循环流化床内局部颗粒混合特性的研究

为了研究流化床内固体粒子的混合特性，从固体粒子运动速度的脉动特性和浓度分布出发，提出了局部颗粒混合因子的概念及数学模型。并利用高速摄影CCD和相关分析等图像处理方法对该模型进行了试验验证和分析。从试验结果来看：混合因子的分布与粒子混合的剧烈程度有较好的对应关系，描述了流化床投影面上粒子的混和特性。在实现上，计算混合因子所需要的信息全部来自粒子运动图像，属于非接触测量，易于在线分析。因此，该因子可以作为一个定性参数来描述流化床内局部区域粒子的混合特性。图6参11     

循环流化床内颗粒停留时间分布

为进一步了解循环流化床床内复杂的流体动力特性,在200mm×200mm的冷态循环流化床试验台上以从床料中筛分出来的某一粒径的颗粒为示踪颗粒,用脉冲加入示踪剂法直接测量了固体颗粒停留时间分布.对试验所得的固体颗粒停留时间分布曲线的分析明显表明床内存在着由于流体动力特性和几何结构引起的颗粒返混.基于循环流化床内特殊的核心-边壁区流体动力结构,建立了能描述循环流化床和下排气旋风分离器内固体颗粒流体动力特性及固体停留时分布的数学模型.该模型计算结果和实验数据吻合良好.     

内构件对CFB-FGD塔内固体颗粒径向运动特性影响实验研究

CFB-FGD(循环流化床烟气脱硫)脱硫塔内脱硫剂固体颗粒沿径向速度分布不均匀,改善脱硫剂颗粒径向运动特性对增强接触反应、提高脱硫效率起着关键作用。针对这一问题,设计水平多孔挡板式、垂直叶轮式、钝体式3种内构件,在冷态的实验装置中,分别安装在塔体密相区,利用粒子图像测速仪测量3种内构件对塔内脱硫剂颗粒径向运动特性的影响。实验结果表明,内构件可以改善气固流动的径向分布,多孔挡板式内构件对固体颗粒的径向运动行为影响很小,垂直叶轮式内构件的效果较好但是仍存在诸多缺陷,钝体式内构件显著改善了固体颗粒沿径向的混合,对脱硫反应最有利。     

循环流化床中气固两相流动特性的可视化研究

在自行设计并搭建的试验台上,利用CCD的图像快速采集功能,获得了不同气速下流化床内的流态图像,并用图像处理方法对这些原始图像进行了有效的处理。研究了贴壁回探流、气体局部扩散系数、局部空隙率随横向位置和高度的分布、气泡的上升速度,给出了实验中气泡边界曲线的分维数。实现了循环流化床内气固两相流体动力学特性的可视化,为图像处理技术应用到循环流化床作了有益的尝试。     

气固流化床流体与颗粒的传热研究

本文介绍了双室流化床依靠固体颗粒循环实现双室间流体热量传递的流化床换热器模式及其热平衡试验;并在此基础上,分析了流化床内气体温度分布规律,理论计算值与实验值比较,吻合较好;讨论了流化床气固传热;提出新的准则数Nu_p·H_d/d及有效传热高度H_b的概念,研究表明,新的准则数Nu_p·H_d/d及特性尺度H_b更适合描述流化床气固传热规律。     

内循环流化床大块物分布特性的试验研究

结合城市固体垃圾的物性特点,采用分层取样技术进行了倾斜布风板内循环流化床内大块物分布特性的试验研究。系统考察了两种不同密度床料中,流化风速和大块物的尺寸、密度等因素对其在床内分布规律的影响,进而探讨了床内大块物的混合、分层机理。结果表明:密度是主要影响因素;以砂子为床料的内循环流化床,能够实现木块、石蜡、橡胶等轻质可烯物的均匀混合,同时灰渣等重质不可燃物能够充分分离。图9表2参7     

