双原子氧气液界面特性的分子动力学模拟

采用分子动力学模拟方法,考虑氧分子中原子间键的谐振势作用,研究了双原子氧的平衡态气液相变特性以及不均匀相界面区的表面张力等性质。根据双原子氧气液相饱和密度的实验数据,确定Lennard-Jones势能模型中氧原子的参数,模拟得到了不同温度下气液相的密度和饱和压强,与实验数据符合良好,验证了确定的氧原子参数的正确性。通过模拟得到了界面压力张量的法向和切向分量的分布曲线以及界面表面张力随温度的变化曲线,在气液界面区,压力张量的法向与切向分量存在较大的势阱和势垒,界面的表面张力随温度线性降低,当达到临界温度时,表面张力减小到0。     

氪氙稀有气体的低温分离模拟

为了回收利用液氧中的氪和氙,采用PR气液平衡状态方程,使用HYSYS软件对氪氙浓缩塔内的精馏分离进行了模拟计算,得出了塔内的温度变化曲线和氧、氪、氙组分的分布曲线,提出利用塔内的平均温度控制塔内精馏工况,并对氪氙浓缩塔的设计提出建议。     

Ar-Kr低温界面传热过程分子动力学模拟

运用非平衡分子动力学原理和LJ势函数仿真研究氩(Ar)与氪(Kr)之间的界面层传热问题,模拟其界面传热的能量变化过程.仿真结果表明,即使界面粗糙度为0,低温固体界面热阻仍然存在.平均温度为40 K,粗糙度为0时,氩(Ar)与氪(Kr)之间界面热阻为0.15～0.18 Wm2/K,相对误差小于17%.     

二元有机物体系相变的分子动力学模拟

采用分子动力学模拟(MD)和NTP系综方法对十七烷、十五烷及十七烷/十五烷混合体系的相变行为进行了模拟研究.根据体系自扩散系数和比体积随温度的突变关系,获得的十七烷、十五烷相变温度值与文献中的实验结果吻合较好,并确定了不同混合体系的相变温度.二元混合体系的相变温度可根据组分比例进行调节,可满足一定温度下相变储能的应用要求.通过分析熔化过程中十七烷分子二面角的变化获得了十七烷分子微观结构变化的特征.在熔化过程中十七烷分子有序度降低.     

氮氖混合蒸气冷凝气液界面的传热特性研究

基于低温下竖直平板冷凝的实验平台,建立了氮氖混合蒸气冷凝的数值模型,并完善了混合物冷凝过程中的两相扩散系数,模拟结果与实验数据吻合良好。分析了混合物中组分浓度场和气液两相场的分布特征,揭示了液膜上方高浓度氖气扩散层阻碍气液界面传质过程的机理。对比了不同的冷凝温差,进口氖气浓度和主蒸气速度对于混合蒸气冷凝过程的影响。模拟结果表明气液界面的平均传质速率受到冷凝过程的传热温差和气相扩散层内的浓度梯度控制,而壁面平均传热系数则受到液膜厚度和流速影响。通过降低混合蒸气中的氖气浓度和提高混合蒸气的速度可以提升氮氖混合蒸气冷凝传热性能。     

纳米尺度通道中气体粘度的分子动力学模拟

利用非平衡分子动力学方法模拟了气体在纳米尺度通道中的运动特性,统计获得通道中流动的速度剖面和剪切应力分布,并利用牛顿粘性定律首次获得了纳米尺度通道中的等效粘度分布。结果表明,纳米尺度通道中的粘度不是一个常数。在壁面附近,由于壁面原子和气体分子的相互作用,存在壁面效应,气体的粘度较小;而通道中心区域的粘度与实验结果符合较好,壁面对粘度的影响范围为20 nm左右。通道高度对中心区域粘度的影响很小,而温度对其的影响较大,粘度值随温度的增加而增大。不同通道高度下,壁面附近粘度的分布几乎一致;不同温度时,壁面附近粘度的分布随温度的增加而增加。     

超临界L-J流体粘度的分子动力学模拟

用分子动力学模拟了超临界Lennard-Jones(L-J)流体在微通道内的剪切应力与速度分布.利用经典流体力学理论中剪切应力和速度分布之间的关系式,得到了超-临界氩与超临界氦在不同温度和密度条件下的动力粘度.结果说明,L-J流体模型得到的超临界氩的粘度与美国国家标准局(NIST)公布的数据十分接近,超临界氦的粘度与NIST中的粘度数据具有相同的数量级,但是数值稍有偏差,说明氦这种量子流体,单纯以L.J流体势能模型为基础是不完全的,需要在此基础上进行量子效应的修正.     

