疏水性对微通道流动与换热的影响

发布时间：2018-08-27 19:47

【摘要】：在微纳米尺度范围内,由于通道内显著的表面效应和极高的面体比使过高的流动阻力成为微纳米系统应用中难以解决的瓶颈问题。因此,探求可靠有效的减阻方法无疑具有重要的工程价值。目前针对微肋片内部流动的研究以及超疏水表面通道减阻的研究较多,但针对微管和微柱群内部疏水表面减阻的研究,尤其微柱群内部表面不同接触角与微柱内部流动减阻关系的研究还很少。文章首先系统论述了疏水性薄膜和疏水性微通道的制备方法,并对去离子水流经疏水性微管的流动减阻特性进行实验研究。同时,对去离子水横掠微针肋阵列热沉的流动和换热特性进行了系统分析。概括起来,本论文主要研究内容以及结论如下：(1)开展了超疏水性微管的制备以及微通道内减阻规律的研究。首先在改性有机硅稀溶液中加入2%全氟辛基氟硅烷以及添加剂配制超疏水液,采用滴定法在内径分别为0.447mm、0.728mm和0.873mm的三种微铜管内壁涂覆微米级超疏水性涂层,可使其水滴表观接触角超过150。。同时建立微管内流动特性实验系统并对超疏水性处理的减阻规律进行了系统研究,分别测量了Reynolds数在100-3000范围内,去离子水流经疏水处理前后微铜管的内部摩擦阻力系数f。研究表明,对微管内壁面的超疏水性处理显著降低了微管内的流动阻力,且影响随微管内径的增加而增大,实验范围内流动阻力系数最大降幅可达29.08%；超疏水涂层使得微管内的流动转捩现象出现滞后,且转捩Re随微管管径增加而略有增大。(2)开展了疏水性微针肋热沉的制备以及疏水性对微针肋热沉流动特性影响的研究。采用向改性有机硅稀溶液中加入2%全氟辛基氟硅烷以及微纳米粒子的方法制备疏水液,并通过改变微纳米粒子添加量调控疏水涂层的表观接触角,可分别制取接触角为99.5。、119.5。和151.5。(水为工质)的疏水表面。并通过实验测试了微针肋阵列热沉的流动阻力和压力降。结果表明,相同雷诺数(Re)下流道内摩擦因子(f)比疏水处理前有明显下降,主要是由于疏水性界面的张力作用所致；相同Re下,接触角越大,疏水涂层双重结构中微纳米突起间距越小,去离子水与空气接触面增大,使得摩擦阻力减小；随Re增加,三种涂层实验段内的减阻率均不断降低。(3)开展了疏水性对微针肋阵列热沉的换热特性影响的研究。对接触角分别为83。、99.5。、119.50和151.50的椭圆形微肋阵传热特性进行实验研究,结果表明：加热功率为100w时,较小的流量下,流量的改变对其底板表面温度影响较大,在较大流量时,流量改变对其影响较小；随着接触角的增大,相同Re下对流换热系数减小；不同接触角椭圆形微针肋热沉的Nu均随着Re的增大而增大；接触角越大导致工质与壁面接触越差,换热效果变差。三种涂层实验段内的减阻率均优于对换热效果的影响。本文对去离子水流经疏水性微管的流动减阻特性进行实验研究。同时,对去离子水横掠微针肋阵列热沉的流动和换热特性进行了系统分析。验证了疏水性涂层在微通道内应用的可行性,发展了一种微通道内减阻新方法,相关研究成果为微通道减阻提供了理论支撑和技术支持,是对现有现有微通道内流动与换热研究的有效补充与完善。
[Abstract]:In the micro-nano scale, because of the remarkable surface effect in the channel and the extremely high surface ratio, the excessive flow resistance becomes the bottleneck problem which is difficult to solve in the application of micro-nano systems. Therefore, it is undoubtedly of great engineering value to explore reliable and effective drag reduction methods. There are many researches on the drag reduction of surface channels, but there are few researches on the drag reduction of hydrophobic surfaces in micro-tubes and micro-columns, especially on the relationship between the different contact angles of the inner surface of micro-columns and the drag reduction of the inner flow of micro-columns. The flow and heat transfer characteristics of microneedle-fin array heat sink swept by deionized water are systematically analyzed. In summary, the main contents and conclusions of this paper are as follows: (1) The preparation of superhydrophobic microtubules and the drag reduction in microchannels are studied. The super-hydrophobic liquid was prepared by adding 2% perfluorooctyl fluorosilane and additives into the dilute solution of organosilicon. The super-hydrophobic coatings were coated on the inner walls of three kinds of micro-copper tubes with inner diameters of 0.447 mm, 0.728 mm and 0.873 mm respectively by titration method. The apparent contact angle of water droplets exceeded 150%. The drag reduction law of water treatment was systematically studied. The internal friction coefficient f of micro-copper tube was measured before and after deionized water treatment in the range of Reynolds number 100-3000. The results showed that the superhydrophobic treatment of the inner surface of micro-tube significantly reduced the flow resistance in micro-tube, and the effect increased with the diameter of micro-tube. With the increase of the diameter of the microtubule, the maximum decrease of the flow resistance coefficient was 29.08%. The superhydrophobic coating delayed the flow transition in the microtubule, and the transition Re increased slightly with the increase of the diameter of the microtubule. (2) The preparation of hydrophobic microneedle fin heat sink and the effect of hydrophobicity on the flow characteristics of microneedle fin heat sink were studied. Hydrophobic solution was prepared by adding 2% perfluorooctyl fluorosilane and micro-nano-particles into dilute organic silicon solution. The hydrophobic surfaces with contact angles of 99.5, 119.5 and 151.5. (water as working fluid) were prepared by adjusting the amount of micro-nano-particles and adjusting the apparent contact angle of hydrophobic coatings. The results show that the friction factor (f) in the runner with the same Reynolds number (Re) decreases significantly compared with that before the hydrophobic treatment, mainly due to the tension effect of the hydrophobic interface; the larger the contact angle, the smaller the nano-and micro-bulge spacing in the double structure of the hydrophobic coating, and the larger the contact surface between deionized water and air. The friction resistance decreases and the drag reduction rate decreases with the increase of Re. (3) The influence of hydrophobicity on the heat transfer characteristics of microneedle fin array heat sinks is studied. The heat transfer characteristics of elliptical microfin array with contact angles of 83., 99.5., 119.50 and 151.50 are studied experimentally. The results show that the heating power is 100w. When the contact angle increases, the convective heat transfer coefficient decreases at the same Re; when the contact angle increases, the heat sink of elliptical micro-needle fins with different contact angles increases with the increase of Re; when the contact angle increases, the heat sink of working medium and wall increases with the increase of Re; when the contact angle increases, the heat sink of the elliptical micro-needle fin increases with the increase of Re; The worse the contact, the worse the heat transfer effect. The drag reduction rate of the three coatings is better than that of the heat transfer effect. In this paper, the drag reduction characteristics of deionized water flowing through hydrophobic microtubules are studied experimentally. The feasibility of coating application in microchannels has led to the development of a new method for drag reduction in microchannels. Relevant research results provide theoretical and technical support for drag reduction in microchannels, and are an effective complement to the existing research on flow and heat transfer in microchannels.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK124

【参考文献】