周友行，谢宝安，高腾腾，杨文佳，宫天宇，彭 丽

湘潭大学 机械工程与力学学院，湖南 湘潭 411105

引用格式：

周友行，谢宝安，高腾腾，等. 换热管表面的分形表征及积灰特性数值模拟［J］. 中国粉体技术，2024，30（6）：1-12.

ZHOU Youhang， XIE Baoan， GAO Tengteng， et al. Fractal characterization of heat exchange tube surfaces and numerical simulation on ash deposition characteristics［J］. China Powder Science and Technology，2024，30（6）：1-12.

DOI：10.13732/j.issn.1008-5548.2024.06.008

收稿日期：2024-06-04，修回日期：2024-09-29，上线日期：2024-10-30。

基金项目：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。

第一作者简介：周友行（1971—），男，教授，博士，博士生导师，研究方向为数字化设计与制造。E-mail：zhouyouhang@xtu. edu. cn。

摘要：【目的】 模拟换热器管束的实际工况，了解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了对颗粒的捕获效果，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，揭示了表面粗糙度与颗粒沉积特性之间的内在关联。

关键词：分形理论；飞灰沉积；数值模拟；气固两相流

Abstract

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 1-3 μm. These particles showed higher deposition rates and wall capture efficiency due to their low inertia. As particle size increased， the number of particle-wall collisions and the overall collision enhancement rate first increased and then decreased. Compared to smooth surfaces， the rough surfaces with an R_q of 1. 50 mm exhibited a higher number of particle collisions， indicating the significant impact of surface roughness on particle collision behavior.

Conclusion The deposition of fly ash particles and the formation of rough surfaces on tube bundles exhibit a positive feedback loop. Particle deposition gradually makes the tube wall surfaces rougher， which in turn further accelerates particle deposition. Vortices generated by rough surfaces increase fluid-wall friction， resulting in greater energy loss， increased turbulent kinetic energy， and reduced flow velocity， thereby intensifying pipe wear and corrosion， ultimately shortening the equipment’s lifespan. Understanding the deposition mechanisms of fly ash particles under actual operating conditions allows for the prediction of deposition rates and distribution. This study provides a theoretical basis for optimizing tube bundle design and maintenance strategies， and offers new data and theoretical support for gas-solid two-phase flow and particle deposition theory.

Keywords：fractal theory； fly ash deposition； numerical simulation； gas-solid two-phase flow

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