基于人工神经网络的滴膜共存冷凝传热模型的研究

为了研究影响滴膜共存冷凝传热特性的因素,如滴膜区间面积比、滴膜相对位置、表面分割方式,表面过冷度等对冷凝传热的特性共同作用,本文应用人工神经网络技术,建立表面分割数、滴膜区面积比、凝液环数、表面过冷度与强化传热比之间的综合评价预测模型。结果表明,基于Matlab语言的人工神经网络模型具有较高的预测准确率及泛化能力,能够很好的评价和预测不同条件下的冷凝传热特性。     

纳米结构表面上部分润湿液滴合并诱导弹跳的理论研究

部分润湿液滴是适宜纳米结构表面上滴状冷凝传热的主要载体,研究纳米结构参数与部分润湿液滴合并弹跳之间的关系有重要意义,本文依据冷凝液滴生长过程中能量增加最小的原理来判断其是否为部分润湿状态,并根据液滴合并前后的体积和界面自由能守恒,确定了合并液滴的初始形状,进而对合并液滴变形过程的动力学方程进行了求解,结果表明:部分润湿冷凝液滴仅在纳米柱具有一定高度、直径间距比较大的表面上形成,而当纳米柱高度过低、直径间距比小于0.1时则形成完全润湿的冷凝液滴;液滴合并后能否弹跳与纳米结构参数紧密相关,仅在纳米柱较高、直径间距比适宜的表面上,部分润湿液滴合并后才能诱发弹跳;液滴尺度及待合并液滴间的尺度比对合并弹跳也有重要影响;多个部分润湿液滴合并后由于具有更多的过剩界面自由能而比两个液滴合并更容易诱发弹跳,本模型对纳米结构表面上冷凝液滴是否合并诱发弹跳的计算结果与绝大部分实测结果相一致,准确率达到95%。     

纳米结构表面上冷凝液滴的生长模式及部分润湿液滴的形成机制

分析并计算了纳米结构表面上冷凝液滴按照不同途径长大的过程中液滴能量的增加速率, 并以能量增加最小为判据来确定液滴的生长途径. 结果表明, 纳米结构内形成的冷凝液斑在初期按接触角(CA)增加的模式生长时, 其能量增加速率远低于其它模式, 于是, 初始液斑先按增大接触角、并保持底面积不变的模式生长, 直至液滴达到前进角状态. 此后, 沿接触角增加的模式长大所导致的能量增加速率开始远高于其它生长模式, 于是液滴三相线开始移动, 底面积开始增加, 但接触角保持不变. 液滴所增加的底面积可以呈润湿或复合两种状态, 分别形成Wenzel 液滴及部分润湿液滴, 前者的表观接触角一般小于160°, 而后者则明显大于160°. 液滴的生长模式及其润湿状态均与纳米结构参数密切相关, 仅当纳米柱具有一定高度、且间距较小时, 冷凝液滴才能呈现部分润湿状态. 最后, 本模型对纳米结构表面上冷凝液滴润湿状态的计算结果与绝大部分实测结果相一致, 准确率达到91.9%, 明显高于已有公式的计算准确率.     

Analysis of meniscus beneath metastable droplets and wetting transition on micro/nano textured surfaces

The expressions of interface free energy(IFE) of composite droplets with meniscal liquid–air interface in metastable state on micro/nano textured surfaces were formulated. Then the parameters to describe the meniscus were determined based on the principle of minimum IFE. Furthermore, the IFE barriers and the necessary and sufficient conditions of drop wetting transition from Cassie to Wenzel were analyzed and the corresponding criteria were formulated. The results show that the liquid–air interface below a composite droplet is flat when the post pitches are relatively small, but in a shape of curved meniscus when the piteches are comparatively large and the curvature depends on structural parameters. The angle between meniscus and pillar wall is just equal to the supplementary angle of intrinsic contact angle of post material. The calculations also illustrate that Cassie droplets will transform to Wenzel state when post pitch is large enough or when drop volume is sufficiently small. The opposite transition from Wenzel to Cassie state, however, is unable to take place spontaneously because the energy barrier is always positive. Finally, the calculation results of this model are well consistent with the experimental observations in literatures for the wetting transition of droplets from Cassie to Wenzel state.     

Molecular dynamics simulation of interaction between nanorod and phospholipid molecules bilayer

Natural and artificially prepared nanorods' surfaces have proved to have good bactericidal effect and self-cleaning property. In order to investigate whether nanorods can kill the enveloped virus, like destroying bacterial cell, we study the interaction between nanorods and virus envelope by establishing the models of nanorods with different sizes as well as the planar membrane and vesicle under the Dry Martini force field of molecular dynamics simulation. The results show that owing to the van der Waals attraction between nanorods and the tail hydrocarbon chain groups of phospholipid molecules, the phospholipid molecules on virus envelope are adsorbed to nanorods on a large scale. This process will increase the surface tension of lipid membrane and reduce the order of lipid molecules, resulting in irreparable damage to planar lipid membrane. Nanorods with different diameters have different effects on vesicle envelope, the larger the diameter of nanorod, the weaker the van der Waals effect on the unit cross-sectional area is and the smaller the degree of vesicle deformation. There is synergy between the nanorods in the nanorod array, which can enhance the speed and scale of lipid adsorption. The vesicle adsorbed in the array are difficult to desorb, and even if desorbed, vesicle will be seriously damaged. The deformation rate of the vesicle adsorbed in the nanorod array exceeds 100%, implying that the nanorod array has a strong destructive effect on the vesicle. This preliminarily proves the feasibility of nanorod array on a surface against enveloped virus, and provides a reference for the design of corresponding nanorods surface.