Hygroscopic Equilibrium Research Articles

Hysteresis and thermodynamic properties of water sorption in ‘Malagueta’ pepper seeds

ABSTRACT The objective of this study was to determine hysteresis, enthalpy, entropy, enthalpy-entropy compensation theory and Gibbs free energy for water adsorption and desorption in ‘Malagueta’ pepper seeds. Hygroscopic equilibrium moisture contents were determined by the static gravimetric method, with water activity in the range from 0.29 to 0.90 and temperatures of 30, 40 and 50 °C. The hysteresis of the ‘Malagueta’ pepper seeds reduces with the increase of temperature. Enthalpy, entropy and Gibbs free energy of adsorption and desorption increase with the reduction of the moisture content of the seeds. The enthalpy-entropy compensation theory is valid for the sorption processes. The sorption of water between seeds and the surrounding air is a non-spontaneous process.

Experimental study of hygroscopic equilibrium and thermodynamic properties of sewage sludge

A good knowledge of the hygroscopic behavior of sewage sludge is one of the keys to a better perception of the subsequent management of Sewage sludge such as drying, storage or other valorization processes. The present work aims to determine, experimentally, the sorption isotherms of sewage sludge generated at the wastewater treatment plant of Marrakesh city in Morocco by using saturated salt solutions method at different temperatures.The obtained results show that, at constant water activity, the increase in temperature leads to a decrease of the sorption curves. Seven statistical models have been used for modeling and analyzing the experimental data of sorption. The Peleg model seems to be the most appropriate to describe the desorption and adsorption isotherm curves of sewage sludge with the highest value of correlation coefficient.Thermodynamic properties of sewage sludge were determined by using the hygroscopic equilibrium data at different temperatures, the net isosteric heat of sorption and entropy of sorption decreased considerably with the increase in equilibrium moisture content. The enthalpy–entropy compensation suggested that the sorption mechanism involved was enthalpy given. Gibbs free energy for adsorption and desorption are respectively 58.87 kJ/mol, and -445.21 kJ/mol, indicating two different processes.

Desorption isotherms of heavy (AZOBE, EBONY) and light heavyweight tropical woods (IROKO, SAPELLI) of Cameroon

This work is centered on the study of the desorption isotherms of heavy (Azobe, Ebony) and heavyweight (Iroko, Sapelli) tropical woods, which contribute in the determination of drying and storage of tropical plank woods. Desorption isotherms of tropical woods were experimentally determined under different temperatures in this study using the gravimetric method. The determination of Henderson’s model isotherms parameters of desorption were obtained for temperatures of 20 °C, 30 °C, 40 °C, and 50 °C. The mean relative deviation between theoretical and experimental moisture contents was calculated and fitted well with the desorption models of tropical woods. We noticed that Henderson models fitted much better with experimental ones for 95% of relative humidity. The sigmoid shapes of results are satisfactory. Hysteresis phenomenon was observed for desorption isotherms of heavy (Azobe, Ebony) and heavyweight (Iroko, Sapelli) tropical woods. Results showed the difference between the stability and use of heavy and heavyweight tropical wood. These results help in the estimation of water content at equilibrium of tropical woods in relative humidity from experimented ones. Hygroscopic equilibrium humidity of heavy tropical woods varied between 0% and 50% while those of heavyweight varied between 0% and 25%. Therefore, these woods can be used in an opened environment; woodwork and decoration.

Effect of homogeneous static magnetic treatment on the adsorption capacity in maize seeds (Zea mays L.).

