温度和相对湿度对褐煤干燥动力学特性的影响

为确定褐煤干燥最佳工艺参数,在恒温恒湿热风干燥实验台上进行了温度为50～90℃,相对湿度为10％～30％条件下的褐煤颗粒热风干燥实验.将实验数据与9种经验、半经验模型进行拟合,利用相关系数、方差、均方根误差3种统计学参数对不同模型进行评价.结果表明:Page模型相比其他模型更适合用于描述干燥过程中褐煤颗粒水分随时间的变...     

Effects of germination time and drying temperature on drying characteristics and quality of germinated paddy

Germination time and drying temperature are very important parameters affecting the quality of the germinated paddy (GP) since the microstructure of starch granules is modified during germination. The experimental results showed that the germination time increasing from 60 to 68 h provided more loosely-packed starch granules, lower hardness of cooked GP, higher γ-aminobutyric acid content (GABA) and larger number of fissured GP after drying. However, the modified microstructure did not cause a difference between drying curves at each germination time. Prediction results of the moisture content from the two-layer model were in good agreement with the experimental results and also showed that the effective moisture diffusion coefficient values of husk were significantly lower than those of germinated brown rice. Drying at a higher drying temperature could reduce the number of fissured GP more significantly. The hardness of cooked GP samples and their GABA contents obtained from drying temperatures changed insignificantly from that of the shade-dried GP. The sensory analysis results revealed that the texture of GP was better than that of the rice without germination and the longer germination time provided the adverse effect on the fermentation odour and texture.     

Effect of elevated drying temperature on rapeseed oil quality

Effect of rapeseed drying temperature on oil quality was investigated over the range 50–250°C. Total oil content was not significantly affected at 5% probability. Amounts of free fatty acids were significantly affected but remained much below the maximum permissible limit. Oil color was also significantly affected but had no specific trend of variation with temperature, and visual differentiation was difficult. Further, visual cracks and blackening were observed in rapeseeds dried at 250°C. Based on this study, elevated drying temperature up to 200°C was recommended for rapeseed without adversely affecting oil quality. This would save up to 80% drying time compared to the present practice of drying rapeseed at a maximum temperature of 93°C.     

Enhanced modeling of moisture equilibrium and transport in cementitious materials under arbitrary temperature and relative humidity history

This paper focuses on behaviors of moisture dispersed in nano‐macro scale pores under various temperature and relative humidity conditions. The authors formulated an equilibrium relationship between liquid and vapor phases and a moisture flux driven by pore pressure, vapor pressure and temperature gradients. In addition, liquid and interlayer water were measured separately by ethanol in order to reveal each temperature sensitivity in saturation‐humidity paths. Based on the experiments, a modified hysteresis model for moisture isotherm was proposed. Verifications with experimental data showed that the proposed method can simulate moisture behaviors under various temperature conditions.     

Effects of environmental temperature and relative humidity on the rehydration of dried pistachios

In this study, the environmental air temperature and relative humidity effects were investigated through rehydration on the dried and roasted Siirt Pistachios (S_PS) and Antep pistachios (A_PS) with an experimental and computational approach. Therefore, an experimental apparatus was set-up in lab conditions. A series of experiments were conducted to evaluate the water activity and weight change as a function of the relative humidity and temperature of ambient air. The experimental results show that there is a combined effect of relative humidity and temperature on the increase in the weight change and water activity (a_w). The shell of pistachio is a good hygroscopic material despite its hard texture. The roasted pistachios are less prone to absorb moisture compared to the unroasted pistachios. Beside this experimental study, an intelligent modeling called “artificial neural network” model was used for prediction of the increase in the weight of different types of pistachios.     

Effects of air temperature and humidity on particle deposition

Particle deposition in a fully developed turbulent duct flow was studied. The random walk model of Lagrangian approach was used to predict the trajectories of 3000 particles with a density of 900 kg/m³. The effects of thermophoretic force and air humidity were also considered. The results were compared with the previous studies with a particle size range of 0.01–50 μm and air flow velocity of 5 m/s. The profile of dimensionless deposition velocity with relaxation time presents a V-shaped curve and the results are in good agreement with the previous studies.The effects of air temperature and humidity on particle deposition with a particle size of 1 μm were also investigated. The results show that thermophoretic force accelerates particle deposition onto the duct walls with increasing temperature difference between air flow and the duct wall surface. Meanwhile, it was found that particle deposition velocity increases with air humidity.     

Application of the reaction engineering approach (REA) for modeling intermittent drying under time-varying humidity and temperature

A ‘good’ drying model is important for the design of dryer, evaluation of dryer performance and prediction of product quality. Among the available models, the reaction engineering approach (REA) is a lumped model, proven to be simple, robust and accurate to model drying of several materials. In this paper, the REA is implemented to model intermittent drying, which is usually practiced for saving energy consumption and maintaining product quality during drying, under time-varying drying air temperature and humidity, which is a challenging drying case to model. For this purpose, the equilibrium activation energy (ΔE_v,b) is defined according to the drying settings in each time period and combined with the relative activation energy (ΔE_v/ΔE_v,b) generated from the convective drying experimental data obtained under constant drying conditions. The mass and heat balances also implement the corresponding drying settings in each time period during the intermittent drying. The results indicate that the REA can describe both the moisture content and temperature profiles of the intermittent drying under time-varying drying air temperature and humidity well. The accuracy, simplicity and robustness of the REA for the intermittent drying under time-varying drying air temperature and humidity are proven here. This has provided a major and significant extension of the REA on modeling challenging drying cases.     

