Effective Diffusion Coefficient Of Water Research Articles

Correlating 3D porous structure in polymer films with mass transport properties using FIB-SEM tomography

Porous polymer coatings are used to control drug release from pharmaceutical products. The coating covers a drug core and depending on the porous structure, different drug release rates are obtained. This work presents mass transport simulations performed on porous ethyl cellulose films with different porosities. The simulations were performed on high spatial resolution 3D data obtained using a focused ion beam scanning electron microscope. The effective diffusion coefficient of water was determined using a diffusion chamber. Lattice Boltzmann simulations were used to simulate water diffusion in the 3D data. The simulated coefficient was in good agreement with the measured coefficient. From the results it was concluded that the tortuosity and constrictivity of the porous network increase with decreasing amount of added hydroxypropyl cellulose, resulting in a sharp decrease in effective diffusion. This work shows that high spatial resolution 3D data is necessary, and that 2D data is insufficient, in order to predict diffusion through the porous structure with high accuracy.

Hot-air drying characteristics of Millettia speciosa Champ. slice and establishment of the kinetic model

[Objective] To explore the influence of different hot air temperatures, slice thicknesses and material loads on Millettia speciosa Champ. slice hot air drying rate, establish model of thermal wind drying kinetic, and provide reference for perfecting M. speciosa Champ. drying processing technology. [Method] Taking hot air temperature (50, 60, 70, 80 °C), slice thickness (2,4,6,8 mm) and material load (100,200,300 g) as investigating factors,real-time measurement of moisture changes during hot air drying of M. speciosa Champ. slices under various conditions. The 5 kinds of drying models were screened and fitted, calculated the effective water diffusion coefficient and theactivation energy in the drying process. [Result] With the increase of the hot air temperature, the slice thickness and material load decreased, the moisture content of dry basis was greatly reduced, and the drying rate was greatly increased. The hot-air drying process of M. speciosa Champ. slices was divided into two stages : acceleration and deceleration, and most of the drying process was the deceleration stage. The kinetic model of hot-air drying of M. speciosa Champ. slices conformed to the Page model, and the predicted value of the Page model had a good fit with the experimental value ( R 2=0.969). the fitting equation ln (-lnMR)= -3.174-0.242 H+0.029 T-0.006 L+(0.721+0.015 H+0.002 T)ln t, k=e -3.174-0.242 H+0.029 T-0.006 L , n=0.721+0.015 H+0.002 T, the effective diffusion coefficient D eff of M. speciosa Champ. under different drying conditions was 1.62114×10 -10-12.96913×10 -10 m 2/s, with the increase of hot air temperature and slice thickness, the material load decreased, and the overall trend was increasing, and the activation energy was 60.7388 kJ/mol. [Conclusion] The Page model can better reflect the moisture change law of hot air drying process of M. speciosa Champ. slice with different slice thicknesses, and by fitting the equation, the content of water ratio in the hot air drying process at a certain time can be accurately predicted. 摘要：【目的】探讨不同热风温度、切片厚度及装载量对牛大力切片热风干燥速率的影响, 并建立牛大力切片热风 干燥动力学模型, 为牛大力干燥工艺探索提供理论依据。 【方法】以热风温度 (50、60、70、80 °C)、切片厚度 (2、4、6、8 mm)和装载量 (100、200、300 g)为考察因素, 实时测定各条件下牛大力切片热风干燥过程中水分变化, 对常见的5种 干燥模型进行筛选, 并计算干燥过程中的有效水分扩散系数和活化能。 【结果】随着热风温度的升高, 切片厚度和装载 量的降低, 牛大力切片的干基含水量明显减少, 干燥速率明显增加。牛大力切片在热风干燥过程分为加速和降速2个 阶段, 其中大部分干燥过程为降速阶段。牛大力切片热风干燥动力学模型符合Page模型, 该模型预测值与试验值拟 合度较高( R 2=0.969), 拟合方程为ln(-lnMR)=-3.174-0.242 H+0.029 T-0.006 L+(0.721+0.015 H+0.002 T)ln t, 可求得K=e -3.174-0.242 H+0.029 T-0.006 L , n=0.721+0.015 H+0.002 T, 不同干燥条件下牛大力切片的有效水分扩散系数在1.62114×10 -10~12.96913×10 -10 m 2/s, 均随着热风温度的升高和切片厚度的增加, 总体呈上升趋势; 活化能为60.7388 kJ/mol。 【结论】Page模型可 较好地描述不同切片厚度的牛大力切片热风干燥过程中水分的变化规律, 且通过拟合方程能较准确预测热风干燥过 程中某时刻牛大力切片的水分比。

