水平液固循环流化床换热器传热性能评价

对管内插入Kenics静态混合器的水平液固循环流化床换热器进行实验研究,实验考察了静态混合器扭率、静态混合器安装方式、液体流速、颗粒体积分数对传热性能和流阻性能的影响,并运用综合强化传热性能评价指标（PEC）对其进行分析。实验发现,传热性能和阻力系数均随扭率增加而减小。当雷诺数在10000~45000之间时,扭率为1.5、2、2.5、3.5的Kenics静态混合器的PEC指标均大于1,说明了水平流化床换热器插入Kenics静态混合器能够改善传热。在雷诺数达到25000左右、Kenics静态混合器扭率为2.5、颗粒体积分数为4%时,水平流化床换热器的PEC指标最高达到1.18。当两个扭率均为2.5的Kenics静态混合器安装间距为200mm时,水平流化床换热器的PEC指标最高。     

Kenics静态混合器在水平液固循环流化床中的研究

为了解决水平液固循环流化床中颗粒分布不均匀问题,在内径29 mm、长4 m的水平有机玻璃管流化床内放入Kenics静态混合器,采用CCD图像测量与数据处理系统考察静态混合器的结构、个数、安装位置对液固二相流中颗粒分布的影响;同时,利用U型管压差计考察不同条件下静态混合器的压降。实验结果表明:Kenics静态混合器能明显地改善管内颗粒分布情况;单个扭率Y=3.5的Kenics静态混合器压降最小;2个扭率Y=3.5的Kenics静态混合器间距为40 mm时对颗粒分布影响长度是最长的。     

Kenics static mixer in liquid-solid horizontal circulating fluidized bed

为了解决水平液固循环流化床中颗粒分布不均匀问题,在内径29mm、长4m的水平有机玻璃管流化床内放入Kenics静态混合器,采用CCD图像测量与数据处理系统考察静态混合器的结构、个数、安装位置对液固二相流中颗粒分布的影响；同时,利用U型管压差计考察不同条件下静态混合器的压降.实验结果表明:Kenics静态混合器能明显地改善管内颗粒分布情况；单个扭率Y=3.5的Kenics静态混合器压降最小；2个扭率Y=3.5的Kenics静态混合器间距为40mm时对颗粒分布影响长度是最长的.     

水平液固循环流化床换热器传热性能研究

通过对管内插入Kenics静态混合器的水平液固循环流化床换热器进行数值模拟和实验研究,考察了静态混合器扭率对颗粒分布、传热性能和流阻性能的影响。结果表明:水平管内安装Kenics静态混合器的扭率越小,管内颗粒分布均匀距离越长。当雷诺数在10 000—45 000之间,扭率为1.5,2.5,4,6的Kenics静态混合器的综合性能评价指标PEC均大于1,说明了水平流化床换热器插入Kenics静态混合器能够改善传热。当流速大于1.5 m/s,在2 m长的水平流化床换热器内安装一个扭率为1.5的Kenics静态混合器能够达到改善颗粒分布和提高传热性能的效果。     

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。     

混合颗粒在内置水平管振动流化床中流体力学研究

在内置水平管的二维振动流化床中研究了玉米粒与塑料珠颗粒混合物的流化特性,考察了颗粒质量分数、振动频率、振幅、内置水平管和振动强度对床层压降及临界流化压降的影响。实验结果表明,在混合颗粒的振动流化床中,固定床阶段,相同条件下床层压降随着玉米粒质量分数的增大而增大,流化床阶段随玉米粒质量分数增大而减小;内置管的引入增大了床层压降;振动的引入增大了固体床阶段的床层压降,降低了流化床阶段的临界流化压降;振动对大粒径的影响小于小粒径;由实验数据拟合出的用于预测带内置水平管的混合颗粒振动流化床临界流化压降的经验公式,经验公式与实验数据基本吻合。     

竖直上升管中密相气力输送压降特性

研究了内径20 mm的竖直上升不锈钢管道中粉煤密相气力输送单位管长压降随输送参数的变化规律,并得到了Zenz相图。结果表明,在实验操作范围内管道压降主要由固相自身静压降和固相摩擦压降组成,气相产生的压降不超过总压降的1%;固相体积分数是影响压降变化的主要因素,并讨论了粉煤流速以及固相体积分数对固相静压降和摩擦压降的影响规律;考察了粉煤流速和固相体积分数对固相摩擦系数的影响,对实验数据拟合得到了固相摩擦系数的关系式,计算结果与实验值吻合较好。     

