The Moisture Distribution of High Moisture Content Rough Rice During Harvesting, Storage, and Drying

The kernel moisture content (MC) distribution of five varieties of double season rice was tested during the process of harvesting, drying, and tempering. Significant kernel MC variance was found to exist within the panicle. Binodal kernel MC distribution frequency was found at harvest. The MC distribution of five varieties during harvesting and drying showed similar trend of uniformity. To investigate the mechanism of moisture transport among rice kernels under low temperature, the kernel MC distribution of rice planted in Northeastern China was also investigated after stacked for over one month under the temperature of -20°C. The moisture exchange among rice kernels was found greatly influenced by environmental factors.     

Breakage and Mass Transfer Models During Drying of Rough Rice

A breakage model was investigated for thin-layer drying of rough rice. The breakage model developed can predict the percentage of head rice (E/E_o) as an exponential function of the grain moisture. Experimental data of the rice moisture content during drying were fitted with a theoretical model of the drying process to obtain the parameters. Experimental data of percentage head rice and moisture content were fitted to obtain the parameters of breakage model. Both functions were used together to obtain a drying-breakage model. This model allows us to predict the drying time required to achieve a rice moisture content desired and to estimate the head rice yield percentage for this moisture content.     

Analysis of Moisture Content and Density of Pears During Drying

Solar dried pears of the “S. Bartolomeu” variety are a very much appreciated and preferred dried food product in Portugal. Nevertheless, the traditional solar drying is carried out at open air during the months of 07 and 08, and this nowadays is a disadvantage for larger productions. This work is to evaluate the possibility of producing dried pears from this and other varieties, maintaining the characteristics of the traditional dried pears. In this study four different types of pears were studied, including “S. Bartolomeu” as a basis for comparison and the drying method employed was the traditional one. From the results it was concluded that, although the behaviour of the four varieties do not vary significantly, one particular variety (“D. Joaquina”) is a good alternative to the “S. Bartolomeu” pear.     

Analysis of Moisture Content and Density of Pears During Drying

Abstract

Solar dried pears of the “S. Bartolomeu” variety are a very much appreciated and preferred dried food product in Portugal. Nevertheless, the traditional solar drying is carried out at open air during the months of 07 and 08, and this nowadays is a disadvantage for larger productions. This work is to evaluate the possibility of producing dried pears from this and other varieties, maintaining the characteristics of the traditional dried pears. In this study four different types of pears were studied, including “S. Bartolomeu” as a basis for comparison and the drying method employed was the traditional one. From the results it was concluded that, although the behaviour of the four varieties do not vary significantly, one particular variety (“D. Joaquina”) is a good alternative to the “S. Bartolomeu” pear.     

Analysis of Drying Kinetics and Moisture Distribution in Convective Textile Fabric Drying

The drying process of crude cotton fabric is analyzed under two main aspects: analysis of moisture distribution inside the textile sheet, and analysis of certain operational convective drying process variables. Experimental apparatus consisted of a drying chamber in which samples of pure cotton textile were suspended inside the drying chamber and exposed to a convective hot air flow. The influence of the operational variables on the drying process behavior was studied by two different ways with generalized drying curves. The behavior of moisture distribution profiles was compared to average moisture content of the textile fabric verifying whether average values were able to represent the textile moisture content during the drying process.     

A Novel Method of Measuring Moisture Content Distribution in Timber During Drying Using CT Scanning and Image Processing Techniques

A new method for the nondestructive measurement of moisture content (MC) distribution in timber during drying was developed using X-ray computed tomography (CT) scanning and image processing techniques. The deformed cross section in the CT images due to shrinkage was corrected with the image registration, and the shrinkage was measured by digital image correlation analysis. The pixel-wise MC distributions during drying were measured and visualized successfully. The total timber MC estimated from the MC values of each pixel were strongly correlated with those measured by calculation without geometrical transformation of CT images. The coefficient of determination (R ²) and the standard error of prediction (SEP) were 0.99 and 0.18%, respectively, within the MC range of 19.2–47.3%. In addition, the measured shrinkage distribution during drying was in accordance with the diamonding deformation observed. The results suggest that CT scanning combined with image processing techniques is an effective tool for nondestructive assessment of MC distribution during drying.     

