Convective drying of mango stone for use as biomass.

Mango stone is an interesting biomass by-product with a considerable net calorific value. Mango production has significantly risen in the last few years, meaning that mango waste has increased as well. However, mango stone has a moisture content of about 60% (wet basis) and it is very important to dry the samples for using them in electrical and thermal energy production. In this paper, the main parameters involved in the mass transfer during drying are determined. Drying was carried out in a convective dryer through a set of experiments based on five drying air temperatures (100 °C, 125 °C, 150 °C, 175 °C and 200 °C) and three air velocities (1 m/s, 2 m/s and 3 m/s). Drying times ranged between 2 and 23 h. The drying rate was calculated from the Gaussian model whose values ranged from 1.5·10-6 to 6.3·10-4 s-1. Effective diffusivity was obtained as an overall parameter in the mass diffusion for each test. These values were found between 0.71·10-9 and 13.6·10-9 m2/s. The activation energy was calculated from the Arrhenius law for each test, made at different air velocities. These values were 36.7, 32.2 and 32.1 kJ/mol for 1, 2 and 3 m/s, respectively. This study provides information for future works on design, optimization and numerical simulation models in convective dryers for standard mango stone pieces according to industrial drying conditions.

Mathematical modelling and characterization of drying of pre-treated sweet corn (Zea mays L.) kernels.

The pre-treated sweet corn samples were dried at temperatures of 55, 60, 65 and 70 °C and thin layer drying characteristics of sweet corn were assessed. Mathematical models were fitted and evaluated using R2, χ2, RMSE values. The effective diffusivities for the drying process were 4.32 × 10-10 to 1.08 × 10-9 m2/s and activation energies were 34.51 to 38.99 kJ/mol. Total sugar and ascorbic acid of dehydrated sweet corn kernels varied from 5.50 to 13.00 g/100 g and 3.30 to 10.50 mg/100 g respectively. The sample pre-treated with microwave blanching and dried at 70 °C obtained higher sensory score after rehydration, indicating suitability of the dehydrated sweet corn.

Minimization of the adverse environmental effects of discarded onions by avoiding disposal through dehydration and food-use.

Onion is a commonly used vegetable in the Cuyo Region, Argentina, and important in the world global vegetable production ranking. Production levels often exceed immediate markets of fresh sale, and excesses, although still edible, are currently discarded (mostly incinerated and disposed in landfill, creating numerous environmental hazards). To minimize these adverse environmental problems, this research investigates upgrading the discarded products by dehydration, hence guaranteeing their ultimate food-use. The dehydration process of discarded onion cv. Crioula Roxa was hence studied at 60 and 70 °C, temperatures selected to maintain the main physicochemical characteristics of the onions, while also creating optimum heat and mass transfer coefficients while significantly reducing the energy consumption and CO2 emissions. When using an electrically-heated convective dryer, the Specific Energy Consumption (SEC) values and the CO2 emissions during dehydration at 70 °C are 738.89 kWh.kg-1 and 264.74 kg of CO2 kg-1, respectively. These values are only 41.61 kWh.kg-1 and 2-4 kg of CO2 kg-1 if a solar dryer is applied. The thermal diffusivities were 1.86✕10-10 m2 s-1 (dehydration) and 1.08✕10-10 m2 s-1 (rehydration), showing a weak effect of the dehydration process on the solid structure and properties.

Drying characteristics of ready-to-eat komal chawal rice: processing and modeling.