In order to analyze the treatment of seeds with homogeneous static magnetic field on the water adsorption process, an experimental-theoretical study of hygroscopic equilibrium in maize seeds (Zea mays L. cv. ICAV305) was carried out. Four treatments with magnetic induction of 80.0, 120.0, 160.0, and 200.0 mT were applied for 10 min, and there was a control group without treatment. The doses were selected because they showed a decrease in mean germination time. Treated seeds were subjected to an environment with a stable temperature of 30.0 °C ± 0.1 °C and atmospheres of different relative humidity (h), using eight salt solutions saturated with water activity between 0.216 and 0.970. Curves were adjusted using the D'Arcy-Watt and modified Oswin models. It was found that the magnetic treatment of seeds affects adsorption, and the 200 mT-10 min one was the most significant in affecting the mechanisms of adsorption of water, and increasing the number of adsorption sites connected to weak binds with D'Arcy-Watt's adjustment. Using the Oswin model for simulation, we verified that the magnetic stimulus affected the enthalpy of adsorption and the mechanism of incorporation of water vapor molecules to the structure of seminal cover. These results show that the magnetic pre-treatment of seeds has an effect on a seed's specific biophysical and physiological processes in the early stages of germination. Bioelectromagnetics. 39:343-351, 2018. © 2018 Wiley Periodicals, Inc.

Mathematical modeling of drying the pulped coffee (Coffea arabica l.) at different air conditions

The aim of the study was to describe the drying kinetics of washed coffee (Coffea arabicaL.) and evaluate the best mathematical model to fit the experimental drying data conducted with different air humidity (40 %, 50 %, and 60 %) and temperatures (23 °C, 40 °C, and 60 °C). The fruit shakes were standardized washing, separation, and manual selection of green coffees, pass cane, and green buoy. Then, approx. 150 L of coffee cherries were pulped and taken directly to the yard. Drying the washed coffee was completed in a mechanical dryer and yard. The obtained results showed that the different conditions of the ambient air significantly influenced the processes of drying pulped coffee. The water content of the hygroscopic equilibrium of pulped coffee is directly proportional to the water activity and relative humidity, decreasing with increasing temperature, for the same value of equilibrium relative humidity. The Oswin model was best represented by the hygroscopicity of the pulped coffee, while the Midilli model shows the best fit to describe the drying curves of the washed coffee. The effective diffusion coefficient increases with increasing temperature of the drying air and reducing of relative humidity, being described by the Arrhenius equation. The aim of the study was to describe the drying kinetics of washed coffee (Coffea arabica L.) and evaluate the best mathematical model to fit the experimental drying data conducted with different air humidity (40 %, 50 %, and 60 %) and temperatures (23 °C, 40 °C, and 60 °C). The fruit shakes were standardized washing, separation, and manual selection of green coffees, pass cane, and green buoy. Then, approx. 150 L of coffee cherries were pulped and taken directly to the yard. Drying the washed coffee was completed in a mechanical dryer and yard. The obtained results showed that the different conditions of the ambient air significantly influenced the processes of drying pulped coffee. The water content of the hygroscopic equilibrium of pulped coffee is directly proportional to the water activity and relative humidity, decreasing with increasing temperature, for the same value of equilibrium relative humidity. The Oswin model was best represented by the hygroscopicity of the pulped coffee, while the Midilli model shows the best fit to describe the drying curves of the washed coffee. The effective diffusion coefficient increases with increasing temperature of the drying air and reducing of relative humidity, being described by the Arrhenius equation

Determination of the hygroscopic equilibrium and isosteric heat of aji chili pepper

ABSTRACT This study focuses on the determination of the hygroscopic equilibrium and isosteric heat of the aji chili pepper (Capsicum baccatum) under different controlled temperature and relative air humidity conditions. In addition, the objective was to adjust the model among the existing literature models that best represent the isothermal sorption behavior, as well as propose a new model to represent this phenomenon. Having obtained the mathematical models and experimental data, the best model and parameters that represent the hygroscopicity and the isosteric heat satisfactorily was determined. The temperatures used were 30, 55, and 70 °C, with water activity levels from 0.11 to 0.84. The model that best fit the data had a R2 value of 0.97. The integral isosteric heat of sorption for ‘Dedo-de-Moça’ chili pepper within a moisture content from 0.07 to 0.55 (dry basis) ranged from 3641.66 to 2614.38 kJ kg-1.

