Moisture Content Gradient Research Articles

SIMULATION HEATING PROCESS FOR WEAKLY REACTIVE COAL IN THE HORIZONTAL REACTOR

In this study results of the active medium parameters influence formed by hot air on the thermal heating process of weakly reactive coal from the formation «Maikubensk 3B» for the extraction of additional heat are represented. In the course of the research the regularities of the hygroscopic moisture and volatile combustible substances release for the obtaining additional heat have been determined. Optimal temperature ranges of the stage heating taking into account thermal destruction of coal in the temperature range from 20 C to 600 C, the main steps of the insulated heating process, the moisture content gradient propagation lines and dependence of the heat transfer and mass transfer coefficients on the temperature and the humidity during the thermal heating process in the horizontal coal heating reactor. The results show that it is possible to release volatile combustible gases with a gradual increase of temperatures in the obtained mode. The heating mode comprises a pre-heating stage with hydroscopic moisture release, in the temperature range from 20 C to 105 C, the stage of isothermal heating in the temperature range from 105 C to 400 C and the phase of flame-free combustion in the temperature range from 400 C to 600 C with the temperature rise above the set value. Process simulation was carried out in the Comsol Multiphisics software environment for the weakly reactive coal real-world heating conditions. Keywords: coal heating, weakly reactive coal, isothermal heating, step-by-step heating, Lagrange method, non-liner equation, non-stationary process.

Non-Uniform Drying Shrinkage in Robocasted Green Body Ceramic Products

The formation of defects, due to drying, in robocasted ceramic objects is an important issue arising from non-uniform shrinkage of the material during this step in the process. Common methods for shrinkage measurement are not well suited to the small size of robocasted cords or the complexity of robocasted objects. Innovative methods for shrinkage measurement were developed using non-destructive optical vision techniques with computer-controlled data acquisition, allowing measurement on millimetric cords and on specific zones of a product. The study of a single porcelain cord revealed an anisometric shrinkage related to the orientation of grains during extrusion. A differential shrinkage at the macroscopic scale was also measured on a robocasted object, indicating a moisture content gradient in the material. The methods presented in this paper are of particular relevance to real-time control of the drying process for robocasted objects.

Utilisation of Lactiplantibacillus plantarum and propionic acid to improve silage quality of amaranth before and after wilting: fermentation quality, microbial communities, and their metabolic pathway.

The aim of this study was to investigate the effects of Lactiplantibacillus plantarum (L. plantarum) and propionic acid (PA) on fermentation characteristics and microbial community of amaranth (Amaranthus hypochondriaus) silage with different moisture contents. Amaranth was harvested at maturity stage and prepared for ensiling. There were two moisture content gradients (80%: AhG, 70%: AhS; fresh material: FM) and three treatments (control: CK, L. plantarum: LP, propionic acid: PA) set up, and silages were opened after 60 d of ensiling. The results showed that the addition of L. plantarum and PA increased lactic acid (LA) content and decreased pH of amaranth after fermentation. In particular, the addition of PA significantly increased crude protein content (p < 0.05). LA content was higher in wilted silage than in high-moisture silage, and it was higher with the addition of L. plantarum and PA (p < 0.05). The dominant species of AhGLP, AhSCK, AhSLP and AhSPA were mainly L. plantarum, Lentilactobacillus buchneri and Levilactobacillus brevis. The dominant species in AhGCK include Enterobacter cloacae, and Xanthomonas oryzae was dominated in AhGPA, which affected fermentation quality. L. plantarum and PA acted synergistically after ensiling to accelerate the succession of dominant species from gram-negative to gram-positive bacteria, forming a symbiotic microbial network centred on lactic acid bacteria. Both wilting and additive silage preparation methods increased the degree of dominance of global and overview maps and carbohydrate metabolism, and decreased the degree of dominance of amino acid metabolism categories. In conclusion, the addition of L. plantarum to silage can effectively improve the fermentation characteristics of amaranth, increase the diversity of bacterial communities, and regulate the microbial community and its functional metabolic pathways to achieve the desired fermentation effect.

Prediction Distribution Model of Moisture Content in Laminated Wood Components.

