Drying Kinetics Research Articles

Fluidized Bed Drying of Wheatgrass: Effect of Temperature on Drying Kinetics, Proximate Composition, Functional Properties, and Antioxidant Activity.

Wheatgrass is a valuable source of nutrients and phytochemicals with therapeutic properties. However, its shorter life span makes it unavailable for use. So, storage-stable products must be developed through processing in order to enhance its availability. Drying is a very important part of the processing of wheatgrass. Thus, in this study, the effect of fluidized bed drying on the proximate, antioxidant, and functional properties of wheatgrass was investigated. The wheatgrass was dried in a fluidized bed drier at different temperatures (50, 55, 60, 65, 70 °C) using a constant air velocity of 1 m/s. With increasing temperature, the moisture content was reduced at a faster rate, and all drying processes took place during the falling rate period. Eight mathematical models under thin layer drying were fitted into the moisture data and were evaluated. The Page model was the most effective in explaining the drying kinetics of wheatgrass, followed by the Logarithmic model. The R2, chi-square, and root mean squared value for Page model was 0.995465-0.999292, 0.000136-0.0002, and 0.013215-0.015058, respectively. The range of effective moisture diffusivity was 1.23-2.81 × 10-10 m2/s, and the activation energy was 34.53 kJ/mol. There was no significant difference in the proximate composition of was seen at different temperatures. The total phenolic content (117.16 ± 0.41-128.53 ± 0.55 mgGAE/g), antioxidant activity (33.56 ± 0.08-37.48 ± 0.08% (DPPH), and FRAP (1.372 ± 0.001-1.617 ± 0.001 mgAAE/g) increased with the rise in temperature. A significant increase was observed in functional properties, except for the rehydration ratio, which decreased with rising temperature. The current study suggests that fluidized bed drying improves the nutritional retention of wheatgrass with good antioxidant activity and functional properties that can be used to make functional foods.

Effect of Turntable Rotation Rate on Drying Kinetics and Functional Properties of Lemon Peel during Microwave Drying

The aim of this study is to investigate the effect of the rotational rate of the turntable on drying kinetics of lemon peels and some functional and flow properties of lemon peel powders. Lemon peels were dried by microwave drying using different rates of rotation (0, 6.5, 9.5, and 12.5 rpm) at different microwave power levels (180W, 300W, 450W and 600W), and dried by oven drying and freeze-drying methods. Drying time was shortened by 72- 95% by microwave drying compared to oven drying. Microwave drying with rotation provided 5.6-23.8% reduction in drying time of peels compared to drying without rotation. Effect of rotation rate on drying time of lemon peels depended on the microwave power level. Page model provided lower SSE, RMSE, and higher R2 values within 5 different thin layer models. The effective moisture diffusivity value, ranging between 1.7x10-8 m2 s -1 -7.6x10-8 m2 s -1, was higher during microwave drying with rotation. The activation energy ranged between 21.3-22.7 W/g. Microwave drying provided higher bulk density, similar or lower water holding capacity and oil retention capacity values compared to freeze drying and oven drying. Freeze dried lemon peel powder had the lowest bulk density due to its porous structure. Microwave drying without rotation and the highest power level caused lower bulk density. At higher power levels, influence of turntable rotation on water holding capacity was more notable. Microwave drying technique can be used as alternative drying techniques to obtain high quality dried lemon peel powder if appropriate processing conditions are selected.

The Drying Kinetics and CFD Multidomain Model of Cocoa Bean Variety CCN51.

The CCN51 cocoa bean variety is known for being highly resistant to diseases and temperature variation and for having a relatively low cultivation risk for the producers. In this work, a computational and experimental study is performed to analyze the mass and heat transfer within the bean when dried by forced convection. A proximal composition analysis is conducted on the bean testa and cotyledon, and the distinct thermophysical properties are determined as a function of temperature for an interval between 40 and 70 °C. A multidomain CFD simulation, coupling a conjugate heat transfer with a semiconjugate mass transfer model, is proposed and compared to the experimental results based on the bean temperature and moisture transport. The numerical simulation predicts the drying behavior well and yields average relative errors of 3.5 and 5.2% for the bean core temperature and the moisture content versus the drying time, respectively. The moisture diffusion is found to be the dominant mechanism in the drying process. Moreover, a diffusion approximation model and given kinetic constants present a good prediction of the bean's drying behavior for constant temperature drying conditions between 40 and 70 °C.

