【作者】 王红波；

【导师】 周云龙；

【作者基本信息】 东北电力大学 ， 热能工程， 2011， 硕士

【摘要】 上世纪90年代初期,为适应可持续发展和高新技术发展的需要,微化工技术成为化工领域内多学科交叉的科技前沿领域。由于相对常规化工过程具有高效性、快速性、灵活性、轻便性、易控制、及高度集成等优点,自MEMS/NEMS概念提出以后,在世界范围内有关微小通道气液两相流动特性研究迅速成为人们关注的热点。国内外公开发表的相关学术论文也层出不穷,但是由于不同的作者以及采用的研究方法等不同,导致得出的结论差异很大。为避免不同的实验系统对研究结果造成差异,本文在同一实验系统上对水力直径均为1.15mm的矩形和正三角形小通道内氮气-水气液两相流动特性进行可视化研究。本文主要从流型、截面含气率和压降这三个层面上对这两种小通道内的气液两相流动进行对比分析研究。本文辅助高速摄像机在表观液速0.01m/s-5m/s,表观气速0.1m/s-30m/s范围内对两种非圆截面小通道内的氮气-水气液两相流流型进行可视化观察。在气液两相垂直向上流动中,矩形小通道内观察到了分散泡状流、弹状流、搅拌流和环状流四种流型;正三角形小通道内观察到了分散泡状流、毛细泡状流、弹状流、拉长的弹状流、搅拌流和环状流等典型流型,通过对比分析得出小通道的截面形状对流型的形成及转变有较大影响。同时本文在水平方向上对矩形小通道内气液两相流动进行了实验研究,在较低的两相表观速度下,观察到了一般在微小通道内极少出现的分层流动,同时也观察到了分散泡状流、毛细泡状流、弹状流、拉长的弹状流、搅拌流和环状流。对于含气率的研究,本文针对小通道内气泡之间相互无遮掩的优势,采用数字图像处理技术对小通道内的气泡进行去噪处理后,进行二值化、边缘检测和区域填充等处理,然后根据不同的流型特征提出的假想的三维气相体积模型进行体积含气率的计算,并结合数据拟合得到了截面含气率的计算公式。最后,根据数字图像处理技术检测计算得到的截面含气率进行摩擦压降的分析计算,将计算结果同均相流模型和分相流模型预测值进行比较发现:对于矩形小通道垂直向上流动,已有的压降模型均不能较好的预测本文实验结果,而对于正三角形小通道垂直向上流动,均相流模型在±20%内能较好的预测其压降特性。因此结合实验数据,对Chisholm模型进行了修正,修正后的两相压降模型能较准确预测矩形小通道内气液两相流动压降变化。更多还原

【Abstract】 The early 90s of last century, In order to meet sustainable development and the needs of high-tech development,Micro-chemical technology was becoming interdisciplinary field of science and technology frontier within the chemical industry. Compared with conventional chemical process, Micro-chemical technology is effective, fast, flexible, lightweight, easy control, and of highly integrated.Since the concept of the MEMS / NEMS was put forward, characteristics of two-phase flow in small channels quickly became the focus of attention all over the world. Although related papers published at home and abroad are endless,different authors use different research methods,which lead to a variety of conclusions.In order to avoid differences of experimental results in different experimental systems, characteristics of nitrogen-water two-phase flow in small rectangular channel and small triangular channel with diameter of 1.15mm are studied by visualization method in the same experimental system. the flow pattern, void fraction and pressure drop of gas-liquid two-phase flow in the two mini-channels are researched by comparison.Within the superficial liquid velocity 0.01m/s-5m/s and the superficial gas velocity 0.1m/s-30m/s, Flow patterns of nitrogen-water two-phase flow in two small non-circular cross-sectional channels were obtained by High-speed camera.In the gas-liquid two-phase flow vertical upward direction, dispersed bubble flow, slug flow, churn flow and annular flow were observed in small rectangular channel,and dispersed bubble flow, capillary bubbly flow, slug flow, elongated slug flow, churn flow and annular flow were observed in small triangular channel; By comparison, we know that the section shape of small channel has a great impact on flow pattern transition.At the same time , flow patterns of two-phase flow in small rectangular channel were studied experimentally in the horizontal direction, In the lower two-phase superficial velocity, stratified flow was observed which rarely occurs in mini-channels, and dispersed bubble flow, capillary bubbly flow, slug flow, elongated slug flow, churn flow and annular flow were also observed in this direction.For the study of void fraction, A method about calculating volume fraction of slug flow was proposed in this paper. According to nonoverlapping among slug bubbles, the flow pattern images were processed by image processing techniques, noise elimination、the edge detection、binarization、area designation and picture fills. According to the proposed three-dimensional volume of gas volume model, volume fraction was obtained.Finally, void fraction which was obtained by Digital Image Processing was used to calculate pressure drop, comparison of the calculated results with the homogeneous flow model and the separated flow model, we find that for two-phase flow in small vertical rectangular channel, the calculated results can not be predicted by the existing pressure drop model and for two-phase flow in small triangular channel, Homogeneous flow model can better predict the pressure drop characteristics within±20%. Therefore, according to experimental data, modified Chisholm model can accurately predict two-phase flow pressure drop in the small rectangular channel.更多还原