Shrinkage cracks are some of the most common defects in timber structures obtained from woods with an uneven distribution of moisture content and are subject to external dynamic environmental changes. To accurately predict the changes in the moisture content of wood components at any time and position, this study first applied the principles of food drying and established a moisture field model for laminated wood based on the analogy between heat and humidity transfer. A model for predicting the moisture content of wood that considers time and spatial distribution was then proposed. Second, by collecting relevant experimental data and establishing a finite element analysis model, three moisture absorption conditions (0-9.95%, 0-13.65%, and 0-17.91%) and four desorption conditions (34-5.5%, 28-8.3%, 31-11.8%, and 25.5-15.9%) were analyzed. In the moisture absorption comparison, the time needed to reach 95% equilibrium moisture content was 2.43 days, 4.07 days, and 6.32 days. The rate at which the internal components reached equilibrium moisture content exceeded 10 days. The temporal and spatial distribution of wood moisture content revealed the correctness of the proposed wood moisture field model. Finally, the moisture content prediction model was applied in the order of characteristic equation solutions, moisture content gradient difference, and laminated wood size. The results revealed that the established humidity field model can predict the wood moisture content and how it changes over time and in space. Notably, 1-2 orders for the solution of the characteristic equation are recommended when applying the prediction model. The greater the difference in moisture content, the faster the equilibrium moisture content is reached. The moisture content varies greatly based on the component size and position. Notably, the influence of moisture gradient and wood size on the average wood moisture content cannot be ignored.

Moisture changes and surface checking development during drying of Masson pine wood

Deformation and surface-checking defects in wood are closely related to the drying stress caused by shrinkage and moisture content (MC) gradients throughout the drying process. In this study, 50-mm-thick Masson pine (Pinus massoniana Lamb.) lumber was used as the research object. The drying stress caused by shrinkage behavior and MC changes was monitored, and the development of surface checks was observed during the drying process. Results showed that when the average MC was 60%, the free water in the surface layer of lumber evaporated completely, causing the MC to decrease below the fiber saturation point (FSP). The surface layer was subjected to tension stresses, resulting in surface checks which primarily distributed in the latewood area and propagated longitudinally. When the average MC was between 30% and 40%, the combined effects of the high MC gradient and anisotropic shrinkage of the wood resulted in further expansion of the checks. As the average MC decreased to less than 20%, the MC of the core layer lumber decreased below the FSP, resulting in the closure or even disappearance of most surface checks. The critical point (average MC of 60%) of drying stress was obtained, which can benefit the fine-tuning of kiln-drying schedules and improve the drying quality of Masson pine wood.

A novel simulation model to analyze rice intermittent drying considering glass transition concept

During rice drying its starch exhibits a variety of thermal properties. It can be transformed from a rubbery state to a glassy state and vice versa due to temperature and moisture content gradients (MCGs) leading to the reduction in head rice yield. Intermittent drying is an effective drying method to overcome this issue. In this research, a novel mathematical model was developed for rice intermittent drying process considering the glass transition concept which has not been done before. In addition, the real 3D body-fitted geometry of the rice kernel was first utilized for simulation. To determine the required coefficients and validate the model, continuous and two-stage intermittent drying (2SID) experiments were performed. A correlation of 99% was found between the drying kinetics obtained from the experiments and those obtained from the model. Regarding the glass transition phenomenon, a quantitative S function was defined to express the local glassy-to-rubbery state at each time. The transitory temperature and moisture distributions inside the rice kernel were displayed and discussed at each stage of the 2SID. Further, the glass transition behavior of the rice kernels was investigated by using the S function's values. The glassy region extended by 28.8%, 3.3%, and 20.1% of the whole kernel rice at the first drying, tempering, and second drying stages, respectively. At the end of the 2SID, 45.6% of the entire kernel was located in the glassy region while the central layers were still located in the rubbery region. Overall, the developed model could be used to determine the optimal intermittent drying parameters for rice to improve its dehydration performance at a low cost.