Desorption isotherms of Lactuca sativa seeds

ABSTRACT Lactuca sativa seeds are highly sensitive to climate conditions; thus, they should be stored securely to maintain their qualitative and quantitative characteristics. Studies on hygroscopicity aim to decrease possible changes in agricultural products under specific environmental conditions. Accordingly, this study aims to develop an appropriate mathematical model to represent the desorption isotherms of Lactuca sativa seeds. The hygroscopic equilibrium was achieved using a static-gravimetric method at temperatures of 10, 20, 30, 40 and 50 °C and water activity in the range 0.11-0.96. Six mathematical models were fitted to the experimental data of the equilibrium moisture content of Lactuca sativa seeds. The best model was chosen based on the determination coefficient (R2), magnitude of mean relative error (MRE), standard deviation of the estimate (SDE), and analysis of residue distribution. The modified Oswin model best represented the hygroscopicity of the Lactuca sativa seeds, with values of 8.02% and 0.55 for the MRE and SDE, respectively; moreover, the residual values were randomly distributed. The shape of the isotherms of the Lactuca sativa seeds estimated using the modified Oswin model is sigmoidal, which is characteristic of a type II curve.

Hygroscopic equilibrium of microencapsulated extract of passion fruit seed and its effect on the antioxidant capacity

AbstractThe hygroscopic behavior of microcapsules of antioxidant extract of defatted passion fruit seed, produced using spray drying technique, was analyzed at 20 and 40 °C by the static method with saturated saline solutions. The isosteric heat of sorption of the microcapsules, concentration of phenolic compounds and piceatannol, and the antioxidant capacity using ABTS and DPPH methods were measured during storage at different relative humidities. The isotherms were classified as GAB isotherms, exhibiting a Type II behavior. Isosteric heat of sorption decreased when the relative humidity increased and critical equilibrium moisture reached 61%. The microencapsulated extracts retained their antioxidant capacities within the evaluated conditions, what suggests that it may be applied in food at any of these water activity values.Practical applicationsPiceatannol is a stilbene with expressive antioxidant capacity which can be found in passion fruit seeds. In this work, the seeds were used to obtain the crude hydroethanolic extract which was microencapsulated by spray drying. The hygroscopic behavior of the microencapsulated extract of piceatannol was evaluated by fitting the data on different isotherm theoretical models. It was possible to verify the interference of the water activity in the antioxidant capacity and establish a relationship with possible critical storage conditions of the microencapsulated extract.

<b>Kinetic modeling of water sorption by roasted and ground coffee

The objective of this study was to model the kinetics of water sorption in roasted and ground coffee. Crude Arabica coffee beans with an initial moisture content of 0.1234 kg w kg dm -1 were used. These beans were roasted to a medium roast level (SCCA # 55) and ground at three particle sizes: coarse (1.19 mm), medium (0.84 mm) and fine (0.59 mm). To obtain the water sorption isotherms and the isosteric heat, different conditions of temperature and relative humidity were analyzed using the dynamic method at 25oC (0.50, 0.60, 0.70, and 0.80 of RH) and 30°C (0.30, 0.40, 0.50, 0.60, 0.70, and 0.80 of RH) and using the static method at 25oC (0.332 and 0.438 of RH). The GAB model best represented the hygroscopic equilibrium of roasted coffee at every particle size. Isosteric heat of sorption for the fine particle size increased with increments of equilibrium moisture content, indicating a strong bond energy between water molecules and the product components. The Gibbs free energy decreased with the increase in equilibrium moisture content and with temperature.

Hygroscopicity of baru (Dipteryx alata Vogel) fruit

ABSTRACT With the knowledge on the hygroscopic equilibrium of the baru (Dipteryx alata Vogel) fruit, the product can be adequately handled to maintain the moisture content at the levels recommended for safe storage. Thus, this paper aimed to determine the water desorption isotherms of baru fruits at temperatures of 20, 25, 30 and 35 °C, and water activity between 0.14 and 0.80, and obtain the values of isosteric heat of desorption as a function of the equilibrium moisture content of the product. The equilibrium moisture content was obtained using the static-gravimetric method. Modified Halsey was the best model recommended to represent the hygroscopicity of baru fruits. The recommended moisture contents for safe storage of baru fruits are not more than 19.9, 19.3, 18.6 and 18.0 (%, d.b.) for the respective temperatures of 20, 25, 30 and 35 °C. The integral isosteric heat of desorption increases as the water content decreases, leading to an increment in the energy required to remove water from the product.

