离心流化床干燥过程中传热传质的数值模拟

通过对典型的多孔湿物料在离心流化床中干燥过程的理论分析和实验研究 ,首次将含湿多孔介质传热传质过程和物料与气流之间的外部传递过程相耦合 ,导出了离心流化床的理论模型和控制方程组 ,对于离心流化床中湿物料的干燥过程引进了数值模拟 ,结果表明增加气体表观流速、控制入口气体的温度和相对湿度以及加大床体转速均对干燥有不同的影响     

流化床喷雾造粒过程的传热传质

This article presents a mathematical model of heat and mass transfer for the process of fluidized-bed spray granulation, which can be applied in the analysis of bed temperature profile, temperature and humidity of outlet gas and moisture content of particles. Effects of operation parameters on the batch granulation are investigated. The theoretical calculation agrees reasonably well with the experimental data.Keywords fluidized-bed spray granulation, mathematical model, heat and mass transfer     

物料干燥过程—传质传热最优化方法的研究

论述了多孔介质干燥过程中传质传热的数学模型及干燥过程最优化准则的建立；并且动用控制理论产物料干燥过程传热的动态优化方法－－准则约束法，且得到了最优解。     

多孔毛细物料整体间断加热干燥过程中耦合的传热传质问题和应力分析

应用Luikov理论和有限元方法求取物料在间断加热干燥不同瞬间的温度、湿度及应力分布,并用自编程序试算的结果与文献中的实验值或理论解进行了比较,本文介绍的方法可望用于求取间断加热干燥过程的最佳操作参数.     

多孔介质内部传热传质规律的研究进展

多孔介质中的热质交换理论及其实验研究是一个涉及面广、研究难度大而又颇具工程应用价值的课题。本文对多孔介质内部传热传质规律的研究从理论和实验两方面作了简要的综述及展望,并对一些描述热质传递过程的数学模型及方程作了介绍。     

超微粉体浆料惰性粒子流化床干燥过程传热传质特性

结合超微钛白粉和磁记录用钡铁氧体磁粉制备中粘性悬浮液混合浆料的脱水干燥过程,研究了在直径为145 mm的惰性粒子流化床中对悬浮液浆料进行脱水干燥的热量和质量传递的基本规律, 所得结果可为工程设计的操作参数选择提供依据, 对其他类似的超微粉体浆料的脱水干燥有参考价值.     

分形多孔介质传热传质过程的格子Boltzmann模拟

针对自然界中实际多孔介质具有的分形特性和随机性,利用中点替代算法和二值化处理构造统计上具有分形特性的随机多孔介质。分析了所构造的多孔介质盒维数与Hurst指数之间的关系。基于随机分形构造的原理,对二维实际多孔介质图像进行了重构。利用两点相关函数,分析了重构图像的结构相关性,并与实际目标多孔介质的结构特征进行比较。在与解析解对比验证的基础上,将基于二元混合理论的格子Boltzmann模型(LBM)用于模拟多孔介质内流体扩散过程。通过计算不同分形特性的二维多孔介质的有效扩散系数,研究了重构多孔介质的分形维数与有效扩散系数的关系。利用热耦合LBM模型计算多孔介质内传热过程,分析了不同的分形特性对多孔介质蓄热过程的影响。     

分形多孔介质传热传质过程的格子Boltzmann模拟

针对自然界中实际多孔介质具有的分形特性和随机性,利用中点替代算法和二值化处理构造统计上具有分形特性的随机多孔介质。分析了所构造的多孔介质盒维数与Hurst指数之间的关系。基于随机分形构造的原理,对二维实际多孔介质图像进行了重构。利用两点相关函数,分析了重构图像的结构相关性, 并与实际目标多孔介质的结构特征进行比较。在与解析解对比验证的基础上,将基于二元混合理论的格子Boltzmann模型（LBM）用于模拟多孔介质内流体扩散过程。通过计算不同分形特性的二维多孔介质的有效扩散系数,研究了重构多孔介质的分形维数与有效扩散系数的关系。利用热耦合LBM模型计算多孔介质内传热过程,分析了不同的分形特性对多孔介质蓄热过程的影响。     

确定生物物料最佳干燥工艺的理论方法研究

物料最佳干燥工艺的确定是保证干燥质量、降低干燥能耗、提高干燥效率的基础。对生物物料有效成分的降解规律、生物物料的传热传质分析模型、生物物料的热物性估算等理论（工具）进行了分析；探讨了利用理论方法确定物料最佳干燥工艺的基本方法和步骤。     

