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。     

三相流沸腾传热

对三相流沸腾传热进行了理论分析和实验研究，研究了三相流沸腾传热特性，提出了三相流沸腾传热系数的计算方法，实验结果表明，由于固体粒子的存在，强化了沸腾传热，三相流沸腾传热系数是相同条件下汽－液两相流沸腾传热系数的两倍。固体粒子的存在，能有效地防止和清除传热壁面上的污垢。     

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.     

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%。     

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     

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.     

垂直管内降膜沸腾传热的研究

本文提出了降膜沸腾传热的物理模型和数学模型,全面考虑了对流流动与核式沸腾对膜传热系数的影响,以及液体流动对液膜内核式沸腾的抑制作用。该模型计算值与实验值吻合较好。     

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。     

垂直管内高粘假塑性流体流沸腾传热

用高粘流体了垂直管内流动沸腾传热实验研究，建立了流动沸腾传热给热系数关联式。     

三相流化床传热模型与计算式分析

为了增强对汽(气)-液-固三相流传热过程的基础理解,并为理论研究和工业应用提供有价值的信息,对三相流化床传热模型与计算式进行分析和比较。结果表明,在各种传热计算式和机理模型中,无因次准数关联式的预测精确度最高;建立反映传热机理的模型与计算式,开展多相流非线性研究和传热数值模拟是未来的研究方向。     

竖直管气固鼓泡流化床传热机理的CPFD模拟

针对细颗粒气固鼓泡流化床中床料与竖直传热管壁面间的传热行为,在前期实验的基础上,采用计算颗粒流体力学(CPFD)方法从颗粒在传热壁面更新的角度,深入分析了传热特性与壁面气固流动行为之间的关联性。结果表明,模拟得到的传热管壁面颗粒更新通量和基于颗粒团更新模型的颗粒团平均停留时间均能很好解释实验测得的传热系数变化规律,这证实颗粒团更新是影响传热过程的控制性因素。模拟还发现随加热管从床层中心向边壁的移动,加热管周向方向上颗粒更新通量和传热系数的不均匀性都呈增大趋势。随着表观气速的增大,气泡行为导致床层颗粒内循环流率增大,这是导致颗粒团在加热管壁面上的更新频率增大以及床层与壁面间传热系数增大的根源。     

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。     

振动流化床中大颗粒与水平管局部传热特性

在二维振动流化床中,以平均粒径1.83 mm的玻璃珠为物料,研究了大颗粒与水平管间局部传热规律;考察了气速、振动频率等因素对局部传热系数的影响,同时与小米和小玻璃珠实验结果进行对比。结果表明:大颗粒与小颗粒局部传热系数有很大差异;对于大颗粒,低速下局部传热系数随振动频率的增大先增加后减小,高速下局部传热系数随着振动频率的增加而降低;一定振动频率下,气速小时局部传热系数在60°左右达到最大,气速逐渐增加后,其最大值向90°转移。通过实验数据得到了计算大颗粒与水平管局部传热系数的关联式,计算值与实验值吻合较好,误差在±20%范围内。结果可为带浸没水平管的振动流化床设计和研究提供参考。     

Studies of the evaporation and scaling mitigation in a recirculating three-phase fluidized bed

Heat transfer of liquid evaporation was studied in a recirculating three-phase fluidized bedin which an inert gas serving as"carrying gas"was introduced.The gas velocities,particle sizes,par-ticle densities and particle concentrations in the liquid were examined.Heat fluxes were measured aswell.Significant enhancement in heat transfer was resulted when an inert gas and solid particles wereintroduced into the flow boiling liquid.Scaling mitigation was to be expected in the process.     

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.     

气固流化床外取热器内流动和换热特性分析

外取热器是维持催化裂化反应-再生系统热平衡和保持装置平稳运行的关键设备之一。外取热器的优化设计和合理调控,要求深入理解外取热器内的流动特性、换热特性及两者之间关系。在一套大型冷模热态实验装置上,分别考察了表观气速、颗粒质量流率对换热管附近的局部固含率和气泡频率、床层与换热管间传热系数的影响。结果表明:增加表观气速可以降低局部固含率、增加局部气泡频率、强化床层与换热管间换热;随着颗粒质量流率增加,局部固含率和局部气泡频率均增加;在较低表观气速下,增加颗粒质量流率不利于换热,而在较高表观气速下,传热系数随颗粒质量流率逐渐增加。不同流型下,气固流动特性对换热特性的影响不同。在鼓泡床流型下,过高的局部固含率不利于颗粒在换热表面的更新,增加换热管附近的局部气泡频率可以明显强化换热;而在湍流床流型下,换热管附近的局部固含率和气泡频率的增加,均使传热系数逐渐增大。建立了针对不同流型的换热经验关联式,预测值与实验值的平均相对偏差分别为6.9%和1.3%。     

Systematic study on heat transfer and surface hydrodynamics of a vertical heat tube in a fluidized bed of FCC particles

Bed‐to‐wall heat transfer properties of a vertical heat tube in a fluidized bed of fine fluid catalytic cracking (FCC) particles are measured systematically using a specially designed heat tube. Two important surface hydrodynamic parameters, i.e. the packet fraction (δ_pa) and mean packet residence time (τ_pa) based on the packet renewal theory, are determined by an optical fiber probe and a data processing method. The experimental results successfully reveal the axial and radial profiles of heat‐transfer coefficient, the effects of superficial gas velocity, and static bed height on heat‐transfer coefficient, most of which can be explained successfully by the measured τ_pa, an indicator of packet renewal frequency. τ_pa is found to play a more dominant role than δ_pa on bed‐to‐wall heat transfer. With a fitted correction factor, the modified Mickley and Fairbanks model is able to predict the heat‐transfer coefficients with enough accuracy based on the determined packet parameters. © 2014 American Institute of Chemical Engineers AIChE J, 61: 68–83, 2015     

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 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.