Numerical simulation of pharyngeal bolus flow influenced by bolus viscosity and apparent slip

Pharyngeal bolus flow was simulated numerically using a finite element method. The bolus liquids were X-ray medium, glucose, and thickener solutions. For a low-viscosity bolus, the simulation showed a reasonable agreement of bolus velocity with X-ray measurements. The influence of bolus density on swallowing velocity was investigated numerically. Although a higher density resulted in a higher bolus velocity, the increase in velocity was modest. When the bolus viscosity was high, it was necessary to apply the slip boundary condition to obtain an agreement for bolus velocity between the simulation and X-ray measurements. The simulations also showed that the method of characteristic shear rate proposed by Zhu et al., Journal of Texture Studies, 2014, 45, 430–439 is effective for predicting the bolus velocity for shear-thinning fluids. In order to discuss the effect of saliva lubrication and the physical meaning of the characteristic shear rate, an immiscible two-layer flow of the core and wall layer was analyzed theoretically by analogy with mesopharyngeal bolus flow. The characteristic shear rate enabled us to correlate the macroscopic flow behavior and the viscosity of the core layer fluid. Lubrication due to the wall layer caused the apparent slip and enhanced the transfer of viscous core fluid. For viscous fluid that presented a large apparent slip in the two-layer model, the slip boundary condition was needed in the swallowing simulation. The numerical simulation and model flow analysis revealed the usefulness of characteristic shear rate and the importance of saliva-layer lubrication in swallowing.     

过电状态下高铁齿轮油失效研究

高铁齿轮箱在用油在过电状态下会提前失效,影响列车的正常运维。通过台架实验模拟高铁齿轮油在过电状态下的失效,探究过电电压和击穿时间与油品的色度、黏度、酸值、生成物、电极损伤之间的对应关系。实验结果表明:在实验设定条件下,临界击穿电压约为1 500 V;在实验加载电压达到2 500 V,击穿次数58次后,油中生成物明显增多;实验电极表面在实验完毕出现少量点蚀剥落。     

Upgrading the lubricity of bio-oil via homogeneous catalytic esterification under vacuum distillation conditions

In order to accelerate the application of bio-oil in the internal combustion engines, homogeneous catalytic esterification technology under vacuum distillation conditions was used to upgrade the crude bio-oil. The lubricities of the crude bio-oil (BO) and refined bio-oil with homogeneous catalytic esterification (RBO_hce) or refined bio-oil without catalyst but with distillation operation (RBO_wc) were evaluated by a high frequency reciprocating test rig according to the ASTM D 6079 standard. The basic physiochemical properties and components of the bio-oils were analyzed. The surface morphology, contents and chemical valence of active elements on the worn surfaces were investigated by scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy, respectively. The results show that RBO_hce has better lubricities than those of BO, but RBO_wc has worse lubricities than those of BO. The tribological mechanisms of the bio-oils are attributed to the combined actions of lubricating films and factors that will break the film. Compared with BO, plenty of phenols in RBO_wc results in corrosion of the substrate and destroys the integrity of the lubricating films, which is responsible for its corrosive wear. However, more esters and alkanes in RBO_hce contribute to forming a complete boundary lubricating film on the rubbed surfaces which result in its excellent antifriction and antiwear properties.     

汽轮发电机组润滑油系统的故障诊断及分析

润滑油系统是汽轮发电机组中非常重要的辅助系统，该辅助系统的安全性直接关系到整个发电机组的工作效率和运行可靠性。润滑油系统在汽轮机中起到润滑、散热、减振的作用，因此，做好汽轮发电机组润滑油系统的故障诊断和分析工作至关重要。     

Adsorption of a silicone‐based surfactant on polyethylene and polypropylene surfaces and its tribologic performance

Aqueous silicone‐based surfactants are widely used in the processing of synthetic fibers in textile industries since they enhance a number of functional and processing properties. In this paper the interactions between silicone‐based surfactants and textile‐relevant surfaces (polyethylene and polypropylene) were investigated by quartz crystal microbalance with dissipation and the tribologic performance was evaluated by lateral force microscopy. Our results showed that the more hydrophobic polypropylene surface had higher affinity with silicone‐based lubricants than polyethylene surface. These adsorbed layers provided lubricity in textile materials when subject to shear forces and offered protection to wear and abrasion. This is explained by the fact that the hydrophobic groups in the surfactant molecules interact more effectively with the polypropylene surface via hydrophobic forces. This information will ultimately help to further our understanding on lubrication phenomena in fiber processing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40838.     

