METHODS FOR EFFECTIVE FLUIDIZATION OF PARTICULATE FOOD MATERIALS

Depending on the size and shape of the materials, methods employed to achieve effective fluidization during fluid bed drying varies from use of simple hole distributors for small, light weight materials to special techniques for larger and/or moist materials. This paper reviews common air distributors used in fluidized bed drying of food particulates. Also it reviews special methods of fluidizing larger irregular food particulates.     

原生纳米级颗粒的聚团散式流态化

在内径为 35mm的小型玻璃流化床中考察了平均原生粒径为 16nm的SiO₂ 颗粒的流化行为 .实验发现 :当操作气速远远超过原生纳米颗粒的最小流化气速时 ,这种超细颗粒可以通过自团聚实现稳定、均匀的散式流化 ,并可获得比GeldartA类颗粒更高的床层膨胀比和更宽的散式操作区 .由于原生纳米级SiO₂ 颗粒在流化时形成的团聚物具有较大的粒径和很小的密度 ,使得该气固体系的流化行为与液固体系有许多相似之处 ,该过程对于研究气固流态化的散式化具有重要意义     

非均质材料有效模量的数值模拟方法

用数值方法模拟非均质材料成为近20多年来细观力学的主要手段之一。本文综述非均质材料有效模量的数值模拟的研究进展,介绍了模拟非均质材料的主要的数值方法与所采用的计算模型,评述了数值方法的特点,最后对非均质材料有效模量数值模拟的前景做了展望。     

由压力波动判断气-固流化床中的流化类型

采用压力波动标准偏差判断散式流化和聚式流化,通过实验得出了聚式流化速度 ｕｈ的经验表达式,发现 ｕｈ／ｕｍ ｆ随颗粒的增大而减小,与［（ρｐ－ ρｇ／ρｇ）（ Ｒｅｐ）ｍ ｆ］０．４８成反比,并提出了产生聚式流化的条件为［（ρｐ－ ρｇ）／ρｇ］（ Ｒｅｐ）ｍ ｆ＞ ２０００     

散式流态化到聚式流态化的混沌识别

散式流态化呈现出一种非常均匀的理想流态化结构 .聚式流态化具有明显的两相结构 .当流型从散式到聚式转变时 ,床层结构发生了变化 .本文在提出用最小二乘法同时计算关联维D2 和K2 熵的计算方法的基础上 ,就A类颗粒在不同气速下的压力波动 ,分析了从散式到聚式转变时所对应的床层结构的变化 ,解释了在不同尺度下两种流型所表现出的不同动力学行为 .以此为基础 ,提出了新的识别流型转变的方法 .     

TWO-FLUID MODEL FOR PNEUMATIC DRYING OF PARTICULATE MATERIALS

The Two-Fluid model has been used for modeling the flow of particulate materials through pneumatic dryer. The model was solved for a one-dimensional steady-state condition and was applied to the drying process of wet PVC particles in a large-scale pneumatic dryer and to the drying process of wet sand in a laboratory-scale pneumatic dryer. A two-stage drying process was implemented. In the first drying stage, heat transfer controls evaporation from the saturated outer surface of the particle to the surrounding gas. At the second stage, the particles were assumed to have a wet core and a dry outer crust; the evaporation process of the liquid from a particle assumed to be governed by diffusion through the particle crust and by convection into the gas medium. As evaporation proceeds, the wet core shrinks while the particle dries. The drying process is assumed to stop when the moisture content of a particle falls to a predefined value or when the particle riches the exit of the pneumatic dryer. Our developed model was solved numerically and two operating conditions, adiabatic and given pneumatic dryer wall temperature, were simulated. Comparison between the prediction of the numerical models of Rocha and DryPak, (Pakowski, 1996), which were presented by Silva and Correa (1998), with the prediction of our numerical simulation reviled better agreements with DryPak then with the models of Rocha. The results of the developed model were also compared with experimental results of Baeyens et al. (1995) and Rocha.     