Estimation of the effective water diffusion coefficient in Nafion® membrane by water balance measurements

AbstractParameters estimation is important in fuel cell modelling and it remains a challenging task to predict. One of the most discussed parameters is the water diffusion coefficient in Nafion® membrane, which has a huge variation (10−9 and 10−5 cm2 s−1), based upon the viewpoints of different authors. In this article, the estimation of the effective water diffusion coefficient through water balance method is presented and the effects of relative humidity gradient and cell temperature are explained. The membrane used in this work is Nafion® NRE 211 tested at a temperature of 60°C and 70°C with air flows. The value of water flux passing through the membrane is used to calculate the effective diffusion coefficient. A value in the range of 1 × 10−7 to 4 × 10−7 cm2 s−1 is reported and it shows that the water balance method can be applied easily to measure an effective membrane water diffusion coefficient.

Drying characteristics and quality of Stevia rebaudiana leaves by far-infrared radiation

The far-infrared drying technique was used to dry Stevia rebaudiana leaves, and the drying rate, drying kinetics, the glycoside content of dried Stevia rebaudiana leaves and surface structure of the dried material were explored at different drying temperatures (45 °C、50 °C、55 °C、60 °C、65 °C), irradiation height (60 mm、120 mm、180 mm、240 mm、300 mm). Under different conditions, the moisture rate decreased and the drying rate increased significantly with the increase in drying temperature and the decrease in irradiation height, Weibull model fits the drying curves well (R2 > 0.99). The range of the estimated water diffusion coefficient Dcal was 0.841 8 × 10−4–2.945 3 × 10−4 m2 s−1, and the range of the effective water diffusion coefficient Deff was 0.835 9 × 10−6–3.629 1 × 10−6 m2 s−1. The activation energy was 28.79 kJ mol−1 determined by Arrhenius equation. By comparing the glycoside content of dried products under different drying conditions, it was found that far-infrared drying could better retain the glycoside content. The drying temperature have the batter effect on active ingredients of samples when it increased from 45 °C to 55 °C, the stevioside and rebaudioside A increased from 7.01 to 7.88 mg to 7.44 and 8.58 mg, respectively. Far-infrared drying technology could increase the number of micropores on the surface and inside the materials and improve the quality of dried products. This study explored the law of water transfer during the drying process of Stevia rebaudiana leaves and provided a theoretical reference for the research and application of Stevia rebaudiana leaf drying technology.

Effects of ultrasonic vacuum drying on the drying kinetics, dynamic moisture distribution, and microstructure of honey drying process.

The aim of this study was to study the strengthening effect of ultrasonic vacuum technique on the drying kinetics, moisture distribution, and microstructure of honey using low-field nuclear magnetic resonance and scanning electron microscopy. Results showed that ultrasonic vacuum drying technique could substantially shorten the drying time from 600 to 60 min, compared with vacuum drying. The sonochemical effects of ultrasonic vacuum drying were enhanced with the increased ultrasonic power and were more obvious in the initial stage of drying. This finding is consistent with the effective water diffusion coefficient results. The non-linear fitting analysis of experimental data on seven kinds of thin-layer drying mathematical models showed that logarithmic model is more suitable for describing the law of moisture change in honey during ultrasonic vacuum drying than the other models because of its higher regression coefficient value (≥0.99) and smaller reduced chi-square and root mean square error values (≤0.01). In addition, low-field nuclear magnetic resonance results showed that the increase in ultrasonic power accelerated the migration of bound water to immobilized water in honey samples. Scanning electron microscopy results showed that the porous structure formed by increasing the ultrasonic power is also conducive to the rapid migration and drying of moisture. In conclusion, ultrasonic vacuum drying technique is an effective and safe way for drying viscous materials compared with vacuum drying technique.