A traditional ready-to-eat rice from Assam, India, known as komal chawal is produced by steaming of steeped chokuwa paddy, which is a low-amylose variety, and by drying the steamed paddy under shade as a measure of controlling the drying rate for sustenance of a quick rehydration quality. As an improvement over this traditional method in terms of production time, komal chawal is produced by parboiling the chokuwa brown rice with model predicted soaking and steaming conditions. Thin-layer drying behavior of the steamed brown rice was studied at drying temperatures of 40-60 °C, at an air velocity of 1 m/s. Among different thin-layer drying models, Page equation fitted best to the drying data, with the coefficient of determination (R2) and root mean square error as the measures for selection of the best fitted model. While the moisture diffusivity values were in the range of 2.08 × 10-10-3.34 × 10-10 m2/s, the effects of drying air temperature on the drying rate was modeled with an activation energy of 20.44 kJ/mol for an the Arrhenius kind of temperature dependence of diffusivity. Based on the effects of drying temperature on rehydration, textural, and pasting properties of the product a lower drying temperature is recommended.

Foaming properties of custard apple pulp and mathematical modelling of foam mat drying.

Foaming of custard apple pulp was carried out using foaming agent and stabilizer for drying of pulp in thin layers. The effect of parameters was studied and optimization was performed using response surface methodology. The concentration of egg albumen (0-20%, w/w) as foaming agent with methyl cellulose (0.0-0.50%, w/w) as stabilizer were added for whipping time (5-25 min). The foam properties were influenced by concentration of foaming agent and whipping time. The desirable foaming properties (high foam expansion, lower foam density and high foam stability) was observed at 15% of egg albumen, 0.37% of methyl cellulose for a whipping time of 17.32 min. Dehydration of optimized foamed pulp was completed within 100-140 min for 60-75 °C temperatures at 2 mm thickness of pulp. Average effective diffusivities remained 2.01-9.67 × 10-08 m2/s and activation energy was 29.99 kJ/mol.

Ultrasound pre-treatment prior to unripe banana air-drying: effect of the ultrasonic volumetric power on the kinetic parameters.

Aiming to decrease the water content during the air-drying process of unripe banana slices, ultrasound (US) pre-treatments (25 °C) for 20 and 25 min at 9.38 and 25.63 W/L ultrasonic volumetric power were evaluated. Air-drying was performed at 50 and 60 °C for 360 min. Unripe banana slices pretreated at 25.63 W/L did not improve water migration, under either air-drying temperature, while slices pretreated at 9.38 W/L resulted in an increase in water effective diffusivity of 4.8 and 13.7% at 20 min US + air-drying at 50 °C and 25 min US + air-drying at 60 °C, respectively. The drying time saving of 7% and 9%, respectively, was achieved, showing that these treatments were alternative for processing unripe banana slices. Thus, ultrasound and air-drying operational parameters required accurately defined to achieve desirable results. Experimental data were adjusted to four models and the Midilli model resulted in the best experimental data fit, with r 2 > 0.9988, RMSE < 0.0873 and χ2 < 0.00996.

Application of novel, low-cost, laterite-based adsorbent for removal of lead from water: Equilibrium, kinetic and thermodynamic studies.

Contamination of groundwater by carcinogenic heavy metal, e.g., lead is an important issue and possibility of using a natural rock, laterite, is explored in this work to mitigate this problem. Treated laterite (TL- prepared using hydrochloric acid and sodium hydroxide) was successfully utilized for this purpose. The adsorbent was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), and Fourier Transform Infrared Spectroscopy (FTIR) to highlight its physical and chemical properties. Optimized equilibrium conditions were 1 g L(-1) adsorbent concentration, 0.26 mm size and a pH of 7 ± 0.2. Monolayer adsorption capacity of lead on treated laterite was 15 mg/g, 14.5 and 13 mg g(-1) at temperatures of 303 K, 313 K and 323 K, respectively. The adsorption was exothermic and physical in nature. At 303 K, value of effective diffusivity of (De) and mass transfer co-efficient (Kf) of lead onto TL were 6.5 × 10(-10) m(2)/s and 3.3 × 10(-4) m/s, respectively (solved from shrinking core model of adsorption kinetics). Magnesium and sulphate show highest interference effect on the adsorption of lead by TL. Efficacy of the adsorbent has been verified using real-life contaminated groundwater. Thus, this work demonstrates performance of a cost-effective media for lead removal.

