Assessing the moisture migration during microwave drying of coal using low-field nuclear magnetic resonance

Microwave drying of coal has the advantage of volumetric and selective heating, which saves energy and time. However, comprehensive assessment of the moisture migration during microwave drying is lacking. In this study, the low-field nuclear magnetic resonance (LF-NMR) was used for moisture characterization during microwave drying. Moisture migration occurs first in larger pores, whereas the smaller pores appear to remain water-saturated. As the microwave power increases, the drying capacity and drying rate both increase because high-power microwave can open the blind pores to promote moisture seepage. Furthermore, moisture migration during microwave drying is usually directional (i.e., along the bedding plane). The LF-NMR method provides a framework for the determination of moisture migration of coals.     

Experimental study on drying characteristics of wheat by low-field nuclear magnetic resonance

The characteristics of transverse relaxation time (T₂) of water in wheat were studied by measuring the relaxation time of low-field nuclear magnetic resonance. Analysis of the exponential distribution of T₂ revealed that wheat contains five water components. The T₂ relaxation time and distribution significantly changed during drying. The dynamic characteristics of five water components during wheat drying were determined using the signal quantity of their characteristic peaks, which showed different features. Weakly chemically bound water (T₂₂) and water ascribed to cell wall (T₂₃) were the main source of water loss. Moreover, most T₂₃ and extracellular water (T₂₄) were removed during drying. Water migration between strongly chemically bound water (T₂₁) and the other water components was bidirectional. This process was not only affected by temperature but also by wheat moisture content and proportion of the five water components. The start time of water migration advanced and growth rate of T₂₁ at the end of drying to that before drying increased at 60, 70, and 80°C. Drying at varied temperatures should be applied according to the characteristics of five water components during the drying process. In addition, high initial temperature was found to be necessary to achieve high drying rate of T₂₃, T₂₄, and free water (T₂₅). The use of drying temperature of 80°C at the early stage and then changing to 70°C reduced the heat consumption by 4.81% and increased the drying time by 9.61%.     

Effect of steam-drying treatment on moisture content,drying rate,color, and drying defects in juvenile wood of Tectona grandis from fast-growth plantations

Tectona grandis is the second most important species for reforestation in Costa Rica, and any improvement in its industrialization process is important, especially the drying process. Lumber obtained from a plantation of 12-year-old T. grandis trees was used to evaluate three drying schedules that include integrated steaming processes to determine the combined effect of the steam-drying system on the dried lumber. The variations in the moisture content (MC) and drying rate (DR) with drying time (DT) both before and after the steaming process were modeled mathematically for boards that have a flat and quarter grain pattern. For both types of boards that were dried with and without steaming, a relationship between MC and DT was observed. There was inflexion at 40%, and two mathematical models were computed. Additionally, the relationship between DR and DT for boards with flat and quarter grain patterns was not affected by the steaming process, and an inflection point was observed at 30?h (40% MC for the lumber). Moderate changes were observed in the CIELAB color system and dried lumber became darker. The steaming process, which was integrated in the drying schedule for boards with the flat and quarter grain pattern, decreased the incidence or magnitude of drying defects depending on the grain pattern and drying schedule used.     

Measurement of water content and moisture distribution in sludge by 1H nuclear magnetic resonance spectroscopy

Moisture distribution in sludge is essential for the examination of dewatering problems; however, sufficiently rapid and accurate methods of sludge moisture measurement are currently lacking. Hence, this study investigated a low-field ¹H nuclear magnetic resonance (NMR) method for measuring water content and moisture distribution in sludge. Moisture content measured by NMR was closely correlated with the thermal drying method (R² = 0.999). The loss of mechanical bound water from sludge was the primary cause of the decrease in water content from 96 to 37% during thermal drying at 40°C. NMR is more accurate, rapid, and nondestructive than other water distribution measurement methods.     

