Effect of surface etching on condensing heat transfer

This study conducted experiments on humid air condensation during heat transfer in an air preheating exchanger attached to a home condensing boiler to improve thermal efficiency. An etchant composed of sulfuric acid and sodium nitrate was used to create roughness on the heat exchanger surface made from STS430J1L. A counter flow heat exchanger was fabricated to test the performance of heat transfer. Results showed that the overall heat transfer coefficients of all specimens treated with etchant improved with respect to the original specimens (not treated with etchant), and the overall heat transfer coefficient of the 60 s etching specimen increased by up to 15%. However, the increasing rate of the heat transfer coefficient was disproportional to the etching time. When the etching time specifically increased above 60 s, the heat transfer coefficient decreased. This effect was assumed to be caused by surface characteristics such as contact angle. Furthermore, a smaller contact angle or higher hydrophilicity leads to higher heat transfer coefficient.

     

The effect of tape overwrap angle and head radius on head/tape spacing and contact pressure in linear tape recording

Linear tape recording devices typically employ contact recording to minimize head/media magnetic spacing and thus maximize recording density. Successful contact recording is a delicate balance between spacing and contact pressure. If an air bearing develops, spacing will exceed the 100 nm upper limit for current high recording density devices. Conversely, high contact pressure can lead to head wear or tape damage. Most recording heads produced today for linear tape devices consist of one or more cylindrical wafer sections that are bonded together to form a rigid structure. Each individual tape bearing surface is cylindrical with straight edges. The tape is held over the head contact surface by tape guides so that the tape is wrapped sharply around the edges where cylindrical surface and flat surface meet. Overwrap angle is defined as the angle between the tape after it leaves the head and a tangent to the cylindrical head surface at the edge where cylindrical surface and flat surface meet. This paper will use one-dimensional finite element modeling to explore how overwrap angle and bump radius affect head/tape spacing and contact pressure. The effects of tape stiffness, tape tension, and tape velocity will be investigated. Feasible combinations of overwrap angle and bump radius will be presented which minimize head/tape separation, yet keep contact pressure within bounds.     

旋转控制头密封胶芯性能三维有限元分析与结构优化

为提升带压起下钻过程中旋转控制头胶芯密封性能,基于虚功原理得到动态密封过程的有限元控制方程,并进行橡胶单轴压缩试验确立胶芯变形过程中的Yeoh本构模型;运用ABAQUS试验平台建立胶芯三维有限元模型,通过模拟起下钻过程中胶芯动态密封过程,得出密封面上受力分布规律;研究胶芯内锥角、外锥角、内径等结构参数对密封性能的影响....     

方柱织构参数对吻合器钛钉表面疏水性能的影响*

对于吻合器钛钉等体内植入物,感染的第一步是细菌在材料表面的黏附,提高表面疏水性是减少细菌黏附的有效方法。基于仿生学和有限元仿真技术,通过在吻合器钛钉表面加工方柱织构,建立织构表面的液滴铺展模型,利用商用CFD软件ANSYS Fluent研究织构宽度、间距和高度对接触角的影响规律,分析织构参数对钛钉表面疏水性能的影响。仿真结果表明,在给定的织构参数范围内,钛钉表面方柱织构有效提升了表面疏水性,织构宽度和间距对接触角影响显著,且接触角随宽度和间距的增加都呈先增大后减小的趋势,最佳疏水结构为宽度略小于间距,而高度对接触角的影响几乎可以忽略,随着高度增加疏水性略微增大。     

化学法粗化医用聚氨酯支架管表面的润湿性研究

针对医用植入支架管在临床使用过程中存在的体液结垢问题,研究医用聚氨酯支架管表面的化学法粗化及其润湿性。采用化学法粗化医用聚氨酯材料,测量粗化后聚氨酯材料的接触角和表面形貌,分析液滴重力对接触角的影响,并探讨影响粗化效果的因素,如粗化液的种类、粗化液混合比、粗化液浓度、粗化温度、粗化时间等对粗化后导管表面润湿性的影响。结果表明:聚氨酯材料表面接触角随着液滴重力的增加,呈先增大后减小的趋势;粗化有助于提高聚氨酯导管表面疏水性能,其中三氧化铬粗化后导管接触角比高锰酸钾粗化后接触角更大;接触角随着三氧化铬与浓硫酸混合比、粗化温度、粗化时间三者的增大,均呈现先增大后减小的趋势,而随着三氧化铬浓度的增大逐渐增大。得到最佳的粗化工艺参数为:三氧化铬与浓硫酸的混合比2∶1,三氧化铬浓度80 g/L,粗化温度50℃,粗化时间30 min。     

