盐泥颗粒热风干燥特性及动力学模型

为优化盐泥颗粒干燥设备及结构参数，搭建热风干燥实验装置对盐泥颗粒进行热风干燥实验，研究不同风温、风速和堆积厚度对盐泥颗粒热风干燥特性的影响。对不同条件下的干燥特性曲线，通过比较决定系数R²、卡方x²和标准误差ESME等指标，评价5种常用干燥动力学模型对干燥曲线的拟合结果。结果表明：Midilli模型可以预测盐泥颗粒热风干燥过程水分的变化规律，模型预测的干燥曲线与实验干燥曲线有较高的拟合度。盐泥颗粒热风干燥过程中干燥速率逐渐下降，热风干燥特性与风温和堆积厚度密切相关。当温度从50℃增加到80℃时，有效水分扩散系数由2.038 39×10^-9 m²·s^-1增加到8.137 643×10^-9 m²·s^-1。     

鼓泡塔反应器中乙烯-苯体系气液传质系数的测定

以乙烯-苯系统为对象,借助计算机图像处理技术,采用单孔进气,研究了常温常压下鼓泡塔反应器内的传质特性.实验结果表明:在塔内液体循环速度0.02m·s-1,空塔气速2.1×10-1~6.1×10-1m·s-1、进气孔径0.8~2mm实验条件下,乙烯在苯中的吸收溶解过程主要与温度、压力及气体和液体的性质有关;吸收过程刚开始时,气泡当量直径较大,气泡消失速率较大,吸收过程类似于CO2在水中的吸收过程;气液传质比表面积α随着空塔气速的增大而增大,孔径和空塔气速的影响可以忽略;气液传质系数κL受空塔气速、进气孔径变化的影响很小,其值约为1.372×10-1m·s-1.     

粘胶短纤维的热风干燥特性研究

利用自行研制的热风干燥实验装置研究了热风温度、纤维层厚度、热风速度、纤维层含水率等对粘胶短纤维干燥特性的影响规律。结果表明:粘胶短纤维的热风干燥过程可依次分为4个阶段,即蒸发预热段、表面自由水分干燥段、纤维内部自由水分干燥段和纤维内部结合水分干燥段;热风温度对纤维第2阶段干燥速率的影响很大,100~140℃的含水率相差37.3%,对后面阶段的干燥速率影响较小,最佳热风温度为120℃;纤维层厚度对粘胶短纤维的第3阶段干燥速率略有影响,纤维层厚度以12 cm为宜;热风速度对短纤维干燥速率的影响很大,热风速度以2.0 m/s为宜,纤维层含水率对第2和第3阶段的干燥速率影响较大,应尽量减少纤维层的表面含水率。     

影响片状湿含物热风干燥效果因素的实验分析

通过在实验室洞道式干燥器里对胡萝卜切片的干燥实验,比较了热风温度、干燥风速、物料片的厚度与形状对胡萝卜干燥过程影响,综合实验数据拟合胡萝卜片热风干燥曲线、干燥速率曲线分析,得到胡萝卜干燥效率较佳的干燥条件是热风温度为70℃,干燥风速为110.3m3/h(或0.946m/s),切片厚度为2mm。随着温度和风速的增加,干燥速率增加,恒速段干燥时间变短。实验分析结果对工业生产中干燥工序如何选用设备、设定操作要求具有指导意义。     

餐厨垃圾烘箱干燥和流化干燥过程动力学

在60—100℃条件下,选择烘箱和流化床分别对餐厨垃圾干燥过程的水分变化动力学特性进行研究,并运用4个模型进行数学拟合处理。结果表明:温度对餐厨垃圾干燥过程的影响显著,随着温度的增加,餐厨垃圾样品的含水率(质量分数)和水分比均快速下降,相同温度下,流化干燥达到平衡含水率所需时间远小于烘箱干燥;餐厨垃圾干燥过程的动力学特性可以用Page模型很好地进行模拟和预测;研究中所用的餐厨垃圾样品,其有效湿分扩散系数在烘箱干燥和流化干燥中分别为3.35×10-10—2.43×10-9,1.00×10-7—2.20×10-7m2/s;活化能分别为46.52,21.93 kJ/mol;餐厨垃圾流化干燥的效率比烘箱干燥要高得多。     

