利用真实气体效应提高激波阶跃压力

本文中提出了在激波管中,利用真实气体效应来提高激波阶跃压力的新方法,它是籍助在高压下计及分子之间作用力、分子体积效应和激励态效应而获得压力增益,试验表明,它可比理想气体获得的阶跃压力高出30％以上。该方法在国内外尚未进行系统研究,是一个有发展前途的新方法。     

印刷油墨粘性的理论分析与测量

印刷油墨的粘性对提高印刷质量和效率有重要影响,本文阐述了雷德式油墨粘性测量系统的结构与组成,采用高精度力传感器有效解决了粘性测量问题,精度可达到0.01N,分析了油墨流变学特性与粘性测量系统的动力学过程,得到了油墨粘性值的实用估算公式并通过实验验证。结果表明:油墨粘性值与转速成线性,与温度成指数关系。研究结果为油墨的生产和使用提供了理论与实验依据。     

FINITE ELEMENT ANALYSES OF THE EXTRUSION FLOWS OF BOGER FLUIDS WITH END DRAWING AND GRAVITY-DRAWING

The spinning flow of Boger fluids and the gravity-drawing extrusion flow of a Newtonianas well as a Boger fluid have been simulated by using the stream-line finite element method and thetechnique of matching the finite element solutions with those of one-dimensional spinning equations.The recoverable shear strain is proved not to be a basic parameter in characterising thespinning flow of Boger fluids.For Newtonian fluids this technique predicts the experimental jetshape accurately.For Boger fluids,the numerical simulation agrees with the experimental data of spin-ning flow reported by Sridhar et al.,but seems to give an insufficient swelling and over contractionof the jets when drawn by its own weight,compared with the experimental results of Trang andYeow.It implies that the Oldroyd-B model fitting the viscometric-flow data fails to describeaccurately the elasticity and extensional viscosity in the extrusion flow of Boger fluids with gravi-ty-drawing.     

高密度聚乙烯等温结晶的流变行为

用旋转流变仪研究了高密度聚乙烯的等温结晶行为,发现结晶速率对夹具表面粗糙度存在依赖性,随着表面粗糙度的增加,结晶速率先增加后减小.粗糙度的增加增大了样品与夹具间的接触面积,减小了热阻,同时界面间可能积存的气泡使得界面热阻较大,都影响着结晶速率.对于相同表面粗糙度的铝、黄铜和不锈钢三种材质的夹具,相应的结晶速率排序为：铝最快,黄铜居中,不锈钢最慢.我们研究发现HDPE样品的结晶速率对夹具的表面能不敏感,而夹具的导热系数越大,热阻越小,结晶速率越大.     

偏心圆环中周期性和非周期性混沌混合

引　言混合是自然和工业中广泛的现象 .然而由于混合过程的复杂性 ,传统上只对具体混合问题分别进行研究 .最近对层流混合研究所取得的进展为系统理解混合过程提供了可行途径[1] .从动力学的观点来看 ,对流混合 (不包括扩散 ) ,仅仅是拉伸流体线和流体面 .在规则区 ,流体的拉伸率是随时间线性变化的 ,而在混沌区随时间成指数增长 .所以 ,增强混合效率的一个基本方法是增大流动中的混沌区域 .然而 ,在通常的时间周期性混沌流中 ,混沌区和规则区(规则岛 )是共存的 ,在规则区中的流体只能通过扩散达到均匀 ,效率非常低 .要获得更好的混合必须消…     

Non-Newtonian steady shear flow characteristics of waxy crude oil

The experimental research on the non-Newtonian flow characteristic of a waxy crude oil was conducted through a rotational parallel-plates rheometer system.The test temperature is about 6.5 ℃ higher than its gel point.The shear stress and viscosity of the waxy crude oil show sophisticate non-Newtonian characteristics in the shear rate of 10-4-102 s-1,in which the shear stress can be divided into three parts qualitatively,i.e.stress-up region,leveling-off region,and stress-up region.This indicates that there is a yielding process in shearing for the waxy crude oil at the experimental temperature,which is similar to the yield phenomenon in thixotropy-loop test discussed by CHANG and BOGER.Furthermore,the steady shear experiment after the pre-shear process shows that the stress leveling-off region at low shear rate disappears for the waxy crude oil and the stress curve becomes a monotonic climbing one,which demonstrates that the internal structure property presenting through yielding stress at low shear rate can be changed by shearing.The experimental results also show that the internal structure of waxy crude oil presenting at low shear rate has no influence on the shear viscosity obtained at the shear rate higher than 0.1 s-1.The generalized Newtonian model is adopted to describe the shear-thinning viscosity property of the waxy crude oil at high shear rate.     

挤出胀大流动的有限元方法研究(Ⅰ)牛顿流体

本文首次成功地将压力不连续的非协调单元和罚函数法用于挤出胀大流动的有限元计算。对牛顿流体的平面流和轴对称流的计算中比较了下列方法:压力连续单元的混合法;压力不连续的混合法;一致性罚函数法;降阶积分罚函数法;改进的降阶积分罚函数法。结果表明压力不连续单元使连续性方程得到更好的满足,从而使自由面迭代更快地收敛,降低了计算量。罚函数法使计算量进一步减少,并且解的精度也足够好。     

Effect of substrates on crystallization of high density polyethylene

The experimental observations about remarkable influence of the substrates on the isothermal crystallization rate of a high density polyethylene(HDPE) were presented.Two methods were used to characterize the crystallization rate:the change of turbidity of the HDPE specimen and the changes of the complex viscosity and storage modulus measured by a rotational rheometer,which gave consistent results showing that the isothermal crystallization rate decreased in sequence as the specimen contacted with aluminum,brass and stainless steel plates,respectively.As to the dominant influence factor,the chemical composition of the substrates can be excluded via insulating the plate by an aluminum foil.Instead,we propose the plate’s ability of removing the latent heat of crystallization from the specimen.Rheological measurement is sensitive to the crystallization process.The colloid like model proposed by BOUTAHAR et al for the crystallization of HDPE gives reasonable predictions of the crystallized fraction from the measured storage modulus.     

FINITE ELEMENT ANALYSIS OF THE FREE EXTRUSION FLOWS OF BOGER FLUIDS

The stream-line finite element method proposed by Luo and Tanner has been improvedand used to simulate the extrudate swell of the so called Boger fluid.The element withdiscontinuous pressure proves to be a successful choice and superior to that with continuous pressureIt is revealed that the visccsity of Newtonian solvent of the Boger fluid has a great influence on thecalculated swelling.The Weissenberg number is suggested to take the place of recoverable shear strainin Tanner′s formula to estimate the swelling of the Boger or Oldroyd-B fluids.