同轴圆筒流变仪初始瞬态黏度的解析与数值研究

同轴圆筒流变仪在恒剪速或恒应力测试初始过程中测试黏度远高于真实值的现象与流场非稳态作用等因素有关。测量间隙内的Couette流动研究主要集中在边界条件为恒值或某一具体时间函数下的理论推导,而测量间隙的边界条件实际为某一动边界。假设动边界为任意f(t),将同轴圆筒间Newtonian流体初始流变测试过程简化为无限大平板间Couette流动,采用特征函数法和Laplace变换推导应力和剪速边界下流场及表观黏度精确解,同时依据不同间隙尺寸和运动黏度对6种边界条件下的瞬态表观黏度进行数值计算。结果表明:当υ20 mm~2·s~(-1)时,控制剪速边界下流场及表观黏度平衡时间更短;当20 mm2·s~(-1)υ20000 mm2·s~(-1)时,控制应力边界下流场及表观黏度平衡时间更短;当υ20000 mm~2·s~(-1)时,两类边界条件下的平衡时间相近。     

小球藻热解油在Ni-Cu/ZrO2催化剂上的加氢脱氧

在小型固定床反应器中以Ni-Cu/ZrO₂为催化剂,对小球藻热解油进行催化加氢脱氧,以改善生物油性能。利用XRD、H₂-TPR、TG、NH₃-TPD等技术对催化剂进行了结构表征。结果表明,Cu的加入有效促进了Ni-Cu/ZrO₂催化剂活性相的表面分散,提高了该催化剂对小球藻热解油加氢脱氧反应的催化活性。在2 MPa、350 ℃反应条件下,随Cu/Ni的增大,Ni-Cu/ZrO₂的催化活性先升高后降低,Cu/Ni质量比为0.40时的催化性能最好,连续运行3 h后所得精制生物油脱氧率达82.0%。Ni-Cu/ZrO₂催化剂在反应过程中,表面结焦少,活性粒子及催化剂性能稳定,连续运行24 h后所得精制生物油脱氧率依然维持在77.0%以上。小球藻热解油经催化加氢脱氧所得的精制生物油,低位热值由31.5 MJ·kg^-1提高至35.0 MJ·kg^-1,40℃运动黏度由20.5 mm²·s^-1降至9.5 mm²·s^-1,且油品中水分更易于脱除。精制生物油中高级脂肪酸的含量减少,油品稳定性大幅提高。     

高压静电场对纤维素Iβ中甲醛扩散的影响

采用分子动力学的方法,进行了在不同高压电场作用下,甲醛分子在纤维素Iβ中扩散运动的模拟。结果表明：当电场强度从0增大到10⁹ V·m^-1时,扩散系数由5.64×10^-10 m²·s^-1增大到7.768×10^-10 m²·s^-1,增大了约38%,说明高压静电场加强了甲醛分子在纤维素Iβ中的扩散运动,提高了扩散系数;电场强度能有限增强纤维素链的整体移动,并不会破坏纤维素的稳定性;高压静电场的施加,改变了甲醛分子与纤维素Iβ相互作用,提高了静电作用、范德华作用和总相互作用。     

密相输运床的团聚物频率和持续时间

在内径0.102 m、高17 m的密相输运床冷态实验台上,以石英砂(属Geldart B类颗粒)作为循环物料,对光纤探针在表观气速8.2~11.2 m·s^-1,固体循环流率139~530 kg·m^-2·s^-1下获得的瞬态信号,采用小波分析的方法研究了团聚物频率、团聚物持续时间。结果表明:提升管边壁与底部区域更易形成大尺度团聚物,径向上团聚物频率中心高边壁低,而团聚物持续时间中心短边壁长。轴向上提升管底部团聚物频率低、持续时间长。团聚物频率随表现气速增大而增大,而团聚物持续时间随表现气速增大而缩短,提升管底部团聚物频率随固体循环流率增大而降低,团聚物持续时间随固体循环流率增大而变长。     

