烧结矿立式冷却装置内颗粒特性和气流阻力特性研究

发布时间：2018-03-29 06:05

本文选题：烧结矿立式冷却　切入点：余热回收　出处：《浙江大学》2016年博士论文

【摘要】：烧结矿立式冷却作为钢铁工业中一种新型的烧结余热回收方式,由于高密封性和高余热回收率引起了研究者的广泛关注。其中的气固流动和传热特性是关系装置可行性的关键问题之一。本文对烧结矿立式冷却装置内的颗粒特性和气体流动展开实验研究,在通过实验手段获取完整而精确的烧结矿颗粒特性及热物性参数的基础上,对气固流动涉及的烧结矿填充床内的气流阻力特性展开全面而深入的研究。对工业烧结矿颗粒进行了基础的结构和热物性表征,成分分析后得出烧结矿试样为碱度1.175的自熔性烧结矿,介观孔径呈现出15-40μm和160-250μm范围内积聚分布的特点;对温度至200℃范围的比热进行了测量,通过外延插值揭示了比热与温度之间的幂函数规律；测量得到的烧结矿颗粒有效导热系数随孔隙率(0.12-0.24)的增加而减小,应用Sierpinski地毯分形模型可以实现烧结矿颗粒在0.036-0.326孔隙率范围内的多尺度孔隙结构建模,并对烧结矿有效导热系数精确预测,平均相对误差为9.72%。对床径比为7-35的烧结矿填充床和用作参照的床径比为6-22的玻璃球填充床阻力特性进行实验测量,研究了壁面效应的影响：壁面引起的近壁环形高空隙率效应在低床径比下起主要作用,壁面粘滞效应在床径比小于40的较大数值下作用增强；颗粒的不规则形态对填充床内的流动状态起主要作用,使得壁面效应对烧结矿填充床流态转变临界速度无显著影响；拟合系数为填充床参数函数的Raichura公式(Exp. Heat Transfer 12 (1999) 309)能够较好地预测含壁面效应的烧结矿和玻璃球填充床气流阻力特性,为此进一步提出了改进参数的Raichura公式,对烧结矿和玻璃球填充床的预测误差小于17%,且能够有效反映壁面效应不同方面的影响机理。对不同比例混合的30-40 mm、40-50 mm和50-60mm烧结矿填充床的气流阻力特性进行实验研究,揭示了粒度分布对烧结矿填充床堆积特性和气流阻力影响：粒度混合导致填充床空隙率的减小,加剧了烧结矿填充床的不均匀性,使得填充床流态转变提前,临界速度减小；混合粒度填充床的壁面修正阻力因子比单一筛分粒度偏小,惯性项和粘性项系数均偏小,且系数随床径比变化的随机性增大,惯性项系数与单一粒度烧结矿颗粒变化趋势不一致。通过实验方法进一步对光滑玻璃球、圆柱木块、光滑不规则汉白玉、粗糙不规则碎石和粗糙不规则且表面含孔隙烧结矿的填充床阻力特性进行对比研究,探索颗粒形状对填充床气流阻力特性的影响。研究发现,随着颗粒越来越不规则,填充床内流态随壁面效应的变化规律越来越不明显,流态转化的临界速度主要受颗粒形状影响；fv=A+BRemn形式公式能够对高雷诺数下各种颗粒的气流压降进行简单而有效的预测,预测最大误差为12%-15%；借助Raichura公式,壁面效应引起的粘滞阻力在粘性项中所占的份额随着颗粒形状因子的增加而增加并趋近于一恒定值,壁面粘滞阻力在规则颗粒填充床中作用更大；当形状因子由1逐渐减小至0.6时,壁面效应引起的填充床近壁面高空隙率“环形区”范围在减小,壁面对惯性效应的影响逐渐减小；目前Raichura公式的拟合参数不能反映形状因子在0.6-0.8范围内的近壁面高空隙率“环形区”的变化,需要进一步提升壁面修正惯性系数中的常数参量对非球形颗粒的适用性。
[Abstract]:In this paper , the characteristics of gas - solid flow and heat transfer characteristic are studied in this paper . The characteristics of gas - solid flow and heat transfer characteristic are studied in this paper .
The effective thermal conductivity of the sintered ore particles is reduced with the increase of porosity ( 0.12 - 0.24 ) . The fractal model of Sierpinski carpet can be used to model the multi - scale pore structure in the range of 0.036 - 0.326 porosity . The effect of wall effect is studied .
The irregular shape of the particles plays a major role in the flowing state of the packed bed , so that the wall effect has no significant influence on the critical speed of the flow state transition of the sintering ore packed bed ;
The fitting coefficient is the Raichura formula of the packed bed parameter function ( Exp . Heat Transfer 12 ( 1999 ) 309 ) can better predict the flow resistance characteristic of sintering ore and glass ball packed bed with wall effect .
The influence of particle shape on the flow resistance of packed bed is investigated . The results show that , as the particles are more and more irregular , the flow state of packed bed is more and less obvious with the wall effect , and the critical velocity of flow state transition is mainly influenced by particle shape .
The formula can predict the airflow pressure drop of various particles under high Reynolds number simply and effectively , and the predicted maximum error is 12 % -15 % .
With the Raichura formula , the proportion of viscous drag caused by wall effect increases with the increase of particle shape factor and approaches a constant value .
When the shape factor is gradually reduced from 1 to 0.6 , the high void ratio of the near wall surface of the packed bed caused by the wall effect is reduced , and the influence of the wall facing the inertia effect is gradually reduced ;
At present , the fitting parameters of the Raichura formula do not reflect the variation of the shape factor in the range of 0.6 - 0.8 and the annular region with high void ratio , and the applicability of the constant parameter in the wall surface correction inertia coefficient to the non - spherical particles needs to be further improved .

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TK124

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