A CORRELLATION FOR CYLINDER-TO-BED HEAT TRANSFER IN AERATED VIBRATED BEDS OF SMALL PARTICLES

Beds of alumina particles (d_p= 27 μm and 100 μm) were vibrated in the vertical direction at frequencies frdm 0-25 Hz and half-amplitudes from 0-4 mm. Air flow rate through a single-hole or multiple-holes bottom plate varied from 0 to 2 times the minimum fluidizing velocity. The contact heat transfer coefficients at resonance are much higher than those in packed beds and in vibrated fluidized beds (up to 1.2 times). The high heat transfer rates are due to enhanced particle mobility which reaches a maximum at the resonant point. A simple semi-empirical correlation is developed for contact heat transfer which is based on particle mobility. Heat transfer coefficients are correlated with frequency using amplitude, bed height and particle size as adjustable parameters. The correlation is found explain the observed trends in the data reasonably well over the range of parameters studied.     

CYLINDER-TO-BED HEAT TRANSFER IN AERATED VIBRATED BEDS OF SMALL PARTICLES

Cylinder-to-bed heat transfer in aerated vibrated beds was studied experimentally. Beds of various model particles were vibrated in the vertical direction with a frequency varying from 0-25 Hz and half-amplitude from 0-4 mm. Alumina and molecular sieve particles of sizes ranging from 27 μm to 1400 μm were used as the model particles. A single-orifice bottom plate was used to supply the air flow at rates varying from 0 to the minimum fluidizing velocity. For small-panicle beds which display resonant behaviour, the cylinder-to bed heat transfer coefficient remains close to the packed bed value as the frequency is increased. Close to the resonant frequency, it increases rapidly to reach a maximum at the resonant frequency. Thereafter, h decreases only gradually with further increase of frequency. The cylinder-to-bed heat transfer coefficients at resonance are much higher than those in packed beds (up to 19 times). The high heat transfer rates are due to particle mobility which reaches a maximum at the resonant point. Surface coverage is greatly affected by both the resonant frequency and aeration rates. It affects the heat transfer rate but is not rate limiting even at low bed bulk densities and surface particle coverage.     

CONVECTIVE HEAT TRANSFER DURING COATING OF PARTICLES IN TWO-DIMENSIONAL SPOUTED BEDS

ABSTRACT

This work deals with the evaluation of gas-to-particle convective heat transfer in a process of coating of particles in two-dimensional spouted beds. A detailed calculus routine is presented and two correlations of heat transfer coefficient, for the spout and annular regions are derived. The study is performed with two, two-dimensional spouted beds with different sizes and with two different particles, placebo and soybean.     

粘性颗粒流化床中聚团大小的计算模型

根据粘性颗粒流化床中聚团所受力的分析,提出了力平衡模型。并对模型中的参数进行了估算。据此模型计算了几种粘性颗粒的聚团大小,计算结果与实测的聚团大小较为接近。与其他研究者的模型比较,计算结果更接近实测值。     

ANALYSIS OF AERODYNAMICS AND HEAT TRANSFER IN VIBRO-FLUIDIZED BEDS

Recent experimental data on aerodynamic and heat transfer characteristics of vibro-fluidized beds of model particles are presented and discussed in the light of the limited prior information. An analysis is presented for the bed dynamics with supporting experimental data. The predicted results for bed flight time, pressure drop and average voidage are shown to agree favorably with experimental data. On the basis of experimental results, a theoretical model and a simple design chart are presented which may be used to determine favorable operating ranges for a vibro-fluid bed apparatus.     

ANALYSIS OF AERODYNAMICS AND HEAT TRANSFER IN VIBRO-FLUIDIZED BEDS

Recent experimental data on aerodynamic and heat transfer characteristics of vibro-fluidized beds of model particles are presented and discussed in the light of the limited prior information. An analysis is presented for the bed dynamics with supporting experimental data. The predicted results for bed flight time, pressure drop and average voidage are shown to agree favorably with experimental data. On the basis of experimental results, a theoretical model and a simple design chart are presented which may be used to determine favorable operating ranges for a vibro-fluid bed apparatus.     

