EXPERIMENTAL AND NUMERICAL INVESTIGATIONS OF SOLIDS MIXING IN A GAS FLUIDIZED BED

Solids mixing in a bubbling gas-fluidized bed was Investigated using two Independent methods. In the first method, distributions of solids mean velocity and bulk density, and dispersion coefficients were measured, employing the single particle mode of the particle tracking technique. This technique tracks the position of a single radioactive particle, dynamically identical to bed particles, by using a bank of scintillation detectors around the bed. Time-differentiation of the instantaneous tracer positions then yields the local velocities which were ensemble-averaged locally after long experimental runs to yield the mean velocity distribution. Lagrangian autocorrelation functions were obtained to determine the radial and axial dispersion coefficients, which were found to differ by an order of magnitude. These experimental data formed the basis of a numerical model of convective-diffusive mixing, formulated to predict the time-dependent concentration distribution for a given set of initial conditions. The second method employed the multiparticle tracking mode in which the downward migration and mixing of a quantity of radioactive particles Introduced at the top of the bed was monitored by the radiation detectors. The variation of the detector outputs with time served as an Indicator of the distribution of the radioactive swarm. When the results were compared with the predicted detector outputs using the model with independently obtained velocity and dispersion coefficient distributions, good agreement was found, especially at higher fluidization velocities.     

SIC COATING OF SMALL PARTICLES IN A FLUIDIZED BED REACTOR

Silicon carbide was chemically vapor deposited on the small particles in the fluidized bed reactor. Methyltrichlorosilane and hydrogen were used as reactants and in some cases argon was added as a fluidizing gas. Thirty-one coating runs were carried out where coating temperature, methyltrichlorosilane concentration and fluidizing gas composition were varied systematically. The deposit composition was found to be beta-SiC or mixture of beta-SiC and silicon by X-ray diffractometry. The coating temperature affected the deposit composition. From the results of the coating experiment, the model of the CVD processes was presented, which was based on the mass transfer mechanism. This model explained the experimental results fairly well.     

PARTICLE REFLUX IN THE RISER OF A CIRCULATING FLUIDIZED BED

Particle reflux has a significant influence on heat and mass transfer and gas back mixing in circulating fluidized beds. An novel heat transfer probe to determine the particle reflux region and details of the experimental procedure are presented and discussed in this paper. Results indicate that the particle velocity is one of the most important factors governing heat transfer between the bed and the surface in a circulating fluidized bed.     

CAFTURE AND RECYCLE OF BYPASSING BUBBLE GAS IN A FLUIDIZED BED: THE “BUBBLE EATER”

The bubble eater is a device which can sense, capture, and recycle bubble gas in a bubbling fluidized bed. The theory describing the enhancement of reactant gas conversion are presented and illustrated by means of a numerical example.     

脉管制冷机中脉管内的气柱位移分析

脉管在脉管制冷机中所起的作用,主要体现在热力学和动力学两方面。由热力学平衡计算可决定脉管制冷机的尺寸,但同时也要进行动力学上的匹配。着重利用Dr.deBoer的热力学分析方法对脉管内的气柱位移进行了定量计算 ,给出了计算结果 ,并进行了讨论     

A NUMERICAL MODEL FOR THE TURBULENT FLUCTUATION AND DIFFUSION OF GAS-PARTICLE FLOWS AND ITS APPLICATION IN THE FREEBOARD OF A FLUIDIZED BED

A numerical model for the turbulent fluctuation and diffusion of gas-particle flows is presented. This model is based on the idea of treating a turbulent gas flow field as a set of k-ε equations, and of modeling the turbulent fluctuation velocity of gas flow as a random Fourier series based on the fluctuation frequency and spectrum. The particle properties (trajectory and velocity) are described by a Lagrangian approach. Hence this model is known as the fluctuation-spectrum-random-trajectory () model. Finally, particle movements in the freeboard of a fluidized bed and in a turbulent gas-particle-laden jet are analyzed to illustrate the applicability of the model.     