Fabrication and characterization of the hierarchical structure for superhydrophobicity and self-cleaning

Hierarchical roughness is beneficial for the superhydrophobicity. Surfaces with microstructure, nanostructure and hierarchical structure were fabricated by replication of micropattern and self-assembly of hydrophobic alkanes. The fabrication technique used is a low-cost two-step process, which provides flexibility in fabrication of variety of hierarchical structures. Fabricated structures and surface chemistry mimic the hierarchical surfaces of superhydrophobic and self-cleaning plant surfaces. The influence of structure on the superhydrophobicity at different length scales is demonstrated by investigation of contact angle, contact angle hysteresis, droplet evaporation and propensity of the air pocket formation as well as adhesive forces.     

航空发动机U形金属密封环的设计与优化

针对某型发动机高压转子连接结构的密封问题,设计一种U形金属密封环,分析研究密封环的密封和强度性能,探究结构参数(包括根部倒圆、壁厚、环高、接触面曲率半径、密封环接触面角度、密封环配合件角度)对密封环最大等效应力、最大接触应力的影响,基于ANSYS Workbench优化设计模块,采用代理模型结合遗传算法的优化技术对密封环结构进行优化。结果表明:安装压缩率范围为3.56%～6.33%时,可保证安装和工作2种工况下密封和强度的要求;最大等效应力与壁厚成正比关系,而与根部倒圆和环高成反比关系;接触面曲率半径对最大等效应力影响较小,但最大接触应力随着接触面曲率半径的增加而增加;选择合适的角度范围时,密封环接触面角度和密封环配合件角度对最大等效应力、最大接触应力影响均较小。密封环结构优化后,最大等效应力在安装和工作2种工况下分别减小了34.3%和30.4%,同时密封环质量减少了6.1%。对设计的U形金属密封环随整机进行了试验,结果表明U形金属密封环密封性能良好,验证了设计的合理性。     

304不锈钢表面离散圆形凹坑液相辅助激光制备及摩擦性能

为改善304不锈钢耐磨性及润湿性，在空气与液相2种介质下使用激光加工技术在304不锈钢表面制备离散型圆形凹坑织构。借助白光干涉仪、扫描电子显微镜及能谱、接触角测量仪对织构试样表面形貌、元素含量及润湿性进行了表征，并通过摩擦磨损试验考察了织构试样在干摩擦和油润滑下的摩擦学性能。结果表明：空气介质下激光加工增强了试样表面疏水性能，接触角为123.3°；液相辅助激光加工增强了试样表面润湿性，接触角为29.3°；液相辅助激光加工表面的微凹坑分布更加均匀，无明显的氧化及熔融物重铸现象，这是因为液相在激光加工时对试样起到了冷却及保护作用；液相辅助激光加工表面织构在2种摩擦工况下的摩擦因数均最小，且磨损有一定改善。液相辅助激光制备的织构表面较为均匀、无较大的微凸峰，且具有较好的润湿性能，有利于润滑油的存储及铺展，进而改善了界面摩擦行为。     

Wettability characterization and adhesion enhancement of arc-treated surface of aluminum alloys

The aim of this study is to determine the wettability-enhancing effects of an atmospheric pressure, direct current (DC) plasma arc discharge on the surface of aluminum alloys. Wettability is a critical factor in engineering applications such as biomedical implants, painting, and adhesive bonding. For example, in the realm of adhesive bonding, greater wettability improves a metal substrate's attraction to an adhesive material and results in a higher bond quality. In this study, the contact angle was determined and compared as a measure of the wettability using two different techniques: the sessile drop and the ballistic deposition with water as a test liquid. The effect of different arc discharge process parameters on the wettability, including arc current and plasma torch velocity, was studied. A two-dimensional finite element analysis based on the volume-of-fluid model was carried out to explore the behavior of droplet (e.g., spreading and stabilization) on an ideal surface. Additionally, the values of the dynamic receding contact angle were measured through the simulation by applying the tilted plate method and considering the surface roughness to compare the results with the values obtained from the ballistic deposition method. Studying the wettability alteration of the surface of aluminum alloys subjected to the arc treatment revealed the wettability reduction over time. Additionally, it was found that there was a linear correlation between the contact angle value and the strength of adhesively bonded joints using two structural adhesives. The results of this study in the wettability modification of aluminum subjected to the arc treatment and wettability alteration of the treated substrate over time may be used as a quality assurance tool to design the production process and achieve the desired quality and strength in adhesively bonded joints.     

