基于变温下圆管内润滑脂流动特性的表征

为研究温度对润滑脂圆管流动特性的影响规律,采用旋转流变仪分析了润滑脂的流变特性,并基于流变特性研究结果和理论分析建立了润滑脂圆管流的速度场和应力场变化模型。结果表明:润滑脂具有高的屈服剪应力,表现出良好的黏温特性和剪切稀化特性,温度升高润滑脂的屈服应力和表观黏度均下降,表现为更好的流动性;利用MATLAB编程绘图对速度场和应力场分析,给出了润滑脂圆管流动特性规律的影响因素及变化关系;揭示了温度对润滑脂圆管流动特性的影响规律,提高输送介质温度利于润滑脂的输送。     

锂基润滑脂热流变特性及其变化机理

采用旋转流变仪探究了变温条件下的锂基润滑脂流动特性和黏弹特性,考察了温度对锂基润滑脂流变特性变化的影响规律,并对热流变过程中壁面滑移效应变化规律进行了讨论。进一步结合锂基润滑脂的微观形貌,探究了锂基润滑脂皂纤维结构与热流变特性变化的关联性。最后基于热流变和皂纤维结构研究结果,分析了锂基润滑脂胶体分散体系结构演化过程,给出了胶体分散体系及壁面滑移效应在热流变条件下的变化机理。     

凝胶推进剂直圆管内流动特性研究现状

总结和探讨了国内近年来关于凝胶推进剂直圆管内流动特性的研究及其试验方法。分析和总结了凝胶推进剂管内的剪切速率、表观粘性以及流阻特性等参数对流动特性的影响规律;归纳总结了关于直圆管内流动特性的各种管流试验法和数值模拟法等研究方法。     

圆管中中性悬浮液流动阻力和流变性的实验测定

对高浓度的液固悬浮液在圆管中的流变特性进行了实验研究,实验体系为聚苯乙烯颗粒在NaCl水溶液中的中性悬浮液。测定了在层流状态下,固体颗粒的体积分数变化（20%～50%）、悬浮液流速变化（0.031～0.22 m•s^-1）以及颗粒粒度变化对悬浮液压降的影响规律。实验结果表明,固体颗粒的浓度会影响悬浮液的流变性质,颗粒粒径对悬浮液流变性影响微弱。悬浮液的压降随颗粒体积分数和流速的增大而增大,悬浮液的流动特性在较高颗粒浓度范围内符合幂率流体模型。     

扭曲椭圆管内降膜蒸发特性研究

高效换热管有利于提高降膜蒸发器的传热性能,通过FLUENT软件对扭曲椭圆管内降膜蒸发过程进行研究,分析了液膜在扭曲椭圆管内的流动以及分布情况。研究结果表明:液膜在扭曲椭圆管内为螺旋流动,因离心力的作用会在垂直于主流方向产生二次流,从而增强对传热边界层的扰动;从壁面到液膜表面,液膜速度及压力都在逐渐增大,速度的变化率在逐渐地减小;相比于圆管,扭曲椭圆管内的液膜流动更为平稳,且液膜厚度的分布因扭矩的存在而具有一定的周期性变化规律;在扭曲椭圆管内,流体速度场与温度场的协同性相对来说比圆管的好,而速度场与压力场的协同性比圆管的差。     

微细管内电渗流动的瞬态热效应

建立微细圆管内电渗流动的非稳态数学模型,模型通过温度将电渗流的Poisson-Boltzmann方程、动量守恒和能量守恒方程耦合起来.详细讨论了在电渗流的初始阶段,焦耳效应对温度场和速度场演化的影响.同时讨论了不同冷却条件和外部电势场强度条件下,电渗流速度场及温度场变化的特点以及自热的发生过程.研究发现,由于速度场的发展主要受温度主控的电解液黏度影响,因此速度场和温度场是同步发展起来的.通过所得到的结果可以为微细管内的电渗流确定合适的冷却条件,以便同时达到有效抑制样品温度和获得较高流动速度的目的.     

基于数值模拟的波纹换热管道流动分析

本文采用Fluent数值模拟软件,对水-油换热器管道的流动特性进行模拟。从速度分布、速度矢量、湍动能、温度分布、强化传热特性分析等方面分析波纹管的流动特性,并与光滑圆管进行对比。结果表明,相比于圆管,波纹管内流体的出口温度和换热量均有较大提高,波纹管的出口总热量比光滑圆管提高35%。     

温度和固相粒径与浓度对水煤浆管内流动壁面滑移的影响

通过改变管径、温度、煤粉粒度和浓度,在中试规模的输送装置上研究水煤浆直管内的滑移流动规律,联合采用Mooney滑移修正方法和Tikhonov正则化方法确定浆体壁面滑移特性。结果表明,随温度和固相粒径的增大,临界剪切应力降低,壁面滑移速度显著增加;浓度越高,临界剪切应力及产生相同滑移速度所需的壁面剪切应力越大,温度升高对临界剪切应力和屈服应力的降低越显著;低壁面剪切应力下的滑移贡献率主要取决于临界剪切应力及屈服应力的相对大小,高壁面应力下主要取决于壁面滑移速度和浆体真实流变特性。     