Impact of rewetting and drying of rough rice on predicted moisture content profiles during in-bin drying and storage

Accurate prediction of moisture content (MC) is vital for effective control of on-farm, in-bin drying and storage of rough rice, especially for systems using recently introduced technology to automate fan run time. The study used simulations, laboratory, and field experiments to investigate the extent to which rewetting and drying, during in-bin drying and storage, affect accuracy of predicted MC—a critical parameter for automated fan control. Vapor sorption analysis (VSA) was used to generate MC prediction models for rough rice. Simulations of in-bin drying and storage, using in-field weather data, were performed while segregating effects resulting from rewetting and drying of the rough rice and the type of fan control strategy used. Predicted MC profiles of rough rice and drying durations were compared with those resulting from using standard constants in the literature for modeling. The root mean square error associated with predicting the MC by model constants developed using the VSA was 0.54% MC and 1.32% MC dry basis (d.b.), for desorption and adsorption, respectively. Deviation in MC logged by in-bin built, field sensors and that simulated by taking into account the influence of rewetting and drying were generally within 1.5% point difference. Therefore, rewetting and drying did not affect drying duration. However, drying duration was significantly influenced by fan control strategy (p?相似文献   

Characterizing the kinetics of free and bound water using a non-isothermal sorption technique

This article presents novel techniques for characterizing the kinetics of the free and bound water in a specimen by performing only one single sorption experiment. By monitoring the time variation of the residual water in a specimen that undergoes a controlled non-isothermal sorption over the range of temperatures of interest, the initial mass of the free and bound water in the specimen, the Arrhenius constants of diffusivity of the free water, and the Arrhenius constants of the rate of dissolution of the bound water can be extracted through a combination of time–temperature transformation and regression.     

Petrophysical characterization of coals by low-field nuclear magnetic resonance (NMR)

Nuclear magnetic resonance (NMR) has been widely used in petrophysical characterization of sandstones and carbonates, but little attention has been paid in the use of this technique to study petrophysical properties of coals, which is essential for evaluating coalbed methane reservoir. In this study, two sets of NMR experiments were designed to study the pore types, pore structures, porosity and permeability of coals. Results show that NMR transverse relaxation (T₂) distributions strongly relate to the coal pore structure and coal rank. Three T₂ spectrum peaks identified by the relaxation time at 0.5-2.5 ms, 20-50 ms and >100 ms correspond to pores of <0.1 μm, >0.1 μm and cleats, respectively, which is consistent with results from computed tomography scan and mercury intrusion porosimetry. Based on calculated producible and irreducible porosities through a T₂ cutoff time method, we propose a new NMR-based permeability model that better estimates the permeability of coals. In combination with mercury intrusion porosimetry, we also propose a NMR-based pore structure model that efficiently estimates the pore size distribution of coals. The new experiments and modeling prove the applicability of NMR in petrophysical characterization of intact coal samples, which has potential applications for NMR well logging in coalbed methane exploration.     

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   

Determination of ethylene oxide content inn-Alcohol ethoxylates by proton nuclear magnetic resonance spectroscopy

Proton Fourier transform nuclear magnetic resonance spectral data were collected onn-alcohol ethoxylates and used to calculate the percent ethylene oxide (EO) content of then-alcohol ethoxylate without an internal or external standard. The accuracy and precision of the method were determined from ten repetitive analyses of hexaethylene glycol monon-dodecyl ether. The standard deviation was 0.23 wt% EO with a relative standard deviation of 0.40%. The method had a relative error of +0.55% and an absolute error of +0.32% EO. This paper was presented at the 20th ISF World Congress/83rd AOCS Annual Meeting and Exposition in Toronto, Canada, May 10–14, 1992.     

Effect of airflow rate on drying air and moisture content profiles inside a cross-flow drying column

Rice at 20.5 and 16.3% initial moisture contents (IMCs) was dried using 57°C/13% RH air at airflow rates (Qs) of 0.36, 0.46, and 0.56 (m³/s)/m² for 30, 60, and 90?min, respectively, in an experimentally simulated cross-flow drying column. Q significantly affected the drying air and rice moisture content profiles within the drying column; for a particular drying duration, the range of MCs within the column decreased as Q increased. Q also impacted the extents of intra-kernel material state gradients created and thus had potential impacts on kernel fissuring and consequent head rice yield reduction. In addition, the impact of Q on the above-mentioned profiles was dependent on the rice IMC.     