大型循环流化床锅炉整体动静态数学模型的建模方法研究

提出了一种建立大型商用循环流化床锅炉动静态整体数学模型的方法。该方法在描述循环流化床悬浮段内气固流动特性时考虑了固体物料的宽筛分特性和“核心－环”流动结构，并详尽考虑了循环流化床锅炉内发生的诸如燃烧、传热、有害物质的生成和还原等主要物理化学过程。针对目前国内容量最大的引进410t/hPyroflow循环流化床锅炉，采用该方法对其整体性能进行了预测。     

流化床表面传热系数的直接数值模拟

采用数值试验方法对表面传热系数进行了直接数值模拟．在流化床表血传热系数模型中,流体相的运动和传热规律以Euler方法描述,对固体颗粒相运动和传热规律则以离散单元法(DEM)在颗粒层次上进行描述．利用该模型,对一个二维鼓泡流化床内瞬时和局部传热系数进行了模拟,得到了瞬态表面传热系数随流化速度的变化规律,以及局部传热系数随高度的变化规律．该规律与Ozkaynak等人的实验研究结果以及Syamlal等人采用颗粒相拟流体模型的数值模拟结果相一致,但与双流体数学模型相比,该模型所需主观假设较少且适用范围更广．     

内旋流流化床内颗粒流动特性的数值模拟研究

利用欧拉双流体模型对内旋流流化床内固体颗粒的流动特性进行数值模拟,模拟结果表明:内旋流流化床内气泡主要产生于高速风侧;非均匀布风和布风板倾角对床内颗粒流动特性有影响;内旋流流化床具备良好的横向和纵向扩散特性,有利于床内物料的强烈混合;模拟结果与实验结果符合较好。     

流化床微观混合过程的定量评价

将离散单元法与计算流体力学相结合,对流化床内物料微观混合过程进行了研究.给出了在水平布风板均匀布风、倾斜布风板非均匀布风两种情况下的示踪颗粒场变化过程,并引入Ashton指数,以定量描述混合发展程度.模拟结果表明:在均匀布风情况下,床内气泡横向运动受到限制,横向混合以扩散方式为主;而对于非均匀布风流化床,床内存在较大的横向颗粒浓度梯度,初始阶段对流混合作用起主要作用,且混合速度较为迅速;随后局部剪切作用使混合进一步细化.     

Kinetic parameters for the oxidation of pulverised coal as measured from drop tube tests

The methodology for measuring the oxidation parameters for pulverised coal combustion from drop-tube tests is reviewed, and some modifications to the traditional procedure (based on Arrhenius plots) are proposed. The work includes the experimental characterisation of an anthracite's combustion in a drop-tube furnace, which will be used as the reference data. One of the main points in the discussion is the consideration of a particle-size distribution instead of a single representative diameter. Since a true monosized sample cannot be obtained by sieving, the particles injected always display a size distribution and, therefore, the experimental results are the outcome of a range of oxidation rates. As a result, the assumption of a single particle size cannot explain some aspects of the experimental results (e.g., the “curvature” of the burnoff curve) and may lead to significant deviations in the calculated parameters. On the other hand, an alternative method for deriving the parameters, based on calculating the particle's full combustion history, is proposed. The analysis presented here enables a more systematic and unambiguous approach for deriving the kinetic parameters for oxidation from experimental measurements. If the actual particle-size distribution is taken into account, the calculations are in good agreement with the experimental results and, in particular, reproduce the progressive decay in apparent oxidation rate while the fuel burns. Even though the deviations might still be reduced by using a more sophisticated model (e.g., accounting for heterogeneity in the particles' properties, or deactivation phenomena), the results obtained suggest that such corrections should be relatively small, the correct treatment of the size distribution of the particles being more important in this case.     

