水平圆管内浆氢的流动与传热特性数值模拟

浆氢是固氢和液氢的混合物,相比于液氢由于浆氢具有更高的密度和热容,更适合用于火箭和航天推进器的推进剂。基于欧拉-欧拉两相流模型,在考虑颗粒动力学的基础上对浆氢在水平圆管中的流动与传热特性进行了数值模拟研究。通过对浆氢在不同热通量、流速和颗粒直径等情况下的研究发现,浆氢相比于液氢可以有效减少液氢气化。流速的提升能够有效提高固相颗粒分布的均匀性,且使得浆氢沿程平均传热系数增大。小直径的固相颗粒相比于大直径颗粒能够增强固液两相间的换热,加快浆氢的融化。     

狭窄矩形通道内液固两相磨蚀特性

液固两相磨蚀研究主要集中于圆管弯头和射流工况,板式换热器等狭窄矩形通道内液固两相磨蚀特性的研究鲜见报道。在Fluent软件及其二次开发框架内构建了描述稀疏颗粒液固两相磨蚀特性的CFD-DPM-磨蚀耦合数学模型框架,研究了存在圆柱体阻挡物的狭窄矩形通道内两相流动特性和壁面磨蚀特性,揭示了壁面和固体颗粒的相互作用机制。研究结果表明：阻挡物的存在显著改变了狭窄矩形通道壁面的磨蚀行为;磨蚀速率随液固流速和壁面粗糙度的增加而增加,因此,保证设备较低的入口流速和壁面粗糙度对延长设备寿命至关重要;磨蚀速率随颗粒粒径的增加先增加后降低,在60μm左右时达到极大值;球形度系数对磨蚀行为影响较小。引入量纲为1颗粒尺寸,阐述了液相边界层束缚颗粒运动的作用机制;与光滑壁面工况相比,颗粒以较大能量高频撞击粗糙壁面,导致了壁面磨蚀较快。液固两相以较低的角度和速度撞击壁面,壁面材料去除机理以微切削为主。     

基于非均质性流动过程量化冰浆流动管道压降

以水平管道内冰浆非均质性等温流动过程为研究对象,结合欧拉-欧拉模型,引入颗粒浓度扩散方程和非均质流动曲面方程,建立适用工程设计阶段冰浆非均质性流动管道压降"准二维"模型。结果表明,"准二维"模型含有冰浆流动时液相载流体相、固相冰粒子相和固液两相间的相互作用各分项,能够分项量化出各流体相的阻力份额。当流速较低时,液体相和冰粒子相所占的压降份额将随流速与冰粒子浓度变化呈现出反向变化趋势;随着流速升高,各流体相所占的压降份额仅对冰粒子的浓度变化具有显著的响应。通过比较不同工况下冰浆流动的管道压降,"准二维"模型的预测值与实验值间的相对误差基本可控制在±10%内。同时,"准二维"模型体现出明显的效率优势。     

微型气液固三相等温微分浆态床反应器的优化

针对气液固三相浆态床催化反应中,传递、反应、催化剂的原位表征均比较复杂的问题,为了有利于气、固相均匀分散于液相和反应温度在反应器中实现等温,通过对气液固三相反应工艺特性和反应器性能要求的分析,对微型气液固三相浆态床反应器进行了优化。根据微型浆态床对气液固三相反应分析的要求,采用图像法研究了分布器为G1、G2、G3,砂板直径为2、2.5、3 cm反应器中的流体力学性能特征,考察了气体流速、温度、反应器直径及气体分布器对气含率、气泡尺寸、气泡上升速率以及气泡分布的影响,并进行流体动力学模拟计算,确定了微型浆态床反应器的直径为2 cm,气体分布器为G3砂板的反应器结构,该反应器可以应用于反应过程中间态及液体产物生成过程的测试。     

