水合物浆体在水平细管中的流动相变换热

实验测量了质量分数为0~19.2%的TBAB水合物浆体在恒热流条件下在小管径内流动时的流动传热特性。利用数值计算获得管内浆体的沿程温度分布,在此基础上得到水合物浆体在小管径内的强制对流传热特性。结果表明加热功率对小管径管道中的浆体传热特性有较大影响;在层流状态下,流速对传热系数的影响相比紊流时要小。在实验数据基础上总结出了TBAB水合物浆体在小管径管内的对流换热经验关联式。     

连续式碳纤维电热机场道面融雪化冰数值模拟与验证

为了研究连续式碳纤维发热线的埋深和间距会对机场道面混凝土板表面的温度均匀性产生的影响,以及XPS隔热层的布设对板面融雪化冰效果的优化程度,利用有限元分析软件Ansys建立连续式碳纤维电热机场道面板温升及融雪化冰的瞬态传热模型,主要模拟道面板的温升及化冰过程,结果发现:在连续式碳纤维发热线布置间距≤100 mm、埋深≥50 mm时,板面温度均匀性良好;通过"有效融化时间"和"能源有效利用率"的定量计算,证明XPS隔热层的布设起到了良好的隔热保温的效果,为其在机场道面融雪化冰中的应用提供一定的理论依据.     

Self-heating fiber reinforced polymer composite using meso/macropore carbon nanotube paper and its application in deicing

A meso/macropore carbon nanotube paper (CNP) and a self-heating fiber reinforced polymer composite of CNP/glassfiber/epoxy (CGE) based on the meso/macropore CNP were fabricated in this article. The pore diameters mainly distribute from 30 to 90 nm characterized using nitrogen adsorption isotherms at 77 K. The electric conductivities of the CNP and CGE composite are 77.8 and 64.9 S cm⁻¹. Electric heating performance of CGE was investigated at different heat flux densities, wind speed and ambient temperature. A uniform temperature distributed was observed on the surface of CGE detected by an infrared temperature camera. The electric heating performance was verified by deicing a certain amount of ice at different heat flux densities under two kinds of ambient conditions: −22 °C without wind and −22 °C with 14 m/s of the wind speed. The deicing time under the two conditions were less than 220 and 450 s, respectively. The feasibility of the deicing performance was demonstrated through a series of experiments and the results indicate this material is a promising candidate as an electric heating material for deicing.     

Adhesion of metals to polymers. I. Study of interfaces modified by inductive heating

The objective of the work reported in this paper is to explain theoretically the observations made in an earlier study that castings of an epoxide resin reinforced by electrically conductive inserts, after having been postcured by inductive heating, had strength properties superior to those achieved by a purely thermal postcure. A search of the literature on adhesion suggested that among the theories presented, those dealing with electrical double layer formation, interdiffusion, and mixed polymer grafting on the insert–polymer interface deserve to be considered. Experiments were then planned in such a manner as to permit a choice between these theories. Epoxide resin specimens reinforced with various metals (pure silver, silver with an oxide layer, pure copper, copper with an oxide layer, aluminum, and stainless steel) were prepared. They were then either postcured in a heated oven, or postcured in an induction furnace for various lengths of time. Bonding strength was determined by a knife-edge method, and the exposed insert and resin surfaces were tested for electrical potential and surface wettability (angle-of-contact). Most strikingly, the curves obtained with increasing induction heating times for bonding strength, electrical potential, and wettability were all sinusoidal in shape, and their maxima and minima generally were found to coincide. For oven-postcured specimens, bonding between different metal inserts and an epoxide resin is explained by double electrical layer formation (insert positive, resin negative), with bonding strength increasing as the stability of the oxide forming the surface layer of the metal decreases. Metals with no oxide surface layer thus have the highest bonding strengths. For inductively postcured specimens, bonding is effected by both electrical double layer formation and mixed polymer grafting through the oxygen atoms in the metal surfaces, with the more stable metal oxide giving the stronger bonding in grafting. Where the insert does not carry an oxygen surface layer, bonding takes place through electrical forces only. Alternating build-up and internal discharge of electrical double layers are the direct cause of the sinusoidal shape of the electrical potential curves and the indirect cause of the comparable shape of the wettability curves. Their combination results in the observed periodicity of the breaking load curves.     

