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。     

汽液固三相流动沸腾传热计算与实验研究

对汽液固三相循环流化床中流动沸腾传热进行了理论分析和实验研究 ,在此基础上结合渐进模型及表面更新机理建立了汽液固三相流动沸腾传热模型 ,模型计算值和实验数据吻合较好 ,最大偏差在 18%以内     

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.     

加入惰性固体粒子的二元物系的流动沸腾传热特性

引　言流动沸腾传热广泛存在于石油、化工、轻工、动力及能源等各个领域 ,但三相流动沸腾传热的研究极少 .李修伦等[1]在流动沸腾系统中加入惰性固体粒子 ,进行了汽 -液 -固三相流沸腾传热的初步研究 .李修伦、闻建平[2 ,3]进一步将三相流和沸腾换热相结合 ,较好地解决了沸腾传热强化和防垢、除垢问题 .李修伦、张利斌等[4 ]又采用循环流化床技术 ,结合粒子在沸腾系统中的强化特性 ,开发了汽 -液 -固三相循环流化床蒸发器 ,它具有良好的强化传热和防、除垢性能 .上述研究均属于单组分三相流动沸腾传热 ,而关于二元物系三相流动沸腾传热的研…     

循环流化床内颗粒运动与换热分析

对循环流化床锅炉床体内部贴近壁面的颗粒团运动和受力特点进行了分析,探讨颗粒团沿壁面下滑贴壁时间的计算方法,由此发展了床体内部颗粒-气体对流换热传热系数的理论计算模型和方法.与现有文献的实验数据资料比较表明,计算的结果较好地反映了实际情况.     

气液固三相循环流化床气液传质行为

<正>气液固三相流化床反应器在石油化工、湿法冶金、环境工程和煤的液化等工业领域得到了广泛应用,其基础研究也取得了很大进展.但是,传统三相床主要应用于低液速(U_L<     

汽液固三相流化床沸腾传热的研究

对垂直管内汽液固三相流化床沸腾传热特性进行了实验研究和理论分析,建立了沸腾传热的计算方法.实验结果表明,由于固体粒子的存在,强化了沸腾传热.传热系数比汽液两相流提高2倍左右.沸腾过程的稳定性明显提高.     

喷液流化床中传热特性

引言流化床反应器由于其特有的众多优点,尤其是传热效果好、床层温度均匀,而在工业上得到广泛的应用．然而随着工业的发展,生产能力的提高,对流化床的换热能力提出了更高的要求．于是出现了许多强化流化床传热的方法,例如乙烯氧氯化反应中的内置换热管法;乙炔制醋酸乙烯中的外加夹套法;催化裂化反应中的粒子循环法．在80年代初期出现了一种流化床带液操作的新方法,它在气相法聚乙烯生产中的应用（其操作工艺被简称为冷凝工艺）具有远大的前景．该工艺是在一般的气相法聚乙烯流化床反应工艺的基础上,在流程中添加易挥发的液体,使反…     

并流下行循环流化床反应器气固传质模型

建立了并流下行循环流化床反应器气固吸附传质模型,并采用稳态示踪的实验研究方法,测定了下行床中气相示踪剂浓度的轴向分布,进而利用Marquardt多元非线性回归方法求得了模型参数即轴向扩散系数和传质系数的值.实验结果的回归得到了模型参数与操作条件的经验关联式.该模型能很好的预计传质过程,包括轴向扩散系数和传质扩散系数的值以反应器中组分浓度的轴向分布,因此可用于描述并流下行循环流化床反应器的气固吸附传质过程.     

EFFECT OF OPERATING VARIABLES ON BED TO WALL HEAT TRANSFER IN A CIRCULATING FLUIDIZED BED

Heat transfer coefficients were measured for 227 and 87 micron size particles of silica sand in a 102 mm dia. and 5.5 m tall circulating fluidized bed made of plexiglass. Effects of solid circulation rate, fluidization velocity, bed density and particle sizes were studied. The heat transfer coefficients were calculated from the temperatures measured along the axis of a 25 mm dia 100 mm long cylindrical heat flux meter.     