PA热熔胶颗粒的压缩空气干燥模型

针对塑料工业中塑料颗粒干燥问题，研究了以压缩空气作为风源的热风干燥特性及其数学模型，为聚酰胺(PA)热熔胶颗粒干燥工艺提供参考。采用正交试验探索温度及风压对干燥的影响，比较了11种薄层干燥模型的适用性。结果得出不同风温下的水分有效扩散系数D_eff为1.0×10^-9～3.2×10^-9 m²/s。PA热熔胶颗粒的干燥活化能E_a为36.438 kJ/mol。描述干燥特性的最佳模型为Logarithmic模型，并进一步给出了0.25 MPa风压下与温度相关的干燥数学模型。     

城市污泥与木屑混合薄层干燥实验及动力学分析

角度研究了比,添加木通过对纯污泥和添加木屑的污泥进行薄层干燥对比实验,分别从混合比例、薄层厚度、干燥温度、风速木屑添加对污泥干燥特性的影响,并引入薄层模型对其干燥过程进行模拟。结果表明：与纯污泥干燥相屑后污泥干燥速率明显加快,且木屑添加比例越大、薄层越薄、干燥温度越高干燥速率越快,风速对干燥速率的影响不大;Wang—singh模型能很好的描述两种污泥薄层干燥,利用费克第二扩散定律导出的无限平板公式求出纯污泥和添加木屑的污泥在温度120℃～170℃时的有效扩散系数分别为6．13×10-6m／s～1．11×10-5m／s、1．07×10-5m／s～1．67×10-5m／s;由阿伦尼乌斯方程分别求得活化能为Es=16．67kJ／mol、Es=12．97kJ／mol。     

番木瓜的自身特性及干燥温度对干燥特性的影响研究

对番木瓜片进行了热风薄层干燥实验,主要考察了番木瓜自身的不同条件(包括成熟度、厚度、形状)与干燥温度对干燥速率的影响,通过实验数据建立了番木瓜片的热风干燥的水分比与干燥时间关系的联系,根据Page模型进行了拟合检验,结果显示模型的预测值与实测值拟合良好。     

动力锂电池石墨系负极极片干燥特性研究

极片干燥是动力电池制造环节最复杂、能耗最大的单元操作之一。对其物质及能量输运的研究可以有效提高干燥设备效率，降低厂家的生产成本。以石墨体系为负极极片材料，探究了恒温干燥和热风对流干燥中不同温度和厚度对极片干燥的影响。结果表明：热风对流干燥中同一厚度的极片干燥温度越高，则干燥时间越短；同一温度下极片厚度越薄，干燥时间越短。当热风干燥温度为80～85℃时，干燥效率较高，且极片与箔材粘结良好。静态干燥实验中温度和厚度对极片干燥的影响规律与热风干燥规律基本一致。     

四氢呋喃水溶液在3(A)分子筛上的吸附平衡与动力学研究

研究了四氢呋喃水溶液在间歇搅拌槽内3 A分子筛上的吸附平衡和动力学,用Langmuir方程拟合了吸附等温线,并用粒内表面扩散模型和Langmuir方程对吸附动力学曲线进行拟合.求取了表面扩散系数Ds,并研究了温度、初始浓度和粒径的变化对Ds的影响.Ds在25℃下C0为6.5%、dp为1 46～1.97mm时为7.83×10-7(cm2·s-1),并随着温度的升高及随着浓度的加大而增加,但不受粒径变化的影响.此外还求取了表面扩散指前因子Dso为1.85×10-5(cm2·s-1)和不同浓度下的活化能E.     

