Hygroscopic Equilibrium Research Articles

Teor de água de equilíbrio: Uso de sensores de umidade relativa do ar intergranular em silos

ABSTRACT Grains are hygroscopic materials and, during storage, they are subject to exchanging moisture with the environment according to temperature and relative air humidity, making it important to monitor these factors. Digital temperature and relative air humidity sensors appear as an alternative for monitoring the moisture of grain mass inside silos; they are simple to install and use. Digital sensors present outstanding precision in temperature measurements. The objective in this study was to assess the efficiency and applicability of intergranular relative air humidity sensors linked to digital temperature sensors in the thermometry system of silos storing soybeans. Two samples of soybeans were analyzed in the upper, middle and lower thirds of the silo, for grain mass temperature, intergranular relative air humidity, estimated equilibrium moisture content according to collected data, and moisture content of the sampled grains. Moisture contents obtained from sensor measurements using the hygroscopic equilibrium equation and determined using the oven method were compared. The equilibrium moisture content estimated by the data provided by the sensors did not differ by the Tukey test (p ≤ 0.05) from the moisture content determined by the oven method. Digital temperature and relative air humidity sensors have proven to be efficient, as they contribute to estimating the equilibrium moisture content with satisfactory precision.

Hygroscopic growth and collision studies of atmospheric aerosols across scaled particle sizes

In this paper, the hygroscopic growth and collision evolution of ammonium sulfate droplets are calculated at both the continuum and transition regime scales, and the results show that the variation of particle size across the scales will have a significant effect on the direction and degree of hygroscopic evolution of particles as well as the number of new particles generated by collision. At the continuum regime scale, solute effects determine whether water vapor condenses on the particle surface or escapes into the atmosphere. At the transition regime scale, curvature effects will result in an 80% overestimation of the hygroscopic growth of ammonium sulfate droplets and a threefold increase in the time to reach hygroscopic equilibrium. Collision results show that the droplet concentration decreased by 97% for 25 nm droplets, and increased by 13% for 250 nm droplets, which suggests that small droplets are more influenced by collision.

Effect of drying temperature on antioxidant activity, phenolic compound profile and hygroscopic behavior of pomegranate peel and seed flours

The aim of this study was to evaluate the effect of drying temperature on the quality of pomegranate peel (PPF) and seed (PSF) flours. The flours were obtained after drying the peel and seed at temperatures of 50, 60 and 70 °C until they reached hygroscopic equilibrium, were crushed and characterized in terms of phenolic compound profile, antioxidant activity and hygroscopic behaviour using water adsorption isotherms. Seventeen individual phenolic compounds were identified, quantified in PSF and 21 in PPF, with PPF having a higher phenolic content and antioxidant capacity compared to PSF; there was an influence of temperature on the profile of total phenolic compounds, with the highest concentrations being observed in samples obtained at 60 °C. All the models fitted to the water adsorption data of the PPF and PSF flours can be used to estimate the isotherms, especially the Peleg model. The PSF isotherms were classified as Type II and the PPF isotherms as Type III. The flours evaluated in this study represent an alternative for the technological and industrial use of pomegranate peel and seeds, favoring the production of new condiments with important bioactive properties.

Mathematical models and X-ray image analysis in the drying of cumbaru seeds

The cumbaru (Dipteryx alata Vog.) is a native species of the Cerrado. The species is of great economic expression for family farming. This study aimed to determine the drying curves and fit mathematical models to the experimental data obtained in the drying of cumbaru seeds. Furthermore, it aimed to define the best-fitted model and correlate the damage caused by the drying process through X-ray images. The Dipteryx alata Vog. seeds were obtained from fruits collected from 20 matrices in the municipality of Cáceres, in the state of Mato Grosso (MT), approximately 255 days after anthesis. The seeds were extracted and stored for 15 days until they reached hygroscopic equilibrium and a 14.5% water content. Drying was conducted in a continuous airflow dryer with an approximate temperature of 40° and a constant airflow velocity of 2.5 m/s. The experimental data were fitted to twelve mathematical models. The values of the coefficients of determination (R2), the relative mean error (P), and the estimated mean error (SE) were used to check the models’ fit degree. After drying, 40 seeds from each treatment were subjected to X-ray testing using the Faxitron MX-20 DC 12 equipment. The Midilli mathematical model was the best fit for the experimental data. The X-ray images showed no cracks or any other damage caused by the drying process.

