气液两相循环流化床停留时间分布的研究

通过脉冲示踪法,研究气液两相循环流化床停留时间分布,并从整个循环体系的停留时间分布曲线中,分离出提升管的停留时间,建立了数学模型,并进行模拟.     

变径流化床反应器内的气固流动特性数值模拟

采用计算颗粒流体力学(CPFD)的数值模拟方法,对直径为160 mm、高度为273 3 mm的变径流化床反应器内的气固流动特性进行冷态模拟,研究不同气速及不同初始物料量对流化床反应器气固流动特性的影响,得到流化床内颗粒体积分数、颗粒速度以及颗粒停留时间的分布。结果表明,当气速不小于2.5 m/s时,流化床内颗粒体积分数轴向分布更为均匀,颗粒速度呈中间高、两边低的倒"U"形分布;壁面附近的颗粒停留时间长于中心处,使得壁面附近的颗粒趋于聚集;流化床的轴径向颗粒体积分数随着初始物料量的增加而增大。     

螺旋管内气液两相流动和传热特性的研究

螺旋管式换热器和蒸汽发生器已经在动力、核电站、化工、石油等工程领域里得到广泛的应用,成为一种十分重要的传热设备.螺旋管式换热器,由于其本身结构、流动和传热特点,己愈来愈受到人们的重视.为了对螺旋管式换热器和蒸汽发生器提供正确的设计和计算方法,需要对气液两在螺旋管内的流动和传热进行深入的研究.目前,对于以工程应用为目的、以高压蒸汽——水系统为对象的研究工作还十分少,缺乏供工程实际应用的试验数据,对于气液两相在螺旋管内流动和传热特性以及机理的了解也很不够.本文分五个方面对螺旋管内气液两相流动和传热特性进行理论分析和试验研究.     

循环流化床锅炉气固两相流动特性的试验研究

对影响循环流化床气固两相流动特性的因素进行了试验研究。结果表明,在循环流化床内存在着两个界限很明显的区域:下部的密相区和上部的快速区;在快速区内部分颗粒均匀地悬浮在上升气流中,另一部分形成颗粒团,它在循环流化床内作剧烈的上下运动,使床内颗粒浓度分布比较均匀;循环流化床内,床层密度在底部较大,风速增加,床层密度下降。     

鼓泡塔中气液两相流与浸没在其中的水平管间的传热研究

本研究对鼓泡塔中气液两相流与浸没在其中的水平管间的对流传热系数进行了实验测定。着重研究了表观气速、液相粘度和液相表面张力对传热系数的影响。实验证明,鼓泡塔内的传热系数与传热管的方位无关,其传热系数可按文献[1]的关联式进行关联。     

利用考虑壁面粗糙度的双流体颗粒-壁面碰撞模型模拟气-粒两相水平槽道流动

建立了考虑壁面粗糙度的双流体颗粒壁面碰撞模型．该模型包括壁面摩擦、恢复、特别是壁面粗糙度等影响碰撞的因素，因此体现了壁面上各方向Reynolds应力之间的相互转化、湍流动能从平均运动中得到能量以及壁面对运动的衰减作用，给出了壁面粗糙度对颗粒湍流的影响．将本模型应用于气粒两相水平槽道流动并用PDPA测量结果验证，结果表明，当前常用于颗粒相的零梯度边界条件和其他碰撞模型可能给出错误的结果，本模型则给出比较符合实际的结果．     

稠密气固两相反应流的拉格朗日法

提出了采用欧拉坐标和拉格朗日坐标相结合研究稠密气固两相反应流的方法,建立了稠密两相反应流中两相运动、传热、化学反应的模型与算法,采用该模型与算法研究了循环流化床排烟脱硫装置内的两相反应过程,得到了详细合理的计算结果.结果表明,采用此模型和算法模拟工程意义上的稠密气固两相反应流是可行的.     

Experiment research on grain drying process in the heat pump assisted fluidized beds

A heat pump assisted fluidized bed grain drying experimental system was developed. Based on this system, a serial of experiments was performed under four kinds of air cycle conditions. According to the experimental analysis, an appropriate drying medium-air cycle for the heat pump assisted fluidized bed drying equipment was decided, which is different from the commonly used heat pump assisted drying system. The experimental results concerning the drying operation performance of the new system show that the averaged coefficient of performance (COP) can reach more than 2.5. The economical evaluation was performed and the power consumption for removing a kilogram water from grains was about 0.485 kW·h/kg (H₂O), which shows its reasonable commercial efficiency and great application potentiality in future market.     

LBE–DEM simulation of inter-phase heat transfer in gas–solid cross jets

Lattice-Boltzmann equation(LBE)–Discrete element method(DEM)coupled simulation of a twodimensional gas–solid cross jet is performed,focusing on the gas-particle two-way coupling effect on heat transfer characteristics.The Reynolds number is 1000,and particle Stokes numbers are 10,25,and 50 under the same number flow rate of particles.The gas phase temperature field and particle distribution as well as the inter-phase heat transfer characteristics are studied and analyzed.The dominating effects,i.e.the mean temperature difference and mean heat transfer coefficient between the gas–solid phases,for the pre-and post-collision stages of the cross jets are illustrated respectively.The change of dominating roles is related to the dynamical response characteristics of particles.     

离心流化床干燥器的传热研究

离心流化床干燥器的传热研究阎红，王维，王宝和，王喜忠（大连理工大学化学工程系１１６０１２）关键词：流化床干燥器，离心式，传热分类号：ＴＱ０２１．３；ＴＱ０２８．６７２；ＴＱ０５１．１３０引言离心流化床干燥器是近年来开发的一项新型干燥设备，它与普通流化...     