Effect of Hot Water Blanching Time and Drying Temperature on the Thin Layer Drying Kinetics of and Anthocyanin Degradation in Black Carrot (Daucus carota L.) Shreds.

This study was conducted to investigate the effect of blanching treatment (98 °C for 3 and 6 min) and air drying temperature of 40, 50 and 60 °C on the thin layer drying characteristics such as drying time, drying rate constant, effective moisture diffusivity and activation energy, as well as on anthocyanin content of black carrot shreds. It was observed that drying temperature affected the drying rate but blanching did not have an effect on drying time. Three thin layer drying models, i.e. Page, Lewis and Henderson-Pabis were evaluated. The goodness of these models was evaluated based on the coefficient of determination (R2), root mean square error, reduced chi square (χ2) and standard error. Page model showed the best fit to the drying data. The effective diffusivity ranges of 1.4·10-9 to 2.6·10-9 m2/s, 1.3·10-9 to 2.1·10-9 m2/s and 1.5·10-9 to 2.2·10-9 m2/s after 3 or 6 min of blanching and control samples respectively were calculated using Fick's second law. The activation energy of 37.5, 26.0 and 34.6 kJ/(mol·K) of the control samples and samples blanched for 3 or 6 min respectively was determined from the Arrhenius plot. The blanching treatment affected the anthocyanin content to a great extent. The anthocyanin content of (231.7±2.9) and (278.8±7.8) mg per 100 g was recorded in samples blanched for 3 and 6 min and then dried at 60 °C, and (153.0±4.3) and (247.0±5.5) mg per 100 g was recorded at 40 °C as compared to the control of (580.1±1.3) at 60 °C and (466.7±1.1) mg per 100 g at 40 °C.

Thin-layer modeling of convective and microwave-convective drying of oyster mushroom (Pleurotus ostreatus).

Oyster mushroom samples were dried under selected convective, microwave-convective drying conditions in a recirculatory hot-air dryer and microwave assisted hot-air dryer (2.45 GHz, 1.5 kW) respectively. Only falling rate period and no constant rate period, was exhibited in both the drying technique. The experimental moisture loss data were fitted to selected semi-theoretical thin-layer drying equations. The mathematical models were compared according to three statistical parameters, i.e. correlation coefficient, reduced chi-square and residual mean sum of squares. Among all the models, Midilli et al. model was found to have the best fit as suggested by 0.99 of square correlation coefficient, 0.000043 of reduced-chi square and 0.0023 of residual sum of square. The highest effective moisture diffusivity varying from 10.16 × 10(-8) to 16.18 × 10(-8) m(2)/s over the temperature range was observed in microwave-convective drying at an air velocity of 1.5 m/s and the activation energy was calculated to be 16.95 kJ/mol. The above findings can aid to select the most suitable operating conditions, so as to design drying equipment accordingly.

Impacts of permeability and effective diffusivity of porous scaffolds on bone ingrowth: In silico and in vivo analyses.

The permeability and the effective diffusivity of a porous scaffold are critical in the bone-ingrowth process. However, design guidelines for porous structures are still lacking due to inadequate understanding of the complex physiological processes involved. In this study, a model integrating the fundamental biological processes of bone regeneration was constructed to investigate the roles of permeability and effective diffusivity in regulating bone deposition in scaffolds. The in silico analysis results were confirmed in vivo by examining bone depositions in three diamond lattice scaffolds manufactured using selective laser melting. The findings show that the scaffolds with better permeability and effective diffusivity had deeper bone ingrowth and greater bone volume. Compared to permeability, effective diffusivity exhibited greater sensitivity to the orientation of porous structures, and bone ingrowth was deeper in the directions with higher effective diffusivity in spite of identical pore size. A 4.8-fold increase in permeability and a 1.6-fold increase in effective diffusivity by changing the porous structure led to a 1.5-fold increase in newly formed bone. The effective diffusivity of the porous scaffold affects the distribution of osteogenic growth factor, which in turn impacts cell migration and bone deposition through chemotaxis effects. Therefore, effective diffusivity may be a more suitable indicator for porous scaffolds because our study shows changes in this parameter determine changes in bone distribution and bone volume.

