基于CFD的新型布浆器混合室结构

为了进一步改善新型布浆器的布浆性能,设计了单腔式混合室（混合室Ⅰ）、以两组支管为单位的多腔式混合室（混合室Ⅱ）及以单组支管为单位的多腔式混合室（混合室Ⅲ）,采用计算流体力学（CFD）方法对混合室内的流动特性进行了模拟。结果表明,单腔混合室内,由于平行射流组各股射流间的强烈干涉作用,导致各股射流向混合室中部聚集,造成出口处质量流量分布呈现中间明显高于两侧的状态。在多腔混合室Ⅱ内,每个混合腔内有两组射流,保证了浆料的良好混合,避免了射流在中部聚集的现象。在多腔混合室Ⅲ内,由于每个混合腔内只有一组支管射流,实现了互补混合过程,混合效果明显好于混合室Ⅰ和混合室Ⅱ。从质量流量分布看,混合室Ⅲ的分布曲线比混合室Ⅰ和混合室Ⅱ的更平缓,其最大偏差仅为0.254%,明显小于混合室Ⅰ的0.538%和混合室Ⅱ的0.294%,更接近于理论混合平均值和期望值。     

圆筒形布浆器多因子影响因素的数值模拟

分析了影响特种纸浆料流动的多因子参数,这些参数主要包括粘度、射流扩散装置结构、不同进口流量等,通过FLUENT软件对布浆器内浆料流动特性进行数值模拟,得到布浆器出口支管流量的分布。结果表明:对于低浓度(小于1.5‰)小流量下的浆料,粘度的变化引起浆料出口支管的波动不超过0.84%;较阶梯过渡结构的射流扩散装置,选用圆锥过渡结构的射流扩散装置可降低出口支管20%以上的流量波动,有效提高布浆器的布浆均匀性;对比不同流量下各支管出口流量,获得较优布浆效果的进口流量,确定生产工艺参数。     

布浆器方锥总管设计方法研究

方锥总管是布浆器的关键部件之一,浆料在方锥总管内流动时压力分布是否均匀决定了流浆箱浆料分布的均匀性及喷浆上网性能。分析了方锥总管内浆料流动损失,并对方锥总管设计方法进行了研究,结果表明,浆料在方锥总管内流动时产生摩擦压头损失、收缩压头损失和分岔压头损失,对浆料产生的流动损失的处理方式不同,形成了不同的方锥总管的设计方法。推导了考虑摩擦压头损失和收缩压头损失的设计方法。由于各种设计方法在推导时均进行了假设,因此,在不同程度上均存在误差。     

水力式流浆箱稳流室的数值研究

流浆箱是造纸机上非常关键的设备,纸页的成形质量很大程度上取决于流浆箱的性能。水力式流浆箱采用稳流室作为浆料匀整装置,利用淹没射流原理,使流浆箱内的浆流具有均匀的速度剖面。稳流室长度是稳流室的一个非常重要的参数。基于可实现k-ε湍流模型,运用Fluent求解水力式流浆箱稳流室内的流场参数,利用PIV测量技术对数值模拟结果进行验证,测量结果与数值模拟结果吻合良好。利用统计学原理计算出稳流室各横截面上的速度均方差,并以速度均方差值的变化趋势来判断稳流室内浆流速度是否达到均匀,对于不同布浆管束直径d和浆料入射速度v,计算出稳流室内浆流达到均匀分布所要求的长度L,结果表明L值随着布浆管束的直径增加和入射速度的提高而增大,并且二者分别符合一次函数关系。利用二元函数拟合得出L值与d和v之间的关系式,该式可作为水力式流浆箱稳流室的设计参考。     

数值模拟微小三通管支管倾角对环状流相分配的影响

微小三通管内的流量分配及相分配特性对微型工程设备的正常运行至关重要。为了研究微三通管流体分配器的相分配特性,采用了计算流体动力学方法,通过改变三通支管的倾角,对微小三通管道模型进行了数值模拟。分析研究了入口流型为环状流时,微小三通管道中的速度分布规律,气相和液相的体积分数分布规律。结果表明,当支管倾角为90°、120°、150°时,液相优先从侧支管中采出;支管倾角为30°时,气相优先从侧支管中采出;支管倾角为60°时可获得最佳的相均匀分配。通过微通道侧支管结构的改进可减少相分配的不均匀性。     

