高温颗粒流绕流换热管束的流动与传热特性研究

The technique that the waste heat of particles is directly recovered by gravity bed boiler to produce steam is proposed. The mechanism of flow and heat transfer and coupling characteristic of flow and heat transfer in elevated temperature particle flows flowing around the heat-exchange tube arrays are analyzed by the numerical method and the experimental method. The DEM model which describes the flow of particles around the tube arrays is established. Combined with the cold experiments data, the flow pattern of particle flows flowing around the heat-exchange tube arrays and the mixing level of particles are investigated. The particle contact heat transfer model of elevated temperature particle flows flowing around the heat-exchange tube arrays is established. Combined the particle contact heat transfer model with DEM model, the heat transfer in elevated temperature particle flows flowing around the heat-exchange tube arrays is analyzed. The experiment on heat transfer in gravity bed boiler is carried out to investigate the mechanism of heat transfer in elevated temperature particle flows flowing around the heat-exchange tube arrays. The DEM model and particle contact heat transfer model are modified by the experiments data. The method of heat transfer enhancement for particle flows is explored, and the optimal technological parameters of gravity bed boiler are determined. The experiment on heat-exchange tubes erosion with elevated temperature particle flows flowing around the tube arrays is carried out to reveal the internal mechnism of erosion. The results can provide a guidance for the design of gravity bed boiler.

提出采用自流床余热锅炉直接回收高温颗粒余热生产蒸汽的技术路线。针对高温颗粒流绕流换热管束的流动与传热过程，采用数值模拟与实验研究相结合的方法对高温颗粒流绕流换热管束的流动机理、传热机理以及流动和传热的耦合特性进行研究。建立描述颗粒流绕流管束运动的DEM模型，结合冷态实验结果，分析颗粒流绕流管束的流动形态，研究颗粒流流型及掺混程度的变化规律；建立高温颗粒流绕流换热管束时颗粒接触传热数学模型，并与DEM模型相结合，分析高温颗粒流绕流换热管束的换热过程；进行自流床余热锅炉热态实验，研究高温颗粒流绕流换热管束的传热机理，并修正、完善流动和传热数学模型；探寻强化高温颗粒流绕流换热管束传热的方法，确定自流床余热锅炉的最佳工艺参数；进行高温颗粒流绕流换热管束的磨损实验研究，揭示磨损的内在机理，为自流床余热锅炉的设计提供指导。

本项目对颗粒绕流圆管流动特性、颗粒绕流圆管传热特性以及颗粒绕流圆管的磨损行为进行了研究。主要研究内容和获得结果如下：. 搭建了颗粒绕流圆管流动的冷态实验平台，分析了圆管直径、颗粒直径、圆管排数、圆管排列方式和出料口尺寸对颗粒流型的影响规律。实验结果表明：圆管直径越大，其下面所形成的死区越大；颗粒的直径越大，颗粒在流动过程中的混合作用越好；圆管的排数越多，圆管对颗粒的阻碍作用越明显，不利于颗粒的均匀流动；在叉排排列时，圆管下部几乎没有死区的存在，强化了颗粒在水平方向上的流动。. 建立了颗粒绕流圆管传热的数学模型，考察了自流床余热锅炉操作参数对换热装置颗粒侧传热系数、颗粒出口温度、热回收率以及第一排换热管处颗粒温降速率的影响规律。模拟结果表明：颗粒侧传热系数随着颗粒直径的增大而逐渐减小，随着颗粒入口速度的增大而逐渐增大；颗粒出口温度随着颗粒直径的增大、颗粒入口温度的升高、颗粒入口速度的增大而逐渐升高；换热装置的热回收率随着颗粒直径的增大、颗粒入口温度的升高、颗粒入口速度的增大而逐渐减小，随着水入口速度的增大而逐渐增大；换热装置第一排换热管处颗粒的温降速率随着颗粒直径的增大而减小，随着颗粒入口温度、颗粒入口速度的增大而增大。. 搭建了颗粒绕流圆管磨损的实验平台，考察了颗粒直径、相对速度、颗粒温度对铜、铝材质圆管的磨损规律。通过实验发现：颗粒直径在0.8-2.25mm范围内，铜、铝圆管的单位磨损量随着颗粒直径的增大而增大，颗粒直径在1.715-2.25mm区间时单位磨损量急剧增大；颗粒温度在293-513K范围内，铜、铝圆管单位磨损量随着温度的升高先减小后增大，出现最小单位磨损量出现在403K附近；磨损深度随着颗粒直径和相对速度的增大而增大，随着颗粒温度的升高先减小后增大；通过实验数据拟合得到回归方程，达到1%显著水平，实验值与计算值吻合较好，回归方程能够准确计算不同材质圆管的磨损量。