Monitoring of intergranular variables for predicting technical breakage of wheat grains stored in vertical silos

The increase in the silos temperature and intergranular relative humidity can alter the equilibrium moisture content of the grains mass causing losses. Thus, the objective was to evaluate the temporal monitoring of temperature, relative humidity, and intergranular carbon dioxide for the prediction of dry matter loss in wheat grains stored in vertical silos, using a mathematical model and machine learning algorithms. Under these conditions, wheat grains had a slight increase in metabolic activity, causing a dry matter loss of 0.035–0.041%. The intergranular temperature, relative humidity, and carbon dioxide results were similar to the measurements on the surface of the grain mass. It was concluded that the monitoring of temperature, relative humidity, and the concentration of carbon dioxide in the intergranular air indirectly and early determined the changes in the quality of wheat grains during storage. Although the metabolic activity of wheat grains was low, as the lots remained in hygroscopic equilibrium with moisture contents close to 12% (w.b.), the temporal detection characterized the loss of dry matter and the reduction of grain weight stored. Finally, the Artificial Neural Networks and Multiple Linear Regression model satisfactorily predicted the dry matter loss of stored wheat grain mass.

Hygromechanical behaviour of wooden panel paintings: classification of their deformation tendencies based on numerical modelling and experimental results

Wooden panel paintings are among the most important historical and artistic artworks from the Middle Ages and the Renaissance period. Currently, they represent a challenge for conservators and scientists who face complex issues related to their conservation. Panel paintings can be considered multilayer objects, that for brevity can be considered to consist of a wooden support and various paint layers. The wooden support is known to be hygroscopic and is continuously seeking hygroscopic equilibrium with the humidity of the environment, thus it tends to deform. Based on various hygroscopic tests carried out on 6 real panel paintings chosen by expert restorers to represent different periods and construction techniques, this paper describes the deformation tendencies of the selected panel paintings. Among possible variables, three most important variables were identified: (a) tree ring orientation of the wooden support, (b) stiffness and (c) emissivity of the paint layers. The internal equilibrium of the forces, governed by the moisture gradients across the thickness of the wood, changes drastically according to the varying characterisation of these factors. To observe their individual contributions, the 6 panel paintings underwent various humidity cycles, were completely free to deform and were always in complete safety. To characterise the stiffness and emissivity of the paint layers, the 6 panel paintings underwent a few humidity cycles with the front face totally waterproofed; thus, the moisture exchange was forced from the back only, and one of the three variables was eliminated. A complex system emerges where the tree ring orientation of the wooden support, the stiffness and emissivity of the paint layers are strongly coupled and determine the deformation modes of the panel paintings. A numerical analysis was conducted to classify the various general deformation modes of panel paintings and the specific classification of the 6 real panel paintings analysed experimentally. The complexity of the interaction of the variables studied suggests that experimental procedures must be conducted in preparation for numerical analyses of real panel paintings.