热泵干燥怀山药片的工艺研究

以提高怀山药干燥效率和产品品质为目标,本文利用热泵干燥方法,研究了热泵温度,风速,怀山药切片厚度对干燥曲线,L值,以及干制品复水率的影响。试验表明,热泵温度,风速及切片厚度都对怀山药片的干燥速率有显著影响。怀山药片热泵干燥的最佳工艺参数为：热泵温度40℃,风速1．0m/s,切片厚度5mm,干燥后怀山药片的L值和复水率分别为82．07和85．08％。     

The Thin-Layer Drying Characterstics of White Onion Slices

A batch-type experimental dryer with a computer-aided data acquisition system was designed and built for the thin layer drying studies of onion (Allium cew L., cv. Southport White Globe) slices. Twenty seven single-layer drying curves were established for a temperature range of 42.5-90⁰C, an air velocity range of 0.6-1.4 m/s, an air humidity range of 0.0093-0.0442 kg of water/kg of dry air: and a slice thickness range of 0.002-0.005 m. The single-term exponential model adequately described the single-layer drying behaviour of the onion slices. l'he dependence of the drying rate constant on air temperature, absolute humidity, velocity and on slice thickness was best explained by an Arrhenius-type relationship. The drying rate constant in which moisture diffusion and shrinkage effects are lumped was greatly influenced by the sample thickness and drying air temperature, and to a lesser extent, by the air humidity and velocity.     

The Thin-Layer Drying Characterstics of White Onion Slices

ABSTRACT

A batch–type experimental dryer with a computer–aided data acquisition system was designed and built for the thin layer drying studies of onion (Allium cew L., cv. Southport White Globe) slices. Twenty seven single–layer drying curves were established for a temperature range of 42.5–90⁰C, an air velocity range of 0.6–1.4 m/s, an air humidity range of 0.0093–0.0442 kg of water/kg of dry air: and a slice thickness range of 0.002–0.005 m. The single–term exponential model adequately described the single–layer drying behaviour of the onion slices. l'he dependence of the drying rate constant on air temperature, absolute humidity, velocity and on slice thickness was best explained by an Arrhenius–type relationship. The drying rate constant in which moisture diffusion and shrinkage effects are lumped was greatly influenced by the sample thickness and drying air temperature, and to a lesser extent, by the air humidity and velocity.     

Guest Editorial: Drying Technology—The Next 25 Years

This work aimed at studying the drying kinetics of yacon slices during vacuum drying and evaluating the effect of drying temperature, slice thickness, and citric acid concentration in the enzymatic inhibition solution on the fractal dimension and rehydration ratio of yacon slices. The drying kinetics was tentatively fitted to various thin-layer drying models, and the best fit was obtained using the modified Page model. The fit was validated after evaluating the values of coefficient of determination and parameters percentage error. The final product's fractal dimension, as calculated by the box counting method, was be between 1.5904 and 1.8358, which confirms that vacuum-dried yacon slices are fractals. Among the studied factors, drying temperature was found to negatively affect the fractal dimension and slice thickness was found to negatively affect the rehydration ratio. A good correlation was established between fractal dimension and moisture content, rehydration ratio, and hue angle, suggesting that the moisture, rehydration, and color measurements during yacon vacuum drying could be substituted or complemented by an image analysis.     

Vacuum dehydration kinetics of onion slices

Onion slices were dried in a single layer of thickness varying from 1 to 5 mm in the temperature range of 50-70 °C in a laboratory scale vacuum dryer. The effect of pretreatment, drying temperature and slice thickness on the drying kinetics of onion slices was studied. Four thin layer drying models namely Lewis model, logarithmic model, Page model and Fick's law model were applied on the experimental moisture loss data with respect to time to predict the drying pattern properly on the basis of coefficient of determination and standard error. The Page model showed better fit to the experimental data compared to other models. Effective moisture diffusivity of the slice was measured using Fick's second law of unsteady state diffusion. The diffusivity values were found ranging from 1.32E−10 to 1.09E−09 m²/s for untreated and 1.32E−10 to 1.09E−01 m²/s for treated onion slices. Effective moisture diffusivity showed increasing trend with increase in temperature and thickness.     

