含硫天然气与氨气的层流火焰速度测量与反应动力学研究

采用热流量法,在常温常压下对不同掺混比例的CH_4/H_2S、NH_3/CH_4/H_2S的绝热层流火焰速度进行了测量,并通过Chemkin软件对实验气体的层流火焰速度进行了模拟计算。采用Mulvihill+Han组合机理,在当量比为0.7～1.5的范围内都给出了较为吻合实验数据的结果。实验结果显示,提高H_2S的比例,CH_4/H_2S和NH_3/CH_4/H_2S的绝热层流火焰速度值都有所下降;并且在不同工况下,层流火焰速度峰值始终在当量比φ=1.05处。     

H_2O_2/Nafion-纳米TiO_2复合膜强化日光光解脱色甲基橙染料研究

用流延法在石墨板上成功制备出用于光催化的Nafion-纳米TiO_2复合膜。在H_2O_2存在的条件下,用Nafion-纳米TiO_2复合膜对甲基橙染料进行可见光照射处理。结果表明,H2_O_2/Nafion-纳米TiO_2复合氧化工艺中甲基橙降解脱色速率显著提高,两者之间存在明显的协同效应。在协同体系中,酸性媒介比碱性媒介更有利于甲基橙染料光解脱色。实验所用的NO_3~-、Cl~-和SO_4~(2-)等阴离子,均对降解脱色有抑制作用,其中NO_3~-对脱色作用抑制最显著。可见光辐射处理前后,UV-Vis谱图分析表明在H_2O_2/Nafion-纳米TiO_2复合膜处理中甲基橙溶液脱色是因为染料发生氧化光解作用。     

纳米SiO2/TiO2-xNx复合粒子的制备与表征

采用在高温管式炉中通入氨氩混合气对SiO_2／TiO_2复合粉体进行掺氮的方法制得新型纳米级复合粒子SiO_2／TiO_(2-x)N_x,其中SiO_2,TiO_2复合粉体是通过钛酸四正丁酯水解法在预先分散于纯水中的纳米SiO_2粒子表面包覆TiO_2所制得。采用多种手段对样品的结构、形貌及光吸收特性进行了表征。结果表明,在450℃下掺氮反应3h后,样品中氮元素摩尔百分含量为1.43％,即复合粒子分子式为SiO_2／TiO_(1.901)N_(0.099),粒径小于20nm,粒子为包覆型结构,外层为锐钛矿相TiO_2,内层为无定型SiO_2,其光吸收阀值由387nm红移至500nm左右。     

化学链重整联合CO2捕集制氢系统热力学分析

化学链重整是一种新型的合成气制备技术,为提高化学链重整气中H_2含量,捕集CO_2,提出化学链重整联合CO_2捕集制氢系统。采用Aspen Plus对化学链重整过程进行模拟,结果表明:化学链重整气组成模拟值较好地吻合实验值。对所提出的系统进行热力学分析,以H_2产率和CO_2捕捉率为系统性能评定指标,得到反应优化条件:吸收反应温度为600~620℃,CaO/CH_4、蒸汽/CH_4、H_2O/CH_4、NiO/CH_4物质的量之比分别为:0.8、0.25、0.3、1.4,所得产品气中H_2含量为91.13%(高于化学链重整气中H_2含量64.12%),H_2产率为1.96,CO_2捕集率达到95.44%。     

纳米SiO_2润滑油改善内燃机气缸套-活塞环润滑摩擦性能的基础试验研究

利用分散法制备了不同质量分数的纳米SiO_2润滑油,并考察其悬浮稳定性。通过四球摩擦磨损试验机对纳米润滑油进行极压试验和长摩试验,以此来模拟活塞靠近上止点附近时气缸套-活塞环摩擦副处于混合润滑的状态,以及活塞远离上止点时气缸套-活塞环摩擦副处于流体动压润滑的状态,分别考察纳米润滑油的极压性能和减摩性能;采用对置往复摩擦磨损试验机模拟内燃机上止点附近气缸套-活塞环的工作环境,以真实内燃机气缸套-活塞环材料作为摩擦副,进一步考察纳米SiO_2润滑油在变工况条件下(变温度、变速度、变载荷)的润滑摩擦性能,利用场发射扫描电镜FE-SEM观测了气缸套磨损表面的形貌,并分析纳米SiO_2润滑油改善润滑摩擦的机理。试验结果表明:应用纳米SiO_2添加剂可以显著提高基础油在混合润滑状态时的抗磨能力及在流体动压润滑状态时的减摩效果,在最佳添加浓度下,磨斑直径和平均摩擦系数分别下降了51.9%、46.7%;在上止点附近,气缸套-活塞环摩擦副的润滑状态为混合润滑,纳米SiO_2粒子的添加可以显著提高润滑油的抗磨减摩性能,在高温、低速、重载条件下摩擦系数分别下降10.5%、10.3%、5.9%;纳米SiO_2粒子在摩擦过程中在摩擦副表面起到"滚珠轴承"和抛光的复合作用。     