Drying Behaviour of Western Hemlock with Schedules Developed for Norway Spruce and Scots Pine

Determining moisture content (MC) distribution during the drying of porous materials such as wood is crucial for developing drying schedules and assessing their suitability to achieve optimised processes. This study aimed to determine the causes of the unique drying behaviour and the well-known unusual longer drying time of western hemlock compared to other similar softwoods. In situ X-ray computed tomography (CT) was used to study the evolution of MC in timber during the drying process. The drying behaviour of western hemlock (Tsuga heterophylla (Raf.) Sarg.) was compared with Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) from green to oven-dried condition with industry-proposed drying schedules used for steering a custom-made experimental kiln combined with a CT scanner. CT scanning was performed at 30 min intervals during the complete drying period of 30 h, and the CT images were processed to calculate the MC evolution within the specimen. Western hemlock showed a considerably slower capillary-phase drying and did not go into the transition and diffusion phases when a schedule adapted to pine and spruce drying was applied for its drying. CT images and MC gradient calculations showed a lower drying rate and severe non-uniformity in MC distribution, which could be due to the effect of higher green MC and the presence of wet pockets. Furthermore, the evaporation front at the first 5 h of drying receded faster into the hemlock specimen, and as drying proceeded, it slowed down compared to other specimens.

Dewatering of Juglans mandshurica Wood Using Supercritical Carbon Dioxide.

Supercritical carbon dioxide (ScCO2), known for such features as good solubility and mass transfer properties, can be an efficient drying medium for various materials, such as wood, by filling the pore space and dissolving water in the cell cavity without altering the microstructure. In this study, two specimens of Juglans mandshurica wood with a length of 30 mm and 140 mm were subjected to ScCO2 dewatering under four different pressure and temperature conditions. The results showed that the drying rate is mainly influenced by pressure and temperature, with pressure having the more significant effect. Moreover, the efficiency of dewatering was not dependent on the sample length under the same conditions. The moisture content (MC) was the same along the longitudinal direction throughout both the surfaces and core of the wood. While there were no significant differences in dewatering rate between tangential and radial directions and lengths of samples, significant MC gradient differences were noted along wood in radial and tangential directions. During ScCO2 dewatering, the dominant water transfer occurred from the middle towards the end surfaces along the wood's longitudinal directions. Furthermore, ScCO2 dewatering did not result in any shrinkage or significant drying stress, but it did cause some swelling in Juglans mandshurica wood.

Review on Wood Deformation and Cracking during Moisture Loss.

Wood, being a natural hygroscopic material, the interaction between wood and moisture plays a crucial role in wood processing and utilization. Moisture affects the physical and mechanical properties of wood, and is also one of the main external factors that cause wood deformation and cracking. Drying shrinkage is a common phenomenon during the processing and utilization of wood induced by moisture loss. Drying stress is the main cause of wood deformation and cracking. The shrinkage differential between tangential and radial direction and moisture content gradient of wood are two reasons induced the generation of drying stresses. In this review, the existing states of moisture in wood and the interaction between water molecules and wood components were systematically summarized. The current research progress and deficiencies in three aspects including the factors resulted in deformation and cracking in wood caused by moisture loss, the correlation between wood mechanical properties and moisture, as well as the development of deformation and cracking in wood under moisture loss were discussed. This review aims to facilitate further research on the deformation and cracking of wood under moisture loss by providing valuable insights and assistance, ultimately reducing the occurrence of wood deformation and cracking. And thus, it will enhance the overall utilization of wood resources, making wood better serve human life.

EVOLUTION AND DISTRIBUTION OF SHAKES IN LARCH LOGS DURING AIR DRYING

This paper analyzed the length, width, and location of shakes in the air-drying process of larch log (Larix principis-rupprechtii Mayr) 1 m long and 66% initial moisture content. The development law and distribution characteristics of shakes during log drying of larch were studied and shake generation and development law were analyzed from two aspects of microstructure and growth defects. The variation of dry shrinkage deformation along the radial direction and knot influence on it was analyzed using the split-shaped stress test strips. At the cellular level, the cell wall shrinkage behavior of heartwood and sapwood and the microstructure of knots were observed. The results showed a significant relationship between eccentricity and shake distribution; the IIa region is the most prone to dry shake. The evolution of shakes is closely related to the drying rate. In the high-speed drying stage (MC ≥ 40%), shakes almost do not occur; in the decelerating drying stage (40% ≥ MC ≥ 20%), the amount, length, and width of shakes increase rapidly. In the low-speed drying stage (20% ≥MC), the area of shakes tends to stabilize or even decline. The main reasons for dry shaking are the dry shrinkage difference between tangential and radial cell walls, early and late wood, heartwood and sapwood, and moisture content gradient during the drying process.