Impact of Microwave-Starch-Blanching on the Drying Kinetics, Transport and Thermophysical Properties of Green Almond

This study aimed to investigate the effect of different pretreatment blanching methods on the drying characteristics of green almonds. Microwave blanching at 300, 450, and 600 W power in the water and/or starch solution (0.5% w/w), water blanching (95℃, 5 min), and starch blanching (0.5% w/w) were preferred. Non-blanched samples were considered as the control samples. All samples were dried at a constant air velocity of 1.5 m/s and temperatures of 70, 90, and 110°C. As drying time increased, moisture ratio of all samples exponentially decreased. Nonlinear regression analysis was used to fit the experimental data to drying models. Effective diffusivities, which ranged from 2.238×10−9 to 6.434×10−9 m2 /s were calculated using Fick's second law of diffusion. Activation energies were determined according to the Arrhenius equation and ranged from 12.32 to 15.39 kJ/kg mol. The highest diffusion coefficient was observed in the microwave starch blanched (600 W-110°C) samples. The highest increases in the diffusion coefficient and decreases in the drying time in comparison with control samples were observed in the microwave-starch (600W- 70°C) samples. Thermal conductivity, density, and specific heat of samples ranged from 0.544-0.586 (W/m K), 3643.85-3900.00 (J/kg K), and 835.80-899.44 (Kg/m3), respectively. The friction drag force, convective heat, and mass transfer coefficients varied from 3.965 to 3.972×10−6 N, 66.29 to 66.44 W/m2 K, and 0.03410 to 0.03428 m/s, respectively. The using microwave-starch blanching pretreatment can significantly decrease the drying time and improve the drying process of green almond at the industrial scale.

Activation energy kinetics in thin-layer drying of onion

The goal of this work was to look at the drying kinetics of onions (Allium cepa L.) and calculate the effective moisture diffusivity and diffusion activation energy. The test was carried out in a constant temperature and humidity test chamber at various temperatures with a relative humidity of 15%. At air temperatures of 45 °C, 50 °C, and 55 °C, the drying time required to reduce the moisture content of onion from 81 percent (wb) to 8 percent (wb) was 23, 19, and 17 hours, respectively. The Henderson-Pabis drying model was used to fit the experimental results to determine the diffusion activation energy (Ea) of onion. Ea was computed as 23.03 kJ/mol. When the drying air temperature was increased from 45 °C to 55 °C, the effective diffusivity of the onion increased from 1.85 109 m/s to 2.42 109 m2/s.

Investigation of the Kinetics of Heat and Moisture Exchange during Heat Treatment and Drying of Thin Wet Thermal Insulation Materials

. The kinetics of drying of thin heat-insulating flat materials has been studied. The approximation of the drying rate curve by various methods is presented. When determining the duration of drying by zonal methods, the equation of the drying rate with the drying coefficient was used. The techniques of processing experimental data by zonal methods of A.V. Lykov, V. V. Krasnikov and by the method of B. S. Sazhin are described. The equation obtained by processing experimental data using the B. S. Sazhin method to determine the duration of the drying process contains only the amount of moisture content of the heating of the material, there is no need to know the critical moisture content. Dependences for calculating the drying coefficient by zonal methods are given. According to the results of the experiment, formulas for determining the duration of heat treatment of thermal insulation materials are presented. The dependence of the relative drying rate on the relative moisture content is presented as well. The processing of experimental data by generalized complex variables creates invariance conditions that allow moving from one variable to another, from one coordinate system to another, which reduces the number of experiments. Formulas with complex variables for determining the duration of drying of materials are given. Based on the drying kinetics equation by A. V. Lykov and the equation for the relative drying rate by G. K. Filonenko, equations are given for determining the density of heat fluxes, the intensity of moisture evaporation and temperature for the period of decreasing drying rate. Solutions of experimental equations are analyzed. The error caused by the processing of experimental data is established. Verification of the reliability of the empirical equations obtained is presented and comparison of the calculated values of the main parameters of the drying kinetics with the experiment is carried out.