低场核磁法测定凝胶过滤介质的孔径分布

凝胶过滤介质在蛋白质、多糖等生物大分子的分离纯化过程中具有非常重要的作用,其中介质的孔径分布是决定分离纯化效果的关键因素。由于绝大部分凝胶过滤介质是软凝胶,因此很难用常规的方法如压汞法、低温氮吸附法等测定其孔径分布。本文探索了利用低场核磁共振测定凝胶过滤介质的孔径分布的方法。首先通过抽滤、自制琼脂糖凝胶块等实验确定了峰的归属,明确了介质孔内水、介质间隙水和自由水在核磁共振横向弛豫时间(T₂)图谱上的分布范围;随后与逆体积排阻层析法(ISEC)测定的结果相对比,得出层析介质孔径和介质孔内水弛豫时间的关系;最后通过高斯正态拟合得到了介质的孔径分布。实验结果证实了低场核磁共振法测定凝胶过滤介质孔径分布的可行性。该法操作简单、测定迅速,并可以为其他层析介质孔径分布的测定提供参考。     

Effect of air velocity in dehumidification drying environment on one-component waterborne wood top coating drying process

In this study, the effect of air velocity in dehumidification drying environment on one-component waterborne wood top coating drying process is analyzed by drying time and moisture content and surface temperature of coating, in which air temperature is 35°C and relative humidity is 50%, and the air velocity is the only change parameter, varying from 0.2 to 1.2?m/s. It is found that drying time of top coating shortens and moisture content of top coating decreases with increasing air velocity. Surface drying time is about 15?min, hard drying time 21?min, and sanded drying time 37?min. To accelerate the drying speed, the air velocity is increased to more than 0.4?m/s. Moisture content of top coating is 58.2% during surface drying, 31.4% during hard drying, and 21.9% during sanded drying time. An infrared thermometer is used to measure the surface temperature of coating. Surface temperature of top coating is 30.0°C when it is dried to the surface drying degree, 33.5°C when the top coating is dried to the hard drying degree, and 34.6°C when the top coating is dried to the sanded drying degree. The drying degree of coating can be judged from the drying time and surface temperature and moisture content of coating. The drying degree of top coating is better when surface temperature is higher and the moisture content is lower.     

Reducing wood drying time by application of ultrasound pretreatment

Industrial wood is typically dried artificially after felling. The drying process is often very lengthy and consumes a large amount of energy, however, and inappropriate drying schedule can cause defects in the wood. Pretreatments such as ultrasound show the potential to reduce wood drying time without impacting quality. This study investigated the influence of ultrasound pretreatment on vacuum drying behavior, hydroxyl content, and microstructural properties of fast-growing wood samples. Pretreatments were performed at ultrasound intensity of 10 W cm^?2 and frequencies of 28 and 40 kHz, respectively, for 30, 60, and 90 min, respectively, then pretreated samples were dried at 40°C temperature under absolute pressure of 0.08 MPa. Results showed that ultrasound pretreatment did shorten the wood vacuum drying time, increase effective water diffusivity, open water channels, decompose wood extractives, and decrease hydroxyl content. In effect, ultrasound pretreatment can be applied to successful reduce wood drying time.     

Modified data handling for rapid low-field nuclear magnetic resonance characterization of lyotropic liquid crystal composites