Experimental study and simulation of vibrated fluidized bed drying

The paper addresses numerical simulation for the case of convective drying of seeds (fine-grained materials) in a vibrated fluidized bed, analyzing agreement between the numerical results and the results of corresponding experimental investigation. In the simulation model of unsteady simultaneous one-dimensional heat and mass transfer between gas phase and dried material during drying process it is assumed that the gas-solid interface is at thermodynamic equilibrium, while the drying rate (evaporated moisture flux) of the specific product is calculated by applying the concept of a “drying coefficient”. Mixing of the particles in the case of vibrated fluidized bed is taken into account by means of the diffusion term in the differential equations, using an effective particle diffusion coefficient. Model validation was done on the basis of the experimental data obtained with narrow fraction of poppy seeds characterized by mean equivalent particle diameter (d_S,d = 0.75 mm), re-wetted with required (calculated) amount of water up to the initial moisture content (X₀ = 0.54) for all experiments. Comparison of the drying kinetics, both experimental and numerical, has shown that higher gas (drying agent) temperatures, as well as velocities (flow-rates), induce faster drying. This effect is more pronounced for deeper beds, because of the larger amount of wet material to be dried using the same drying agent capacity. Bed temperature differences along the bed height, being significant inside the packed bed, are almost negligible in the vibrated fluidized bed, for the same drying conditions, due to mixing of particles. Residence time is shorter in the case of a vibrated fluidized bed drying compared to a packed bed drying.     

Measurement of constant drying rate of wet material placed in a fluidized bed of inert particles under reduced pressure

The objective of this study is to estimate the drying characteristics of a relatively large material immersed in a fluidized bed under reduced pressure by measuring the constant drying rate. The constant drying-rate period in a fluidized bed under reduced pressure is difficult to measure because it is extremely short. To maintain the constant drying-rate period, distilled water is directly supplied to the drying material. Through our experiment, the heat transfer coefficient of the material surface was also determined. The results were compared with data on hot air drying. The constant drying rate is higher for fluidized bed drying than for hot air drying. It suggests that the heat transfer coefficient on the surface of the drying material is much larger for fluidized bed drying than for hot air drying. For fluidized bed drying, the effect of pressure in the drying chamber on the heat transfer coefficient is slight at the same normalized mass velocity of dry air (G/G_mf). The temperature difference between the inside of the drying chamber and the drying material is much smaller for fluidized bed drying than for hot air drying. The constant drying rate increases as the pressure in the drying chamber decreases.     

Experimental and numerical analysis of oil shale drying in fluidized bed

The main objective of this work was to experimentally and numerically investigate the Liu Shu River oil shale drying by the means of flue gas in a fluidized bed dryer. Several experiments were performed under different temperatures conditions. The moisture content of oil shale was measured during the experiments. The two-stage drying model was incorporated in computational fluid dynamics (CFD) package FLUENT via user-defined functions (UDF) and utilized for simulation of heat and mass transfer of oil shale drying in the fluidized bed dryer. The simulation results for solid moisture content agreed well with experimental data. The effects of the temperature and velocity of flue gas, initial bed height, and the particle size on the drying characteristics were predicted and analyzed. It is shown that the gas temperature and velocity are the important parameters in the whole drying process. The particle size has more obvious influence in the falling drying period than the constant drying period. The temperatures of gas and solid phases were monitored. It is shown that the so-called “near gas distributor zone” is the most effective heat transfer zone, which agrees well with the calculated value. The system quickly reached thermal equilibrium, characterizing a nearly isothermal bed. The developed model provides a very good demonstration to describe the oil shale drying in the fluidized bed dryer, and may provide important information for design, optimization of operation conditions.     

Microwave drying process of corns based on double-porous model

Current microwave drying of food product models have generally neglected mass transfer physics, which have resulted in higher predicted temperatures within the food matrix. It is necessary to include mass transfer physics in modeling microwave drying of food products, especially when they are dry for longer durations. In the actual drying process, most of the dry material is a double-porous media formed by the mutual accumulation of porous media, and there is no systematic theory to analyze the drying process of double-porous media. This work presents a new theoretical model based on the ractive pellet bed to achieve the simulation of microwave drying in situation of stacked corns. Compared with the applicable to porous model and analyzed the difference, finally through the change of temperature and moisture was measured by experiments to verify the rationality and accuracy of the double-porous model.     

