管排换热器碳烟颗粒沉积分布特性的数值模拟  

Numerical Simulation on Soot Particle Deposition DistributionCharacteristics of Tube Heat Exchangers

作　　者：田华[1] 张钊 陈天宇 舒歌群[1] Tian Hua;Zhang Zhao;Chen Tianyu;Shu Gequn(State Key Laboratory of Engines,Tianjin University,Tianjin 300072,China)

机构地区：[1]天津大学内燃机燃烧学国家重点实验室,天津300072

出　　处：《天津大学学报（自然科学与工程技术版）》2021年第8期825-833,共9页Journal of Tianjin University：Science and Technology

基　　金：国家重点基础研究发展计划(973计划)资助项目(2017-JCJQ-ZD-001-02).

摘　　要：烟气换热器是内燃机余热回收系统中重要的组成部分,而内燃机排气中的碳烟颗粒会沉积在烟气换热器表面,形成的沉积层具有很低的导热系数,这种沉积现象会降低换热器传热效率,增加系统的运行成本和维护费用,同时给换热器设计带来较大的不确定性.目前针对内燃机排气碳烟颗粒沉积相关的研究大多关注于颗粒在换热器上的沉积总量变化,对于碳烟颗粒在换热面上沉积分布的研究较为匮乏,而沉积分布研究可以直观地体现出颗粒沉积集中的区域,从而更有针对性地指导换热器结构优化.为探究碳烟颗粒在管排换热器中的沉积分布情况,在FLUENT离散相模型的基础上,利用用户自定义函数(user-defined functions,UDFs),建立了考虑颗粒黏附和反弹行为的碳烟颗粒沉积数值模型,研究了不同流速与粒径下的颗粒沉积分布,并针对沉积分布情况探究了纵向管间距对颗粒沉积率的影响.结果表明:由于第3排管相较于前两排管的管后尾流区形成更加充分,同一条件下第3排管处的沉积率最大,沉积占比最高达57.8%;颗粒在换热管表面的沉积位置主要集中在第1排的管前滞止区附近和各排的管后尾流区附近,即颗粒速度较小且与换热表面碰撞几率较大的区域;综合考虑沉积和换热压降性能,在不同流速下纵向管间距与管径之比为1.75时为最优.An exhaust heat exchanger is an important part of the waste heat recovery system of an internal combustion engine.However,the particulate matter in the diesel engine exhaust will be deposited on the surface of the heat exchanger.As fouling grows,the deposition surface is gradually covered by the fouling layer with low thermal conductivity.This phenomenon will reduce heat transfer efficiency,increase equipment operation costs and maintenance costs,and bring uncertainty to the heat exchanger design.At present,research on the deposition of soot particles from internal combustion engine mostly focuses on the change in the total number of particles deposited on the heat exchanger.Studies on the deposition distribution of the soot particles on the heat exchange surface are relatively scarce.This research can directly reflect the area where in the particle deposition is concentrated,which consequently guides the structure optimization of a heat exchanger.A numerical model is developed to explore the deposition distribution of soot particles in a tubular heat exchanger considering particle adhesion and rebound behavior based on the discrete phase model of the software FLUENT,extended by user-defined functions(UDFs).The particle deposition distribution for different flow rates and particle diameters is examined.The influence of longitudinal pipe spacing on the particle deposition ratio is also explored.Results show that compared with the first two rows of tubes,the third row has the highest deposition ratio(57.8%)because of the fully formed wake region.The particle deposits accumulate primarily in the stagnation region of the first row of tubes and the wake region of each tube.In other words,the particle deposition occurs mainly in areas with low particle velocity and a high probability of collision with heat exchange surfaces.Considering the deposition and heat transfer performance,a tube-spacing value of 1.75 is recommended at different flow rates.

关 键 词：余热回收 烟气换热器 碳烟颗粒 沉积分布 

分 类 号：TK172[动力工程及工程热物理—热能工程]