Analysis of mixing distribution in an engine-like configuration

A study of gaseous fuel/air mixing in a simplified two-dimensional axisymetrical cylinder shaped chamber with centrally located orifice inlet condition is performed using multi-dimensional computational fluid dynamic analysis. The gaseous fuel concentration distribution formed by in-cylinder charge motion is also predicted. The effect of swirl on global mixing is examined, and the optimal swirl is determined for a particular value of engine speed. A measure of global uniformity is defined and used to gain information about the fuel concentration distribution within the chamber. The computational results show that the flow field has a great effect on charge mixing. The charge mixing is satisfactorily close to the desirable mixing distribution when the fuel charge is prescribed properly. Copyright © 2003 John Wiley & Sons, Ltd.     

A coupling study of ignition position on fuel-air mixing and diffusion of a linear hydrogen engine

Linear hydrogen engine (LHE) is a new technology of hydrogen energy utilization due to its flexible compression ratio coupling with ignition, fuel-air mixing, and combustion to optimize thermal efficiency. Fuel-air mixing in LHE is expected to be promoted by using ignition, which differs with conventional engine. This paper develops a full-cycle model which couples with dynamics, hydrogen-air mixing and combustion to describe the effect of ignition position, meanwhile a loop iterative calculation method is proposed to solve the coupling model for hydrogen-air mixing predication. The results show that ignition position variation can cause the piston trajectory to change significantly, and the higher equivalent speed is obtained in the medium ignition position. Besides, the higher equivalent speed in the injection stage is conducive to the diffusion of hydrogen, but the higher equivalent speed is not conducive to diffusion and mixing in the diffusion stage. More importantly, the equivalence ratio distribution at the ignition position is more uniform for the later ignition position due to the longer mixing stroke, and the mixture uniformity index at the ignition position is inversely proportional to the advance of the ignition position. Therefore, the late ignition is recommended to obtain a uniform hydrogen mixture.     

水煤膏在二维流化床内的混合

利用图像处理技术在二维流化床试验装置上研究了水煤膏的混合过程。分析了垂直向上射流的脉动特性。利用数字图像相关性分析方法得到了水煤膏在流化床内的混合过程 ,指出水煤膏在流化床内混合的机理 ,并且发现由于射流的引入使颗粒的内循环运动加强     

河口水质SDKZ模型及其有限元解的稳定性

根据强混合型河口海域的水流条件及边界特点，针对热污染源提出ＳＤＫＺ模型，并对模型有限元法解的稳定性条件进行了分析，通过实际河口海域流速场和温度场的模拟计算年出 ，该模型具有较镐的精度。     

基于CFD的天然气管道混气扩散规律研究

随着我国多气源天然气市场发展和整体供气管网的形成,多气源直接接入管网混输已成为必然,不同气质气源直接管道混气的技术问题亟待研究和解决。基于CFD模拟,对不同气源混合输运的气质扩散规律进行研究,为混输管网合理设计和准确设定气质监控点提供依据,以保证燃气管网系统的安全可靠运行。重点对典型混气管路(Y型管)的天然气气质扩散规律进行数值模拟,获得掺混流体剪切层质量传递特征和天然气气质扩散规律。根据混气湍流形态和浓度场分布特征,获得Y型管的三类混气类型。通过对气质扩散浓度的不均匀性理论分析和模拟结果的综合数据分析,建立了预测混气管道达到气质均匀的混合长度无因次准则方程,为工程设计提供理论方法和计算基础。     

河口海域热污染综合模型及其应用

根据强混合型河口海域的水流条件及边界条件，针对温热排水污染源，从物理机制入手，提出了三维－多层二维平面扩散综合模型。通过对实际河口海域流速场和温度场的模拟计算可知其具有较高的精度和实用价值。     

主支管动量比对T型管道流体混合过程影响

采用大涡模拟(large-eddy simulation,LES)的方法对T型管道内主管与支管不同动量比的流体混合过程的流动情况进行了数值模拟,采用时均值和均方根值来描述速度的平均大小和波动强度。通过改变主管和支管的速度比即动量比,将流体分为三类:碰撞射流、偏射流和壁面射流,研究其对速度的平均值和波动的影响,并研究其所反映的惯性力对流动的影响。该研究揭示了流体混合过程中动量比对波动的影响规律,对预测和校核管壁疲劳失效具有重要的指导意义。