纳米通道内纳米流体流动特性的分子动力学模拟

利用分子动力学方法对铜-氩纳米流体和基础流体在不同剪切速度下的纳米尺度的Couette流进行模拟计算。结果表明:在纳米尺度通道内,纳米流体流动过程中颗粒存在旋转运动和平移运动,从而加强湍流效果,强化传热并影响整个流动区域内的流动速度分布,造成纳米流体速度呈非线性分布。壁面和纳米颗粒表面都会形成一层排布更为规则的液体原子吸附层,吸附层内液体分子在流体流动过程中一直伴随着壁面和纳米颗粒进行运动,且吸附层具有"类固"特性,可以增强纳米流体的传热能力。     

等离子体辅助甲烷燃烧的主要反应路径/通道

通过实验和模拟的方法,对等离子体辅助甲烷燃烧主要基元反应进行了研究.实验测量了等离子体辅助甲烷燃烧火焰不同位置的发射光谱图,得到了参与该过程的重要组分;模拟过程中,基于密度泛函理论,研究了甲烷燃烧反应中O_2+H→OH+O、CH_4+OH/O/H→CH_3+H_2O/OH/H_2、CH_3+O→CH_2O+H、CH_2O+OH/O/H→CO+H_2O/(H+H_2O)/(H+H_2)等几个重要基元反应,在B3LYP/6-311++G**水平找到了各反应可能的反应路径/通道,并进行分析.在此基础上,对比分析了放电等离子体作用下各反应路径/通道的变化,结果表明,在研究等离子体辅助甲烷燃烧机理时,应基于甲烷燃烧机理进行完善,通过加入*2HO(v)、O(1D)、CH_4(v)等激发态组分,并对一些基元反应进行拆分或合并,重新计算各反应活化能;生成的激发态组分会提升反应势能面,降低活化能,加速反应进程;在CH_2O与O/OH/H的反应中,放电等离子体可将生成的HCO直接分解,降低了HCO对H原子的消耗,同时还会释放一个H原子,有利于燃烧反应的进行.     

建立余热回收中纳米工质的导热系数预测模型

采用两步法制备质量分数为1%的Cu/Al2O3-H2O/EG混合纳米流体。首先,研究其导热系数随温度和基液混合比的变化情况。然后,根据多项式回归理论建立Cu/Al2O3-H2O/EG混合纳米流体的导热系数预测模型。实验结果表明,纳米流体的稳定性随乙二醇含量的增大而增强,由于不同种类粒子间的分子吸附力不同,导致相同种类粒子容易结合形成团聚体,而Cu粒子与Al2O3粒子的团聚体则较少。导热系数随着温度的升高非线性升高,随基液中水含量的增大而下降。根据实验数据,拟合了导热系数与温度及基液混合比的多项式预测模型,回归系数R2达0. 998,精度较高可以很好地预测Cu/Al2O3-H2O/EG混合纳米流体的导热系数。该模型可以指导工程应用。     

掺钒TiO_2可见光催化氧化SO_2的动力学和机理

利用溶胶-凝胶法制备掺钒纳米TiO_2,研究其在可见光条件下对SO2气体的催化氧化效果。采用烟气分析仪和碘量法测定SO2的浓度。利用XRD、BET、TEM、SEM、XPS、UV对掺钒TiO_2进行表征;研究焙烧温度、时间以及掺杂量等制备条件,对TiO_2脱除SO2的影响效果,探讨光催化氧化SO2的机理。结果表明:有O2条件下,在焙烧温度为700℃,时间为3 h,掺钒量物质的量含量为1.0%时,制备的TiO_2光催化氧化性能最好,SO2的脱除效率大于97%,氧化产物为SO3;光照和催化剂是SO2氧化的必要条件;光氧化效率随初始浓度的增大而增大,光催化反应符合一级反应动力学,且包括吸附和表面反应两部分,其中吸附为速控步骤;钒的掺杂使TiO_2产生红移,增强可见光催化活性,提高SO2气体的氧化效率。     