Multivariate analysis in mathematical model selection to describe Croton urucurana Baill drying kinetics

The Croton urucurana Baill species is known in Brazil as “sangra d’água” and is popular due to its medicinal properties. For better processing of herbal medicines, it is essential that efficient drying and storage techniques are developed and that compounds are preserved. Therefore, this study aimed to select models through multivariate cluster analysis applying Akaike (AIC) and Bayesian information criteria (BIC) to describe Croton urucurana leaves drying kinetics at different temperatures (40-70 °C). The initial moisture content in Croton urucurana leaves was 1.791, 1.841, 2.196 and 2.144 kg water kg dry matter-1, and 8.25, 7.75, 4.25 and 2 hours were required to reach hygroscopic equilibrium, with a final moisture content of 0.134, 0.105, 0.065 and 0.0601 kg water kg dry matter-1, at 40, 50, 60 and 70 °C, respectively. The models with the greatest similarity to the experimental data were Diffusion Approximation; Cavalcanti Mata; Two-term; Two-term Exponential; Modified Henderson & Pabis; Logarithmic; Midilli; Page and Verma. The multivariate cluster technique associated with AIC and BIC criteria during model selection is a great applicability tool to help decision-making when evaluating the drying plant leaves. The Cavalcanti Mata mathematical model was selected to represent the drying kinetics.

Sorption and diffusion properties of untreated and thermally modified beech wood dust

Dynamic water vapor sorption experiments were carried out using beech wood dust (from untreated and thermally modified wood) of two-particle sizes, (< 25 and 80–250 µm), obtained from abrasive sanding. Sorption isotherms were parameterized with the GAB and GDW models. Dust from thermally modified wood had significantly lower equilibrium moisture content compared to dust from untreated material, due to the reduction in primary sorption sites in treated material. The observed changes were quantified by the coefficients of the GAB and GDW models. Thermal modification and size of wood dust particles had no influence on binding energy of water molecules being linked to the secondary sorption sites. Water diffusivity decreased significantly with increasing moisture content, but only for monolayer sorption. For higher moisture content values, water diffusivity was practically independent of moisture content. These results were found for untreated and thermally modified material as well as for both dust size fractions. The influence of thermal modification on water diffusivity was unclear, which is attributed to the diffusion model, which represents dust particles as spheres and assumes instant hygroscopic equilibrium. Overall, this study indicates that the effectiveness of filtration processes likely depends strongly on sorption and diffusion properties of wood dust only at low moisture contents within the hygroscopic range.

Experimental Determination and Modeling of the Moisture-Sorption Isotherms and Isosteric Heat of Tobacco Leaves

During a forced convection sun drying and storage operation, the equilibrium water content of a product to be dried is critical. These figures are frequently derived using isothermal sorption curves. The calculation of isotherms is a necessary step in determining the distribution and intensity of water connections in products. for that this paper concentrates on the experimental determination of the adsorption-desorption isotherms for various temperatures (40, 50, and 60℃) of the Nicotiana Tabacum L plants. From which we had established the relationship between the water activity and the water content in the product. However, the aforementioned determination was carried out by the static gravimetric method. Eight saturated salt solutions have been utilized in applications such as (KOH, KCl, MgCl2, MgNO3, K2CO3, BaCl2, K2SO4, and NaCl). Hygroscopic equilibrium was completed after 13 days for temperature 40℃, 11 days for 50℃, and 9 days for 60℃. The overall experimental sorption curves are summarized by six models (HENDERSON, modified HALSEY, OSWIN, GAB, modified BET, and PELEG). The sorption isotherms built using the Clausius–Clapeyron equation were used to determine the net isosteric temperatures of desorption and adsorption of Nicotiana Tabacum L. The results for the adsorption-desorption isotherms found are type III according to IUAPC. Following the smoothing of the experimental results by different used models, it was found that the models of GAB and Peleg allow having the lowest mean relative errors and correlation coefficient.