Drying of Castor Bean Fruits (<i>Ricinus communis </i>L., "BRS Energia" Variety): An Experimental Investigation

This work aims to realize an experimental investigation of the drying of castor bean fruits (Ricinus communis L., “BRS Energia” variety) in oven. Results of the average moisture content and surface temperature of the product as a function of time were analyzed for different drying air temperatures (40, 50, 60, 70, 80, 90 and 100°C). Results shows that increasing drying temperature and decreasing air relative humidity we have an increases in the drying rate and more quickly the castor fruits reaches both thermal and hygroscopic equilibrium. It was found that high drying rates generates hydric and thermal stresses inside the product, causing cracks and deformations in the castor bean fruits.

Modelagem matemática das curvas de secagem de grãos de feijão carioca

This work aims to characterize the kinetics of the drying process of Carioca, BRS Estilo and Canadense beans, to adjust different mathematical models. The product has undergone a drying process in an oven at temperatures of 35, 55 and 65oC. Samples were placed in metal trays with grille fund, in three repetitions. During the drying process, trays with samples were weighed periodically until it reached the constant mass. The mathematical models were adjusted according to collected data provided by Statistica 12.0 software, and parameters to select the best model were: the adjusted coefficient of determination, the average relative error, and the estimated average error. The time required for BRS Estilo achieve constant mass was 58.33, 48.83 and 21.58 h at temperatures of 35, 55 and 65°C, respectively, The mathematical Midilli model was recommended for modeling the drying process at temperatures of 35, 55 and 65°C, respectively, and the mathematical model Midilli of two terms was recommended at temperature of 55°C. The time required by Canadiens to achieve hygroscopic equilibrium was 57.42, 46.00 and 20.91 h on 35, 55 and 65°C, respectively, the most recommended mathematical model at 35°C was the Midilli and model for the temperatures of 55 and 65oC the Thompson model.

Non-Fickian moisture diffusion in thermally modified beech wood analyzed by the inverse method

Non-Fickian diffusion in native and thermally modified wood was analyzed by the inverse method. A low quality of the identified diffusivity values was found for the diffusivity which was either constant or varying with water content. This was explained by the non-Fickian behavior. It was especially distinct for thermally modified wood for which an increased delay in obtaining the hygroscopic equilibrium was clearly shown. Such a delay was explained by time required for molecular reorganization to produce new sorption sites. This phenomenon was accounted to improve the physical model by modifying the convective boundary condition. A relaxation mechanism was used for this purpose with an adequate time constant.

Particle size and roasting on water sorption in conilon coffee during storage

The aim of this work was to evaluate alterations on the water sorption of coffee due to the effect of roast, grind and storage in two temperatures (10 and 30 oC) during 180 days. Crude grain coffee (Coffea canephora) with average initial moisture content of 12.61 % (d.b.) was used. Grain was roasted at two levels: medium light (ML) and moderately dark (MD). Afterwards, grain was processed in three different particle sizes: fine (0.59 mm), medium (0.84 mm) and coarse (1.19 mm), besides the whole coffee lot. Samples prepared were then stored in two temperatures (10 and 30 oC). These were analyzed during six months, at five distinct times (0, 30, 60, 120 and 180 days) regarding moisture content and water activity. Furthermore, mathematical modeling and thermodynamic properties acquisition of the coffee moisture adsorption process were accomplished. A split plot design was used, in which plots consisted of storage period and split-plots consisted of a 2 x 4 x 2 factorial (two roasting degrees, four particle sizes and two storage temperatures), with five repetitions.It was concluded thatparticle size did not significantly affectedmoisture content of coffee, independently of roast degree; Sigma-Copace model best represented hygroscopic equilibrium for sorption of roasted coffee; with moisture content reduction, an increase of differential enthalpy and entropy of sorption and Gibbs free energy occurs.

