Evolution Of Moisture Content Research Articles

مدل سازی ریاضی فرآیند خشک شدن کیوی در یک خشک کن تحت خلاء

مدل سازی ریاضی فرآیند خشک شدن کیوی در یک خشک کن تحت خلاء

Application of a kiln drying technique to Quercus suber L. cork planks

At present, all of the cork used to manufacture natural stoppers is air dried for a minimum of 6 months. This study evaluates the feasibility of applying a kiln drying technique to cork planks. We used a sample of 65 planks, each of which was divided into two pieces. One sub-set of planks was air dried for 6 months following the traditional procedure, while the other was kiln dried for 14 days. The evolution of moisture content was controlled, and both methods were compared by means of a statistical analysis of the thickness, quality, porosity coefficient, color and compressive properties of the cork.The reduction in moisture content was similar for both traditional air drying and kiln drying. At the end of the drying, cork thickness increased with both methods, although a larger increase was observed for the kiln drying method. Statistically significant differences were not found for the mean porosity coefficient or quality. Although statistically significant differences in the color of the cork were detected, it would be necessary to verify if such differences are detectable by the human eye. No differences were found in the compressive properties of the cork for a significance level of less than 1%.This feasibility study concludes that kiln drying is a suitable technique as it significantly reduces the drying time and holding costs of the raw material. The application of this technique would constitute an innovation in the transformation process by controlling the climatic variables that affect the drying process.

Modeling and Simulation of the Drying of Beech Timber (Fagus sylvatica)Using Oscillating Regimes

This paper represents a numerical study of the massive (60mm) and thin (38mm) wood drying using oscillating drying regimes applied on beech timber (Fagus sylvatica). All thermo-physical properties relative of studied wood are taken from the literature on appropriate experiments. We showed that Luikov’s model can be used to predict temperature and moisture content evolutions using oscillating regimes. First numerically tests on 60mm timber wood consists in increasing and decreasing alternation of the drying parameters (temperature), at the rising 12-15°C and at the descent 10- 12°C, every alternation being higher than the precedent with 2-4°C. Second numerical test consists to oscillate the values of equilibrium moisture content with the oscillation amplitudes of ±10% and ±20% at the frequencies of 6hours. These practical experiments are detailed in the literature. Luikov’s model gives satisfactory results, according to the experiments obtained in the literature. But, convective transfer coefficients are function of each experiment and we observed a short difference between oscillation amplitudes of ±10% and ±20% on moisture content evolution. Thus, Luikov’s model can be a tool to study oscillation drying timber in order to reduce consumption of energy during the drying process.

Effect of Thermophysical Properties on Coupled Heat and Mass Transfer in Porous Material during Forced Convective Drying

The convective drying kinetics of porous medium was investigated numerically. A mathematical model for forced convective drying was established to estimate the evolution of moisture content and temperature inside multilayered porous medium. The set of coupled partial differential equations with the specified boundary and initial conditions were solved numerically using a MATLAB code. An experimental setup of convective drying had been constructed and validated the theoretical model. The temperature and moisture content of the potato samples were dynamically measured and recorded during the drying process. Results indicate that thermal diffusion coefficient has significant positive impact on temperature distribution and mass diffusion coefficient might directly affect the moisture content distribution. Soret effect has a significant impact on heat flux and temperature distribution in the presence of large temperature gradient.

Respuesta hidrológica en los medios semiáridos : las cuencas experimentales en la Sierra de Picarcho, Murcia

The hydrology of semiarid areas is characterized by irregular and sporadic events and a tremendous spatio-temporal variability of control factors. In 1997, experimental watersheds were installed in Sierra del Picarcho (Cieza, Murcia) to identify the factors controlling runoff generation at different study scales, to study the spatial and temporal variability of control factors, and to model the hydrological response. The runoff data measured in experimental plots and catchments for three years are showed.At catchment scale, temporal evolution of soil moisture content was studied and the jactors that controlled identified.

Innovative experimental-numerical method for quality control during sausages production

A reliable assessment and control of water content in food products maximise product quality, safety, and shelf-life while minimising undesirable changes. Product considerations include sensitivity to flavour and related deteriorations, colour changes, vitamin loss, microbial activity, and amount of flavour available. Nevertheless the majority of food related processes, also at an industrial level, lack of suitable instrumentation and technologies for monitoring the humidity content and its variation during the different phases of the product life. This paper presents the implementation of an innovative numerical-experimental method for monitoring moisture content evolution during the ripening process of sausages.

