Anisotropic Wettability of Biomimetic Micro/Nano Dual‐Scale Inclined Cones Fabricated by Ferrofluid‐Molding Method

Learning from nature, a series of cone‐shaped structures resembling trichomes of plants are fabricated by ferrofluid molding to understand the influence of geometry on wettability. Experimentally, ferrofluid microdroplets are generated under an external magnetic field, and their shape can be changed from right cones into oblique cones by tilting the external magnetic field. Followed by hard molds made with UV‐curable tri(propylene glycol) diacrylate, polydimethylsiloxane microcones with different inclination angle (θ) are subsequently generated. Nickel thin film is deposited onto the microcones to form micro/nano dual‐scale structures. The largest contact angle (CA) is obtained in nickel‐deposited right cones (CA = 163.1° ± 2.5°). Anisotropic wettability is exhibited in oblique cones and the retention forces in the pin and release directions differ up to 12 μN (cones θ = 50°). As explained by a model as a function of the inclination angle of the cone structures, the contact and retention forces of droplet move in pin and release directions exhibit considerable differences. Results suggest the inclination of the trichomes assist the balance between repellency and retention of water in a direction‐selective manner.     

磁流体薄片中聚焦激光束对交流磁场的相位独立响应

报导了磁流体薄片中聚焦激光束在探测50Hz交流磁场时产生与磁场相位无关响应的效应。聚焦于并通过磁流体薄片的633nm激光束的偏转角仅与交流磁场的幅度相关。为了探寻其机理，还研究了磁流体中聚焦激光束对开／关磁场或激光的瞬态响应。提出了基于磁熵守恒的磁流体中磁性粒子密度再分布正反馈模型来解释这一效应。这一模型也可以预 磁流体中一种磁－热失稳现象。     

Visualization of pool boiling heat transfer of magnetic nanofluid

To increase heat transfer, ferrofluids have been utilized to study the effective parameters of pool boiling. Changes and possible enhancement of pool boiling heat transfer of magnetic fluids is a function of magnetic field and concentration of nanoparticles. To the best knowledge of the authors, no systematic experiments have been conducted to visualize the phenomena during the boiling of ferrofluids with different concentrations. In this study an experimental investigation has been conducted, by designing and fabricating a novel hele‐shaw vessel with glass sides, to explore via visualizations some details in the pool boiling of ferrofluids. Boiling patterns of ferrofluids at various concentrations have been visualized –both in the presence of a constant magnetic field and without any magnetic field. Pure water tests were performed as a baseline, and the experimental program has been conducted at four different concentrations, namely 30, 40, 50, and 500 ppm. The primary focus of the visualization is to study how different concentration of ferrofluid affects the boiling ebullition cycle through a high‐speed camera. The results showed that in the boiling process of ferrofluids with a low concentration (10 to 50 ppm), the rising bubbles lead to enlarge the active nucleation sites and create cavities. The formation of cavities changes the solid layer of the surface to a porous medium and enhances the wettability of the surface and boiling heat transfer coefficient. In the ferrofluid boiling with high concentration (500 ppm), bubbles rising is hindered by nanoparticles.     

磁性流体密封系统的试验研究

针对如何保证高性能磁源，防止漏磁，准确注入磁流体量以及如何保证密封间隙误差为最小。设计了磁流体静密封统系统试验台，加工了实验试件，验证了齿距，磁化强度，径向间隙，磁流体的注入量等参数对密封耐压能力的影响，最后，对实验现象和结果进行了详细的分析。     

国外铁流体换能器的研究情况

本文简要评述了国外铁流体换能器的研究情况,分析了铁流体换能器研究背景以及它的工作原理,提供了美国海军研究所所研制的两种铁流体换能器的设计方案,讨论了铁流体换能器的特点.文章对我国研制铁流体换能器的可能性和必要性提出了看法,并提供了有关的参考文献.     

冲击载荷下不同载液磁流体直齿圆柱齿轮的弹流润滑数值分析

建立磁流体润滑渐开线直齿轮的弹流润滑模型,应用多重网格法和多重网格积分法,求得直齿轮非稳态弹流润滑问题的完全数值解,分析冲击载荷对不同载液磁流体弹流润滑的影响。冲击载荷作用下,探究两直齿轮接触点压力和膜厚的变化规律。结果表明:二酯基D01磁流体的膜厚最大,压力最小;酯基H02磁流体的膜厚最小,压力最大;二酯基D01磁流体润滑膜在冲击载荷作用下,传动比越大,压力越小,膜厚越大;二酯基D01磁流体润滑膜在冲击载荷作用下,传递功率越大则轮齿上的载荷越大,压力越大,膜厚越小。     

磁性液体离心密封深沟球轴承设计与试验

将磁性液体特殊的零泄漏密封性能与流体离心密封可获较高压强的特性有机结合,在动力学计算分析基础上,开展磁性液体离心密封件的磁场仿真模拟,实施磁性液体离心密封深沟球轴承的优化设计与试制。在对两组轴承分别实施无密封处理及磁性液体离心密封处理后,本实验将两组轴承置于密闭空间内并对其运转时释放的微粒进行探测实验。实验发现未经密封处理的轴承释放出大量微粒,而实施磁性液体密封处理的轴承对密闭空间几乎没有明显微粒释放。结果表明,这种磁性液体离心密封的深沟球轴承能有效地减少润滑剂的散失和磨损微粒的排放,适用于高度洁净和真空的特殊环境。     

Electromagnetic composite films based on polypyrrole hydro-sponge and Fe3O4 ferrofluid

The preparation of free-standing electromagnetic composite films based on conductive polypyrrole (PPy) hydro-sponge and the Fe₃O₄ ferrofluid have been successfully accomplished via self-assembly in the presence of β-cyclodextrin sulfate and under static condition. Transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD) are used to study the morphology of the PPy-Fe₃O₄ composite. Structural characterizations by Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) have proved the interactions between Fe₃O₄ and PPy chains. As-prepared films possess high electrical conductivity, remarkable magnetic response as well as appropriate flexility. Both the conductivity and magnetization of the composite, the latter in particular, depend strongly on the Fe₃O₄ content and thus can be optimized by adjusting the relative content of Fe₃O₄ in the composite. The combination of both magnetic and conducting activities of the resulting composite makes it be a potential candidate as functional material in electromagnetic devices, such as magnetic-controlled switches.     

扬声器用磁性流体

在FeCl3.6H2O、FeSO4.7H2O水溶液中加入强碱,通过调节pH值制备纳米粒径的Fe3O4磁粉,将磁粉均匀分散到有机溶剂中并加入表面活性剂,再分别均匀分散于聚a-烯烃和多元醇酯载液中,制备出聚a-烯烃和多元醇酯基两种扬声器用磁性流体。通过加入添加剂提高其化学和磁稳定性。用增粘剂调节其粘度、粘度指数和磁饱和强度,得到扬声器用磁性流体。通过在汽车高音扬声器中的应用,检测了该磁性流体在扬声器中的应用效果。     

Reduction of cavitation in refrigerant fluid flow through micro passages in the presence of external transverse magnetic fields

This paper presents a numerical study of cryogenic fluid flow cavitation in a microchannel and annulus, with forward‐facing step. Two‐phase mixture model is used to simulate the effects of magnetic fields produced by an electrical wire and magnetic doublet on the cavitation region. The results show that considerable reduction of vapor generation due to pressure drop is possible in the presence of an external magnetic fields. This phenomenon occurs due to effect of magnetic field on the pressure distribution in the contraction region and it is observed in both types of studied magnetic fields.