the moisture diffusion, a multilinear model was adopted to simulate the moisture dependent diffusivity. The developed model and finite deferential method can well predict the moisture distribution as well as its variations with time. Good agreement between model predictions and experimental results is found. These results can subsequently be used in shrinkage induced stress field analyses, and further be used for cracking control of concrete structures.

Explicit analytical solution for drying kinetics of flat materials

This research features a theoretical framework to describe the transport of moisture content in convective drying of flat materials. A new set of formulations is developed on the basis of the spreading-pressure concept as the driving force rather than using the traditional Fick’s law. The suggested method also provides a possibility to abandon both conventional isotherms: the two-parameter Brunauer-Emmett-Teller (BET), and the three-parameter Guggenheim-Anderson-de Boer (GAB) models. As a result, the proposed procedure creates a moisture dependent diffusivity embedded in a certain non-linear diffusion equation which can be solved explicitly.

유채 종자의 수본확산계수에 관한 연구

The effective moisture diffusivity and its dependence on drying temperature during drying of rapeseed were experimentally investigated. The data were recorded from thin layer drying experiments at nine different combinations of drying air temperatures of 40, 50, and <TEX>$60^{\circ}C$</TEX> and the relative humidities of 30, 45, and 60%. The moisture diffusion equation was analyzed using stepwise multiple regression analysis. Effective moisture diffusivities were calculated based on the moisture diffusion equation for a spherical shape using Fick's second law. The effective diffusivities during the drying of rapeseed were <TEX>$l.72{\times}10^{-11}$</TEX>, <TEX>$2.41{\times}10^{-11}$</TEX> and <TEX>$3.31{\times}10^{-11}\;m^2{\cdot}s^{-1}$</TEX> at 40, 50 and <TEX>$60^{\circ}C$</TEX>, respectively. The activation energy for moisture diffusion during drying was <TEX>$28.47\;kJ{\cdot}mol^{-1}$</TEX>. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation. Drying occurred in the falling rate period and the internal moisture diffusion phenomenon is the governing physical mechanism of the moisture movement in the particles.

Moisture Diffusion Coefficient of Amaranth Seeds determined by the Regular Regime Method

In this work the dependence of moisture diffusivity of amaranth seeds on water concentration is studied. An expression for the moisture diffusion coefficient as a function of temperature and moisture content was determined departing from experimental drying curves obtained in a moisture chamber and employing the regular regime method developed elsewhere. A weak, but noticeable, dependence of this parameter on the moisture concentration was found. The diffusivity values obtained with the method applied in this work were similar to those previously reported and based on an Arrhenius-type expression for the moisture diffusion coefficient of amaranth seeds as a function of temperature.

AN INVERSE MOISTURE DIFFUSION ALGORITHM FOR THE DETERMINATION OF DIFFUSION COEFFICIENT

The finite difference approximation is applied to estimate the moisture-dependent diffusion coefficient by utilizing test data of isothermal moisture desorption in northern red oak (Quercus rubra). The test data contain moisture distributions at discrete locations across the thickness of specimens, which coincides with the radial direction of northern red oak, and at specified times. Also, the rate of moisture variation at each specified time and location must be known or correctly estimated. The functional form of the diffusion coefficient as well as the boundary conditions at the surfaces are not known a priori. The resulting system of finite difference equations defines an inverse problem, whose solution may be sensitive to small changes of input data. Results indicate that the diffusion coefficient increases with increasing moisture content below the fiber saturation point, which defines the upper limit applied by the diffusion theory. †The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright.

Approximate Isothermal Drying Curves of Hygroscopic Porous Materials with Variable Surface Concentration.

The governing equations for isothermal drying of slabs of hygroscopic porous material are analyzed to develop a method for the approximate calculation of drying rate curves. Gradual decrease in surface moisture content is incorporated in the model by considering the effect of the desorption isotherm. The proposed method enables one to estimate drying rate curves for any conditions without solving drying equations when the dependence of moisture diffusivity and the desorption isotherm are given as functions of moisture content. Accuracy of the drying rates calculated by the method is examined by comparing with numerical solutions of the drying equations. When one of the internal and superficial mass transfer resistances is dominant, approximate drying rate curves show very good agreement with numerical solutions. When both resistances are comparable, the method underestimates drying rates with errors of less than 6%.

Moisture diffusion in soil-cement mixtures and compacted lean concrete

The process of drying in lean concretes and soil-cement mixtures is investigated experimentally and the moisture dependent diffusion coefficient is calculated by the use of the method of Matano. Moisture losses predicted with the nonlinear diffusion theory are in better agreement with the test data, than those with the linear theory, especially after 50% of the evaporable water has been dried. The relation between drying rate and shrinkage strain is not linear. In the case of soil-cement mixtures, the shrinkage surpasses the drying, whereas in lean concrete there is an opposite trend, which is explained with the pore size distribution.