A MODEL FOR BED-TO-SURFACE HEAT TRANSFER IN CIRCULATING FLUIDIZED BEDS

Experiments on bed-to-surface heat transfer in the axial and radial directions were carried out in a cold flowmodel of the circulating fluidized bed of 244mm i.d.and with FCC catalysts(d_p=83.4μm)as the fluidized particles.A simplified gas-solid flow model comprising of the cluster-particulate phases upflowing cocurrentlywas proposed.By taking into account the alternative contacts of cluster and particulate phases with the immersedsurface,a composite heat transfer model was developed.The model gave good predictions as compared withthe experimental results of this work and those of others.     

通气振动流化床与浸没水平管间局部传热系数

提出了测试振动流化床与浸没水平管局部传热系数的新方法 ,就通气振动流化床与浸没水平管间的局部传热特性进行了实验研究 .结果表明 ,局部传热系数随水平管圆周位置而变 ,这种变化受流化气速、振动频率和振幅的影响 ,通气条件下达到最佳传热效果的振动强度比不通气时低 ,振动条件下达到最佳传热效果的流化气速比不振动时小 ,通气条件下振幅和频率对局部传热系数具有大致相同的影响趋势 .实验还表明 ,局部传热系数随颗粒粒径的增加而减小 .     

萘热管小倾角放置时冷凝段内的传热

通过可视化试验,就萘热管小倾角放置时．冷凝段内的特点,建立相应的物理模型和数学模型,通过对数学模型进行解析,从而获得相应的萘热管冷凝段内的凝结换热的计算公式及适用于萘热管设计的结论。     

萘热管小倾角放置时传热极限的研究

根据萘热管的工作温度范围，对萘热管小倾角放置时的传热极限进行了实验研究。实验中发现，当萘热管达到传热极限时，出现干涸点的位置有一定的规律性，分析讨论了其原因，并对有关萘热管的设备设计提供了一些建议。     

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.     

COMPUTER SIMULATION OF MASS TRANSFER IN AGGREGATIVE FLUIDIZED BEDS

A mathematical model for simulation of unsteady-state mass transfer in an aggregative fluidized bed of porous particles is proposed. A quasi-steady state approach is being used to solve the model. A computer program is written for solving the model and the rate of drying of air in a fluidized bed of silica-gel particles is calculated as an example. To evaluate the accuracy of the proposed model, a pilot-scale fluidized bed is erected and the experimental results are compared to the calculated values. A good agreement is observed between them.     

气固流化床传热特征区域的定量分析

基于作者在近期提出的一个新的综合考虑传导、对流和辐射热量传递模式的鼓泡流化床传热机理模型,对传热特征区域进行了定量的分析,提出了一个基于表征颗粒流化特性的Archemides数和传导与辐射相对重要性的Planck数的新的传热区域图。根据主导传热机理的变化,定义出9个特征区域,可供流化床设备的优化设计和正常操作参考。     

A THEORETICAL STUDY OF THE LIMITING HEAT TRANSFER COEFFICIENT IN FLUIDIZED BEDS

A new model is presented to describe the heat transfer process occurring in fluidized beds under the limiting condition of very short contact times between the heat transfer surface and the emulsion phase. Unlike other work in this area the proposed model assumes that the particles are in constant motion close to the surface throughout the heat transfer process. The effect of the non-continuum gas film assumption (the Smoluchowski effect) when particles are very close to the surface is found to be of secondary importance when compared with the movement of particles close to the surface. Expressions for both the instantaneous and time averaged heat transfer coefficients for individual and a spatial distribution of parlicles are presented.     

基于流型的小直径圆管内流动凝结换热机理

通过流型的可视化观察和传热实验 ,探讨不同管径下小直径圆管内流动凝结过程中流型的演化规律以及不同流型的凝结换热特性 .分析表明 ,随着管径的减小 ,以凝结液沿管壁周向均匀分布为主的环状流型在流型图上的面积增加 ,相应地换热温差对凝结换热数Nu的影响降低 .本研究深化了对小尺度下凝结换热机理的认识 ,为推动相关技术的进一步发展提供了理论依据