Effect of three drying methods on the drying characteristics and quality of okra

The objective of this study was to compare the drying characteristics and quality of dried okra obtained by vacuum freeze drying (VFD), microwave vacuum drying (MVD), and pulse-spouted microwave vacuum drying (PSMVD). The quality parameters include color (L*, a*, and b*), texture (hardness and fracturability), shrinkage ratio (SR), nutrient retention (chlorophyll, flavonoids, and vitamin C), and sensory score was investigated. Vacuum freeze drying maximally preserved the original properties of samples. And the samples dried by PSMVD showed higher quality and more uniformity compared to MVD. Considering of all aspects comprehensively, such as cost-effectiveness, practicability, and scale-up, PSMVD was a promising technique which would match results obtained by vacuum freeze drying.     

Air drying characteristics and moisture diffusivity of carrots

The effects of air temperature on drying kinetics of carrot cubes were investigated. Convective drying characteristics of carrot cubes in a spout-fluidized bed were evaluated through the effect of air temperature on drying kinetics. Drying was carried out at 60, 70, 80 and 90 °C and the falling drying rate data were used to calculate the effective diffusion coefficients from the Fick's equation. Four mathematical models available in the literature were fitted to the experimental data. The Two-term model is given better prediction than the Henderson and Pabis, Page and Lewis model and satisfactorily described drying characteristics of carrot cubes.     

碳酸钙干燥设备概况与发展

对碳酸钙（轻钙，重钙，纳米钙，专用钙等）的干燥及其有关设备的现状和发展作了回顾，并就轻钙、重钙、纳米钙等干燥效率的提高、设备的改进以及组合干燥的应用实际效果作了阐述。     

Microwave-convective drying characteristics of pharmaceutical powders

Common pharmaceutical excipients and active ingredients, wetted with specific solvents, were dried in a combined microwave-convective system (2.45 GHz, 90 W). The drying curves showed a constant drying rate period, followed by two falling rate periods. Cross-flow air velocity had little effect on solvent evaporation rate in the initial stages; however, an increase in drying rate was observed during the falling rate period. Increasing air temperature increased the drying rate throughout the entire process, with reductions in drying time of up to 78% being observed. Average and maximum sample temperatures were found to decrease on addition of air-flow, the extent of which was dependent on material and operating conditions.     

Effects of drying conditions, admixtures and specimen size on shrinkage strains

The paper presents the results of an experimental investigation on the effects of drying conditions, specimen size and presence of plasticizing admixture on the development of shrinkage strains. The measurements are taken in a harsh (50 °C and 5% R.H.) and a moderate environment (28 °C and 50% R.H.). The results include strain development at various levels of cross sections of concrete prisms. The drying conditions are found to be the dominant parameter affecting the shrinkage strain development particularly in specimens of smaller sizes. The effect of plasticizing admixture on shrinkage strains is negligible.     

Effects of air drying properties on drying kinetics and stability of cactus/brewer's grains mixture fermented with lactic acid bacteria

The present work examined the effect of air drying conditions on drying kinetics of cactus/brewer's grains mixture fermented with Lactobacillus plantarum HG328248. The drying kinetics was performed in a convective dryer for three air temperatures (40, 50 and 60 °C) and three air velocities (0.7, 1.0 and 1.3 m/s). Four mathematical models were tested to fit the drying curves. The Page model seemed the most appropriate to describe experimental data. The experimental drying curves showed two periods: that at constant rate and that of falling rate. The air temperature was the main factor in controlling the drying rate. The characteristic drying curve equation was determined.The influence of air drying conditions on color, water activity and microbiological quality of the fermented product was also studied. The temperature affected these parameters more significantly than air velocity. All dehydrated products had a satisfactory microbiological quality and consequently could be introduced in ruminant feed.     

Impacts of different drying strategies on drying characteristics,the retention of bio-active ingredient and colour changes of dried Roselle

The drying kinetics of Roselle(Hibiscus sabdariffa L) of variety Terengganu(UMKL-1) and the quality attribution of Roselle were studied. The experiments were conducted using four different drying methods, including solar greenhouse drying(SD), solar greenhouse with intermittent heat pump drying(SIHP), hot air drying(HA) and heat pump drying(HP). Among the four drying methods, HP achieved the highest drying rate at a range from0.054 g H_2 O·(g DM)~(-1) ·min~(-1) to 0.212 g H_2 O·(g DM)~(-1)·min~(-1) while SD had the lowest drying rate, measured at 0.042 g H_2 O·(g DM)~(-1)·min~(-1).The analysis on colour kinetics revealed that there is no significant colour loss(p 0.05) observed from HP's dried Roselle. Greater amount of flavonoid compounds i.e. protocatechuic acid was found in SD and SIHP dried finished product whereas HP's dried Roselle contains higher percentage of catechin as compared to other drying methods.     

