直热式转筒干燥过程物料停留时间理论推导

为了对物料在直热式转筒干燥机内理想扬料板作用下停留时间进行计算研究,根据扬料板作用下的物料在转筒内撒落分布均匀状态,建立了理想扬料板的截面方程,采用建立的理想扬料板的截面方程,导出了随着转筒转动到不同位置的扬料板持料量,在此基础上,分析物料在直热式转筒干燥机内的实际运动情况,建立转筒内物料运动的数学模型,导出物料在转筒内的停留时间,对现有停留时间计算方法进行了修正。研究为扬料板作用下直热式转筒干燥过程物料停留时间的计算提供一种参考。     

回转式烘干机物料空间运动建模和数值分析

目前,回转式烘干机筒体内物料运动方式的研究方法主要是建立扬料板持料、撒料模型及物料在筒体内滞留时间模型,但大多数计算公式过于依靠经验常数,且物理意义不明确。本文以物料空间抛落运行机理为基础,采用数值分析法建立了回转式烘干机内的物料运动模型。首先研究了回转式烘干机内物料的空间运动规律,以位于任意回转位置扬料板翼端点处的物料颗粒为研究对象,建立了物料运动模型,并用Matlab绘图工具箱绘制了物料在筒体内运动状态的三维空间图像。然后,推导了物料在筒体轴向运动距离解析式和以扬料板持物量为权重的滞留时间数值分析模型,这些模型综合考虑了干燥介质推力、筒体倾斜度、转速及填充系数等因素的影响,物理意义明确,与生产实例和文献公式计算结果基本一致。     

布风方式对流化床混合特性的影响

通过将离散单元法同计算流体力学相结合,对流化床内物料混合过程进行了研究。给出了水平布风板均匀布风、倾斜布风板非均匀布风2种情况下的示踪颗粒场历变过程。模拟结果表明:瞬时颗粒场组图能够较为直观表征床内混合现象;其中,在均匀布风情况下,床内气泡横向运动受到限制,颗粒整体横向运动能力较弱,混合方式以扩散混合为主;而对于非均匀布风流化床,床内存在较大的横向颗粒浓度梯度,对流混和起主要作用,且混合速度较为迅速。     

连续进出料鼓泡流化床颗粒停留时间分布

针对双流化床气化或双床热解气化工艺中鼓泡床反应器的设计,采用脉冲法研究了Geldart B类固体颗粒在连续颗粒进料和出料的矩形流化床内的停留时间分布(RTD),考察了气速、床料高度、粒径、物料流率等操作参数对RTD的影响. 结果表明,物料流率、床料高度、粒径是影响颗粒RTD的主要因素,而气速则是次要因素. 随物料流率和粒径增加,鼓泡床内颗粒流动向平推流靠近;随床料高度增加,物料在床内的混合更加充分,颗粒流动向全混流靠近. 根据实验结果,推荐采用比理想平推流时间低9%~18%计算平均颗粒停留时间.     

滚筒筛的原理及程序计算

1 原理与构造 滚筒筛又称旋转筛,多用于筛分较大颗粒的物料。其构造为一稍微倾斜的转筒,筒面为筛网。筛分时物料由入口加入筒内,细料穿过筛孔     

料饼中颗粒分布的无损精准测定方法

对于物料经高压料床挤压粉碎后形成的料饼中细粉含量难测定、在不破坏级配的情况下难打散的问题,提出一种用于测定料饼中颗粒分布的方法：采用球磨机中装入轻质低密研磨体（橡胶球等）的料饼打散装置;通过试验和数据分析设置研磨体的参数、研磨打散时间T;在此参数配置下用磨机打散挤压后的料饼,再对打散的物料进行筛析。如此,既可实现料饼的充分打散,而又能在不改变此物料级配的情况下得到粒度的分布。进一步地,可用于开展辊压机等料床粉碎设备的挤压破碎和闭路循环挤压的实验研究工作,为料床粉碎设备的闭路循环挤压实验研究提供新的分析手段和方法。     

均衡运动旋转振动筛DEM数值模拟

旋转振动筛广泛应用于各行业对于粉体和胶体的分级。单电机旋振筛的激振力不通过振动体质心,使振动体随质心作圆运动和绕质心作圆锥摆运动。这种运动使得筛面上的垂直振幅不均匀,存在着颗粒物料向筛面周边扩散较快、物料层较厚、筛分效率较低、颗粒均匀度较差的问题。因此提出了一种均衡运动原理的旋振筛,通过DEM数值模拟,从筛分效率的角度直观比较了旋振筛在常规运动和均衡运动下的筛面物料运动规律、颗粒粒度分布情况、固相筛分效率及颗粒运动速度。研究表明：均衡运动下物料向筛面周边旋转扩散更为均匀,其物料层较薄,能有效提高旋振筛的固相筛分效率及筛分颗粒的均匀度,可较好解决颗粒粒径与筛孔孔径比在0.7~1.0之间时颗粒透筛相对困难的问题。     

