Determination of Drying Kinetics for Biomass by Thermogravimetric Analysis under Nonisothermal Condition

The nonisothermal drying kinetics of wheat straw and corn stalk has been studied by thermogravimetry. The experimental data have been obtained in order to fit to semitheoretical models widely used to describe drying behavior of agricultural products. Nonisothermal drying models—Newton, Henderson and Pabis, logarithmic, and Page—were evaluated based on the coefficient of determination (R ²), reduced chi-square (χ ²), and root means square error (RMSE). Page's model has been found to be the best for describing the nonisothermal drying characteristics of wheat straw and corn stalk. The activation energy values of wheat straw and corn stalk are determined to be 14.144 and 6.113 kJ mol^?1, respectively.     

Mathematical modeling and influence of ultrasonic pretreatment on microwave vacuum drying kinetics of lotus (Nelumbo nucifera Gaertn.) seeds

The people of Southeast Asia often use lotus as a highly sought-after food source. Here, the effects of ultrasonic pretreatment on the drying kinetics of lotus (Nelumbo nucifera Gaertn.) seeds under microwave vacuum drying were investigated. The best fit model to predict the drying kinetics was also proposed. Lotus seeds were subjected to ultrasonic pretreatment at frequencies of 20, 35, and 80?kHz and power intensity of 0.75 and 1.50?W/g for 10?min using an ultrasonic bath and then to microwave vacuum drying. Five different mathematical models were fitted to the experimental data and a newly proposed model was selected based on model with highest regression coefficient (R²), lowest root mean square error (RMSE), sum square error (SSE), and chi-square (χ²), respectively. Time-domain nuclear magnetic resonance and field scanning electron microscope were used to describe the water state of ultrasonic samples and examine microstructure, respectively. The results showed that ultrasonic pretreatment performed at a relatively low frequency and relatively high power intensity had a positive effect on reducing the drying time (6.25–31.25%) during microwave vacuum drying because of the redistribution of water and the formation of microchannels. In parallel studies, the new model showed the best fit to the drying curve.     

Microwave Drying Kinetics of a Thin-Layer Liquorice Root

Liquorice root (LR) (Glycyrrize glabra) is known as a sweetener and medicine plant. Drying kinetics of LR with initial moisture content of 49.5% (wet basis (w.b)) were experimentally investigated in a microwave drying system. The drying experiments were carried out at different drying temperatures (40, 45, 50, and 55°C) and microwave power levels (250, 500 and 750 W). Several models from literature were selected to fit the experimental data. The fit quality of models was evaluated using the coefficient of determination (R²), sum square error (SSE), and root mean square error (RMSE). A new model has been proposed for LR drying in the microwave drying. This new model best describes the experimental data for LRs. The activation energy was calculated to be 46.807 kJ/mol and effective diffusivity ranged from 2.9 × 10^?9 to 5.41 × 10^?9 m²/s, depending on drying temperatures at constant microwave power level.     

SHRINKAGE OF APPLE DISKS DURING DRYING BY WARM AIR CONVECTION AND FREEZE DRYING

ABSTRACT

Volumetric and thickness shrinkage evaluated by direct measurement and n-heptane displacement were determined during convective and freeze drying of Golden delicious apples. For convective drying, the influence of blanching and diameter/thickness ratio of the apple disks used were analysed at different levels of moisture content under constant conditions. It was found that shrinkage of dried samples, both by convection and by freeze-drying, is anisotropic to a level which depends on sample geometry (ratio diameter/thickness) used. Blanching did not affect shrinkage results.

Based on results obtained a new model to predict bulk density of materials during drying is proposed, showing a better fit to experimental data than previous models reported in the literature. This model was further used to predict changes in apple porosity during drying.     

Characterization of isotherms and thin-layer drying of red kidney beans,Part I: Choosing appropriate empirical and semitheoretical models

Desorption and adsorption isotherms and drying characteristics of red kidney beans were studied using static and dynamic methods, respectively. The desorption and adsorption isotherms were determined at 60, 50, 40, 30, 20, and 10°C with 32–91% relative humidity (RH). The constant RHs were generated using six saturated salt solutions at constant temperatures. The drying characteristics were determined using a thin-layer dryer with drying air at 50, 40, and 30°C with 35 and 50% RH. The dimensions of the kidney beans before and after drying were measured and shrinkage and sphericity of the beans were calculated. A new method to evaluate the best-fitted equation to characterize the thin-layer drying data was developed. The best-fitted equations to describe the desorption and adsorption isotherms were the modified Chung–Pfost and modified Guggenheim–Anderson–deBoer. The red kidney beans only experienced a falling rate drying period and had a largest shrinkage in the length direction during drying. The Henderson and Pabis model and the modified Page model were the best-fitted models to describe the thin-layer drying data. Using only the values of R² and mean squared error to evaluate the semitheoretical and empirical models might not be enough. The method developed in this study could help develop a semitheoretical or empirical model with a higher accuracy of drying constant, which could be used to estimate the effective water diffusivity.     