Mathematical modeling of drying of pretreated and untreated pumpkin.

In this study, drying characteristics of pretreated and untreated pumpkin were examined in a hot-air dryer at air temperatures within a range of 40-80 °C and a constant air velocity of 1.5 m/s. The drying was observed to be in the falling-rate drying period and thus liquid diffusion is the main mechanism of moisture movement from the internal regions to the product surface. The experimental drying data for the pumpkin fruits were used to fit Exponential, General exponential, Logarithmic, Page, Midilli-Kucuk and Parabolic model and the statistical validity of models tested were determined by non-linear regression analysis. The Parabolic model had the highest R(2) and lowest χ(2) and RMSE values. This indicates that the Parabolic model is appropriate to describe the dehydration behavior for the pumpkin.

Mathematical modeling on vacuum drying of Zizyphus jujuba Miller slices.

The thin-layer vacuum drying behavior of Zizyphus jujuba Miller slices was experimentally investigated at the temperature of 50, 60, and 70 °C and the mathematical models were used to fit the thin-layer vacuum drying of Z. jujuba slices. The increase in drying air temperature resulted in a decrease in drying time. The drying rate was found to increase with temperature, thereby reducing the total drying time. It was found that Z. jujuba slices with thickness of 4 mm would be dried up to 0.08 kg water/kg dry matter in the range of 180-600 min in the vacuum dryer at the studied temperature range from 70 to 50 °C. The Midilli et al. model was selected as the most appropriate model to describe the thin-layer drying of Z. jujuba slices. The diffusivity coefficient increased linearly over the temperature range from 1.47 × 10(-10) to 3.27 × 10(-10) m(2)/s, as obtained using Fick's second law. The temperature dependence of the effective diffusivity coefficient followed an Arrhenius-type relationship. The activation energy for the moisture diffusion was determined to be 36.76 kJ/mol.

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.

Smelling Peppers and Pout Submitted to Convective Drying: Mathematical Modeling, Thermodynamic Properties and Proximal Composition.

Pepper (Capsicum spp.) is among the oldest and most cultivated crops on the planet. Its fruits are widely used as natural condiments in the food industry for their color, flavor, and pungency properties. Peppers have abundant production; on the other hand, their fruits are perishable, deteriorating within a few days after harvesting. Therefore, they need adequate conservation methods to increase their useful life. This study aimed to mathematically model the drying kinetics of smelling peppers (Capsicum chinense) and pout peppers (Capsicum chinense Jacq.) to obtain the thermodynamic properties involved in the process and to determine the influence of drying on the proximal composition of these peppers. Whole peppers, containing the seeds, were dried in an oven with forced air circulation, at temperatures of 50, 60, 70, and 80 °C, with an air speed of 1.0 m/s. Ten models were adjusted to the experimental data, but the Midilli model was the one that provided the best values of coefficient of determination and lowest values of the mean squared deviation and chi-square value in most of the temperatures under study. The effective diffusivities were well represented by an Arrhenius equation, appearing in the order of 10-10 m2·s-1 for both materials under study, since the activation energy of the smelling pepper was 31.01 kJ·mol-1 and was 30.11 kJ·mol-1 in the pout pepper, respectively. Thermodynamic properties in both processes of drying the peppers pointed to a non-spontaneous process, with positive values of enthalpy and Gibbs free energy and negative values of entropy. Regarding the influence of drying on the proximal composition, it was observed that, with the increase in temperature, there was a decrease in the water content and the concentration of macronutrients (lipids, proteins, and carbohydrates), providing an increase in the energy value. The powders obtained in the study were presented as an alternative for the technological and industrial use of peppers, favoring obtaining a new condiment, rich in bioactives, providing the market with a new option of powdered product that can be consumed directly and even adopted by the industry as a raw material in the preparation of mixed seasonings and in the formulation of various food products.

