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     

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。     

垂直管内三相流化床沸腾传热特性

研究了三相流化床沸腾传热的特性和影响传热系数的诸因素。在传热过程中，由于固体粒子的存在，强化了传热。以玻璃球粒子为固相的三相流化床沸腾传热系数，是相同条件下汽液两相流沸腾传热的二倍。以铜粒子为固相的三相流化床沸腾传热系数，是相同条件下汽液两相流沸腾传热系数的３倍。     

气液固三相流动沸腾传热与抗垢性能的研究

在流动沸腾的液体中引入少量惰性气体与固体颗粒,使之成为气液固三相流态化沸腾过程,对其传热性能与抗垢性能进行实验研究。结果表明,引入惰气与流态化固体颗粒,可使传热显著强化,表现出明显的防垢抗垢效果,且具有一定的线清洗作用。     

三相循环流化床蒸发器强化传热的研究

采用汽-液-固三相循环流化床新型蒸发器蒸发麦草浆黑液,讨论了热通量、流速和粒子体积分数对三相流沸腾传热系数的影响。试验表明,三相流沸腾传热系数随热通量、黑液流速和粒子体积分数的增加而增大。且对黑液这种高粘度流体使用该蒸发器,其三相流沸腾传热系数比汽液两相流沸腾传热系数提高约20%～30%。     

循环流化床的沸腾传热

A model is proposed to predict boiling heat transfer coefficient in a three-phase circulating fluidized bed (CFB), which is a new type of evaporation boiling means for enhancing heat transfer and preventing fouling. To verify the model, experiments are conducted in a stainless steel column with 39 mm ID and 2.0 m height, in which the heat transfer coefficient is measured for different superficial velocities, steam pressures, particle concentrations and materials of particle. As the steam pressure and particle concentrations increase, the heat transfer coefficient in the bed increases. The heat transfer coefficient increases with the liquid velocity but it exhibits a local minimum.The heat transfer coefficient is correlated with cluster renewed model and two-mechanism method. The prediction of the model is in good agreement with experimental data.     

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。     

气液固三相流化床流区及其过渡的混沌分析

运用确定性混沌分析技术、研究了气液固三相流化床内压力波动时间序列的混沌动力学行为,结果表明,非线性特征量最大Ｌｙａｐｕｎｏｖ指数可以用来定量表征三相流化床的流区及其过渡。并给出了以最大Ｌｙａｐｕｎｏｖ指数为基准的三相流区图,混沌分析还发现,三相流化床内存在着两混沌特性相差较大的塞状泡流区。     

汽液固三相循环流化床蒸发器强化传热和防垢研究

本文在已开发的汽液固三相循环流化床蒸发器装置上进行了条件试验研究。试验表明,这种新型的蒸发器具有明显的强化传热和防垢效果,其传热系数比汽液两相流沸腾传热膜系数提高１．５倍￣２．０倍,并能有效防止污垢的产生。文中对强化传热和防垢的机理进行了探讨。     

气(汽)-液-固三相流研究进展

纵观气 -液 -固三相流研究进展 ,大体上出现了三种趋势 :(1 )为实际应用而开发新型的三相循环流化床 ;(2 )对床内的汽泡行为和粒子行为进行基础研究 ;(3 )以计算流体力学和气液、气固以及固固相间流体力学理论为基础 ,依靠计算机模拟来进行设计优化和放大服务     

Heat transfer and bubble dynamics in a three-phase inverse fluidized bed

In this study, surface-to-bed heat transfer experiments were performed to gain insight on heat transfer and hydrodynamics in a three-phase inverse fluidized bed. Air, tap water or 0.5 wt.% aqueous ethanol, and polypropylene were, respectively, the gas, liquid and solid phases. The solid loading was varied from 0 to 30 vol.%, and the gas and liquid superficial velocities from 2 to 50 mm/s and 0 to 21 mm/s, respectively. Visual observations were associated with measured phase holdups and instantaneous heat transfer coefficients. Larger gas velocities lead to an increase in bubble size due to the transition to the coalesced bubble flow regime. The greater turbulence induced by the larger bubbles increases the average heat transfer coefficient. On the other hand, adding ethanol reduces the heat transfer coefficient. Solid concentrations up to ∼13 vol.% increase the average heat transfer coefficient whereas higher solid concentrations tend to lower it. The distribution of instantaneous heat transfer coefficient peak height is wider at higher gas and liquid velocities while the addition of a surfactant narrows it. Gas holdups and average heat transfer coefficients are both compared with existing correlations, which are then adjusted for a better fit.     

