【作者】 刘征；

【导师】 于志家；

【作者基本信息】 大连理工大学 ， 化学工程， 2010， 硕士

【摘要】 本文对水在超疏水微通道内的传递特性进行了研究,研究内容包括：超疏水微通道传热研究、传热模型数值模拟、流动模型数值模拟。在制备了铝基超疏水表面的基础上,研究了超疏水微通道的传热特性。实验结果表明：超疏水微通道的表面传热系数要略低于超亲水微通道,超疏水表面的固-液界面上存在一层由微纳米气泡构成的气膜,气膜的存在显著降低了水与壁面之间的剪切力,降低了水流过微通道时的摩擦阻力系数,产生了滑移,但由于空气热导率低,一定程度上阻碍了传热。将“无滑移边界条件”的静止气泡层的导热考虑在内,计算了含有空气层的超疏水表面微通道的表观传热系数,发现其表观传热系数低于超疏水表面的实验值。考虑了超亲水与超疏水传热热阻之差,本文计算了差值相当于的空气层厚度,结果均小于600nm,然而超疏水表面凹槽属于微米级,必然存在强化传热的机制。根据实验结果,建立了超疏水表面凹槽传热模型,模拟了超疏水表面凹槽的速度场和温度场,并计算出了超疏水表面凹槽内部传热系数分布,结果表明分布规律符合场协同强化传热原理。分别模拟计算了半径为2μm,3μm和4μm凹槽的传热系数与Nu数。结果表明,计算得到的传热系数随着凹槽尺寸的减小而增大。接着根据模拟结果计算出了内径为0.68mm超疏水微通道的表观传热系数,结果均比超亲水传热系数并考虑与凹槽具有相同厚度的静止空气层的表观传热系数大。而由2μm凹槽所得到的传热系数与实验值吻合性较好,最大相对误差不超过2%。接着考察了内径为0.72mm的超疏水微通道的传热系数,也具有同样的规律。对超疏水微通道流动进行了数值模拟。根据流动在壁面上产生滑移的特点建立了流动模型,模拟了在滑移壁面与无滑移壁面速度场分布的特点,并对流动的相关特性也进行了考察。考察了无滑移壁面与滑移壁面的压差,结果表明具有滑移壁面的微通道由较小的压降。分析了无量纲压降百分比随着Re数的增加而减小,与实验趋势一致。根据推导出的圆管内滑移长度的表达式计算结果的综合分析,表明随着Re数的增加,壁面滑移效应在减小,滑移长度也能反映这种滑移效应。又对模拟的摩擦系数f与Po数进行了考察,进一步说明了滑移壁面的减阻效应。更多还原

【Abstract】 Water transfer characteristics in super-hydrophobic micro-tubes is studied. Emphasizes are put on heat transfer characteristics, numerical simulation of heat transfer and water flow in super-hydrophobic micro-tubes.With super-hydrophobic surface successfully fabricated in aluminous micro-tubes, heat transfer characteristics in it is researched. It is found that the apparent heat transfer coefficient of super-hydrophobic micro-channels is a little lower than that of super-hydrophilic micro-tubes. The analysis result is that the air-layer existing in the micro-nanostructures of the super-hydrophobic surface decreases flow resistance evidently and blocks heat transfer. Considering difference between heat resistance of super-hydrophobic and super-hydrophilic micro-tubes, the equivalent thickness of air layer is calculated in this paper. The result is that it is less than 600nm, however, the scale of cave on the super-hydrophobic surface investigated in SEM is micron-sized. Therefore, the enhancement of heat transfer mechanism exists in super-hydrophobic micro-tubes.With heat transfer in the super-hydrophobic micro-tubes investigated, heat transfer for caves on the super-hydrophobic surface is modeled. With the inner flow field and temperature field analyzed, heat transfer coefficient distribution in the cave is found to be explained in field synergy principle. Heat transfer coefficient of the cave with 2μm,3μm and 4μm-semidiameters is simulated and it is found that heat transfer coefficient is increasing with the decrease of cave scale. According to experimental heat transfer coefficient of super-hydrophilic micro-tube with 0.68mm diameters, heat transfer coefficient of super-hydrophobic micro-tube is computed, and result is that heat transfer coefficient of super-hydrophobic is higher than that of super-hydrophilic micro-tube considering heat conductance of air layer of which thickness equals to the cave scale. The simulate heat transfer coefficient of the cave with 2μm agree with experiment results well, and the maximum relative error is less than 2%. The result of super-hydrophilic micro-tube with 0.72mm diameters have the same trend with that of 0.68mm diameters.Water flow in super-hydrophobic micro-tubes is numerical simulated. Flow model is established on the basis of slip velocity existing on the wall and inner velocity field in tubes is simulated on the slip wall and no-slip wall and flow characteristics is analyzed. The dimensionless pressure drop is decreasing with Reynolds number (Re) increasing, and the trend is the same with experimental results. The slip effect is decreasing with Re number increasing. With the deduced expression for slip length in circular tubes analyzed, the slip effect weakens with Re number increasing, and slip length can reflect the slip effect. Finally friction factor and Poiseuille number (Po) are computed by simulate results, which prove the resistance reduction on slip wall.更多还原