【作者】 王书中；

【导师】 由世俊；

【作者基本信息】 天津大学 ， 供热、供燃气、通风及空调工程， 2008， 博士

【摘要】 为提高一次能源利用率PER,溴化锂吸收式制冷系统中的热力部件广泛采用真空条件下以水平管束作为承载结构的降膜式热力装置。长期以来,由于水平管束外表面降膜流动与传热传质基础理论体系的缺失,吸收式制冷机的传热计算与结构设计还处于非常粗放的模式之中,提高热力部件性能的研究无从下手。本文在综合分析现有理论研究进展的基础上,搭建了“水平管束降膜流动模态转变实验装置”、“水平管束液滴形成数字图像高速采集实验装置”以及“水平管束界面传递性能实验装置”,开展了对水平管束降膜流动与传热传质过程微观发展机理的初步研究。首次提出了“水平管束降膜动力学”的概念,引入了“界面传递过程”的概念。从吸收式制冷中降膜吸收、降膜蒸发、降膜冷凝、降膜发生四大热力过程共有的动力学特征出发,研究绝热条件下流体在水平管束外表面的降膜流动模态辨识以及模态转变的微观发展机理;引入“界面现象”的概念,把四大热力学过程中共有的“自由界面传热传质过程”统一在“界面传递过程”的概念之中,通过界面现象与水平管束降膜动力学之间的有机结合,形成了“水平管束降膜式热力装置基础理论体系”的基本架构。首次提出单元流体(UF)的概念,实现了从研究宏观统计现象到微观发展机理的转变;首次给出了水平管束单元流体模态转变(UF-MTM:Unit Fluid-Mode Transition Mechinism)图谱,解释了水平管束降膜流动模态从滴状向帘状转变过程中的驱动力及微观发展机理:认为连续液颈促使了滴状向滴柱状的转变、表面波谷到表面波峰的形成促使了顺排柱状流向叉排柱状流的转变、管底悬垂液的存在是相邻单元液柱吸合的前提与源动力、液牙生成和流形分叉现象是单元液柱相互吸合中的必然现象、融合形变促使了柱状向帘状的转变。借助高速摄像机研究了水平管束滴状模态的微观发展机理,发现了液滴生成、长大、拉伸、液颈底部与主液滴破裂、马鞍形表面铺展、液颈自相似收缩、尖锐液颈顶部破裂、卫星液滴生成等一系列极为复杂的拓扑结构;首次提出了RSB (Ratio of tube Spacing to total Breaking length)的重要概念,用于描述管间距与总的破裂长度的比值对液滴形成拓扑结构的影响;首次提出了水平管束液滴形成过程的九个拓扑转变关键相,分析了不同RSB之间液滴形成拓扑转变的差异。基于图像信息处理技术,通过像素坐标系到笛卡尔坐标系的转换、Canny边缘检测、三次样条光滑曲线拟合和自适应Simpson积分,对水平管束滴状和柱状模态的微观机理进行数字化描述,分析了单元液滴表面积与体积随时间的变化规律。通过宏观尺度到微观尺度液滴形成过程的拓扑相似,把水平管束滴状模态纳入到了液滴形成非线性动力学领域,通过量纲理论与相似分析,得到了复杂流体近破裂点处最小液颈的拓扑相似表达式。基于混合水平多因子实验设计和多元因子响应面RSM方法,得到了界面传热系数与界面传质系数的回归方程,搭建了基于Matlab的水平管束降膜式热力装置可视化研究平台。通过本课题的研究,对水平管束降膜动力学特征进行了初步的探讨,为进一步研究降膜式热力装置的界面传递性能奠定了基础。更多还原

【Abstract】 To increase the primary energy ratio(PER), vertical array of horizontal tube bundles under vacuum condition, as one kind of falling film thermal-dynamic device, is used widely in the absorption refrigeration system. For a long time, the heat transfer calculation and structure design of absorption chiller is in rough status at the absence of the study of falling film flow over the horizontal tube bundles and the fundamental theory of heat and mass transfer. For the same reason, research about the enhancement of thermal component performance is hardly to carry out. At the basis of the past research, three experiments were set up to study the falling film flow microcosmic mechanism of different fluids on horizontal tube bundles and the process of the heat and mass transfer. The first experiment is primarily on the falling film flow mode transition on horizontal tube bundles; the second is on the digital graph high speed collection of the droplet deformation on horizontal tube bundles and and the third is on the interface absorption performance on horizontal tube bundles.The concept of horizontal tube bundles falling film dynamics and interface transfer process is proposed for the first time. Based on the common dynamic characteristic of four main thermal processes such as falling film absorption, falling film evaporation, falling film condensation and falling film generation in the absorption chiller, the falling film flow mode transition on the horizontal tube bundles and the microcosmic mechanism of flow mode transition is investigated. By introducing the concept of interface phenomenon, the common characteristic in the four thermal processes of heat and mass transfer over free surface can be concluded to the interface transfer process. By the integration of falling film dynamics and interface phenomenon, the fundamental theory frame of horizontal tube bundles falling film thermal device is built up.Transition from macroscopical statistics to microcosmic mechanism of horizontal tube bundles is realized by the concept of Unit Fluid. The map of Unit Fluid-Mode Transition Mechanism (UF-MTM) on horizontal tube bundles is given for the first time. The microcosmic mechanism that drives the flow mode from droplet to sheet is interpreted. The main results are that the transition from droplet to columns mode is driven by the continuous liquid neck; the transition from inline columns to stagger column flow is driven by the formation of the surface crest; the pendant liquid under the horizontal tube is the source force of the merging between the adjacent columns; the generation of the liquid tooth and the stagant point is the inevitable phenomenon during the adjacent column merging process; the transition from columns to sheet mode is driven by the merging deformation.The microcosmic development mechanism of droplet formation process on horizontal tube bundles is investigated using high speed video. A series of complex topology structures such as the droplet generation ,growing up, elongation, breakup of the main droplet at the bottom of the liquid neck, the saddle extension on the tube surface, the self-similar shrink of liquid neck, the breakup at the top of the aculeate liquid neck, the generation of the satellite droplets etc. are observed. The innovative significant concept of RSB is proposed to describe the effect of the Ratio of tube Spacing to total Breaking length on the topology structure during droplet formation. The nine important topology transition phases of droplet formation on horizontal tube bundles are proposed for the first time and the topology transition difference of droplet formation under various RSB is analyzed.Based on the graphic information treatment technology, the digital description of microcosmic mechanism of the droplet and columns mode on horizontal tube bundles is presented and the variation of surface area and the volume of unit droplet from its existence duration is analyzed by using the methods of conversion of the pixel coordinate system to the Cartesian coordinate system, the edge detection, the cubic spline smooth curve fitting and self-adaptive Simpson integral, Through the topology similarity analysis of droplet formation process from the macroscopic dimension to microcosmic dimension, the droplet mode on the horizontal tube bundles is involved in the multifarious droplet formation nonlinear dynamics scopes. The topology similar expression near the breakup point of the minium liquid neck of complex fluid is introduced using dimension theory and similar analysis.Based on the mixing level multi-factorial experiment and the multi-factorial Response Surface Methodology, the regression equation of interface heat transfer and mass transfer coefficients is educed. The visualization study platform based on Matlab of horizontal tube bundles falling film thermal-dynamic device has been set up.Throgh above study, the primary discuss on falling film dynamic characteristic of horizontal tube bundles is carried out, the basis of next study about the interface transfer performance of falling film thermal-dynamic device is thereforce established.更多还原