基于铁矿石载氧体25 kWth串行流化床生物质化学链气化实验研究

设计并建立了25kW_(th)串行流化床生物质气化反应器,基于此反应器,以赤铁矿石作为载氧体,开展生物质化学链气化实验研究,考察气化反应器温度、S/B、载氧体添加比例对生物质气化特性的影响。当赤铁矿占床料比例高于40%时,该气化装置的气化反应器温度保持平稳,铁矿石载氧体的再生及传热性能优良。燃料反应器出口烟气的成分为H_2、CO_2、CO、CH_4和少量的C_2H_4。随着气化反应器温度升高,气化反应器出口烟气中CO、CH_4和C_2H_4体积分数逐渐降低,相应的CO_2体积分数逐渐升高。随着S/B由0.6升高到1.4,气化反应器出口烟气中H_2和CO_2体积分数逐渐升高,CO、CH_4和C_2H_4体积分数逐渐降低。另外,载氧体添加比例增加,生物质气化反应器出口烟气中CO、H_2、CH_4和C_2H_4体积分数呈减小的趋势,而CO_2体积分数显著增加。     

光催化法对分解硫化氢制氢的影响

文中采用波长为253.7 nm的紫外光为光源,以Na2S/Na2SO3混合水溶液作为反应介质,采用不同种的光催化剂进行紫外光液相分解硫化氢(H2S)制氢反应。考察了不同种紫外响应的光催化剂对产氢的影响、TiO2-P25光催化剂、TiO2-P25光催化剂加入量、焙烧温度对ZnO光催化剂活性对产氢的影响。研究结果表明,加入光催化剂有助于反应的进行,使反应的产氢量有所提高,不同的光催化剂对分解硫化氢制氢的影响不同;TiO2-P25光催化剂其分解Na2S溶液与紫外光子激发HS-有协同作用;250 mL 0.1 mol/L Na2S水溶液中最佳催化剂用量为0.05 g;不同焙烧温度下制得的ZnO光催化剂对反应体系的产氢速率影响较大,随着焙烧温度的提高,反应的产氢速率也相应提高。     

Impacts of the periodic wall conditions on the hydromagnetic convective flow of viscoelastic fluid through a vertical channel with Hall current and induced magnetic field

In this study, a mathematical analysis is presented for the hydromagnetic convective flow of an incompressible, chemically reacting, and electrically and thermally conducting viscoelastic fluid through a vertical channel bounded by the porous regime under the action of an applied magnetic field with Hall current and induced magnetic field effects. The left wall of the channel is considered to be nonmagnetic, whereas the right wall of the channel is periodically magnetized. The flow within the channel is induced due to the nonuniform wall temperature and concentration, periodic pressure gradient, and periodic movement of the right wall. The method of separation of variable is used to convert the flow governing coupled partial differential equations into the ordinary differential equations that are solved analytically, and the solution for fluid velocity, induced magnetic field, temperature, and concentration is presented in a closed form. Numerical computation has been performed to demonstrate the impact of various system parameters on the fluid flow behavior. It is observed that oscillations increase the primary flow and primary induced magnetic field. Buoyancy forces have a tendency to lessen the secondary induced magnetic field. Furthermore, it is examined that magnetic diffusivity increases the primary flow, whereas it decreases the secondary flow and primary induced magnetic field.     

TiO2光催化反应过程的"场流"理论分析

在简要阐述TiO2光催化反应机理及“场流”理论的基础上，通过对TiO2光催化反应过程的综合分析，将TiO2光催化反应过程分解为简单的几种“流”和“场”的耦合。着重分析了“流”以及外加“场”对TiO2光催化反应的影响，同时对H2O2，Fe^2 /Fe^3 ,O3紫外光，超声波，电场，微波，磁场协同提高了TiO2光催化反应效率的机理进行了解释。     

Field ionization effect on hydrogen adsorption over TiO2-coated activated carbon

Behaviors of hydrogen adsorption over TiO₂-coated activated carbon under various electric potentials were studied. TiO₂ particles were introduced onto carbon via the hydrolysis of TiCl₄ in acid solution. The results showed that the hydrogen adsorption first increased and then decreased with the increase of electric field. The improved storage was due to a stronger interaction between charged carbon surface and polarized hydrogen molecule caused by field induced polarization of TiO₂ coating. When the electric field was sufficient to cause considerable ionization of hydrogen, the decrease of hydrogen adsorption occurred. The electricity detected at 3000 V was a sign of ionization of hydrogen. The DFT calculations showed a much stronger binding between TiO₂-doped coronene and hydrogen molecule under an electric field, which is consistent with our experimental observations.     