Isothermal drying characteristics and kinetic mechanism for tobacco with different water content

The effect of drying temperature on the drying characteristics of tobacco was investigated with different water content. The isothermal drying characteristics and kinetics of three kinds of tobacco on the production line of a tobacco factory in Hubei were studied by halogen water analyzer. The drying characteristics of tobacco with different water content under isothermal conditions were evaluated by water loss characteristics, water diffusion coefficient, and activation energy. The results showed that the drying time of cut tobacco was reduced by increasing the drying temperature within a certain range. The water diffusion coefficient of cut tobacco decreased with the increase of temperature from 70 to 100 °C, and increased with the increase of initial water content. The activation energy of cut tobacco was related to the production process. The activation energy in the experiment was as follows: CT-2 > CT-3 > CT-1. Five drying models were used for non-linear fitting of the drying behavior of tobacco. The fitting degree of the Midilli model was the highest, reaching 0.9944. This data will be useful in the design of tobacco drying equipment.

Earthen-based building: In-situ drying kinetics and shrinkage

Present work focuses on the study of drying and shrinkage kinetics in cob and light earth layers constituting a hybrid walling system. In-situ measurements were performed on the walls of a CobBauge prototype building under construction in Saint-André-de-Bohon (France). To do so, an adapted monitoring system has been designed and implemented. Thus, volumetric water content sensors and dial indicators were immersed and placed in different positions in different walls of the building. Drying kinetic and shrinkage rate in both layers have been measured. Results show that drying and shrinking processes follow an exponential decay in both structural and thermal layers. Correlations between water content and materials shrinkage have been found and discussed. This study will contribute to the optimization of earth construction times in general, and in particular, form-stripping times.

A Review of the Parameters Related to the Rubber Sheets Production: Major Constituents of Rubber Latex, Rubber Particles, Particle Interaction of Rubber Latex, Rubber Porous Structure, Rubber Drying Kinetics and Energy Consumption

Natural rubber (NR) is obtained principally from Para-rubber trees of the species Hevea brasiliensis which grow in tropical regions. Using ultra-centrifugation method, fresh latex (FL) from Para-rubber trees can be mainly divided into four fractions; an upper white layer consists of rubber particles, Frey-Wyssling particles in a yellow or an orange layer, C-serum phase and lutiods particles in the bottom fraction [1-3]. The averages of rubber particles have diameters of 0.02 to 3.0 micron, and they are protected by a complex film containing lipids and proteins [4-8]. The main forces of attraction between neighboring rubber particles in latex system can be divided into five force types; Structural Forces (SF), Van der Waals Interaction (VWI), Electrostatic Force (EF), Exclusion Interaction (EI) and Polymer-Polymer Interaction (PPI) [9]. The porous model of rubber structure used to describe moisture transfer was based on the existence of two different regions referred to as non-hygroscopic region and hygroscopic region. The rubber products drying always produced a considerable shrinkage effect which considered in the physical of the product, such as the diffusion coefficient, mass and heat transfer. An initial moisture content of raw material, the experimental temperature and the drying equipment had affect to the EMC isotherms and the drying kinetics. Finally, discussions on the implications of the results for strategies to reduce the energy consumption in RSS and STR20 block rubber are also presented.

A Pulsed Electric Field Accelerates the Mass Transfer during the Convective Drying of Carrots: Drying and Rehydration Kinetics, Texture, and Carotenoid Content.

The pulsed electric field (PEF) is a non-thermal food processing technology that induces electroporation of the cell membrane thus improving mass transfer through the cell membrane. In this study, the drying and rehydration kinetics, microstructure, and carotenoid content of carrot (Daucus carota) pretreated by PEF during convective drying at 50 °C were investigated. The PEF treatment was conducted with different field strengths (1.0-2.5 kV/cm) using a fixed pulse width of 20 µs and at a pulse frequency of 50 Hz. The PEF 2.5 kV/cm showed the shortest drying time, taking 180 min, whereas the control required 330 min for the same moisture ratio, indicating a 45% reduction in drying time. The rehydration ability also increased as the strengths of PEF increased. PEF 2.5 kV/cm resulted in 27.58% increase in moisture content compared to the control after rehydration (1 h). Three mathematical models were applied to the drying and rehydration data; the Page and Peleg models were selected as the most appropriate models to describe the drying and rehydration kinetics, respectively. The cutting force of the sample was decreased as the strength of PEF increased, and a more homogeneous cellular structure was observed in the PEF pretreatment group. The reduction in drying time by PEF was beneficial to the carotenoid content, and PEF 2.5 kV/cm showed the highest preservation content of carotenoid. Overall, these results suggested that the pretreatment of PEF and the drying and rehydration rate influence the quality of products, functional components, and cellular structure.