Synergetic effects of ultrasound and sodium alginate coating on mass transfer and qualities of osmotic dehydrated pumpkin

This research studied the effects of combined ultrasound and 3% sodium alginate (SA) coating pretreatment (US + Coat) on mass transfer kinetics, quality aspects, and cell structure of osmotic dehydrated (OD) pumpkin. The results of the pretreatment were compared with the results of control (non-pretreated osmotic dehydration) and other three pretreatment methods, which were 1) ultrasound in distilled water for 10 min (USC), 2) ultrasound in 70% (w/w) sucrose solution (US) for 10, 20 and 30 min, and 3) coating with 1%, 2%, 3% (w/w) SA. The coating pretreatments with SA resulted in a higher water loss (WL) but lower water activity and solid gain (SG) than other treatments. US pretreatments resulted in the highest effective diffusion coefficients of water (Dw) and solid (Ds) but the cell structure of the product was deformed. The 3% SA coating treatment had the highest WL/SG (5.28) but with the longest OD time (12 h). Using the US + Coat pretreatment gave satisfactory high WL/SG (5.18), Dw (1.09 × 10−10 m2s−1) and Ds (5.15 × 10−11 m2s−1), reduced the OD time to 9 h, and preserved the cell structure of the product. This research suggests that US + Coat pretreatment can be an effective processing step in the production of OD pumpkin.

Influence of Moderate Hyperosmotic Stress on Ultrastructure and Indicators of Energy Metabolism of Chlorella vulgaris (Chlorophyta)

A comparison of the response of freshwater alga Chlorella vulgaris Beijer. on a quantitatively identical change in tonicity of growth medium by different osmotics (NaCl and sucrose) has been studied. Upon an increase in growth-medium osmotic potential (regardless the nature of osmoticum), increased thermogenesis and decreased oxygen absorption by Chlorella is observed first. The difference in the reaction of Chlorella to equiosmotic concentrations of NaCl and sucrose is revealed. Upon an increased salt background, thermogenesis and photosynthetic activity decreases in comparison with the control and the respiration rate is close to the control. In the presence of sucrose, the culture has a higher level of thermogenesis, respiration, and photosynthesis. Sodium chloride does not cause significant changes in ultrastructure of Chlorella and does not lead to significant changes in the diffusional decay of water magnetization in comparison with the control. Under sucrose stress, a change in the cell shape indicating cytorhysis is revealed. The effective water-diffusion coefficient (according to NMR data) decreases, which also indicates the reduction of cell sizes. Sucrose affects Chlorella as a nonpenetrating osmotically active substance. Under moderate hyperosmotic stress, the toxicity of NaCl is a smaller problem for freshwater microalga Chlorella than the partial dehydration caused by sucrose.

Applicability of Pulsed Electric Field (PEF) Pre-Treatment for a Convective Two-Step Drying Process.

Available literature and previous studies focus on the Pulsed Electric Field (PEF) parameters influencing the drying process of fruit and vegetable tissue. This study investigates the applicability of PEF pre-treatment considering the industrial-scale drying conditions of onions and related quality parameters of the final product. First, the influence of the PEF treatment (W = 4.0 kJ/kg, E = 1.07 kV/cm) on the convective drying was investigated for samples dried at constant temperatures (65, 75, and 85 °C) and drying profiles (85/55, 85/65, and 85/75 °C). These trials were performed along with the determination of the breakpoint to assure an industrial drying profile with varying temperatures. A reduction in drying time of 32% was achieved by applying PEF prior to drying at profile 85/65 °C (target moisture ≤7%). The effective water diffusion coefficient for the last drying section has been increased from 1.99 × 10−10 m2/s to 3.48 × 10−10 m2/s in the PEF-treated tissue. In case of the 85/65 °C drying profile, the PEF-treated sample showed the highest benefits in terms of process efficiency and quality compared to the untreated sample. A quality analysis was performed considering the colour, amount of blisters, pyruvic acid content, and the rehydration behavior comparing the untreated and PEF-treated sample. The PEF-treated sample showed practically no blisters and a 14.5% higher pyruvic acid content. Moreover, the rehydration coefficient was 47% higher when applying PEF prior to drying.