Roasting, Grinding, and Storage Impact on Thermodynamic Properties and Adsorption Isotherms of Arabica Coffee

This work aimed to evaluate alterations on the water sorption of coffee due to roast, grind, and storage. Crude grain coffee (Coffea arabica) was roasted at two levels: medium light and moderately dark. Grain was grinded in fine (0.59 mm), medium (0.84 mm), and coarse (1.19 mm) particle sizes, besides the whole coffee lot. Samples were then stored at polypropylene bags and kept at biochemical oxygen demand type chambers in two storage temperatures (10 and 30C). These were analyzed at 0, 30, 60, 120, and 180 days, regarding water content and water activity. Mathematical modeling and thermodynamic properties of coffee moisture adsorption process were accomplished. It was concluded that particle size did not significantly affect water content of coffee, independently of roast degree. Sigma-Copace model best represented hygroscopic equilibrium of roasted coffee. Water content reduction increases the differential enthalpy and entropy of sorption and Gibbs free energy. Practical Applications Commercialization of crude grain coffee, soluble coffee, roasted, and grinded coffee, among others (extract, essences, and concentrated) represents 9.2% of Brazilian exportation. Higher distances lead to physical, chemical, and microbiological changes in agricultural products. This trend could cause the deterioration of food products. Information on the sorption characteristics of roasted and grinded coffee could not be found in the literature, regardless of this culture importance. Sorption isotherms data are key information to predict optimum storage and trading conditions to ensure quality. Finally, the lack of quality may affect employees, entrepreneurs, and other professionals that works with coffee. This article presents the adsorption isotherms and thermodynamic properties of roasted and grinded coffee (Coffea arabica L.).

Desorption isotherms and isosteric heat of 'cajuzinho-do-cerrado' achenes

ABSTRACT The objective of this study was to determine the desorption isotherms of 'cajuzinho-do-cerrado' achenes (Anacardium humile St. Hil.) in various conditions of temperature and water activity, as well as to select the one that best represents the phenomenon and to determine the isosteric heat of desorption. The fruits were collected at the Emas National Park, in the municipality of Mineiros-GO, Brazil, pulped and then subjected to drying in silica gel at temperature of 25 ± 2 °C until the moisture contents of 17.6, 13.6, 11.1, 8.7 and 5.3 (d.b.%). After drying, the desorption isotherms were determined by the indirect static method. The water activity (Aw) was determined at different temperatures, and the achenes were placed in a B.O.D. chamber, regulated at 10, 20, 30 and 40 °C. Data of hygroscopic equilibrium moisture content were fitted to different mathematical models through non-linear regression analysis, using the Gauss-Newton method. The Copace model was the one that best represented the hygroscopicity of 'cajuzinho-do-cerrado' achenes, while the integral isosteric heat of desorption of 'cajuzinho-do-cerrado' achenes for the moisture content range of 4.51 to 13.40 (% d.b.) varied from 2,734.82 to 2,548.49 kJ kg-1.

Efeito do Tipo de Chapa de Partículas nas Propriedades Físicas e Mecânicas

RESUMO Este trabalho teve como objetivo avaliar chapas de partículas do tipo aglomerado convencional, chapas tipo Medium Density Particleboard (MDP) e as do tipo aglomerado com inclusão laminar. As chapas avaliadas foram fabricadas com partículas de Acacia mangium e no aglomerado com inclusão laminar utilizaram-se lâminas de Schizolobium amazonicum. O aglomerado convencional e o aglomerado com inclusão laminar apresentaram umidade de equilíbrio higroscópico estatisticamente superior ao MDP. O aglomerado com inclusão laminar apresentou maior índice de inchamento em espessura após duas horas de imersão em água, valores de módulo de ruptura em flexão estática maiores e maior resistência ao arrancamento de parafuso. As chapas do tipo MDP apresentaram maior resistência à tração perpendicular. Não foram observadas diferenças significativas nas demais propriedades. Conclui-se que a inclusão laminar melhorou o módulo de ruptura e o arrancamento de parafuso, enquanto a utilização de partículas finas nas faces melhorou as propriedades físicas das chapas.