滚筒干燥设备的开发研究

通过对比分析已有干燥技术在同类产品干燥造粒过程中的应用效果,结合液体聚合硅酸铝物性特征,设计研制了一台用于实验室研究的单滚筒浸液式滚筒干燥机,同时系统地研究了料膜湿度与温度的变化关系。研究结果对实际生产应用具有重要的指导意义和参考价值。     

The Drying Kinetics and Equilibrium Moisture Content of MDF Fibers

An experimental device was constructed to study the drying kinetics of wood fibers under controlled conditions. The device consisted of a drying chamber in which a net basket filled with the fiber material was connected to a load cell. The drying medium was then forced through the basket at controlled levels of humidity and temperature.

Experiments were performed with spruce fibers and the drying medium at varying temperature (50–170°C) and relative humidity (1–86%). In general, the drying rate increased with increasing temperature and decreasing relative humidity. A constant drying rate period was observed in all cases. The critical moisture content was approximately 1.25. The characteristic drying curve has a slight downward concave shape. The equilibrium moisture contents obtained at ambient temperature agree well with data in the literature.     

Modeling Equilibrium Moisture Content of γ-Ray Irradiated Rough Rice

Experimental studies show that gamma irradiation dose affects the values of equilibrium moisture content of grain at the same relative humidity and temperature of ambient. Values of the equilibrium moisture content decreased with increasing dose of γ-ray irradiation during both adsorption and desorption. Factor of irradiation dose was included in three widely used models for equilibrium moisture content; the parameters in the models were estimations from experimental data. Based on the correlation coefficient, mean relative error, and standard error of moisture, the modified Chung-Pfost equation and the modified Henderson equation were found to fit the desorption and adsorption isotherms for rough rice in the range of experimental conditions studied.     

Modeling of Moisture and Temperature Changes of Wheat during Drying in a Triangular Spouted Bed Dryer

A mathematical model of temperature and wheat moisture content distribution inside a triangular spouted bed dryer was developed. The model is based on analysis of heat and mass transfer inside the dryer. In addition to that, an empirical bulk density model has been developed for wheat and included in the drying simulation. A laboratory-scale triangular spouted bed (TSB) dryer was used to dry wheat grain to validate the model. The dryer was divided into three sections, namely spouting, downcomer, and fountain. A series of drying runs were conducted to record moisture and temperature profile. There were two distinct regions observed during wheat drying. A constant rate period was observed during the initial drying stage and the falling rate period took place at the later drying stage. Initial moisture content and operating drying temperature governed the timing of transition from constant rate period to falling rate period. The model can be used to accurately predict the moisture content of wheat during drying. The temperature prediction inside the TSB dryer was less accurate, especially at high temperatures due to heat losses in the experimental dryer. Further studies are needed to improve the accuracy of this model, especially with regard to the temperature prediction.     

Modeling of Moisture and Temperature Changes of Wheat during Drying in a Triangular Spouted Bed Dryer

A mathematical model of temperature and wheat moisture content distribution inside a triangular spouted bed dryer was developed. The model is based on analysis of heat and mass transfer inside the dryer. In addition to that, an empirical bulk density model has been developed for wheat and included in the drying simulation. A laboratory-scale triangular spouted bed (TSB) dryer was used to dry wheat grain to validate the model. The dryer was divided into three sections, namely spouting, downcomer, and fountain. A series of drying runs were conducted to record moisture and temperature profile. There were two distinct regions observed during wheat drying. A constant rate period was observed during the initial drying stage and the falling rate period took place at the later drying stage. Initial moisture content and operating drying temperature governed the timing of transition from constant rate period to falling rate period. The model can be used to accurately predict the moisture content of wheat during drying. The temperature prediction inside the TSB dryer was less accurate, especially at high temperatures due to heat losses in the experimental dryer. Further studies are needed to improve the accuracy of this model, especially with regard to the temperature prediction.     