微裂缝内液固两相流动特性研究

应用欧拉-拉格朗日模型,对微裂缝中液-固两相流动过程进行数值模拟。在数学模型中,液相采用连续相模型,颗粒当做离散分散在连续相中,并考虑了相间耦合作用。对于物理模型,建立了二维直微裂缝模型,研究裂缝的液相粘度、液相速度和颗粒密度等因素对裂缝中两相流动的影响。模拟得到了微通道内颗粒瞬时分布状态、颗粒运动轨迹、颗粒停留时间、颗粒轴向速度分布、液相轴向速度分布等参数的变化规律,定性的揭示了储层裂缝内液固两相流动过程。     

稠密固液循环流化床内流体湍流脉动对颗粒分散的影响

通过计算流体动力学模拟研究了固液循环流化床内流体湍流对高浓度颗粒的扩散作用。根据湍流机制下高浓度颗粒在液体中的分散机理,建立了同时考虑颗粒碰撞、流体拖拽和流体湍流扩散输运的欧拉-欧拉双流体模型。利用该模型对稠密固液循环流化床提升管内颗粒的分散运动进行了数值模拟,预测出颗粒轴向速度和体积浓度的径向分布,与相应条件下的实验数据符合很好。表明考虑流体湍流扩散输运的理论模型更能精确预测高浓度颗粒在循环流化床提升管内的运动情况;也表明即使针对以颗粒碰撞为主的稠密固液湍流体系,尺度较大的流体湍流涡也会因促使颗粒扩散输运,影响颗粒空间分布。工作为稠密固液循环流化床内两相流体动力学分析奠定了基础。     

倒置液固流化床内液固两相流动特性的数值模拟

基于欧拉-欧拉双流体模型,数值模拟倒置液固流化床内液固两相流动行为.数值模拟预测了床内颗粒的速度、浓度分布以及空隙率的变化.研究结果表明颗粒在床内分布呈现非均匀分布,床内形成局部高空隙率的流体团;随着床层高度增加,颗粒轴向速度增大:数值模拟床内空隙率与Renganthan等的实验结果相吻合.     

流化床内颗粒流体两相流的CFD模拟

采用先进的CFD模拟技术分析流化床内两相复杂体系的非线性流体动力学特征已得到普遍认同,但是由于不同研究者对颗粒与颗粒以及颗粒与流体之间相互作用力认识的差异,导致欧拉-欧拉框架下动量守恒方程的不同表达形式。本文在总结文献中有关颗粒黏性力、固相压力和两相间作用力的基础上,从双流体理论出发,提出了一个考虑拟平衡态下固体颗粒对流体相和固相动量守恒方程均有影响的简捷流体动力学模型。该模型的主要特点是表征颗粒离散属性的特征长度视为颗粒直径的同一数量级。随后在CFX4.4商业化软件平台上通过增加用户自定义子程序,对网格尺度、时间步长和最大颗粒堆积率的无关性进行检验,介绍了作者近年来采用该模型模拟二维/三维流化床内液固体系的散式流态化、气固Geldart A类物料的散式/聚式流态化和床层塌落特性以及Geldart B/D类物料的鼓泡/射流流态化和床层塌落的研究进展。模拟的主要结果与经典理论、本研究实验和文献报道数据相一致,说明该模型可以用来预测流化床内密相颗粒流体体系的动力学特性。     

分解槽搅拌过程数值模拟研究

建立了一个工业分解槽的计算流体力学CFD模型,采用稳态多重参考系法以及欧拉一欧拉多相流模型对槽内固液两相搅拌过程进行数值模拟计算。分析了流体速度分布、颗粒相分布以及搅拌功率变化过程。     

