微通道粗糙度对甲烷催化燃烧影响的数值研究

采用详细化学反应机理对甲烷空气预混气体在不同粗糙度下微通道内催化燃烧进行了数值模拟。结果表明:粗糙度的存在使得微通道内甲烷转化率减小,出口温度降低,粗糙表面将阻碍催化反应的进行,而且粗糙度越大这种阻碍作用越大;在同一粗糙度下,随着当量比、混合气入口速度的增加,粗糙度对催化反应的阻碍作用越明显,粗糙度越大,燃烧效率越低。     

甲烷微尺度催化燃烧的数值模拟

本文联合使用计算流体力学软件FLUENT和可以计算表面反应的化学反应动力学软件DETCHEM对有逆流换热的微尺度燃烧器进行了数值计算。计算中忽略空间反应。燃料-空气混合物的当量比为0.4,反应器壁面采用等温边界条件。计算结果表明,采用催化燃烧可以实现微尺度下通常情况下无法实现的甲烷稳定燃烧。通过适当设置催化表面,可以实现燃料低温、高效转变。甲烷的总转变率受流动状态、反应温度和催化表面的大小等因素的影响。     

甲烷在逆流换热微燃烧器内催化燃烧的数值模拟

本文联合使用CFD软件FLUENT和化学反应动力学软件DETCHEM对甲烷-空气混合物在有逆流换热的微燃烧器内的催化燃烧进行了数值模拟。计算中只考虑了甲烷在催化表面上的反应。燃料-空气混合物的当量比为0.4,燃烧器外壁面与环境采用对流换热边界条件。计算结果表明,同时采用逆流换热和表面催化燃烧可以实现常规方法无法实现的甲烷稳定、高效转变。     

表面催化反应对空间预混气体着火影响的研究

催化燃烧中表面反应和空间反应的相互影响是一个非常重要的问题,本文计算了表面有催化剂的高温小球利用催化反应放热点燃空间预混气体的温度和浓度分布情况,从而得到当空间预混气体着火时表面催化小球的温度低于无催化时空间预混气体着火温度,同时得到在利用催化反应放热点燃空间燃烧时,空间预混气体着火的温度却远远高于无催化下的空间预混气体着火温度,该结果与试验相符。     

甲烷入口条件对紧凑型重整器燃烧管道化学反应与产热特性影响

紧凑型甲烷重整器燃烧管道由燃料气体通道、多孔层以及固体平板组成.采用三维数值模拟方法,对甲烷入口速度、温度等对催化燃烧反应以及产热特性影响进行了研究.结果显示,甲烷入口速度由2.5 m/8增大到10 m/s时,最大化学反应速率提高了20.4%,CH4利用率下降了41.2%,最大热流量提高了11.8%;温度由873 K升...     

温度对微通道CH4/O2/H2O自热重整暂态特性的影响

利用计算流体力学软件CFD和化学反应动力学软件CHEMKIN研究了微通道内催化壁面温度、反应混合气体初始温度对镍基催化剂上CH₄/O₂/H₂O自热重整反应暂态特性的影响。结果表明,微通道内的甲烷自热重整反应暂态特性与温度关系密切。温度越高,反应趋于平衡所需的时间越短;当反应器壁面温度较高时,提高反应混合气入口温度对反应影响不大;在相同的温升下,提高反应器壁面温度比提高反应混合气体初始温度对反应过程中氢气的产生和甲烷的转化更有利。     

微通道内氢气和氧气混合的DSMC模拟

气体混合是微流动系统的重要应用之一.本文使用DSMC方法,数值模拟了不同进出口压力下简单和复杂微通道内H2和O2的混合过程,并从满足完全燃烧的氢氧摩尔流量比的角度,讨论了进出口压力以及两种气体入口压力比和宽度比(截面面积比)对摩尔流量比的影响.     