分布板开孔率对气固流化床流动特性的影响

在内径0.14 m,高1.6 m的气固流化床中,以空气和流化催化裂化颗粒为气相和固相,采用PV-6A型光纤测速仪和U形管压差计分别测定三种不同开孔率分布板时的颗粒浓度分布和分布板压降,同时应用流体力学软件Fluent 6.2分别对三种不同开孔率分布板压降,径向固含率分布进行了模拟计算,模拟结果与实验值吻合较好.研究结果显示,分布板压降随开孔率的增大而减小,分布板开孔率大于0.86%后对压降影响较小;径向固含率波动随开孔率的增大而增大,开孔率0.46%的分布板径向固含率分布曲线波动最小,气固分布最均匀.     

组合约束型提升管出口气固分布器的压降

在一套组合约束型提升管冷态实验装置上,通过实验研究了不同操作条件下提升管出口气固分布器的压降,并与常规气体分布器压降进行了对比。实验结果表明,在零床层及有床层的操作模式下,气固分布器压降均随提升管内表观气速和颗粒循环强度的增加而增大,在颗粒循环强度较低时,气固分布器压降曲线变化的斜率随着表观气速的增加而增大,在颗粒循环强度较高时,气固分布器压降曲线变化的斜率随着表观气速的增加而减小;随着开孔率及上部流化床层压降增加,气固分布器压降呈降低趋势,当流化床层压降达到一定程度后,分布器各孔方可实现有效布气,此后气固分布器压降趋于近似不变;在相同表观气速及开孔率下,气固分布器压降大于常规气体分布器压降。     

组合约束型提升管出口气固分布器的压降

在一套组合约束型提升管冷态实验装置上,通过实验研究了不同操作条件下提升管出口气固分布器的压降,并与常规气体分布器压降进行了对比。实验结果表明,在零床层及有床层的操作模式下,气固分布器压降均随提升管内表观气速和颗粒循环强度的增加而增大,在颗粒循环强度较低时,气固分布器压降曲线变化的斜率随着表观气速的增加而增大,在颗粒循环强度较高时,气固分布器压降曲线变化的斜率随着表观气速的增加而减小;随着开孔率及上部流化床层压降增加,气固分布器压降呈降低趋势,当流化床层压降达到一定程度后,分布器各孔方可实现有效布气,此后气固分布器压降趋于近似不变;在相同表观气速及开孔率下,气固分布器压降大于常规气体分布器压降。     

SMV静态混合器内气液两相流压降的研究

以气-液两相流动的均相流模型为前提,运用流体力学计算软件对SMV静态混合器中的气液两相流的压力场进行模拟计算,分析其压降的规律,并与水平直圆管内压降和混合器内单液相流压降做了对比分析.结果表明:气液两相流流经SMV混合器的沿程压降及局部压降均随着雷诺数的增大呈现明显增大趋势,且管路总压降与元件数成正比;静态混合器两相流...     

KENICS型静态混合器结构参数的改变对单相流的阻力和传热的影响

文中对八种规格的Kenies型静态混合器进行了立式装置内的空气阻力和传热对比试验,得到了Re=2300—20000范围内的f～Re和Nu～Re关联式;分析了机理;评价了性能;认为适当增加它的标准型元件的扭率和扭角以及使元件之间有一定的间距,可显著降低流动阻力损失,而仍能基本保持标准到的较高的强化传热效果.     