Evaluation of briquettes made from textile industry solid waste

The biosludge was mixed with cotton textile industry residues in ratios of 0, 25, 50, 75 and 100% and briquettes were manufactured in a lab-scale machine at three compaction pressures 6205, 8274 and 10342 kPa. The heating value, chemical characteristic, density, resistance to compression and hygroscopic moisture equilibrium were analyzed. The compaction pressure of 6205 kPa proved ideal for the briquetting process in the laboratory scale because in this pressure the briquettes had the higher percentages of fixed carbon, high heating value and compressive strength, and the lowest ash content. Pressure had no effect on density and hygroscopic equilibrium moisture content of the briquettes. The best mixing proportion between the two residues was 25% of sludge because, with this percentage, it is possible to obtain briquettes with high contents of volatile matter, fixed carbon, higher heating value, density and compressive strength, and lower ash content and hygroscopic equilibrium moisture. It was possible to conclude that the mixing of residues for the production of briquettes can optimize their physical-chemical and mechanical characteristics depending on the mixing ratio used.

<b>Priming and stress under high humidity and temperature on the physiological quality of <i>Brachiaria brizantha</i> cv. MG-5 seeds

Palisade grass is a forage plant that is widely used in pasture cropping in the Brazilian savannah. The aim of this experiment was to evaluate palisade grass (Brachiaria brizantha cv. MG-5) seeds subjected to priming and stress at high humidity and temperature (before and after conditioning). The experimental design was completely randomized in a 2x5 factorial arrangement. Seeds were exposed to stress under high humidity and temperature (before and after conditioning) and five priming treatments (Water (Control), potassium nitrate (KNO3) at 0.2%, calcium nitrate Ca(NO3)2 at 0.2%, gibberellin (GA3) at 0.2% and glucose at 10%) with four replications. Two experiments were performed: Experiment I - seed with chemical scarification using H2SO4 and Experiment II - without scarification. The stress on the seed was applied using artificial aging at 41°C for 96 hours. Seed priming was accomplished by immersion at 25°C for 2 hours. Thereafter, the seeds were oven-dried at 35°C until they regained hygroscopic equilibrium. Seed germination and vigor were evaluated. Priming using KNO3 and Ca(NO3)2 produced seeds with high tolerance to stress under high temperature, and this process is efficient to overcome dormancy.

Physical and mechanical properties of heat treated wood from Aspidosperma populifolium, dipteryx odorata and mimosa scabrella

Heat treatment improves some wood properties namely: equilibrium moisture, dimensional stability and durability and mechanical properties. In this study, the heat treatment was applied to woods of three natural species from Brazil: Aspidosperma populifolium (peroba mica), Dipteryx odorata (cumaru) and Mimosa scabrella (bracatinga). The woods were heated in an oven under vacuum and under nitrogen, at 180, 200, and 220°C for one hour. The untreated and heat-treated woods were characterized in relation to equilibrium moisture content, basic density, shrinkage, Janka hardness, and bending MOR and MOE according to NBR 7190 standards. All the thermal rectified woods showed a reduction in the hygroscopic equilibrium content, especially when the heating was under vacuum from 13-15% in the untreated woods to 1-3% for vacuum treatment at 220 °C. The dimensional stability was improved to only a small extent e.g. volumetric shrinkage tended to decrease with increasing temperature. The mechanical properties were affected differently for the three wood species. Heat-treated cumarushowed increased Janka hardness, MOR and MOE; and peroba mica increased MOR and MOE but not Janka hardness; while bracatinga was less influenced by the heat treatment.