啮合同向双螺杆挤出机中组合螺杆性能的数值研究（Ⅰ）瞬态流场分析

采用聚合物流动分析软件POLYFLOW,数值模拟了聚合物熔体在组合式啮合同向双螺杆挤出机ZSK60的组合螺杆中的三维等温流动。在计算所得速度场和压力场的基础上,全面分析并讨论了由不同厚度和不同错列角的捏合块元件组成的组合螺杆的流场分布规律;研究了组合螺杆的输送性能和挤出稳定性;并分别采用平均剪切速率、平均特征剪切应力以及平均拉伸流动指数等瞬态混合指数表征了组合螺杆的瞬态混合特性。此外还考察了两种不同流变性质的聚合物熔体在组合螺杆中的瞬态流场分布规律。所得结论可为双螺杆挤出的数值模拟研究提供一定的方法指导,并为其工程实践提供一定的理论指导。     

水焦浆的流变特性与壁面滑移效应

在浆体流动试验系统上采用不同管径的直管考察了水焦浆的流变特性以及壁面滑移效应对水焦浆流动特性的影响。采用Tikhonov 正则化方法确定了水焦浆的真实流变特性和壁面滑移特性。结果表明：浓度为59.8%的水焦浆随剪切速率增大呈现由伪塑性流体到胀塑性流体的转变,浓度增加,水焦浆变为单一的胀塑性流体,当浓度达到63.4%时,水焦浆表现为由胀塑性流体到伪塑性流体的转变;水焦浆的流变特性对滑移速度的变化趋势具有较大影响,滑移速度在水焦浆为胀塑性流体时随剪切应力增加呈加速增加,水焦浆为伪塑性流体时滑移速度随剪切应力的增长速率变化不明显;滑移贡献率的变化趋势迟滞于流变特性曲线。     

Rheology of lubricating greases modified with reactive NCO‐terminated polymeric additives

A comprehensive rheological characterization of lithium lubricating greases modified with NCO‐terminated polymers has been performed in this work, with special emphasis on the effect of temperature. With this aim, NCO‐terminated polymers were prepared from several di‐ and tri‐functional polyols and polymeric MDI. Afterwards, the reaction between terminal isocyanate groups and 12‐hydroxystearate lithium soap, used as thickener for lubricating grease formulations, was promoted. Transient and steady‐state viscous flow, rheo‐destruction and stress relaxation tests were performed on the different samples studied. In this sense, the influence that temperature, free NCO content, molecular weight, and functionality of the reactive polymers exert on the rheological response of lubricating greases was analyzed. The most important rheological modification was achieved by using the lowest molecular weight polymer. In general, NCO‐terminated polymers significantly dampen the influence of temperature on the rheological functions of the additive‐free lubricating grease. In some cases, the viscosity and/or viscoelastic functions even increase with temperature, especially in formulations with residual free NCO groups. Several experimental flow problems, such as fracture and sample expelling from the measuring tool, are generally found, more frequently in formulations with high NCO content. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of soap/polymer concentration ratio on the rheological properties of lithium lubricating greases modified with virgin LDPE

The main goal of this work was to study the feasibility of using a low-density polyethylene (LDPE) as additive to improve the rheological properties of lithium lubricating greases. The combined effect that both soap and LDPE concentrations exerts on the rheology of lithium lubricating greases and its relationship with grease microstructure were studied according to an experimental design based on the response surface methodology (RSM). Different lubricating grease formulations were manufactured by modifying lithium 12-hydroxystereate and LDPE concentrations. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as mechanical stability tests, were performed. In addition to these, environmental scanning electronic microscopy (ESEM) was used to determine grease microstructure. LDPE was found to be a useful additive to modify grease rheology, acting as filler in the entangled soap network. The values of both apparent viscosity and linear viscoelasticity functions increase with soap and LDPE concentration. However, the addition of LDPE distorts soap microstructural network, yielding greases with lower relative elastic characteristics.     

The effect of recycled polymer addition on the thermorheological behavior of modified lubricating greases

This article deals with the influence of temperature on the rheological behavior of lithium lubricating greases modified with three different types of recycled polymers, high‐density polyethylene (HDPE), low‐density polyethylene, and polypropylene (PP), all deriving from waste plastic recycling plants. Grease formulations containing diverse polymers were manufactured and rheologically characterized. Small‐amplitude oscillatory shear and viscous flow measurements over a temperature range of 25–175°C were carried out. The experimental results obtained suggest that a blend of HDPE and PP could be considered a suitable potential viscosity modifier for lithium lubricating greases in a wide range of in‐service temperature. Thus, the lubricating greases studied modified by HDPE or PP show quite promising results at low or high temperature, respectively. In addition, thermomechanical reversibility has been studied by applying different combined stress–temperature protocols. Lubricating greases containing any of the recycled polymers studied show a significant irreversible structural breakdown when the sample is submitted to temperatures and stresses higher than 75°C and 200 Pa, respectively. Regarding lubricating grease viscous flow behavior, a minimum in the shear stress versus shear rate plots appeared at temperatures above 50°C, more pronounced as temperature increased, resulting from material flow instabilities. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