Biofunctional calcium titanate coating on titanium by simple chemical treatment process using calcium-hydroxide slurry—Effects of the heating temperatures

The present study investigates the effect of the heating temperature on the characteristics of the surface layer in a simple treatment process using calcium-hydroxide slurry. Furthermore, biofunctions of the treated titanium surfaces, such as bioactivity in a simulated body fluid and corrosion resistance under a bio-environment, are also investigated. Our treatment process using calcium-hydroxide slurry is as follows: a titanium substrate is buried in calcium hydroxide slurry, and the slurry is then heated in air. The calcium hydroxide slurry was prepared by mixing of calcium hydroxide powder and water. When treated at heating temperature beyond 873 K, a crystallized calcium titanate coating is formed on a titanium substrate and further, the thickness increases with the increase of heating temperature. On the crystallized calcium titanate coating, calcium phosphate is precipitated in a simulated body fluid; therefore, the treated titanium surface has bioactivity. Furthermore, anodic current density of the treated surface is 10–10³ times lower than that of the non-treated surface.     

纳米结构表面液体沸腾传热的分子动力学模拟

为了从纳米尺度了解表面结构和润湿性对池沸腾液体与固体壁面的传热性能,本文采用分子动力学方法研究了超亲水至超疏水不同润湿性的液体氩在光滑表面和含凹、凸半球纳米结构表面的沸腾传热过程,分析了三种表面上液氩在受热过程的形态、温度、热流密度等相关参数的变化情况。结果表明,液氩层沸腾过程大致可分为液氩层吸附于固体表面和液氩层从壁面脱离两个加热阶段,当液氩层吸附于固体表面时,温度升高、热流密度及气态氩原子产生速度均大于液氩层脱离壁面时的情况,在这两个阶段亲水表面上氩原子温度变化有明显的拐点,而疏水表面在两个阶段加热过程相差不大。亲水表面上的微结构能吸附更多液氩原子,促进了气泡产生及加速温度、热流密度的变化,而在疏水及超疏水微结构表面,微纳结构与液氩间的气膜层促进了气泡产生,计算结果为池沸腾传热及微结构选择提供了理论依据。     

炉壁黑度对炉膛辐射换热影响的研究

分析了炉壁黑度对炉膛辐射换热流的影响，分别对火焰直接加热炉和间接加热炉进行了讨论。结果表明：炉壁黑度对制品表面净辐射热流几乎没有影响，因而增大或减少炉壁黑度对强化炉内辐射换热没有意义。     

非均匀受热条件下螺旋管内流动沸腾换热特性

目前对螺旋管在其管外表面均匀受热,管内两相流动换热的研究已十分丰富;但是在其管外表面非均匀受热条件下,管内两相流动沸腾换热特性的研究鲜有报道。为了解决螺旋管在实际运用中遇到的非均匀受热问题、得到其换热特性,本文采用了实验的方法研究了卧式螺旋管周向非均匀受热条件下管内流动沸腾换热特性。其中实验工况范围为系统压力P=0.7~1.0MPa,质量流速G=181~364kg/(m²·s),质量干度χ=0.07~0.69。实验考察了螺旋管管外壁在两种非均匀受热条件下管内的两相流动沸腾换热系数与热流密度、质量流速、质量干度的关系,并与管周向均匀受热工况进行了比较。结果表明,在螺旋管外壁面“外半周绝热、内半周受热”情况下管内流动沸腾换热系数值最大,而管外壁面“内半周绝热、外半周受热”情况下最小。     

双面蒸发器环路热管的瞬态特性

环路热管是一种高效的两相热控装置,主要应用于航天航空热控和地面高热流电子器件的散热。现有的平板式环路热管只有一个面可以进行散热,一方面,不利的背向导热使得环路热管在低热负荷的条件下启动困难,另外,蒸发器的另一个面也存在散热的潜能。针对上述不足,提出了平板型甲醇-铜双面蒸发器环路热管。在重力辅助倾角为10°,热沉温度为0℃的条件下,对单面加热和双面加热的启动性能和变工况运行进行了实验研究。实验结果表明:该新型环路热管在单面加热和双面加热条件下,均可以成功启动和正常运行,且双面工况时的启动性能比单面更稳定、迅速;在加热面的温度不超过(90±2)℃的情况下,单面可以传递的最大热负荷为210 W,对应热流为21.8 W·cm^-2,而双面传递的最大热负荷为240 W;双面交替运行时,LHP能够快速从一个面转向另一个面运行,没有出现运行失败。     