Dynamics of intercellular water transfer in the roots of intact Zea mays L. plants under elevated concentrations of atmospheric CO2

In this study, the effect of atmospheric carbon dioxide concentration increase on the dynamics of radial intercellular water transfer in the root suction zone of intact maize plants was evaluated. To this end, a unique growth chamber, associated with 1H NMR PGMF (proton nuclear magnetic resonance with a pulsed gradient of the magnetic field) equipment, was used. As the atmospheric CO2 concentration increased up to 800 ppm and 1200 ppm, and the intensity of water transfer in the roots significantly decreased. The average effective water diffusion coefficient (Def) and the water permeability in root cells (P) decreased by approximately 30–35% within 5–6 h after the increase in CO2 concentration. At a higher concentration of CO2, 1200 ppm, the rate of decrease in water permeability increased. After a day of exposure to elevated CO2, the intensity of water transfer was partially restored but remained below the control level (before CO2 enrichment) over the next 7 days. Inhibitory analysis showed that root cell aquaporins (AQPs) made a significant contribution to the observed decrease in the intensity of water transport in the roots. The decrease in water permeability of root cells under elevated CO2 concentrations possibly occurs due to the regulatory decrease in water conductivity of AQPs via shoot-to-root long-distance signaling.

Mutual transformation of the water binding state and moisture diffusion characteristics of Chinese yams during microwave freeze drying

The moisture distribution changes in Chinese yam slices subjected to microwave freeze drying (MFD) were analyzed using low-field nuclear magnetic resonance (LF-NMR). During this process, the mutual transformation of the water binding state and moisture diffusion characteristics of Chinese yam were analyzed together with changes in the effective water diffusion coefficient, water content, drying rate and pore network structure. Notably, moisture migrated from a high to a low degree of freedom during the MFD process. The effective water diffusion coefficient and water migration velocity increased with increasing microwave power density, and the extent of the conversion of unbound to bound water also gradually increased. During the early stage of drying, moisture diffusion was mainly dominated by liquid phase diffusion. At later stages of drying, moisture diffusion shifted gradually from liquid phase diffusion to gas phase diffusion and was eventually dominated by the latter.

Effect of pretreatment on water migration and volatile components of heat pump dried tilapia fillets

In this study, ultrasonic assisted osmotic pretreatment and pulsed vacuum assisted osmotic pretreatment were applied to investigate their effects on water migration and volatile components of heat pump dried Tilapia fillets. To achieve that, some effective parameters including sample drying rate, water diffusivity, microstructure, water morphology, water distribution, and volatile components were compared and analyzed with some advanced measurement devices. The water diffusivity, water distribution characteristics, and composition of volatile components were obtained after different pretreatment methods. As the drying process progresses, the sample moisture content decreases. Meanwhile, the high-degree-of-freedom water migrates to the low-degree-of-freedom water and the water-solid bond strength increases. Subsequently, the effective water diffusion coefficients of control group (without pretreatment samples), ultrasonic assisted osmosis pretreatment group and pulsed vacuum assisted osmosis pretreatment group were measured as 4.304 × 10−7m2/s, 6.109 × 10−7m2/s, and 5.003 × 10−7m2/s, respectively. In addition, the control group, ultrasonic assisted osmosis group, and pulse vacuum assisted osmosis group contained 52, 59, and 41 volatile compounds, respectively. Compared to the results from the control group, the water diffusion coefficients of ultrasonic osmotic pretreatment and pulse vacuum osmotic pretreatment increased by 41.94% and 16.24%, respectively. From the point of view of increasing drying rate, the ultrasonic penetration pretreatment provided better improvement, which was exactly consistent with the results of microstructure. On the other hand, the ultrasonic assisted osmotic pretreatment group had more types of volatile compounds, which could stimulate more flavored substances to be released. Evidently, the samples with ultrasonic assisted osmotic pretreatment showed less drying time and more aromatic substances whereas the samples from the pulsed vacuum assisted osmotic pretreatment had better protein protection feature. Although the dried samples had higher ratio of bound water and better storage stability after these two pretreatment methods, from the point of view of increasing drying rate and stimulating flavor substances, the ultrasonic assisted osmosis pretreatment method had more advantages. The research outcomes can contribute to optimize better pretreatment methods for the process of heat pump dried Tilapia fillets.