Desorption isotherms and isosteric heat of baru almond flour

Baru almond (Dipteryx alata Vogel) is a nutritional and tasty product; the flour of this product is used in culinary recipes. In the processing of the almond, the chemical composition and structure of the product changes, influencing the hygroscopicity of the material. Thus, the objective was to determine the behavior of the water activity of baru almond flour at different temperatures, adjusting the best mathematical model to estimate the isotherms, as well as to determine the isosteric heat of desorption. The almonds were dried for moisture contents in the range of 5.4 to 3.3 ± 0.03% dry basis (d.b.), then the almonds were processed in an industrial blender to obtain the flours. To determine the desorption isotherms, the static-indirect method was used, in which the water activity was obtained at temperatures of 10, 20, 30, and 40 ºC, using the Hygropalm Model Aw1 equipment. The hygroscopic equilibrium moisture content of baru almond flour was directly proportional to water activity and decreased with increasing temperature, to the same water activity value. The Chung-Pfost model was the one that best represented the product’s isotherms. The integral isosteric heat of desorption of baru almond flour ranged from 2590.69 to 2519.52 for the moisture content range of 3.24 to 5.43% d.b.

Moisture adsorption isotherms of baru almond flours

The whole meal (WBF) and partially defatted Baru almond (PDBF) flour have commercial and nutritional attractions. The study of the adsorption behavior is essential for correct storage. Thus, the objective was to determine the moisture adsorption isotherms for WBF and PDBF, at temperatures of 20, 30, and 35 °C, in the range of water activity from 0.070 to 0.975. The static gravimetric method was used. Fourteen models were adjusted to the experimental hygroscopic equilibrium humidity data. The GAB model better represented the moisture adsorption isotherms for WBF, while the BET model represented the PDBF. The curves of the two flours were classified as type III. Safe storage for WBF occurs at equilibrium humidity of 6.41, 7.12, and 7.49% d.b., and for PDBF at 9.04, 9.26, and 9.41% d.b., at the respective temperatures of 25, 30, and 35 °C.

Direct measurement of aerosol acidity using pH testing paper and hygroscopic equilibrium under high relative humidity

Acidity is a critical characteristic of aerosol particles that impacts many atmospheric chemical reactions. However, the measurement of aerosol acidity remains challenging because of the high ionic strength of atmospheric aerosol particles. In this study, we developed and evaluated a direct method for measuring the pH of atmospheric aerosol samples using pH testing paper. We first examined the color responses of six pH testing papers under various ionic strengths and selected the best performing paper for further testing at higher ionic strength. This paper was then tested under realistic high-ionic-strength conditions created using hygroscopic equilibrium under high and constant relative humidity (RH). A KNO3 saturated solution was used to maintain an RH of 92% in an airtight box. Under these conditions, the hygroscopic constituents in aerosol particles form droplets of aqueous solutions that possess high ionic strength. On the basis of these results, a method for the direct pH measurement of aerosol particle samples was developed. The pH of the atmospheric aerosol samples was measured using this method under high RH to demonstrate its versatility. Our results indicate that this method requires more than approximately 12 μg per spot of fine (PM0.2–2.0 in this study) particles to form a detectable droplet. Compared with previous methods, our direct pH measurement method is simpler, more convenient, and reliable for wide application without excess dilution in practice, and it may be used to obtain important basic information required to study atmospheric aerosols.

THERMODYNAMIC PROPERTIES OF WHITE BEAN GRAINS FOR DIFFERENT EQUILIBRIUM WATER CONTENTS

In drying processes and in the storage of agricultural products, the study of thermodynamic properties is indispensable in the search for solutions to issues of stability and optimization of the conditions of agro-industrial processes. The aim of this work was to determine hygroscopic equilibrium isotherms and study the thermodynamic properties of white bean grains submitted to different equilibrium temperatures and relative humidity levels. Phaseolus vulgaris L. grains were used, with an initial water content of 0.142 (dry basis), temperature variations ranging between 18 and 50 °C, and relative humidity between 19% and 78%. Fifteen mathematical models were tested to determine the hygroscopic equilibrium isotherms, and the Sigma model was the one that best suited the experimental data. The thermodynamic properties of the beans were determined from Sigma-Copace model. The integral isosteric heat of desorption and the differential entropy increased with the reduction of the water content, and the phenomenon of water desorption of white bean grains was a non-spontaneous process controlled by enthalpy.