Kinetics and Mass Transfer during Atmospheric Freeze Drying of Red Pepper

Drying is applied for moisture removal to allow safe and extended storage. Red pepper (Capsicum annum) samples were heat pump dried in fluidized bed at different air temperatures. A slightly modified solution of the diffusion equation was used to describe the kinetics and drying rates of red pepper. The model well described the low- and medium-temperature drying processes. The determined effective mass diffusivities varied from 0.7831 to 4.0201 × 10^?9 m²/s and increased consistently with drying air temperature. The mass diffusivity was correlated to temperature by linear regression with coefficient of determination equal to 0.999 and negligible standard error.     

Effect of salting techniques on salt uptake and drying kinetics of African catfish (Clarias gariepinus)

Effect of dry salting (DS) and brine salting (BS) techniques on salt uptake and drying kinetics of African catfish (ACF) was investigated. Salt uptake kinetics during BS using the Peleg model at different salt concentrations (0.15–0.27 gNaCl/g) and salting temperatures (30–38 °C) was studied while the drying experiments took place at 60 °C and 1.5 m/s under forced convection. Salt uptake was affected by brine concentration, salting time and temperature during the BS technique but its diffusion among the treated samples was similar. Salt uptake was rapid at the initial salting time but decreases as the process progresses. The Peleg model predicted the salt uptake of ACF better than Zugarramurdi and Lupin model during BS based on high values of coefficient of determination (R²) of 0.930–0.999, very low Chi square (χ²) of 0.16–8.0 × 10⁻¹² and low root mean square error (RMSE) of 0.97–13.93 × 10⁻². The effective salt diffusivity was observed to vary between 1.1 and 9.72 × 10⁻⁷ m²/s. Significant differences in the drying pattern was not observed for both techniques but took place in the falling rate period, although drying rate was faster in DS samples. The Page and modified Page models based on high R² (0.999), low χ² (2 × 10⁻²) and low root mean square error of 1.05 × 10⁻⁴ predicted appropriately the drying kinetics of ACF irrespective of the technique used.     

Thin-Layer Drying Characteristics and Quality Evaluation of Air-Dried Ganoderma Tsugae Murrill

Ganoderma is normally dried to extend its shelf life without using chemical preservative and to concentrate the medicinal value in the fruiting body. Convective hot air drying characteristics of Ganoderma tsugae Murrill were evaluated in hot air circulated oven at different drying temperatures, sizes, and air flow rates. The drying kinetics of Ganoderma tsugae in kidney shape and slices were investigated and compared at different drying conditions. The variation of effective moisture diffusivity values at decreasing moisture contents during drying was determined from the drying data. Four well-known thin-layer drying models were fitted to the experimental data and the Midilli model was found to satisfactory describe the drying characteristics of kidney-shaped Ganoderma tsugae. Ganoderma tsugae dried at 50°C with air velocity of 1.401 ms^?1 showed the highest retention of crude ganoderic acid content compared to other drying conditions.     

An Experimental Study on Freeze-Drying Behavior of Strawberries

In this article, the freeze-drying behavior and the drying kinetics of strawberries were investigated. Drying experiments were performed in a freeze-drying experimental setup constructed in the Department of Mechanical Education, Faculty of Technical Education, Gazi University, Ankara, Turkey. In experiments, 5- and 7-mm-thick sliced strawberry samples have been used. Some models, which were given in the literature, have been used to predict the drying behavior of strawberries. Experimental data findings were fitted for determining the best model to represent the drying behavior of strawberries and the drying kinetics used in these models. It was seen from the correlation coefficient, reduced chi-square, and root mean square error (0.9984, 2.688 × 10^?4, 0.015 and 0.9976, 4.669 × 10^?6, 0.002, respectively) that the Page model could sufficiently describe the drying behavior of 5- and 7-mm strawberry samples.     

Drying of Lentil Including Shrinkage: A Numerical Simulation

Abstract

This article presents a theoretical study about drying of lentil including shrinkage. The two-dimensional unsteady-state diffusion modeling written in the oblate spheroidal coordinates system considers the volume variation effect, convective boundary condition at the surface of the solid, and variable thermo-physical properties. The governing equation was discretized using the finite-volume method and the linear equations system was solved by Gauss-Siedel iterative method. To validate the model, numerical results of the average moisture content were compared with experimental data from eight experiments and a good agreement was obtained. The diffusion coefficients for all drying experiments are determined using the least square error technique.     