Continuous real-time monitoring and neural network modeling of apple slices color changes during hot air drying

A hot air drying system equipped with real-time computer vision system was used to investigate the effects of drying variables on apple slices color changes. Drying experiments were conducted at drying air temperatures of 50–70 °C, drying air velocities of 1–2 m/s, and samples thicknesses of 2–6 mm. A multilayer perceptron (MLP) artificial neural network (ANN) was also used to correlate color parameters and moisture content of apple slices with drying variables and drying time. The effects of drying air temperature and sample thickness on color changes were dominated over the effect of drying air velocity. However, non-linear and somewhat complex trends were obtained for all color parameters as function of moisture content. The MLP ANN satisfactorily approximated the color and moisture variations of apple slices with correlation coefficient higher than 0.92. Therefore, the computer vision system supplemented with ANN can be used as a non-invasive, low cost, and easy method for fast and in-line assessing and controlling of foodstuffs color and moisture changes during drying.     

MODELING OF ROUGH RICE DRYING IN THIN VERTICAL COLUMNS

The solution of classical diffusion equation based on the assumption of average moisture diffusion coefficient did not adequately represent natural convection drying of rough rice in thin vertical columns exposed on both sides to hot air. Instantaneous moisture diffusivity coefficients determined from experimental drying curves decreased continuously with an increase in exposure duration and were linearly related to moisture ratio. The proponionality constant which was called apparent moisture diffusion coefficient was distinctly related to air temperature, relative humidity, and initial moisture content of rough rice. The modified moisture diffusion model using the instantaneous moisture diffusion coefficient was found to best represent the moisture removal from bulk rough rice.     

Mathematical Model of Fixed-Bed Drying and Strategies for Crumb Rubber Producing STR20

The objectives of this research were to investigate empirical and diffusion models for thin-layer crumb rubber drying for producing STR20 rubber using hot air temperatures of 110–130°C and to study the effect of drying parameters such as inlet drying temperature, volumetric flow rate, and initial moisture content on the quality of dried rubber. Finally, a mathematical drying model for predicting the drying kinetics of crumb rubber was developed using inlet air flow rates of 300–600 m³/min-m³ of crumb rubber (equivalent to 1.8–5.0 m/s) with the crumb rubber thickness fixed at 0.25 m. The average initial moisture content of samples was in the ranges of 40 and 50% dry basis while the desired final moisture content was below 5% dry basis. The results showed that the drying equation of crumb rubber was highly related to the inlet air temperature, while the drying constant value was not proportional to the initial moisture content. Consequently, the experimental data were formulated using nine empirical models and the analytical solution of moisture ratio equation was developed by Fick's law of diffusion. The result showed that the simulated data best fitted the logarithmic model and was in reasonable agreement to the experimental data. The effective diffusion coefficient of crumb rubber was in the range of 1.0 × 10^?9 to 2.15 × 10^?5 m²/s corresponding to drying temperatures between 40 and 150°C, respectively. The effects of air recirculation, inlet drying temperature, initial moisture contents, air flow rate, and drying strategies on specific energy consumption and quality of samples were reported. The experiments were conducted using two different drying strategies as follows: one-stage and two-stage drying conditions. The results showed that initial moisture content and air flow rates significantly affected the specific energy consumption and quality of rubber, while the volumetric air flow rate acted as dominant effect to the specific energy consumption. The simulated results concluded that the percentage of recycled air between 90 and 95% provided the lowest specific energy consumption as compared to the others.     

MODELING OF ROUGH RICE DRYING IN THIN VERTICAL COLUMNS

ABSTRACT

The solution of classical diffusion equation based on the assumption of average moisture diffusion coefficient did not adequately represent natural convection drying of rough rice in thin vertical columns exposed on both sides to hot air. Instantaneous moisture diffusivity coefficients determined from experimental drying curves decreased continuously with an increase in exposure duration and were linearly related to moisture ratio. The proponionality constant which was called apparent moisture diffusion coefficient was distinctly related to air temperature, relative humidity, and initial moisture content of rough rice. The modified moisture diffusion model using the instantaneous moisture diffusion coefficient was found to best represent the moisture removal from bulk rough rice.