Drying of Sisal Fiber: A Numerical Analysis by Finite-Volumes

Vegetable fibers have inspired studies in academia and industry, because of their good characteristics appropriated for many technological applications. Sisal fibers (Agave sisalana variety), when extracted from the leaf, are wet and must be dried to reduce moisture content, minimizing deterioration and degradation for long time. The control of the drying process plays an important role to guarantee maximum quality of the fibers related to mechanical strength and color. In this sense, this research aims to evaluate the drying of sisal fibers in an oven with mechanical air circulation. For this purpose, a transient and 3D mathematical model has been developed to predict moisture removal and heating of a fiber porous bed, and drying experiments were carried out at different drying conditions. The advanced model considers bed porosity, fiber and bed moisture, simultaneous heat and mass transfer, and heat transport due to conduction, convection and evaporation. Simulated drying and heating curves and the hygroscopic equilibrium moisture content of the sisal fibers are presented and compared with the experimental data, and good concordance was obtained. Results of moisture content and temperature distribution within the fiber porous bed are presented and discussed in details. It was observed that the moisture removal and temperature kinetics of the sisal fibers were affected by the temperature and relative humidity of the drying air, being more accentuated at higher temperature and lower relative humidity, and the drying process occurred in a falling rate period.

Isotermas e calor isostérico de dessorção das sementes de tungue

&lt;p&gt;&lt;span class="fontstyle0"&gt;The tung is a species that has potential for biodiesel production, so for safe storage there is a need to get to know its hygroscopicity. The objective of this work was to determine the desorption isotherms based on the recommendation of a mathematical model, to define the safe moisture content for storage, and to obtain the isosteric heat for the tung seeds. In order to obtain the hygroscopic equilibrium water content, the static method was used, with 20g of seeds surrounded by a permeable tissue, and placed inside the desiccators containing salt solutions, in a BOD chamber with temperatures of 20, 25, At 30 and 35 ºC, water activity ranged from 0.14 to 0.812 decimal.The Akaike information criterion (AIC) and Bayesian Schwarz information criterion (BIC) were used to adjust the mathematical models and to help choose the best one. Among the tested models, ChungPfost was elected to represent the desorption isotherms of tung seeds. Integral isosteric desorption heat values in the equilibrium moisture content range from 2.08 to 8.35 (% b.s.) ranged from 3754 to 2555 kJ kg&lt;/span&gt;&lt;span class="fontstyle0"&gt;-1&lt;/span&gt; &lt;br /&gt;&lt;br /&gt;&lt;/p&gt;

Solar drying of residue from Brazil nut processing

Abstract Brazil nuts are often used for direct consumption or in the preparation process of water-soluble extract. After obtaining the water-soluble extract, a large amount of Brazil nut residues with good sensory characteristics are generated. Thus, this study aimed to dry Brazil nut processing residues in layers with different thicknesses in a direct solar dryer as well as by direct exposure to the sun, in order to fit different mathematical models to the experimental data of drying kinetics, and calculate the drying rates and effective diffusivity. The drying procedures began at 9 a.m. on a concrete base, for samples dried by direct exposure to the sun, and in a solar dryer constructed with expanded polystyrene foam zinc plated and a glass cover. The mass loss of the samples was monitored by weighing at regular times until the hygroscopic equilibrium was obtained. The direct solar dryer had temperatures about 80% higher than those recorded in the open environmental air temperature. Drying rates were higher in dehydrations performed in the solar dryer compared to the drying by exposure to the sun. The Midilli model was selected as the most adequate for predicting the drying of the samples under all experimental conditions, showing coefficients of determination above 0.99. The effective diffusion coefficients of moisture were higher in samples dehydrated in the solar dryer when compared to those dried by exposure to the sun. Regarding the research conducted under the experimental conditions of this study, the performance of the solar dryer to dry Brazil nut processing residues was satisfactory.

