Online measurement of moisture content,moisture distribution,and state of water in corn kernels during microwave vacuum drying using novel smart NMR/MRI detection system

Moisture content is unevenly distributed and hard to measure when agricultural products are dried using microwave drying. A low-field nuclear magnetic resonance/imaging (NMR/MRI) and microwave vacuum drying (MVD) combination equipment was developed. The residual moisture content, distribution, and state of water (free, immobilized, and bound) in fresh corn kernels during MVD were quickly measured in real time. NMR results indicated that the amplitude of free and immobilized water decreased very rapidly at the early stage of MVD, while the amplitude of bound water experienced a similar rapid decrease at the last stage. MRI results indicated that the moisture content was always distributed unevenly during MVD, especially at the early stage. The moisture distribution tended to become uniform when drying progressed and the bound water became dominant. The residual moisture content of corn kernels and integral (total) amplitude of NMR were found to fit well with a linear model (R²?>?0.991, P?相似文献   

Computer model of drying behaviour of ceramic green bodies with particular reference to moisture content dependent properties

A numerical model was developed to predict the drying behavior of ceramic green bodies. Resolution of the simultaneous heat and mass transfer equations involved finite elements and the Backward Euler method. Based on experimental data, the model uses equivalent moisture diffusivity, water activity, thermal conductivity and heat capacity as input parameters which depend on moisture content. In particular, the equivalent moisture diffusivity is a key parameter controlling water transport from the body interior to the surface. A simple method was used to estimate the effect of shrinkage on drying rate during the initial drying stage. Predictions of the internal moisture distribution, drying rate and surface temperature as a function of time gave good agreement to experiment for green bodies of alumina paste. External conditions of convection coefficient and relative humidity are shown to sensitively control drying rate and surface temperature evolution during the constant rate period.     

Determination of moisture content and moisture content profiles in wood during drying by low-field nuclear magnetic resonance

In this article, the low-field nuclear magnetic resonance was used to measure the moisture content (MC) and MC profiles in poplar wood during real-time drying. The T₂ distribution curve at each drying stage measured using the Carr–Purcell–Meiboom–Gill pulse sequence provided detailed information in the dynamic change of free water as well as bound water of the whole wood sample. In addition, a new developed SE-SPI pulse sequence was first used to evaluate the spatially resolved T₂ distribution of the successive nondestructive sliced layer of wood. Combined with the area integration method, the moisture content in each layer was calculated, and the change of MC profiles within wood at the MC above and below fiber saturation point was well reflected.     

Evaporation and Diffusion Transport Properties and Mechanical Properties of Alginate Dried Film

The effects of alginate concentration and drying temperature on drying kinetics/characteristics of alginate solution and mechanical property of formed solid films were examined. Solid films were fabricated through thin-layer drying of 1 to 4%w/w sodium alginate solution at 40, 60, and 80°C using the solvent-evaporation method. The water weight loss profile of alginate solution undergoing drying was recorded with time. The polymer weight of all solid films was kept constant. The plasticity of films was evaluated using thermomechanical analyzer. The findings indicated that both constant rate and falling rate periods existed during drying of dilute alginate solution or at low drying temperature since both surface and core waters were available for drying. The falling rate period dominated in drying of an alginate solution of high polymer concentration and at high drying temperatures with internal diffusion being the governing transport phenomenon for water. In the latter, an exponential relationship between water content and drying time was obtained. The drying process of 4%w/w alginate solution at 60 and 80°C was relatively simple as there was only a single drying stage, viz. the falling rate period requiring no consideration of critical moisture content. The drying rate was faster than those obtained from the dilute alginate solution or conducted at low temperature, such as 40°C. The plasticity attributes of films prepared from 4%w/w alginate solution can be modulated to a degree similar to films prepared from dilute alginate solution or dried at low temperature via changing the drying temperature between 60 and 80°C.     

Optimal Control of the Secondary Drying Stage of Freeze Drying of Solutions in Vials Using Variational Calculus

Abstract:

The problem of operating freeze drying of pharmaceutical products in vials loaded on trays of freeze dryer to obtain a desired final bound water content in minimum time is formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In the type I freeze dryer design, upper and lower plate temperatures were controlled together, while in the type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Only the scorch temperature was considered as a constraint on the system state variables during the secondary drying stage, because all the free water content (frozen water) is removed from the solid matrix during the primary drying stage of freeze drying. Necessary conditions of optimality for the secondary drying stage of freeze drying process in vials were derived and presented by using rigorous multidimensional unsteady-state mathematical models. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in drying times of the secondary drying stage of the freeze drying process in vials were observed and more uniform bound water and temperature distributions in the material being dried were obtained compared to the conventional operational policies.     