TWO-FLUID MODEL FOR PNEUMATIC DRYING OF PARTICULATE MATERIALS

The Two-Fluid model has been used for modeling the flow of particulate materials through pneumatic dryer. The model was solved for a one-dimensional steady-state condition and was applied to the drying process of wet PVC particles in a large-scale pneumatic dryer and to the drying process of wet sand in a laboratory-scale pneumatic dryer. A two-stage drying process was implemented. In the first drying stage, heat transfer controls evaporation from the saturated outer surface of the particle to the surrounding gas. At the second stage, the particles were assumed to have a wet core and a dry outer crust; the evaporation process of the liquid from a particle assumed to be governed by diffusion through the particle crust and by convection into the gas medium. As evaporation proceeds, the wet core shrinks while the particle dries. The drying process is assumed to stop when the moisture content of a particle falls to a predefined value or when the particle riches the exit of the pneumatic dryer. Our developed model was solved numerically and two operating conditions, adiabatic and given pneumatic dryer wall temperature, were simulated. Comparison between the prediction of the numerical models of Rocha and DryPak, (Pakowski, 1996), which were presented by Silva and Correa (1998), with the prediction of our numerical simulation reviled better agreements with DryPak then with the models of Rocha. The results of the developed model were also compared with experimental results of Baeyens et al. (1995) and Rocha.     

生物质与煤混合颗粒流化特性的实验研究

在 D1 1 5 mm× 1 0 0 0 mm有机玻璃制成的圆柱型流化床中 ,对玉米秆、稻秆、煤及其混合物的流化特性进行了实验研究 .实验结果表明 ,单一生物质颗粒不能形成良好的流化状态 ,而加入一定量煤构成生物质和煤二组分混合颗粒可以实现稳定流化 .当生物质和煤混合颗粒中生物质的质量分率小于 5 0 %时 ,可以达到很好的流化状态 ,生物质和煤二组分混合颗粒的最小流化速度随生物质质量分率的增加而减小 .     

流态化过渡状态描述

用模糊集合描述流化床的状态,从流化床空隙率脉动谱归纳出其不均匀度作为模糊集合的隶属函数.流化床在任何状态下的不均匀度或聚式化度都可用0～l之间的1个数值表示.对液固流态化和气固流态化实验进行观测和描述说明,模糊数学方法能够反映流化床两相结构的存在、漂移和转化,也能体现密度、粘度、粒度和表面性质的因素对流态化状态的影响.     

固体返料气流-流化组合干燥器的湿含量分布

分析了固体返料气流 -流化组合式干燥器出口粒子湿含量分布特性 ,建立了湿含量分布密度函数 ,并就硫酸亚铁的干燥过程进行了模拟计算 结果表明 ,具有降速段的流化床干燥器的优化设计 ,除了应满足干燥过程的热量供求平衡并由此确定流化床底面积外 .还应满足 :①保证湿分传质汽化所需的停留干燥时间 ,应根据干燥所需的平均停留时间来确定流化床容积 ;②控制湿含量的分散程度 ,应由干燥产品的均匀性指标来确定流化床室数 .     

固体表面活性对液固流态化的影响

用硅烷化试剂对改性聚苯醚（PPO）颗粒进行表面脱活性处理，发现其流化性能得到改善，同时水在颗粒间流动的阻力略有减小。     

采用双转鼓流化工艺生产大颗粒尿素的理论与实践

较全面地总结了双转鼓流化工艺技术在大颗粒尿素生产中的应用原理和实践业绩,属国内首创,大幅度降低了尿素大颗粒造粒装置的建设投资和生产费用.     

PULSED MICROWAVE-VACUUM DRYING OF FOOD MATERIALS

ABSTRACT

Microwave drying of food materials has been investigated over several years as a potential means for reducing the total drying time. However, some quality loss almost always accompanied when foods were dried completely using microwaves due to nonuniform temperature and moisture distribution. Some strategies used to improve dried product quality include combination of microwave and conventional hot air drying. pulsed or intermittent drying, and microwave-vacuum drying. Combination of pulsing and vacuum drying is a useful technique to maximize energy use efficiency and product quality especially for temperature sensitive products such as fruits. Some results of pulsed, microwave-vacuum drying of cranberries are presented. Pulsed drying is more energy efficient than continuous drying. In pulsed drying, the longer the pulsing ratio (i.e. longer power-off time in relation to power-on time) was more energy efficient. The quality of pulse-dried product was also generally better than that of continuous-dried product. The cycle power-on time and pulsing ratio should be carefully selected to obtain maximize the benefits of pulsed, microwave vacuum drying     

EFFECTIVE PROPERTIES OF POROUS AND COMPOSITE MATERIALS

Based on a previously modified version of Bruggerman's method, a dependence of the effective diffusion coefficient in porous media on the porosity is deduced and compared with available experimental data. Based on the same method, a dependency of the effective elastic coefficients of composite materials on the volume fraction of inclusions is deduced in the case of different types of inclusions. Comparison with available experimental data shows good agreement between the theory predictions and the experimental data. In the case of the elastic properties of laminated composite materials, application of the same method yields results identical to those obtained using the averaging procedure. A theory of effective viscosity of concentrated suspensions is applied for calculations of dependency of effective viscosity on applied shear rate using available experimental data.     