用压差变化阈值确定外循环流化床的起始外循环流化速度

起始外循环流化速度是影响气液固外循环流化床正常操作的重要参数之一。提出了以流化床内压差随表观液速的变化阈值来确定流化床起始外循环流化速度的方法。通过实验研究,考察了颗粒直径、颗粒体积分率和表观气速等操作参数,对强制循环条件下流化床起始外循环流化速度的影响。结果表明,液固流化床起始外循环流化速度远大于单个颗粒终端速度,与颗粒体积分率、颗粒平均直径成正比;强制循环时,颗粒体积分率较小的情况下,加入气体后的起始外循环流化速度比液固两相起始外循环流化速度要大,颗粒体积分率较大时,几乎与液固两相相同。     

基于双流体模型的液氢流动沸腾数值模拟

基于双流体模型,建立了液氢管内流动沸腾的数值模型,在液体Reynolds数67000～660000、壁面热通量16300～317800 W/m²、饱和温度22～29 K、入口过冷度0～8 K的范围内,对管径5.95和6.35 mm的圆管内液氢流动沸腾开展了数值模拟研究,并与试验结果进行了对比。对比显示,液氢流动沸腾传热系数的模拟结果与试验数据的平均误差（MAE）为7.79%,94%的模拟数据都在±20%误差带范围内。     

Particle‐scale simulation of the flow and heat transfer behaviors in fluidized bed with immersed tube

A kind of new modified computational fluid dynamics‐discrete element method (CFD‐DEM) method was founded by combining CFD based on unstructured mesh and DEM. The turbulent dense gas–solid two phase flow and the heat transfer in the equipment with complex geometry can be simulated by the programs based on the new method when the k‐ε turbulence model and the multiway coupling heat transfer model among particles, walls and gas were employed. The new CFD‐DEM coupling method that combining k‐ε turbulence model and heat transfer model, was employed to simulate the flow and the heat transfer behaviors in the fluidized bed with an immersed tube. The microscale mechanism of heat transfer in the fluidized bed was explored by the simulation results and the critical factors that influence the heat transfer between the tube and the bed were discussed. The profiles of average solids fraction and heat transfer coefficient between gas‐tube and particle‐tube around the tube were obtained and the influences of fluidization parameters such as gas velocity and particle diameter on the transfer coefficient were explored by simulations. The computational results agree well with the experiment, which shows that the new CFD‐DEM method is feasible and accurate for the simulation of complex gas–solid flow with heat transfer. And this will improve the farther simulation study of the gas–solid two phase flow with chemical reactions in the fluidized bed. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

三相循环流化床中沸腾传热特性

提出了一种新型蒸发沸腾传热方式,即汽液固三相循环流化床沸腾传热。实验表明:该传热方式具有强化传热和防、除垢效果;其传热系数比汽液两相流沸腾传热膜系数高1.5～2.0倍,并能长期保持传热壁面的洁净。实验中研究了不同种类的固体粒子(玻璃球、陶瓷球、钛粒和钢球)、粒子体积分率、液相流速以及加热蒸汽压力等因素对循环流化床沸腾传热的影响。     

Heat Transfer in a Liquid-Solid Circulating Fluidized Bed Reactor with Low Surface Tension Media

Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 ...     

节能型立式热虹吸再沸器的模拟

为了提高再沸器的用能效率，特将固体颗粒引入立式热虹吸再沸器的管程形成气－液－固多相流系统，以强化传热，并提出了该节能型立式热虹吸再沸器的数学模型。模拟计算表明，流态化技术的引入能够强化再沸器的传热，减小换热面积或系统的有效能损失。颗粒的密度对传热的影响较大，其增加可使管内传热系数增大；随着固含率的增加，管内传热系数增大；随着粒径的增加，管内传热 数先增加后减小，有一极大值，颗粒密度的增加可使该极值增大并出现得更早。     