制作试样的小型注射机

<正> ニチメン公司着手销售美CSI公司设计、制作的超小型注射机,这是结构紧凑、可制作0.3克的哑铃形试片的微型注射机。 使用时先将物料投入固定的料筒里,通过支杆和转子运动(同方向旋转)使物料熔融,熔融物料随着转子上、下运动进行树脂交换,经充分搅拌后注入料筒下的模具中,成型后取出试样。     

气流旋转干燥器

1 旋风气流干燥器 旋风气流干燥器的干燥室结构以圆筒形居多,但也有锥形结构,锥形干燥室可使物料颗粒旋转速度由小到大,能达到强化干燥的目的. 旋风气流干燥器由内筒和外筒组成.外筒呈上大下小的锥形,物料从上部切线进入干燥器后,随热风向下部进行旋转运动,在干燥室内物料被干燥.到达底部后受气流夹带,粉体从内筒向上运动,经出料口排出.旋风气流干燥器的优点是使物料及热空气在干燥器内形成的转向降低了设备的高度,延长了物料在干燥器内的停留时间.     

能破拱、不堵塞、流量可调的颗粒粉体料仓

中华人民共和国国家知识产权局于 2 0 0 1年 9月 5日公告了实用新型专利《能破拱、不堵塞、流量可调的颗粒粉体料仓》(专利号 0 0 2 30 831.2 )。该颗粒粉体料仓包括破拱器、旋转轮、流量控制板、流量控制器、驱动装置等组成传动箱并与料斗、料筒组成料仓。启动驱动装置 ,破拱器、旋转轮、流量控制板旋转 ,物料由料仓流出。接通流量控制器 ,物料流量可调。该实用新型专利是一种集仓内破拱、落料口不堵塞、落料面均匀、物料流量可远距离控制调节等多功能于一体 ,且投资少、无噪声、无粉尘污染 ,是值得推广的、工作可靠、运行安全的环保型颗粒…     

Transversale Schüttgutbewegung und konvektiver Stoffübergang in Drehrohren. Teil 1: Ohne Hubschaufeln

The type of transverse bed motion in rotary cylinders depends on the Froude number and the ratio of the cylinder to particle diameter. In the case of the “rolling bed”, the radial velocity profile can be obtained by modelling the bed as a viscous-inelastic, dilatant fluid. In comparison with experimental data on the thickness of the so-called active layer, this model shows good agreement. The convective mass transfer coefficient at the surface of the bed generally depends on the axial gas velocity, particle size, rotational speed and cylinder geometry. However, the influence of the rotational speed can be reduced to the transverse particle velocity at the surface. Experimental data obtained from drying experiments allow a general correlation to be fitted for the heat and mass transfer at the surface of the bed.     

Rotary cylinders: Transverse bed motion prediction by rheological analysis

A method for predicting the transverse motion of a granular bed in a rotary cylinder is proposed, based on a non-Newtonian rheological model of the pseudo-plastic type, i.e. with a flow behaviour index (n) between 0 and 1. For a good simulation of bed motion, the model must be able to adequately reproduce the bed velocity profile in both the upper (downward flowing) and the lower (upward moving) zones. It is shown that to do so there is the need to adjust not only the consistency index K but even more importantly the flow behaviour index, n. The mass and momentum conservation equations are solved by the CFD code FLUENT. The model is applied to the simulation of the motion of an alumina bed and the computed results compared with experimental data.     

Effect of macroscopic heterogeneity of the medium on the solid-state combustion wave characteristics in thermally and chemically heterogeneous media

A macroscopically heterogeneous medium is modeled by a set of cylinders (rods) pressed from a mixture of solid reagents, which have coaxial cylindrical cores made from an inert material. A three-dimensional mathematical model describing propagation of combustion waves over one cylinder is studied by numerical methods. The influence of the distance between the centerlines of the neighboring cylinders and transverse sizes of the cylinders on characteristics of combustion waves propagating over a heterogeneous medium is considered. It is demonstrated that there exists an optimal distance between the inert rods, which ensures a much higher velocity of the combustion wave along the specimen than the theoretically predicted velocity of the classical combustion wave propagating over a solid specimen. New types of spinning waves are described, whose motion makes the high-temperature spot move inside the charge mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 39–49, May–June, 2008.     