Infrared drying of sweet potato (Ipomoea batatas L.) slices.

The effect of different infrared power levels (104, 125, 146 and 167 W) on drying kinetics and rehydration ratio of sweet potato slices was investigated. It was observed that the power levels affected the drying time and rehydration ratio. The increase in infrared power level decreased the drying time. The experimental data obtained from drying study were fitted with Newton, Henderson and Pabis and Logarithmic models to evaluate the drying kinetics of the sweet potato slices. The fit quality of the proposed models was evaluated by using the determination of coefficient (R (2) ), mean relative percent error (P), reduced chi-square (χ (2) ) and root means square error (RMSE). Among the three drying models, the Logarithmic model gave a better fit over the other two models. Effective diffusivity varied from 1.31 × 10(-10) to 3.66 × 10(-10) m(2)/s and was significantly influenced by infrared power.

Mathematical modelling of thin layer hot air drying of carrot pomace.

Thin layer carrot pomace drying characteristics were evaluated in a laboratory scale hot air forced convective dryer. The drying experiments were carried out at 60, 65, 70 & 75 °C and at an air velocity of 0.7 m/s. Mathematical models were tested to fit drying data of carrot pomace. The whole drying process of carrot pomace took place in a falling rate period except a very short accelerating period at the beginning. The average values of effective diffusivity ranged from 2.74 × 10(-9) to 4.64 × 10(-9) m(2)/s for drying carrot pomace. The activation energy value was 23.05 kJ/mol for the whole falling rate period.

Effects of temperature and grain size on diffusivity of aluminium: electromigration experiment and molecular dynamic simulation.

Understanding the atomic diffusion features in metallic material is significant to explain the diffusion-controlled physical processes. In this paper, using electromigration experiments and molecular dynamic (MD) simulations, we investigate the effects of grain size and temperature on the self-diffusion of polycrystalline aluminium (Al). The mass transport due to electromigration are accelerated by increasing temperature and decreasing grain size. Magnitudes of effective diffusivity (Deff) and grain boundary diffusivity (DGBs) are experimentally determined, in which theDeffchanges as a function of grain size and temperature, butDGBsis independent of the grain size, only affected by the temperature. Moreover, MD simulations of atomic diffusion in polycrystalline Al demonstrate those observations from experiments. Based on MD results, the Arrhenius equation ofDGBsand empirical formula of the thickness of grain boundaries at various temperatures are obtained. In total,DeffandDGBsobtained in the present study agree with literature results, and a comprehensive result of diffusivities related to the grain size is presented.

Kinetics of moisture loss applied to the baking of snacks with pregelatinized cassava starch.

Moisture loss kinetics is a complex process defined as the liquid removal from a solid by thermal application. The purposes of the study were to obtain kinetic curves of moisture loss during the baking of cassava snacks and establish which processes govern the moisture loss, recognize which mathematical models describe the moisture loss curves more precisely, and determine activation energy (Ea) and effective diffusivity (Deff ). Experimental data were obtained through baking at four temperatures formulations for snacks with different dehydrated cassava puree (DCP) proportions. Page's and Chávez Méndez's models showed the best fits. We calculated Deff and Ea employing the analytical solution of Fick's Second Law for the geometry of plane plates. Deff values increase with DCP but did not show a trend. The range found was from 5.22E-06 to 2.93E-05 m2 /s. The results of Ea showed that the mixture of flours produced an increase in the energy necessary to initiate the effective diffusion (24.84 kJ/mol) compared to the samples without mixing (15.54 kJ/mol). Moisture loss curves show that the diffusion process governs a large part of the process. PRACTICAL APPLICATION: Given the need to increase research for the development of the cassava industry, which currently has low competitiveness compared to less expensive products such as corn, various efforts are being made to generate new products that can replace wheat flour, at least in part. However, it is necessary to research how this substitution affects the various steps of the production system, including baking. During baking, one of the most significant processes is moisture loss. In this sense, the kinetic modeling of the moisture loss process parameters is mainly helpful in the food industry. The mathematical models of moisture loss processes are used to design new or improved baking systems or even control the process.