The formation mechanism of microcracks and fracture morphology of wood during drying

The surface checks or internal cracks from drying could significantly affect the processing and utilization of the wood. Therefore, it is of great significance to investigate the formation mechanism of cracks and reduce its occurrence. In this work, the development of cracking was quantified and its relationship with moisture content (MC) gradient and anisotropic shrinkage was analyzed. Results showed that the slight shrinkage occurred at the MC of 40%, and the shrinkage ratio at the end of drying was about 7.38% in the tangential (T) direction and 4.35% in the radial (R) direction. The shrinkage ratio of T/R in the MC range of 30%–15% was about 1.8, which was higher than that (1.65) in the MC range of 15%–5%. Cracks initiation was observed at average MC of 45%. The area and number of cracks reached a maximum at 15% MC. During the late stage of drying, the drying stress of the surface layer was reversed from tensile to compressive, which leads to the narrowing or closure of the cracks. Moreover, the fracture morphology of wood cells was observed at the microscopic level, indicating that the failure firstly occurred in the intercellular layer between the ray tissue and the tracheid in the latewood. The ray cells presented intact, and the lamellar structure between ray tissues and between the ray cells and the tracheids were the weak points of wood during drying. The results would contribute to keeping in minimum drying defects and improving the drying quality of wood.

Tempering Drying and Energy Consumption

Abstract The aim of this work is to optimize the drying process through the reduction of energy consumption and the improvement of the dried product quality using tempering or intermittent drying. The effectiveness of intermittent drying was evaluated by the determination of the sensible, latent, and total energies necessary to perform the drying process. The obtained results show that tempering drying is more effective than continuous drying. This effectiveness was evaluated by the energy consumption. A reduction of energy consumption varying from 13% to 67% was achieved. The drying time, energy consumption, and product quality were improved when using temporary drying. The decrease of the gradient of moisture content in the material during the period of no heating is considered as the main factor that increases the rate of moisture removal when the heating is resumed.

Moisture transfer and drying stress of eucalyptus wood during supercritical CO2 (ScCO2) dewatering and ScCO2 combined oven drying

Supercritical CO2 (ScCO2) dewatering is a lumen water expulsion process, in which CO2 is cycled between atmospheric pressure and supercritical phase and results in a fast expulsion of free water. In this study, specimens of 100 mm length Eucalyptus exserta F.V. Muell. wood were dewatered using ScCO2, then the dewatered and un-dewatered wood were dried in oven at 100 °C to investigate moisture transfer and drying stress. The ScCO2 dewatering was very fast. When the moisture content (MC) was over 40%, the MC distribution and gradient after dewatering and oven drying were different. The oven drying MC showed a ring contour distribution, but the ScCO2 showed a higher MC in one side and a lower MC in the opposite; the oven drying MC gradient was great in the middle and small in the end part of wood, but the ScCO2 MC gradient was small and roughly consistent. The oven drying moisture migration rates along the fiber and transverse directions were similar; however, the ScCO2 migration rate was faster in the transverse directions. The MC distributions of the dewatered and un-dewatered wood after oven drying were similar at 30% MC. The ScCO2 dewatering reduced wood residual stress, and it affected the stress development in the subsequent oven drying.

The Characteristics of Moisture and Shrinkage of Eucalyptus urophylla × E. Grandis Wood during Conventional Drying.

