太阳能流化干燥的数值模拟与试验研究

设计了太阳能流化床干燥的试验装置,通过试验的方法研究了流化干燥特性和太阳能利用的效益。对冷热态,不同流量,不同物料层高等参数变化,进行了测试,对比进行了多次试验,得到了不同参数的试验结果。分析总结了各参数对物料干燥的影响,表明空气流量,料层高度和冷热态均会影响物料干燥程度,且热管传递的热量只有部分传递给了物料。应用Fluent商用计算软件,对热管换热开展了数值模拟,获得了换热效率的变化,研究结果说明数值计算与试验结果符合较好。     

颗粒表面料层干燥过程的数值模拟

建立单颗粒表面料层干燥的物理及数学模型,并将方程组无因次化,采用全隐法对该无因次模型方程进行求解,从而分析惰性载体的直径、薄层物料厚度、薄层物料孔隙分布标准方差、均值、干燥气体温度、流速对干燥时间的影响.     

聚合物颗粒气流振动耦合作用干燥效果

针对初始含水率在20%以下,粒径在5～20 mm,密度为1. 2～2 g/cm3的高聚物颗粒的颗粒物料,分阶段对干燥过程中高聚物颗粒含水率变化趋势进行研究,研究气流振动耦合作用对高聚物颗粒物料干燥过程中不同阶段的影响程度,确定物料达到0. 5%～1%的含水率所需要的干燥时间,根据实验结果设计并优化工程实验样机。研究结果表明,在气流振动耦合作用下,含水颗粒物料的干燥过程分为缓慢降速与快速降速2个阶段,分别对应物料表面水与内部结合水的干燥; 5～20 mm的含水颗粒物料的含水率从20%降至0. 5%～1%,所需时间为7～12. 5 min;在气流振动干燥状态下,颗粒物料干燥时间比单一热风情况下减少了20%～30%;设计并加工的气流振动干燥样机可以满足实际生产需求。     

大颗粒作用下微细粉流态化干燥研究

为了克服湿微细粉易于结团形成“细粉群”、不易流化和干燥的缺点，在微细粉中加入惰性大颗粒物料，由于大颗粒的“搅动”作用，使细粉分散，可提高流化质量，从而提高微细粉的流化干燥热效率．在实验基础上进行了物料衡算和热量衡算，并进行连续干燥热效率的计算．该方法为微细粉的流化干燥提供一条新的途径．     

对流化床喷雾制粒工艺过程控制的研究

通过实验探讨了流化床喷雾制粒机中流化空气温度及喷嘴液流速度对颗粒尺寸的影响,以获得借助调节流化空气温度及喷嘴液流速度来控制颗粒生长的方法。结果发现:在球化阶段,降低流化空气的温度可促进颗粒生长,而在干燥阶段,则可适当提高流化温度;喷嘴的液流速度较高可促进颗粒生长,液流速度过高则会使颗粒的均匀性变差     

流化振动连续造粒干燥过程分析

介绍了流化振动连续造粒机的连续造粒及振动干燥过程的原理、工艺流程及其相关的计算。经多次多种物料的试验及分析 ,得出了流化振动连续造粒机生产疏松颗粒的主要操作参数。这对该机型的进一步开发、应用具有指导意义     

振动式流化干燥床的设计与应用

振动式流化干燥床是近年来发展的新设备,它适合于干燥颗粒太粗或太细、易粘结、不易流动的物料,它已广泛应用于医药、食品、塑料等行业.     

脉动流化干燥过程的实验研究

将热气体引入流化床，对流化床中的矩形波脉动干燥过程进行了实验研究。实验中使用了小米和硅胶两种物料，考察了物料湿含量及床层温度变化情况，并将脉动流化干燥与无脉动流化干燥效果进行比较，发现小米在一定的脉动条件下能够节能，而硅胶的节能效果不明显。文章还对气流脉动流化干燥的应用和进一步研究方向进行了分析和展望。     

污泥颗粒与河砂混合流化特性的实验研究

在内径f105 mm、高800 mm的冷态流化床实验装置上进行了污泥颗粒与河砂混合流化特性的实验研究,获得了污泥颗粒水分、污泥颗粒与河砂的质量比对混合物料的流化特性的影响规律. 实验结果表明,污泥颗粒的水分、污泥颗粒与河砂的质量比会影响混合物料的最小流化速度,也影响污泥颗粒与河砂混合的均匀程度. 污泥颗粒的质量比越大,混合物料的最小流化速度越大;污泥颗粒的水分含量越高,混合物料的最小流化速度也越大;污泥颗粒与河砂的质量比越接近1:1,越容易实现充分混合. 在对实验数据进行分析处理的基础上,提出了污泥颗粒与河砂混合物料的最小流化速度经验方程,为流化床污泥颗粒干燥工艺提供基础数据和设计依据.     