循环流化床蒸发器中的压降与颗粒分布的研究

为研究汽-液-固三相多管循环流化床蒸发器中的压降和颗粒分布特性,设计并构建了汽-液-固多管循环流化床蒸发系统。利用压力传感器、CCD图像采集和数据处理系统,研究了液体循环流量、热通量、颗粒加入量等参数对于加热管束中压降和颗粒分布的影响。结果表明：随着液体循环流量和颗粒加入量的增加,颗粒分布的不均匀度明显降低,管束压降变大;随着热通量的增大,颗粒分布的不均匀度降低,管束压降呈现波动状态,但管束压降值始终小于加热功率为0时的值。     

管式搅拌反应器中流动特性实验及模型研究

为进一步研究带机械搅拌装置的新型管式反应器内流动特性,采用刺激-响应技术,测定流体在不同操作条件下的停留时间分布(RTD)曲线并与无搅拌停留时间分布曲线作对比,计算了平均停留时间分布的统计特征值。用混合时间表征混合特性,用Peclet操作准数表征轴向扩散特性。结果表明,适当增大转速、流量或降低水位,都有利于反应器内流体的均匀混合。大体上随流量的减少和液位的升高停留时间有延长的趋势,转速变化对停留时间的影响不显著。在搅拌转速不超过400 r/min时,混合时间随着搅拌转速的增大而缩短。在实验范围内,反应器相当于3个串联全混槽反应器。     

烷基化废硫酸处理反应浮选塔进料分布器CFD模拟

新型烷基化废硫酸资源化处理工艺在反应浮选一体化设备内实现了反应过程与除油除杂质过程的耦合。本文应用计算流体力学(CFD)方法对关键设备反应浮选塔内的废硫酸分布器和氨气分布器内部流场进行预测和分析,模拟结果显示,废硫酸分布器结构和分布孔设计基本可以满足宏观全塔截面的流量均布,通过流场模拟,发现局部流量较大的区域,内件设计和操作过程中应强化此类区域的混合与换热;氨气分布器安装曝气头后,各分布支管的流量分布更均匀,分布孔最大流量与最小流量差异小于1%。以上CFD模拟结果为设备结构优化和稳定运行提供了指导意见和理论支撑。     

新型洗涤冷却室内气液两相的分布特性

采用双头电导探针法对新型洗涤冷却室环隙鼓泡床内气液两相的局部气含率、气泡直径等分布规律进行了实验研究,并用Fluent商业软件对床层内气含率分布进行了模拟计算,模拟结果与实验结果吻合较好。研究结果表明：新型洗涤冷却室内部构件对环隙鼓泡床内气液两相的分布特性影响显著,气相分布更加均匀,液面波动更趋平稳,有效地减少了气体带水问题,相比国外技术具有更好的操作弹性。     

气泡雾化喷嘴泡状流出口喷雾脉动特征

采用实验和仿真方法,对一特定气泡雾化喷嘴泡状流时混合室内的气液两相混合形态以及喷孔出口喷雾脉动特征进行了研究。研究结果表明,泡状流时气泡尺寸呈近似正态分布,气泡尺寸随液相质量流量和气液质量比增大而减小;喷雾形态和喷孔出口气液流动参数存在较大脉动,喷雾锥角脉动超过20°;气泡数量密度小且气泡直径较大时,喷雾平均锥角相对较小,且喷雾脉动现象比较严重;随着气泡数量密度增加,喷雾平均锥角呈现先快速增大后缓慢增大趋势,而喷雾锥角变异系数先快速增大随后逐渐减小并趋于稳定;复杂的流场结构是喷孔内气泡表观形态发生较大变化以及喷孔出口气液流动参数产生较大脉动的主要原因。     

Distribution performance of gas-liquid mixture in the shell side of spiral-wound heat exchangers