三相循环流化床内流化固体颗粒的防除垢机理

汽液固三相循环流化床蒸发器已应用到盐化、烧碱、中药和造纸等工业中,表现出良好的防除垢性能。文中研究了这种新型流化床蒸发器的防、除垢机理。首先揭示出汽液固三相流剪应力对延长污垢的诱导期起主要作用,并对汽液固三相流剪应力和三相流剪应力增长率进行了定量计算,分析其影响因素。其次从污垢附着和剥蚀的角度,考察了固体颗粒的除垢作用。根据理论分析指出三相流剪应力对污垢附着需要的时间和污垢剥蚀比率的影响,从而计算了剥蚀比例和剥蚀速率及其影响因素。     

Liquid-Solid mass transfer in a slurry bubble column and a gas-liquid-solid three-phase fluidized bed

Mass transfer coefficients between particles and liquids in a slurry bubble column and a three-phase fluidized bed containing small size particles were obtained with two mass transfer systems: (1) K⁺ –Na⁺ ion-exchange in cation-exchange resin bead beds, including anion-exchange resin beads as inert particles; (2) zinc dissolution by HCl in zinc-plated glass bead beds, and in beds of non-plated glass beads. Operating parameters were gas velocity, liquid velocity, particle diameter, and particle concentration. The dependence of mass transfer coefficients on these parameters is discussed from the viewpoint of the energy supplied into the systems. Correlations of the experimental data using dimensionless groups are compared to previous correlations.     

纳米级颗粒气液固三相流化床性能研究

文中评述了国内外有关纳米级颗粒气液固三相流化床性能研究的现状及进展,建议从应用小波分析技术、开发先进测试技术、采用计算机实验、三相流直接数值模拟技术等方面深化和拓展纳米级颗粒气液固三相流化床性能的实验与理论研究。     

振动流化床浸没水平管传热特性研究

为了深入研究振动流化床浸没水平管的传热特性,分别以沙子和玉米细颗粒作为实验物料,用水平探头测定了振动流化床中这2种床层颗粒与浸没水平管间的传热系数,分析了操作气速、振动频率、空气进口温度等因素对传热过程的影响。结果表明:在低气速下,振动是影响振动流化床中传热的主要因素,振动的引入可以明显改善流化作用,可以在低气速下得到较好的传热效果,同时达到节能的效果。通过分析实验结果,建立了振动流化床的传热关联式,模型计算值与实测值能较好吻合。研究结果可为干燥膏状物料时确定适宜的操作参数提供参考。     

Heat transfer between an isolated bubble and the dense phase in a fluidized bed

Heat transfer between the bubble and dense phases of a bubbling fluidized bed plays a very important role in the system performance, especially for applications involving solids drying and gas‐phase combustion. However, very few experimental data are available on this subject in the literature. An experimental and modelling investigation on the heat transfer behaviour of isolated bubbles injected into an incipiently fluidized bed is reported in this paper. A new single‐thermocouple technique was developed to measure the heat transfer coefficient. The effects of bed particle type and size, and bubble size on the heat transfer coefficient were examined. The heat transfer coefficient was found to exhibit a maximum as the bubble size increased in the bubble size range investigated. The bed particle size had a comparatively small effect on the heat transfer coefficient. A simple mathematical model was developed which provides good agreement with experimental data.     

Wall-to-bed heat transfer in three-phase fluidized beds of low density particles

Bed-to-wall heat transfer was measured in three-phase fluidized beds under conditions typical of biochemical process applications. The thermal resistance of the fluidized bed, which was significant in the absence of gas, became negligible when gas was introduced. Decreasing the particle density at constant gas and liquid velocity increased the bed-to-wall heat transfer coefficient. Previously published heat transfer correlations were used and gave poor predictions of our data. A new correlation was developed which predicted very well all the heat transfer coefficient results in this paper.     

Heat transfer mechanism due to particle convection in circulating fluidized bed

The nature of heat transfer in circulating fluidized beds (CFBs) by particle convection was revealed from the experimental results of the particle flux in the lateral direction. As particles contact and rebound from the heat transfer surface because of their lateral motion, they establish a large local temperature gradient. Heat from particles is then transferred primarily through the gas to the heat transfer surface. The data of the lateral particle flux provide a basis to establish a model of heat transfer in CFBs.