轻组份燃料对乳化油蒸发与着火影响的研究

本文研究了较组份添加剂对单滴乳化油着火规律的影响。实验采用挂滴法。实验中,测量了体积比为十二烷：正庚烷：水6：0：4,5：1：4,4：2：4,3：3：4的着火延迟时间。实验结果和数值计算表明,在乳化油中加入易挥发添加剂能有效缩短乳化油的着火延迟时间,着火延迟时间随着添加剂加入量的增加而缩短,当易挥发添加剂含量较大时,着火延迟随着添加剂加入量的增加,变化越来越缓慢。这一结果对解决在掺水量大的条件下保证柴油机中乳化燃料的正常点火与启动具有实用价值。     

基于各向异性表面的液滴驱动

驱动液滴实现各种动态行为在生物医学、微流控、痕量检测等领域具有重要应用。液滴的驱动主要依赖于对液滴不同位置受力的调节。具有浸润性差异或结构差异的各向异性表面,在对液滴进行驱动时具有操作简便、节约能源等优势,逐渐成为液滴操控领域的研究热点之一。本文结合本课题组的研究工作,对近年来利用各向异性表面驱动液滴的相关研究进行了综述。首先,分析了各向异性表面驱动液滴的基本原理。依据制备方法的不同,将各向异性表面分为浸润性各向异性表面、结构各向异性表面和协同各向异性表面三类,分别归纳了其常见制备方法和在液滴驱动领域的主要应用。最后,本文对各向异性表面驱动液滴的局限性和发展方向进行了总结和展望。     

Oldroyd-B黏弹性液滴弹跳行为的改进SPH模拟

基于光滑粒子流体动力学SPH(Smoothed Particle Hydrodynamics)方法对Oldroyd-B黏弹性液滴撞击固壁面产生的弹跳行为进行了模拟与分析。首先,为了解决SPH模拟黏弹性自由表面流出现的张力不稳定性问题,联合粒子迁移技术提出了一种改进SPH方法。然后,对Oldroyd-B黏弹性液滴撞击固壁面产生的铺展行为进行了改进SPH模拟,与文献结果的比较验证了方法的有效性。最后,通过降低Reynolds数捕捉到了液滴的弹跳行为;并在此基础上,分析了液滴黏度比、Weissenberg数和Reynolds数对液滴弹跳行为的影响。结果表明,改进SPH方法可有效地模拟黏弹性自由表面流问题;液滴黏度比、Weissenberg数和Reynolds数对液滴最大回弹高度均有显著的影响。     

液滴撞击不同湿润性固壁面上静止液滴的格子Boltzmann研究

采用单组分多相的伪势格子Boltzmann方法,在大小液滴粒径比为1.5的情况下,对大液滴竖直撞击壁面上静止小液滴的过程进行模拟,研究亲水与超疏水壁面上大液滴竖直碰撞小液滴的过程,得到液滴铺展因子和相对高度随时间的变化。结果表明：增大We数会使液滴的铺展因子增大,铺展直径变大,相对高度减小;并且随着We数的增加,在超疏水表面,液滴在铺展过程中底部会出现空腔,空腔大小随着We数增大而增加;此外,We数增加到107.35时,液滴发生了断裂。     

Effect of droplet size on the dielectric properties of PDLC films

Polymer dispersed liquid crystal (PDLC) films (5CB/PMMA, 60/40) of different droplet size were prepared by a solvent-induced phase separation method under different N₂ flow speeds. The effects of droplet size on the thermal transitions of the LC and various dielectric properties such as dielectric constant, conductance, dielectric loss, and the electric field induced in a droplet were examined. The configuration of the LC in the film with smaller droplets can be identified by comparing the dielectric constant of the film with the one predicted by Boettcher's mixture formula. In addition, the effect of droplet size on the electro-optical response of the PDLC film was investigated. Variations of the conductance and the dielectric constant of the film were analyzed under various AC frequencies, with the purpose of elucidating the polarization mechanism of the LC molecules in the droplet. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1373–1381, 1997     

NUMERICAL PREDICTION OF SEMI-CONFINED JET IMPINGEMENT AND COMPARISON WITH EXPERIMENTAL DATA

The standard k–ε eddy viscosity model of turbulence in conjunction with the logarithmic law of the wall has been applied to the prediction of a fully developed turbulent axisymmetric jet impinging within a semi-confined space. A single geometry with a Reynolds number of 20,000 and a nozzle-to-plate spacing of two diameters has been considered with inlet boundary conditions based on measured profiles of velocity and turbulence. Velocity, turbulence and heat transfer data have been obtained using laser–Doppler anemometry and liquid crystal thermography respectively. In the developing wall jet, numerical results of heat transfer compare to within 20% of experiment where isotropy prevails and the trends in turbulent kinetic energy are predicted. However, stagnation point heat transfer is overpredicted by about 300%, which is attributed directly to the turbulence model and inapplicability of the wall function.     

Engineering the Morphologies of Block Copolymer Particles from the Confined Self-assembly within Emulsion Droplets†

Block copolymers (BCPs) can automatically assemble into various regulated nanoparticles when they are confined within the emulsion droplet because of the structural frustration of polymer chains and the soft template effect of the oil/water interface. In the past few years, great efforts have been made to regulate the morphologies of the resulting BCP particles. In this review article, various strategies for tuning oil/water interfacial properties to engineer the as-formed BCP particles were summarized. Then, the comprehensive scenarios of the applications of the resulting BCP particles were discussed. Finally, the future tendency and challenge of the self-assembly of BCPs confined in emulsion droplet were suggested.     

On-line monitoring of emulsion polymerisation using conductivity measurements

This work investigates the feasibility of implementing conductivity measurements for the purpose of the on-line monitoring of particle generation by following the evolution of free surfactant concentration during SDS/styrene emulsion polymerisations. The conductivity and temperature were measured on-line during the reactant addition and reaction stages of a number of batch emulsion polymerisations. Samples were collected for off-line analysis of particle size and conversion. Observation of the evolution of the conductivity enabled us to measure the effect of surfactant and monomer addition. The maximum size of the monomer droplets was calculated from the decrease in conductivity that represented the adsorption of surfactant molecules onto the droplet surface. The division of SDS between the particle interface and the aqueous phase was also determined giving an indication of the particle stability.