Effect of Anhydride Modification on the Thermal Stability of Cultivated Acacia mangium

Abstract

This paper tests the hypothesis that propionic and succinic anhydride modification will improve the thermal stability of cultivated Acacia mangium wood. The thermal stability of modified wood was characterized with thermogravimetric analysis. Evidence of modification was confirmed by Fourier transform infrared analysis. Our results show that chemical modification with anhydrides improves the thermal stability of the Acacia wood. The higher thermal stability of anhydride-modified Acacia wood compared with unmodified wood is attributed to the reduction in hydrophilic nature of the wood due to esterification. Succinylated wood has better thermal stability than propionylated wood based on the values of on-set degradation temperatures, the temperatures at which 30, 50, and 70% degradation occurred, and the activation energy. The improved thermal stability of modified wood compared with the unmodified wood will offer potential for better utilization of Acacia mangium.     

Modeling of combined far-infrared radiation and air drying of a ring shaped-pineapple with/without shrinkage

A ring shape is commonly used for industrial process of pineapple. Unfortunately, there has been no study on modeling of pineapple rings. Therefore we developed the mathematical model of pineapple rings during combined far-infrared radiation and air convection drying to investigate the evolutions of moisture content and qualities. The drying model based on the solution of Fick's law was used to estimate moisture diffusion coefficient (D). The D values with and without taking into account shrinkage phenomenon of dried products were compared. The kinetics of dried pineapple qualities such as color, shear force ratio and shrinkage during drying also were studied. Pineapples were pretreated, cut into rings and dried at far-infrared intensities of 1–5 kW/m² combined with air temperatures of 40–60 °C and air velocities of 0.5–1.5 m/s. The D values were found to increase with increasing intensity and air temperature. The D values with shrinkage consideration were lower than the D values without shrinkage consideration for all drying conditions. The quartic model gave a better fit over the other three polynomial models for describing the color kinetics. The thin layer drying models such as Page, Henderson and Pabis, Logarithmic and Midilli–Kucuk were modified in order to describe shear force ratio (SFR) of dried pineapple. The statistically analyses from this present study indicated that modification of drying models can be used to describe the kinetics of SFR and Midilli–Kucuk's form gave a better fit over the other form. The quadratic model was better than the linear model to predict shrinkage kinetics for all four dimensions (outer radius, inner radius, thickness and volume) of pineapple rings.     

An Experimental Study on Drying of Green Apples

Drying behavior of green apples in a laboratory dryer was examined. Prior to drying, the apples were cut in 8 mm thick slices, which were then treated with citric acid solution and blanched hot water at 80°C. Next, they were dried at 65°C with an air velocity of 2.0 m/s. The shortest drying time (270 min) was obtained with apples pretreated with citric acid solution. The drying data were fitted with 11 mathematical models available in the literature. Selection of the best model was investigated by comparing the determination of coefficient (R ²), reduced chi-square (χ²), root means square error ( RMSE ), and mean relative percentage error (P) between the experimental and predicted values. The results showed that the Wang and Singh, logarithmic, and Verma et al. models gave the best results in describing thin-layer drying of apple slices. The effective moisture diffusivity of pretreated samples with citric acid solution was higher than the other samples.     

Ultrasound-assisted heat pump drying of pea seed

ABSTRACT

The work is for the purpose of studying the influence of drying temperature and ultrasound on drying kinetics, antioxidant enzymes, and germination performance of pea seeds. The drying experiments were performed at air temperature of 30, 35, and 40°C without ultrasound and with three ultrasonic levels of 28?kHz?+?60?W, 28?kHz?+?100?W, and 40?kHz?+?60?W. The antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) and the toxic substances such as malondialdehyde (MDA) of the dried seeds were determined, and germination percentage (GP), germination index (GI), and mean germination time (MGT) were measured. The result showed that high temperature and ultrasound application had significant (P?<?0.05) enhancing of pea seed drying kinetics, which shortened the drying time and improved the diffusion coefficient from 3.528?×?10^?11 to 5.668?×?10^?11?m²/s. Page model can well describe the drying curves under different experiment conditions. Ultrasound application significantly (P?<?0.05) improved the activities of SOD, POD, and CAT and reduced the MDA content. In addition, high ultrasonic power contributed to the increase in GP and GI and the reduction of MGT of seeds.     

Mathematical Modeling of Withering Characteristics of Tea Leaves

The withering characteristics of tea leaves were examined for different temperatures. Tea leaves were withered at a temperature range of 20–45°C with a constant air velocity of 1.1 m/s. The experimental results illustrated the absence of constant-rate drying period and withering took place only in the falling-rate period. During the falling-rate period, at constant drying air flow rate, the drying rate increased and drying time decreased with the increase in drying air temperature. Drying models of Henderson and Pabis and Page were evaluated based on mean bias error (E_MB), root mean square error (E_RMS), correlation coefficient (R²), and the chi square (χ²). The Henderson and Pabis model was found to be a better model for describing the withering characteristics of tea leaves for each of the temperatures of 20, 25, 30, and 35°C. The values obtained from Page model were found to be more reasonable for temperatures of 40 and 45°C than the other model. Both the models closely fitted the withering data within a certain range of temperature. The Henderson and Pabis model gave better prediction and satisfactorily described the withering characteristics of tea leaves at temperatures lower than 40°C whereas the Page model fitted well at temperatures greater than 40°C.     