A refined nuclear magnetic resonance (NMR) technique was developed to determine the relative volumetric proportions of various phases present in lyotropic liquid crystal (LLC) composites such as soap/detergent bars. Conventionally, the FID (free induction decay, referred to hereafter as Method 1) technique is used for analysis of these systems. This technique is suitable only for composites containing a high concentration of solids and liquid crystals. Method 1 gives erroneous results for composites with a high proportion (>10%) of isotropic liquid phase (L ₁). The procedure currently practiced (Method 2) for analyzing systems containing >10% L ₁ entails a considerable amount of experimental and analysis time and involves subjectivity in data analysis. Typically, the phase characterization of the composite using conventional low-field NMR techniques takes more than 1 h. Furthermore, the hardware and data acquisition features of currently available conventional low-field NMR spectrometers are inadequate for accurate estimation of relative phase volumes in LLC composites. We developed a modified data-handling technique (FID—Carr-Purcell-Meiboom-Gill technique, or FIDCPMG technique) which enabled rapid phase characterization of LLC composites and minimized subjectivity while analyzing the data. The standard design of a conventional low-field NMR spectrometer was upgraded by incorporating a high-power transmitter and a fast digitizer. The phase composition of four model LLC composites (with L ₁ percentages varying from 7 to 90%) was determined using FIDCPMG technique and was compared with results from conventional techniques. Phase composition of the LLC composite could be determined in less than 5 min.     

高固含、快干型水性木器白色底漆的配方设计

探讨了用于封闭中纤板的水性白色底漆的配方设计思路,重点讨论了整个配方设计过程中乳液的选择、填料的选择、成膜助剂、流变助剂以及消泡剂的相互搭配,研制出具有良好打磨性和填充性以及高固含的快干型水性白色底漆。     

Dehydration modeling of Cordyceps militaris in mid-infrared-assisted convection drying system: Using low-field nuclear magnetic resonance with the aid of ELM and PLSR

Abstract

The changes in moisture content and shrinkage ratio of Cordyceps militaris during mid-infrared-assisted convection drying (MIRCD) with different drying temperatures (40, 50, and 60?°C) and velocities of airflow (1 and 2?ms^?1) were studied. The relationship between low-field nuclear magnetic resonance (LF-NMR) information and moisture content/shrinkage ratio was modeled using partial least-squares regression (PLSR) and extreme learning machine (ELM). Results indicated that the influence of drying temperature was more pronounced than that of air flow velocity. Both types of models showed good predictive ability with R²>0.90. The ELM models exhibited superior predictive performance than that of the PLSR models.     

Effects of gluten and moisture content on water mobility during the drying process for Chinese dried noodles

To investigate the water mobility during a drying process, noodles were prepared with different gluten contents (10.0%, 12.5%, 15.0%, 17.5%, 20.0%, 22.5%, or 25.0%) and moisture contents (30%, 32%, or 34%), and dried on a food moisture analysis technology platform. Three types of water were deduced from relaxation signals measured by low-field nuclear magnetic resonance (LF-NMR) spectroscopy. Peak time T₂₂ increased with gluten and moisture content but decreased with drying time from 4–6 to 1.0–1.7?ms after 1.5?h. Gluten content mainly affected the drying rate (DR) in the middle drying period, whereas initial moisture content had an influence in the middle drying period and final drying period.     

Simultaneous determination of moisture and oil content in oilseeds by pulsed nuclear magnetic resonance

Pulsed nuclear magnetic resonance technique using Carr-Purcell-Meiboom-Gill (CPMG) sequence has been used for simultaneous determination of moisture and oil content in rapeseed-mustard. This method involves sampling the free induction decay (FID) following 90° pulse in the CPMG sequence and resolving the trace of the amplitude of the CPMG echo signals into exponentially decaying liquid components of oilseeds. The data show that water in oilseeds generally exists in 2 phases and the relatively slow decaying component disappears around moisture content of 7% and below. The moisture and oil content have been determined by the method for 34 samples of 5 different varieties of seeds at varying moisture levels (∼3% to 22%). The measured moisture and oil content have been compared with the values obtained by the oven drying method and earlier known FID method of pulsed nuclear magnetic resonance (NMR) respectively, and the agreement is fairly good for rapid estimation with standard deviation of 0.70% for oil content and 0.99% for moisture content. This is a rapid and nondestructive method for determination of both moisture and oil content without weighing and drying the seeds and also seems suitable for other matrix samples.     

微波干燥在聚氨酯水性木器涂料中的应用与研究

阐述了微波加热干燥的原理,以及微波干燥聚氨酯水性木器涂料的优势,研究和分析了微波干燥在单组分和双组分聚氨酯水性木器涂料中的应用。     

Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.