Kenics静态混合器的应用及研究进展

介绍了Kenics静态混合器的混合机理及其在流体混合和强化传热等操作过程中的应用,重点介绍了Kenics静态混合器的压力降计算方法以及拉伸混合和无序混合等方面的研究进展。     

流化床液固两相传质过程的模拟研究进展

液固两相流化床具有液固相接触效率高、传质和传热性能好、颗粒分布均匀等优点，已被广泛应用于众多工业过程中。然而，流化床中与传质过程耦合的颗粒流化的复杂非线性特征及其湍动特性，使得对传质过程特性的研究十分困难。且仅依靠实验观测和理论预测难以揭示多相流相互作用规律，无法获得全面和详细的速度场和浓度场分布情况。近年来，数值模拟的快速发展为深入探索流化床中液固两相流动行为及其与传质过程耦合问题提供了重要的途径。本文对流化床液固两相流动与传质过程模拟方法进行了综述，并对其未来研究趋势进行了展望。借助于计算传质学理论可以更精确地预测局部浓度的分布情况，进而可以深入分析液固两相流化床中的传质过程规律与传质特性，为液固两相流化床的设计和优化提供理论基础。     

LAMINAR FLOW HEAT TRANSFER WITH INLINE MIXERS INSERTS

Heat transfer coefficients were measured for heat transfer to a Newtonian fluid flowing in laminar flow through a tube with inline mixer inserts. Kenics “Static” mixer and Ross LPD mixer inserts were studied as heat transfer augmentation devices. The mixer inserts were in the inner tube of a concentric tube heat exchanger. Steam was condensed in the annulus of the exchanger. Significant heat transfer enhancement was obtained with both inserts at the expense of even greater pressure drop increases. The use of the Ross mixer insert gave greater augmentation than did the use of the kenics insert. An analysis using the analogy between momentum and heat transfer allowed the prediction of heat transfer coefficients from pressure drop measurements. The predicted coefficients were in good agreement with experimentally measured heat transfer coefficients for laminar flow.     

LAMINAR FLOW HEAT TRANSFER WITH INLINE MIXERS INSERTS

Heat transfer coefficients were measured for heat transfer to a Newtonian fluid flowing in laminar flow through a tube with inline mixer inserts. Kenics “Static” mixer and Ross LPD mixer inserts were studied as heat transfer augmentation devices. The mixer inserts were in the inner tube of a concentric tube heat exchanger. Steam was condensed in the annulus of the exchanger. Significant heat transfer enhancement was obtained with both inserts at the expense of even greater pressure drop increases. The use of the Ross mixer insert gave greater augmentation than did the use of the kenics insert. An analysis using the analogy between momentum and heat transfer allowed the prediction of heat transfer coefficients from pressure drop measurements. The predicted coefficients were in good agreement with experimentally measured heat transfer coefficients for laminar flow.     

Heat transfer between very shallow fluidized beds and an immersed horizontal tube

A new correlation is proposed for the heat transfer coefficient between an immersed horizontal tube and very shallow fluidized beds (static bed heights of 10-40 mm). The correlation is based upon experimental data obtained in this work for a horizontal tube with an outside diameter of 13.1 mm, immersed in beds of spherical alumina particles with mean particle sizes of 335-1261 microns. The maximum bed pressure drop was 92.5 mm water. The effects of tube elevation, static bed height and distributor design were investigated. Nine different distributors were used, with maximum pressure drops ranging from 3 to 800 mm water and open areas from 2.2 to 36%. A comparison between the proposed correlation and data reported in the literature showed an agreement of approximately ±10%.     

Performance of Kenics static mixer over a wide range of Reynolds number

The present study deals with the numerical simulation of flow patterns and mixing behaviour in Kenics static mixer over a wide range of Reynolds number. Three different sets of Kenics mixer (aspect ratio = 1.5) comprised of 3, 9 and 25 elements each have been characterized. The Reynolds number was varied in the range of 1 to 25,000 (i.e., from laminar to turbulent flow regime). The numerical approach takes into account the aspects of the fluid flow at higher Reynolds number values including circumferential velocity profiles at different cross-sections within the Kenics mixer, which were neglected in previous studies. It was observed that cross-sectional mixing in the turbulent flow regime takes place up to 30% of each element length at element-to-element transition; beyond that velocity profiles were uniform. The experiments were also carried out to measure the circumferential and axial velocity profiles and pressure drop in three different Kenics Mixers using air as fluid. The pressure drop per unit element (ΔP/η) was found to be independent of the number of Kenics mixing elements used in the system. The total pressure drop across Kenics mixer obtained by CFD simulations were compared with the experimental pressure drop values and correlations available in the literature. The numerical results were found in good agreement with the experimental as well as the results reported in the literature. A new pressure drop correlation in the Kenics static mixer has been developed.