Tribological behaviour of silver based self-lubricating composite

Abstract

Silver based composites with varying concentration of graphite and/or MoS₂ were prepared by powder metallurgy method. Impacts of composition on the tribological performance of the composites in ambient air and vacuum were investigated. The lowest friction in air was achieved by Ag–20G (vol.-%) composite, while Ag–20MoS₂ exhibited the best lubricity in vacuum. XPS evaluation revealed the oxidation of MoS₂ in air and a decrease concentration of graphite on the surface of the wear tracks under vacuum. As the proportion of graphite to MoS₂ increased, the friction coefficient and the wear rates ascended gradually in air while decreased sharply under vacuum. As compared with other compositions, Ag–15MoS₂–5G exhibited a comparable stable and good tribological performance as the environmental condition changed for its friction coefficient and wear rate remained around 0·14 and 5×10^?6 mm³ N^?1 m^?1.     

Transient Pressure and Temperature Field Measurements in a Lightly Loaded Circumferential Groove Journal Bearing from Startup to Steady-State Thermal Stabilization

The fluid film pressure and temperature fields have been measured simultaneously under laboratory conditions at one land of a circumferential groove journal bearing (CGJB), together with friction torque and oil flow rate, during a time span from stand-still startup to the development of a thermally stabilized steady operating regime.A very fine measurement grid—that is, 216 pressure and 180 temperature points spread across the axial and circumferential directions—has been obtained by joining and synchronizing measurements from separate test runs while rigorously re-creating the test conditions.The study confirmed that the pressure field is established faster than the temperature field, that film rupture occurs both from cavitation nuclei downstream the minimum film thickness and through air ingestion from the environment. Furthermore, the high pressures in the convergent zone stabilize relatively quickly, whereas the low pressures in the divergent zone cavitated region require a longer time to stabilize. The cavitated region reverse flow appearance has been identified thermally through upstream-oriented isotherms. This study is the first to present the transient evolutions of pressure and temperature fields.     

石化设备“漆膜”形成机制与防范

"漆膜"问题近年来成为困扰石化关键动设备润滑维保的重要难题之一。结合石化关键机组的不同特点,探讨"漆膜"的形成机制,分析漆膜的危害和防范方法,提出既要做好日常在用油漆膜的去除,同时也要做好日常润滑管理,才能有效防范机组漆膜故障。     

From a compressible fluid model to new mass conserving cavitation algorithms

This study investigates two algorithms proposed to solve a new cavitation model. This new cavitation model is based on a compressible Reynolds equation in which the density–pressure relation is obtained from a barotropic–isentropic assumption. It can be viewed as an approximation of the Jakobson–Floberg–Olsson/Elrod Adams cavitation model. Two algorithms are proposed to solve it. The first one is explicit and needs an important number of nodes. The second is implicit and can be used for steady-state and unsteady problems. Its implementation is easy and needs only minor modifications for a computer code in which cavitation is ignored. It can also be used to compute the solution of the usual J.F.O./E.A. model. Faster convergence is obtained using a relaxation parameter.     

空间固体润滑材料的研究现状

固体润滑材料以其蒸发率低、耐高低温、抗辐照、耐腐蚀等优点在工作于空间苛刻环境中的器械上得到了广泛的应用。综述了目前常用的层状结构物、软金属、聚合物、无机化合物和复合材料5类固体润滑材料的摩擦学特性、制备工艺和应用情况,指出了我国在空间固体润滑材料研究领域与国外先进水平的主要差距和今后的研究方向。