INTERACTION BETWEEN PRESSURE DROP OF GAS AND FLOW OF MEDIUM IN A MOVING GRANULAR BED FILTER

Gradually increasing pressure drop, which ultimately leads to a rapid increase, is a problem encountered in moving granular bed filters when gas velocity is elevated during dust collection from the top gas of a blast furnace. The relationship between dust collection and pressure drop was mathematically simulated, and then a half-size test model moving granular bed filter was used to examine the conditions under which the medium can flow. The increase in gas pressure drop proceeds as a circular chain of interrelated events. When gas velocity is increased and the gas pressure gradient exceeds a certain critical value, the medium flow stalls along the gas discharge side of the bed. Dust accumulates in the stalled medium, raising the pressure gradient even further. The growth in pressure drop is thus accelerated, finally resulting in a rapid and undesirable increase that prevents further operation.     

输油气钢管腐蚀渗漏原因分析

某油井钢管使用不到一年即发生渗漏。采用化学分析、力学性能测试、金相及超声波检验和电镜能谱分析等方法，对渗漏钢管进行了分析。结果表明，该钢管实为焊管，不是技术规范所要求的无缝钢管。加上该焊管的焊接质量较差，加速了输送介质对焊管的腐蚀，最终导致焊管短期内发生渗漏。     

MODELING OF SOLID FLOWS IN A FLUIDIZED BED WITH SECONDARY TANGENTIAL AIR INJECTION IN THE FREEBOARD

The Vortexing Fluidized-Bed Combustion (VFBC) technique was recently developed for small- and medium-scale coal-burning boiler applications. Experimental observations showed that the general solid flows in the freeboard of a vortexing fluidized bed consisted of three successive stages: (1) spirally ascending motion before colliding the freeboard wall, (2) bouncing on the wall, and (3) sliding on the wall and exiting the freeboard. This study attempts to model these three stages of solid flows. The dimensionless governing equations for particle motion in the swirling field were presented taking into account the interactions of particle inertia, centrifugal force, viscous fluid drag, and gravity. Numerical solutions of particle velocities and trajectories were pursued, and effects of particle momentum transfer number, Froude number, and particle-wall restitution coefficient were delineated. The experimental validation of solid flows in the swirling freeboard was furnished with an 18 cm ID laboratory fluidized bed.     

MODELING OF SOLID FLOWS IN A FLUIDIZED BED WITH SECONDARY TANGENTIAL AIR INJECTION IN THE FREEBOARD

Abstract

The Vortexing Fluidized-Bed Combustion (VFBC) technique was recently developed for small- and medium-scale coal-burning boiler applications. Experimental observations showed that the general solid flows in the freeboard of a vortexing fluidized bed consisted of three successive stages: (1) spirally ascending motion before colliding the freeboard wall, (2) bouncing on the wall, and (3) sliding on the wall and exiting the freeboard. This study attempts to model these three stages of solid flows. The dimensionless governing equations for particle motion in the swirling field were presented taking into account the interactions of particle inertia, centrifugal force, viscous fluid drag, and gravity. Numerical solutions of particle velocities and trajectories were pursued, and effects of particle momentum transfer number, Froude number, and particle-wall restitution coefficient were delineated. The experimental validation of solid flows in the swirling freeboard was furnished with an 18 cm ID laboratory fluidized bed.     

CONTINUOUS COOLING OF WET FOUNDRY SAND USING A FLUIDIZED BED

Abstract

In order to establish the optimum cooling system for hot returned sand in metal casting processes, a mathematical model including simultaneous heat and mass transfer has been constructed. The present study is especially directed towards clarifying the dynamical behavior of sand cooling in a one-pass fluidized bed. A series of continuous cooling experiments has been made for various conditions. Characteristics of both transient and steady-state bed temperature are explained reasonably by the present model. Furthermore, a possible proposal has been given on the optimal operation, which raises heat exchange efficiency in fluidization cooling of hot molding sand.     

CONTINUOUS COOLING OF WET FOUNDRY SAND USING A FLUIDIZED BED

In order to establish the optimum cooling system for hot returned sand in metal casting processes, a mathematical model including simultaneous heat and mass transfer has been constructed. The present study is especially directed towards clarifying the dynamical behavior of sand cooling in a one-pass fluidized bed. A series of continuous cooling experiments has been made for various conditions. Characteristics of both transient and steady-state bed temperature are explained reasonably by the present model. Furthermore, a possible proposal has been given on the optimal operation, which raises heat exchange efficiency in fluidization cooling of hot molding sand.     

