摘要
换热器的工程应用广泛,但换热面结垢问题会造成管道堵塞,能耗增加,为经济有效地解决该问题,将固液两相流除垢技术应用到换热器的防、除垢中。通过数值模拟方法,研究了沙粒对管道壁面的剪切力、壁面磨损及传热系数的提升情况。研究发现,随着流速的增加固体颗粒对壁面的磨损率先降低后增加,沙粒对管道的最大的磨损率出现在90°弯头处且最大磨损率随着沙粒直径的变大增长明显;在未加入沙粒时,正常换热器流速下,管道内壁面所受的切应力平均为16.8 Pa,加入沙粒后壁面剪切应力平均值为158.4 Pa,超过污垢所能承受的100 Pa剪切力,可有效除垢。在相同的速度下,在流速0.6~2 m×s^(-1),加入颗粒后,其表面传热系数的提升为2.6%到23%。以畅通式污水换热器作为流态化除垢强化换热实验台,对换热器流态化除垢强化换热进行实验研究。实验研究表明,将固液两相流流速提升到0.87 m×s^(-1)时,成功实现了95%的直径为2~3 mm的沙粒在线循环清洗,与理论计算的0.85 m×s^(-1)扬动流速几乎吻合。随着沙粒体积分数的增大,其除垢效果越好;沙粒体积分数为6%时,运行24 h后,传热系数提高了25.6%。当污水流速为扬动流速且沙粒体积分数为4%时,既可减小沙粒对壁面的磨损,又可保证高效除垢效率。
Heat exchangers are extensively used but fouling problems may cause heat transfer tube clogging andenergy consumption increase.Therefore,a solid-liquid two phase flow defouling technique was applied toprevent and remove fouling on heat exchanger wall.Effects of sand particles on shear stress,erosion andpromotion of heat transfer coefficient were studied through simulation.The results show that the maximumerosion decreases first and then increases with the increase of flow rate.The highest erosion rate appears at90°corners.The maximum erosion increases quickly with the increase of sand concentration and diameter.Thesimulation results also show that the shear stress at pipe wall without sand is16.8Pa.However,thearea-weighted average shear stress on the pipe wall is158.4Pa after adding sand into heat exchanger pipes,which is enough to remove fouling.When the flow rate increases from0.6to2m.s-1at the same workingvelocity,the heat transfer coefficient increases from2.6%to23%after adding sands to the heat exchanger.Asewage heat exchanger was used as an experimental platform,and the solid-liquid fluidized defoulingtechnology was studied.The experimental results show that sands with diameter of2mm can be fluidized if thesewage water flow rate is over0.87m.s-1.The sand recycling efficiency is95%.4%volume fraction of sand isenough to guarantee high removal efficiency and also reduce wall abrasion.
作者
陈霄
杨启容
吴荣华
王勇
CHEN Xiao;YANG Qi-rong;WU Rong-hua;WANG Yong(School of Electromechanic Engineering, Qingdao University, Qingdao 266071, China)
出处
《高校化学工程学报》
EI
CAS
CSCD
北大核心
2017年第4期818-826,共9页
Journal of Chemical Engineering of Chinese Universities
基金
国家"十二五"科技支撑计划项目(2014BAJ02B03)
山东省自然科学基金项目(ZR2015EM003)
关键词
污水换热器
流态化除垢
强化换热
磨损
sewage heat exchanger
fluidization descaling
enhanced heat transfer
abrasion