DRYING OF SOLIDS: THE INFINITE SLAB CONDITION

ABSTRACT

Fourier's second law was solved using convective boundary conditions without considering the shrinkage of the solid. The solutions for a finite and an infinite slab were compared to determine the dimensions for a slab to be considered as infinite. The solutions obtained for Bi = 0.1 and Bi = 100 correspond to heat and mass transfer-controlled processes, respectively, during drying. The results show that the finite slab cannot be considered as infinite, even for R²/R¹ > 20. The relative error obtained when the finite slab was assumed to be infinite was not significant for small Fourier numbers, but it increased as the Fourier number increased; errors were also higher for higher Biot numbers. When the numerical solution of a drying model was obtained for finite and infinite slabs, significant differences in drying kinetics and temperature evolution were observed.     

Drying equations of Thai Hom Mali paddy by using hot air,carbon dioxide and nitrogen gases as drying media

The objective of this study was to develop a drying equation for predicting the thin layer drying kinetics of dried Thai Hom Mali paddy using different drying gases. Thai Hom Mali paddy cv. Khao Dok Mali 105 with initial moisture content of 32% dry basis was dried in a heat pump dryer at 0.4 m/s fixed superficial velocity, 60% fixed evaporator bypass air ratio, and varied drying temperatures of 40, 50, 60 and 70 °C using hot air, CO₂ and N₂ gases as drying media. Drying rate was not affected by drying gases but increased with drying temperatures. Moisture ratios, at any given time during the drying process, were compared among various models, namely, Newton, Page, Modified Page I, Henderson and Pabis, two-term, approximation of diffusion, and Midilli. The effect of drying air temperatures on the coefficients of the best moisture ratio model was determined by single step regression method. The R² coefficient, root mean square error (RMSE) and chi-square (χ²) were criteria for selecting the best model. The study found that the Midilli model was the best model for describing the drying behavior of Thai Hom Mali paddy in every evaluated drying gas. It should be possible to predict the moisture content of a product with a generalized model that shows the effect of drying air temperature on the model constants and coefficients.     

DRYING CHARACTERISTICS OF THE HAZELNUT

Abstract

Equilibrium moisture content isotherms for Spanish hazelnut (Corylus avellana L.) at different temperatures (30°C-80°C) were determined using static gravimetric method. Thin layer drying experiments were done with forced air circulation and were conducted with different operating conditions to determine the drying characteristics of hazelnuts. The effect of air temperature (30°C-70°C), air velocity (0.5 m/s - 2 m/s) and drying bed loading density (50 kg/m² - 150 kg/m²) on drying of unshelled and shelled hazelnuts was studied. Six mathematical models were used to fit the experimental equilibrium moisture content data, from which the G.A.B. model was found to give the best fit. Diffusion coefficients were determined by fitting experimental thin-layer drying curves to the Fick's diffusion model. Variation of the effective diffusion coefficient with temperature was of the Arrhenius type. The Page equation was found to describe adequately the thin layer drying of hazelnut. Page equation drying parameters k and n were correlated with air temperature and relative humidity.     

EFFECT OF CHEMICAL PRETREATMENT ON THE PHYSICAL PROPERTIES OF DEHYDRATED GRAPES

Abstract

The effects of chemical pretreatment and air drying temperature on drying kinetics, shrinkage, density and rehydration ratio of grapes were determined at various moisture contents. It was observed that the chemical pretreatment employed - a solution of 2% CaCCb with 0 to 3% ethyl oleate - increased considerably the drying rate. It was established that the shrinkage increased with drying temperature between 40 to 80°C and decreased with increasing concentration of ethyl oleate in the chemical pretreatment solution.     

KINETICS OF THE CLAY ROOFING TILE CONVECTION DRYING

ABSTRACT

Kinetics of the convection drying process of flat tile has been investigated experimentally in an industrial tunnel dryer. Several velocities of wet tile movement through the dryer were tested to obtain maximum allowable drying rate curve. As there are various models to describe the kinetics of convection drying, finding a model that would fairly well approximate the kinetics of the whole drying process was part of the research. Especially the polynomial and exponential models were tested.

It was found that exponential model of the type: B(t) = (a-B_e. EXP(?bt²) +B_et (?dB(t)/dt) = 2bt(B(t)?B_e significantly correlates the kinetics of the whole tile drying process.

Applying the maximum allowable drying rate curve obtained for flat tile in the first period of drying, a grapho–analytic model for the optimal conducting of the process has been developed.