聚乳酸玻璃化转变行为的分子模拟

采用等温等压(NPT)正则系综,用分子动力学方法研究了聚乳酸的玻璃化转变行为,获得了玻璃化转变温度.在230～440K范围内,通过模拟体系的密度、比体积及相关径向分布函数等参数,最终确定了聚乳酸的玻璃化温度,模拟计算的结果与实验值吻合.     

MgO材料高压熔化特性的分子动力学模拟

用Shell模型分子动力学(MD)方法对MgO材料的高压熔化特性进行了研究,势函数取Buckingham形式.将计算得到的熔化曲线与实验以及其它理论结果在0～140GPa的压力范围内做了比较,通过修正得到的MgO熔化温度和实验测量能够很好地符合.MgO熔化模拟的结果对固体材料一阶相变分子动力学模拟的过热理论做了进一步的验证.另外,我们对反映体系微观结构的MgO径向分布函数(RDF)进行了分析.     

模拟聚乙烯块体相变和导热的粗粒化模型和势场建立EI北大核心CSCD

建立适用于介观尺度聚乙烯块体相变和导热分子模拟的粗粒化模型及势场,并对其进行验证。基于全原子分子动力学模拟结果,采用多态-迭代玻尔兹曼变换法进行粗粒化分子动力学模拟来获得粗粒化势场。结果表明:粗粒化势场采用函数形式的势能描述,易于使用;对比全原子模拟结果,粗粒化势场能够较准确地模拟聚乙烯块体的静态结构性质;聚乙烯块体在300 K和500 K下密度的模拟值与实验值误差小于3%,玻璃化转变温度和熔化温度的模拟值与实验值相符较好;单链聚乙烯导热系数的粗粒化势场模拟值与全原子模拟值较一致,无序聚乙烯块体导热系数的模拟值与实验值吻合较好。研究结果为介观尺度聚乙烯的导热研究提供了一种更高效的模拟方法。     

Viscosity of a binary fluid in narrow slot-like pores

The concentration dependences of the shear-viscosity coefficient of a fluid, representing a binary mixture of components with molecules of approximately equal sizes, in narrow slot-like pores filled to a different degree (from a rarefied gas to a liquid) have been theoretically investigated with the use of a lattice-gas model accounting for the characteristic volume of atoms and interactions between them in the quasichemical approximation. This model allows one to determine the self-consistent equilibrium characteristics of a vapor-liquid system and the shear-viscosity coefficients of molecules with the use of a unique set of energy parameters. The influence of the activation energy of the surface migration of molecules on the local coefficients of viscosity has been considered. A molecular interpretation of the sliding friction of a fluid near the walls of pores has been given; this effect was explained by the surface migration of the mixture components. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 1, pp. 121–132, January–February, 2006.     

复叠温区混合工质制冷机的研究

简述混合工质制冷机的构造及其工作原理,分析该系统循环方式的特点。对自复叠式循环(ACR)系统热力性能进行初步研究,分析混合工质气液相平衡特性数学建模方法,并概述现阶段混合工质热力性质和循环系统的研究成果。     

乙醇水溶液真空膜蒸馏分离过程的模拟分析

真空膜蒸馏技术可用于分离水溶液中的有机挥发性化合物(VOCs),是一种治理遭受VOCs污染工业废水的新方法.对低浓度乙醇水溶液二元体系下的真空膜蒸馏过程展开了模拟分析,膜内的传质按Knudsen扩散原理考虑,界面上的平衡关系按Van Laar活度系数法给出.模拟结果表明:过程的操作参数对分离效率有较大的影响,进口温度、料液流量、浓度和真空度增加,膜通量将增加;分离因子随进口温度、真空度、浓度增加而减少,料液流量对分离因子影响与真空侧流动形式有关.真空侧流动形式对分离因子有一定的影响,并流条件下,分离因子最大.     

The sub-micron hole array in sapphire produced by inductively-coupled plasma reactive ion etching

The sub-micron hole array in a sapphire substrate was fabricated by using nanosphere lithography (NSL) combined with inductively-coupled-plasma reactive ion etching (ICP-RIE) technique. Polystyrene nanospheres of about 600 nm diameter were self-assembled on c-plane sapphire substrates by the spin-coating method. The diameter of polystyrene nanosphere was modified by using oxygen plasma in ICP-RIE system. The size of nanosphere modified by oxygen plasma was varied from 550 to 450 nm with different etching times from 15 to 35 s. The chromium thin film of 100 nm thick was then deposited on the shrunk nanospheres on the substrate by electron-beam evaporation system. The honeycomb type chromium mask can be obtained on the sapphire substrate after the polystyrene nanospheres were removed. The substrate was further etched in two sets of chlorine/Argon and boron trichloride/Argon mixture gases at constant pressure of 50 mTorr in ICP-RIE processes. The 400 nm hole array in diameter can be successfully produced under suitable boron trichloride/Argon gas flow ratio.     