粒状物料在辐射-对流组合加热倾斜振动流化床中的干燥

固体颗粒在倾斜振动流化床(IVFB)中极易以较低气速流化。在振动作用下,流化颗粒沿气流方向混合良好,床层表面不断更新。因此,当以干燥机顶部表面辐射加热时,该床层表面对辐射热的吸收比无振动的流化床层更有效。这种特性表明IVFB适用于太阳能干燥机和其它类似的干燥机。本文描述了所进行的模型实验结果。其目的是确认辐射加热对颗粒状湿物料干燥的适用性。     

On the drying kinetics of non-spherical particle-filled polymer films: A numerical study

During the coating and drying of thin polymer-particle composites, the particle geometry has a big impact on the prediction of concentration profiles in the dry film. In this work, a plate-like geometry is used to evaluate the mass transport of the particles with the aspect ratio as a variable. The experimental determination of the viscosity and sedimentation rates allows to simulate concentration profiles in the wet film while drying. A previous simulation model was automated to describe the drying of the plate-like particles—polyvinyl alcohol-water material system using COMSOL with the initial concentration, aspect ratio, Péclet number, and sedimentation number as input parameters. The results are summarized in drying regime maps, which show an increase in the evaporation regime when the aspect ratio decreases due to lower particle mobility. This shows the importance of the geometry while predicting the particle distribution in the dry film and designing coating and drying processes.     

TEE EFFECIS OF EXTENDED THIN FILM EVAPORATION AND EXPWNAL DIFFUSION RESISTANCE DURING THE CONSTANT DRYING RATE PERIOD

Extended thin film evaporation with external diffusion resistance is analyzed for the constant rate period of the drying process, in which a polar liquid evaporates from porous bodies made of glass. The extended thin film is defined as the Liquid film in which the disjoining pressure dominates the fluid flar field and works as the driving force replenishing the evaporating Liquid. The results of the analysis shows that due to the existence of the evaporating thin Liquid film, the evaporation fran the extended thin film can compensate the reduction of evaporation rate caused by the increase of the dry spots and keep the drying rate the same as or even greater than that of the completely wetted surface. The external diffusion resistance makes the vapor concentration near the porous solid surface remain constant and therefore keeps     

STRUCTURE FORMATION OF COATED FILMS WITH DISPERSED PIGMENTS DURING DRYING

ABSTRACT

In the drying of coated films with dispersed pigments, such as floppy disks, the structure of the film is formed during the drying process and depends on the drying condition. It is important to understand the structure formation during drying for the design of the dryer and die better quality of the product. We measured die drying characteristics of the film and determined the structure of dried film experimentally. A qualitative model for the structure formation during drying of the coated film is suggested.     

TEE EFFECIS OF EXTENDED THIN FILM EVAPORATION AND EXPWNAL DIFFUSION RESISTANCE DURING THE CONSTANT DRYING RATE PERIOD

ABSTRACT

Extended thin film evaporation with external diffusion resistance is analyzed for the constant rate period of the drying process, in which a polar liquid evaporates from porous bodies made of glass. The extended thin film is defined as the Liquid film in which the disjoining pressure dominates the fluid flar field and works as the driving force replenishing the evaporating Liquid. The results of the analysis shows that due to the existence of the evaporating thin Liquid film, the evaporation fran the extended thin film can compensate the reduction of evaporation rate caused by the increase of the dry spots and keep the drying rate the same as or even greater than that of the completely wetted surface. The external diffusion resistance makes the vapor concentration near the porous solid surface remain constant and therefore keeps     

Fluidized bed spray granulation: Investigation of the coating process on a single sphere

The coating and granulation of solid particles in a fluidized bed is a process which converts pumpable and atomizable liquids (solutions, slurries, melts) into granular solids in one step by means of drying. The solution to be processed is sprayed onto a fluidized bed. Particle growth can take place either via surface layering or agglomeration. In the case of surface layering the atomized droplets deposit a thin layer of liquid onto the seed particles. The solvent is then evaporated by the hot fluidizing, leaving behind the dissolved material on the surface. Although fluidized bed spray granulation and film coating have been applied in industry for several years, there is still a lack of understanding of the physical fundamentals and the mechanisms by which spherical granules are formed. Hence a new method was developed which allows the direct observation of the subsequent particle-forming mechanisms such as droplet deposition, spreading, wetting and drying. The authors present a laboratory scale apparatus in which a single freely suspended particle can be coated under well defined and constant coating and drying conditions. With this device, particle-growth-rate and the development of particle morphology were measured and investigated under various experimental conditions.     

