换热管表面的分形表征及积灰特性数值模拟  

Fractal characterization of heat exchange tube surfaces and numerical simulation on ash deposition characteristics

作　　者：周友行[1] 谢宝安 高腾腾 杨文佳[1] 宫天宇 彭丽[1] ZHOU Youhang;XIE Baoan;GAO Tengteng;YANG Wenjia;GONG Tianyu;PENG Li(School of Mechanical Engineering and Mechanics,University of Xiangtan,Xiangtan 411105,China)

机构地区：[1]湘潭大学机械工程与力学学院,湖南湘潭411105

出　　处：《中国粉体技术》2024年第6期85-96,共12页China Powder Science and Technology

基　　金：国家自然科学基金项目,编号:52175254;湖南省研究生科研创新项目,编号:CX20230550。

摘　　要：【目的】模拟换热器管束的实际工况,研究不同粒径飞灰颗粒在粗糙管束表面的沉积特性。【方法】基于分形理论,通过改进的Weierstrass-Mandelbrot函数建立不同粗糙程度的管束表面模型,使用Fluent软件,结合用户自定义函数,分析表面形貌对流体流动的影响以及不同粒径下的颗粒沉积与碰撞特性。【结果】换热器管束表面粗糙度对壁面附近流速和湍流强度影响显著,粗糙表面会使湍流强度增大、流体速度降低,进一步加快颗粒沉积;流体压降随着管束表面粗糙度的增大而增大;相对于光滑管束表面,粗糙表面通过涡流卷吸作用增强对颗粒的捕获效果,导致颗粒具有更高的沉积率和壁面碰撞概率。【结论】飞灰颗粒的沉积与管束粗糙表面的形成具有正反馈效应,揭示表面粗糙度与颗粒沉积特性之间的内在关联。Objective The surfaces of heat exchanger tube bundles become increasingly rougher due to prolonged use.To explore the deposition characteristics of fly ash particles on heat exchanger tube surfaces with varying roughness and the mechanisms affecting this process,the deposition behavior of fly ash particles of different sizes under actual working conditions is simulated.The study aims to reveal the intrinsic relationship between particle deposition and surface roughness.Methods Tube bundle surface models with different roughness levels were developed using fractal theory and the improved Weierstrass-Mandelbrot(W-M)function.The surface models were generated using Matlab,and mesh generation was conducted using ICEM software.Numerical simulations were performed in Fluent,combined with a user-defined function(UDF).The renormalization group(RNG)k-epsilon(k-ε)turbulence model was employed to simulate the incompressible turbulent flow,and the computational fluid dynamics-discrete phase model(CFD-DPM)was applied to track and analyze the motion of fly ash particles of different sizes in gas-solid two-phase flow.Particle deposition behavior was modeled using energy conservation and critical velocity theory.Results and Discussion Increasing surface roughness of the heat exchanger tube led to a significant increase in both inlet pressure and pressure drop,indicating increased energy loss during fluid flow.This was attributed to the enhanced internal friction caused by higher surface roughness.Greater surface roughness also intensified fluid velocity and turbulent kinetic energy.Reducing near-wall fluid velocity would in turn promote particle deposition.Rough surface peaks influenced fluid flow,generating vortex structures on both windward and leeward sides,which further enhanced fluid-wall interactions.As surface roughness increased,the particle deposition rate rose significantly,especially for small particles with diameters of 1-3μm.These particles showed higher deposition rates and wall capture efficiency due to their low

关 键 词：分形理论 飞灰沉积 数值模拟 气固两相流 

分 类 号：TB44[一般工业技术]