流化床内煤燃烧的传热过程DEM数值模拟

采用离散单元法（DEM）对流化床内煤颗粒燃烧过程中的传热过程进行了数值模拟．气相湍流采用融e模型,颗粒相采用离散单元法（DEM）．颗粒传热过程考虑了颗粒与气相的对流传热、颗粒与床层的辐射传热、煤颗粒的燃烧热以及颗粒碰撞传热;燃烧过程中化学反应包括焦炭与O2和CO2的异相反应、挥发分燃烧及CO和O2的均相反应．模拟得到了煤颗粒的加热升温和燃烧过程中各种热量对煤颗粒传热的贡献大小,并对不同颗粒刚度系数、考虑颗粒旋转与不考虑颗粒旋转以及不同颗粒摩擦系数对各种传热量的影响敏感性进行了模拟．     

流化床非平衡态热力学分析模型

用非平衡态热力学的分析方法分析了流化床系统的熵、熵产生、熵流,讨论了流化床系统的热力学分支和耗散结构分支,论证了流化床系统的能量最小原则,使热力学第二定律同流化床理论研究有机地相结合。建立了鼓泡流化床的数学模型和过渡态判据。热力学第二定律的引入,使热力学和流体动力学与流化床理论研究、耗散结构分支与系统运动形式的多样性、系统总体稳定与局部非稳定在理论描述上相统一。     

循环流化床锅炉炉内传热的影响因素

为定量分析受热面布置、床内流动、管内流动和床温等对循环流化床内传热和炉内辐射换热份额的影响,利用已有循环流化床炉内传热计算模型,比较了工程中常见工况下传热系数与设定标准工况下传热系数的偏差。结果显示:局部物料浓度是影响传热系数的最重要因素,相对偏差可达50%;流化风速、床温、工质温度或受热面金属导热系数影响下的传热系数相对偏差在5%~50%内变化;而烟气辐射厚度、管节距和管径的影响相对较小,传热系数相对偏差在5%以下;工质侧换热系数大于3 kW.m-2.K-1时,对传热系数的影响较小。工程上传热系数的辐射贡献通常约为60%。     

单回路脉动热管传热性能的试验

通过对单回路紫铜-水脉动热管在风冷方式和定热流加热条件下,稳定运行时的传热性能的试验研究,得到管壁温度沿管长的变化规律,冷热段均温和温降(或温升)、传热温差、传热热阻随传热功率的变化特性.分析了充液率和管径对热管传热性能的影响.结果表明:冷热段均温、传热温差随传热功率的增加而增大,传热热阻随传热功率的增加而减小;小传热功率时,传热热阻对传热功率、管内径和充液率的变化较为敏感;减小充液率,增大管内径,增加传热功率可明显降低热管的传热热阻;较高传热功率时,充液率、管内径和传热功率对传热热阻的影响较小,影响传热热阻的主要因素是冷却热阻,可通过增加管外径或改善冷却条件来降低传热热阻,提高传热性能.     

Surface-particle-emulsion heat transfer model between fluidized bed and horizontal immersed tube

A mathematical model, surface-particle-emulsion heat transfer model, is presented by considering voidage variance in emulsion in the vicinity of an immersed surface. Heat transfer near the surface is treated by dispersed particles touching the surface and through the emulsion when the distance from the surface is greater than the diameter of a particle. A film with an adjustable thickness which separates particles from the surface is not introduced in this model.The coverage ratio of particles on the surface is calculated by a stochastic model of particle packing density on a surface. By comparison of theoretical solutions with experimental data from some references, the mathematical model shows better qualitative and quantitative prediction for local heat transfer coefficients around a horizontal immersed tube in a fluidized bed.     

A stochastic model of bubble distribution in gas-solid fluidized beds

On the basis of the Langevin equation and the Fokker-Planck equation, a stochastic model of bubble distribution in a gas-solid fluidized bed was developed. A fluidized bed with a cross section of 0.3 m×0.02 m and a height of 0.8 m was used to investigate the bubble distribution with the photographic method. Two distributors were used with orifice diameters of 3 and 6 mm and opening ratios of 6.4% and 6.8%, respectively. The particles were color glass beads with diameters of 0.3, 0.5 and 0.8 mm (Geldart group B particles). The model predictions are reasonable in accordance with the experiment data. The research results indicated that the distribution of bubble concentration was affected by the particle diameter, the fluidizing velocity, and the distributor style. The fluctuation extension of the distribution of bubble concentration narrowed as the particle diameter, fluidizing velocity and opening ratio of the distributor increased. For a given distributor and given particles the distribution was relatively steady along the bed height as the fluidizing velocity changed.     

布风装置对流化床流动特性的影响

以欧拉双流体模型和颗粒动力学方法为基础,采用基于压力的PC-SIMPLE算法,标准k-ε的分散湍流模型,数值模拟了在3种不同气体布风装置下流化床内气固两相流动,获得了其床内颗粒体积分率和速度的分布规律.相对于单层多孔板流化床,管式和凹形多孔板流化床达到稳定流化状态的时间较短.在相同的床高和径向位置处,管式和凹形多孔板流化床内颗粒体积分率随时间的变化较强烈.不同布风装置的流化床总体上在床内形成了中心区域体积分率较小,向上运动;近壁面区域体积分率较大,向下运动的"环核"结构.