Potential of Briquette Produced with Torrefied Agroforestry Biomass to Generate Energy

Agroforestry industries, such as sugar-alcohol, food, and logging, produce large quantities of waste, used to generate energy from direct burning. The application of other processes, such as torrefaction and briquetting, can increase the profits from the use of agro-industrial waste for energy generation. Briquetting is an alternative for using these wastes, allowing the compaction of the biomass, generating a biofuel with high energy density, and which is more homogeneous and easier to store and transport. The objective of this study was to evaluate the physical and chemical properties of four biomass types (wastes from sawed eucalypt and pine wood, coffee pruning wastes, and sugarcane bagasse) torrefied at 300 °C and compacted (briquetting) at pressures of 6.21, 8.27, and 10.34 MPa. The torrefaction increased the fixed carbon content, ash, and calorific value, and reduced the volatile material content and hygroscopic equilibrium moisture of the biomasses. The volatile material content was lower and the fixed carbon higher in the coffee pruning waste, the ash content higher in the sugarcane bagasse, and the calorific value higher in the pine and eucalypt wood. The briquetting and the torrefaction processes increased the biomass bulk density, and the useful calorific value, respectively, and consequently the energy density of the briquettes produced with torrefied raw material under high pressure. The mechanical properties of the briquettes produced with all materials increased with the compaction pressure. Torrefaction and briquetting increased the energy potential of the biomasses evaluated to produce energy from clean technology.

Secagem de fibras de sisal em leito fixo: uma análise preditiva usando modelos concentrados

Fibras de sisal tem despertado o interesse da academia e indústria, devido as suas excelentes características para uso em diversas aplicações. Essas fibras, ao serem extraídas da planta, estão úmidas e, são submetidas a secagem para redução do teor de umidade. O controle do processo de secagem é de grande importância para garantir a qualidade das fibras em termos de resistência mecânica e coloração. Nesse sentido, este trabalho tem como objetivo estudar teoricamente a secagem de fibras de sisal em estufa com circulação forçada de ar. Foram propostos modelos matemáticos para predizer o comportamento transiente do teor de umidade médio e temperatura superficial, e do teor de umidade de equilíbrio das fibras, em função da temperatura do ar de secagem e concentração de vapor de água no leito de fibras. Resultados preditos das cinéticas de secagem e aquecimento, e do teor de umidade de equilíbrio higroscópico das fibras são apresentados e comparados com os dados experimentais, em diferentes condições operacionais. Verificou-se que um bom ajuste foi obtido, com coeficiente de correlação maior que 0,99, para todos os modelos analisados.

Drying kinetics and thermodynamic properties of bitter melon (Momordica charantia L.) leaves

ABSTRACT Bitter melon (Momordica charantia L.) is a versatile plant that can be consumed as a food and has therapeutic applications. Studying its drying process is important to maintain their leaf quality during storage. The objective of this study was to evaluate the drying kinetics of bitter melon leaves and determine their thermodynamic properties. The leaves were placed in polyethylene trays and subjected to drying in an oven at temperatures of 20, 30, 40, and 50 °C until reaching hygroscopic equilibrium. The experimental data were fitted to several non-linear regression models to characterize the drying process. The Arrhenius model was used to obtain the coefficients of diffusion and the activation energy, which were used to calculate the enthalpy, entropy, and the Gibbs free energy. Midilli and Page were the best models to represent the drying kinetics of bitter melon leaves at temperatures of 20, 30, 40, and 50 °C. Increases in the drying air temperature increased the Gibbs free energy and water diffusivity in the interior of the leaves. Enthalpy and entropy decreased as the temperature was increased.

Quantification of Changes in Relative Humidity and Seed Moisture Contents of Canola Cultivars under Different Temperatures Using Hygroscopic Equilibrium Curve

Quantification of Changes in Relative Humidity and Seed Moisture Contents of Canola Cultivars under Different Temperatures Using Hygroscopic Equilibrium Curve