EFFECTIVE PROPERTIES OF POROUS AND COMPOSITE MATERIALS

Based on a previously modified version of Bruggerman's method, a dependence of the effective diffusion coefficient in porous media on the porosity is deduced and compared with available experimental data. Based on the same method, a dependency of the effective elastic coefficients of composite materials on the volume fraction of inclusions is deduced in the case of different types of inclusions. Comparison with available experimental data shows good agreement between the theory predictions and the experimental data. In the case of the elastic properties of laminated composite materials, application of the same method yields results identical to those obtained using the averaging procedure. A theory of effective viscosity of concentrated suspensions is applied for calculations of dependency of effective viscosity on applied shear rate using available experimental data.     

食品加工废水处理工程

应用预曝气调节-气浮-生物接触氧化工艺对食品加工废水进行处理,实践表明,在进水COD、BOD5和SS分别为1800mg／L、250mg／L和230mg／L的情况下,出水的COD、BOD5和SS分别为41mg／L、6mg／L和50mg／L以下,出水水质达到《污水综合排放标准》（GB8978-1996）一级标准。     

COMPARISON OF TWO ANALYTICAL METHODS FOR THE DETERMINATION OF AZAARENES IN ATMOSPHERIC PARTICULATE MATTER

In this paper, the development of an analytical method for the separation and quantification of 20 azaarenes is described. Two methods are compared: high performance liquid chromatography with fluorescence detection (HPLC-fluorescence) and gas chromatography with mass spectrometry detection (GC-MS).

Although HPLC-fluorescence was proven to be the most sensitive method, GC-MS was selected in particular for the efficiency of the separation of the 20 azaarenes. The detection limits of the HPLC-fluorescence and GC-MS methods varied between 0.04 μ g.L^?1 (dibenz[a,c]acridine) and 1.30 μ g.L ^?1 (acridine) and between 1.50 μ g.L ^?1 (benz[c]acridine) and 2.56 μ g.L ^?1 (dibenz[a,c]acridine) respectively.

The GC-MS method was applied to particulate matter (PM ₁₀ ) samples collected over 48–72 h periods between April 2006 and February 2007 in Strasbourg (East of France). Before analysis aerosol samples were Soxhlet extracted and concentrated to a final volume of about 1 mL of hexane.

The seasonally mean concentrations of all azaarenes for this urban site have shown a seasonal variation in which the maximum concentration occurred in the winter (6.0 ng.m ³ ) and the minimum in the summer (0.90 ng.m³). For all the seasons the 2 rings species were the predominant azaarenes while the > 4 rings species were the less abundant.     

炭素材料灰分组成测定方法的改进

对炭素材料灰分组成的测定方法进行了改进。通过对比试验发现：测定炭素材料中二氧化硅的含量，熔融法的分析结果比氢氟酸法更稳定、准确；测定炭素材料中氧化钙的含量，紫脲酸铵指示剂法的分析结果比铬蓝黑R指示剂法更稳定、准确。讨论了该标准方法的使用范围、操作步骤，以及各测定项的测定方法的精密度。     

鼓泡流态化向湍流流态化过渡的影响因素分析

本文在对前人有关鼓泡流化向湍流流化过渡的工作进行总结评述的基础上,分别考察了颗粒直径及分布、密度,床尺寸及内构件等对于临界湍流速度的影响,指出了影响比临界速度的根本因素是气泡。最后分别针对挡板床和自由床分析了比临界速度与气泡的关系。     

尿素造粒机流化风机轴弯曲在线处理

介绍造粒机硫化风机因轴弯曲引起振动大的故障情况,阐述探索采用热处理与施加外力相结合的校轴法对弯曲轴进行在线处理的过程。