Study on low temperature moisture regain drying characteristics of different grades of Angelicae Sinensis Radix based on Weibull distribution function

The drying process of different grades of Angelicae Sinensis Radix under low temperature and resurgence conditions was simulated based on the Weibull distribution function,in order to clarify the low-temperature moisture regain drying characteristics of different grades of Angelicae Sinensis Radix,and explore the effect of grade and drying conditions on the drying process of Angelicae Sinensis Radix. Research results indicated that the Weibull function can be used to simulate different grades of Angelicae Sinensis Radix low-temperature moisture regain drying process,and the lower the drying temperature,the smaller the grade,and the better the simulation effect. The grade and drying temperature showed a significant effect on the low-temperature moisture regain drying process of Angelicae Sinensis Radix,and the effect of temperature on the relative moisture regain rate of Angelicae Sinensis Radix was greater than the grade. The relative moisture regain rate of different grades of Angelicae Sinensis Radix at 40 ℃ was higher than 55 ℃,and the relative moisture regain rate at 40 ℃ was first class > second class > third class. After drying,the moisture ratio at 40 ℃ was lower than that at 55 ℃; the effect of the grade on the effective diffusion coefficient of dry water was greater than the temperature. Under different conditions of 40 ℃ and 55 ℃ moisture regain,the effective diffusion coefficient of water was between 2. 941 6×10-6-7. 991 5×10-6 and3. 093 8×10-6-8. 483 8×10-6 for different grades. Under the same temperature conditions,the effective diffusion coefficient of water was first class > second class > third class. Therefore,Weibull function can be used to study and simulate the drying characteristics of different grades of Angelicae Sinensis Radix under low-temperature moisture regain conditions,providing experimental basis for the improvement of traditional drying technology of Angelicae Sinensis Radix and the optimization of drying process of different specifications or grades of Angelicae Sinensis Radix.

Impact of pulsed electric fields on physical properties of freeze-dried apple tissue

Abstract The aim of this study was to analyze the impact of pulsed electric field (PEF) pre-treatment of apple tissue on kinetics of freeze-drying preceded by vacuum freezing and physical properties of such processed material. PEF intensified freeze-drying kinetics and thus reduced processing time by 57% in comparison to untreated apples slices. Furthermore, the effective water diffusion coefficient increased by 44% as a result of PEF application. Water activity changes during storage of freeze-dried apple tissue were more evident in the case of untreated material albeit initial water activity was higher in the case of electroporated samples. As proved by thermal properties measurements these differences were linked to higher crystallinity of the PEF treated samples (35.5%) in comparison to the untreated material (11.0%). The freeze-dried fruits subjected to PEF pretreatment absorbed more water than the untreated samples while no changes were observed for hygroscopicity and loss of the soluble solids during rehydration. Industrial relevance Obtained results confirm that application of pulsed electric field before freeze-drying makes possible to obtain high quality freeze-dried product preceded by vacuum freezing performed inside freeze-dryer which could reduce freeze-drying time. Since the rehydration capacity of PEF treated material, expressed as ability to absorb water, is better than untreated samples the application of this method could be beneficial when designing instant products. Performed research indicates also that PEF treated freeze-dried apples exhibit better stability expressed by water activity which in turn is related to crystallinity. What more, higher crystallinity of PEF pre-treated freeze-dried samples not only complements the explanation of different physical properties in comparison with intact freeze-dried material but also suggest that sensorial properties may vary.