HEAT TRANSFER IN THREE-PHASE FLUIDIZED BEDS WITH NON-NEWTONIAN PSEUDOPLASTIC SOLUTIONS

Heat transfer experiments have been conducted in three-phase fluidized beds (TPFB) of 3 and 5 mm glass spheres. To assess the effect of non-Newtonian flow behavior, concentrated pseudoplastic xanthan solutions were employed. The gas and liquid superficial velocities range from 0.81 to 14.4 cm/s and 1.27 to 9.0 cm/s respectively. The impact of these parameters as well as the effect of the effective liquid viscosity, and the solid size on heat transfer in TPFB are discussed. All heat transfer coefficients can be discribed satisfactorily by a new correlation which predicts the Nu-values in TPFB with pseudoplastic solutions with ±9.13% average standard deviation.     

循环床非流化回料管内竖管传热的强化

非流化移动床内颗粒的流动为柱塞流，颗粒间无相对运动，竖管传热主要靠颗粒间导热。由于导热热阻大，在管壁周围的颗粒吸热后不易传出，而在其周围形成一个热边界层，阻止了传热。利用在竖管上加上的扰流圈，使近壁处颗粒发生扰动，而使热颗粒传出，冷颗粒得以进入管壁周围，从而起到强化传热的作用。强化后的平均传热系数可增加２０％左右。平均传热系数值可达２２０Ｗ／（ｍ￣２·Ｋ）。     

AN EXPERIMENTAL STUDY OF LIQUID-PARTICLE FLOW IN CIRCULATING FLUIDIZED BED

A liquid-solid circulating fluidized bed (LSCFB) is operated at high liquid velocity, where particle entrainment is highly significant and between the conventional liquid fluidized bed and the dilute phase liquid transport regimes. LSCFB has potential applications in the fields of food processing, biochemical processing, and petrochemical and metallurgical processing. It is well known that the flow characteristics in a liquid-solid circulating fluidized bed are different from those of a conventional liquid-solid fluidized bed. The limited studies available in literature do not provide complete understanding of the flow structure in this typical regime.

In the present work, experiments were carried out in a 0.0762 m ID and 3 m height laboratory-scale liquid-solid circulating fluidized bed apparatus by using various solid particles and tap water as fluidizing medium. In the experimental setup, two distributors (specially designed) were used to monitor solid circulation rate in the riser. The effects of operating parameters, i.e., primary liquid flow rate in the riser (Up), solid circulation rate (G_s), and particle diameter (dp), were analyzed from the experimental data. Finally, a correlation was developed from the experimental data to estimate average solid holdup in the riser, and it was compared with present experimental and available data in the literature. They agree well with a maximum root-mean-square deviation of 7.83%.     

ＣＦＢ稀相段直长对颗粒内循环流动规律的影响

采用光纤探头测定Ｄ１m射流循环流化床（半圆形）稀相区颗粒速度、颗粒浓度和颗粒流通量的径向分布规律,并考察了操作条件及其轴向的影响,实验结果表明,在循环流化床（ＣＦＢ）中,颗粒流动在床层径向有较大的不均匀性,并呈明显的内循环流动结构,进而考察了影响其流动规律的,以期进一步理解循环流化床颗料流动机理,强化和改善反应器的设计操作。     

三相循环流化床蒸发器防除垢机理

引　言结垢是蒸发器加热壁面上经常遇到的问题 .垢层严重地降低了换热效率 ,使传热过程迅速恶化 ,蒸发器的防、除垢问题受到人们的普遍重视 .张利斌、李修伦等[1] 研究了汽液固三相循环流化床蒸发器沸腾传热和防、除垢性能 ,本文进一步考察该蒸发器的防、除垢机理 ,并对其进行了分析 .1　汽液固三相流剪应力“混相流”模型根据文献 [1],蒸发管内的汽液固三相流动呈现“混相流”的特性 ,因此为便于分析及突出问题的基本特征 ,假设 :(1)温度场引起的物性变化忽略不计 ;(2 )蒸发管内的汽液两相流动视为均相流动 ,蒸汽的惟一效果是改变了“流体…     