Dewatering of spontaneous-coagulation-cast alumina ceramic gel by filtrating with low pressure

Water removal in colloidal processing is a tough and crucial problem because deformation and cracking of the wet body easily happen during the drying process. Inspired by conventional pressure filtration (PF), we combined spontaneous coagulation casting (SCC) with PF to partially remove water from the gelled sample before drying for the purpose of lessening the risk of cracking and shortening the drying period. The effect of pressure, holding time, and solid loading on the particle packing ratio of wet samples, the drying process, and the bulk density and homogeneity of green and sintered bodies was surveyed systemically. The PF process of 0.4 MPa for 2 h was optimized based on dewatering ratio from ceramic slurries. The particle packing ratio of the pressure-filtrated samples increased with the solid loading of ceramic slurries, and 61 vol% was obtained for the slurry with 56 vol% solid loading. The drying time of the pressure-filtrated samples was shortened by as much as 42%–53% compared with that of the gelled samples, and the linear shrinkage for the pressure-filtrated samples during drying was only approximately 0.5%, much smaller than that of the gelled samples (2.4%–4.6%). Furthermore, the bulk density of the pressure-filtrated green bodies was more than 2% higher than that of the gelled green bodies, and more homogeneous green bodies were obtained by PF than by SCC. The alumina ceramic with 98.8% relative density and a homogenous density distribution was obtained after being sintered at 1550 °C for 2 h.     

水基SiC浆料的喷雾造粒特性

以水为液体介质,制备分散稳定的水基SiC料浆,并利用喷雾造粒技术对水基SiC浆料进行造粒,研究了碳化硅浆料固含量及喷雾干燥工艺对造粒粉特性的影响。研究结果表明:浆料固相含量对造粒粉体粒径分布影响明显,粉体粒径随固含量的增加而增大。在最佳的干燥工艺条件下,碳化硅粉体流动性得到较大改善,素坯密度增加,陶瓷力学性能提高。     

Influence of pore structure and impregnation–drying conditions on the solid distribution in porous support materials

Deposition of solids within porous materials from a drying solution is an important phenomenon in numerous natural and industrial processes. A profound knowledge about influences of different parameters on the solid distribution in the material is required for an effective targeted impregnation process. Experimental investigations and simulations are used to study the influence of pore structure, drying conditions, and solute concentration on the solid distribution in porous support materials after impregnation and drying. It is found that low drying rates lead to strong solid accumulation at the material surface, whereas high drying rates reduce the solute transport to the surface and result in more uniform solid distributions. A small pore diameter and distribution width reduce solute migration during drying and lead to uniform solid distributions without being influenced by the drying conditions. A higher initial concentration of the impregnation solution causes pronounced surface accumulation, while low initial solute concentrations result in more uniform distributions. Fundamental effects during drying are captured in an existing pore network model by adaption of experimental pore structures and impregnation–drying conditions, resulting in a good general agreement of experiments with simulations.     

EFFECT OF DRYING METHOD ON SHRINKAGE AND POROSITY

The effect of drying method on bulk density, particle density, specific volume and porosity of banana, apple, carrot and potato at various moisture contents was investigated, using a large set of experimental measurements. Samples were dehydrated with five different drying methods: conventional, vacuum, microwave, freeze and osmotic drying. A simple mathematical model was used In order to correlate the above properties with the material moisture content. Four parameters with physical meaning were incorporated in the model: the enclosed water density p_w, the dry solid density p_s, the dry solid bulk density p_bo and the volume shrinkage coefficient β'. The effect of drying method on the examined properties was taken into account through its effect on the corresponding parameters. Only, dry solid bulk density was dependent on both material and drying method. Freeze dried materials developed the highest porosity, whereas the lowest one was obtained using conventional air drying.     

Formation Mechanism of Cracks During the Freeze Drying of Gelcast Ceramic Parts

The near‐net shaping of gelcast ceramic parts can be achieved using freeze‐drying technology. It was discovered that the cracks probably occurred inside the part during freeze drying due to the formation of liquid water. To explain the formation mechanism of cracks, the electrical resistance method was employed to measure the part's eutectic temperature which can be used to determine the freezing and melting state of the part. Affecting factors on cracking were investigated by testing the temperature and water loss of the part during the drying stage, and the cracks inside the part were detected through computed tomography (CT). It was found that when the temperature of the part was higher than the eutectic temperature, the ice crystals at the sublimation front would melt, resulting in the formation of wet green body. The cracks will occur inside the part because great capillary forces are formed in the wet green body. Cracks could be controlled through reducing heat supply by lowing shelf temperature, decreasing pressure of the drying chamber or lowering the dried layer resistance against water vapor by improving the freezing temperature or reducing the solid loading of the part.     