高水分玉米真空低温干燥工艺生产性试验研究

东北是我国玉米的主产区，产量占全国的30％～40％。受自然条件的影响，玉米收获水分常达22％～30％；成熟度及含水率都不均匀。根据玉米热敏性物料干燥的热特性及市场要求，考虑到它的热稳定性及破碎敏感性的特点，采用真空低温干燥技术进行了生产性试验，设计了300t／d高水分玉米真空低温连续干燥工业自动化生产线，对生产性试验关键技术进行了分析和研究。依据试验结果，分析玉米含水率、干燥介质温度、真空度、玉米温度、干燥时间、汽化蒸发温度等参数之间的联系与相互作用。生产试验表明：玉米含水率在24％时，维持干燥塔内真空度，采用高温水加热，汽化蒸发温度40～43℃，一次降水幅度达到10％～15％，保证了玉米品质的色、香、味、形及营养成分，具有干燥品质好、降水速度快、产量高、能耗低、操作方便、经济性价比高等优点。     

The Dynamic of Shrinkage/Moisture Content Behavior Determined During Drying of Microsamples for Different Kinds of Wood

This article presents the results obtained from an experimental device designed for the accurate determination of wood/water relationship on microsamples. The moisture content of the sample is measured with a highly sensitive electronic microbalance and two dimensions of the sample are collected continuously without contact using high-speed laser scan micrometers. The whole device is placed in a climatic chamber. The microsamples investigated were prepared with a diamond wire saw. The unique ability of this device to work with small samples allowed normal, opposite, and reaction wood to be characterized separately.

Experiments were carried out on three wood species (beech, spruce, and poplar). In the case of beech, a deviation from the linear relation between tangential shrinkage and moisture content between 40 and 20% is particularly noticeable for the first desorption. A localized collapse of ray cells could explain this result. Compared to normal wood, an important longitudinal shrinkage and a low tangential shrinkage were observed in compression wood of spruce. Both the tension wood and opposite wood of poplar exhibit a high longitudinal shrinkage, but no significant difference between the three types of wood is noticeable in the tangential direction.     

Energetic Analysis of Drying Biological Materials with High Moisture Content by Using Microwave Energy

One of the most important parameters in the drying process is the efficiency of energy transfer. Although it is well known that the absorbed component of the referred energy in the dehydration process under microwave conditions is theoretically lower—especially during the falling rate period of drying—by an order of magnitude than that of convective drying, the real efficiency of energy transfer in the microwave field depends on numerous—partly unknown—factors. In this study, the most significant relations between the energy transfer efficiency and the drying parameters were investigated. During the experiments, two power levels were used to study the effects of domain variables in apple, potato, and onion dehydration processes. The results showed that variations in microwave power level played an important role in overall drying kinetics.

Based on the recorded data, we determined the typical energy efficiency factors for microwave drying of apple, potato, and onion. The specific energy consumption was calculated to compare the energy efficiency of a single measurement series. It was evident that by applying higher power levels, the energy utilization was more efficient. Furthermore, we theoretically proved and experimentally showed the nonthermal effects of the microwave energy.     

Non-destructive Measurement of Moisture Distribution in Wood during Drying Using Digital X-ray Microscopy

The objective of this study was to develop a nondestructive method by which moisture distribution in wood during drying could be predicted. A newly developed digital X-ray microscope was used to measure the moisture content of wood and its accuracy and resolution was evaluated compared to the classic oven-dry method.

