【作者】 李健；

【导师】 郭成龙；

【作者基本信息】 中国矿业大学 ， 动力工程及工程热物理， 2024， 硕士

【摘要】 工业废水高效治理在我国“高质量发展”和“双碳”战略实施过程中占有十分重要的地位。其中,蒸发法作为工业废水处理技术的一种,因其高效节能且处理效果好等优点而备受关注。横管降膜蒸发器具有传热系数较高且适应范围广等优势,是蒸发法工业废水处理工艺中的核心设备。由此可见,对横管降膜蒸发流动特性及传热性能的研究将有助于工业废水的高效治理。本文将对横管降膜蒸发器内单个传热单元进行三维数值模拟研究,分析多种因素对传热系数的影响规律。基于数值模拟结果设计加工横管降膜蒸发器,进而完成横管降膜蒸发传热实验平台的搭建。采用纯水作为实验工质开展传热实验研究,探求不同工况下传热系数的变化情况,进而以杂盐溶液作为实验工质来模拟易起泡的含盐废水,得出在不同泡沫特征下传热性能的变化规律。本文主要研究内容及结论如下:（1）对横管管外降膜流动蒸发过程进行数值模拟研究,分析在滴状流和柱状流下喷淋密度、管径和管间距对流动特性及换热性能的影响。结果表明,在滴状流流型下,液膜分布和传热系数呈现出周期性变化的特点。随着喷淋密度的增加,周期时长减小,平均传热系数得以增加;随着管径的增加,传热系数降低;管间距的增加使得液膜运动速度加快,但过大的管间距会引起平均传热系数的减小。在柱状流流型下,液体流动呈现出稳定的柱状流型,平均传热系数维持在稳定区间,换热管外壁面区域根据传热系数的分布情况可划分为冲击区,热发展区和完全发展区。随着喷淋密度的增加,液膜流速增大,传热系数提高,但与此同时,液膜厚度增加,传热系数的增长趋势放缓。管径的减小将使冲击区与热发展区在管面积上的占比变大,进而引起传热系数的升高。管间距的增加也使得柱状流下的传热系数得到提升。（2）设计加工横管降膜蒸发器,搭建横管降膜蒸发传热实验平台,采用纯水作为实验工质,探究了多种因素对传热系数的影响。结果表明,在本实验设定的测试范围内,传热系数随喷淋密度和蒸发温度的增加而增大,但随换热管管内外温差的增加而减小。（3）针对横管降膜蒸发器在易起泡含盐废水处理中的应用,本文将选取含杂质的Na₂SO₄配置不同盐浓度的溶液来作为实验工质开展横管降膜蒸发传热性能研究。结果表明,在不同工况下换热管管外起泡的状态存在显著差异,根据起泡的状态可划分为三类:未充分发展状态、过渡状态和充分发展状态。在未充分发展状态下,杂盐溶液的传热系数一般低于同等工况下的纯水;在过渡状态下,受气泡运动引起的强化换热效应影响,杂盐溶液的换热性能优于纯水;在充分发展状态下,受强烈气泡运动的影响,杂盐溶液的传热系数得到大幅度的提升。本篇论文共有图46幅,表4张,参考文献105篇。更多还原

【Abstract】 Efficient treatment of industrial wastewater holds a crucial position in the implementation of China’s"high-quality development"and"double carbon"strategies.Among them,evaporation method,as a kind of industrial wastewater treatment technology,has attracted much attention due to its advantages of high efficiency,energy conservation,and good treatment effect.Horizontal tube falling film evaporator,with high heat transfer coefficient and wide adaptability,is the core equipment in the evaporation method of industrial wastewater treatment process.Therefore,the research on the flow characteristics and heat transfer performance of horizontal tube falling film evaporation will contribute to the efficient treatment of industrial wastewater.This thesis will conduct a three-dimensional numerical simulation study on a single heat transfer unit in the horizontal tube falling film evaporator,and analyze the influence of various factors on the heat transfer coefficient.Based on the numerical simulation results,the horizontal tube falling film evaporator is designed and processed,and then the horizontal tube falling film evaporation heat transfer experimental platform is built.Pure water is used as the experimental working fluid to carry out heat transfer experimental research,and the changes of heat transfer coefficient under different working conditions are explored.Furthermore,sulphate solution is used as the experimental working fluid to simulate the easily foaming sulphate-containing wastewater,and the change rule of heat transfer performance under different foam characteristics is obtained.The main research contents and conclusions of this thesis are as follows:（1）A numerical simulation study was conducted on the falling film flow evaporation process outside the horizontal tube,analyzing the influence of spray density,tube diameter,and tube spacing on flow characteristics and heat transfer performance under dripping flow and columnar flow.The results indicate that under dripping flow,the liquid film distribution and heat transfer coefficient exhibit periodic changes.As the spray density increases,the period duration decreases and the average heat transfer coefficient increases.As the tube diameter increases,the heat transfer coefficient decreases.An increase in tube spacing accelerates the liquid film’s movement speed,but excessively large spacing can cause a reduction in the average heat transfer coefficient.Under columnar flow,the liquid flow exhibits a stable columnar flow pattern,and the average heat transfer coefficient remains stable.The outer wall surface of the heat exchange tube can be divided into three zones based on the distribution of heat transfer coefficients:impact zone,thermal development zone,and fully developed zone.As the spray density increases,the liquid film flow rate rises,leading to an increase in heat transfer coefficient.However,simultaneously,the thickness of the liquid film also increases,slowing down the growth trend of the heat transfer coefficient.A decrease in tube diameter enlarges the proportion of the impact zone and thermal development zone on the tube surface,resulting in a higher heat transfer coefficient.An increase in tube spacing also enhances the heat transfer coefficient under columnar flow.（2）The horizontal tube falling film evaporator was designed and processed,and an experimental platform for heat transfer in horizontal tube falling film evaporation was established.Pure water was used as the experimental working fluid to investigate the influence of various factors on the heat transfer coefficient.The results showed that within the test range set in this experiment,the heat transfer coefficient increased with the increase of spray density and evaporation temperature,but decreased with the increase of the temperature difference between the inside and outside of the heat exchange tube.（3）To investigate the application of the horizontal tube falling film evaporator in the treatment of easily foaming sulphate-containing wastewater,this thesis selected solutions with different sulphate concentrations of Na₂SO₄ containing impurities as the experimental working fluid to study the heat transfer performance of horizontal tube falling film evaporation.The results indicated that there were significant differences in the bubbling state outside the heat exchange tube under different operating conditions,which could be classified into three categories:underdeveloped state,transitional state,and developed state.In underdeveloped state,the heat transfer coefficient of the sulphate solution was generally lower than that of pure water under the same operating conditions.In the transitional state,due to the enhanced heat transfer effect caused by bubble movement,the heat transfer performance of the sulphate solution was better than that of pure water.In developed state,the heat transfer coefficient of the sulphate solution was significantly improved due to the intense bubble movement.This thesis includes 46 figures,4 tables,and 105 references.更多还原