液氦温区脉管制冷机的频率特性

着重研究了操作频率对液氦温区脉管制冷机性能的影响,在实验和分析的基础上,明确了制冷温度、制冷量、制冷效率与工作效率之间的关系,并与4K G－M制冷机的情况进行比较,得出了一些有益的结论。通过频率优化,脉管制冷性能得以较大提高。在初步试验中,分别在1．2Hz和1．1Hz获得了30W@70K,500mW@4.2K以及20W@65K,590mW@4.2K的制冷量。同时还给出了脉管制冷湿度稳定性的测试结果。试验结果表明,研制的脉管制冷机温度波动均小于同类商品型4K GM制冷机及脉管制冷机。     

MESUREMENT OF SOLIDS CONCENTRATION PROFILE AROUND THE PERIPHERY OF AN IMMERSED TUBE IN A THREE-DIMENSIONAL GAS-FLUIDIZED BED

To adequately describe the heat transfer process at the surface of an immersed tube in a gas-fluidized bed, it is imperative to know the solids concentration at the tube surface. The knowledge of particle dynamics will also enable to establish the likely metal erosion and thus the heat exchanger life. However, determination of such parameters is not straightforward and here we describe the development of an image carrying fiber optic probe with a potential to generate such information. Using such a borescope in conjunction with a CCTV camera, TV monitor and video-cassette recorder, solids concentration profiles have been measured around the periphery of horizontal tubes (outside diameters 11 and 28 mm) immersed in an air-fluidized bed of 1.4 mm average diameter glass beads. In both the cases, it is found that the bulk bed voidage is considerably smaller than the voidage at the tube surface. The latter also varies with the location around the tube periphery. The smallest values are found for the downstream side, largest values for the equatorial sides, and intermediate values for the upstream side. These values are dependent on the fluidizing velocity and the tube diameter. Estimate are also given of the air film thickness at various locations between the tube and the particles.     

高频微型脉冲管制冷机的数值研究

利用数值方法模拟了高频微型同轴脉冲管制冷机内部气流交变流动和换热过程。给出了小孔型，双向进气型和多路旁通型脉冲管制冷机内部气流动态参数的瞬态变化。分析了各动态参数变化对制冷机整机性能的影响。     

ELECTRIC ADHESION FORCE OF A SINGLE PARTICLE AND OF A POWDER AT ROOM TEMPERATURE AND ABOVE AMBIENT TEMPERATURE AND ITS APPLICATION TO A FLUIDIZED BED

Adhesion forces of a single particle and of a powder in the presence of d.c. electric field were analysed both at and above room temperature. At room temperature the adhesion force was measured and found to increase almost linearly with the increase of applied electric field strength and decrease with the decrease of air humidity. Calculated forces showed good agreement with experimental ones. Above ambient temperature calculated electric adhesion forces increased with the increase of temperature up to 400^°c.

In a separate experiment a d.c. electric field was applied for the purpose of controlling bubbles in a gas-solid fluidized bed being used as dust collector. The bubbles were shown to play an important role in the dust collection efficiency, and large bubbles give unfavorable effects. The effects of the d.c. electric field on bubble frequency, bubble diameter and the rise velocity of bubbles were measured. It was confirmed that bubbles were favorably controlled and the rise velocity of bubbles was reduced by the applied electric field.     

两级脉冲管制冷机穿梭和泵气热损失计算分析

脉冲管制冷机以空管取代了G-M和斯特林型制冷机中的冷端活塞,分析了由这种特点和交变流动引起的两级脉冲管制冷机的穿梭热损失和泵气热损失,以及损失的来源,并进行了详细的定量计算。     

某燃气轮机试验工艺基架结构静动力分析

本文采用有限元法及子结构技术,建立了某燃气轮机试验主设备工艺基架结构体系的力学模型,计算分析了各结构的静位移,静应力,固有特性,动态响应和动应力,并了各主设备之间振动的相互影响。     

中和室脉冲进气的蒙特卡罗模拟及实验验证

对于中和室内的脉冲气体，用蒙特卡罗方法模拟了气体压力沿轴向的分布。并用模拟进气系统和气压瞬时测量系统，对模拟结果进行了验证。得到与模拟结果较为一致的曲线，从而为注入器真空系统的设计提供了可靠的依据。并通过实验结果，给出了气体靶厚的建立时间约为６０ｍｓ。     

涡流管研究的进展与评述

对涡流管的发展作了较为详细的回顾。指出了涡流管研究的前景和重要意义,综述了涡流管的理论研究、实验研究和应用研究的进展,并对已有的研究成果进行了一定的评价。