Study on Drying Organic Sludges by Thermal Jet Dryer—Part 1: Drying Performance of Thermal Jet Dryer

The authors are developing a thermal jet dryer (TJD), with a vertical disc-shaped drying tank, for the purpose of weight and volume reduction of solid wastes with high water content, such as organic sludges. In order to obtain the drying performance of TJD, drying experiments using three kinds of solid wastes were carried out. The following results were obtained: (1) Drying performance depended most on the disintegration characteristics of sample. (2) There was little influence of the samples' properties on the gas–solid multiphase flow in the tank. (3) There was a critical feed rate at which the drying performance changed drastically.     

Modeling coupled heat and mass transfer during drying in tape casting with a simple ceramics–water system

In many industrial processes such as in tape casting for electronics or in the food industry, drying is one of the determining physical phenomena. In this study, the evaporation of water from a ceramic–water mixture is investigated with the purpose of understanding the drying rate in the drying process of thin sheets produced by the tape casting process. The rate of mass loss in the drying process is a key factor that often is of interest, as it affects the final properties of the tapes. The 1D heat conduction equation is solved numerically to obtain the temperature field in a ceramic sheet. The change in the concentration of the water content is then used as the driving force for diffusive mass transport of the water. Mass–averaged thermal properties are assumed for the ceramic–water mixture in the initial stage. As the water evaporates, the thermal properties of the solid ceramic become more dominant since the fraction of water approaches zero. The developed model is used to simulate a simple test for the drying process. The drying rate is simply calculated by examining the water content in each time step. It is found that the mass loss due to the evaporation is increasing close to linearly with the drying time corresponding to an almost constant drying rate. However, the rate starts to decrease after some time in the simulation. It is also shown that too extensive surface drying results in a slow diffusion rate from the bottom, which in turn reduces the drying rate in general and hence is not favorable from a process viewpoint.     

EFFECT OF DRYING METHOD ON SHRINKAGE AND POROSITY

ABSTRACT

The effect of drying method on bulk density, particle density, specific volume and porosity of banana, apple, carrot and potato at various moisture contents was investigated, using a large set of experimental measurements. Samples were dehydrated with five different drying methods: conventional, vacuum, microwave, freeze and osmotic drying. A simple mathematical model was used In order to correlate the above properties with the material moisture content. Four parameters with physical meaning were incorporated in the model: the enclosed water density p_w, the dry solid density p_s, the dry solid bulk density p_bo and the volume shrinkage coefficient β'. The effect of drying method on the examined properties was taken into account through its effect on the corresponding parameters. Only, dry solid bulk density was dependent on both material and drying method. Freeze dried materials developed the highest porosity, whereas the lowest one was obtained using conventional air drying.     

褐煤等温干燥过程及动力学研究

为研究褐煤干燥过程,利用煤质水分分析仪和微分热重分析方法,对不同粒级的褐煤在不同干燥温度下进行等温干燥试验,得到了样品含水率与干燥时间、干燥速率与含水率的关系曲线。通过粒级分布系数对褐煤进行含水率折算,并用不同干燥模型对试验数据进行拟合,得到了在介质温度140℃下3个干燥阶段的干燥方程及干燥动力学参数。结果表明,引入粒级分布系数得到的干燥速率特征常数k值,与不同粒级的干燥速率特征常数k的均值相近。根据褐煤的干燥速率和水分的存在形式,将褐煤干燥过程分为3个干燥阶段,分析得出干燥方程模型分别用线性干燥模型、Wang经验模型、Page模型较为合理。根据Arrhenius经验公式建立了ln k与1/T的关系,得到褐煤干燥的界面蒸发活化能Ea=17.088 k J/mol,指前因子A=12.47 min~(-1)。     

Effect of operating parameters on the drying performance of multicylinder paper machine dryer section

The drying performance of multicylinder dryer section in a paper machine was investigated under various operating parameters: Inlet paper solid content (48–50%), inlet paper temperature (45–50°C), supply air temperature (100–90°C), and exhaust air humidity (75–85?g H₂O/kg dry air). The variation in environmental conditions was also considered. In this study, an improved static model was utilized to study the influence of these operating parameters on paper drying. The model was constructed using sequential modeling approach based on the drying techniques of multicylinder dryer section of a paper machine. The calculated paper solid content leaving each paper drying module and energy use is in agreement with the measured results. The simulation results showed that higher paper solid content and temperature entering the dryer section, lower supply air temperature, and higher exhaust air humidity were favorable for drying performance within the studied range of these parameters.     