Formation of Particle Layer Within Coated Slurry Characterized by Thickness Variation

An understanding of the conversion process from slurry to particle layer on a substrate is required for the precise control of the particle alignment and the material distribution in the coated slurry. In this work, variation of coated slurry thickness during drying was applied to evaluate drying and particle layer formation simultaneously. The slurry used consisted of micron-sized silica or poly (methyl methacrylate) particles and an aqueous solution of poly-vinyl alcohol (PVA) possessing differing degrees of hydrolysis. During the drying process, initially the thickness of the coated slurry was observed to decrease at a constant rate in the concentration stage, and subsequently it began to show large fluctuations due to the emergence of particles on the drying surface in the packing stage. In the final fixing stage, the fluctuation of film thickness was restricted because particles were immobilized by highly viscous concentrated PVA or by PVA molecule bridging. Based on the variation and fluctuation of film thickness, we introduced two characteristic dimensionless time ratios: (a) void fraction in a packed particle layer at the end of concentration stage; and (b) the time required to fix particle position after the end of the packing stage. We concluded that the dispersed state and settling velocity of the particle determines the space between particles in a loose packing layer, and we found that the distribution of polymers in a particle layer has a strong influence on the mobility of particles in a tightly packed layer.     

TEE EFFECT OF EXTENDED THIN FILM EVAPORATION DURING TEE CONSTANT DRYING RATE PERIOD

ABSTRACT

The extended thin film evaporation is analyzed during the constant drying rate period. The extended thin film is defined as the liquid film which the disjoining pressure dominates the fluid flow field and works as the driving force of replenishing the evaporating liquid. The results of the analysis show that the extended thin film evaporation can compensate the reduction of evaporation rate due to the increase of dry spots and keep the evaporation rate nearly constant. Experimental data in the literature are in good agreement with the results of this work. This implies that the extended thin film evaporation may be an important part of the mechanism for drying.     

Drying-Induced Cracks in Thin Film Fabricated from Colloidal Dispersions

As a colloidal dispersion is coated and dried on a nonporous rigid substrate, the enormous stresses developing during the drying process can fracture the thin film. The drying-induced cracks can produce serous technological consequences and even destroy the efficacy of coatings, which is not desirable in most industrial cases. Therefore, as the first step of controlling cracks in thin film, understanding of crack properties and cracking mechanisms leading to fracture is of vital significance. Although numerous experiments and models have been proposed for cracking during drying of colloidal dispersions, there is little consensus on even the most basic mechanisms, and the effect of heat transfer on cracks as well as optimization of drying process are rarely taken into account. Additional, the broad employments of nanosuspensions bring both opportunities and challenges for this area. This review will give a comprehensive physical picture of thin film fabrication by drying of colloidal dispersions and cracking phenomenon, present current investigations for drying-induced cracks, and point out some prospects for cracking researches especially for industrial R&D, as well as propose combination of thin film preparation with drying technique for exploring crack-free thin film.     

Surface nonuniformities in latex paints due to evaporative mechanisms

A model is developed for predicting long‐wavelength nonuniformities in the thickness of drying latex paint films. The model includes the effects of temperature, latex particle volume fraction, surface surfactant density, bulk surfactant density, and several material and environmental factors. After the model is simplified by applying the lubrication approximation, equations for spatially independent base state solutions are derived. The base state solutions describe a drying latex paint film of uniform thickness. The equations for the base states are solved numerically and a linear stability analysis is conducted. This analysis indicates that evaporation, slow surfactant kinetics, low initial surface tension, substrate permeability, and high initial latex particle volume fractions destabilize the uniform film, while fast surfactant kinetics, high initial surface tension, and high viscosity are stabilizing. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1841–1858, 2018     

多通道支撑体制备氧化铝无机膜干燥技术探讨

以异丙醇铝为主要原料，用溶胶-凝胶法，在多通道管状α-Al2O3支撑体上浸涂成膜。对多通道支撑体溶胶膜浸涂时间、支撑体处理技术进行讨论，选择不同的凝胶干燥温度和干燥方式，利用扫描电镜观察不同干燥制度下薄膜的形貌。结果表明，得到光滑、无裂纹薄膜在凝胶膜干燥过程中对支撑体处理、浸涂时间和温度控制非常重要，采用水蒸气保护下分级干燥方式可以得到质量良好的凝胶膜。