Vapor-liquid equilibrium,coexistence curve,and critical locus for binary HFC-32/HFC-134a mixture

Two kinds of equilibrium measurements of binary R-32/134a mixtures were carried out. The vapor-liquid equilibria were measured by the static method in the temperature range between 283 and 313 K. On the basis of the present experimental data, the temperature dependence of the binary interaction parameterk ₁₂ for two equations of state, namely, the Soave-Redlich-Kwong equation and Carnahan-Starling-De Santis equation, was discussed. The vapor-liquid coexistence curve near the critical point was also measured by the observation of meniscus disappearance. The critical temperatures and critical densities of 30 and 70 wt% R-32 mixtures were determined on the basis of the saturation densities along the coexistence curve in the critical region. In addition, a correlation of the critical locus for this mixture is proposed as a function of composition.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

交联反应统计理论在RTM固化过程数值模拟中的应用

树脂传递模塑工艺的固化过程数值模拟有助于化学反应、材料结构与性能的控制,具有重要的科学意义和工程价值.根据该工艺的固化反应动力学模型、交联反应统计理论和温度方程,采用有限元法开展了固化过程的数值模拟,分析了温度、固化率、交联度和官能团浓度等物理量的影响因素以及变化规律.     

Precise Measurements of the Vapor-Liquid Equilibria (VLE) of HFC-32/134a Mixtures Using a New Apparatus

A new apparatus for precise measurements of the vapor-liquid equilibria of mixtures by the circulation method has been developed. This apparatus has two special components: a high-stability temperature control system and a helium pressurization system. The temperature in the liquid bath surrounding the sample cell is kept constant within ±0.5mK. The helium pressurization system increases the pressure of the sampled mixture when measuring the compositions at low temperatures by gas chromatography. With these components, the uncertainty in measuring the vapor-liquid equilibria has been reduced. Using this apparatus, the vapor-liquid equilibria of HFC-32/134a mixtures were measured in a temperature range of 263.15 to 293.15K. These results are in good agreement with the calculated results from REFPROP (Ver. 6.01) with a relative pressure difference of about 2%.     

电磁微锻机构热效应模拟与实验研究

为研究电磁微锻机构在工作过程中的温度分布情况以及提高其功率密度,首先,在现有电磁微锻机构的基础上,从能量角度对其热效应与输出功率的关系进行分析,明确了热效应会限制机构的最大输出功率。然后,利用COMSOL Multiphysics软件分别对风冷和水冷方式下电磁微锻机构的温度场进行CFD （computational fluid dynamics, 计算流体力学）仿真分析,确定了不同入口边界条件下的等效对流换热系数;同时,根据等效对流换热系数与入口边界条件的关系,建立了该机构的瞬态温度分析模型。最后,搭建了电磁微锻机构温度测量实验平台,并对该机构的温升特性和稳态温度特性进行了实验研究。实验结果表明,所提出的电磁微锻机构热效应仿真分析方法较为合理、准确,可为微锻机构的温度控制和结构优化提供参考。     

Measurements of the vapor-liquid coexistence curve and the critical parameters for 1,1,1,2-tetrafluoroethane

Measurements of the vapor-liquid coexistence curve in the critical region for 1,1,1,2-tetrafluoroethane (R134a; CH₂FCF₃), which is currently considered as a prospective substitute for conventional refrigerant R12, have been performed by visual observation of the disappearance of the meniscus at the vapor-liquid interface within an optical cell. Twenty-seven saturated densities along the vapor-liquid coexistence curve between 208 and 999 kg·m^–3 have been obtained in the temperature range 343 K to the critical temperature. The experimental uncertainties in temperature and density measurements have been estimated to be within ±10mK and ±0.55%, respectively. On the basis of these measurements near the critical point, the critical temperature and the critical density for 1,1,1,2-tetrafluoroethane were determined in consideration of the meniscus disappearing level as well as the intensity of the critical opalescence. In addition, the critical exponent ß along the vapor-liquid coexistence curve has been determined in accord with the difference between the density of the saturated liquid and that of the saturated vapor.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

矩形翅片椭圆管束性能研究及场协同分析

利用CFD方法对空冷系统的基本换热元件矩形翅片椭圆管进行了数值模拟;与实验数据相比较,研究了其在不同迎面风速下的阻力特性与换热特性,拟合出了三排管对流换热系数和协同角随迎面风速的变化关系;并采用场协同原理分析讨论了温度梯度与速度矢量方向的夹角对矩形翅片椭圆管换热特性的影响;结果表明,随着夹角的增大,换热效率变低,以致换热量非线性增加。