颗粒物料沉降速度的工程计算

物料沉降速度的工程意义颗粒物料(或液滴)在自由空间及有限空间内沉降速度的计算,对气流干燥器操作速度的选定,流化床干燥器、反应器层上部颗粒物料扬析及带出,气力输送装置中管道速度的选择,除沫器     

湿污泥颗粒的流化床干燥实验及模型

在鼓泡流化床内以河砂为干燥介质,对单颗粒湿污泥的流态化干燥特性进行实验研究,得到了流化床温度、污泥初始水分、污泥粒径及流化速度对干燥速率的影响规律：流化床温度及污泥粒径对干燥速率的影响都呈指数规律;污泥的水分越大,干燥速率越大;在鼓泡流化床流化速度达到2倍临界流化速度以上时,充分流化,流化速度再增大(2~5倍临界流化速度)对干燥速率没有明显影响. 在基本的扩散传质理论的基础上,利用实验数据回归得到湿污泥在鼓泡流化床内干燥的半经验模型,为流化床污泥干燥器的设计提供了基础数据和依据.     

组合式干燥系统的分段优化设计方法

提出了分离过程的分段设计法：将一个任务分解为多个子任务,根据各个子任务的不同特点进行设计. 对干燥过程进行优化设计,以年费用最小为目标,将干燥过程表示为最多3段的超结构,每段有2个干燥设备可以选择,给出了单元和过程系统的模型和经济模型. 实例研究结果表明,当物料含水量大于物料在该条件下的临界含水量时,宜采用两段干燥的方法,将回转圆筒干燥器和流化床干燥器组合进行干燥;当物料含水量低于临界含水量时,宜采用一段干燥,将物料直接放入流化床干燥器进行干燥.     

流化床热交换器

<正> 所谓“流化床”,指的是在管内或某一容器内,随着操作流体上升速度的增加而相互脱离,在流体中作不规则流动的固体颗粒床层。流体速度达到流化点速度(也称临界流化速度)后,速度继续增加,当其速度等于或低于颗粒的沉降速度时,固体颗粒只在管内或容器内流动,当流体速度大于沉降速度时,则固体颗粒将随操作流体流出管外或客器外。与固定床比较,流化床具有如下优     

均热式流化床技术的开发

针对现有流化床存在换热不均、进气分布不均、物料回床等问题,开发了一种新型流化床技术,即均热式流化床干燥器、双锥导流式进气分布器及颗粒直接回床技术.依据基本的质量与热量平衡关系,推导出了均匀取热流化床干燥器换热面积的计算方法;对流化床干燥器其它基本参数的选择方法作了说明.     

振动流化床临界流化速度理论预测与实验研究

根据振动流化床床层动力学特性,提出了第一、第二流化段,第一、第二临界流化速度的概念.从流化床临界流化速度的定义出发,得出了振动流化床第一临界流化速度数学模型.在二维振动流化床内,以不同粒径的玻璃珠为床料进行实验研究,分析了振动和其它操作条件对临界流化速度的影响,通过实验数据关联得到了振动能量传递系数的数学表达式,并将模型预测与实验结果进行了对比.结果表明振动强度增加,第一、第二临界速度均减小,振动对第一临界流化速度影响更显著,当振动强度超过1.57后,不通气体床层也能流化,第一临界流化速度降为零,模型预测与实验结果有较好的一致性.     

搅拌流化床干燥器流体力学性能研究

分析对比了搅拌流化床和普通流化床的流体力学特性,研究了搅拌转速,物料直径,物料密度和床载量对搅拌流化床床层压降和临界流化速度的影响,提出了临界流化速度的准数关联式,计算结果与实验数据吻合较好。     

振动流化床在尤里卡沥青干燥中的应用

以工业原料尤里卡沥青为研究对象，分析和讨论了振动流化床干燥器的动力学特征，传热特性及干燥特性，对振动流化床干燥器设计选型的主要参数进行了整理和计算。     

具有恒速和降速干燥段的卧式多室流化床干燥器湿含量分布研究

分析了具有恒速干燥段和降速干燥段的卧式多室流化床干燥器的湿含量分布, 提出了湿含量分布的密度函数式。利用该式就造纸黑液中回收木质素的干燥实例进行了计算。结果显示： 流化床出口粒子湿含量Ｅ分布曲线在临界湿含量处出现拐点,表明恒速干燥段和降速干燥段湿含量分布规律各不相同;随着流化床室数的增加,湿含量分布趋于集中;适宜的流化床室数应根据干燥产品的均匀性指标来确定。     

雷诺数的应用浅析

围绕雷诺数的表达式、临界值和应用三方面探讨雷诺数在教与学中的难点,总结了雷诺数在流动阻力、传热系数、吸收系数、颗粒沉降速度以及流化床和气流干燥器设计等方面的应用。结果说明,雷诺数在不同的应用领域,表达式和临界值各有不同,应该区别对待,根据具体情况具体选择使用。     

几种常用干燥设备的简捷计算方法

为简化干燥设备的设计步骤,根据工业生产实践和经验公式,提出了流化床、振动流化床、内热流化床、惰性粒子流化床、离心喷雾干燥、压力喷雾干燥、旋转闪蒸干燥及气流干燥8种常用干燥设备的主体尺寸的简捷设计方法,并介绍了所有干燥设备都适用的基础计算。所述简捷计算采用了许多来自生产实践的经验数据,对设计工业应用的干燥器有重要的指导作用。除了设备主体尺寸之外,尚有诸多结构尺寸需要确定,设计者需根据自己的经验或参考更为详尽的资料才能完成。     

A Model for the Relative Velocity of a Particle in an Impingement Dryer: Application to Heat Transfer

A simplified mathematical model for the relative gas-particle motion in a confined jet impingement dryer is developed. Model predictions based on an unsteady momentum balance are in good agreement with the observed cycling motion of a spherical particle. The model is applied to coriander seeds submerged in a flow field of superheated steam. It is found that relative motion occurs in unsteady turbulent regime, and that steady settling velocity of particles is never achieved. Model results are applied to correlate experimental heat transfer data of an impingement dryer. Experimental Nu numbers compare fairly well with correlations for fluidized systems.     