二氧化碳水合物浆在圆管中的流动特性

实验研究了固相分数为8.2%～23.1%的CO₂水合物浆在内径为8 mm的圆管中的流动特性。结果发现水合物浆在管内的流动压降随着流速的增加而增大。当流速低于0.60 m·s^-1时,浆体流变指数小于1,且随着固相体积分数的增大而减小,CO₂水合物浆为H-B流体,其表观黏度随着流速的增大而减小,呈剪切变稀特性。剪切速率为600 s^-1时,CO₂水合物浆的表观黏度为8.5～10.6 mPa·s。实验得到了CO₂水合物浆的流变特征参数及其流变方程,可为CO₂水合物浆的流动及其应用研究提供理论指导。     

挤出塑料管喷淋冷却的数值模拟

冷却系统是塑料挤出管道生产工艺中的关键设备,其冷却的均匀性和效率直接影响管道产品的质量及生产速度。首先基于ANSYS对喷淋冷却瞬态传热进行模拟,结果表明：对流传热系数小于180 W·m^-2·K^-1时,冷却至目标温度（47℃）所需的时间随传热系数的变化明显;传热系数大于180 W·m^-2·K^-1时,冷却至目标温度所需的时间随传热系数的变化不大。然后基于FLUENT软件对喷淋喷嘴进行模拟,研究了喷淋入口速度、喷嘴高度对喷淋传热系数的影响,结果表明：随着喷淋入口速度的增加（6～15 m·s^-1的范围内）,总体对流传热系数增大,驻点处的传热系数由217 W·m^-2·K^-1增加到386 W·m^-2·K^-1;随喷淋高度的减小（68～128 mm范围内）,壁面传热系数呈增加趋势,驻点处传热系数由227 W·m^-2·K^-1增加到311 W·m^-2·K^-1。基于以上研究,为真空定径喷淋冷却水槽的整体优化提出合理建议。     

LiF对Na3AlF6-Al2O3熔盐电解阴极过程的影响

电解铝工业中铝在阴极上析出,铝析出反应的机理对电解铝生产具有理论指导意义。在运用循环伏安法研究的基础上,通过理论计算,对Na₃AlF₆-Al₂O₃和Na₃AlF₆-Al₂O₃-LiF体系中金属铝在钨电极上的电化学沉积行为以及铝钨金属间化合物的形成机理进行了研究。结果表明：两体系中铝钨金属间化合物在50 mV·s^-1≤ν≤150 mV·s^-1扫描速率下的形成过程是受扩散控制的准可逆过程。在化合物形成的过程中,两体系中Al³⁺的扩散系数从4.54×10^-9 cm²·s^-1增长到5.71×10^-9 cm²·s^-1,Al³⁺反应的活化能分别为11.14 kJ·mol^-1和10.47 kJ·mol^-1。在Na₃AlF₆-Al₂O₃-LiF体系的还原过程中,Li并没有还原析出,而在氧化过程中Al在金属间化合物中的氧化电流增大;在恒电流电解时,Al-W金属间化合物并不溶于熔盐中,会附着在工作电极表面,LiF的加入会使电极表面的WAl₄量变小,取而代之的是Al₂O₃的增加,说明LiF的加入使电解更加稳定,抑制了电极表面WAl₄的生长。     

绝缘衬底上化学气相沉积法生长石墨烯材料

利用化学气相沉积法,在Si衬底、蓝宝石衬底和SiC衬底上生长石墨烯材料,研究石墨烯的表面形貌、缺陷、晶体质量和电学特性。原子力显微镜、光学显微镜和拉曼光谱测试表明,Si₃N₄覆盖层可以有效抑制3C-SiC缓冲层的形成;低温生长有利于保持材料表面的平整度,高温生长有利于提高材料的晶体质量。5.08 cm蓝宝石衬底上石墨烯材料,室温下非接触Hall测试迁移超过1000 cm²·V^-1·s^-1,方块电阻不均匀性为2.6%。相对于Si衬底和蓝宝石衬底,SiC衬底上生长石墨烯材料的表面形态学更好,缺陷更低,晶体质量和电学特性更好,迁移率最高为4900 cm²·V^-1·s^-1。     

湍动流化床内固体颗粒扩散系数

将高速摄影及基于互相关原理的图像处理技术与颗粒扩散规律的研究进行结合,对湍动流化床中甲醇制烯烃催化剂SAPO-34颗粒的扩散系数进行了实验研究。实验表明,对于Geldart A类的SAPO-34颗粒,颗粒纵向扩散系数在10^-2～10^-1 m²·s^-1量级之间,横向扩散系数在10^-3～10^-2 m²·s^-1量级之间,两者均随流化风速的上升而增大。另外,在相同的流化风速下,粒径较小的颗粒具有更大的扩散系数。该结果对湍动床颗粒运动规律的研究有一定意义。     