随机粗糙微通道内流动特性研究

采用计算流体动力学的方法, 研究了微通道内气体在速度滑移和随机表面粗糙度耦合作用下的流动特性. 其中, 利用二阶速度滑移边界条件描述气体的边界滑移, 利用分形几何学建立随机粗糙表面. 研究发现, 综合考虑二阶速度滑移边界条件和随机表面粗糙度在较大的平均Knudsen数范围内 (0.025-0.59) 得到的计算结果与实验数据符合得很好, 而一阶速度滑移边界条件只在平均Knudsen数较小时(<0.1)符合实验结果. 随机表面粗糙度对气体在边界处的滑移有显著影响, 相对粗糙度越大, 速度滑移系数越小. 并针对计算结果, 给出了滑移系数与相对粗糙度近似满足的关系. 随机粗糙表面对气体流动过程中的压强、速度、Poiseuille数也有显著影响. 关键词： 随机表面粗糙度 二阶速度滑移边界条件 分形 微通道     

微通道内滑移区气体-颗粒流动传热数值模拟

本文针对微通道内气粒间流动传热过程开展数值研究,所建模型中气体处理为可压缩/变物性流体,并在气固交界处采用速度滑移和温度跳跃边界条件以考虑其微尺度效应。在数值研究基础上,分析了微通道受限空间、克努森数、气体流速以及颗粒表面温度对微通道内气粒换热的影响。研究结果表明,受限空间结构将强化气粒间换热过程,颗粒表面平均传热努赛尔数随微通道气体流量增大而增大,克努森数增大以及颗粒表面温度升高都将导致颗粒表面平均传热努赛尔数减小。     

喷管直径对微尺度扩散火焰特性的影响

对均匀空气流中微尺度甲烷扩散燃烧进行了数值模拟,重点考察微喷管内的流动和传热传质对微尺度燃烧特性的影响.研究结果表明,在保持燃料喷出速度一定的条件下,随着喷管直径的减小,喷管内与甲烷喷出速度相反方向上发生热量和质量的传递,燃料与空气的混合在喷管内已经发生,火焰的一部分热量回流到喷管内顶热了未燃混合气,同时也增加了火焰的热损失.当管径为0.15 mm时,甲烷在微喷管内就开始发生化学反应,在进行微尺度解析计算时,必须包含一定的喷管区域.     

Experimental Study on Flow and Heat Transfer in a 19.6-μm Microtube

The flow and the heat transfer characteristics in a quartz microtube with an inner diameter of 0.0196 mm are investigated experimentally. Measuring the pressure drop between the inlet and outlet of the microtube and the average temperature of the microtube wall heated by steam when the working fluid is distilled water, the corresponding friction factors and Nusselt number are obtained. The experimental results show the friction factors in the microtube exceed those of the Hagen–Poiseuille prediction due to the predominance of the effects of the electrical double layer and the entrance. Also, the experimental Nusselt number is less than the classical laminar at Reynolds number < 500 due to the effect of the variation of the thermophysical properties with the temperature.     

微圆管内环状流凝结换热特性的数值模拟

本文提出了微圆管内环状流凝结换热的分析模型,考虑了重力、汽液界面剪切力、表面张力以及界面凝结热阻的作用。文中主要研究凝结换热过程中重力、入口蒸汽Re数及外壁面温度的影响。模拟的结果表明,重力对微圆管流动凝结换热的影响非常小,可被忽略;凝结液的排除主要依赖于汽液界面的剪切应力作用,使Nu随蒸汽进口Re数的增加而明显增大;冷却外壁面的温度对凝结换热也具有一定的影响, Nu将随外壁面温度的降低而增大。     

Synthesis and properties of aligned ZnO microtube arrays

Two kinds of different aligned zinc oxide (ZnO) crystal microtube arrays were prepared on silicon (1 0 0) substrates by using of a simple thermal chemical reaction vapor transport deposition method. The synthesizing processes were done by using of heating the mixture of zinc oxide and graphite powders at 1150 °C in a quartz tube with one side opened to the air. The O₂ gas (99.9%) and air had been introduced as the assistant gases, respectively. Both the flow rates were 100 ml/min. And the temperature of the Si (1 0 0) substrate region was about 400 °C. There is no other metal catalyst on the Si wafers in the process. After growing for 30 min, one kind of synthesized sample is trumpet-shaped hexagonal microtube arrays assisted with O₂ gas and another produced sample is the uniform hexagonal microtubes only assisted with air. As the increasing of preparing time, their maximal lengths can range from several 10 μm to mm scale. The microstructure, room temperature photoluminescence properties and growth mechanism of both aligned microtube arrays were investigated and discussed.     