High quality lumbers produced from Eucalyptus plantations can be used to make higher value-added solid wood products. Moisture flow affects shrinkage, deformation, and quality of Eucalyptus wood during conventional drying. In this study, 50 and 100 mm long samples were dried using a conventional drying method. The drying curves, drying rate, moisture content (MC) gradient and distribution, moisture flow, and shrinkage during the drying process were investigated. The results show: Drying was much faster in the first 15 h for all samples and became slow as MC decreased. The drying rate above fiber saturated point (FSP) was about 3.5 times of that below FSP for all samples. The drying rate of 50 mm samples above and below FSP is 1.40 and 1.33 times of 100 mm samples; MC gradients are greater in tangential, radial directions, and cross-sections for both samples when the MC is above FSP, especially at an average MC of 50%. MC gradient along the tangential and radial direction depends on the samples size and MC stages. The short samples have much greater MC gradients than the longer samples above FSP. Moisture distributions on the cross-sections of wood coincide with the moisture gradient in the cross-sections. At an average MC of 50%, the moisture distributions of 50 mm are highly uneven, while they are relatively even in the middle of 100 mm samples, and become much more even at the end of the sample. Moisture distributions become even as MC decreases in all of the samples. Water migration directions vary by state of water. In the short samples, most free water migrates more in the fiber direction from the wood center toward the end surfaces, but bound water diffusion becomes weak. The collapse in the 50 mm samples is significantly larger than that in the 100 mm samples, indicating that the collapse is affected by the dimension of the sample.

Identification of Moldy Peanuts under Different Varieties and Moisture Content Using Hyperspectral Imaging and Data Augmentation Technologies.

Aflatoxins in moldy peanuts are seriously toxic to humans. These kernels need to be screened in the production process. Hyperspectral imaging techniques can be used to identify moldy peanuts. However, the changes in spectral information and texture information caused by the difference in moisture content in peanuts will affect the identification accuracy. To reduce and eliminate the influence of this factor, a data augmentation method based on interpolation was proposed to improve the generalization ability and robustness of the model. Firstly, the near-infrared hyperspectral images of 5 varieties, 4 classes, and 3 moisture content gradients with 39,119 kernels were collected. Then, the data augmentation method called the difference of spectral mean (DSM) was constructed. K-nearest neighbors (KNN), support vector machines (SVM), and MobileViT-xs models were used to verify the effectiveness of the data augmentation method on data with two gradients and three gradients. The experimental results show that the data augmentation can effectively reduce the influence of the difference in moisture content on the model identification accuracy. The DSM method has the highest accuracy improvement in 5 varieties of peanut datasets. In particular, the accuracy of KNN, SVM, and MobileViT-xs using the data of two gradients was improved by 3.55%, 4.42%, and 5.9%, respectively. Furthermore, this study provides a new method for improving the identification accuracy of moldy peanuts and also provides a reference basis for the screening of related foods such as corn, orange, and mango.

Seed Characteristics and Germination of Quercus leucotrichophora A. Camus Tree along the Elevation Gradient in Central Himalaya, India

Quercus leucotrichophora seeds were analyzed for color changes, seed size, weight, moisture content and germination elevation gradient. The seed germination was between 51.2 and 55.2 percent when the seed moisture content was between 35.9 and 38.8 percent .The change in mean weight of 100 seeds varied between 64.4 and 164.2 g at low elevation and the change in mean seed size was in between 31.2 and 222.6 mm respectively. The change in mean weight of 100 seeds ranged between 74.7 and 63.3 g at middle elevation, and 2 the change in mean seed size was in between 79.6 and 219.3 mm Similarly at high elevation change in mean weight of 100 seeds was i 2 . between 63.6 - 90.2 and g and seed size was between 146.1 and 227.6 mm respectively. The change in seed color was from dark green to 2 , dark brown, and the mean seed size was larger at the lower elevation than that of middle elevation, and the seed moisture content between 35.9 and 38.8 % during the first and second week of December considered to be a reliable indicator of maturity.