The non-uniformity of gas-liquid mixture is a critical issue which leads to the heat transfer deterioration of spiralwound heat exchangers (SWHEs). Two-phase mass flow rate and the content of gas are important parameters as well as structural parameters which have prominent influences on flow distribution uniformity of SWHE shell side. In order to investigate the influences of these parameters, an experimental test system was built using water and air as mediums and a novel distributor named "tubes distributor" was designed. The effects of mass flow rate and the content of gas on two-phase distribution performance were analyzed, where the mass flow rate ranged from 28.4 to 171.9 kg·h^-1 and the content of gas changed from 0.2 to 0.8, respectively. The results showed that the mixture mass flow rate considerably influenced the liquid distribution than that of gas phase and the larger mass flow rate exhibited the better distribution uniformity of two-phase flow. It was also found that the tubes distributor had the better two-phase uniformity when the content of gas was around 0.4. Tube diameter played an important role in the distribution of gas phase and slit width was more significant for the uniformity of liquid phase.     

一种新型板翅式换热器气液分配器分配特性的敏感性分析

两相流动分配不均是影响板翅式换热器换热效率的主要因素。传统的"先混合,后分配"方法不能解决在导流翅片中流向突变时气液分离引起的气液两相流体分配不均问题,因此采用"先分配,后混合"的理念提出了一种新型的气液分配器,气体和液体分别从各自的通道进入分配器,在分配器内均匀混合后进入换热器的翅片换热通道进行换热。通过对分配器内部流场的数值模拟,发现:分配器的气液分配不均匀度随流量的增加而增加,且不均匀度受液相流量的影响比气相大。该气液分配器的气液分配不均匀度相比传统封头结构降低了一个数量级,能够有效改善板翅式换热器层间通道的气液分配特性,提高板翅式换热器的换热效率。     

Design of an Efficient Gas Distribution System for a Fluidized Bed Dryer

Fluid bed dryers are commonly used to process granular solids. The design of the gas distributor has a significant impact on the performance of heat and mass transfer with or without chemical reactions in fluidized beds because it affects the quality of the fluidization obtained. In this work, an extensive study was carried out to design an optimal gas distribution system for a fluidized bed dryer. The air distribution chamber, also called a plenum chamber or gas chamber, was modified to obtain uniform air distribution across the bed cross section. Percentage maldistribution of the flow is considered as the basic evaluation parameter to quantify uniformity of the fluidizing gas distribution. Effects of various relevant design parameters such as the ratio of the orifice diameter to plate thickness (d_o/t), percentage free area, superficial gas velocity, etc., were examined experimentally and via modeling. The gas chamber was redesigned by inserting different types of packings in the chamber. In addition, the effect of height-to-diameter ratio (H/D) of the chamber on flow distribution was studied. Chambers of different H/D ratios and different air inlet nozzle diameters at various positions were examined to evaluate their effect on flow uniformity across the distributor. Three-dimensional computational fluid dynamic studies were carried out to evaluate the effects of pertinent parameters on flow uniformity, which has a direct bearing on the quality of fluidization and hence heat and mass transfer rates obtained.     

孔盘式液体分布器内液体流动对布液孔出流均匀性的影响

借助包括双欧拉均相多相流模型、VOF界面追踪方法和SST k-ω湍流模型的CFD模型,对孔盘式液体分布器内的流场对布液孔出流均匀性的影响进行研究。首先以单孔流动时的液体流量为标准值,通过与标准值的偏差来评估布液孔的出流不均。根据偏差的大小,可以衡量分布器内流动对布液孔出流的影响。然后结合孔前流动区概念对模拟结果进行分析,发现布液孔出流不均是由分布器内液体流动不均造成的。最后,提出了通过改变进料管位置来优化盘式液体分布器结构。计算结果表明,改变进料管的位置可以避免大规模不良分布,进而提高液体分布器的性能。     

高气液化下分布器设计对结构化床层气液分布的影响(英文)

Experiments were carried out to investigate the liquid flow distribution at high gas/liquid ratios in a cold model monolith bed of a 0.048 m diameter with 62 cells per cm2.Three types of distributor for the liquid distribu-tion were used to evaluate their distribution performance.Local liquid saturation in individual channels was meas-ured using 16 single-point optical fiber probes mounted inside the channels.The results indicate that 1) The optical fiber probe technique can measure phase distribution in the monolith bed;2) Liquid saturation distribution along the radial direction of the monolith bed is not uniform and the extent of non-uniformity depends on the distributor de-sign and phase velocities;and 3) The tube array distributor provides superior liquid distribution performance over the showerhead and nozzle distributors.     