二水硫酸钙溶解动力学

采用电导率法测量匀速旋转的石膏块试样(CaSO₄·2H₂O,质量分数为98%)在纯水中的溶解速率,数据采集时间间隔1 s,测试期间试样表观形状(7 cm×4 cm×2 cm)和面积(100 cm²)基本不变。在溶解过程为表面反应控制条件下,依据溶解反应动力学模型,拟合得到25、45、65、85℃下二水硫酸钙溶解反应速率常数分别为1.91×10^-8、3.46×10^-8、4.92×10^-8、7.07×10^-8 mol·cm^-2·s^-1,反应级数为1.27。经Arrhenius公式回归得到溶解反应表观活化能为19.07 kJ·mol^-1。本实验方法排除了溶解过程试样面积不确定因素,拟合得到的模型参数使动力学方程计算值与实验值更为吻合,更接近溶解速率理论预测文献值。     

A Survey of Rheological Properties of One-Component Epoxy Adhesives

Flow characteristics of seven commercially available one-component epoxy adhesive pastes were measured using a controlled shear stress rheometer and a controlled shear rate rheometer over a temperature range from 5°C to 60°C. Combining data obtained from both controlled rate and controlled stress experiments over a wide range of shear rates, we observed Newtonian flow (shear stress proportional to shear rate) at very low shear rates, a plateau “shear thinning” region at intermediate shear rates, and a second region of linear dependence of shear stress on shear rate at high shear rates. The adhesive pastes exhibited a very broad range of rheological behavior. Two flow parameters important to adhesive application technology, the plastic viscosity and the apparent yield stress, were measured for each adhesive. The plastic viscosity ranged from 11.6 to 329.5 Pa. s; the apparent yield stress ranged from 56.2 to 413 Pa. The temperature dependence of the rheological parameters of the epoxy adhesive pastes was also determined. The results are reported as the activation energies, E_η and E_σ, of plastic viscosity and apparent yield stress, respectively. The apparent yield stress of each adhesive paste was much less sensitive to changes in temperature than was the plastic viscosity. This suggests that the processing characteristics are likely to show qualitative as well as quantitative changes with temperature.     

高含硫气田集输净化管道缓蚀剂预膜稳定性

针对高含硫气田集输净化系统两相湍流流动条件下缓蚀剂预膜稳定性问题,利用高温高压动态循环腐蚀反应釜实验系统,开展高含硫气田典型管流流动条件下缓蚀剂膜稳定性评价研究:当流速在6 m·s^-1以下时,缓蚀剂预膜稳定性较好;当流速超过7.5 m·s^-1后,缓蚀剂预膜开始出现局部破坏;当流速达9 m·s^-1时,缓蚀剂膜在较高的流动剪切应力作用下已完全失效。流体动力学研究表明剪切应力为6.5 N·m^-2时为缓蚀剂膜发生整体破坏的临界点。     

Gas separation using sol-gel derived microporous zirconia membranes with high hydrothermal stability☆

A microporous zirconia membrane with hydrogen permeance about 5 × 10?8 mol·m?2·s?1·Pa?1, H2/CO2 permselectivity of ca. 14, and excellent hydrothermal stability under steam pressure of 100 kPa was fabricated via polymeric sol–gel process. The effect of calcination temperature on single gas permeance of sol–gel derived zirconia membranes was investigated. Zirconia membranes calcined at 350 °C and 400 °C showed similar single gas permeance, with permselectivities of hydrogen towards other gases, such as oxygen, nitrogen, methane, and sulfur hexafluoride, around Knudsen values. A much lower CO2 permeance (3.7 × 10?9 mol·m?2·s?1·Pa?1) was observed due to the interaction between CO2 molecules and pore wall of membrane. Higher calcination tem-perature, 500 °C, led to the formation of mesoporous structure and, hence, the membrane lost its molecular siev-ing property towards hydrogen and carbon dioxide. The stability of zirconia membrane in the presence of hot steam was also investigated. Exposed to 100 kPa steam for 400 h, the membrane performance kept unchanged in comparison with freshly prepared one, with hydrogen and carbon dioxide permeances of 4.7 × 10?8 and~3 × 10?9 mol·m?2·s?1·Pa?1, respectively. Both H2 and CO2 permeances of the zirconia membrane de-creased with exposure time to 100 kPa steam. With a total exposure time of 1250 h, the membrane presented hydrogen permeance of 2.4 × 10?8 mol·m?2·s?1·Pa?1 and H2/CO2 permselectivity of 28, indicating that the membrane retains its microporous structure.     