纯水和氯化钠溶液凝固过程的实验研究

近几年国内外学者对冰浆的各种特性进行了大量研究,但大多都集中在冰浆生成器的装置设计、冰浆在管道中的流动及传热特性,很少有从冰晶颗粒在壁面生成及结晶过程的机理进行研究讨论。本文对纯水和不同浓度氯化钠溶液在不同材料表面的凝固特性进行了实验研究,搭建了多组分溶液表面凝固性能研究装置,并对装置布置测点同时可更换测试表面。实验采取不同浓度的氯化钠溶液,分别记录在粗糙度不同的铜板、铝板以及塑料板表面凝固时的温度、时间,分析不同表面粗糙度、不同材质以及氯化钠浓度对溶液成核能的影响。通过对实验数据的分析和处理分别得出开始凝固温度与粗糙度的变化关系以及凝固时间与过冷度的变化关系。实验结果表明：溶液在平板表面凝固的初始温度会随着粗糙度的增大而逐渐升高。溶液在平板表面凝固的凝固时间会随着过冷度的增大而逐渐降低。     

Numerical study of the effect of burnout on the ignition characteristics of polymer under local heating

This paper presents the results of a numerical study of the effect of burnout on the ignition delay of a typical thermoplastic polymer (polymethylmethacrylate) by a metal particle heated to a high temperature. The initial temperature of the energy source was varied from 960–1150 K. Three ignition modes of the polymer can be distinguished according to the temperature of the heat source, ignition delay, and the position of the ignition zone in the vicinity of the hot particle. It is found that under local heating conditions, the burnout of the heated region of the near-surface layer of the polymer has an insignificant effect (less than 5%) the increase in the basic characteristic of the process—the ignition delay. At the time of initiation of combustion, the degree of thermal decomposition of the polymer (degree of conversion) does not reach even 15% in the section corresponding to the maximum heat flux from the heat source. It is shown that the ignition delay increases more significantly when accounting for the temperature dependence of the thermal properties of polymethylmethacrylate than when accounting for the burnout factor. The induction period is increased by 15–25% due to an increase in the accumulating capacity of the polymer and heat transfer rate from the heated region of the near-surface layer into the depth of the material.     

DRYING OF OPTICALLY SEMITRANSPARENT MATERIALS BY COMBINED RADIATIVE-CONVECTIVE HEATING

The objective of this work has been to basically elucidate the drying characteristics of an optically semitransparent material by combined radiative and convective heating. The experiments were conducted for a graphite suspension, a slurry of surplus activated sludge and a wet silica sand. The time-change of the drying rate as well as of the surface temperature of the brimfully wet material layer were measured under the step heating conditions using an infrared lamp bundle and a blast of hot air heated by an electric heater.

The experimental data obtained show satisfactory agreement with the calculated results from unsteady heat and mass transfer equations derived on the basis of a semitransparent drying model during the preheating and the constant drying rate periods.     

Role of nanoparticles on nanofluid boiling phenomenon: Nanoparticle deposition

Suspended nanoparticles inside the nanofluids can modify the characteristics of heated surfaces and the physical properties of the base liquids, offering a great opportunity to optimize boiling heat transfer. This paper reviews the mechanisms of nanoparticle deposition and the effects induced by deposited nanoparticles on surface roughness, force balance at the triple line, surface wettability, active nucleation site density, receding and advancing contact angles, boiling heat transfer coefficient and critical heat flux. Both enhancement and deterioration effects on boiling heat transfer coefficient and critical heat flux have been discussed. Most of the existing experimental data confirms the enhancement of critical heat flux using alumina nanofluid, however there is no consistency about its boiling heat transfer coefficient.     

The Relationship between Water Wetting and Ice Adhesion

Ice accretion on aircraft leads to difficulties in aircraft flight control due to weight increase and change in weight distribution. Conventionally these difficulties are overcome using anti-icing or de-icing products, such as freezing depressants and heating devices. A more cost effective way to solve these problems would be to use ice repellent surfaces (ice-phobic). As a first step in this direction the relationship between water wettability and ice adhesion was investigated. Using the appropriate chemistry and tailoring the surface roughness a variety of polycarbonate-coated surfaces were created: these included ultra-hydrophilic and ultra-hydrophobic surfaces and surfaces with surface properties in between the extreme ultra-surfaces. Ice adhesion tests and contact angle measurements indicated that the higher the contact angle the lower is the adhesion of ice. The best results were obtained in the case of ultra-hydrophobic surface treatment that led to an 18 fold decrease in ice adhesion compared to the untreated aluminum surface.     