A Model for the Relative Velocity of a Particle in an Impingement Dryer: Application to Heat Transfer

Abstract

A simplified mathematical model for the relative gas-particle motion in a confined jet impingement dryer is developed. Model predictions based on an unsteady momentum balance are in good agreement with the observed cycling motion of a spherical particle. The model is applied to coriander seeds submerged in a flow field of superheated steam. It is found that relative motion occurs in unsteady turbulent regime, and that steady settling velocity of particles is never achieved. Model results are applied to correlate experimental heat transfer data of an impingement dryer. Experimental Nu numbers compare fairly well with correlations for fluidized systems.     

二维气雾两相射流锥内速度分布的计算和验证

结合单顶粒动力学模型与普朗特混合长度理论,对二维气雾两相射流体系中颗粒的时均速度和脉动速度进行了求解,结果表明颗粒在径向的轴向流速呈正态分布,射流轴收线附近紊动较强,随着射流向外发展,紊动逐渐降低,实验证明模型计算值与实验值吻合较好,能较好地体现二维气雾两相射流特性,具有一定的可行性和实用性。     

活性污泥沉降速率模型的研究进展

活性污泥沉降速率是二沉池模型的核心内容,以固体通量理论为基础的沉降速率模型主要包括幂函数模型、指数模型、Cho模型、双指数模型和颗粒分类沉降模型。在二沉池模拟中,指数模型和双指数模型较为实用且应用较多。指数模型的参数估计可通过模型参数与SVI关联实现,而双指数模型的参数则需将批沉降试验与最优化技术相结合才能确定。对活性污泥沉降速率模型的进一步研究工作提出展望。     

Cocurrent Downflow Fluidized Bed Dryer: Experimental Equipment and Modeling

Product damage, high energy consumption, and nonhomogeneous final properties are present in typical drying operations such as pneumatic drying, fluidized-bed dryers, and upward circulating fluidized-bed dryers. The downer bed has been shown to be a good technique for this processes. The objective of this work is to test an experimental downflow dryer and model its operation. The equipment consists of a 5-m-high stainless steel duct with 0.17 m i.d. Gas velocity was varied between 0.3 and 8 m/s in co-current solid flow varying between 0 and 50 kg/m²s. Drying rates, pressures, and total flux for solid and gas are determined. Temperature profiles for gas and solid along the radial and axial directions are determined and tested with model predictions. The solid particles were previously dried turnip (Brassica napus) seeds. The equipment shows good operational conditions and facilities for parameter determination, but must be complemented with better equipment for particle concentration determinations. The model's predictions of pressure, gas velocity, solid concentration, and temperature are compared with our experimental values or those reported in the literature.     

对炸药驱动飞片速度的理论计算方法的分析与评价

通过文献调研,介绍和分析了6种炸药爆轰驱动飞片速度的计算模型,并指出每一种计算模型的适用范围。讨论了格尼模型以及后人针对格尼模型应用中存在的问题,提出了改进计算模型,主要包括有效装药量、不同空气间隙大小、不同mc／mm比情况、多层装药贡献法、爆速法、炸药示性值法等,可为不同应用场合提供不同的参考模型。     

Cocurrent Downflow Fluidized Bed Dryer: Experimental Equipment and Modeling

ABSTRACT

Product damage, high energy consumption, and nonhomogeneous final properties are present in typical drying operations such as pneumatic drying, fluidized-bed dryers, and upward circulating fluidized-bed dryers. The downer bed has been shown to be a good technique for this processes. The objective of this work is to test an experimental downflow dryer and model its operation. The equipment consists of a 5-m-high stainless steel duct with 0.17 m i.d. Gas velocity was varied between 0.3 and 8 m/s in co-current solid flow varying between 0 and 50 kg/m²s. Drying rates, pressures, and total flux for solid and gas are determined. Temperature profiles for gas and solid along the radial and axial directions are determined and tested with model predictions. The solid particles were previously dried turnip (Brassica napus) seeds. The equipment shows good operational conditions and facilities for parameter determination, but must be complemented with better equipment for particle concentration determinations. The model's predictions of pressure, gas velocity, solid concentration, and temperature are compared with our experimental values or those reported in the literature.     

高海拔地区大型循环流化床锅炉特性研究

结合青海盐湖工业股份有限公司供热中心4×480 t/h循环流化床(CFB)锅炉的启动调试,通过理论论证及实际应用,对高海拔地区大型循环流化床锅炉特性进行研究,解决了低气压地区流化床锅炉高负荷工况下频繁结焦问题。给出了流化床锅炉正常运行所要维持的流化风速范围,明确了高海拔地区循环流化床锅炉流化风速计算应选用标态风量,与低海拔地区一致,使得此类技术具备实际可参考性及可操作性,对解决同类型问题有一定的参考价值。     

SCALE-UP OF PNEUMATIC CONVEYING DRYERS

Scale-up of pneumatic conveying dryers has until now been largely empirical. A theoretical model is outlined which predicts dryer performance effectively. It depends on some uncertain parameters, notably agglomeration and wall friction, but these can be found more accurately by checking the predictions against results from the small-scale dryer. The model can then be used to scale up to the full size dryer. The required duct length falls as the gas velocity is reduced and the duct diameter increased, subject to satisfactory conveying and dispersion at the feedpoint.