A Survey of Rheological Properties of One-Component Epoxy Adhesives

Flow characteristics of seven commercially available one-component epoxy adhesive pastes were measured using a controlled shear stress rheometer and a controlled shear rate rheometer over a temperature range from 5°C to 60°C. Combining data obtained from both controlled rate and controlled stress experiments over a wide range of shear rates, we observed Newtonian flow (shear stress proportional to shear rate) at very low shear rates, a plateau “shear thinning” region at intermediate shear rates, and a second region of linear dependence of shear stress on shear rate at high shear rates. The adhesive pastes exhibited a very broad range of rheological behavior. Two flow parameters important to adhesive application technology, the plastic viscosity and the apparent yield stress, were measured for each adhesive. The plastic viscosity ranged from 11.6 to 329.5 Pa. s; the apparent yield stress ranged from 56.2 to 413 Pa. The temperature dependence of the rheological parameters of the epoxy adhesive pastes was also determined. The results are reported as the activation energies, E_η and E_σ , of plastic viscosity and apparent yield stress, respectively. The apparent yield stress of each adhesive paste was much less sensitive to changes in temperature than was the plastic viscosity. This suggests that the processing characteristics are likely to show qualitative as well as quantitative changes with temperature.     

Kinetic study on reactive extraction of phenylalanine enantiomers with BINAP-copper complexes

Enantioselective liquid–liquid extraction has attracted considerable attention for its potential use in large-scale production. Kinetic data are needed for the reliable scale-up of the process. This paper reports the kinetic study of reactive extraction of phenylalanine (Phe) enantiomers with BINAP–copper complex (BINAP–Cu) as a chiral selector. The theory of extraction accompanied by a chemical reaction was applied. The effects of agitation speed, interfacial area, pH value of aqueous phase, initial concentration of Phe enan-tiomers and initial concentration of BINAP–Cu on the specific rate of extraction were investigated. The for-ward rate constants of the reactions in the reactive extraction process are 7.93 × 10?5 m5/2·mol?1/2·s?1 for D-Phe and 1.29 × 10?4 m5/2·mol?1/2·s?1 for L-Phe.     

填充泡沫铜圆管内R32单相流动换热

在泡沫金属纤维两端布置电极,采用电加热方法,实验测量了填充泡沫金属的管内R32流体和泡沫金属纤维的温度分布,得到了泡沫纤维与流体之间的对流传热系数。实验条件为：实验段管径5 mm,泡沫铜孔隙率0.95,孔隙密度15、45 PPI,流体温度280~325 K,热通量1~18 kW·m^-2,质量流速20~200 kg·m^-2·s^-1。实验及模拟结果表明：泡沫纤维与单相R32的对流传热系数随Re、泡沫铜的孔隙密度的增大而增大。基于流体外掠光滑圆管换热实验数据的Zukauskas经验关联式的预测值与泡沫金属纤维和R32流体之间的对流传热系数的实测值偏差为-35%~-67%,即该关联式不适用于泡沫金属纤维与流体之间的对流传热系数的预测。     

Predictability of apparent viscosity in a vibratory shearing flow field

A self‐developed experimental facility by the National Engineering Research Center of Novel Equipment for Polymer Processing, called a coaxial barrel dynamic rheometer, was used to test the predictability of the apparent viscosity equations of polymer melts in flat vibrating shear flows. The testing principle of the rheometer is to transform the shear power of a motor and extrusion pressure in a shear field to melt viscosity. The shear field can simulate an orthogonal superposed vibratory flow, boundary vibrating pressure flow, and their combined flow. By comparing equation predictions with experimental results, we show a qualitatively satisfactory and quantitatively reasonable predictive ability, which verifies the work of our mathematical derivations. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009