Convective drying kinetics of faecal sludge from VIP latrines.

In striving to achieve sustainable sanitation, one challenge is to ensure hygienic treatment of faecal sludge from on-site sanitation. Thermal drying is an important treatment step for moisture removal and disinfection. Improved understanding of the drying process is crucial for the proper design of treatment technologies for faecal sludge. In this study, faecal sludge from ventilated improved pit (VIP) latrines from Durban, South Africa, were dried in a convective drying thermobalance by varying the temperature from 40 to 80 °C, the relative humidity from 0 to 25% and the air velocity from 0.3 to 1.2 mm/s. The faecal sludge samples were in the form of a thin layer and pellets with different diameters from 8 to 14 mm. Kinetic parameters were determined from the experimental data, were compared to classical drying models in literature and were then used to develop a correlative drying model. Drying rates ranged between 1 and 40 g/min/m2, leading to drying times comprised between 100 and 300 min. The drying kinetics increased as temperature was higher, and pellet diameter and relative humidity were lower. Temperature had the greatest influence on the drying kinetics (in both the constant and falling rate periods), followed by the effect of pellet diameter. The drying kinetics were affected in a moderate way by the relative humidity in the constant rate period and part of the falling rate period. The air velocity had a slight effect of drying kinetics during the constant rate period, but this becomes insignificant during the falling rate period. The effective diffusivities increased from 7.81 × 10-8 to 1.97 × 10-7 m2/s by increasing the temperature from 40° to 80 °C, leading to an activation energy of 23 kJ/mol. These values are typical from those found for wastewater sludge. The sludge exhibited a critical moisture content varying between 2.4 and 3.2 g/g db during drying without a clear trend as a function of the operating conditions and suggested that sludge was composed of considerably more bound moisture than unbound. The experimental data fitted the most closely to the Page model and, based on this, a new model was proposed for the prediction of drying times across the range of explored temperatures and pellet diameters in this study. The results of the proposed model fitted the experimental data with acceptable accuracy, so that the developed model could be employed as an analytical tool for the design, operation and optimisation of drying equipment.

Effect of Swell-Drying on Mango (Mangifera indica) Drying Kinetics.

Swell-Drying operation (SD) was applied on mangoes to evaluate its effect on drying kinetics: starting accessibility (δW), apparent drying coefficient (Dapp), and time to obtain a final moisture content of 20% d.b (tf = 20% d.b). Swell-drying consisted of (1) submitting fresh mangoes to a first pre-drying stage under Convective Air Drying (CAD) until a moisture content of 37% d.b; (2) applying Instant Controlled Pressure Drop (DIC) treatments on pre-dried mangoes by following a central composite rotatable design (steam pressure: 0.2-0.6 MPa and treatment time: 5 and 55 s); and (3) apply post-drying of mangoes under CAD. In both cases, CAD was performed at 60 °C and airflow of 1 m/s. Results showed that both the treatment time and the steam pressure impacted the Dapp and the δW. By comparing to the control, SD (0.54 MPa and 48 s) increased the Dapp and δW to 12.2 and 2.7 times, respectively. Moreover, SD triggers a significant reduction in post-drying time (tf = 20% d.b), being this of 2.4 h vs. 30.8 h. These results could be linked to the expansion of the internal pores of mangoes generated by the instant autovaporization of residual water triggered by DIC treatment.