Optimization of Drum Drying Parameters for Low Amylose Rice (KDML105) Starch and Flour

Abstract

An attempt was made to study and model the effects of drum drying process variables on the physico–chemical properties of low amylose rice (KDML105) flour and starch. Drum surface temperature, holding time and solid content of the slurry were varied at three levels: 115–135°C, 14–84 s and 20–40%, w/w, respectively. The dependent variables were moisture content (MC), degree of gelatinization (DG), water absorption index (WAI), water solubility index (WSI) and pasting property. High solid content led to a decrease in DG, WAI and initial peak viscosity (IPV) and increase in WSI of dried samples. Longer holding time resulted in increased DG while surface temperature had no significant effect on all characteristics. Predictive correlations were developed using stepwise multiple linear regression to predict MC, DG, WAI, WSI, and IPV of dried products from drum drying variables.     

Modeling the moisture sorption isotherms of two‐phase solid olive oil by‐product

The moisture sorption isotherms of two‐phase solid olive oil mill by‐product (SOB) were measured at different temperatures (15–50 °C) in order to thoroughly know the hygroscopic properties of this material. SOB is like a slurry with a high water content (60–70%). It is obtained in the olive oil two‐phase extraction process and is currently used as the raw material for obtaining pomace oil by extraction with hexane; prior to the extraction, drying of the SOB is required. Other uses of SOB are composting, animal feeding and solid fuel; in such cases, the previous drying of the material is also required. Sorption moisture isotherms for the two‐phase SOB were obtained by a static method. Eight models were fitted to the experimental data: BET, GAB, Halsey, Smith, Henderson, Oswin, Ferro‐Fontan and Peleg. The GAB equation was the best option to describe the water sorption behavior of SOB within a very wide range of water activities (0–0.90). A generalized GAB model, in which temperature is taken into account, was obtained by multivariable fitting of the complete set of the experimental isotherms.     

Thin-Layer Drying of Green Peas and Selection of a Suitable Thin-Layer Drying Model

The thin-layer drying of three varieties of green peas was carried out in hot air-drying chamber using an automatic weighing system at five temperatures (55–75°C) and air velocity of 100 m/min. The green peas were blanched and sulphited before drying. The variety Pb-87 dried at 60°C was judged to be best for quality on the basis of sensory evaluation and rehydration ratio. The Thomson model was found to represent thin-layer drying kinetics within 99.9% accuracy. The effective diffusivity was determined to be 3.95 × 10^?10 to 6.23 × 10^?10 m²/s in the temperature range of 55 to 75°C. The activation energy for diffusion was calculated to be 22.48 kJ/mol. The variation in shrinkage exhibited a linear relationship with moisture content of the product during drying. The Dincer number at drying air temperature 60°C and drying air velocity 100 m/min was determined to be 2,838,087. The difference between temperatures of drying air and that of green pea kernels was found to decrease with drying time for all the drying temperatures taken for investigation.     

Tape casting of nanocrystalline ceria gadolinia powder

A ceramic ceria gadolinia solid solution membrane for solid oxide fuel cells was fabricated by tape casting using a nanopowder of 37 nm average particle size. A novel combination of solvent and dispersant was used to disperse the nanoparticles. The polymer was added in a dilute stage to guarantee a homogeneous distribution. After casting a remarkable densification of the cast tape suspension from a solid loading of 20 up to 42 vol.% was observed during drying. The green tape was sintered to >92% theoretical density and was dense towards perfusion. The resulting grain size in the sintered specimen still was <200 nm.     

Preparation of Cold Brew Tea by Explosion Puffing Drying at Variable Temperature and Pressure

Cold brew tea was prepared using explosion puffing drying at variable temperature and pressure. The influences of moisture content of predried tea leaves, freezing pretreatment times at ?18°C, and puffing temperature on water extracts content of cold brew tea were studied according to the orthogonal experiments of processing of cold brew tea based on single factors. The biochemistry ingredients of cold brew tea and hot air–dried green tea were determined and compared. The optimum processing conditions of cold brew tea were obtained as follows: predried tea leaf moisture content 50%, freezing pretreatment three times, puffing temperature 105°C. Under these optimized processing conditions, cold brew tea was obtained. When cold brew tea was soaked in cold water for 30 min at 20°C, the water extracts content, caffeine, tea polyphenols, and free amino acids of cold brew tea reached 18.21, 0.88, 11.86, and 1.02%, respectively. High-performance liquid chromatography (HPLC) analysis showed that the amount of tea catechins in cold brew tea and hot air–dried green tea were 11.74 and 11.47%, respectively. The caffeine in cold brew tea was 3.06%, equal to that in hot air–dried green tea. Experimental results showed that biochemistry ingredients of cold brew tea prepared by explosion puffing drying at variable temperature and pressure difference were easy to extract by low-temperature water. This research provides theory and technical support for industrialized production of cold brew tea.