Impact of continuous drying method on drying quality of southern pine sawn timber

The continuous drying of timber is attracting increasing international interest for softwood drying because of several reported advantages, e.g., improved energy efficiency and improved grade recovery. This study aimed to investigate the impact of continuous drying kiln technology on the quality of dried Queensland plantation-grown southern pine timber, compared to the current ultra-high temperature batch drying process adopted by many softwood processors. End matched boards were dried using continuous and high-temperature drying schedules. The moisture content and moisture gradient of each board was assessed in accordance with AS/NZS standard 1080.1 (2012), AS/NZS standard 2796.3 (1999), respectively, while the drying stress was assessed in accordance with AS/NZS standard 4787 (2001). The boards dried with continuous drying schedules resulted in slightly lower bow and spring values and similar cup and twist values compared to the high temperature dried boards. The moisture gradient and drying stress were significantly lower in boards using continuous drying kiln technology compared to the high temperature dried boards. This study will allow the Australian softwood industry to better understand the dried timber quality obtained using new continuous drying technology to make informed investment decisions.

A theoretical analysis of the potential effect of negative pressure in wood drying based on a CT-scanner study

A CT-scanner was used to scan 25 mm thick radiata pine boards during drying at 90 °C dry-bulb and 60 °C wet-bulb temperatures. Twenty transverse sections spaced by 10 mm along the length of the boards were CT-scanned six times during drying, and an elastic image registration technique was used to transform the CT-scanned images into moisture content profiles. The resulting images suggested that moisture content distributions did not always resemble diffusion-like moisture transfer mechanism, so common assumptions based on moisture content gradients as the main driving force for wood drying may not always be enough to explain the development of wet and dry zones coexisting below and above fiber saturation point. This paper discusses these findings based on both experimental CT-scanner data and the theory of water potential, which it is argued provides a more complete description of driving forces in wood drying.

Effect of Temperature and Pressure of Supercritical CO2 on Dewatering, Shrinkage and Stresses of Eucalyptus Wood

Supercritical CO2 (SuCO2) dewatering can mitigate capillary tension and reduce wood collapse. In this study, Eucalyptus urophylla × E. grandis specimens were dewatered by SuCO2 at temperatures of 35, 40 and 55 °C, in pressures of 10 and 30 MPa, respectively, for 1h. Effects of temperature and pressure on dewatering rate, moisture content (MC) distribution and gradient, shrinkage and residual stress of wood after dewatering were investigated. The results indicate that the SuCO2 dewatering rate is much faster than that of conventional kiln drying (CKD). The dewatering rate increases with increasing of temperature and pressure; however, pressure has a significant influence, especially for the high-temperature dewatering process; the MC distribution after 1h dewatering is uneven and MC gradients decrease with reducing of mean final MC of wood. MC gradients along radial direction are much smaller than that in tangential direction; collapse of wood significantly reduces after dewatering due to SuCO2 decreasing the capillary tension, and residual stress of wood during dewatering is mainly caused by pressure of SuCO2, which decreases with increasing temperature. SuCO2 dewatering has great potential advantages in water-removal of wood prone to collapse or deformation.

Experimental and numerical study of intermittent drying of rough rice in a combined FIR-dryer

Moisture variation and fissure formation of rice kernels during multi-stage intermittent drying (MSID) were simulated and analyzed based on the experimental data obtained in a laboratory-scale infrared-assisted vibratory bed dryer. The variations of drying parameters included far-infrared radiation (FIR) intensity (0, 1000 and 2000 W m−2), inlet drying air temperature (30, 40 and 50 °C), drying duration (15, 30 and 40 min), and tempering ratio (0, 2, 4 and 6). Two-dimensional moisture distribution within individual kernel was predicted. Drying rate, percentage of the cracked kernel (PCK), and specific energy consumption (SEC) were also determined, experimentally. By assessing PCK and SEC and simulation results, it was found that the magnitude of 10% d.b. mm−1 was considered as an index for the critical value for moisture content gradient (MCG) to achieve the suitable drying and tempering duration. It was further recommended that the intermittent drying duration at each stage should be selected in such a way that the MCG value does not exceed the critical level and the shortest possible tempering duration should be chosen in a manner that at least 40% of critical level of MCG be eliminated. The suitable treatment for intermittent drying was selected at FIR intensity of 1000 W m−2, inlet air temperature in 40 °C, drying duration in 30 min, and tempering ratio in 4.