Potential application of domestic solar dryers for coriander leaves: Drying kinetics, thermal efficiency, and quality assessment

AbstractCoriander (Coriandrum sativum L.) is a highly perishable crop with a shelf‐life of a few days under refrigerated conditions. Solar drying is one of the economical, hygienic and eco‐friendly methods of food preservation. During this study, fresh coriander was pre‐treated in a solution of 0.1% magnesium chloride, 0.1% sodium bicarbonate and 2.0% KMS for 15 min before solar or open sun drying. There were two types of solar dryers used, namely: PAU advanced domestic solar dryer and PAU domestic solar dryer. Solar dryers were evaluated and compared with open sun drying for drying kinetics, thermal efficiency, and product quality. The quality parameters determined were total color difference, total flavonoid content, total chlorophyll content, and ascorbic acid content. For drying of coriander, ADSD achieved the maximum thermal efficiency (18.56%) and minimum solar energy input (12.56 MJ/kg) out of the various drying systems under consideration. Additionally, ADSD samples had the highest quality retention in terms of the highest total flavonoid content (1.23 mg/100 g), total chlorophyll content (24.14 mg/100 g) and ascorbic acid content (24.29 mg/100 g).

The Effect of Nonthermal Pretreatment on the Drying Kinetics and Quality of Black Garlic.

Black garlic is obtained from regular garlic (Allium sativum L.) through the aging process and consequently gains many health-promoting properties, including antidiabetic and antioxidant. However, the material is still prone to microbiological deterioration and requires a long time to dry due to its properties. Therefore, this study aimed to investigate the effect of various drying methods on the quality of black garlic as well as determine the influence of selected nonthermal pretreatments on the drying kinetics and quality of black garlic, which is especially important in the case of the materials that are difficult to dry. The Weibull model was chosen to describe drying kinetics. Additionally, color, water activity together with antioxidant activity, phenolic compounds, and antidiabetic potential were determined. This study found that the application of a pulsed electric field (PEF), a constant electric field (CEF) as well as a magnetic field (MF) significantly reduced the time of drying (by 32, 40, and 24 min for a PEF, a CEF, and a MF, respectively, compared to combined drying without the pretreatment), and resulted in high antidiabetic potential. However, the highest content of phenolic compounds (1123.54 and 1125.36 mg/100 g dm for VMD125 and CD3h-VMD, respectively) and antioxidant capacity (ABTS = 6.05 and 5.06 mmol Trolox/100 g dm for VMD500 and CD6h-VMD, respectively) were reported for black garlic treated by vacuum-microwave drying and combined convective pre-drying followed by vacuum-microwave drying. Overall, the nonthermal pretreatment decreased the time of drying and showed very good efficiency in maintaining the antidiabetic potential of black garlic, especially in the case of the materials pretreated by a constant electric field (IC50 = 99 and 56 mg/mL, for α-amylase and α-glucosidase, respectively).

Influence of Cross-Linking Conditions on Drying Kinetics of Alginate Hydrogel.

Hydrogels are three-dimensional cross-linked polymeric networks capable of a large amount of fluid retention in their structure. Hydrogel outputs manufactured using additive manufacturing technologies are exposed to water loss, which may change their original shape and dimensions. Therefore, the possibility of retaining water is important in such a structure. In this manuscript, kinetic analysis of water evaporation from sodium alginate-based hydrogels exposed to different environmental conditions such as different temperatures (7 and 23 °C) and ambient humidity (45, 50 and 95%) has been carried out. The influence of the cross-linking method (different calcium chloride concentration-0.05, 0.1 and 0.5 M) of sodium alginate and cross-linking time on the water loss was also considered. Studies have shown that a decrease in the temperature and increase in the storage humidity can have a positive effect on the water retention in the structure. The storage conditions that led to the least weight and volume loss were T 7 °C and 95% humidity. These experiments may help in selecting the appropriate hydrogel preparation method for future applications, as well as their storage conditions for minimum water loss and, consequently, the least change in dimensions and shape.