High‐frequency proximity heating for injection molding applications

High‐frequency proximity heating was used to rapidly heat injection molds. The principle is based on the proximity effect between a pair of mold inserts facing each other with a small gap and forming a high‐frequency electric loop. Because of the proximity effect, the high‐frequency current will flow at the inner surfaces of the facing pair, thus selectively heating the mold surface. With this method, the electrical insulation layer beneath the mold surface can be eliminated, resulting in a mold insert made of a single metal. A mold with a cavity of 25 × 50 mm² was constructed with careful design on its electrical, structural, and thermal performance. Air pockets with reinforcing ribs were embedded right beneath the mold surface for enhancing the heating performance. The resulting mold cavity can be rapidly heated from room temperature to about 240°C in 5 s with an apparent heating power of 93 W/cm². The new mold heating method was applied to thin‐wall molding and micromolding, and in all testing cases, short cycle times less than a minute were achieved. POLYM. ENG. SCI. 46:938–945, 2006. © 2006 Society of Plastics Engineers     

CaCO_3结垢诱导期的理论分析与实验研究

在区别结晶和结垢诱导期前提下,建立了CaCO_3在加热表面非均相成核结垢诱导期的数学模型,计算得到了该诱导期与壁面过饱和度、壁面温度、流体流速及表面性能的关系。以离子注氮的表面改性技术,制备低表面能无附加热阻的金属基新表面,实验研究了该表面对结垢诱导期的影响,发现它可延长结垢诱导期0.5～1倍以上,证实了表面性能同结垢诱导期的关系。     

Ice adhesion on different microstructure superhydrophobic aluminum surfaces

The adhesion of ice to high -voltage overhead transmission lines should be small to ensure ease of ice shedding under small external forces. In this work, we studied the influence of the microstructure of superhydrophobic surfaces on the strength of ice adhesion at a working temperature of ?6?°C. Compared to a bare aluminum surface, the microstructure superhydrophobic aluminum surfaces did decrease ice adhesion strength. The superhydrophobic aluminum surfaces with a larger number of micro-holes produced the lowest strength of ice adhesion; its ice adhesion strength was ～163.8 times lower than that for the bare aluminum samples. Furthermore, such microstructure aluminum surfaces had water contact angles larger than 150° and water sliding angles of less than 8.2° even at a working temperature of ?6?°C. The low values of the ice adhesion strength of the above samples were mainly attributed to the superhydrophobic property, which was obtained by creating a structure of micro-nanoscale holes on the aluminum surface after treatment with a low- surface-energy fluoroalkylsilane (FAS).     

大液滴撞击结冰传热过程及介质阻挡放电除冰实验研究

对大液滴撞击过冷壁面结冰的传热和相变过程进行了实验研究,采用高速成像技术与红外测温成像技术对液滴撞击不同温度过冷壁面时的动态过程进行拍摄记录。另外提出一种新的除冰方式,利用高频纳秒脉冲介质阻挡放电等离子体激励器进行了除冰的实验验证,并进行了热力学分析。实验结果表明：壁面温度的变化对液滴铺展过程影响较小,最大铺展系数几乎不变,但对液滴收缩与振荡过程以及最终结冰冰形有较大的影响;结冰从液滴底层开始,壁面温度越低,液滴与过冷壁面温差越大,底层液滴结冰更快,而上层液膜经过回缩、振荡之后,液膜厚度更薄,结冰相变所需时间也更短;利用高频纳秒脉冲介质阻挡放电除冰效果显著,其放电区域作用相当于是一个“热源”且根据其作用方式的不同,除冰过程可分为两个阶段。     

金属基耐高温陶瓷涂层抗热冲击性能的研究

为提高金属基陶瓷涂层的抗热冲击性能，以无机胶粘剂磷酸二氢铝、耐磨陶瓷骨料氧化铝、碳化硅和氧化镁混合后涂覆于金属表面制得陶瓷涂层。通过交替加热及冷却试验测试该陶瓷涂层的抗热冲击性能，并与其他人的研究数据进行比较。所得涂层抗热冲击次数超过10次，超过了其他人的实验数据，这是由于涂层与基体在界面处相互扩散形成过渡层。另外，宏观上的机械联锁有利于提高涂层与基体在界面处的结合，从而提高了其抗热冲击性能。     

Pool boiling of nanoparticle-modified surface with interlaced wettability

ABSTRACT: This study investigated the pool boiling heat transfer under heating surfaces with various interlaced wettability. Nano-silica particles were used as the coating element to vary the interlaced wettability of the surface. The experimental results revealed that when the wettability of a surface is uniform, the critical heat flux increases with the more wettable surface; however, when the wettability of a surface is modified interlacedly, regardless of whether the modified region becomes more hydrophilic or hydrophobic, the critical heat flux is consistently higher than that of the isotropic surface. In addition, this study observed that critical heat flux was higher when the contact angle difference between the plain surface and the modified region was smaller.