Small green wood specimens of Sugi (Cryptomeria japonica D. Don) were cut and dried under constant temperature and humidity. As the weight was decreasing during drying, X-ray microscope images of cross section were obtained. From these digital images and specimen weight, the moisture content during drying was measured by the two methods. After the shrinkage of the specimen was canceled, the standard error achieved finally was about 1% moisture content within the experimental range. As the image was divided into small subimages, the clear moisture distribution can be seen. It was found that the image divided into 32 × 32 subimages in each size of 0.625 × 0.625 mm might be valid to determine the moisture distribution, and that the drying rate in early wood is larger than in late wood.     

Study of Temperature and Moisture Distribution in Paddy in a Triangular Spouted Bed Dryer

A triangular spouted-bed dryer has been designed as part of a hexagonal continuous dryer for paddy. In the triangular-bed dryer, the spout of drying air is placed in one corner of the drying chamber. Combining six triangular units with the spout located in the center of the dryer allows a continuous process and reduces energy consumption due to the reduction of heat losses. The current study focuses on the distribution of moisture and temperature in an individual triangular bed. Models of distribution have been developed in order to provide a better understanding of the phenomena and to help in scaling-up of the design.     

Effects of High-Temperature Fluidized Bed Drying and Tempering on Kernel Cracking and Milling Quality of Vietnamese Rice Varieties

Studies on the effects of high-temperature fluidized bed drying and tempering on physical properties and milling quality of two long-grain freshly harvested Vietnamese rice varieties, A10 (32±1% wet basis moisture) and OM2717 (24.5±0.5% wet basis moisture), were undertaken. Rice samples were fluidized bed dried at 80 and 90°C for 2.5 and 3.0 min, then tempered at 75 and 86°C for up to 1 h, followed by final drying to below 14% moisture (wet basis) at 35°C by thin-layer drying method. Head rice yield significantly improved with extended tempering time to 40 min. Head rice yield tended to increase with decreasing cracked (fissured) kernels. The hardness and stiffness of sound fluidized bed dried rice kernels (in the range of 30–55 N and 162–168 N/mm, respectively) were higher than that of conventionally dried ones (thin layer dried at 35°C). The color of milled rice was significantly (P < 0.05) affected by high-temperature fluidized bed drying, but the absolute change in the value was very small.     

NHD脱碳溶液水含量高的原因及应对措施

结合脱碳系统工艺流程及实际运行情况,分析NHD溶液水含量高的原因,并介绍其应对措施。     

A General Form of Thermal Conductivity Equation for an Apple Sample During Drying: Variation with Moisture Content and Temperature

ABSTRACT

The general correlation developed by Rahman¹ to predict the isothermal thermal conductivity of foods is limited to use when porosity approaches to 1.0. An improved equation is proposed which is applicable for all porosity ranges, wide ranges of temperatures moisture contents. This new model is tested against the experimental data on thermal conductivity of an apple sample and is shown to be appropriate. In this paper, another general model proposed by Krischer² is also applied and the results are discussed.     

Variation in Drying Behavior and Final Moisture Content of Wood during Conventional Low Temperature Drying and Vacuum Drying of Betula pendula Timber

Conventional and vacuum drying experiments were conducted on Betula pendula timber, which was sawn from trees felled during three different seasons. The influence of the wood procurement season on drying behavior differed, on the one hand, between the drying phases above and below 30% moisture content in the conventional drying, and, on the other hand, between the conventional and vacuum drying methods. During the first steps of the conventional drying process, relative humidity in the kiln, as well as drying time and drying rate, varied according to the felling season. Variations in environmental conditions outside the kiln and the seasonal variation in the physical properties of the wood were presumed to be the reasons for differences in drying behavior. The difference in moisture content gradient, i.e., the difference in final moisture content between the inner wood and the surface layer of boards, was greater in conventionally dried timber than in vacuum-dried timber. In conventionally dried timber there was a clear seasonal variation in the gradient of final moisture content, which was greatest for winter-felled wood. The premature drying of the surface layer during the first steps of the conventional drying process of winter-felled wood was the reason for the higher gradient of moisture content. Storage of wood as logs decreased the standard deviation of the final moisture content.