Mathematical Modeling of the Fluidized Bed Drying of Cubic Materials

The unsteady‐state simultaneous heat and mass transfer between gas and potato cubes during the drying process in a batch fluidized bed was described by a mathematical model. Mass transfer was considered to occur in three dimensions whereas heat transfer between the gas and dried material was assumed to be lumped. It was found that the model could describe the drying process with acceptable accuracy. The moisture profile inside the material at any cross‐section and at any time can be predicted by the model.     

烧结床层的热质分析

基于烧结生产的复杂物理化学过程,建立了烧结床层传热、传质和流动的二维非稳态数学模型,考虑了孔隙率、物料颗粒当量直径等床层结构影响参数的变化,并对气固传热系数进行了修正。通过数值计算,获得了烧结床层的温度场、结构变化和烟气的流场、温度场、浓度场等。烟气出口温度、床层总压降与生产实测值吻合较好,验证了数学模型的正确性。进一步分析了燃料配比、风量和给料温度等操作参数对烧结过程的影响。研究结果表明：燃烧带的厚度、最高温度随着烧结过程的进行而逐渐增加。床层孔隙率、颗粒当量直径的变化主要发生在燃烧带的熔融、冷凝阶段。料层压损最大的是燃烧熔融层,其次是混合料带,最小的是烧结矿层。增加焦粉含量、提高烧结混合料的初温,有利于提高成矿质量;风量过大时,会造成成矿质量下降、生产成本提高。     

Predicting the fraction of the mixing zone of a rolling bed in rotary kilns

The thermal efficiency of a rotary kiln is predominantly influenced by the amount of lateral mixing of the material bed. In this paper, the fraction of the mixing zone in the material bed is predicted for the rolling motion. For a given material, the fraction is found to depend only on three dimensionless variables—the ratio of the particle diameter to the kiln diameter, the Froude number and the filling degree. Experiments were carried out on a rotating cylinder with beans as testing material. The predicted results are in good agreement with the measurements with a maximal error of 12%. The fraction of the mixing zone is then analyzed for industrial rotary kilns. Its value is found to increase approximately linearly with increasing Froude number and the dynamic angle of repose of the material. For all investigated cases, the fraction of the mixing zone lies in the range of 20–45%. Results of this study can provide orientating values of the mixing zone fraction, which are needed to calculate the thermal efficiency of the rotary kiln.     

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     

往复式压缩机网状阀倾侧运动研究

把往复式压缩机网状阀片的运动看作平动和转动的复合运动，并以偏离气缸截面安装的带缓冲片网状阀为例，建立由于气流偏吹引起的阀片倾侧运动的数学模型，并通过实验得到验证，最后与阀片单质点数学模型的结果进行了比较。     

The influence of physicomechanical characteristics of microspherical supporters and dehydrogenation catalysts on their abrasive activity in fluidized bed conditions

In industrial lower paraffin dehydrogenation reactor units with a microspherical chromoalumina catalyst fluidized bed, abrasive wear of internal equipment surfaces proceeds by the fatigue and plastic deformation mechanism, and the wear direction coincides with the catalyst motion trajectory. The wear degree is defined by wearing material and granule physicomechanical properties, which have been taken into account along with hydrodynamic conditions for the formation of fluidized bed to suggest a mathematical model, describing the influence of physicomechanical, structural characteristics and sizes of granule on the abrasive ability of industrial microspherical paraffin dehydrogenation catalysts and aluminum oxide supporters. The most significant factors have been revealed: salient item density on the granule surface, abrasion resistance, microhardness, and sphericity degree. The developed mathematical model permits to predict the abrasive activity of granules under their operation, to estimate the internal reactor surface wear time necessary to attain the critical thickness, and to choose optimal methods for the synthesis of catalysts and supporters with minimal abrasive activities.     

Mass transfer from cylinders and plane surfaces buried in packed beds in alignment with the flow direction

The present work describes the mass transfer process between a moving fluid and a slightly soluble cylinder buried in a packed bed, in alignment with the direction of flow. The bed of inert particles is taken to have uniform voidage.Numerical solution of the partial differential equation (PDE) describing mass conservation of the solute gave the concentration field near the soluble surface and the mass transfer flux was integrated to give values of the Sherwood number as a function of the relevant parameters. A mathematical expression is proposed (given as Eq. (32) in the paper) that describes accurately the dependence found numerically between the value of the Sherwood number and the values of Peclet number and aspect ratio, L/d₁, of the cylinder. For large enough diameter of the cylinder, the problem degenerates into mass transfer from a plane surface and the same equation applies, with L/d₁=0.The equation was tested through the measurement of diffusivity for different solutes released by slightly soluble solids, and the experimental values obtained were in excellent agreement with the values found in literature.An important feature of the paper is the detailed discussion of the finite difference method adopted, with emphasis on the high-resolution schemes used in the discretisation of the convection term of the PDE.