复合锂基润滑脂的基础研究

锂基润滑脂是由天然脂肪酸锂皂稠化中等粘度的矿物润滑油或合成润滑油制成。复合锂基润滑脂具备了锂基润滑脂优良的机械安定性、胶体安定性和氧化安定性,还具有滴点高等高温使用性能。利用硼酸或己二酸为复合剂合成了两种复合锂基润滑脂,并利用差动热分析仪对其进行滴点的测定,得到最佳配方。研究表明,硼酸或己二酸对提高复合锂基润滑脂脂滴点可以起到一定的的作用,但用一步法的生产工艺更适合硬脂酸／己二酸复合锂基脂的生产。     

Experimental study of rheological properties of solid propellant slurry at low-shear rate and numerical simulation

The steady state rheological properties of a three-component hydroxyl-terminated polybutadiene binder (HTPB) solid propellant slurry at low shear rate were investigated using a rotational rheometer. The data were analyzed and the rheological characteristics of the slurry were determined. The effect of shear rate on apparent viscosity and shear stress as well as the viscosity–time effect of the slurry were also analyzed. Herschel–Bulkley (H-B) model was applied for the simulation of the flow process of a two-dimensional container using CFD Ansys-polyflow software. Experimental results showed that solid propellant slurry had yield pseudoplasticity. Yield characteristics were determined based on the fact that when shear stress was greater than yield stress, the slurry began to flow and the relationship between shear stress and shear rate obeyed power law function. Simulation results further verified the correctness of experimental results.     

复合锂基润滑脂的研究进展

复合锂基润滑脂具有良好的高温多效性能,自发明以来持续受到广泛研究和应用.同时复合锂皂良好的基础油稠化能力和添加剂感受性,使其可以制备满足各种工况要求的润滑脂.综述了复合锂基脂组成和制备工艺对其性能及结构的影响,探讨了复合锂基脂成脂机理,并对复合锂基润滑脂的未来发展进行了展望.     

Thermal and strain rate sensitive compressive behavior of polycarbonate polymer - experimental and constitutive analysis

The mechanical behavior of polycarbonate (PC) polymer was investigated under the effect of various temperatures and strain rates. Characterization of polymer was carried out through uniaxial compression tests and split Hopkinson pressure bar (SHPB) dynamic tests for low and high strain rates respectively. The experiments were performed for strain rates varying from 10 ^?3 to 10³ and temperature range of 213 to 393 K. By conducting these experiments, the true stress–strain (SS) curves were obtained at different temperatures and strain rates. The results from experiments reveal that the stress–strain behavior of polycarbonates is different at lower and higher strain rates. At higher strain rate, the polymer yields at higher yield stress compared to that at low strain rate. At lower strain rate, the yield stress of the polymer increases with the increase in strain rate while it decreases significantly with the increase of temperature. Likewise, initial elastic modulus, yield and flow stress increase with the increase in strain rate while decreases with the increase in temperature. The yield stress increases significantly for low temperature and higher strain rates. On the basis of experimental findings, a phenomenological constitutive model was employed to capture the mechanical behavior of polymer under temperature and loading rate variations. The model predicted the yield stress of polymer at varying strain rate and temperature also it successfully predicted the compressive behavior of polymer under entire range of deformation.     

Mechanical behavior of polytetrafluoroethylene around the room-temperature first-order transition

The effect of the room-temperature first-order transition on the plastic yield behavior of polytetrafluoroethylene (PTFE) has been investigated. Stress-strain curves were measured at different strain rates and temperatures. Tensile creep under constant dead load was also measured as a function of temperature and stress level. The effect of degree of crystallinity was investigated by using both a rapidly quenched and slow-cooled polymer. Observations were extended to large deformations, so that the phenomenon primarily observed was plastic yield rather than linear viscoelastic behavior. The curve of yield stress vs. temperature in the temperature range from –50 to +68°C was found to be almost identical with the curve of elastic modulus vs. temperature; the yield stress shows a marked local decrease at the first-order transition. The yield elongation was almost constant (at about 5%) over this same range, which is in accord with the above result. The more highly crystalline polymer is always more rigid than the less crystalline polymer at small deformations, but above 19°C its stress-strain curve shows a “cross-over” in stress level with the curve of the less crystalline polymer as extension increases. That is, above 19°C the less crystalline polymer shows a more rapid rate of “strain hardening”, even though the strain-hardening effect is pronounced in both polymers. Attempts to apply time-temperature superposition to creep data at different temperatures were partially successful; the lateral shifts required corresponded to an activation energy of approximately 80 kcal. The experimental observations suggest a model of the solid-state structure of PTFE which could be described as an “elastic-plastic network”, in which crystalline domains are connected by elastic amorphous regions, and in which the crystalline domains can flow plastically at sufficiently high stress or temperature.