Influence of sugar composition on water sorption isotherms and on glass transition in apricots

Desorption isotherms of fresh and osmotically treated (70%, 30°C) apricots have been measured at 30, 45 and 60°C by the static gravimetric method. A differential scanning calorimeter was used to determine the Tg of samples equilibrated with several water activities. The osmotic pretreatment affected the shape of the desorption isotherms because of biopolymer binding at low activities values and dissolution of sucrose at high activities values. At 45°C, isotherms of fresh and sucrose impregnated apricots are identical. At 60°C, sucrose impregnation depressed water activity, while at 30°C the opposite effect is observed. Evolution of moisture content at the first saturation layer expresses these effects of sucrose impregnation and temperature. Peleg model fitted the best experimental desorption isotherms of the fresh and osmotically treated apricots (0.990⩽r2⩽0.999, 0.005⩽S⩽0.045). A strong plasticizing effect of water on the Tg was found, with a great reduction in this value with increase in water activity.

Hydrological effects of a layer of vegetation ash on underlying wettable and water repellent soil

Hydrological processes after a wildfire may take place under soil conditions altered by heat and by the presence of ash. Soil and ash interact as a two-layer system with poorly understood hydrological properties, especially when ash covers water repellent soil. Here we quantify the effect of an ash layer (0, 5, 15 and 30mm depth) covering wettable and water repellent soil on (i) the hydrological response and the mechanism of runoff generation and (ii) the water repellency dynamics, for a rainfall event followed by different drying periods and a second rainfall event. Laboratory rainfall simulation experiments (82.5mmh−1 during 40min) at small plot-scale (0.09m2) were performed and surface and subsurface flow, sediment yield, splash detachment and moisture content evolution determined. Wettable soil without ash cover generated no surface runoff, but as a two-layer system temporary surface runoff was produced when ash became saturated, until water drained through the soil. Wetting and drying changed the hydrological properties of ash, increasing surface runoff for all ash depths. Over water repellent soil, the ash layer delayed and reduced surface runoff proportionally to ash depth (r=0.99), reduced soil water repellency and promoted fingered subsurface flow. Ash protected the soil from splash and sheet erosion, particularly for water repellent soil. The results demonstrate that (i) the presence of an ash layer can have contrasting effects on surface runoff, depending on the wettability of the underlying soil, and (ii) a single wetting and drying event can substantially modify ash hydrological properties.

A New Control‐Volume Finite‐Element Scheme for Heterogeneous Porous Media: Application to the Drying of Softwood

AbstractAn improved mesoscopic model is presented for simulating the drying of porous media. The aim of this model is to account for two scales simultaneously: the scale of the whole product and the scale of the heterogeneities of the porous medium. The innovation of this method is the utilization of a new mass‐conservative scheme based on the Control‐Volume Finite‐Element (CV‐FE) method that partitions the moisture content field over the individual sub‐control volumes surrounding each node within the mesh. Although the new formulation has potential for application across a wide range of transport processes in heterogeneous porous media, the focus here is on applying the model to the drying of small sections of softwood consisting of several growth rings. The results conclude that, when compared to a previously published scheme, only the new mass‐conservative formulation correctly captures the true moisture content evolution in the earlywood and latewood components of the growth rings during drying.

Modelling batch drying of sand in a draft-tube conical spouted bed

A model has been built to predict the evolution of sand drying in a conical spouted bed with a non-porous draft tube. Three regions have been considered in the model, i.e., spout, annulus and fountain, and unsteady-state mass balances have been written for water in the solid and gaseous phases. The model has been validated by comparing its results with the experimental ones obtained in a previous study and it allows predicting the moisture content evolution of both the air and the sand during the drying process.

Modeling on heat and mass transfer in stored wheat during forced cooling ventilation

A mathematical model based on the theory of heat and mass transfer in porous media was developed to simulate the evolution of grain temperature and moisture content in a wheat storage bin during ventilation with cooling air at the constant temperature and humidity. Unlike the previous works on this aspect, the present work was not focused on cooling the stored grain by ventilation with ambient air, but with the refrigerated air. Validation was performed by comparing between predicted and measured grain temperature and grain moisture content for two cases. Predicted data were in reasonable good agreement with measured ones. The model and the parameter values used in the model are applicable for predicting temperature and moisture of stored grains under ventilation conditions.