Oscillating Swelling–Shrinking Dynamics and Diffusive Properties of Weakly Cationic Poly(Aminoalkyl Methacrylate)‐Based Cryogels: Quantifying the Influence of Polymer Network Parameters

AbstractThermodynamic properties of swelling equilibria and variability of dynamic response of pH‐sensitive polybases are examined. Poly(aminoalkyl methacrylate)‐based cryogels and hydrogels are prepared in a facile way by crosslinking polymerization of amine functional monomer N,N‐dimethylaminoethyl methacrylate (DMAEMA) in the presence of diethyleneglycol dimethacrylate as crosslinker at temperatures below and above freezing point of polymerization solvent, water, via cryogelation and conventional crosslinking polymerization. The effect of polymerization temperature on swelling characteristics of the prepared polybasic gels is investigated as a function of the gel‐preparation concentration. The overshooting effect is observed during pH‐dependent swelling of poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) hydrogels in acidic medium. Protonation/deprotonation of tertiary amine groups in network‐forming polymer demonstrates critical swelling behavior as pH of the swelling medium increases. Oscillating swelling–shrinking studies are performed and effective diffusion coefficient of water within PDMAEMA cryogel and hydrogel matrices is estimated using the dynamic swelling profiles. The mechanism of cyclic swelling–shrinking process of PDMAEMA cryogels and hydrogels are analyzed to control their pulsatile output patterns in metabolic oscillations. Considering the swelling process occurs through Fickian diffusion mechanism in acidic solutions, polybasic cryogels and hydrogels prepared in this study are thus proposed as good candidates for delivery applications.

STUDI PENGERINGAN BAMBU DENGAN PEMANFAATAN GAS BUANG ( FLUE GAS ) PEMBAKARAN GERABAH

Suhu gas buang dari hasil pembakaran gerabah relatif masih tinggi, suhunya masih sekitar 200oC. Gas buang hasil pembakaran gerabah ini diharapkan bisa dimanfaatkan sebagai media pengering, misalnya untuk mengeringkan bambu. Dalam penelitian ini, media pengeringan yang digunakan adalah udara panas. Tujuan dari penelitian ini adalah untuk menghitung parameter-parameter pengeringan yang diharapkan dapat diterapkan pada pengeringan bambu dengan media gas buang dari pembakaran gerabah. Dimensi dari masing-masing sampel bambu adalah panjang 45 cm, lebar 8 cm dan ketebalan1 cm. Berat awal masing-masing sampel ditimbang, kemudian sampel itu dimasukkan ke dalam unit pengeringan. Selanjutnya udara panas dialirkan ke dalam unit pengering. Suhu udara panas yang digunakan adalah 60oC, 80oC dan 100oC. Setiap 30 menit, perubahan massa bambu dicatat dan suhu termometer bola kering dan termometer bola basah diukur. Pengeringan dilakukan sampai massa sampel bambu tidak berubah. Dalam penelitian ini, pengeringan bambu terbagi dalam dua periode yaitu periode laju menurun dan periode laju konstan. Teramati bahwa, laju pengeringan konstan berlangsung dalam waktu yang singkat. Laju pengeringan bambu dikontrol oleh difusi air di dalam bambu dan transfer massa air dari permukaan bambu ke udara. Koefisien difusivitas efektif air (Deff) yang diperoleh adalah 0,02 cm2/jam untuk suhu udara panas pengering 60oC, 0,03 cm2/jam untuk 80oC dan 0,08 cm2/jam untuk 100oC.

