【作者】 唐选平；

【导师】 刘明言；

【作者基本信息】 天津大学 ， 化学工程， 2004， 硕士

【摘要】 汽液固三相循环流换热器具有良好的防、除垢和强化传热的作用，在各工业领域具有广泛应用前景。但是，目前对该系统的流动、强化传热、以及防除垢机理的研究尚有不足之处，这与该系统本身比较复杂和已有的研究多是在不透明的设备中进行等因素有关。本文采用CCD测量和图像处理技术对汽液固三相自然循环流动沸腾系统进行了可视化研究。首先在总结了多相流强化传热和防除垢技术的研究现状、测试手段及其图像处理方法研究进展的基础上，提出了本文的研究思路与方法。本文利用一套采用透明膜电加热的汽液固三相自然循环流沸腾蒸发装置系统为实验台，在自行开发的CCD测量和图像处理软件及硬件系统以及片光源系统的基础上，对热模情况下的汽液固三相自然循环流内部的分散相的流动及分布情况，汽液固三相流传热特性等进行了研究。结果表明：固含率的轴向分布具有波动的特性，而且随热通量的逐渐增加先增加后减小，随固体颗粒加入量的增加而增加。在液固两相区内，固体颗粒的径向分布规律是管壁附近多而管中心少，而在汽液固三相区，其分布规律恰恰相反。固体颗粒的轴向速度的轴向分布也是波动的，轴向速度随热通量的增加而增加，而固体颗粒对其影响是多方面的。无论是轴向、径向固含率还是固体颗粒的径向速度都是随时间波动的。汽液固三相流动沸腾传热系数随热通量和固体颗粒加入量的增加而增加，是汽液两相流动沸腾传热系数的1.5-3.5倍。在本文中初步讨论了流化床中的汽含率、液含率以及汽泡速度等随操作参数的变化规律。并根据实验结果，将渐进模型和表面更新机理结合起来，建立了汽液固三相流动沸腾传热系数模型。模型计算结果与实验结果吻合较好。更多还原

【Abstract】 The vapor-liquid-solid (V-L-S) circulating fluidized bed heat exchanger can effectively enhance heat transfer and prevent and remove the fouling, and has been widely applied in many industrial process. However, the mechanisms of flow and heat transfer are still not well understood due to the system complex and the limitation of the measuring methods due to the opaque characteristic of the system in practice. In this paper, a CCD measuring system and techniques of image dealing are used to carry out a visual investigation on a vapor-liquid-solid three-phase natural circulating flow boiling system.Based on summarizing the development and research situations of techniques of enhancing heat transfer and preventing and removing the foulings for multi-phase flow, measuring means and method of image dealing. The idea of this paper is given.A set of new type vapor-liquid-solid three-phase natural circulating flow boiling system, whose flow-up bed and flow-down bed are glasses plated with transparent electrically heating film, is established as experiment apparatus. Flow characteristics, distributions of suspensions and characteristics of heat transfer in the V-L-S system are investigated by using the CCD measuring system, software of image dealing developed by own-self, system of laser sheet and other hardware system. The results show that the axial distributions of solid holdup occupy the character of fluctuation. Solid holdup increases with the increase of the amount of solid particles and the increase of heat flux when it is relatively low, but decreases when heat flux is relatively high. The radial distribution rule in liquid-solid two-phase region is that radial solid holdup is greater near the wall than in the center of the heating tube, which is contrary to that in V-L-S three-phase region. Axial velocity of solid particles increases with the increase of heat flux, whose distributions also occupy the character of fluctuation. However, the amount of solid particles influences axial velocity of solid particles on many aspects. Axial and radial holdups of solid particles and radial velocity of solid particles are all fluctuating with time. Heat transfer coefficient of V-L-S three-phase flow increases with the increase of heat flux and the additive amount of solid particles, which is 1.5 or 3.5 times larger than that of vapor-liquid flow. <WP=5>In addition, the changes of holdups of liquid and vapor and velocity of bubble with the operation parameters are discussed in this paper. A flow boiling heat transfer model of the V-L-S three-phase flow incorporating the asymptotic model and the mechanism of surface renewal is proposed here. The values calculated by this model agree well with the experimental data.更多还原