Validation of soil moisture simulations from the PAMII model, and an assessment of their sensitivity to uncertainties in soil hydraulic parameters

Soil moisture simulations by the Canadian prairie agrometeorological model (PAMII) were validated against in situ observations from three sites on the Canadian prairies. Skill scores indicate that PAMII shows significant skill in simulating the evolution of bulk root-zone soil moisture content during the growing season, and that PAMII also captures the salient features of the soil moisture at each site. Specifically, correlation coefficients between simulated and observed bulk root-zone soil moisture content varied between 0.65 and 0.90, while the relative mean absolute errors were typically less than 10%. We adopted an ensemble approach to quantify the uncertainty in simulating soil moisture that results from errors in the soil hydraulic properties. The ensemble was assembled by running PAMII using soil hydraulic properties from 20 pedotransfer functions (PTFs). Our results suggests that the uncertainty in soil moisture estimates is typically less than 10% of the bulk root-zone soil moisture content, and that there appears to be merit in using a PTF ensemble to improve estimates of the soil's hydraulic properties. In addition, the simulated soil moisture was quite sensitive to the reference stomatal resistance term. For the grassland sites, a reference value of 100 s m −1 yielded the best results. The accuracy of the soil moisture simulations was insensitive to errors <5% in the initial plant-available soil moisture content. The skill of PAMII is strongly modulated by errors in the estimated permanent wilting point and field capacity, with the skill of model simulations typically increasing as the errors decrease. Consequently, the correct modelling of soil moisture is contingent on accurately specifying the site-specific soil hydraulic properties.

USE OF IMMERSION AND VACUUM IMPREGNATION IN MARINATED SALMON (SALMO SALAR) PRODUCTION

The kinetics of mass transfer during the production of marinated salmon were compared for the traditional dry processing method (D) and alternative processes involving immersion in ternary solution (sucrose and NaCl), both at atmospheric pressure (I) and with vacuum pulse (VI). The evolution of water activity, moisture, salt and sugar content and weight loss was measured during marination trials. Immersion marination (I and VI) processes reduced both the process time (approximately 85%) and the weight loss (approximately 48%), increasing yield. PRACTICAL APPLICATIONS The results of this article can be used by processing industries for the elaboration of salmon. The technologies of marinating salmon by immersion in ternary solution, with (IV) and without (I) vacuum pulse, have advantages in comparison with dry marinating technology. These are related principally to a reduction of processing time by 50% and of weight loss by 48%. Considering the growth of the production and consumption of salmon at a world level, we think that marinating technologies by immersion in an osmotic solution represent a good alternative to the industrialized production of marinated salmon.

Estimation of an effective water diffusion coefficient during infrared‐convective drying of a polymer solution

AbstractThis article deals with the drying of an aqueous solution of polyvinyl alcohol mixed with a plasticizer. A heating combining forced convection and short‐infrared radiation was investigated. A one‐dimensional model taking into account the shrinkage of the product was developed to get the temperature and moisture content evolutions during the drying. The water diffusion coefficient was estimated by an inverse method. A sensitivity analysis and numerical tests showed the relevance of using an objective function taking both mass and temperature measurements into account for the estimation procedure. This estimation was performed on several convective and infrared‐convective experimental drying kinetics. The model predictions fit well mass and temperature experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Modelling of convective drying of carrot slices with IR heat source

This study deals with modelling of convective drying of carrot slices with infrared heat source. Desorption isotherms of carrot were determined at 30, 40 and 60 °C. The GAB model was used to modelize the measured desorption isotherm. The shrinking factor of carrot slice was determined experimentally. A relationship between solid displacement and moisture content of carrot was determined. A simultaneaous heat and moisture transfers model taking into account the product deformation and based on Fick diffusion equation was developed. The model accuratelly predicts moisture content and temperature evolutions as a function of drying time and position in the carrot slices.