The Temperature Influence on Drying Kinetics and Physico-Chemical Properties of Pomegranate Peels and Seeds.

Pomegranate is a fruit desirable for its nutritional and medicinal properties which has a great industrial potential that is yet under-explored. Notable for its integral use, the peels are used in medicinal infusions and the seeds consumed without restrictions. In this sense, the objective of this work is to determine the drying kinetics of pomegranate peels and seeds in a hot air circulation oven, at temperatures of 50, 60, and 70 °C, adjust mathematical models to experimental data, determine the effective diffusivities and thermodynamic properties of the process and the physicochemical characteristics of peels and seeds of fresh pomegranates and in their flours. Twelve models were used to adjust the drying kinetics, obtaining better results with the Diffusion Approximation model, Verma, and modified Henderson and Pabis. The effective diffusivities were well represented by an Arrhenius equation, with activation energies of 31.39 kJ/mol for seeds and 10.60 kJ/mol for peels. In the drying process, the seeds showed higher values of enthalpy, entropy, and Gibbs free energy concerning peels. Pomegranate peel and seed flours have proximal composition and distinct physicochemical characteristics, with high fiber, carbohydrate, and energy content. In addition, peel flours stand out for their mineral content, and seed flours do for their lipid and protein content.

Understanding the Impact of Microstructures on Reconstitution and Drying Kinetics of Lyophilized Cake Using X-ray Microscopy and Image-Based Simulation

The drying time of lyophilization and resultant cake microstructure are dependent on each other as water and solvent leave a lyophilized cake. The drying rate affects the size, distribution, and tortuosity of the pores as these macropores evolve during the primary drying phase, which in return impact the further removal of water and solvent from the cake throughout the drying period. This interplay results in a microstructure that determines the reconstitution time for a given formulation. The current study employs advanced X-ray Microscopy (XRM) coupled with mathematical models to correlate the microstructure with the drying kinetics and the reconstitution time. The normalized diffusion coefficients, derived from the reconstructed 3D microstructure of the cake, correlate with the solid content of the pre-lyophilization solution and agree with the mass transfer coefficients from a semi-empirical drying model built with lyophilization process data. Specifically, a solution with less solid content leads to a lyophilized cake with larger pores, thinner walls, and a greater pore volume compared to a solution with more solid content. Consequently, models from the microstructure and drying experiments reveals faster mass transfer independently. While the mass transfer models from the cake structure and the lyophilization process data accurately represents the drying kinetics, both models are inadequate to describe the reconstitution process due to the significant impact from formulation ingredients that alter the mass transfer mechanism via solubility and wettability. In summary, X-ray microscopy imaging and mathematical models are powerful tools that provide insights into the lyophilization process from a new angle.

Experimental Analysis of Drying Conditions’ Effect on the Drying Kinetics and Moisture Desorption Isotherms at Several Temperatures on Food Materials: Corn Case Study

This work studied the effect of external conditions on the drying kinetics of a thin layer of corn during convective drying. The density and the specific volume of the corn grain were reported and the desorption isotherms of the corn were determined at three temperatures and for a water activity from 0.1 to 0.9 using the static gravimetric method. Initially, a thin layer of corn about 7 mm thick with an initial moisture content of 45% (d.b) was investigated, and the external conditions were tested. Afterwards, a comparison between the experimental convective drying of a packed bed and a thin layer was performed under the same conditions. Finally, the values of equilibrium moisture contents, water activities and temperatures obtained were fitted using seven sorption models. It was found that the experimental desorption data exhibited type II behavior, according to Brunauer’s classification. The GAB model was found as the most suitable semi-empirical model which was well suited to represent the desorption equilibrium moisture content of corn kernels in the suggested ranges of temperature and water activity. It can be concluded from the entropy–enthalpy compensation theory that the desorption process of the corn kernels is controlled by the enthalpy mechanism.