Ag微米管阵列修饰的聚合物光子晶体光纤制备工艺研究

以聚合物光子晶体光纤空气孔阵列为模板,制备了Ag微米管阵列修饰的聚合物光子晶体光纤.讨论了银氨溶液和葡萄糖溶液浓度以及反应时间和温度对银微米管形貌的影响.在Ag(NH3)+2与C6H6O浓度比为2,反应时间为20 min,温度为65℃条件下光纤孔洞表面获得了规则的Ag微米管状结构,并对Ag的生长机理进行了讨论.     

Selective polarization mode excitation in InGaAs/GaAs microtubes

We report on selective polarization mode excitation in InGaAs/GaAs rolled-up microtubes. The microtubes are fabricated by selectively releasing a coherently strained InGaAs/GaAs quantum dot layer from its host GaAs substrate. An optical fiber abrupt taper is used to pick up the microtube, while an adiabatically tapered optical fiber is used to couple light into the resonant optical modes of the microtube. By varying the polarization of the light in the adiabatically tapered fiber both transverse electric and transverse magnetic modes are observed in the microtube. We also show that the microtube can be used as a red (0.6?μm) to infrared light (1.5?μm) optical-optical modulator taking advantage of the thermal-optical effect.     

Electrical conductivity of individual polypyrrole microtube

Conducting microtubes (0.4－0.5μm in outer diameter) made of polypyrrole (PPy) doped with p-toluene sulfonic acid (PTSA) were synthesized by a self-assembly method. We report the electrical conductivity of an individual PPy microtube, on which a pair of platinum micro-leads was fabricated by focused ion beam deposition. The measured room-temperature conductivity of the individual PPy microtube was 0.29S/cm, which is comparable to that of template-synthesized PPy micro/nanotubes. The temperature dependence of conductivity of the individual microtube follows the three-dimensional variable-range hopping (3D VRH) model.     

Optical microcavities formed by semiconductor microtubes using a bottlelike geometry

We report on the realization of optical microtube resonators with a bottlelike geometry. The measured eigenenergies and the measured axial field distributions of the modes can be described by a straight and intuitive model using an adiabatic separation of the circulating and the axial propagation. The dispersion of the axial mode energies follows a photonic quasi-Schr?dinger equation including a quasipotential which can be determined for the actual geometry of the microtube in a precise and simple way. We show that tailoring the geometry of the microtube bottle resonators enables the realization of a wide variety of mode distributions and dispersion relations.     

Growth and Characterization of Trumpet-Shaped ZnO Microtube Arrays on Si Substrates

Aligned trumpet-shaped zinc oxide microtube arrays have been successfully prepared on silicon （100） substrates via the chemical vapour deposition method with a mixture of ZnO and active carbon powders as reactants. The results show that two types of trumpet-shaped ZnO microtubes can be obtained. A plausible growth mechanism based on the studies of scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, x-ray diffraction （XRD）, and room-temperature photoluminescence spectroscopy is proposed and discussed. The initial metastable zinc-rich ZnOx embryos play a key role in the formation of trumpet-shaped ZnO microtubes. On the different surfaces of metastable zinc-rich ZnOx （x 〈 1）, embryos exhibit different stabilities and resistivities to oxidation; these tiny embryos are gradually extended with different growing rates along the directions of its long axis and circular boundary around its oxide shell. Just this special reason creates the formation of trumpet-shaped microtubes and results in the inerratic and imperfect hexagonshaped cross section that appears. Moreover, the analytical results also show that the as-synthesized ZnO microtube arrays can exhibit better room-temperature photoluminescence behaviour.     

壁面轴向导热对微细管内对流换热的影响

本文通过数值解析的方法研究了考虑壁面轴向导热时微细管内的对流换热。结果表明,当管外为对流换热边界条件时,管内充分发展对流换热的Nu依然在3.66～4.36之间。但若忽略壁面轴向导热,采用一维热阻模型整理微细管内对流换热的实验数据将会导致错误的结论。