液氢缩比贮箱蒸发特性数值模拟及实验验证

地面缩比贮箱用来模拟箭载液氢贮箱热物理过程及运行特性，包括筒段和壳段，壳段用于支撑筒段。筒段和部分壳段使用泡沫绝热，壳段结构部分裸露在环境中，成为液氢贮箱的主要漏热源。基于计算流体力学方法数值研究了液氢缩比贮箱蒸发特性，构建了基于VOF两相流模型以及Level-set界面跟踪方法的贮箱两相氢流动和相变传热传质数学框架，其中气液界面传质率基于Lee模型计算。框架中的系数、边界条件等作如下考虑：Lee模型中的液化/蒸发系数通过与实验数据对比获得；通过理论分析低温面有/无泡沫保温层的结冰特性，对暴露在环境的泡沫和铝壳表面施加对流换热或常热流边界条件；当贮箱压力达到约2个大气压(0.2 MPa)时，安全阀打开放气保持内部压力不变，基于自定义函数方法模拟阀门开闭实现控制贮箱压力的目的。与实验测量的液位下降速率和气相温度非稳态变化对比表明，构建的数值模型能够较好地模拟液氢贮箱自增压过程的复杂流动、相变传热传质特性。为模拟真实箭载液氢贮箱停放阶段的热物理过程打下基础。     

Pressure drop and flow pattern of slush nitrogen in a horizontal pipe

Slush nitrogen is a mixture of solid nitrogen particles and liquid nitrogen, and its flow characteristics in a horizontal pipe are investigated experimentally and theoretically in this study. Pressure drop of slush nitrogen is higher than that of subcooled liquid nitrogen due to the viscous and the mechanical frictions, and the dependence of pressure drop on the mean velocity varies under different flow conditions. The solid volume fraction distributions and the velocity throughout the pipe cross‐section of slush nitrogen flow are investigated with the Eulerian–Eulerian multiphase approach incorporated with the kinetic theory of granular flow. The flow patterns of slush nitrogen are determined as the pseudo‐homogeneous flow, the heterogeneous flow and the bedload flow from the experimental and numerical results. The relationship between the friction factor and the Reynolds number for slush nitrogen with various solid volume fractions is obtained by using the slush Reynolds number. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1762–1773, 2013     

Modelling of transient mass transfer in liquid and liquid‐solid pulsating systems: Applications and extension to heat transfer

The dynamic surface renewal model of Maucci et al. (2001) is applied to transient mass transfer problems and extended to transient heat transfer measurements in pulsating, two‐phase flows. The model is also used to simulate mass transfer for square‐wave liquid velocity pulses in a liquid‐solid column. Experiments and simulation show that, when flow reversal occurs, the average mass transfer for a pulsating flow can be significantly higher than for steady state flow at the same bulk flow rate. This increase depends mainly on the relative pulse magnitude. The influence of pulse frequency and symmetry is second‐order. Apparent differences between various published studies are resolved.     

FLOW BOILING HEAT TRANSFER WITH FLUIDIZED SOLID PARTICLES

In order to solve the fouling problems in boiling processes,a boiling system was designedby adding solid particles to the boiling liquid In this paper.both theoretical analyses andexperimental studies on the boiling heat transfer in such a three-phase flow boiling were carried out.Based on the analysis of heat transfer characters of this three-phase flow boiling,a mathematical mod-el for the heat transfer coefficient of flow boiling was developed.The experiments show that,in thepresence of particles the boiling heat transfer is enhanced and is about 2 times that of the vaporliquid two phase one with better flow stability.The fluidized particles rub the heat transfer wall toprevent and to clean the fouling.     

Prediction of heat transfer to liquid-solid fluidized beds

Heat transfer coefficients to a liquid-solid fluidized bed in a cylindrical tube have been measured using water as liquid phase and three types of cylindrical steel particles, as well as glass, nickel, copper and lead spheres of different sizes as solid phase. The independent varaibles included heat flux, liquid velocity and particle physical properties. The experimental results as well as a data bank containing a large number of measured heat transfer coefficients for solid-liquid fluidization over a wide range of operational parameters have been compared with the predictions of most published correlations. A model for the prediction of heat transfer coefficients is proposed which predicts the present experimental data and the data of other investigators with good accuracy.