Design method of flow distribution in nuclear reactor systems

Flow distribution is encountered widely in nuclear reactor systems including distribution of liquid coolant, feedwater or steam sparger, and high energy fluid into condenser of steam turbine. Distributors with parallel ports or openings are common designs which may be very sensitive to variations of structure and dimensions of a manifold and its ports. Non-uniformity of flow distributions causes largely potential malfunction and poor efficiency, even failures. In this paper, a theoretical model was developed for a tapered distributor. Analytical solutions were obtained for evaluation of influence of operating conditions and structures and dimensions of distributor and ports on flow distributions. Structural parameters were identified and hydraulic characteristics were analysed. The orifices, slope and tube protrusion are useful for improvement of the flow distributions. The uniformity of the flow distributions can be improved about 10–60% by fitting orifice rings or tube protrution with a range of the minor loss coefficients: 0.5–3. Finally design criteria were suggested for industrial applications. This provides a simple and easy-to-use tool for design of the flow distribution in nuclear reactors and power boilers.     

Numerical study of the effect of the gas and solids distributors on the uniformity of the radial solids concentration distribution in CFB risers

The non-uniform radial solids distribution usually has a negative effect on the performance of the circulating fluidized bed (CFB) riser since it may greatly decrease the reactor efficiency and controllability. In order to improve the performance of industrial CFB risers, the numerical study of the effects of the gas distributor and solids distributor at the CFB riser inlet on the uniformity of the radial solids distribution was carried out in this study. Two potential approaches to improve the uniformity of radial solids concentration profile were proposed: (1) the use of the center-sparse side-dense air jets arrangement for the gas distributor and (2) the use of the side-covered arrangement for the solids distributor. The Eulerian-Eulerian computational fluid dynamics (CFD) model with kinetic theory of granular flow was adopted to simulate the gas-solids two-phase flow in a CFB riser with FCC particles. The numerical results show that the patterns of the inlet gas distributor and solids distributor have significant effect on the flow structure in both the entrance region and the fully-developed region in the riser. The gas distributor with center-sparse side-dense air jet arrangement improves the uniformity of the radial solids distribution, while the center-dense side-sparse air jet arrangement steepens the non-uniformity of the solids radial profile. The core-annulus structure can be greatly flattened by applying a side-covered solids distributor, while it can be heavily steepened by employing the center-covered solids distributor.     

增强反应注射成型机混合头内流体高压高速对撞过程模拟与分析

以型号为MK?8/12UL?2K的L 形混合头为模型，运用了CFD数值模拟软件对混合头腔内两相物料流体的高压高速对撞进行了模拟分析。通过控制变量法分别探究了流量和黏度对混合结果的影响，同时为了更好地表征玻璃微珠在混合过程中的运动情况，还对整个流场进行了粒子示踪分析。结果表明，增加质量流量会导致混合腔内速度压力的提升，也就是对撞程度变高，对撞的位置会更加偏向于黏度高的物料出口侧；增加黏度会导致混合腔内物料的压力提升速度降低，同时对撞的位置会明显更加偏向于黏度高的物料出口侧，且摩擦力显著增加；粒子停留时间则随质量流量的提高而减短，随物料黏度的提高而增加；通过模拟获得的这些结果为混合头设计及工艺优化工作提供了一定的参考价值。     

固液分布器中主分布器的实验研究

在不同结构形式的主分布器条件下，研究了表观液速对换热管中固含率、下管箱内床层高度、静压降及平均固含率的影响。利用体积容积法测量了换热管束中的固含率、刻度尺测量了下管箱中的床层高度、U形管测量了下管箱的静压降，并运用差压法测量了下管箱中平均固含率。采用不均匀度函数衡量了不同结构条件下管束间固含率的不均匀程度。实验结果表明：在换热管下方增加优化后的主分布器可以均匀分布固液两相；主分布器直径变化时对下管箱内流动特性的影响大于主分布器轴向位置改变时的影响。