Water diffusion in carbon fiber reinforced polyamide 6 composites: Experimental, theoretical, and numerical approaches

Diffusion of moisture through composites is one of the main environmental causes of their deterioration and loss of service life. This paper deals with water diffusion in the unidirectional continuous carbon fiber reinforced polyamide 6 composites by experimental measurement, theoretical analysis, and numerical simulation. Immersion experiment is respectively conducted in distilled water at 25°C, 70°C, and 95°C for the pure polyamide 6 resin and the carbon fiber/polyamide 6 composite. Then, the theoretical Fickian and Langmuir models are employed to fit the gravimetric data of the specimens. Subsequently, water diffusion in the composite is also simulated using finite element method. Moreover, to capture the real distribution of fibers in the matrix, the random algorithm is developed to generate the computational composite models with randomly dispersed fibers. Finally, the comparison between the experimental, theoretical, and numerical results is made to assess the applicability of theoretical models and the influences of fiber distribution and interphase on the effective water diffusion coefficient of composite.

Kinetics study and modelling of sorghum grain hydration

Sorghum grains were soaking to evaluate the effects of time and temperature on moisture and process modelling was maked with different mathematical equations. Then, sorghum BRS 310 and BRS 655 were hydrated at 30 °C, 40 °C, 50 °C and 60 °C, for 12 hours. The hydration kinetics modelling with empirical equations of Peleg and Page and phenomenological equations of Diffusion and Omoto-Jorge were considerad. The time and temperature affected significantly the hydration kinetics of grain sorghum. The Peleg and Diffusion models showed the best fitting for soaking and, therefore, these models were used to create generalized models. The effective diffusion coefficient of water during the grain sorghum hydration ranged from 2.02x10-11 to 6.34x10-11 m².s-1 for BRS 310 and from 2.76x10-11 to 4.38x10-11 m².s-1 for BRS 655 with activation energies of 11.52 and 31.21 kJ.mol-1, respectively.

Influence of ambient conditions on the process of clay-like body vacuum drying

The first experiments on the vacuum drying of spherical clay sample are presented and the theoretical model of the process is considered. The model is based on the solution of the heat and the moisture transfer equations with the effective thermal conductivity and water diffusion coefficients for wet porous clay-like medium. The time and radial dependence of the temperature and the moisture were calculated for different initial conditions. The results obtained for the time dependence of the moisture content are in good agreement with the experimental results obtained in the initial period, when all the moisture in the sample did not freeze to form an ice crust.

Numerical modelling of heat and moisture transfer in a clay-like porous material

A new model for the convective drying of a kaolin spherical sample is presented. The model is based on the self-consistent solution of the heat and the moisture transfer equations with the effective thermal conductivity and water diffusion coefficients for wet porous clay-like medium. The radial distributions of the temperature and the moisture content were calculated for different boundary conditions for heat and moisture fluxes on the surface of the kaolin sample. To test the model, the drying kinetics of the kaolin sample heated up to 60°C and 100°C were calculated. The results show a good agreement with the experimental and numerical data of the other authors. In the process of the sample cooling, the effect of the overcooling to the temperatures lower than the ambient temperature was found.

Mass transfer modeling during osmotic dehydration of cambuci (Campomanesia phaea (O. Berg) Landrum) slices and quality assessment

The osmotic dehydration of cambuci slices was studied using binary and ternary solutions containing sorbitol (S) and calcium lactate (CL) at different concentrations. Experiments were conducted at 25 °C. The mass and the physical-chemical properties of fruit slices were measured along the process. The results showed significant reduction in moisture (X), water activity (aw) and titratable acidy (TA). Soluble solids (SS) and pH increase were also observed. Osmotic solutions with higher sorbitol concentrations enabled higher water removal, but no significant difference was observed when CL was added to the osmotic solution. The content of soluble solids (SS) was higher in samples treated with higher sorbitol concentrations. The experimental results of water loss and soluble solids gain were modeled using Peleg's equation, and the equilibrium moisture and content of soluble solids were estimated. The effective diffusion coefficient of water was lower when CL was added to the osmotic solution, indicating modifications in the internal resistance for the mass transfer.