Optimal constrained control of an infrared-convective drying of a polymer aqueous solution

This paper deals with the optimization of the infrared-convective drying of an aqueous solution of polyvinyl (alcohol) mixed with a plasticizer. Thanks to a knowledge model giving the temperature and moisture content evolutions during drying, the process control is firstly investigated in proportional close-loop approach. Then, the optimization is performed by minimizing an objective function which takes several criteria on drying time, energy consumption, and constraints on product (temperature and moisture content) into account. Particular attention is brought to the improvement of the final quality of the product by limiting the decreasing of surface moisture content during drying. The principle was to determine off-line the infrared irradiation and then to test it by means of a drying setup. The experimental tests are performed in open-loop. The infrared irradiation calculated by using proportional controller and optimal control is applied by adapting the infrared emitters’ power in real time.

The flood event that affected Badajoz in November 1997

Abstract. The flooding episode of November 1997 in Badajoz was one of the most dramatic catastrophes in Spain: as a result, there were 21 fatalities and huge financial damages. The main purpose of this work is to assess the prevailing synoptic conditions as well as detailing the mesoscale effects by means of moisture sources and dynamic and thermodynamic instability analysis involved in the November 1997 Spanish severe weather episode. In order to achieve the above, this flood event is described in terms of moisture content evolution by means of individual particle simulation along 3-day back-trajectories. A Lagrangian model is applied in order to characterize the atmospheric particles involved in the focused case (localization, height and specific humidity) which give rise to sudden precipitation stream. Geopotential height and temperature fields were used to describe the synoptic situation. Thermodynamic indices, such as CAPE, SWEAT and KI, and dynamic parameters like potential vorticity anomaly at 330 K isentropic surface and Q vector divergence were also calculated in order to complete the analysis and to give a thorough weather frame taking into account the atmospheric instability. The results of this work suggest this flood event was due mainly to strong dynamic instability along with large amounts of moisture advected by a trough, while the thermodynamic instability played a secondary role. Finally, a new methodology based on a technique proposed by Tremblay (2005) has been developed in order to separate the precipitation into stratiform and convective components. It is evident that the event was associated with a predominant convective regime.

Modeling the Drying of a Deep Bed of Ilex paraguariensis in an Industrial Belt Conveyor Dryer

The evolution of temperature and moisture content of leaves and twigs of yerba maté on different levels of a through-flow dryer was investigated by modeling heat and mass transfer using the finite-difference method. To validate the model, the temperature and moisture profiles were used to estimate chlorophyll losses. Great variations were obtained in moisture, temperature, and chlorophyll content at different levels of the bed. Leaf temperature quickly increased in the former nodes, and it then increased slowly until it reached air temperature. In the twigs, the temperature increase was slow and the air temperature was never reached.

Constant and Intermittent Drying Characteristics of Olive Cake

The drying kinetics of olive cake, the solid by-product of the olive oil extraction process, has been experimentally investigated in a small-scale tray dryer using both constant and intermittent (on/off) heating schemes. The parameters investigated include inlet air temperature and intermittency of heat input. The drying kinetics was interpreted through two mathematical models, the Page equation and the Lewis equation. The Page equation was most appropriate in describing the drying behavior of olive cake. A diffusion model was used to describe the moisture transfer and the effective diffusion coefficient at each temperature was determined. The dependence of the effective diffusion coefficient on drying temperature can be adequately explained based on an Arrhenius-type relation. The effective diffusion coefficient varied between 7.6 × 10−8 and 2.5 × 10−7 m2/min with an activation energy of 38.55 kJ/mol. Comparison of time evolution of material moisture content due to intermittent and constant drying is also made.

The effect of rock fragment size and position on topsoil moisture on arid and semi-arid hillslopes

Rock fragments on arid hillslopes affect rainwater redistribution and overland flow, through various hydrological processes. The present study focuses on the evolution of topsoil moisture content under rock fragments following rain events. Measurement was taken under rock fragments in various sizes (large and small) and positions (‘on top’ of the soil surface and 'partially embedded' within the soil surface) at north- and south-facing hillslopes in arid and semi-arid areas. The main findings: (1) the topsoil moisture content under rock fragments was higher over time than that of bare soil areas; (2) rock fragments affect the topsoil moisture content for a longer time in semi-arid areas than in arid areas; and (3) large rock fragments and ‘partially embedded’ ones are favorable micro-environments for accepting and retaining rainwater and overland flowing water. This may have eco-geomorphic implications regarding the mosaic-like patterns of source and sink areas on arid hillslopes.