Investigation into Solar Drying of Moroccan Strawberry Tree (Arbutus unedo L.) Fruit: Effects on Drying Kinetics and Phenolic Composition

Solar drying is affordable, requiring low energy and an eco-friendly method. Thus, the present paper studies the efficiency and characteristics of the indirect solar convective drying in the fruits of Arbutus unedo L. as well as its effects on the fruit phenolic compounds. The fruit samples were dried at 60 °C, 70 °C, and 80 °C. Phenolic compounds were investigated using a Liquid Chromatography platform. Experimental results revealed that the effective moisture diffusivity determined by Fick’s second law varied from 1.51 × 10−9 to 4.68 × 10−9 m2/s, and the activation energy recorded was 2203.62 kJ/kg. Both the total energy consumption and the specific electrical energy of the dried fruits decreased as temperature increased. The Midilli–Kucuk model was selected as the best-fitted model for drying Arbutus unedo L. Significant effect of temperature on phenolics was observed. The concentration of the phenolic compounds decreased by 15.54, 39, and 40.63% at 60, 70, and 80 °C, respectively.

Methods of calculating the kinetics of drying of natural leather

A method for calculating drying kinetics based on A. V. Lyikov’s kinetics equation and drying rate curves for the drying process of natural leather is presented. Methods of approximating velocity curves to determine the drying time are considered. An equation for calculating the drying time of natural leather with a variable drying factor is presented. Based on the processing of experimental data on drying of natural leathers, equations for calculating heat flux densities, intensity of moisture evaporation and material temperature in the period of falling drying rate are presented. Based on the approximation of drying speed curves for natural leathers, the equations for calculating the drying time by the methods of A. V. Lyikov, V. V. Krasnikov, and N. S. Mikheeva are considered. The dependence of the relative drying rate on the dimensionless moisture content is presented. The reliability of the experimental equations was checked and the calculated values of the drying time and material temperature were compared with the experiment. The proposed approximate methods of calculating the skin drying speed curve make it possible to evaluate the nature of the drying process of a particular material by individual zones of the second period and when changing the drying mode. They also make possible determination of the most important parameters of drying kinetics and reduction of the number of experiments.

MASS CONDUCTIVITY OF FLAT FIBROUS MATERIALS DURING THEIR CONVECTIVE DRYING

The kinetics of drying dense woolen fabric under various temperature conditions was experimentally investigated. The mass-conducting properties of the fabric were determined depending on its moisture content and the temperature of the drying agent. Data on the thermophysical characteristics of drying objects, including mass conductivity coefficients, are necessary for calculating the kinetics of the drying process. Information on mass conductivity coefficients is not available for many materials, including fabrics, since their experimental determination is difficult. Experimental studies of the kinetics of convective drying of dense woolen fabric were carried out on a specially created installation under conditions excluding external diffusion resistance. To calculate the mass conductivity coefficients, a zonal method was used to determine the concentration dependence of the mass conductivity coefficient from the drying kinetics curves obtained at different temperatures. The nonlinear nature of the dependence of the mass conductivity coefficient on the moisture content of the material and the temperature of the drying agent is established. For the convenience of engineering calculations, the obtained data on the mass conductivity coefficients are approximated by formulas expressing their dependence on the moisture content of the material and temperature. The coefficients of mass conductivity calculated by the zonal method using experimental curves of drying kinetics are compared with the coefficients of mass conductivity calculated using the obtained dependence of the coefficients on the moisture content of the material and the temperature of the drying agent. The good quality of the approximation of the experimental curves obtained for the mass conductivity coefficient in this study and the applicability of the latter for calculations are shown. The obtained data on the kinetic coefficients of mass conductivity can be used to calculate the kinetics of the drying process of various dense woolen fabrics.

Effect of slice thickness and hot-air temperature on the kinetics of hot-air drying of Crabapple slices

This study was investigated the effects of hot-air temperature and slice thickness on drying characteristics of Crabapple slices. Drying experiments were carried out in the ranges of 60-90 °C. The thickness conditions of Crabapple slices for thin layer drying were 3mm and 5mm. The increase in the temperature of the hot-air and the decrease in the thickness of the slicing causes the drying time to be significantly shortened. Fick’s diffusion model was applied to describe the water transfer of the Crabapple slices, and the effective diffusion coefficients varied from 0.6142 × 10-8m2/s to 1.9867 × 10-8m2/s in a given range of drying temperature. The effective diffusivity increases with increasing temperature. The activation energy values of Crabapple were 17.46 and 23.82 kJ/mol for the thickness of 3 and 5 mm, respectively. The Page model was revealed to be a better fit to describe the drying curve of Crabapple compared to other models.