油封正态分布结构参数的可靠性灵敏度分析

以油封的泵吸率为可靠性指标,将理论接触宽度、油侧唇角、空气侧唇角、过盈量和腰厚5种结构参数作为因子,泵吸率作为响应输出,运用正交试验法对油封性能进行分析;运用曲面响应法拟合泵吸率的极限方程,基于可靠性原理建立油封泵吸率的可靠性模型,运用二阶矩法和蒙特卡洛2种方法进行可靠性敏感度计算,分析呈正态分布的随机参数对均值的灵敏度和标准差的灵敏度。结果表明：2种计算方法的结果基本一致,基于均值的敏感度,对可靠度影响最大的是理论接触宽度,油侧唇角、空气侧唇角和过盈量对可靠度为正面影响;基于标准差的敏感度,过盈量的标准差对可靠度影响最大,5种结构参数的标准差均对可靠度有负面影响。     

采用移动式阴极制备大尺寸超亲水/超疏水铝板

基于电化学加工方法和氟化处理技术,采用移动式阴极制备了大尺寸超亲水/超疏水铝板,用扫描电子显微镜和能谱仪分别对该铝板表面的形貌和成分进行了分析,并采用接触角测量仪测量了所得表面的接触角和滚动角。结果表明:采用移动式阴极加工大面积超亲水/超疏水铝板是可行的;电化学加工后的超亲水铝板表面存在二元微纳米粗糙结构,对水的接触角约为0°;该超亲水表面经氟化处理后可转变为超疏水表面,对水的接触角为167°,滚动角小于3°。     

An easy way to measure surface free energy by drop shape analysis

The drop shape analysis is a conventional method to evaluate wettability and surface free energy. The analysis of drop profile is commonly used for the contact angle measurement between the liquid drop and sample surface.In many cases such as confined surfaces, it is difficult to carry out this measure, therefore it is necessary to evaluate the shape of the drop from top view point.The aim of this work was to develop a procedure in order to measure wettability and surface free energy values by means of the analysis of the drop shape from top view point. Starting from Tadmor equation, a polynomial function was obtained to correlate the drop diameter to its contact angle on a flat horizontal sample surface.In addition, analyses were carried out in order to study the shape of liquid drop varying the tilt of sample surface. In this case was shown a correlation between the tilt grade and the maximum characteristic lengths (parallel and orthogonal to pitch) of a drop shape on a tilt surface sample.Using the maximum characteristic lengths and a polynomial function previously obtained, it is possible to establish values of pitch, surface free energy and wettability of sample surface.In order to confirm the developed procedure, tests on three different materials have been performed obtaining these three performance indexes.All results obtained by means of this alternative analysis have been compared and corroborated by the classical method using the contact angles of the drop analyzed from a lateral view.     

Ultra-low-flying-height design from the viewpoint of contact vibration

The design of a head-disk interface for ultra-low flying height has been studied from the viewpoint of contact vibration. It is known that a super-smooth disk is necessary for a slider to fly at an ultra-low flying height; however, such a disk increases the friction force, which potentially increases the vibration of the slider. To solve this problem, the head-disk interface must be optimized to reduce this increased vibration. It has been shown that a large pitch angle and center-pad-mounted read/write elements have advantages in terms of slider/disk contact. It has also been found that a micro-texture on the air bearing surface can prevent contact vibration. Moreover, a frequency-shift-damping slider was found to damp the vibration effectively. To further investigate these findings, numerical simulation and modeling of slider dynamics during contact have been performed. Their results revealed two zones of contact vibration: a stable zone and an unstable zone.     

Effect of Air and Helium on the Head–Disk Interface During Load–Unload

The tribological characteristics of the head–disk interface are investigated during load–unload for air and helium-filled drives as a function of the pitch static angle and the roll static angle between slider and disk. A custom-made experimental tester inside a sealed environmental chamber was used to determine the regions of “safe” pitch static angle and “safe” roll static angle in air and helium environment during the load–unload process. The presence of head–disk contacts during load–unload were evaluated by measuring the acoustic emission signal and the decrease in rotational speed of the spindle. Scanning electron microscopy and optical surface analysis were used to investigate wear of the slider and the redistribution of lubricant on the disk surface after 10,000 load–unload cycles. The results indicate that the tribological performance of the head–disk interface is improved in helium environment compared to air environment.     