微细通道内氢气辅助甲烷催化氧化的数值模拟

对微圆管内低浓度氢气、甲烷混合气在铂表面的催化氧化进行了数值模拟,重点研究了添加氢气对甲烷反应的影响机理.结果表明,氧气占据空位活性中心抑制了甲烷的吸附,导致较高的催化着火温度;氢气的掺入可以降低甲烷氧化反应的起始温度和着火温度;在铂催化剂表面,甲烷的催化氧化发生在氢气的燃烧过程中,氢气在燃烧过程中消耗氧气,为甲烷的反应提供必需的空位活性中心(Pt(s));甲烷的着火主要受其自身的激发,甲烷着火以前,壁面活性中心几乎全被氧占据,而甲烷着火以后,O(s)和Pt(s)同为主要壁面组分.     

Plumbene: A next generation hydrogen storage medium

Plumbene, a recently discovered 2D material, has been examined for hydrogen storage. First principles calculations have been performed to investigate the hydrogen adsorption on pristine plumbene monolayer. The hydrogen molecule prefers to adsorb on three adsorption sites, i.e. H (hollow-site), T (top-site) and B (bond-site), of plumbene surface with desired adsorption energy. The adsorption energy is highest (−149 meV) at hollow site and lowest (−104 meV) at bond site. One side hydrogen decorated plumbene exhibit 3.37 wt% Hydrogen Gravimetric Density (HGD). Whereas 6.74 wt% (HGD), with the average adsorption energy of −117 meV/H_2, has been achieved in both side hydrogen decorated plumbene monolayer. Applied electric field can effectively controls the adsorption and desorption processes. Positive electric field makes the adsorption strong while the negative electric field results in weakening of hydrogen adsorption. It means electric field act as a switch to store and release hydrogen with good control and usage selectivity. Present study reveals that the plumbene is a strong candidate for hydrogen storage to meet the desired target of HGD suggested by U.S. Department of Energy by the year 2021.     

Numerical investigation of nonuniform transverse magnetic field effects on the flow and heat transfer of magnetic nanofluid in a sintered porous channel

In this paper, fluid flow and convective heat transfer of a ferrofluid (water and 4 vol% Fe₃O₄) in sintered Aluminum porous channel, which is subjected to a nonuniform transverse magnetic field have been studied. The numerical simulations supposed an ordinary cubic and staggered arrangement organized by uniformly sized particles with a small contact area for the porous media and constant heat flux at the surface of the microchannel. A wire, in which the electric current passes creates a nonuniform magnetic field, which is perpendicular to the flow direction. To do this simulation, the control volume technique and the two‐phase mixture model have been employed. The results show that the obtained local heat transfer coefficient on the channel surface increased with increasing mass flow rate and decreased slightly along the axial direction. Moreover, exerting the above‐mentioned magnetic field increases the Nusselt number that enhances the heat transfer rate while it has no effect on the pressure drop along the channel.     

Effects of interface wettability on microscale flow by molecular dynamics simulation

Non-equilibrium molecular dynamic simulations have been carried out to study the effect of the interface wettability on the pressure driven flow of a Lennard-Jones (LJ) fluid in a nanochannel. The results show that the hydrodynamic boundary condition at the solid-liquid interface depends on both the interface wettability and the magnitude of the driving force. For a LJ fluid in a nanochannel with hydrophilic surfaces, the velocity profiles have the traditional parabolic shape. The no-slip boundary condition may break down when the driving force exceeds a critical value that overcomes the interfacial resistance. In such a case, the MD results show a pattern of an adsorbing layer sliding along the solid wall. For a LJ fluid in a nanochannel with hydrophobic interfaces, the results show that a gap exists between the liquid and the surface, resulting in almost frictionless resistance; the velocity shows a plug flow profile and the slip length is not constant but depends on the driving force. Furthermore, it is found that the non-uniform temperature and pressure profiles near the solid walls are owing to the effect of interface wettability.     

Numerical Study of an Electro-Osmotically Driven Microchannel Flow with Joule Heating Effect

A convection-diffusion reaction scheme is applied to solve the transient transport equations for the prediction of steady electro-osmotic microchannel flow behavior. The governing equations for the total electric field include the Laplace equation for the effective electrical potential and the Poisson-Boltzmann equation for the electrical potential established in the electric double layer. The transport equations governing the hydrodynamic field variables comprise mass conservation equation for the electrolyte and equations of motion for the incompressible charged fluid flow subject to an electro-osmotic body force. The main aim of the study is to elucidate the effect of Joule heating, which can affect the electrohydrodynamic behavior. Investigation into the region near the negatively charged channel wall is made through the simulated velocity boundary layer, diffuse layer, and electric double layer.