换热管束壁面颗粒沉积状况的数值模拟

Numerical simulation of particle deposition on wall surfaces of heat exchange tube bundles

随着计算流体力学的不断发展,许多学者提出了受热面结渣沾污状况的预测模型,然而,由于灰颗粒的沉积过程较为复杂,为了简化计算,很多因素在现有模型中并未考虑。本研究在现有模型的基础上,综合考虑了还原性气氛对灰颗粒黏度的影响以及灰中碱金属对颗粒黏结概率的影响,基于数值模拟研究了不同模型下换热管束颗粒沉积状况,并探究了纵向节距和壁面温度对管束壁面颗粒沉积状况的影响。结果表明:考虑不同的修正模型后,颗粒沉积效率均有一定程度的增加,且同时考虑还原性气氛及碱金属对沉积过程的影响时,其颗粒沉积效率相对于基础模型颗粒沉积效率的变化率为22.24%。颗粒在同列管束壁面上沉积质量的分布并不一致,对于第一排管束,颗粒主要沉积在30°~150°位置上,且90°附近区域颗粒沉积质量最大;而随着管排数的增大,颗粒沉积质量分布越来越均匀。随着纵向节距的增加,第一排管束颗粒沉积质量基本不变,而后排管束的颗粒沉积质量逐渐增加;随着温度的升高,各管束颗粒沉积质量略有增加,但变化并不明显,这是因为沉积过程受到多种机理耦合作用。

Many prediction models have been put forward to assess the slagging and fouling conditions on the heating surfaces as computational fluid dynamics continues to advance.Nevertheless,when considering the intricate deposition process of ash particles,some potentially critical factors have been overlooked in these existing models in order to simplify the numerical simulation.In this paper,two factors were taken into consideration based on the available model:the impact of reducing atmosphere on the viscosity of ash particles,and the effect of alkali metals in ash on the particle bonding probability.A comparative study was conducted on the particle deposition phenomenon on the wall surface of heat exchange tube bundles using different combinations of models.Furthermore,the influences of longitudinal pitch and wall temperature were investigated in detail.The results reveal that all particle deposition efficiencies predicted by different modified models increase to a certain extent.Besides,considering the aforementioned two factors together can result in a 22.24%increase in ash deposition efficiency compared to the basic model.The distribution of particle deposition mass on the same row tube wall is inconsistent:the particle deposition mass in the first row mainly occurs between 30°to 150°,with the largest value observed at around 90°;the distribution tends to become increasingly uniform in each successive row as the number of tube rows increases.Moreover,it is suggested that increasing the longitudinal pitch has no significant effect on the ash deposition mass of the first-row tube but leads to a gradual increase in the ash deposition mass on subsequent tubes.Meanwhile,the ash deposition mass of each bundle exhibits a slight increase with rising temperatures.However,this change is not particularly significant due to the complex interplay of various mechanisms influencing the ash deposition process.