Effects of adsorbed water and sample aging in air on the μN level adhesion force between Si(100) and silicon nitride

The microscale adhesion force of single crystal silicon (100) to silicon nitride was studied using a newly developed micro/nanoadhesion measurement apparatus. The effect of water adsorption on adhesion between clean surfaces and surfaces aged in air was determined. During experiments, varying relative humidity (RH) controlled water adsorption. Clean and aged samples showed measurably changed water adsorption and adhesion above 60% RH only, and aged samples showed more water adsorption and adhesion than clean ones above 90% RH. A contaminant film grew to a saturated thickness of about 6 Å over 50 days of aging, and the film changed surface chemistry which resulted in higher contact angle. The contaminated surface with higher contact angle exhibited more affinity for water and microadhesion on the molecular scale, which is contrary to the common interpretation of contact angle data. The divergence of water adsorption and adhesion force behavior between clean and aged samples above 90% RH may indicate that the Kelvin radius became comparable to a characteristic length on the contaminated surface at high RH. A molecular model is proposed in which the contaminant film provides porosity, which allows capillary condensation and the growth of a multilayer water film.     

pH值和浓度对CeO2抛光液性能影响的研究

研究了氧化铈抛光液颗粒浓度和pH值的变化对抛光液悬浮性能、接触角和粘度的影响。结果表明：随着浓度和PH值的变化,氧化铈抛光液悬浮性能、接触角和粘度均出现变化。随着原始抛光液被逐渐稀释．抛光液的悬浮性能下降,接触角和粘度也减小,然而pH值的变化对它们的影响则较为复杂。     

超声纵扭辅助铣削高强铝合金表面润湿性能研究

针对超声辅助加工在工件表面形成微刻划表面可以提高高强铝合金表面的微结构性能的现象,进行了单激励旋转超声纵扭复合铣削表面微观结构的试验,基于水接触角理论和纵扭铣削运动学理论分析了加工参数对水接触角的影响;搭建了单激励超声纵扭铣削试验平台,采用正交试验法研究了不同加工参数对表面粗糙度、铣削力以及表面润湿性能的影响。结果表明：超声振幅为4μm时表面质量最佳,切削速度和进给量与表面粗糙度和水接触角呈正相关的关系;超声加工方式下的表面水接触角较普通方式更大,而在超声加工时低振幅加工比高振幅加工的表面水接触角大,当转速达到一定值时,高振幅和低振幅所加工的表面水接触角差别不大。合适的加工参数条件下超声纵扭加工方式可以降低加工表面的粗糙度,改变表面的润湿性。     

Characteristic analysis of condensate carry-over according to the surface tensions in the wet and the dry conditions on the fin surfaces of heat exchangers

Typically, condensate forms as droplets on the fin surfaces and may bridge the space between the fin surfaces. This is due to the dry characteristics inherent to the fin surface. The droplets increase the air-side pressure drop. In the case of high air velocities, these droplets may be blown off the fins and entrained in the air stream. To minimize the formation of condensate droplet, the wet ability of the fins must be improved. The carry-over velocity is affected by fin surface characteristics. To avoid carry-over in the air conditioner having the highest air velocity of 1.5 m/sec, the dynamic contact angle (DCA) should be at least lowly under 60°.     

超疏水表面膜的制备

通过化学气相沉积的方法,在具有规则微形貌的硅片表面沉积硅的有机物制备出了超疏水表面,进而对表面的润湿性进行了对比。结果表明:不同的成膜时间和微形貌的结构尺寸直接影响着表面的润湿性;表面的接触角随着时间的增长而增大,但有一时间极限,此后接触角基本不受影响;当微形貌深度一定,随着形貌宽度的增加接触角无明显变化,但超过某一临界值时,接触角下降明显,不再形成超疏水表面。     

Geometric design of a face gear drive with a helical pinion

The application of face gear drives, which have been used recently instead of bevel and hypoid gears for helicopter transmission, has resulted in renewed interest in such drives. A helical pinion must be utilized to change the composition of the contact surface freely. In this work, the problem of where to place the pinion with respect to a gear is solved by defining a reference point. The effect of the helix angle on the composition of the surface contact lines is clarified. A geometric design method that recognizes meshing singularity is proposed. Two unique lines on which specific sliding becomes infinite are regarded as design indexes. Results show that the contribution of the surface contact lines changes significantly depending on the helix angle, and the offset distances influence the effective tooth width of the gear.