脱硅中液固循环流化床清洁传热

考察了铝土矿熟料溶出粗液脱硅加热过程中的结垢行为,采用有机-无机复合材质的惰性固体颗粒研究了循环流化床对脱硅加热过程中硅渣结垢的清除及防止性能.结果表明：硅渣结垢曲线为具有诱导期的渐近式曲线,硅渣结垢机理为结晶结垢和微颗粒沉积结垢混合机理;循环流化床不仅能有效防止硅渣结垢的形成,而且能完全清除已有的硅渣垢层,硅渣结垢的清除速率随操作流速及固体颗粒浓度的增大而增大;惰性固体颗粒的引入不影响硅渣结垢的机理.根据液固流化床的防垢机理建立了结垢模型,其预报值与实验值吻合较好.     

流化床反应器气固传热面积模型

研究了流化床反应器内发生气固反应时间的传热机理,认为气固间的传热面积包括两部分,即气泡内所含颗粒的表面积与一气泡和泡晕间的有效传热面积 ,据此首次导出了气固传热面积模型A＝u0-umf/22.26db0.5-umf[4.5unf ρgCpg/db 5.85(λgρgCpg)0.5g^0.25/db^1.25]LmS/a将该模型 应用于半间歇的裂化催化剂烧炭再生过程,与实验数据的比较表明,模型预测是可靠的。     

离心流化床中强制对流换热的实验研究

对离心流化床干燥器中气体与被干燥颗粒物料之间的强制对流换热进行了实验研究,获得了各主要运行参数对气固换热系数的影响规律,并利用场协同原理分析了对流换热强化的机理. 实验证明,在一定转速范围内,在气流速度方向和热流方向（温度梯度方向）一致时,换热的准则关联式具有Nu＝CRePr的形式. 获得了满足Nu～RePr呈直线关系的Pe(Pe=RePr)数变化范围和临界Pe数,当Pe数大于临界值后,离心流化床中对流换热强度随Pe数增加而增大的趋势会明显减缓并偏离线性区.     

HYDRODYNAMICS AND HEAT TRANSFER OF LIQUID FLUIDIZED BED SYSTEMS

After some genera] remarks about liquid/solid fluidization, various aspects of liquid fluidization hydrodynamics and heat transfer have been analyzed on a coherent basis. For each of these cases, the state-of-the-art has been reported, together with some indication of areas that deserve further attention. Major emphasis is placed on the hydrodynamic behavior of fluidized beds, heat transfer mechanisms from surface-to-bed and on the effect of various parameters on the type of fluidization and heat transfer coefficient. This review covers the various correlations developed over the years for the prediction of bed voidage, heat transfer coefficient and optimum conditions of liquid/solid fluidized beds.     

INVESTIGATION ON THE INCIPIENT FLUIDIZATION AND HEAT TRANSFER IN A CENTRIFUGAL FLUIDIZED BED DRYER

Abstract

Based on the continuum theory, a physical model of gas-solid two phase flow in a centrifugal fluidized bed has been proposed. A set of governing equations to describe the fluidization state are obtained and solved numerically after some simplifying. The quantitative experimental study on the characteristics of the incipient fluidization in the centrifugal fluidized bed is performed to examine the proposed model. Gas-solid two phase heat transfer in CFB during a drying process is also conducted. The influences of bed thickness, particle diameter, physical properties of particle, rotating speed of the bed and the gas superficial velocity on heat transfer characteristics are examined. A correlation that can be used to calculate the heat transfer coefficients in the drying process in CFB is obtained.