The air temperature modulation impact on the drying of soybeans in a fixed bed

This work aimed to explore an alternative to reduce costs in the soybean drying process using a periodic drying operation, which can enhance mass and energy transfer, leading to lower energy consumption in comparison with the conventional operation carried out with entrance drying air in steady-state conditions. A fixed bed dryer for laboratory scale was used to dry soybean grains and experiments were carried out, applying the periodic and conventional operations with the same drying time and energy consumption. Results indicated with 5% of significance that the experiments conducted with entrance air temperature modulation achieved higher levels of the percentage of evaporated water improving the dryer performance. These results were in agreement with predicted data obtained with heterogeneous models and they indicated that the periodic drying operation can demand less energy to achieve a specific safe level of soybean moisture content for storage.     

Microwave drying method investigation for the process and kinetics of drying characteristics of high-grade rutile TiO2

Titanium dioxide has been extensively applied in aviation, cosmetics, the chemical industry, and coatings. Currently, the primary way to prepare high-grade rutile TiO₂ is the chlorination method, which mainly uses ilmenite or titanium slag as raw material through the chlorination process and then reacts it in an oxidation furnace to prepare titanium powders. However, the TiO₂ material produced by the liquid-phase method contains a large amount of water, which makes the equipment vulnerable to corrosion in the subsequent process. Meanwhile, the sharp temperature change will lead to the accumulation of water vapor, which may lead to explosion and severe agglomeration, resulting in high research costs and reduced product performance. Therefore, drying equipment with high drying efficiency, high product quality, and low carbon is urgently needed. This paper used microwave drying equipment to assist in drying rutile TiO₂ powders. Results indicated that the microwave power, moisture content, and initial mass positively related to the drying rate. The drying process was simulated and analyzed using four common thin-layer kinetic models. A good agreement was that the Modified Page model was in good agreement with the actual drying process of TiO₂. The effective diffusion coefficient was calculated. After calculation, the activation energy of microwave-drying TiO₂ was 8.22 g/W. This article offers a kinetic theoretical basis and abundant data guidelines for actual products to reinforce the drying of high-grade TiO₂ powders.     

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%.     

Effects of intermittent microwave drying on quality characteristics of pistachio nuts

In this research, the effect of intermittent microwave drying (IMD) on drying time and quality characteristics for three varieties of Iranian pistachio nuts was investigated and compared with the sun drying method. The quality parameters, such as chemical characteristics, physical parameters, and sensory evaluation were considered. Three varieties, Kal-Khandan, Kaleh-Bozi, and Ghermez, were dried in an 800-W, 2,450-MHz domestic microwave oven. Experiments were conducted in three material loads of 50, 100, and 150?g under intermittent method at 6?s of power-on and 70?s of power-off with three replications. The total drying time was in the range of 114.03–266.07?min, depending on material loads and varieties. The higher the material load, the longer the drying time. The results showed that the effect of drying method on the shell splitting size was very significant (p?p?相似文献   

Direct and indirect power ultrasound assisted pre-osmotic treatments in convective drying of guava slices

Application of ultrasound to osmotic dehydration of guava slices via indirect sonication using an ultrasonic bath system and direct sonication using an ultrasonic probe system was studied. Pre-treatments were designed in three osmotic solution concentrations of 0, 35, and 70 °Brix at indirect ultrasonic bath power from 0 to 2.5 kW for immersion times ranging for 20–60 min and direct ultrasonic probe amplitudes from 0 to 35% for immersion times of 6–20 min. The calculated ultrasound intensities from calorimetric ultrasound power dissipated indicated that direct sonication was more intensive than indirect sonication. The general linear model (GLM) showed that ultrasound input (power and amplitude), osmotic solution concentrations, and immersion time increased the water loss, solid gain, and total colour change of guava slices significantly with P < 0.0005. Indirect sonication in osmotic solutions contributed to high water loss and solid gain with acceptable total colour change than direct sonication. Applying ultrasound pre-osmotic treatment in 70 °Brix prior to hot-air drying reduced the drying time by 33%, increased the effective diffusivity by 35%, and decreased the total colour change by 38%. A remarkable decrease of hardness to 4.2 N obtained was also comparable to the fresh guava at 4.8 N.     

Energy consumption and quality aspect by intermittent drying

The aim of this paper is to examine the effectiveness of intermittent drying with respect to drying time, energy consumption, and quality of dried samples. By intermittent drying is meant here the convective drying with periodically changing both the temperature and the humidity of drying air. The cylindrically shaped kaolin samples were used for tests in these studies. The acoustic emission (AE) method was applied to monitor on line the development of material fracture for the purpose of detection of the material crack commencement, and thus to establish the moment at which the changes of drying conditions should be initiated. The kinetics of drying, the consumption of energy, and the quality of the dried samples were examined. It was shown that drying at intermittent conditions leads to products of much better quality than drying at stationary conditions by almost the same duration of these processes. The energy consumption was smaller by intermittent drying realized with variable air temperature and greater by variable air humidity in comparison to drying at stationary conditions.