More comprehensive 3D modeling of clay‐like material drying

Drying process plays an important role in the manufacturing of many products such as ceramic, kitchenware and building materials, some of which have complex three‐dimensional (3D) geometry. To deal with many restrictions found in literatures, a 3D numerical approach was used to describe the drying process of a porous Clay‐like material. The problem investigated involves highly coupled equations considering heat, mass, and mechanical aspects. The model is validated through the comparison of experimental measurements with simulation result. Simulation results show that increasing the initial moisture content and reducing the initial temperature have the same privilege and without significant increase in drying time, it reduces slightly the amount of maximum stress but delays the occurrence time of maximum stress. The nonuniform heat expansion induced stresses are very small in comparison to nonuniform moisture shrinkage induced stresses and can be neglected in drying simulation. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1469–1478, 2018     

具有初始孔隙的多孔物料冷冻干燥

实验研究了具有一定孔隙的非饱和多孔物料对液体物料冷冻干燥过程的影响。以甘露醇为主要溶质的待干料液采用“液氮制冰激凌法”制备非饱和物料进行冷冻干燥,并与常规饱和的冷冻物料相比较。结果表明,非饱和冷冻物料确实能够显著地强化液体物料的冷冻干燥过程。干燥产品SEM形貌分析显示,初始非饱和冷冻物料具有连续均匀的固体骨架和孔隙,固体基质更加纤细,孔隙空间更大,可以大大减小传质阻力。考察物料内部各点的温度变化发现,初始非饱和物料内部冰晶确实发生整体升华,但仍然存在主要升华区域;非饱和多孔物料的冷冻干燥过程主要是传热控制,而常规饱和物料冷冻干燥主要是传质控制。操作压力对过程的影响可以忽略。采用辐射/导热组合加热方式可改善初始非饱和多孔物料冷冻干燥过程的传热,进一步缩短干燥时间。     

柱形流化床传热特性的数值模拟

对Shedid等搭建的圆柱体流化床采用欧拉?欧拉法进行三维数值模拟,考察了颗粒球形度、表观进气速度和床料初始堆积高度对流化床内垂直加热壁面与流动床料之间对流传热特性的影响,采用有效导热系数分别计算气相和固相的对流传热系数。结果表明,随表观进气速度增大,流化床内颗粒物料湍流运动加剧,加热壁面平均温度和流体平均温度下降,壁面流体间传热平均温度差减小,壁面流体间对流传热系数增大;随初始床料高度增加,流化床内颗粒与加热壁面的接触面积增大,导致固相平均对流传热系数增大。     

半干法循环流化床脱硫反应器内构件研究进展

常规脱硫反应器存在着床内气固流动不均匀、脱硫剂利用效率低等问题。安装内构件可以破碎气泡和颗粒团聚,改善流化质量,强化脱硫反应器内的气固传质和反应过程,提高脱硫效率。本文介绍了近年来半干法循环流化床脱硫反应器内构件的研究现状,主要介绍了惯性式内构件、钝体式内构件、孔板式内构件、复合型内构件;阐述了各种内构件的形式及特点,其中惯性式内构件能够强化气固分离,但不能优化流场;钝体式内构件能够增强反应器内气固湍动程度,但对轴向混合影响不大;孔板式内构件能够均布流场,但易堵塞;复合内构件能够改善流化性能,强化气固接触,但床层压降较高。通过对装有不同内构件的循环流化床脱硫反应器中气固两相流动特点的分析,指明了各类内构件对流化床内气固流动的作用原理及优缺点,综合床层压降及颗粒浓度分布,并根据现有流化床脱硫反应器内构件特点提出了促进气固高效接触、降低床层压降等新型内构件的开发方向。     

Drying characteristics of porous material immersed in a bed of hygroscopic porous particles fluidized under reduced pressure

A relatively large wet material was immersed in a fluidized bed of hygroscopic porous particle (silica gel beads) under reduced pressure. And then the drying characteristics were compared with those in the case of inert particle (glass beads). The comparison of drying characteristics is performed experimentally and theoretically. In calculation, the water transfer from the sample to the fluidized bed was considered. The calculation results are in good agreement with the experimental data. The effects of the operational conditions (the pressure in the drying chamber and the temperature of the drying gas) on the drying characteristics were also examined in both fluidizing particles.The drying finishes earlier in the case of hygroscopic porous particle than in the case of inert particle regardless of pressure in the drying chamber, since the water transfer from the sample facilitates the drying in the case of hygroscopic porous particles. The temperature decrement in drying appears in the case of inert particle. This phenomenon is also observed in the case of hygroscopic porous particle, but the decrement degree of the temperature is much smaller than that in the case of inert particle. The difference of the minimum temperature in the sample in drying between the cases of hygroscopic porous particle and inert particle is very slight for different pressures in the drying chamber.